  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.
