Objectives: The purpose of this project is to develop efficient and ultra-stable dual-frequency lasers at 1.55 µm. This laser will feed photomixers developed by ULIL and other partners to generate powerful and coherent THz radiation. Expected Results: Realization of a THz source based on a 100 mW compact and transportable Dual Frequency Laser (DFL) that will generate an optically-carried tunable THz signal by beating of the two optical IR modes, whose frequency spacing will be fixed at 280 GHz +/-3%. Also, because the two wavelengths share the same cavity in our DFL configuration, lower phase noise and smaller linewidth (< kHz) are expected. This research addresses Challenge I and V Planned secondment(s): To ULIL (Prof. Guillaume Ducournau), M24, ~2 months for generation of THz signals using photomixer developed at ULIL and telecom systems tests. To UCL (Prof. Cyril Renaud), M34, ~2 months for telecom systems tests

Objectives: The purpose of this research is to study optical mediated THz mixers and detectors. Expected Results: The vision of this research work is to enable monolithic integration of a low-barrier diode mixers and high power photodiodes as LO pump source. The aim is to pump a low-barrier diode mixer with a THz LO signal generated by optical heterodyning in a high-power wideband THz photodiode. The research will contribute to the fundamental research challenge of optically mediated THz mixing and detection. Optical heterodyne LO signal generation has been demonstrated with lower phase noise and a much wider tuning bandwidth as compared to electrical approaches. The integration of a low-barrier mixing diode and a high-power frequency-tunable photodiode would thus enable an ultra-wideband THz mixer for the first time. The research work will provide key metrics such as NEP, noise figure, conversion efficiency of such an approach (optically pumped THz mixers) and it will analyse the applicability of such a device for applications including the development of a future ultra-broadband (DC to THz) network analyser (NWA) and THz spectroscopy. The methodology of the proposed novel approach is to substantially reduce LO power requirements by using low-barrier diode mixers and to provide a frequency-tunable (DC – 1 THz) low-phase noise LO signal generated by an InP UTC photodiode or photodiode array. The research work will also address the monolithic integration of on-chip planar THz antennas with the mixer diodes to allow coupling of the THz signal and the LO signal. This research will contribute to answering TERAOPTICS’ research Challenge III and V. Planned secondment(s): to UDE (Prof. Stöhr), M12 for ~2 months for designing an integrated mixer with optical LO. to UC3M (Prof. Guillermo Carpintero), M16 for ~ 1 month, for broadband antenna integration to MWP (Dr. Klein), M28 for ~1 months for testing the developed optically mediated mixers

Objectives: The purpose of this research is to build an integrated heterodyne THz receiver for ≥ 300 GHz. Expected Results: This project targeted outcome is for the ESR to apply power combining approaches to build a GaAs or InGaAs heterodyne receiver with a photonic local oscillator. The researcher will work to combine UCLs strength in UTC photodiodes with RAL waveguide Schottky diode technology. They will first investigate and trade off on-chip and hollow metal waveguide power combining from UTC photodiodes. She or he will design the devices, then assemble and test the power combined source. The optimum combination will then be packaged with a Schottky diode based frequency multiplier to generate the local oscillator signal for a sub-harmonic mixer. The resulting device will be characterised in terms of conversion loss, noise temperature and tuning bandwidth, with the goal to attain the current state of the art, as reached by microwave pumped mixers. This project will achieve several integration firsts, and will provide the ESR with an excellent training in numerical and practical aspects of photonic and conventional Schottky terahertz design. This research work will contribute to answering TERAOPTICS’ research Challenge III and V. Planned secondment(s): to MWP (Dr. Klein), M12 for ~2 months, for preparing high power photodiodes to UCL (Prof. Cyril Renaud), M30 for ~ 2 months, for testing the integrated receiver using high optical power

Objectives: The purpose of this project is to develop photomixing terahertz receivers that are fully compatible to photonic and hybrid integration technologies. On the emitter side waveguide integrated photonic THz sources such as UTC-PDs and PIN-PDs have been demonstrated. On the receiver side, photomixers are still top-illuminated, which prevents them from being directly compatible with photonic integration technologies that rely on optical waveguides. This research work will contribute to answering TERAOPTICS’ research Challenge III and V. Expected Results: The project’s long-term vision of a fully integrated THz system with a transceiver array including all driving electronics on a single chip. Until today, scientific work has mainly focused on integrating the laser source and the THz emitter. Hence, the main objective of the project is the realization of a required integrated optoelectronic THz receiver array that exploits InP-based photonic integration technology and miniaturized electronics. Waveguide-integrated THz receivers will be investigated, which will be integrated with the required electronics, i.e. transimpedance amplifiers, I/Q mixers and RF drivers close to the antenna array. For a profound understanding of the entire system, including the interactions of all components, simulations (e.g. optical mode distribution inside the waveguide, coupling efficiency, dynamic properties of the ultrafast photomixer, high frequency behavior of the receiver array and coupling efficiency of the antenna structure) will be performed. The integrated receiver arrays will be fabricated using the InP fabrication line at Fraunhofer HHI. The components will be characterized both individually and as a array in a THz-imaging system. Through the comparison of simulation and experiment we aim to develop an understanding of the physical limitations and possible improvements of integrated THz systems and devices. Key performance parameters of the novel receivers will be compared to standard, top-illuminated photomixers. Planned secondment(s): to UDE (Prof. Andreas Stöhr), M15 for 1.5 months, for design and simulations of phased antenna arrays to ULIL (Prof. Guillaume Decournau) M22 for 1.5 month, for testing the receivers in a wireless communications link to TOPTICA (Dr. Patrick Leisching), M30 for 1.5 months, for integrating the novel receivers into a THz spectrometer

Objectives: The purpose is to develop high efficiency diffractive lenses in order to replace refractive optics. The silicon-based multi-level phase-correcting Fresnel lenses including antireflective structures as well as the free-standing-film Soret zone plate lenses for up to 4.7 THz for high focusing efficiency and very short focal length will be developed. This research work will contribute to answering TERAOPTICS’ research Challenge IV and V. Expected Results: A huge variety of THz systems employs different THz lenses made of metal reflectors (reflection mode) or dielectric refractors (transmission mode). Aiming to maintain compactness and robustness of the THz systems, such elements should be replaced by phase zone plates that are thinner and lighter. In this work we will also develop solutions for integration of the diffractive lenses and antireflective structures on-chip with the THz detectors and emitters. Previously scientific work has mainly focused on development of diffractive lenses with a moderate foci and small number of phase-correcting steps because of technological challenges of surface patterning of silicon especially for the THz frequency range below 500 GHz (wavelengths above 0.6 mm). Recently, the mask-less direct laser ablation technology has been developed for THz patterning of silicon, allowing more sophisticated profiles with the increase of the component performance which makes the integration in compact THz systems possible. Planned secondment(s): to UDE (Prof. Andreas Stöhr), M18 for ~1 months, for introduction to low-loss optical phase and TTD modulators to ULIL (Prof. Guillaume Ducournau), M24 for ~1.5 months, for diffractive optics integration with UTC-PD source to DAS (Dr. Valentin Polo), M30 for ~1,5 months, for testing devices in spectroscopic imagers

Objectives: The purpose of this project is to enable smart approaches for core THz devices integration by investigation of new methods for packaging at mm-wave and THz frequencies. In this project, we target to develop smart integration of mm-wave and THz devices using laser-machined micro-packages, enabling ‘functional packaging’ at THz range. Core devices to be integrated here will be considering both III-V and silicon THz photonics devices This research work will mainly contribute to answering TERAOPTICS’ research Challenge III, IV and V. Expected Results: This project targeted outcome is the smart integration of core devices like photomixers and/or detection diodes/harmonic mixing diodes, the building blocks being compatible within several technologies (SiPho, InP, BiCMOS...). Planned secondment(s): to RAL (Prof. Peter Huggard), M12 for 2 months, for understanding metal waveguide cavity blocks using CNC technology to STM (Daniel Gloria), M18 for 2.5 months, to be trained on STM technology in semiconductor SiGE and SiPho technologies

Objectives: The purpose of this project is to develop THz sources tackling the actual power limitations within photomixers. This implies both arrayed structures to be developed at THz frequencies and coherent and stable dual-frequency lasers or frequency combs to feed these arrays to enhance the optical to THz conversion ratio. This research work will contribute to answering TERAOPTICS’ research Challenges I and V. The developed devices will be used to demonstrate wireless data links in the THz range. Expected Results: Powerful and stable THz sources for THz communications at 300 GHz - 1 THz Planned secondment(s): to UC3M (Prof. Guillermo Carpintero), M12 for ~ 1 month, for antenna arrays design to TRT (Dr. Daniel Dolfi), M24 for ~ 2 months, for dual laser to enable stable optical beat-notes to UCL (Prof. Cyril Renaud), M34 for ~ 2 months, system-level tests using III-V Photomixers in the THz communication test-benches (common work between UCL and ULIL partners)

Objectives: While development in photomixers has progressed in the last 20 years, one of the key remaining problem has been to optimise the out-coupling of the THz wave for a given application. The work will concentrate on Earth observation and will look at optimising antenna designs for the given bands of interest. This research work will contribute to answering TERAOPTICS’ research Challenge IV and Challenge V. Expected Results: The work will first concentrate in design of optimised antenna for the set of bands used in Earth observation that are accessible with UTC-PD photomixers. Great care will be taken in matching the impedance of the UTC -PD with the antenna over the band of interest. Further we envisage looking at antennas not emitting through the substrate to enable the possibility to easily fabricate phased arrays with a minimum risk of on-chip interference. The ESR will be expected to investigate all the different solutions to couple the signal out and possibly in for detection (Conventional metalized bow ties, slot antennas, plasmonic based antennas, metamaterials…). The research and development work will mainly contribute to the targeted THz key application “space”. Planned secondment(s): to ULIL (Dr. Guillaume Ducournau), ~M20 for ~ 1.5 months, for antenna measurement and emission patterns to RAL (Prof. Peter Huggard), M28 for 3 months, for testing devices with THz receivers

Objectives: This project will look at the possibility to create a highly sensitive room temperature operating THz receiver that can be pumped optically. This research work will contribute to answering TERAOPTICS’ Challenges III, IV & V. Expected Results: For this work the ESR will be expected to develop a fully integrated receiver for THz signal. This will include the study to develop a novel InP based Schottky Barrier Diode that could be easily integrated within the standard growth of a UTC-PD, while also looking at hybrid integration with GaAs based SBD. The design work will also look at optimising the coupling of the UTC-PD signal with the SBD on chip for THz frequencies, in particular looking at different on-chip waveguides solutions (Dielectric rectangular, Plasmonic, metamaterial…). Ultimately the output will be an integrated device demonstrating state of the art sensitivity in the THz range, with tuneability beyond the state of the art. This will benefit the targeted key application THz communications but will also be applicable for coherent THz spectroscopy systems used in Earth observation and radio-astronomy. Planned secondment(s): to AIRBUS (Dr. Ralf Green), ~M10 for 1.5 months, for key metrics and requirements for satellite receivers to UDE (Prof. Andreas Stöhr), M16 for 1 months, for round-robin optically mediated THz signal generation to RAL (Prof. Peter Huggard), ~M24 for 2 months, packaged SBD fabrication and experiments on hybrid integrated systems.

Objectives: This research project will develop a photonic integrated THz frequency domain spectrometer THz FDS, using the self-heterodyne technique based on an optical heterodyne source. This research work will contribute to answering TERAOPTICS’ research Challenge III and Challenge V. Expected Results: The key expected outcome of this research work is a Terahertz frequency domain spectrometer light engine prototype. The aim is to demonstrate the superior performance of the photonic integrated self-heterodyne technique, since influence of frequency fluctuations of the RF signal are eliminated by using the same LO in Tx and Rx, and phase uncertainties are eliminated by integration. Frequency tuning between 30 GHz to 3 THz will be achieved by changing wavelength difference, and phase scanning over 180º using a phase shifter. The research and development work will mainly address the targeted key THz application “material characterization”. Planned secondment(s): to FTMC (Dr. Irmantas Kašalynas), M10 ~1 month, on introduction to solid state THz sources and spectroscopic THz imaging to DAS (Dr. Valentin Polo), M30 for 2 months, on using the prototypes for spectroscopic THz imagers