Subhasish Chakraborty

Terahertz semiconductor laser sources have been an active area of research at a handful of leading institutions around the globe over the last decade, including the Universities of Cambridge and Leeds in the UK, and MIT and Harvard in the USA. By developing new laboratory facilities here, as the results to date show, the University of Manchester is the latest addition to this group. This facility enabled him to carry out work aimed at developing, for the first time, photonically mediated wavelength tuning of terahertz quantum cascade lasers grown by his collaborators in the University of Cambridge. This facility is world leading, providing a micro-manipulated cryogenic probe system, which allows one to couple in both microwave and telecom signal into an electronically tunable terahertz quantum cascade laser through waveguides and optical fibres, respectively.  This is an extremely flexible system, which will open up a broad range of opportunities for developing terahertz system concepts.

Terahertz photonic devices remain a strong sector worldwide and the field is now moving into applications areas in medicine, security and terabit/sec data communication and the research work from Dr Chakraborty’s group is ideally placed to take advantage of this trend. In particular, the new Terahertz-over-Fibre initiative, a doctoral thesis on which has recently been awarded to one of his PhD students (Md. Khairuzzaman), is adding a new and major strength to the UK effort. For example, this approach complements extremely well plans on UCL’s £6.5M EPSRC joint programme grant with Cambridge and Leeds, where they hope to develop systems for use in fundamental science (e.g. the study of nanostructured and mesoscopic electron systems) and for applications including short-range high-data-rate wireless communications, information processing, materials detection and high resolution imaging in three dimensions.

There is a new dimension to Dr Chakraborty’s work which needs to be emphasised here.  It has emerged in the past few years that Graphene is a near perfect material for aperiodic grating fabrication on these THz lasing devices. Graphene is highly conducting, virtually transparent and offers highly efficient evanescent coupling: it possesses all of the materials properties required for the plasmonic interactions which feed the wavelength tuning discovered and theoretically modelled by Dr Chakraborty.  Engineering applications of Graphene are at the core of the mission statement for the National Graphene Institute and that Institute is urgently seek in engineering input from the relevant Schools within the University of Manchester. Dr Chakraborty has developed a strong collaborative link with Prof Kostya Novoselov in the School of Physics and Astronomy. They have been working on a Graphene-THz project now growing within the group, and he is currently supervising a PDRA and two PhD students within that project. The research outcomes from Dr Chakraborty’s recent work on Graphene have several key applications. This work was reported in the postdeadline session (Paper CTh5c) in CLEO-2013 and UMIP are now actively pursuing the development two worldwide patent applications.

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