Description: The objective of this program is to develop, demonstrate and implement a 1550-nm sensitive photon-counting detector array with monolithically integrated time-tagging electronics, suitable for free-space optical communications, where high data volume returns from space missions are critical, such as in the Lunar Laser Communication Demonstration (LLCD) and other future NASA missions. Conventional photon counting detector arrays are implemented in either Silicon (Si) or Mercury Cadmium Telluride (HgCdTe), negating detection at 1550 nm in the case of Si or incurring high cost and complexity for HgCdTe. In this program, Freedom Photonics will partner with the University of Nevada Las Vegas (UNLV) and Arizona State University (ASU) to develop a novel Geiger-mode Avalanche Photodiode (APD) arrayreceiver for photon counting applications with sensitivity for wavelengths in the range from 1000 nm to 1600 nm, which utilizes standard CMOS processing for electronics, coupled with selective growth of APDs in the SiGeSn materials system, resulting in a low-cost, high-sensitivity, high-speed and radiation hard receiver for long-range optical communications.

Benefits: In this program, Freedom Photonics proposes to develop a photon-counting detector array, sensitive in the 1550 nm wavelength range, suitable for Free-Space-Optical (FSO) communications where high data rates from space missions are critical, such as the Lunar Laser Communication Demonstration (LLCD). The proposed photodetector array is akin to the well known Silicon Photomultiplier (SiPM) but using the SiGeSn ternary alloy, rather than just Si, to extend the detection wavelength range to 1550 nm. To our knowledge, no such solid state "photomultiplier" device exists currently for detection at 1550 nm. This SiGeSn Semiconductor Photomultiplier (SPM) will be epitaxially grown on a CMOS wafer, so that it will include monolithically integrated time tagging electronics for a significant reduction in Size, Weight and Power (SWaP), compared to current state-of-the-art lasercom receivers. Potential NASA customers for these products include: o Space Technology Directorate o Science Directorate o Human Exploration and Operations Directorate o Deep Space Optical Communications (DSOC) o Laser Communications Relay Demonstration (LCRD) o Space Network (SN) o Near Earth Network (NEN) o Lunar Laser Communication Demonstration (LLCD) o International Space Station o New Horizons: Pluto and Beyond

Potential applications for the FSO high sensitivity photodetector include: - Space communications - Aircraft-to-aircraft and aircraft-to-ground communications - Communication links for internet-by-balloon or internet-by-drone as currently being developed by Google and Facebook - Building-to-building connectivity, where the improved detector sensitivity would improve performance under some adverse weather conditions Customers for these products include: Other Government o Department of Defense o Department of Agriculture o Department of Homeland Security o Department of Energy Non-Government Commercial o Companies developing aerial internet distribution such as Google and Facebook o Space exploration companies such as SpaceX and Orbital ATK o FSO link manufacturing companies such as fSona and Lightpointe