James Seddon

University College London | UCL · Department of Electronic and Electrical Engineering

Terahertz (THz) near-field imaging and spectroscopy provide valuable insights into the fundamental physical processes occurring in THz resonators and metasurfaces on the subwavelength scale. However, so far, the mapping of THz surface currents has remained outside the scope of THz near-field techniques. In this study, we demonstrate that aperture-t...

Terahertz (THz) continuous wave (CW) spectroscopy systems can offer extremely high spectral resolution over the THz band by photo-mixing high-performance telecommunications-band (1530-1565 nm) lasers. However, typical THz CW detectors in these systems use narrow band-gap photoconductors, which require elaborate material growth and generate relative...

Continuous Wave (CW) Terahertz spectroscopy enabled by photomixing is a promising high precision spectroscopic tool for the examination of a wide variety of samples including biological, chemical, and solid state. However, often it would be of interest to examine isolated samples free from bulk effects that broaden spectral features. In this form s...

Photonics-based technologies are key players in a number of emerging applications in the terahertz (THz) field. These solutions exploit the well-known advantages of optical devices, such as ultra-wide tuneability and direct integration with fiber networks. However, THz receivers are mainly implemented by fully electronic solutions, where Schottky b...

We have demonstrated a novel approach to photonically integrated optical frequency comb generation on Indium Phosphide (InP) using generic foundry platforms. The optical comb utilized a recirculating loop technique to generate 59 comb lines (within a 20 dB power envelope) which are separated by 6.7 GHz frequency spacing. All comb lines exhibit stro...

Terahertz generation using high-speed photodiodes has found commercial application in many areas ranging across spectroscopy, imaging and communications. In this paper we discuss the optimization of high-speed photodiodes in terms of bandwidth and output power. We identify some of the main limitations in the generation of high output power in the T...

We investigated theoretically a waveguided EAM (Electro-Absorption Modulator) based on ISBT (Intersubband Transitions) in an In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(0.53)</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(0.47)</sub> As/...

A novel technique for high-resolution $1.5\;\unicode{x00B5}{\rm m}$ 1.5 µ m photonics-enabled terahertz (THz) spectroscopy using software control of the illumination spectral line shape (SLS) is presented. The technique enhances the performance of a continuous-wave THz spectrometer to reveal previously inaccessible details of closely spaced spectra...

Monolithic optoelectronic integrated circuits, OEICs are seen as key enabling technologies to minimal power loss criteria. Monolithic OEICs combine, on the same die, cutting-edge optical devices and high speed III-V electronics able to generate terahertz signal targeting beyond-5G networks. Computationally efficient compact models compatible with e...

The first waveguide coupled phosphide-based UTC photodiodes grown by Solid Source Molecular Beam Epitaxy (SSMBE) are reported in this paper. Metal Organic Vapour Phase Epitaxy (MOVPE) and Gas Source MBE (GSMBE) have long been the predominant growth techniques for the production of high quality InGaAsP materials. The use of SSMBE overcomes the major...

The first waveguide coupled phosphide-based UTC photodiodes grown by Solid Source Molecular Beam Epitaxy (SSMBE) are reported in this paper. Metal Organic Vapour Phase Epitaxy (MOVPE) and Gas Source MBE (GSMBE) have long been the predominant growth techniques for the production of high quality InGaAsP materials. The use of SSMBE overcomes the major...

High resolution (900 Hz full-width at half maximum) frequency domain spectroscopy near 0.2Terahertz is achieved using an exact frequency spacing comb-source in the optical communications band, filtering and photo-mixing in a custom Uni-Travelling-Carrier Photodiode (UTC-PD) for THz signal generation and coherent down-conversion for detection. Via t...

Monolithic optoelectronic integrated circuits (OEICs) are seen as key enabling technologies for future terahertz communications and upcoming beyond-5G networks. Co-design of monolithic OEICs requires computationally efficient compact models compatible with existing methodology/tool/design flow for timely and cost-effective realization of OEICs. Thi...

The research in this thesis is concerned with the design of a lab on chip operating in the sub millimetre - Terahertz (THz) region of the spectrum. The lab on chip design utilises Uni-Travelling Carrier (UTC) photodiodes for Continuous Wave generation of THz and optoelectronic downconversion of THz. The system forms an integral part of a THz Freque...

We propose and demonstrate a miniature microwave device capable of detecting wide-band ultrasound without the use of piezo materials. By the nature of the transduction mechanism, the scheme naturally implements orthogonal frequency division multiplexing (OFDM): each device can be assigned its own microwave band, mitigating electrical cross-talk bet...

This study reports the experimental demonstration of a free space frequency domain self-heterodyne spectrometer utilising a high-speed Uni- Travelling Carrier photodiode (UTC-PD) as a coherent receiver. The transmission signal through the glucose solution was measured in the V-band (50 - 75 GHz) frequency range with a frequency resolution step of 4...

High speed photodiodes are a key element of numerous photonic systems. With the development of potential applications in the THz range such as sensing, spectroscopy and wireless transmission, devices with integrated antenna covering the frequency range from 0.1 THz to 3 THz will become essential. In this paper we discuss the development of uni-trav...