Abstract
(Englisch)
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The aim of the WANTED programme is to develop high-bandwidth solid-state emitters and detectors operating between 1THz and 10THz, and investigate their feasibility for a wireless-area-networking environment. This would allow workers to move freely through their workplace accessing information servers and databases via personal communicators or lightweight laptops. Terahertz radiation is safe, has limited range (allowing secure data transmission), and relatively large band-width with data transfer rates >3Tbps theoretically possible. This programme will investigate two parallel paths for developing THz sources, the first based on building quantum cascade lasers, the second on investigating inter-mixing of two visible or mid-IR lasers. For the detector, two approaches will also be adopted: the first based on multi-quantum-well hot electron bolometers; the second on electro-optic sampling.
Objectives:
1) Develop high-bandwidth terahertz (THz) solid-state emitters (operating between 1-10THz) in GaAs-AlGaAs. We will design and fabricate far-infrared quantum cascade lasers, building on our extensive experience of mid-infrared cascade lasers. We will also study the mixing in non-linear media of inter-band diode lasers and, specifically-designed mid-infrared quantum cascade lasers (including two-colour lasers).
2) Develop two detection schemes, one based on multi-quantum-well thermionic emission (in either InP or GaAs material systems), the other based on the AC Pockels effect.
3) Determine optimum emitter/detector combination and evaluate its potential for wireless-area-networking applications.
Work description:
Our project to produce THz emitters is centred on development of quantum cascade laser (QCL) stuctures, already pioneered in the mid-infrared by members of the current consortium. First, we seek to model and fabricate a design of QCL which will operate for the first time in the far infrared - specifically aiming at the 1-10THz frequency range pertinent to future wireless-area-networking applications. There are formidable technical issues to be addressed, with radically new schemes required compared with those previously established for mid-infrared (MIR) QCLs. This consortium brings together the necessary expertise to meet this challenge, containing experts in QCL design, extremely high quality GaAs-AlGaAs growth, and detailed Monte Carlo theoretical modelling. We seek in the first instance to produce an electroluminescence structure, prior to attempting the THz laser. Three other generation approaches will be pursued - each using difference frequency mixing in either an antenna structure or a non-linear material. The first uses mixing from two mode-locked semiconductor lasers, the second uses two MIR QCLs. Whilst the fabrication of these MIR QCLs is well understood, specific frequencies are needed for the non-linear mixing, and essential parameters need to be obtained for modelling the growth of the THz QCLs. Finally, we will investigate mixing from two-colour MIR QCLs. To realise wireless-area-networking, there is a need for appropriate detectors, and we will investigate two schemes. We will design and fabricate devices based on thermionic emission in multi-quantum wells (both GaAs and InP based), in addition to using the AC Pockels effect. Both techniques have the required sensitivity and response time in the 1-10THz range. The optimum detector/emitter combinations for wireless-area-networking will be identified, and the feasibility of their practical implementation evaluated.
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