Precision photonic readout for cryogenic IR focal planes

Maintaining fidelity (signal-to-noise, bandwidth, linearity) of the signals from high performance IR focal planes on their way from the cold finger to the warm outside is as important as generating them in the first place. They are susceptible to EMI and it is often important to minimize heatload on the cryogen. We describe a photonic readout that addresses these issues and uses a passive input transducer in the form of an optical waveguide phase modulator to encode the focal plane voltages as differential phase shifts between guided optical beams, a fiber optic link to the outside and a fast, high resolution optical receiver and digital interferometer to recover the focal plane signals induced phase shifts as digital numbers. The high input impedance of the transducer and minimal heatloss through the single mode optical fibers all contribute to a greatly reduced heatload. We present quantitative data demonstrating signal-to-noise, bandwidth as well as visible and IR imagery transmitted and processed by a prototype design.