Superconducting quantum detectors

Abstract:

In previous work, we have described novel smoothwalled multiple flare-angle horns designed using a genetic algorithm. A key feature of these horns is that they can be manufactured very rapidly and cheaply in large numbers, by repeated direct drilling into a single plate of aluminium using a shaped machine tool. The rapid manufacturing technique will enable the construction of very low cost focal-plane arrays, offering an alternative to conventional electroformed corrugated horn arrays. In order to experimentally demonstrate the new technology, we constructed a 230 GHz focal-plane array comprising 37 smooth-walled horns fabricated by direct drilling. We present the measured beam patterns for a large sample of these horns across the array, demonstrating the suitability of our manufacturing techniques for large format arrays. We have measured the cross coupling between adjacent feeds and have shown that it is negligible. We also present high quality beam patterns measured for a much smaller 700 GHz horn, showing the promise of extending this technology to THz frequencies.

Abstract:

We present the design of two niobium singleended Superconductor-Insulator-Superconductor (SIS) mixers optimized to work in the frequency range of 600-700 GHz. A key feature of this new mixer design is the utilization of a unilateral finline taper. This transition is significantly easier to design and simulate than the previously employed antipodal finline, and more importantly it simplifies the chip fabrication considerably since the fins do not overlap at any stage. RF power propagating in the finline is coupled to the microstrip either directly from the slotline to microstrip, or more efficiently via a coplanar waveguide (CPW). Another novel feature of our design is the fabrication of the mixer chip on a very thin silicon substrate which will be achieved using Silicon-On-Insulator (SOI) technology. This will allow easy matching of the incoming signal from the feed horn to the loaded waveguide and allows the lightweight mixer chip to be held in the E-plane of the waveguide using gold beam leads, eliminating the need for a deep groove in the waveguide wall. These new features yield a significantly shorter chip and allow wider RF bandwidth since the excitation of higher order modes in the groove has been avoided. The mixer block is extremely simple, composing a smooth-walled horn and a waveguide section without any complicated mechanical features. In this paper, we present the details of the mixer chip, including various transition sections, tuning circuits and mixer block designs, supported by electromagnetic simulations. We describe the design procedure in detail and predict the full mixer performance using the SuperMix software package.