Belio-Apaolaza, Inigo; (2025) Integrated optoelectronic terahertz receivers. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Photonic technologies offer intrinsic advantages in terahertz generation and detection, making them key enablers for a wide range of applications. In terahertz receivers, these advantages are imparted to local oscillator (LO) generation and distribution, providing ultra-high-frequency tunability, remote signal distribution, and compatibility with existing 1550 nm equipment. Wireless communications at 300 GHz, fully enabled by photonics, can leverage these features for efficient and seamless convergence with fibre networks. However, current photonic-based tera hertz receivers exhibit higher conversion loss compared to state-of-the-art electronic solutions. This thesis introduces an alternative optoelectronic terahertz receiver concept based on photonically pumped Schottky mixers. By integrating low-barrier Schottky barrier diodes (SBDs) with uni-travelling-carrier photodiodes (UTC-PDs), this approach combines high-performance down-conversion efficiency with the advantages of photonic LO signal generation and distribution. The modelling, design, and characterisation of such receivers are presented. The study first focuses on integrating UTC-PDs and SBDs, designing three subharmonic receivers operating at 220–330 GHz. The first is a monolithic receiver using InP Schottky contacts with a standard UTC-PD epitaxy. The second and third explore hybrid integration with InGaAs air-bridged SBDs: a quasi-optical receiver and a rectangular waveguide (WR3) receiver. The quasi-optical receiver was fabricated and tested, along with a nonintegrated receiver used to validate the concept and provide a performance com parison. Results indicate a minimum conversion loss of approximately 14 dB the non-integrated and 18 dB for the integrated receiver, approaching the state-of-the-art in this frequency band. The UTC-PD is shown to provide sufficient LO power to saturate the mixer response, and the modelling and design process is vali-dated through agreement between simulations and measurements. To showcase the receiver’s potential for wireless communications, a multi-channel 300 GHz link was demonstrated, achieving an aggregate data rate of 180 Gbps.

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