The improvements in 3D-printing increasingly enable their use for Terahertz components. Here we present helical antennas integrated with WR3 rectangular waveguides produced by a 3D metal printer. The constrains in resolution forces the design to deviate from the ideal dimensions for gain, but the flexibility of the production technique allows for the integration of reflector dishes directly on the waveguide, which mitigates these effects. Despite the deviation from traditional helical antenna design rules, the circular polarization is maintained. Hence, this fabrication method delivers orientation insensitive antennas for polarization-division multiplexing. © 2022 IEEE.

We demonstrate a broadband terahertz coupling between InP-based coplanar waveguide and silicon dielectric rod waveguide for hybrid integration. A coupling efficiency of around -2 dB has been experimentally achieved in frequency range between 70-120 GHz. Numerical simulations reveal an operational 3dB-bandwidth >100 GHz. © 2022 IEEE.

A compact planar fixed-beam leaky-wave antenna that radiates its main beam at broadside is presented, that consists of two folded branches of periodically distributed series-fed microstrip patches. The antenna is fed from the center through a 50 Ω transmission line that subsequently feeds two constituent 100 Ω parallel branches, each consisting of eight series-fed microstrip patches. Fixed-beam operation is achieved by the combination of the two oppositely directed beams that are generated by the two branches. The proposed structure achieves a significant reduction of the longitudinal size by incorporating a 180° bend at the center of each branch, thus effectively folding the antenna in half. This results in a longitudinal size that is 1.8 times smaller than the analogous unfolded antenna. The antenna maintains a measured fixed beam at broadside over a wide zero beam-squinting bandwidth of 3 GHz in the 28 GHz band, with a radiation efficiency above 60% and a maximum measured gain of 14 dBi at 27.4 GHz, with an overall compact size of 5.8 × 1.1 cm. © 2002-2011 IEEE.

This paper proposes a contact-less non-invasive diagnostic technique for skin cancer detection and screening based on millimeter-wave (mmW) to terahertz (THz) photonic near-field imaging. Key photonic technologies required for developing multi-spectral sensors are fabricated and reported. This includes broadband photodiodes and wideband near-field antennas, both offering an operational frequency tuning range in excess of 0.2 THz and a maximum operational frequency beyond 0.3 THz. Furthermore, a compact photonic Ka-band mmW imaging sensor has been developed. The sensor head consists of a broadband photodiode for mmW signal generation and a Schottky barrier diode for incoherent power detection within the Ka-band. Calibration of the integrated sensor head is performed using a manufactured gelatin-based skin phantom. Calibration results reveal that the expected refractive index difference of 1 between healthy skin tissue and malignant squamous cell carcinoma (SCC) tumor in the mmW range can be easily detected. Finally, the principal function of the developed photonic imaging sensor is proven in the first in-vivo experiments using human skin tissue and skin tumor tissue (SCC). Experimental results indicate that the tumor can be clearly distinguished from healthy skin. © 2022 IEEE.

A novel photonic-assisted 2-D Terahertz beam steering chip using only two tuning elements is presented. The chip is based on an array of three leaky wave antennas (LWAs) with a monolithically integrated beamforming network (BFN) on a 50 µm-thick indium phosphide substrate. The THz beam angle in elevation (E-plane) is controlled via optical frequency tuning using a tunable dual-wavelength laser. An optical delay line is used for azimuth (H-plane) beam control. The simulated beam scanning range is 92° in elevation for a frequency sweep from 0.23 THz to 0.33 THz and 69.18° in azimuth for a time delay of 3.6 ps. For the frequency range from 0.26 THz to 0.32 THz, it is confirmed experimentally that the THz beam scans from −12° to +33°, which is in good agreement with the numerical simulations. The beam direction in azimuth scans with a total angle of 39° when applying a delay difference of 1.68 ps. A good agreement is found between theoretically predicted and experimentally determined THz beam angles with a maximum angle deviation below 5°. The experimental scanning angles are limited due to the mechanical constraints of the on-wafer probes, the on-chip integrated transition and the bandwidth of the THz receiver LNA. The mechanical limitation will be overcome when using a packaged chip. © 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement.

High-speed detection and identification of mobile terminals located in the vicinity of highly directive base stations is essential for future mm-wave communication systems. We propose a novel optoelectronic frequency modulated continuous wave (FMCW) radar system for detection, localization and identification of multiple mobile terminals. The simultaneous localization and identification of multiple mobile terminals is achieved by using frequency scanning mm-wave leaky-wave antennas (LWAs) and backscattering communications. LWAs provide RF-based beam steering for estimating the direction of arrival of the echoes using a FMCW radar signal. Additionally, the implementation of backscattering technology in the mobile terminals allows the identification of users. Hence, simultaneous user localization and identification without the use of any complicated radar signal post-processing algorithms is possible. Finally, the introduced modulated backscattering reflection shifts the signals of the targets at higher frequencies, which exhibit lower noise floor and thus have higher signal to noise ratio (SNR). © 2013 IEEE.

High-speed photodiodes stand out as potential candidates to enable next-generation communication systems working as mmWave/THz sources due to their intrinsic broadband behaviour. Impedance matching is an essential task in microwave engineering that enables an efficient delivery of the power generated by the source (i.e. photodiode) to the load (i.e. antenna). In this work, we analyse the impedance of a generic uni-travelling carrier photodiode and its dependency with frequency, bias voltage and other operational parameters. In addition, we present some calculations and use cases, highlighting the importance of properly matching this impedance in an actual system. © 2021 IEEE.

For mobile THz applications, integrated beam steering THz transmitters are essential. Beam steering approaches using leaky-wave antennas (LWAs) are attractive in that regard since they do not require complex feeding control circuits and beam steering is simply accomplished by sweeping the operating frequency. To date, only a few THz LWAs have been reported. These LWAs are based on polymer or graphene substrates and thus, it is quite impossible to monolithically integrate these antennas with state-of-the-art indium phosphide (InP)-based photonic or electronic THz sources and receivers. Therefore, in this article, we report on an InP-based THz LWA for the first time. The developed and fabricated THz LWA consists of a periodic leaking microstrip line integrated with a grounded coplanar waveguide to microstrip line (GCPW-MSL) transition for future integration with InP-based photodiodes. For fabrication, a substrate-transfer process using silicon as carrier substrate for a 50-μm thin InP THz antenna chip has been established. By changing the operating frequency from 230 to 330 GHz, the fabricated antenna allows to sweep the beam direction quasi-linearly from-46° to 42°, i.e., the total scanning angle is 88°. The measured average realized gain and 3-dB beam width of a 1.5-mm wide InP LWA are ∼11 dBi and 10°. This article furthermore discusses the use of the fabricated LWA for THz interconnects. © 2011-2012 IEEE.

We present photonic-assisted on-chip multi-beam THz leaky wave antennas for short-range Terahertz 6G. Experimentally, multi-beam mobile communications at 0.3 THz with an overall capacity of 48 Gbps, maximum net user data rate up to 20.4 Gbps and beam steering with a speed of ~18°/s is demonstrated. © 2021 IEEE.

THz communications is envisaged for wide bandwidth mobile communications eventually reaching data capacities exceeding 100 Gbit/s. The technology enabling compact chip-integrated transceivers with highly directive, steerable antennas is the key challenge at THz frequencies to overcome the very high free-space path losses and to support user mobility. In this article, we report on mobile and multi-user THz communications using a photonic THz transmitter chip featuring 1D beam steering for the first time. In the proposed approach, 1D THz beam steering is achieved by using a photodiode excited leaky-wave antenna (LWA) in the transmitter chip. The on-chip LWA allows to steer the directive THz beam from 6° to 39° within the upper WR3-band (0.28-0.33 THz). The antenna’s directivity is 14 dBi which is further increased to 23 dBi using an additional hemicylindrical Teflon lens. The 3-dB beam width and coherence bandwidth of the fabricated THz transmitter chips with lens are 9° and 12 GHz, respectively. The proposed approach allows steering the THz beam via the beat frequency of an optical heterodyne system at a speed up to 28°/s. Without using a THz amplifier in the transmitter chip, a data rate of 24 Gbit/s is achieved for a single user for all beam directions and at short wireless distances up to 6 cm. The wireless distance is successfully increased to 32 cm for a lower data rate of 4 Gbit/s, still without using a transmitter amplifier. Also, multi-user THz communications and the overall capacity of the developed THz transmitter chip is studied revealing that up to 12 users could be supported together with a total wireless data capacity of 48 Gbit/s. Fully integrated 2D transmitter chips are expected to reach wireless distances of several meters without additional amplifiers. © 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

An indium phosphide (InP)-based E-plane transition for monolithically integrating terahertz photodiodes with standard rectangular waveguide (WR)-outputs is presented for all standard WR-frequency bands from 0.22 THz to 2.2 THz, i.e., from WR3 to WR0.51. The integration concept comprises a modified uni-travelling carrier photodiode (MUTC-PD) chip, an E-plane transition and a stepped impedance low-pass filter (LPF), which are all monolithically integrated on InP substrate. The E-plane transition converts the quasi-TEM coplanar waveguide (CPW) mode of the MUTC-PD output to the dominant TE10 mode of the WR. To our knowledge, this is the first frequency-scalable monolithic integration concept that enables packaging of photodiodes with standard WR-outputs up to 2.2 THz. The recommended thickness of the InP substrate and the proposed E-plane transitions design parameters are investigated by numerical analysis to achieve minimum insertion loss (IL) and a wide operational bandwidth (BW). The presented optimized transitions exhibit a maximum IL of 1.4 dB, a return loss (RL) better than 10 dB and a minimum 1 dB IL BW of 92.23% for all WR-bands up to 2.2 THz. To prove the proposed monolithic integration concept, a MUTC-PD is integrated with a CPW-to-WR3 E-plane transition (220-320 GHz) on a 95 m-thick InP substrate. At 300 GHz, the maximum achieved RF output power of the fabricated MUTC-PD chip is -12.4 dBm at a photocurrent of 18.5 mA. For experimental characterization, the MUTC-PD chip with the integrated E-plane transition has been mounted on a 1 mm-thick soda-lime glass substrate as carrier and it has been manually aligned within a WR-3 together with an adjustable back-short. Due to non-perfect alignment of the chip and the back-short as well as the additional losses and substrate modes due to the thick glass carrier, the calculated average IL is increased to 5.3 dB. Experimentally, an average IL of 8.6 dB is measured within the WR3-band from 220 GHz to 320 GHz. Integration of the chip in a real package without misalignment and without the glass carrier is expected to improve the IL by ~4.8 dB. Author

A transition to couple an antenna to spoof plasmon-polariton waveguides at terahertz frequencies is presented. The optimization of the transition is discussed. Examples of how antenna coupling can enable THz on-chip applications are given in a biosensor and a phase shifter. The sensing of deeply subwavelength biological cells demonstrates the high sensitivity to even small concentrations of bacteria. And while the phase shifter only exhibits a small angle range, its high transmission, and easy integration makes it suitable for applications such as an on-chip phased array. © 2021 EurAAP.

In this paper, the successful demonstration of a 100 Gbit/s wireless backhaul link in the V-band is reported for the first time. The proposed system has potential for real-world deployment since it exploits the contiguous unlicensed spectrum of 14 GHz in the 60 GHz V-band between 57 GHz and 71 GHz. Optical baseband modulation and free-running lasers for photonic up-conversion are employed in the wireless transmitter and simple Schottky-barrier diodes (SBD) for envelope detection are used in the wireless receiver. This combination makes perfect use of the scalability of photonic technology with respect to modulation bandwidth while being robust against phase-noise and frequency drifts at the same time. By utilizing a dual-polarization (DP) 16-QAM IF-OFDM signal no local oscillator is required at the wireless receiver. To achieve the required high spectral efficiency for 100 Gbit/s wireless transmission in the available spectrum as well as a low baseband bandwidth, signal-signal beat interference (SSBI) has been substantially reduced. This is attained by analyzing non-linearities in the wireless transmitter for identifying and setting the optimum power relation between the IF carrier and the OFDM signal. Experimentally, we report 100 Gbit/s wireless V-band transmission using a DP IF-OFDM 16-QAM modulation over 1 m distenace. The achieved overall BER before FEC and overall wireless spectral efficiency are 2.4.10^{-3}, and ∼ 7 bit/s/Hz, respectively. For simplicity, experiments were carried out in a laboratory environment. By using commercially available high-gain antennas and RF power amplifiers, the link budget could be increased by about 7080 dB which would lead to longer wireless distances in the range of several 100 meters up to kilometers. © 2020 URSI.

For mobile THz applications, integrated beam steering THz transmitters are essential. Beam steering approaches using leaky-wave antennas (LWAs) are quite attractive in that regard since they do not require complex feeding control circuits because beam steering is simply accomplished by sweeping the operating frequency. To date, only a few THz LWAs have been reported. These LWAs are based on polymer or graphene substrates and thus it is quite impossible to monolithically integrate these antennas with state-of-the-art indium phosphide (InP) based photonic or electronic THz sources and receivers. Therefore, in this paper, we report on an InP-based THz LWA for the first time. The developed and fabricated THz LWA consists of a periodic leaking microstrip line integrated with a grounded coplanar waveguide to microstrip line (GCPW-MSL) transition for future integration with InP-based photodiodes. For fabrication, a substrate-transfer process using silicon as carrier substrate for a 50 m thin InP THz antenna chip has been established. By changing the operating frequency from 230 GHz to 330 GHz, the fabricated antenna allows to sweep the beam direction quasi-linearly from -46 to 42, i.e. the total scanning angle is 88. The measured average realized gain and 3 dB beam width of a 1.5 mm wide InP LWA are ~11 dBi and 10. The paper furthermore discusses the use of the fabricated LWA for THz interconnects. CCBY

A novel 3-D multilayer packaging technology for integrating an array of indium phosphide (InP)-based terahertz photodiodes (THz-PDs) with a rectangular waveguide power combiner (WR-PC) is proposed. The packaging concept is based on a vertical integration of an InP THz-PDs array with a multilayered WR-PC made of metallized glass-reinforced epoxy FR4 laminates using direct wafer bonding. The key motivation of this work is to develop a low-cost packaging technology for coherent power combining in the THz regime. The proposed multilayered packaging technology is generic, i.e., in principle, it would allow the integration of different and multiple planar arrays featuring photonic or electronic devices. To our knowledge, this is the first 3-D packaging concept for the THz frequency range that enables the integration of 2-D arrays of photonic or electronic devices. As a proof of concept, we here report on the design, fabrication, and experimental characterization of a straight hollow rectangular waveguide (WR-waveguide) and a 2 × 1 WR-PC for the WR3-band (220-320 GHz). Both packages feature standard cross-sectional hollow WR3-waveguides (862 μm × 431 μm) and corresponding standard UG-387/U-M flanges. They are fabricated using a stack of vertically bonded unit cells, each consisting of a 50-μm-thick glass-reinforced epoxy FR4 laminate with a 23-μm-thick top and bottom metallization. The size of a single quadratic FR4 unit cell is 24 mm × 24 mm. The fabricated straight WR3-waveguide consists of a stack of 57 FR4 unit cells of a total length of 5.4 mm. The measured transmission loss is less than 0.3 dB/mm and the return loss (RL) is less than 10 dB, within the entire WR3-band. Next, a multilayered FR4 2 × 1WR3-PC is reported. Its design is based on that of a T-junction in H-plane where the inputs are modified to be on the same plane for facilitating subsequent integration with the planar InP chips of THz-PDs. The length of the WR3-PC is intentionally reduced for compactness and its impedance is gradually matched to achieve a low insertion loss (IL) over the entire WR3-band. The fabricated multilayered WR3-PC consists of 41 FR4 unit-cells resulting in a total thickness of only 3.9 mm. For the frequency range from 240 to 320 GHz, the simulated IL, minimum isolation, and RL are 0.16, 4.2, and 6.5 dB, respectively. For the experimental characterization using a WR3-band vector network analyzer (VNA), two multilayered FR4 2 × 1 WR3-PCs are connected back-to-back (B2B). The measured average IL and RL within the frequency range from 240 to 320 GHz are found to be 3.6 dB and below 5.2 dB, respectively. The measured average IL for a single WR3-PC is 1.8 dB, which is higher than expected because of imperfect fabrication and misalignment losses during the integration. An improved fabrication and packaging process will allow mitigating the losses in future runs. © 2020 Institute of Electrical and Electronics Engineers Inc.. All rights reserved.

In this Letter, the authors report on a 26 GHz joint communication- radar system. By exploiting the beam steering features of leaky-wave antennas, angle-of-arrival estimation and multi-user transmission are achieved. Furthermore, the Zadoff-Chu preamble of the OFDM waveform is used to provide a frequency-modulated continuouswave radar signal. This way, the wide operational bandwidth is used for both, communications and radar, yielding high data throughput and precise user localisation. Experimentally, spectral-efficient 16-QAM multi-user 5 × 4 Gbit/s communications and user localisation with an accuracy of about 2 cm and ±1.5° is demonstrated. © 2020 The Institution of Engineering and Technology.

This paper reports on the successful demonstration of a frequency-modulated continuous wave (FMCW) photonic radar system based on direct laser modulation, optical mm-wave signal generation and beam steering antenna technology. The developed radar system is designated for mobile user localization in future 26 GHz mm-wave 5G communications. The optical sweep allows effective use of radio-over-fiber distribution and sector scanning via steerable PCB high gain leaky-wave antennas (LWAs), developed to support user mobility. Experimentally, a high ranging accuracy with an error of 2 cm at 600 cm distance, corresponding to a relative error of only 0.33% is demonstrated. © 2020 IEEE.

We report on a fully-ballistic (FB) p-i-n diode operating as a continuous-wave (CW) photomixing source at 1550 nm and optically fed from the side through a passive optical waveguide (POW) integrated within the diode heterostructure, demonstrating a dynamic range (DR) above 35 dB at 1 THz and obtaining photocurrents of at least four times the photocurrent of top illuminated diodes. © 2020 IEEE.

Leaky-wave antennas (LWAs) are quite attractive for image scanner or communication applications featuring the beam steering capability by simply sweeping the operation frequency. In this work, we report on an InP-based periodic microstrip leaky-wave antenna with a grounded coplanar waveguide to microstrip line (GCPW-MSL) transition. The InP substrate allows the monolithic integration of the LWA with state-of-art InP based THz sources to achieve highly compact THz transmitters for mobile THz applications. © 2020 IEEE.

We report a two-port slot bowtie antenna with two monolithically integrated photodiodes for THz power-combining. Numerical simulations show a S_{11}-parameter below-10 dB in almost the complete operation bandwidth from 200 GHz to 400 GHz. An experimental proof of concept evaluation of the fabricated power combiner with one radiating element shows a power enhancement around the ideal 3 dB in the whole J-band. © 2020 IEEE.

In this paper, we demonstrate a phase-sensitive photonic terahertz imaging system, based on two-tone square-law detection with a record-low phase noise. The system comprises a high-frequency photodiode (PD) for THz generation and a square-law detector (SLD) for THz detection. Two terahertz of approximately 300 GHz tones, separated by an intermediate frequency (IF) (7 GHz-15 GHz), are generated in the PD by optical heterodyning and radiated into free-space. After transmission through a device-under-test, the two-tones are self-mixed inside the SLD. The mixing results in an IF-signal, which still contains the phase information of the terahertz tones. To achieve ultra-low phase-noise, we developed a new mixing scheme using a reference PD and a low-frequency electrical local oscillator (LO) to get rid of additional phase-noise terms. In combination with a second reference PD, the output signal of the SLD can be down-converted to the kHz region to realize lock-in detection with ultra-low phase noise. The evaluation of the phase-noise shows the to-date lowest reported value of phase deviation in a frequency domain photonic terahertz imaging and spectroscopy system of 0.034°. Consequently, we also attain a low minimum detectable path difference of 2 μm for a terahertz difference frequency of 15 GHz. This is in the same range as in coherent single-tone THz systems. At the same time, it lacks their complexity and restrictions caused by the necessary optical LOs, photoconductive antennas, temperature control and delay lines. © 2020 OSA - The Optical Society. All rights reserved.

In this paper we outline a concept to provide 2-dimensional photonic-assisted beam steering at mm-wave frequencies by utilizing leaky-wave antennas and integrated optical beam forming networks. Thereby, heterodyne detection is employed to tune the RF for leaky-wave antenna (LWA) beam scanning by remotely changing the optical frequency of a tunable laser. Beam steering in the other dimension is provided via an optical true time delay (TTD) beam forming network, which is compatible to the LWA beam scanning even for multiple GHz of bandwidth. Through wavelength-division multiplexing and optical filters, multiple beams can be generated even at the same RF. To prove the concept a system based on discrete components is set up and used to demonstrate 2D beam steering of a 1 Gbit/s data signal in the 60 GHz band over 1.5 m wireless distance. © 2019 IMA - Institut fur Mikrowellen- und Antennentechnik e.V.

In this paper, we report a phase-sensitive photonic THz two-Tone self-mixing imaging system, comprising a self-developed vertical illuminated triple transit region photodiode (TTR-PD) and a commercial square law Schottky barrier diode as THz emitter and THz detector, respectively. Using the two-Tone self-mixing approach, the phase information of a device-under-Test can be extracted by down-mixing two THz signals inside the SBD, whereas the phase information remains in the output signal. The THz tones are generated by two free-running lasers and the TTR-PD, while one optical signal is externally modulated for double sideband carrier suppression. By means of the self-mixing, the phase noises of the free running lasers are canceled out. Using a second PD for the trigger, lock-in detection allows fast imaging speed, only limited by the integration constant. Beside the imaging system, we present the characteristics of the used vertically illuminated terahertz triple transit region photodiodes with thin depletion zone and small active areas. Numerical analysis by energy-balance model based TCAD simulations show transit-Time limitations over 200 GHz, due to the electron field management within the active photodiode layers and the resulting high electron velocities. Therefore, the fabricated TTR-PDs show a flat ± 2dB frequency response within the frequency range from 225 GHz to 305 GHz. By employing the proposed photonic two-Tone imaging system with the fabricated TTR-PDs, amplitude and phase difference vector images are taken at 299.5 GHz and 300.5 GHz. Metal and acrylic glass items inside a paper envelope are clearly visible, which demonstrates the potential of the system. © 2019 IEEE.

We report a photonic frequency-modulated continuous wave (FMCW) radar system that provides 3D localization with a simple radar frontend. This is achieved by exploiting linearly polarized leaky-wave antennas (LWAs) for simultaneously scanning azimuth and elevation. As such, the FMCW frequency sweep is employed for radar operation as well as LWA beam steering for target angle estimation. The LWAs are based on series fed patches and provide beam steering from-20.7° to +18° in the frequency range of 24-33 GHz in the H-plane and a field of view from-18.9° to 33.3° in the E-plane. The FMCW signal is photonically generated from the wavelength chirp of a low-cost DFB laser. Coherent radio-over-fiber transport with photonic upconversion provides low loss distribution and frequency scaling. Finally, 3D radar localization is experimentally demonstrated by two orthogonal LWAs. A ranging accuracy of better than 4 cm and an angular accuracy of \approx 0.5{\circ} have been achieved without any dedicated radar post processing. © 2019 IEEE.

In this paper, an endfire transition from coplanar-to-rectangular waveguide (CPW-to-WR3) for operation in the WR3-band (220-320 GHz) is presented. The transition is designed for providing connectivity between a monolithically integrated InP-based terahertz photodiode (PD) to a WR3 rectangular waveguide. The presented transition is based on a CPW-fed planar dipole antenna designed on InP substrate which placed in the E-plane of the rectangular waveguide. The dipole-based transition converts the direct coupled quasi-TEM CPW mode of the PD output to the TE10 mode of the rectangular waveguide. The proposed design provides a simple approach avoiding complex integration and packaging techniques like air bridges, ribbon-bonds, or via holes. Numerical analysis of the designed transition shows a wideband performance with a 3 dB insertion loss (IL) over 88 GHz bandwidth and a 10 dB return loss (RL) over 53 GHz bandwidth within the WR3-band. © 2019 IEEE

Novel compact fully-hermetic E-band (71-86 GHz) coherent photonic mixer (CPX), featuring a rectangular waveguide WR12 output and providing an RF output power up to +15 dBm, is reported in this work. According to our knowledge, this is the highest reported output power level radiated directly from a photonic mixer module in the E-band frequency range. The fabricated WR12-CPX allows direct optical-to-wireless conversion of optical baseband or IF-band signals, e.g. for radio-over-fiber (RoF) fronthauling in mobile communications. The module comprises an InP-based balanced-PD (BPD) chip, a GaAs HEMT MMIC medium power amplifier, and a laminate-based grounded coplanar waveguide to rectangular waveguide (GCPW-WR12) transition. The transition couples the optically generated, e.g. via heterodyning, millimeter-wave signal from the output of the BPD chip to the WR12. It is based on a double-slot antenna structure and developed on a Rogers RT/duroid 5880 laminate with a thickness of 127 μm. The presented GCPW-WR12 transition enables the development of fully-hermetic photonic packages, which is required to improve the durability of the BPD chip. The transition design is optimized by utilizing a 3D electromagnetic simulation software for achieving a wide operational bandwidth with an average insertion loss (IL) of about 1.6 dB and a return loss (RL) higher than 15 dB in the frequency range of 71-86 GHz. Finally, the RF responsivity of the WR12-CPX module and the hermeticity of the transition are experimentally characterized. © 2019 IMA - Institut fur Mikrowellen- und Antennentechnik e.V.

This paper reports on photonic multiuser 5G hot-spots, that provide multiple beams by employing frequency steerable leaky-wave antennas. Therefore, a 60 GHz periodic leaky-wave antenna (LWA) has been developed, based on low loss substrate-integrated waveguide (SIW) technology, which is fabricated through standard PCB processes. The developed LWA operates in the V-band between 50 and 70 GHz and provides over 40° beam steering in the H-plane via frequency scanning. The capability for beam steering and multiple simultaneous beams from only one feeding port is combined with Radio-over-Fiber (RoF) techniques to provide a simple, compact and low-cost system for new applications in mm-wave communications. The proposed system enables centralized photonic beam steering in fiber-wireless transmission links, where up to 6 Gbit/s data rates are demonstrated using 64 QAM with IF-OFDM and simple receiver architectures. The multibeam capabilities provide a strong addition to RoF links by utilizing dense WDM channels to support multiple wireless users. Thereby, multiple low latency and high data rate wireless services can be provided via a single fiber-fed antenna. Finally, this concept is demonstrated by lab experiments, where three 1 Gbit/s OOK data signals were simultaneously transmitted and by a week-long field trial in a shopping mall, where two 1.5 Gbit/s real-time SDI video streams were transmitted. © 2019, Springer Nature Singapore Pte Ltd.

In this paper a coplanar waveguide (CPW) periodically loaded with resonant tunneling diodes (RTDs) and air bridges (AB) is presented as a travelling wave (TW) structure for modelling the FitzHugh-Nagumo (FHN) equation and emulating the behaviour of the nerve axon. Based upon an electrical equivalent circuit, the principle of operation is discussed in the context of a lumped-element circuital model being compared to a distributed structure. The phenomena of wave formation and propagation are studied by computer experiments of the underlying nonlinear ordinary difference-differential equations (ODEs) and that of the approximated model nonlinear partial differential equations (PDEs). A key achievement is that this medium supports stable propagating shock waves (kinks and antikinks) when effects of AB are neglected as well as stable traveling pulses only determined by the parameters of the circuit. As a result, compact electronic circuits with features of real neural systems are developed to be an experimental medium mimicking neural activity and to be applied in ultra-fast signal processing. © 2019 The Author(s).

This paper discusses the use of advantageous photonic integrated chips for beam switching antennas and beam steering antennas in the millimeter-wave and THz frequency ranges. Planar directive (up 15.4 dBi) frequency scanning leaky wave antennas (LWAs) connected to photodiodes for 5G beam steering (26 GHz and 60 GHz) with scanning angles up to 110° are reported. One and two dimensional (1D/2D) beam steering for wireless communication with multiple users as well as mobile terminal localization is demonstrated. Also, THz beam switching using lensed-assisted THz antenna arrays as well as THz beam steering using THz LWA and novel photonic integrated circuits (PICs) providing phase shift and true time delay (TTD) based optical beam forming networks are presented. © 2019 IEEE.

In this paper, we report on the integration of a photonic beam steering transmitter for the 5G26 GHz band. The transmitter, designed for fiber-To-The-Antenna applications, is based on an optical polarization diversity receiver and a PCB leaky-wave antenna. Therefore, an integrated photoreceiver with polarization dependent couplers and high frequency waveguide photodiodes provides optoelectronic conversion of an incoming radio-over-fiber (RoF) signal. The antenna is fabricated from low-cost PCB processes and includes a bias-Tee to provide an integration platform for the photodiode. The leaky-wave antenna further operates in the frequency range from 24 GHz to 33 GHz, where it scans its beam angle with changing the radio frequency. Thus, the integrated transmitter provides photonic beam steering via changing the beat frequency of the optical RoF signal due to the LWA frequency scanning behavior. A prototype transmitter has been successfully integrated, with which the photonic beam steering properties are experimentally demonstrated. © 2019 IEEE.

An efficient multi-user transmission scheme at 60 GHz using a single-feed leaky wave antenna (LWA) and hence requiring only a single radio-over-fiber link and single RF chain is presented. A subcarrier multiplexed signal carrying different users' data is transported over 2.2 km of optical fiber and then upconverted to the 60 GHz band for transmission to multiple spatially separated users through the beam steering characteristics of the LWA. An overall sum data rate, the combined rate from all users, of 10.6 Gb/s using 16-QAM modulation serving ten users over a transmission bandwidth of 3.05 GHz or 20 users with QPSK over 6.1 GHz span, is achieved experimentally. The theoretical sum data rates for 6.1 GHz bandwidth for different numbers of users are calculated, considering the SNR degradation due to the angularly dispersed LWA beam, showing that data rates over 30 Gb/s can be obtained. Finally, a system design that improves coverage and spectrum efficiency through operating multiple LWAs with a single RF chain is demonstrated. © 1983-2012 IEEE.

Indium-Phosphide (InP) is one of the most common materials used for realizing active devices working in the millimeter frequency range. The isotropic etching profile of InP substrates limits the realization of passive devices, thus requiring an expensive and lossy hybrid platform. This paper presents a via-less, cost-effective and efficient solution for InP substrate. By using the proposed planar solution, it is demonstrated that rectangular waveguides can be realized on InP by fabricating a bed of nails structure which acts as a reflecting boundary for an impinging millimeter wave. As a proof of concept, a transition from microstrip to rectangular waveguide structure is realized within H-band (220-320 GHz) with a return loss of-18dB over a bandwidth of 30 GHz. © 2019 IEEE.

In this paper, we report on a novel all photonic FMCW radar system for detection and localization of multiple objects. This is achieved by utilizing the self-sweeping functionality of tunable external cavity lasers (ECL) in combination with optical heterodyning for generating a millimeter-wave FMCW radar signal. In order to also localize the objects, frequency scanning mm-wave leaky-wave antennas (LWAs) are used. The LWAs enable beam steering via the FMCW signal for estimating the direction of arrival (DoA) of the radar echos. Overall, this approach yields very compact all photonic radar systems that do not require electrical oscillators or optical modulators. In addition, thanks to the LWAs, multiple objects can be localized within a single sweep and without any clock or control signals. Experimentally, the performance of a developed all photonic 60 GHz radar with a 10 GHz bandwidth is demonstrated for multiple object detection and localization. It is shown that the developed radar provides a range and DoA angle estimation error of <1 cm and ∼3°, respectively. This is achieved without using any dedicated radar signal post-processing algorithms. © 2018 IEEE.

In this work, we present a compact optoelectronic THz frequency domain spectroscopy (FDS) system for determination the real part of the refractive index of a semiconductor wafer with a given thickness. The concept is based on the detection of transmission maxima, which appear due to Fabry-Perot interferences inside the wafer and which depend on the refractive index of the semiconductor material. This all-fiber based THz FDS setup consists of two external cavity laser diodes and an uni-traveling-carrier photodiode (UTC-PD) module on the emitter side, while a Schottky barrier diode (SBD) is used as THz receiver. Since we don't need any additional lenses and because of the small device dimensions, this setup is compact in size, compared with traditional bulky TDS systems. We prove our THz FDS concept by characterizing of a semi-insulating iron-doped indium phosphide (InP:Fe) wafers with different thicknesses within a frequency range from 220 GHz up to 450 GHz. Based on the determination of the free spectral range (FSR) between the Fabry-Perot transmission maxima, a refractive index of 3.475 for this frequency region is obtained. Additional THz time domain spectroscopy experiments match the THz FDS results very well and confirm our results. Furthermore, analytic calculations are in excellent agreement with the measurements. A planned transfer of this THz FDS approach to a completely hybrid or monolithic integration of all photonic devices in a compact module could be offer a very small and full mobile THz spectroscopy setup. © 2018 IEEE.

THz spectroscopy with continuous wave lasers is typically based on the frequency tuning of the lasers. This process is rather slow, and some systems require additional sophisticated postprocessing. We propose a multimode system without postprocessing requirements to reduce measurement time. For this, we use a modulation scheme with multiple laser sources to enable snapshot amplitude THz spectroscopy. As the detection is performed with a Schottky barrier diode the scheme is very fast but discards phase information. This approach makes amplitude THz spectroscopy possible without frequency tuning or any moving mechanical parts. © 2018 IEEE.

A PCB based leaky-wave antenna (LWA) design for wide angle beam steering is presented. This design employs longitudinal slots inserted into a substrate-integrated waveguide for operation in the mm-wave V-band. It is optimized for a reduced open-stopband and linear through broadside beam steering. The base design is outlined and adapted for three high frequency laminates with different dielectric constants. It is further described how the dielectric constant directly affects the beam steering properties of the LWA and how to scale the achieved beam angle for the given design by only changing the PCB material. The three LWA designs achieve beam steering from about 45° at ϵr =2.2, over 60° at ϵr =6.15 to 75° at ϵr =10.2. The simulated radiation patterns show a flat gain of up to 18.0 dBi, 17.85 dBi and 15.27 dBi respectively. Furthermore, the effect of the modified PCB permittivity on the radiation efficiency as well as multiuser support with a beam per user is investigated. © 2018 IMA.

A novel direction of arrival (DoA) estimation system based on a PCB substrate-integrated waveguide (SIW) leaky-wave antenna (LWA) is presented. The antenna provides high broadside efficiency and low return loss in the frequency range of operation from 50 to 70 GHz. The antenna consists of an array of SIW fed microstrip antennas and can be fabricated through cost-effective PCB processes. The proposed scheme only requires a low-cost passive LWA antenna and is thus much more cost and power efficient when compared to the traditional DoA estimation techniques based on phased array antennas, which also require a high processing gain. One power detector is utilized to estimate the DoA by measuring the received power at the LWA port. This technique has a coverage range of +/- 8 degrees and can be employed to estimate received signal DoA of a mobile user which is up to 1 m away from the receiver. An experimental measurement for the proposed DoA estimation technique is presented along with the LWA radiation pattern. © 2017 IEEE.

A novel monolithic integration concept of an indium phosphide (InP) THz-photodiode (PD) featuring a rectangular waveguide output is presented. The concept is based on a planar grounded coplanar waveguide to rectangular waveguide (GCPW-to-WR3) transition designed on an InP substrate. The presented integration eliminates the need for complex and high-cost hybrid integration and packaging techniques, like flip-chip, wire-bonding, and split-block. The numerical analysis of the designed transition shows a 3dB bandwidth of 44 GHz within the WR3-band. Its electrical performance and bandwidth are compared with the ultra-thin low-dielectric liquid crystalline polymer-based GCPW-to-WR3 transition. © 2018 IEEE.

In this work, a low-cost and low-latency 60 GHz transceiver supporting beam steering in 5G hot-spots is presented. Beam steering is achieved via carrier frequency tuning by using a voltage-controlled oscillator (VCO) and a PCB based leaky-wave antenna (LWA). Besides enabling inherent beam steering, which does not add to the link latency, the LWA also requires only one RF port even for multiple beams. The fabricated LWA provides up to 20 dBi directivity within the 50-70 GHz band. Within this bandwidth, over 40 deg beam steering is achieved. The employed SiGe 60 GHz transceiver RFIC is highly integrated. It includes RF and baseband amplifier chains, mixers, filters and the VCO with a control loop. The transceiver RFIC is fabricated using a BiCMOS foundry process providing scalability and low-cost. By integrating the SiGe RFIC with the LWA, a Gigabit-Ethernet (GbE) wireless transceiver is developed providing time division duplex (TDD) 60 GHz wireless communication with a standardized GbE interface. The 60 GHz transceivers are employed in a 2 m long wireless communication link, which is experimentally evaluated using an IP traffic tester. A latency of about 0.4 ms and an aggregated data rate of almost 1 Gbit/s is experimentally achieved. © 2018 IMA.

In this work, laser beam melting (LBM) is used for direct 3D printing of hollow-metallic rectangular waveguides (WRs) within the WR3-band (230-320 GHz). By using laser beam melting of stainless steel (SS) 316L powder, a WR3 waveguide is fabricated in a single 3D printing process. This eliminates the need for costly mechanical and chemical post-printing processes required in traditional micromachining and non-metallic 3D printing technologies. In addition, the metallic LBM waveguides outperform the non-metallic ones in mechanical robustness. On the other hand, the surface roughness for LBM SS316L is typically higher as compared to non-metallic printed structures. For rectangular waveguides, this leads to slightly higher transmission losses. According to these performances, 3D metallic printing can be considered as a suitable technology for rapid prototyping, e.g. for high-frequency photodiode (PD) packages, where complex PD packages are printed in a single fabrication step. Since the length of the rectangular waveguide in the terahertz photodiode package is only a few millimeter long, slightly higher transmission losses can be accommodated. To investigate the use of LBM technology for THz PD packages, the impact of the surface roughness on the electrical performance of the fabricated waveguides is numerically and experimentally analyzed. The measured average inner surface roughness is about 50 μm, whereas it is about 47.7 μm at the WR3 flange surface, resulting in an RF insertion loss of about 0.7 dB/mm. By smoothing the WR3 flange surface to values as low as 2 μm via a simple milling process, RF losses are reduced down to 0.3 dB/mm. © 2018 IEEE.

The generation and detection of radiation in the THz frequency range can be achieved with many different electronic and photonic concepts. Among the many different photonic THz systems the most versatile are based on diode lasers. In this paper we describe and review the different concepts and optimization ideas for diode laser based THz systems in order to achieve the best performance for different types of THz setups. © Author(s) 2018.

Terahertz phase delay of high-resistive Silicon based Fabry-Perot resonators (FPR) is experimentally investigated using a photonic two-tone THz spectroscopy system with a self-heterodyne receiver. The photonic spectroscopy system consists of two free-running lasers of which one is externally modulated and an InP-based photodiode for two-tone THz signal generation. A Schottky barrier diode (SBD) is employed as self-heterodyne THz receiver. This way, spectroscopic THz phase and amplitude characterization is enabled without bulky delay lines and the phase noise of the two free running lasers is canceled out. By employing the developed photonic spectroscopy system, phase delay and transmission of a THz FPR is experimentally characterized between 270 GHz and 305 GHz. It is furthermore shown, that the measured THz phase delay difference and FSR of 23 degrees and 13 GHz, respectively, as well as the measured THz transmission coefficient agree well with an analytic model for the phase delay of a Fabry-Perot resonator. © 2018 IEEE.

This manuscript discusses photonic assisted beam steering and beam switching millimeter-wave and THz antennas. Planar frequency scanning 60 GHz band leaky wave antennas (LWA) providing up to 15.4 dBi gain and scanning angles up to 110° are reported next to 300 GHz band LWAs with a max. directivity of 16 dBi and 72° scanning angle. Furthermore, photonic beam forming networks (OBFN) for true time delay (TTD) and phased array wideband (275-350 GHz) THz antennas are described. Finally, multiple beam antenna arrays for 1D and 2D beam switching are shown. Experimentally, 1D THz beam switching of 18° is demonstrated. Simulation results for 2D beam switching show a scanning angle of 70°. © 2018 IEEE.

Compact planar laminate-based transitions for integrating high-frequency photodiodes (PDs) with rectangular waveguides (WRs) are presented for the WR15 to WR1 standard waveguide bands, i.e. from 0.05 THz up to 1.1 THz. The transitions couple the optically generated (e.g. via heterodyning) millimeter-wave or terahertz signals from the grounded coplanar waveguide (GCPW) output of the PD chip to the WR. To our knowledge, this is the first scalable integration concept that enables hermetic photodiode packaging up to the terahertz frequency range. For the WR15-WR6 bands, all transitions are designed on ultra-thin microfiber reinforced PTFE composites (127 &#x03BC;m Rogers RT/duroid 5880 laminate). For the WR5-WR2.2 and the WR1.5-WR1 bands, liquid crystalline polymer ULTRALAM 3850 laminates are used with a thickness of 50 &#x03BC;m and 25 &#x03BC;m, respectively. The proposed GCPW-WR transition design is based on a double-slot antenna structure and enables the development of fully-hermetic photonic packages, which is required to improve the durability of the PD chip. The transition designs are optimized by systematic EM-wave propagation modelling for achieving a wide operational bandwidth of up to 30% of the respective center frequency for each WR band. The optimized transitions exhibit an average insertion loss (IL) of about 1.5 dB and a return loss (RL) of about 10 dB for all waveguide bands (WR15-WR1). Based upon the systematic numerical modeling, generic guidelines are developed that allow designing a specific transition for any given waveguide band to 1.1 THz. In addition to the numerical analysis, GCPW-WR12 transitions for E-band (60-90 GHz) operation are fabricated and integrated with InP-based balanced-PD (BPD) chips and GaAs HEMT MMIC medium power amplifiers in a fully-hermetic package. Furthermore, hermetic WR12 coherent photonic mixer (CPX) modules are developed. The packaged WR12-type CPX allows direct optical-to-wireless conversion of optical baseband or IF-band signals e.g. for radio-over-fiber (RoF) fronthauling in mobile communications. The WR12-CPX modules provide RF output power of up to +15 dBm at 77.5 GHz. OAPA

A public field trial showcasing an operational RAT mobile network was implemented in one of the largest shopping malls in Warsaw, Poland. The network supports novel 60 GHz 5G mobile access as well as legacy LTE and WiFi services All mobile access services of the network are interconnected via optical fiber to the data centers of a mobile network operator and an Internet service provider. Fronthauling for the 60 GHz 5G hotspot Rau and for LTE is realized by analog RoF via a fiber optic DAS. The 60 GHz 5G Raus for the eMBB use case and the WiFi AP are both backhauled via optical Gigabit Ethernet. The 60 GHz Raus for the eMBB and hotspot use case feature 2D beam-switching and 1D beam-steering, respectively. Inter-RAT switching between the different mobile services with seamless user experience is achieved using a Mobile IP system with FILS. © 2002-2012 IEEE.

A system for serving a large number of users at millimeter-wave (mmW) frequencies using a single Radio Frequency (RF) chain is presented. A single Remote Antenna Unit (RAU) supported by Radio-over-Fiber transport is used to transmit multiple 60GHz band signals to various users located at different spatial locations using the beamsteering characteristics of a Leaky Wave Antenna (LWA). Error Vector Magnitude analysis has been performed for each user signal up to a maximum of seven users per RF chain with wireless transmission over 2m. A performance comparison for different user-signal frequency spacings has been provided to understand the limitations of the system and results show that the proposed system design with the LWA performs better than systems using waveguide and horn antenna transmitters. A realization to double the number of served users is also presented which shows that up to 10 users can be served using half region of the LWA, with each user transmitting 1Gb/s data rate, delivering an aggregate data rate of 10Gb/s. © 2018 IEEE.

In this paper an FMCW radar system for simultaneous distance and direction estimation of multiple objects with a single sweep is reported. Therefore, a frequency scanning leaky-wave antenna (LWA), providing 60°beam steering from 50 to 60 GHz and over 110°within the V-band, is utilized. The radar is operated to cover the full section within a single frequency sweep. Thus, fast radar operation is enabled, and the distance and direction of multiple objects is obtained from the time dependent spectral components of the received IF signal. © 2018 IEEE.

A novel compact terahertz near field coupling (NFC) based hybrid integration platform for interconnecting active III-V semiconductor devices, e.g. a high frequency photodiode (PD), on Silicon is designed, simulated, and fabricated. The studied NFC approach allows mounting InP-based triple transit region photodiodes (TTR-PD) with integrated log periodic toothed antenna (LPTA) as Terahertz transmitter on a highly resistive silicon (HR-Si) substrate receiving the terahertz radiation via a second LPTA. The electrical THz output power of the TTR-PD is transferred using electromagnetic NFC to the receiving antenna. Numerical simulations of the NFC integration technique show an insertion loss (IL) of 2 dB at 250 GHz with a return loss (RL) better than 10 dB. A 3dB operating bandwidth of 43 GHz (234 GHz-277 GHz) is achieved. © 2018 IMA.

We report a coherent Radio-over-Fiber (CRoF) THz communication link supporting both, off-line high data-rate 59 Gbit/s transmission using a record spectral efficient 64-QAMOFDM modulation as well as real-time HDTV transmission at 328 GHz carrier frequency. © 2017 OSA.

In this paper, we report on a field trial, demonstrating the seamless wireless extension of a real-world 2.5 Gbit/s Gigabit passive optical network (GPON) using a hybrid fiber wireless (HFW) bridge. Direct optic-to-RF conversion using a novel coherent photonic mixer (CPX) and direct RF-to-optic radio access units (RAU) were developed and employed to extend the reach of the GPON network using a 455 m long-distance 73.5 GHz millimeter-wave point-to-point (PTP) wireless link. The wireless GPON bridge was synchronized to the downlink transmission line rate of 2.5 Gbit/s. In the field trial, as total downlink traffic of about 2.5 Gbit/s was transmitted over SMF and the wireless bridge between the OLT and three ONU. The total uplink traffic from two ONUs to the OLT was about 1.2 Gbit/s. © 2017 IEEE.

We present a steerable 60 GHz band multibeam antenna for high-capacity 5G hot-spot-scenarios. The developed SIW-LWA-antenna provides about 40° beam steering and a 14 dBi H-plane directivity. Wireless transmission to multiple users and maximum user data rates up to 6 Gbit/s are demonstrated. © 2017 IEEE.

This paper presents photonic-assisted 60 GHz mm-wave and 325 GHz system approaches that enable the transmission of spectral-efficient and high data rate signals over fiber and over air. First, we focus on generic channel characteristics within the mm-wave 60 GHz band and at the terahertz (THz) band around 325 GHz. Next, for generating the high data rate baseband signals, we present a technical solution for constructing an extreme bandwidth arbitrary waveform generator (AWG). We then report the development of a novel coherent photonic mixer (CPX) module for direct optic-to-RF conversion of extreme wideband optical signals, with a >5 dB higher conversion gain compared to conventional photodiodes. Finally, we experimentally demonstrate record spectral efficient wireless transmission for both bands. The achieved spectral efficiencies reach 10 bit/s/Hz for the 60 GHz band and 6 bit/s/Hz for the 325 GHz band. The maximum data rate transmitted at THz frequencies in the 325 GHz band is 59 Gbit/s using a 64-QAM-OFDM modulation format and a 10 GHz wide data signal. © 2017 Walter de Gruyter GmbH, Berlin/Boston.

A plasmonic photodetector based on nanomonopoles is proposed and investigated. The detection region is a thin film of InGaAs, placed on a n-doped InP substrate. The responsivity of the photodetector is estimated to be ∼200 mA/W, while its 3 dB electrical bandwidth is ∼ 1 THz. © 2017 IEEE.

We report on a record spectral efficient terahertz communication system using a coherent radio-over-fiber (CRoF) approach. High spectral efficient back-to-back and wireless THz transmission around 325 GHz is experimentally demonstrated using a 64-QAM-OFDM modulation format and a 10 GHz wide wireless channel resulting in a data rate of 59 Gbit/s. © 2017 Optical Society of America.

A periodic leaky-wave antenna (LWA) design based on low loss substrate-integrated waveguide (SIW) technologywith inset half-wavemicrostrip antennas is presented. The developed LWA operates in the V-band between 50 and 70 GHz and has been fabricated using standard printed circuit board (PCB) technology. The presented LWA is highly functional and very compact supporting 1D beam steering and multibeam operation with only a single radio frequency (RF) feeding port. Within the operational 50–70 GHz bandwidth, the LWA scans through broadside, providing over 40° H-plane beam steering. When operated within the 57–66 GHz band, the maximum steering angle is 18.2°. The maximum gain of the fabricated LWAs is 15.4 dBi with only a small gain variation of +/–1.5 dB across the operational bandwidth. The beam steering and multibeam capability of the fabricated LWA is further utilized to support mobile users in a 60 GHz hot-spot. For a single user, a maximum wireless on-off keying (OOK) data rate of 2.5 Gbit/s is demonstrated. Multibeam operation is achieved using the LWA in combination with multiple dense wavelength division multiplexing (WDM) channels and remote optical heterodyning. Experimentally, multibeam operation supporting three users within a 57–66 GHz hot-spot with a total wireless cell capacity of 3 Gbit/s is achieved. © 2017 by the authors. Licensee MDPI, Basel, Switzerland.

Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz-30 THz) have developed rapidly over the last 30 years. For most of the 20th Century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to 'real world' applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2017, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 18 sections that cover most of the key areas of THz science and technology. We hope that The 2017 Roadmap on THz science and technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies. © 2017 IOP Publishing Ltd.

In this work, we present a novel compact rectangular-waveguide-type (WR-12) coherent photonic mixer module, featuring a balanced photodetector. The module enables the direct fiber-to-the-antenna connectivity for the upcoming 5G links. Experimental results with respect to the output RF power (e.g., -7.3 dBm at 73 GHz) and the frequency response deviation (±0.5 dB) are presented within the 71-76 GHz range. © 2016 IEEE.

A compact E-band (71-76 GHz) conductor-backed coplanar waveguide (CBCPW) to hollow metallic waveguide (WR-12) transition has been designed and fabricated. The fully-planar two-layer transition makes use of a double-slot antenna, which efficiently couples the millimeter-wave (mm-wave) signal from the CBCPW to the WR-12 waveguide. The introduced transition, together with an integrated high-speed balanced photodetector (BPD), enables the development of a compact coherent photonic mixer featuring a WR-12 output (WR12-CPX). The mm-wave generation is realized by heterodyne coherent optical detection in the BPD chip. The WR12-CPX allows direct optical-to-wireless conversion, enabling fiber-to-the-antenna connectivity for mobile backhauling. The transition is designed and fabricated on a 127 μm thick ROGERS RT/duroid 5880 laminate (ϵr = 2.2). The experimental results of the fabricated transition show a maximum insertion loss of 3 dB and an average return loss of ∼20 dB. In addition to that, the packaged transition is presented as part of a novel WR12-CPX module. © 2016 IEEE.

An E-band 76-GHz coherent radio-over-fiber (CRoF) system has been developed employing an integrated coherent photonic mixer (CPX) in the radio access unit (Rau) and a Schottky envelope detector in the wireless receiver. The CPX basically consists of a 2 × 2 multi-mode interferometer (MMI) coupled to a balanced photodiode (PD). It enables direct conversion of the optical baseband signal to the wireless RF signal with a carrier frequency at 76 GHz using a local oscillator located in the Rau. The developed CPX module features a V-type connector. The 3-dB cut-off frequency and 1-dB saturation output power of the CPX module are estimated as ∼70 GHz and -2.43 dBm, respectively. It is shown that due to the integration of the MMI and the balanced PD, the developed CPX outperforms a commercial 110-GHz PD in terms of conversion efficiency up to 92 GHz. Experimentally, long-distance wireless transmission is shown using the constructed CRoF system and highly directive antennas with a gain of 43 dBi each. A wireless transmission of 1 Gb/s non-return-to-zero data signal at 76 GHz carrier frequency is demonstrated up to 230 m. The receiver sensitivity of the constructed wireless receiver for a pre-FEC bit error rate of 10-3 has been measured to be -34.8 dBm. This has enabled wireless data transmission over 92 m and 230 m at transmit power levels as low as -11.17 dBm and -3.36 dBm, respectively. It is shown that the experimental transmit power levels agree well with the expected figures calculated using an analytic Friis model describing the wireless channel. It is also estimated that the system could support maximum wireless distances up to 2000 m. © 1983-2012 IEEE.

This paper reports on the development of a packaged coherent photonic mixer (CPX) for coherent Radio-over-Fiber (RoF) systems. The developed integrated CPX performs direct optical-to-RF up-conversion with a 5 dB better conversion efficiency at 60 GHz as compared to a commercially available 110 GHz photodiode. The 3 dB bandwidth and maximum RF output power of the CPX are 65 GHz and +7 dBm, respectively. By utilizing the developed CPX module in a CRoF system, we demonstrate 1 Gbit/s NRZ data transmission over 25 km long fiber and a 230 m long wireless link within the 71-76 GHz band. Furthermore, a novel IF-CRoF architecture is presented enabling high-capacity 21 Gbit/s wireless 60 GHz transmission using a 64 QAM-OFDM modulation format and record spectral-efficiency (9 bit/s/Hz) wireless transmission using a 512 QAM-OFDM modulation. © 2016 IEEE.

Here, we propose a novel leaky-wave antenna operating in the V-band. The antenna provides high broadside efficiency and low return loss in the frequency range of operation from 50 to 70 GHz. The antenna consists of an array of substrate integrated waveguide fed dipoles and can be fabricated through cost-effective PCB processes. High peak directivities of over 20 dBi are obtained for a compact (4 × 80 mm2) array consisting of only 20 unit cells. The directivity is flat (+/-1 dB deviation) and can be further increased by enlarging the array. Furthermore the antenna provides over 40 deg of beam steering in the frequency range of operation. © 2016 IEEE.

As an emerging topic, photonic-assisted microwave measurements with distinct features such as wide frequency coverage, large instantaneous bandwidth, low frequency-dependent loss, and immunity to electromagnetic interference, have been extensively studied recently. In this article, we provide a comprehensive overview of the latest advances in photonic microwave measurements, including microwave spectrum analysis, instantaneous frequency measurement, microwave channelization, Doppler frequency-shift measurement, angle-of-arrival detection, time–frequency analysis, compressive sensing, and phase-noise measurement. A photonic microwave radar, as a functional measurement system, is also reviewed. The performance of the photonic measurement solutions is evaluated and compared with the electronic solutions. Future prospects using photonic integrated circuits and software-defined architectures to further improve the measurement performance are also discussed. (Figure presented.). © 2016 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A planar 71-76 GHz integration platform is designed and fabricated for high-power radio-over-fiber (RoF) wireless photonic transmitters (PTs). The platform enables the integration of high-electron-mobility-transistor RF amplifiers and millimeter wave photodiodes (PDs), e.g., the waveguide triple transit region PD. An efficient electrical coupling between the PD chip and the rectangular waveguide (WR-12) output is attained through a low-loss grounded coplanar waveguide to a rectangular waveguide transition. The integration platform features a novel planar bias-tee design making use of a single quarter-wave coupled-lines (SCLs) section and slotted splitring resonators (SRRs). The bias-tee network enables proper biasing for the PD chip and protects the hybrid integrated RF amplifier from being damaged by the DC bias voltage. The introduced design together with the WR-12 output enables the development of high-power (>17 dBm) PTs for mobile backhaul links and radar applications. Experimental characterization of the designed platform is introduced and compared to numerical results.

A nanoantenna-based plasmonic photodetector is proposed and investigated theoretically. An array of interconnected nanomonopoles on a film of InGaAs on n-doped InP is modeled. The infrared (∼1550 nm) responsivity of the structure can reach ∼200 mA/W for a 20-nm-thick InGaAs layer. The optimum 3-dB electrical bandwidth of the device is calculated to be ∼1 THz for the case of a 20-nm-thick InGaAs layer and a 4 × 4 nanomonopole array. The electrical bandwidth is shown to increase by decreasing the number of elements in the array. A simple linear model for the total resistance of the structure is proposed and validated. The total resistance increases by increasing the thickness of the InGaAs layer and by decreasing the number of array elements. © 1983-2012 IEEE.

The extension of ultra-dense WDM passive optical networks (PONs) by millimetre-wave coherent radio-over-fiber (RoF) links is investigated. For a seamless and transparent integration of the RoF links coherent heterodyne detection is used for the generation of the wireless RF signals out of the optical baseband data signals. Simulations of the optical SIR in the PON are carried out in dependence on the WDM channel spacing. The projected impact on the transmission quality is derived and WDM CRoF experiments are performed. In the experiments three data modulated optical channels are transmitted over 10 km SMF to simulate the PON, before arriving at the E-band radio access unit (RAU). The RAU utilizes heterodyne detection with an optical LO for converting the 1 Gb/s optical baseband signal to a 75 GHz RF signal. After 40 m wireless transmission the signal is received by an antenna and downconverted to baseband using a low-cost SBD based receiver for envelope detection. The filtering of WDM channels with an optical channel spacing of down to 10 GHz showed very little penalty versus single channel transmission, relying only on the filter characteristic of the used LNAs and antennas and using no optical filters. Still the receiver's sensitivity is only -57 dBm for a bit error rate (BER) of 2·10-3, thus it is shown that an ultra-dense WDM PON can be extended wirelessly using coherent RoF techniques without the need for optical filtering. © 2015 IEEE.

This paper focuses on the development and characterization of a novel E-band planar bias-tee (BT) circuit featuring a high-speed millimeter wave photodiode (mm-wave PD) module to be integrated in next generation access and mobile networks (5G). The designed bias-tee circuit together with the integrated mm-wave PD chip, i.e., triple transit region photodiode (TTR-PD) allows the development of high-power Radio-over-Fiber (RoF) E-band (70/80 GHz) photonic transmitters (PTs) to be used in wireless extension and mobile backhaul links. The introduced BT circuit provides the protection to the hybrid integrated RF amplifier from being damaged by the PD bias voltage and prevents the leakage of the RF signal through the DC path. The vector network analyzer (VNA) measurements of the BT circuit show that in the frequency range from 70 to 75 GHz, the return loss (RL) is higher than 11 dB, the RF signal suppression level (IS) in the DC path is higher than 30 dB, while the insertion loss (IL) is lower than 2 dB. For optical RF signal generation, two laser sources are used to generate an optical heterodyne signal. Lower dark current levels and a 3-dB bandwidth in the frequency range from 71 to 86 GHz have been demonstrated at the BT output. © 2015 IEEE.

Here, we present a compact photonic transmitter module featuring an integrated InP-based 1.55 μm triple transit region photodiode (TTR-PD) chip and a WR-12 rectangular waveguide output for E-band (60-90 GHz) radio-over-fiber applications. In order to enable work capability in broadband wireless E-band communications over long- and medium-range distances, the fabricated TTR-PD module provides excellent frequency flatness exhibiting a maximum deviation of ±1 dB within the complete 71-86 GHz band and high-power levels in excess of -5 dBm (without external amplification) at a photocurrent of 10 mA. In addition, we report for the first time on non-isothermal analyses of TTR-PDs using the drift-diffusion model with integrated Joule heat generation. © 2015 IEEE.

An integrated 110 GHz coherent photonic mixer (CPX) is designed and fabricated for coherent RoF (CRoF) mobile backhaul links. The CPX simultaneously performs optical WDM channel selection and direct optical-to-RF conversion. Due to its broadband performance, the CPX simultaneously supports future wireless systems operating in the 57-64 GHz, 71-76 GHz, 81-86 GHz bands and even research-type W-band systems. The RF frequency response of the CPX in the 60 GHz and 70/80 GHz bands is about 4 dB higher as compared to a commercial 110 GHz photodiode. A CRoF experiment is carried out to also prove the advantageous performance of the new 110 GHz CPX against a commercially available 110 GHz photodiode in a CRoF system experiment with a 25 km standard single-mode fiber (SMF) and a 40 m long 71-76 GHz wireless link. This experiment reveals a significant improvement in optical receiver sensitivity of the radio access unit (Rau) with a required optical signal power as low as -32 dBm at a BER=2×10-3 for a 1 Gbit/s NRZ-OOK data signal. © 2015 IEEE.

Here, we report on a completely passive InGaAsP/InP-based Ψ-type optical polarization splitter (as part of an integrated 1.55 μm photonic polarization diversity receiver), which exhibits splitting ratios up to 14.1 dB and 22.3 dB for TE- and TM-polarized light, respectively. © 2015 Viajes el Corte Ingles, VECISA.

Here, a millimeter wave photodiode (mm-wave PD) integration platform for development of high-power Radio-over-Fiber (RoF) wireless photonic transmitters (PTs) is presented. The platform features a novel planar bias-tee network design making use of a single quarter-wave coupled-line (CL) technique and two slotted split-ring resonators (SRRs) integrated in the DC bias line. The introduced bias-tee network enables proper biasing for mm-wave PDs, e.g. the triple transit region photodiode (TTR-PD), and protects the hybrid integrated RF amplifier from being damaged by the bias voltage. The 3D full-wave electromagnetic field simulations of the designed bias-tee network show that in the whole 71-76 GHz band, the return loss (RL) is higher than 20 dB, the RF signal suppression level (IS) is higher than 30 dB, while the insertion loss (IL) is lower than 0.6 dB. A fence of via holes surrounds the bias-tee network to reduce the RF propagation losses into the laminate and to ensure that the grounded coplanar waveguide (GCPW) supports only a quasi-static transverse electromagnetic mode (TEM). The bias-tee network integrated together with high-electron-mobility transistor (HEMT) RF amplifiers and GCPW-to-rectangular waveguide (WR) transition enables the development of high-power (>17 dBm) PTs with WR-12 output. The IL of the complete integration platform is ∼2.2 dB. © 2015 IEEE.

This paper presents a novel planar bias-tee (BT) circuit comprising a quarter-wave single coupled-line (SCL) section designed on 127 μm thick ROGERS RT/duroid 5880 laminate for E-band (71-76 GHz) wireless photonic transmitters. The BT circuit enables proper biasing for millimeter wave photodiodes (mm-wave PDs) through the RF-choke, and in addition, protects the hybrid integrated RF amplifier from being damaged by the DC voltage using the SCL DC-block. The planar RF-chock design is based upon two slotted split-ring resonators (SRRs) and is integrated in the DC bias line in order to prevent the leak of the RF signal into the voltage circuitry. Numerical results of the DC-block section show that in the entire 71-76 GHz band, the return loss (RL) is higher than 36 dB while the insertion loss (IL) is lower than 0.4 dB. The overall performance of the complete BT circuit (DC-block and RF-choke) has been calculated by the 3D full-wave electromagnetic field simulator based on the finite element method (RL > 20 dB, IL < 0.6 dB and RF signal suppression in the DC bias line (IS) > 30 dB). A via hole fencing surrounds the BT circuit to reduce the RF propagation losses into the laminate and to ensure that the grounded coplanar waveguide (GCPW) supports only a quasi-static TEM mode. © 2015 IMA: IMATech e.V.

A novel transition from a grounded-coplanar waveguide to a substrate integrated-waveguide (SIW) is presented featuring a fully planar bias tee for the development of 60 GHz radio-over-fibre photonic transmitters for indoor applications. The transition is intended to serve as a connection between a 60 GHz photodiode chip and SIW antennas suitable for indoor data distribution. Simulations show that in the whole 57-64 GHz communication band, the return loss (RL) is at least 15 dB, whereas the insertion loss (IL), is < 0.9 dB. Measurements of a back-to-back configuration confirm the numerical results, with a IL of ~2 dB and a RL > 12 dB. © The Institution of Engineering and Technology 2014.

A new coherent optical heterodyne radio-over-fiber (CRoF) scheme is proposed for seamless integration of next generation millimeter-wave wireless systems into a (ultra-dense) next generation passive optical network (NG-PON2). For seamless integration with the (ultra-dense) WDM infrastructure of high-capacity and longer-reach NG-PON2 networks, we propose novel radio access units (RAU) using coherent optical heterodyne detection for the generation of the millimeter-wave radio signals. The proposed CRoF concept supports the provision of multiple services over a single optical distribution network including next generation optical and wireless access services and high-capacity fixed wireless links for mobile backhaul. A proof-of-concept experiment is demonstrated in the context of backhauling. An E-band RAU utilizing CRoF is used for converting 2.5 Gb/s optical baseband data after 20 km fiber transmission to a 76 GHz wireless signal. After subsequent wireless transmission over 40 m (limited by the lab environment), the wireless E-band signal is directly reconverted to 2.5 Gb/s baseband data using a low-cost 76 GHz wireless receiver with RF envelope detection. The receiver's sensitivity is only -47 dBm for a bit error rate (BER) of 2.10-3. Within international regulations, the transmit RF power can be further increased by about 68 dB, i.e. wireless distances way beyond 2 km can be expected even in the case of rain. © 2014 IEICE.

We report on the generation of low phase noise millimeter-wave signal at 100 GHz with a dual-frequency laser and a high-speed photodiode. The laser beatnote is phase-locked on the tenth harmonic of a 10 GHz synthesizer through a new photonic down-converter based on a phase modulator. The spectral purity of the millimeter-wave signal has been fully characterized: it is spurious free over a large bandwidth and its phase noise is limited by the synthesizer itself (-90 dBc/Hz at 10 kHz). © 2012 IEEE.

A radio-over-fibre system using coherent optical heterodyne detection scheme is proposed, to achieve seamless integration of a photonic Remote Antenna Unit (RAU) into a Next Generation Dense Wavelength Division Multiplexed Passive Optical Network (NG DWDM-PON). The proposed scheme significantly simplifies the optical mm-wave generation and data recovery as it doesn't require any high-bandwidth modulator at the central office or high-frequency Local Oscillators (LOs) at either the central office or the customer unit; or optical phase-locking techniques to generate the mm-wave wireless signal. A proof-of-concept transmission utilizing 1 Gb/s On-Off Keying is experimentally demonstrated. © 2014 IEEE.

We propose and investigate a surface plasmon photodetector concept, based on the enhancement of electrical near-field in low-defect, low-doped In 0.53Ga0.47As detection volumes located in the gaps of an array of metal nanodipole antennas. We report enhancement in responsivity in the presence of nanodipoles and predict a maximum responsivity of ∼100 mA/W at wavelengths near 1550 nm. The 3 dB electrical bandwidth of the device is estimated based on its RC rise time and the hole transit time through the detection volume for the cases of conventional and ballistic transport in InGaAs and is found to range from ∼0.7 to 4 THz. Also, trends are observed relating the responsivity to the gap dimensions, revealing a trade-off between the field-enhancement in the gap and its volume, and leading to an optimum gap length producing the maximum responsivity. © 2014 AIP Publishing LLC.

This paper describes a robust radio-over-fiber wireless link system for use in wireless extension and mobile backhaul applications. The wireless link operates at 71-75 GHz E-band carrier frequencies and can transmit ultra-high access data such as Gigabit Ethernet or OC-48 up to 2.5 Gbps. Enabling photonic technologies, system configurations, and lab trials are presented. © 2014 OSA.

A surface plasmon nanoantenna-based photo-detector is proposed and investigated. An array of nanodipoles on an InP substrate is assumed, where the detection region consists of volumes of InGaAs located in the gaps of the nanodipoles. The responsivity of the photodetector is estimated to be ∼100 mA/W at its peak value. A trend is observed for the power absorption in the detection region as a function of gap size; an optimum gap size exists that maximizes the product of the gap volume and the electric field enhancement in the gap. The 3 dB electrical bandwidth of the device is calculated assuming conventional and ballistic carrier transit in the detection region, yielding 0.7-4 THz. © 2014 IEICE.

A new coherent optical heterodyne radio-over-fiber (CRoF) scheme is presented for the transparent integration of millimeter-wave wireless systems into next generation optical WDM networks. For seamless integration with the (ultra-dense) WDM infrastructure of high-capacity and longer-reach optical access networks, we propose novel radio access units (RAU) based upon a coherent optical heterodyne detection approach. The proposed CRoF concept supports the provision of multiple services over a single optical distribution network including next generation optical and wireless access services and high-capacity fixed wireless links for mobile backhaul. Proof-of-concept experiments for transparent integration of 60 GHz wireless access systems and 70/80 GHz wireless backhauling links will be presented. © 2014 IEEE.

We report on a novel triple transit region (TTR) layer structure for 1.55 μm waveguide photodiodes (PDs) providing high output power in the millimeter wave (mmW) regime. Basically, the TTR-PD layer structure consists of three transit layers, in which electrons drift at saturation velocity or even at overshoot velocity. Sufficiently strong electric fields (&gt;3000 V/cm) are achieved in all three transit layers even in the undepleted absorber layer and even at very high optical input power levels. This is achieved by incorporating three 10 nm thick p-doped electric field clamp layers. Numerical simulations using the drift-diffusion model (DDM) indicate that for optical intensities up to ∼500 kW/cm2, no saturation effects occur, i.e. the electric field exceeds the critical electric field in all three transit layers. This fact in conjunction with a high-frequency doublemushroom cross-section of the waveguide TTR-PD ensures high output power levels at mmW frequencies. Fabricated 1.55 μm InGaAs(P)/InP waveguide TTR-PDs exhibit output power levels exceeding 0 dBm (1 mW) and a return loss (RL) up to ∼24 dB. Broadband operation with a 3 dB bandwidth beyond 110 GHz is achieved. © 2014 Optical Society of America.

We present a novel transition from grounded coplanar waveguide (GCPW) to substrate integrated waveguide (SIW), designed on a ROGERS 5880 laminate for 60 GHz Radio-over-Fiber (RoF) photonic transmitters. The transition serves as connection between a 60 GHz photodiode (PD) chip and a suitable SIW antenna. In contrast to previous designs, our approach makes use of a quarter-wave coupled-lines (CL) section to transfer the signal carried by the GCPW to the SIW. This technique, creating a DC-block between the GCPW signal track and the ground layers, allows for correctly biasing the PD. In order to reduce the propagation of parasitic modes as well as the risk of interferences, the transition is fully enclosed by a fence of via holes. Simulations show that in the whole 57-64 GHz band, the return loss (RL) is higher than 17 dB, while the insertion loss (IL) is &Sim; 0.4 dB. To prevent the loss of RF power through the DC path, a planar RF-choke (RL > 22 dB, IL < 0.4 dB and RF-to-DC isolation (IS) higher than 28 dB) is additionally integrated. © 2013 IEEE.

The millimeter-wave spectrum above 70 GHz provides a cost-effective solution to increase the wireless communications data rates by increasing the carrier wave frequencies. We report on the development of two key components of a wireless transmission system, a high-speed photodiode (HS-PD) and a Schottky Barrier Diode (SBD). Both components operate uncooled, a key issue in the development of compact modules. On the transmitter side, an improved design of the HS-PD allows it to deliver an output RF power exceeding 0 dBm (1 mW). On the receiver side, we present the design process and achieved results on the development of a compact direct envelope detection receiver based on a quasi-optical SDB module. Different resonant (meander dipole) and broadband (Log-Spiral and Log-Periodic) planar antenna solutions are designed, matching the antenna and Schottky diode impedances at high frequency. Impedance matching at baseband is also provided by means of an impedance transition to a 50 Ohm output. From this comparison, we demonstrate the excellent performance of the broadband antennas over the entire E-band by setting up a short-range wireless link transmitting a 1 Gbps data signal. © 2013 Springer Science+Business Media New York.

Wireless links using carrier waves in the millimetre-wave spectrum above 70 GHz provide a cost-effective solution to increase the data rate. Reported is the development of a photonically enabled link, based on two compact modules, both operated uncooled, transmitting a 1 Gbit/s data signal over several metres. The first module includes an optimised high-speed photodiode, delivering an output RF power exceeding 0 dBm (1 mW). Also reported is the development of a direct envelope receiver based on a quasi-optical Schottky barrier diode (SBD) module. Over the carrier frequency range, the broadband log-periodic antenna impedance has been optimised to match the SBD, while at the baseband frequency, the receiver was optimised to a 50 O output through an impedance transition. These have been key issues for the excellent performance of the compact receiver module over the entire E-band. © The Institution of Engineering and Technology 2013.

A quasi-hermetic photodiode module featuring a WR-12 rectangular waveguide (RW) output has been developed for operation in the E-band. The module makes use of a grounded coplanar-waveguide-to-rectangular-waveguide transition implemented on a Rogers RT/duroid 5880 laminate that does not require any mechanical modifications of the RW. Simulations show that the transition has excellent radio frequency (RF) characteristics (return loss larger than 30 dB, insertion loss smaller than 2 dB, maximum group delay deviation smaller than 1 ps). Measurements confirm the simulated results and highlight the importance of via-holes to reduce the overall loss. The maximum output power delivered by the module, at a DC photocurrent of 10 mA, is rm -12.5 dBm. At 73 GHz, the 1-dB compression point is found to be at a photocurrent of ∼ 9 mA, with an RF output power of ∼ -13.5 dBm. The measured output power has less than 1 dB ripple in the frequency range of interest. © 1989-2012 IEEE.

In this paper, we present a photonic wireless system operating in the W-Band (75-110 GHz) featuring ultra-high bandwidth as well as simple NRZ-OOK modulation format. By using a cascaded optical RF and data modulation approach on the transmitter side, flexible adjustment of the wireless RF carrier in the W-Band is achieved, while direct electrical to optical conversion with advanced photonic components on the receiver side enables true photonic wireless bridging. In first experiments, data rates up to 10 Gb/s have been experimentally demonstrated. © 2013 IEEE.

We present a substrate integrated waveguide (SIW) antenna designed for 60 GHz indoor Radio-over-Fiber photonic transmitters. For broad-band applications (57-64 GHz) a return loss (RL) higher than 7 dB and a front-to-back ratio (FTBR) of 17 dB are achieved. Alternative resonant solutions are also introduced to achieve RL > 10 dB and FTBR = 21 dB. © 2013 IEEE.

Here, we report on planar photonic transmitters employing high-speed 1.55 μm photodiodes. Within the 200-300 GHz band, the device exhibits a 6-dB bandwidth along with a polarization penalty of ∼2.2 dB. Besides, the chip area is reduced thanks to a novel integration approach in the antenna structure. © 2013 IEEE.

We report on the generation of a low phase noise millimeter-wave signal at 100 GHz with a dual-frequency laser and a high-speed photodiode. The laser beatnote is phase-locked on the 10th harmonics of a 10 GHz synthesizer through an original photonic down-conversion scheme. The spectral purity of the millimeter wave signal has been fully characterized: it is spurious free over a large bandwidth and its phase noise is limited by the synthesizer itself (-90 dBc/Hz at 10 kHz). © 2012 IEEE.

A grounded coplanar waveguide (GCPW) to rectangular waveguide (WR) transition is presented for operation in the E-band from 71 to 76GHz, a worldwide allocated frequency slot for wireless communication. The GCPW-to-WR transition is designated for the E-band radio-over-fibre (RoF) wireless transmitter where it connects the 50 Ω coplanar waveguide (CPW) output of a high-frequency photodiode chip to a WR-12 waveguide. The presented transition is implemented on a ROGERS RT/Duroid 5880 RF laminate, it allows for quasi-hermetic packaging without the need of radomes and enables the use of a commercially available WR without the need for any mechanical modifications. Full-wave electromagnetic simulations show that the optimised transition presents a return loss of at least 30dB and an insertion loss (IL) of only 2dB. Experimental results confirm an average IL of only 2.5dB. The key role of via-holes in reducing the IL is experimentally proven. © 2012 The Institution of Engineering and Technology.

High data rate photonic wireless systems operating at millimeter wave carrier frequencies are considered as a disruptive technology e.g. for reach extension in optical access networks and for mobile backhauling. Recently, we demonstrated 60 GHz photonic wireless systems with record data rates up to 27 Gbit/s. Because of the oxygen absorption at 60 GHz, it is beneficial for fixed wireless systems with spans exceeding 1 km to operate at even higher frequencies. Here, the recently regulated 10 GHz bandwidth within the E-band (60-90 GHz) is of particular interest, covering the 71-76 GHz and 81-86 GHz allocations for multi-gigabit wireless transmission. For this purpose, wideband waveguide photodetectors with high external quantum efficiency are required. Here, we report on double mushroom 1.55 μm waveguide photodetectors for integration in an E-band wireless transmitter module. The developed photodetector consists of a partially p-doped, partly non-intentionally doped absorbing layer centered in a mushroom-type optical waveguide, overcoming the compromise between the junction capacitance and the series resistance. For efficient fiber-chip coupling, a second mushroom-type passive optical waveguide is used. In contrast to the conventional shallow ridge waveguide approach, the mushroom-type passive waveguide allows to shift the center of the optical mode further away from the top surface, thus reducing waveguide losses due to the surface roughness. Experimentally, a very flat frequency response with a deviation up to ±1 dB in the entire E-band has been found together with an output power level of -15.7 dBm at 10 mA photocurrent and at a frequency of 73 GHz. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Here, we present novel high-power partially p-doped, partly non-intentionally doped absorbing double mushroom-type 1.55 μm waveguide photodiodes for integration in compact photonic transmitter modules employed in E-band (60-90 GHz) radio-over-fiber systems. Besides the high-output power levels approaching 0 dBm and a high linearity in the 70 GHz band, the developed photodiodes also exhibit an excellent frequency flatness and a return loss of ±0.5 dB and ∼24 dB, respectively. For low-cost packaging, the photodiodes are hybrid integrated with 71-76 GHz high-electron-mobility- transistor amplifiers followed by a low-loss radio frequency laminate-based grounded-coplanar-waveguide-to-WR-12 transition in order to enable broadband wireless communications over longer medium-range distances. © 2012 IEEE.

Microwave photonics can provide superior advantages towards ultra-wideband wireless communications. In this work, we present an integration platform for 72GHz photodiode based wireless transmitter. The placement and positioning of discrete LNA and PA components, the bias-tee design parameters of photodiode, LNA and PA, and the design parameters for low-loss transition from CPW output of amplified electrical signal at the output of PA to E-band WR12 rectangular waveguide have to be carefully determined. We present general design principles of 72GHz photodiode integration platform. Further, we compare different substrates, which have been implemented into the platform, based on numerical results. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

We demonstrate a low-phase noise frequency-tunable photonic source for generating 100 GHz W-band signals. The source offers up to twelve times optical multiplication by exploiting nonlinearities in MZM and FWM in UL-SOA. Wide frequency tuning (95-115 GHz) with average output power of -24 dBm @ 4.18 mA photocurrent and output power variations <0.5 dB is demonstrated. The absolute phase noise of the W-band signals is measured to be <-91 dBc/Hz at 10 kHz. By using an optical reference LO, the residual phase noise from the photonic source is confirmed to be even <-103 dBc/Hz at 10 kHz offset. © 2012 IEEE.

An E-Band quasi-hermetic photodiode module featuring a WR12 rectangular waveguide output has been developed using an RF transition implemented on ROGERS 5880 laminate. Its simulated maximum group delay deviation of less than 1 ps makes it suitable as wireless transmitter for Radio-over-Fibre (RoF) applications. The manufactured prototype exhibits a flat frequency response with a maximum variation < 1 dB within the band of interest (71-76 GHz). The maximum measured output power is -12.5 dBm, while the 1-dB compression point is at 9 mA, with -13.5 dBm of corresponding RF power. Error-free 1 Gb/s RoF transmission (BER< 10-9) has been demonstrated, with only 1.2 dB of measured power penalty over the 71-76 GHz band. © 2012 IEEE.

This paper presents photonic technologies enabling high data rate (>10 Gb/s) wireless access systems operating within the E-band (60-90 GHz) and the W-band (75-115 GHz). © 2011 IEEE.

This paper presents a novel concept of a hermetic E-Band Photodiode (PD) Transmitting Module for Radio-over-Fiber (RoF) applications. A commercial PD chip with 50 Ω coplanar waveguide (CPW) output is wire-bonded to a 50 Ω grounded coplanar waveguide (GCPW) based on ROGERS RT/Duroid 5880 substrate. From the GCPW board a hermetic transition that makes use of a double-slot coupling approach is designed and optimized for the 71-76 GHz band. This concept allows to efficiently coupling the electrical power delivered by the PD chip to a Rectangular Waveguide WR-12 output with an insertion loss of only 3 dB. © 2011 IEEE.

We propose and demonstrate a tunable 50 GHz photonic synthesizer using nonlinearities in a Mach-Zehnder modulator (MZM) in conjunction with the four-wave mixing (FWM) effect in an ultra-long semiconductor optical amplifier (UL-SOA). The operation principle is based on an external modulation scheme using a low phase noise local oscillator (LO) source to multiply the LO frequency in the optical domain. We experimentally demonstrate tunable and low phase noise millimeter-wave (mm-wave) signal generation up to 50 GHz using a low frequency reference LO source. A multiplication of eight-times the LO frequency has been achieved resulting from the nonlinear behavior of the MZM in conjunction with the UL-SOA. Phase noise measurements of the fundamental LO frequency as well as of the generated mm-wave signal with a multiplication factor of N=8 have shown phase noise levels of -96 dBc/Hz and -78 dBc/Hz at 10 kHz offset from the carrier, respectively. © 2011 IEEE.

We report on advanced millimeter-wave (mm-wave) photonic components for broadband radio transmission. We have developed self-pulsating 60-GHz range quantum-dash FabryProt mode-locked laser diodes (MLLD) for passive, i.e., unlocked, photonic mm-wave generation with comparably low-phase noise level of -76 dBc/Hz @ 100-kHz offset from a 58.8-GHz carrier. We further report on high-frequency 1.55-μm waveguide photodiodes (PD) with partially p-doped absorber for broadband operation f3 dB ∼ 70-110 GHz) and peak output power levels up to +4.5 dBm @ 110 GHz as well as wideband antenna integrated photomixers for operation within 30300 GHz and peak output power levels of -11 dBm @ 100 GHz and 6-mA photocurrent. We further present compact 60-GHz wireless transmitter and receiver modules for wireless transmission of uncompressed 1080p (2.97 Gb/s) HDTV signals utilizing the developed MLLD and mm-wave PD. Error-free (BER =10 -9, 2 31 -1 PRBS, NRZ) outdoor wireless transmission of 3 Gb/s over 25 m is demonstrated, as well as wireless transmission of uncompressed HDTV signals in the 60-GHz band. Finally, an advanced 60-GHz photonic wireless system offering record data throughputs and spectral efficiencies is presented. For the first time, we demonstrate photonic wireless transmission of data throughputs up to 27.04 Gb/s (EVM 17.6%) using a 16-QAM OFDM modulation format resulting in a spectral efficiency as high as 3.86 b/s/Hz. Wireless experiments were carried out within the regulated 57-64-GHz band in a lab environment with a maximum transmit power of -1 dBm and 23 dBi gain antennas for a wireless span of 2.5 m. This span can be extended to some 100 m when using high-gain antennas and higher transmit power levels. © 2006 IEEE.

We propose and demonstrate a 50 GHz opto-electronic dual-loop oscillator with low phase noise of -95 dBc/Hz at 10 kHz offset from a 50 GHz carrier and a frequency tunability of more than 100 MHz. ©2010 IEEE.

We propose and demonstrate a K-band optoelectronic oscillator with ultralow phase noise performance and a frequency tuning range exceeding 1 GHz. The operation principle is based upon using two parallel optoelectronic loops with similar but not equal length and an electrical phase shifter for frequency tuning. We experimentally demonstrate tunable microwave signal generation within 20.7-21.8 GHz with a coarse frequency resolution of ∼100 MHz. Fine tuning of the generated signal within a range of ±5 MHz is also achieved. The linewidth and phase noise of the generated microwave signal are <3 Hz and - 105 dBc/Hz at 10-kHz offset, respectively. Within the full gigahertz tuning range, the phase noise and output power of the generated microwave signal varies by only ±1.5 and <1 dB, respectively. © 2010 IEEE.

Microwave Photonics is widely considered as a disruptive technology for high data rate wireless communications. This paper discusses technological trends in enabling photonic solutions for high data rate wireless access systems operating in the millimeter-wave regime. Besides technical achievements, a focus is also put on worldwide regulations for wireless communications in the E-band (60-90 GHz). ©2010 IEEE.

In this paper we present the remarkable characteristics of quantum dash mode-locked lasers and how they could be used for low phase noise signal generation, for high data rate wireless transmission and radar in the millimeter wave frequency range. ©2010 IEEE.

A thermopile structure is proposed for the detection of microwave/millimeter wave radiation. The thermopairs in the suggested linear arrangement function as antennas. 5.58 V/W responsivity was achieved at 100 GHz with 40 serial connected thermopairs. The experimentally observed polarity and frequency dependence convincingly verify the proper detector operation. © 2010 American Institute of Physics.