Characterization of fiber-coupled, 125um InAlAs/InGaAs APDs for free space optics communications

Low-noise, high bandwidth avalanche photodiode (APD) detectors are instrumental in free space optical communication systems as communications receivers. APDs with large active areas help mitigate the challenge of focusing received optical power onto a detector after being distorted due to atmospheric turbulence. However, larger active areas increase the capacitance of the detector and reduce its bandwidth performance. Therefore it is necessary to weigh the increased field of view provided by larger active areas against the bandwidth performance of such devices. Details of an APD characterization testbed, and initial performance results, will be presented.