Compact MMIC Terahertz Sources in the 0.1 - 1 THz Range

This project addresses the bottleneck of Terahertz Science and Technology, where the fabrication of room temperature, continuous wave, compact, tunable and powerful sources (at low cost, if possible) is the prime challenge. Terahertz (THz) radiation, whose frequency range lies between microwaves and infrared light in the electromagnetic spectrum, opens the possibility for a new imaging and spectroscopic technology with a broad range of applications, from medical diagnostic (without the damage produced by ionising radiation such as X-rays), industrial quality control or security-screening tools. Unfortunately terahertz technology suffers from some significant difficulties that requires research to overcome. Bright terahertz sources are difficult to make, so considerable effort is needed to improve what we have at the moment. The sources must be obtained at the limits of electronics from one side and optical systems from the other, resulting in a lack of efficient and practical radiation sources. This project is therefore dedicated to developing a compact high performance solid-state source.
The potential for employing resonant tunnelling diodes (RTDs) to realise THz sources is well known and so are the circuit design challenges (unwanted oscillations and low output power) to achieve this task. This grant proposal seeks to develop this potential, by exploring and exploiting novel circuit concepts that allow the use of multiple (and optimally sized) RTDs in single oscillators. We aim to fabricate the RTD sources using the conventional microwave monolithic integrated circuit (MMIC) technology. By the conclusion of this project, we aim to demonstrate a simple single pixel THz imaging system. These developments should pave the way for adoption of this technology by British industry.

Compact and affordable THz imaging systems have the potential to improve the quality of life of UK and international citizens, through improved security and healthcare. Additional improvements in quality of life are expected from applications in areas such as high-bandwidth telecoms, pharmaceuticals, material science and non-destructive testing. In 2008 the global market for THz radiation devices and systems was worth an estimated $77.2 million, with imaging systems accounting for $71.8 million (93%) of this total. These markets are expected to be now significantly bigger. For example, by 2018 it is anticipated that the THz imaging and systems industry will be worth over $500 million with imaging systems contributing $206.7 million (~40%) of the total. However, current commercial systems must be improved in order to realise these gains. One of the key limiting factors of the existing commercial systems is the use of expensive femtosecond lasers as sources and therefore cost >£250k and no cheap and practical THz systems are available. Due to cryogenic cooling requirements for the laser, these systems are bulky with high power consumption. This proposal has the aim of delivering cheap, high power (>1mW), compact (cm3) and portable room-temperature sources which would be enabling for THz technology (0.1 - 1 THz) to enter a number of markets including medical and security imaging. The healthcare (oncology) market requires far cheaper THz imaging systems which could be significantly helped by the success of the proposal. At present, all skin cancer detection requires an appointment with a consultant at a hospital and significant savings could be made if a safe and reliable diagnosis technique could be employed at GP surgeries. This is especially important, as early detection is key for high survival rates. This would significantly reduce trauma and patient time in hospital compared to present biopsy techniques, thereby significantly reducing NHS treatment costs. Skin cancer imaging systems for GP surgeries would require an affordable (<£10k) complete imaging system with source powers > 10mW at room temperature for parallel imaging which could achieved with sources on this proposal. Recent UK statistics show the enormous rise in the dangerous malignant melanoma, with 11,767 UK citizens diagnosed with this form of cancer in 2008. The success of this proposal could therefore have significant benefits to UK society by increasing the quality of living by fast detection of skin cancers and in doing so also significantly reduce the treatment costs in NHS.
From the security side, low cost THz sources would be an enabling technology for portal security screening systems for airports, civil buildings and public places. The proposed technology has the advantage that arrays of oscillators could be developed for parallel imaging applications. Safe screening through clothing at video rates for short stand-off distances compatible with portal systems would be possible. A compact THz source would also be useful for non-destructive testing of aircraft parts. The usage of composite materials in aircraft is growing rapidly, and airlines would benefit from the cost savings in extending aircraft lifetime through THz inspection of the panel integrity during regular maintenance. This could also prevent loss of life through detection prior to failure if there are emerging issues with ageing composite airframes. As the probability of terrorist attacks in the UK is higher than ever before, fast detection using THz radiation in public places could potentially save many lives. The detection of suicide bombers before detonation will not only save lives but also significantly reduce the costs of first responders, the cost of medical care of victims and the cost of clean-up operation. In summary, THz technology is exciting and very promising. New research in all aspects of system implementation is essential for the field to deliver many benefits to society.