Low-Noise, Wide-Bandwidth, Large-Area APDs for Free-Space Optical Links

For future satellite to ground optical links, large-area high-performance photodetectors are a key component. The APD is a natural choice, owing to its inherent sensitivity advantage compared to photodetectors that do not provide internal gain. Theoutput of Phase I of this program is an APD design that achieves 3 GHz of bandwidth, a quantum efficiency greater than 50%, and noise performance comparable to silicon APDs, with a light sensitive diameter of 200 mm. In order to achieve these performancetargets, Impact Ionization Engineering (I2E) will be used to incorporate an optimized InAlAs multiplication structure within a large area device. APDs designed for telecommunications applications incorporating these I2E InAlAs multiplication layers haveachieved the lowest noise and highest gain-bandwidth product ever reported for any APD technology. Agility has an exclusive license to these low-noise structures and is therefore uniquely positioned to both successfully complete Phase I with a viabledesign and to implement the design by building APDs in Phase II that meet the program performance goals. Successfully designing a large area APD that meets the objectives of this SBIR will yield a device that not only facilitates space to groundcommunication, but also will find wide commercial applications in instrumentation as well as other space, avionics, and terrestrial free-space optical communications where large-area wide-bandwidth detector technologies currently do not exist.