Paper detail

Optical leakage mitigation in ortho-mode transducer detectors for microwave applications

Planar ortho-mode transducers (OMTs) are a commonly used method of coupling optical signals between waveguides and on-chip circuitry and detectors. While the ideal OMT-waveguide coupling requires minimal disturbance to the waveguide, when used for mm-wave applications the waveguide is typically constructed from two sections to allow the OMT probes to be inserted into the waveguide. This break in the waveguide is a source of signal leakage and can lead to loss of performance and increased experimental systematic errors. Here we report on the development of new OMT-to-waveguide coupling structures with the goal of reducing leakage at the detector wafer interface. The pixel to pixel optical leakage due to the gap between the coupling waveguide and the backshort is reduced by means of a protrusion that passes through the OMT membrane and electrically connects the two waveguide sections on either side of the wafer. High frequency electromagnetic simulations indicate that these protrusions are an effective method to reduce optical leakage in the gap by ~80% percent, with a ~60% filling factor, relative to an standard OMT coupling architecture. Prototype devices have been designed to characterize the performance of the new design using a relative measurement with varying filling factors. We outline the simulation setup and results, and present a chip layout and sample box that will be used to perform the initial measurements.