Large-area SNSPD array for RF/Optical Hybrid 7-segment pathfinder receiver

In this work we describe the development, characterization, and integration of a 16-channel, 400-mu m diameter active area, double-ended read-out NbTiN superconducting nanowire single-photon detector (SNSPD) array and the supporting electronics used in an RF/Optical hybrid telescope for deep-space laser communications. This is the first field-demonstration of a multi-channel, co-wound, double-ended read-out SNSPD array. With the number and complexity of future space exploration missions expected to increase, NASA is investigating ways to augment the information capacity of the Deep Space Network (DSN) global array of RF receivers used to track and communicate with these spacecrafts. Optical communication offers a path toward increasing the overall bandwidth of the DSN while allowing for higher data throughput for the same size weight and power (SWAP) transmitter on the spacecraft. NASA's RF/Optical Hybrid (RFO) program proposes using a segmented, 8-10-meter equivalent aperture primary mirror mounted on existing 34-meter diameter beam waveguide (BWG) RF antennas to couple light into photon counting detectors for pulse position modulation (PPM) and on-off keying (OOK) data formats. JPL has deployed a pathfinder hybrid telescope on a DSN BWG antenna in Goldstone, California. The pathfinder couples light from a 1.2-meter effective diameter, 7-hexagonal-segment mirror assembly to a 400-mu m core graded-index multimode fiber. This fiber is then routed to a cryostat and coupled to an SNSPD array through free-space optics. Coupling from a large diameter fiber to an SNSPD array while maintaining a small number of readout channels from the cryostat presents some unique challenges for the SNSPD array and receiver design.