Photodetectors in free space optical communication systems perform two functions: reception of data communication signals and position sensing for pointing, tracking, and stabilization. Traditionally, the optical receive path in an FSO system is split into separate paths for data detection and position sensing. The need for separate paths is a consequence of conflicting performance criteria between position sensitive detectors (PSD) and data detectors. Combining the functionality of both detector types requires that the combinational sensor not only have the bandwidth to support high data rate communication but the active area and spatial discrimination to accommodate position sensing. In this paper we present a large area, concentric five element impact ionization engineered avalanche photodiode array rated for bandwidths beyond 1GHz with a measured carrier ionization ratio of less than 0.1 at moderate APD gains. The integration of this array as a combinational sensor in an FSO system is discussed along with the development of a pointing and stabilization algorithm.
Mike S. Ferraro, Rita Mahon, William S. Rabinovich, James L. Murphy, James L. Dexter, William R. Clark, William D. Waters, Kenneth Vaccaro, and Brian D. Krejca, "Simultaneous data communication and position sensing with an impact ionization engineered avalanche photodiode array for free space optical communication," Proc. SPIE 10096, Free-Space Laser Communication and Atmospheric Propagation XXIX, 100960N (Presented at SPIE LASE: January 31, 2017; Published: 24 February 2017); https://doi.org/10.1117/12.2250545.
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