High Power Uni-Travelling Carrier Photodiodes for THz Wireless Communications

Lead Research Organisation: University College London
Department Name: Electronic and Electrical Engineering

Abstract

To enable ultra-high speed and capacity wireless data systems (providing data rates of more than 10 Gbit/s), we need to look to higher carrier frequencies, in particular at currently unallocated regions of the electromagnetic spectrum above 275 GHz (USA) or 300 GHz (Europe), the Terahertz frequency range. One of the most promising techniques for compact, high power, broad band, room temperature THz sources is optical heterodyne generation (or photomixing) in ultra-fast photodetector, uni-travelling-carrier photodiodes (UTC-PD).

The current achieved highest THz output power from UTC-PD at 300GHz and 450GHz are: Two identical UTC-PDs and a T-junction are monolithically integrated in a single chip exhibiting peak output power of 1.2mW at 300 GHz; Travelling-wave uni-travelling-carrier photodiodes (TW-UTC-PD) delivers narrow-band output power of 0.15mW at 450 GHz. These reported advanced designs and technologies can cover wireless communication ranges of up to 10 metres, with data rates of 10~20Gbit/s. To cover wider ranges (eg: double the transmission distance) at higher data transfer speed, the THz transmitter's output power needs to be increased to at least twice the current level.

The objective of this project is to model and develop UTC-PD structures capable of higher output powers, to achieve 2.5mW at 300GHz and 0.3mW at 450GHz.

UTC-PD output power is dependent upon input optical power absorption distance, O/E (optical to electric) conversion efficiency and power loss in the device. To enhance optical power absorption distance and coupling efficiency, the absorption layer shape and structure, for example, planar multimode waveguide can be optimised. To increase the O/E conversion efficiency, high performance spot size converters can be developed. To control the device heating from optical carrier generation, epitaxial growth on relatively high thermal conductance silicon substrates can be considered. The two key concepts to be investigated in this project are: a) growing UTC-PD structures epitaxially on silicon substrates to improve heat-sinking; b) creating arrays of UTC-PDs on silicon to achieve spatial power combining.

Relevance to EPSRC thematic areas: Engineering (sub-theme: RF and microwave devices), Information and communication technology (sub-theme: optical communications), Physical sciences (sub-theme: optoelectronic devices and circuits).

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S022139/1 01/10/2019 31/03/2028
2259136 Studentship EP/S022139/1 01/10/2015 28/02/2021 Xiaoli Lin