Authors

Abstract

Othro-mode transducers (OMT) are a commonly used method of coupling opti-cal signals between waveguides and on-chip circuitry and detectors. While the ideal OMT-waveguide coupling requies minimal disturbance to the waveguide, when used for mm-wave applications the waveguide is often slide though and the OMT probes inserted on athin support membrane. This interface is a potential source of signal leakage and can leadto signal loss and experimental systematics (e.g. in CMB polarization experiments wherelost signal can result in temperature to polarization leakage). Here we report on the devel-opment of new OMT- waveguide coupling structures with the goal of reducing leakage atthe horn-to-detector-wafer interface. The pixel to pixel optical leakage due to the gap be-tween the coupling waveguide and the backshort is reduced by means of a protrusion thatpasses through the OMT membrane and connects the waveguide sections on each side ofthe wafer. High frequency electromagnetic simulations indicate that these protrusions canreduce optical leakage in the gap by80% percent, with a60% filling factor, respectto an ordinary OMT coupling without protrusion, using designs that are compatible withcurrent fabrication processes. We describe the design of the new coupling structure includ-ing the impact of varying two key parameters: wafer to optical coupling gap and protrusionfill factor. Prototype devices have been designed that will characterize the performance ofthe new design using a relative measurement with varying filling factors. We describe thesimulation setup and results, and present a chip layout and sample box designed to performan initial measurement.