More efficient and powerful continuous-wave photonic mixers as terahertz sources are motivated by the need of more versatile local oscillators for submillimeter/terahertz receiver systems. Uni-Travelling Carrier (UTC) photodiodes are very prospective candidates for reaching this objective, but so far only have been reported as lumped-elements or as edge-illuminated optical-waveguide travelling-wave (TW) devices. To overcome the associated power limitations of those implementations, we are developing a novel implementation of the UTC photodiodes which combines a travelingwave photomixer with vertical velocity-matched illumination in a distributed structure. In this implementation called velocity-matched travelling-wave uni-travelling carrier photodiode, it is possible to obtain in-situ velocity matching of the beat-fringes of the two angled laser beams with the submm/THz-wave on the stripline. In this way, minimum frequency roll-off is achieved by tuning the angle between the two laser beams. A first design of these TW-UTC PDs from our Terahertz Photonics Laboratory at University of Chile has been micro-fabricated at the MC2 cleanroom facility at Chalmers Technical University.
More efficient continuous-wave photonic nearinfrared
mixers as terahertz sources are investigated
with the motivation to develop a universal photonic
local oscillator for astronomical submillimeter/terahertz
receiver systems. For this, we develop new concepts for
vertically illuminated traveling-wave (TW)
photomixers, TW Uni-Travelling Carrier (UTC)
photodiodes. Device simulation/modeling and
optical/terahertz testing is being done in the new
terahertz photonics laboratory at the Electrical
Engineering Department of the University of Chile,
whereas device fabrication is performed at the MC2
cleanroom facility at Chalmers Technical University.
We report on first progress in this direction.
A 1.5 THz superconducting receiver has been in operation at the Receiver Lab Telescope of the Smithsonian
Astrophysical Observatory in Northern Chile since December 2004. This receiver incorporates a Hot Electron Bolometer
(HEB) mixer chip made from a thin film of Niobium Titanium Nitride (NbTiN), which is mounted in a precisionmachined
waveguide mixer block attached to a corrugated waveguide horn assembly. With a noise temperature of
around 1500 K, this receiver is sensitive enough for use in the pioneering field of ground-based terahertz spectral-line
astronomy. A number of innovative techniques have been employed in the construction and deployment of this receiver.
These include near-field vector beam mapping to enable accurate coupling to the telescope optics, the use of tunerless
planar-diode based local oscillator unit capable of generating a few μW at 1.5 THz, and special calibration techniques
required for terahertz astronomy. In this paper, we will report on the design, set-up and operation of this state-of-the-art
instrument.
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