Description: To demonstrate (benchtop experiment) a DPSK receiver with a free-space interferometer, showing that fiber-optic coupling, associated adaptive optics, and optical preamplification can be avoided, with potential large cost savings; To rigorously quantify the performance (capacity and photon-budget) tradeoff between conventional (adaptive optics + optical preamplification) systems and our proposed free-space photon-counting-array approach; To develop extensions to orthogonal phase-modulated signaling over multiple symbols and associated photon-counting receiver structures, which enable approaching the photon efficiency of high-order pulse position modulation.

Benefits: Results from a successful bench-top demonstration would enable infusion into near-Earth and terrestrial communication links in development that utilize DPSK modulation (e.g., NASA LCRD, DARPA FOENEx, other DoD applications). Removing requirement for AO would provide a significant reduction in cost of a DPSK system, putting JPL at a competitive advantage in bidding for free-space DPSK. Successful implementation of multiple-symbol phase-shift-keying would represent a breakthrough in practical implementation of low duty-cycle modulations, providing performance and SWAP gains.