Hybrid SPAD/PD Receiver for Reliable Free-Space Optical Communication

Free-space optical (FSO) communication provides wireless optical connectivity with high data rates and low-cost implementation; however, its performance is strongly influenced by the power attenuation due to the infrequent adverse weather conditions. This article proposes a novel highly sensitive dual-mode receiver comprising an array of single-photon avalanche diodes (SPADs) and a PIN photodiode (PD) to enhance the availability of FSO links. In adverse weather conditions, the receiver operates in the SPAD-mode; whereas, in the clear weather conditions, the receiver works in the PD-mode. A hybrid receiver controller is employed in the proposed receiver to adaptively control the switching process based on the received light levels. The adaptive controller also adjusts the incident photon rate of the SPAD array using a variable optical attenuator (VOA) to optimize the performance of the SPAD unit. Our extensive performance analysis illustrates the superior achievable data rates of the proposed receiver under various weather conditions compared to the traditional FSO receivers with either PD or SPAD array.