Photon Counting Communication Sensor

The objective of this research is to investigate the use of photon-counting avalanche photodiodes as a laser communication sensor. This detector technology allows reduction of the received optical power. The system will also incorporate a cesium atomic line filter to eliminate background light and a wavelength locked communication laser matched to the atomic line filter. This configuration will enable use of the extremely high gain of photon-counting avalanche photodiodes by reducing noise generated by background light. Conventional avalanche photodiodes utilize a lower gain and higher signal levels to provide an acceptable signal-to-noise ratio. The proposed detector will also require an innovative signal processing system to recover the received data. The photon-counting APD will output a pulse if a single photon is detected, if multiple photons are detected, or if a dark count event occurs, when no photons were detected. For this reason, the signal pulse will need to be divided into mined by how many bins contained detected photons. By contrast, conventional APDs have an analog output signal, and the decision process is based on the relative level of the output signal. This design is expected to produce an additional 12 dB of sensitivity over conventional avalanche photodiode technologies.