2.5G large area avalanche photodiodes for free space optical communication

Congestion of the RF spectrum has driven the development and proliferation of Free Space Optical Communication (FSOC) technology across multiple application platforms including terrestrial, air-to-ground, and space-based telecommunication network architectures. For atmospheric FSOC links, large area Avalanche Photodiodes (APD) are advantageous for a number of reasons. Owing to their internal gain mechanism, APDs provide superior performance compared to PIN detectors. Advances in heterostructure design and device fabrication have also led to improved APD noise performance relative to those developed in decades past. A large active area allows for: 1) improved tolerance to atmospheric turbulence impacts such as beam wander, break-up, and expansion, and 2) an enhanced field-of-view relative to fiber-coupled receiver architectures that are constrained to the numerical aperture of the coupling fiber. A common system design tradeoff, however, for implementation of large area APDs is given by the inverse relationship between active area and bandwidth. Here, we present performance results of low noise, 100μm active diameter APDs capable of data rates beyond 2.5Gbps.