N. Brewster

280 GHz frequency multiplied source for meteorological Doppler radar applications

We report on the design, fabrication and characterization of a Schottky diode frequency tripler to 280 GHz. The narrowband multiplier features six GaAs Schottky planar diodes in a balanced configuration. Measured room temperature conversion efficiencies are in the range 1 to 5 % across the band 240-290 GHz for 100 mW of input power. The corresponding 3 dB bandwidth is 6 % centred at 280 GHz. When driven by 300 mW tripler exhibits a peak output power of 15 mW at 276 GHz.

Development of Terahertz Frequency Quantum Cascade Lasers for the Applications as Local Oscillators

We report the development of terahertz frequency quantum cascade lasers for applications as local oscillators. A range of active region designs and waveguide structures have been characterised in order to develop the devices for operation at high temperatures, with high output power and low dissipated power. Quantum cascade lasers based on a LO-phonon bound-to-continuum design emitting at 3.5 THz, suitable for the detection of hydroxyl, were fabricated with a double-metal (gold-gold) waveguide structure. These devices operated in continuous-wave up to 94 K, with an output power of 0.4 mW and dissipated power of 1.7 W at 10 K. A new, mechanically robust packaging and waveguide-integration scheme is also presented for operation outside laboratory environments, which further allows integration of quantum cascade lasers with terahertz waveguides, mixers and other system components. This integration scheme yielded a better beam quality, with a divergence of <20°, compared to standard double-metal devices. Its impacts on the device performance, such as operating temperature range, spectral emission, output power and electrical properties, are presented.

High sensitivity broadband 360GHz passive receiver for TeraSCREEN

TeraSCREEN is an EU FP7 Security project aimed at developing a combined active, with frequency channel centered at 360 GHz, and passive, with frequency channels centered at 94, 220 and 360 GHz, imaging system for border controls in airport and commercial ferry ports. The system will include automatic threat detection and classification and has been designed with a strong focus on the ethical, legal and practical aspects of operating in these environments and with the potential threats in mind. Furthermore, both the passive and active systems are based on array receivers with the active system consisting of a 16 element MIMO FMCW radar centered at 360 GHz with a bandwidth of 30 GHz utilizing a custom made direct digital synthesizer. The 16 element passive receiver system at 360 GHz uses commercial Gunn diode oscillators at 90 GHz followed by custom made 90 to 180 GHz frequency doublers supplying the local oscillator for 360 GHz sub-harmonic mixers. This paper describes the development of the passive antenna module, local oscillator chain, frequency mixers and detectors used in the passive receiver array of this system. The complete passive receiver chain is characterized in this paper.

Local oscillator development for focal plane array and supra-THz astronomy receivers

Ultra-sensitive superconducting tunnel junction heterodyne receivers used for astronomy research require relatively low levels of local oscillator (LO) power. When configured as an imaging array, however, the LO power required substantially increases and the provision and distribution of a harmonically generated LO signal to multiple pixel elements becomes a technically challenging task. Furthermore, the difficulty of generating LO power is compounded as the operational frequency is increased into the supra-THz region (<1 THz). We will present our programme of research directed towards the provision of future THz astronomy receivers, in which we have been pursuing the development of enhanced harmonic up-conversion LO technology.