Spatial diversity detection using single-photodetector coherent receiver array for free-space optical communications

The spatial diversity detection is experimentally demonstrated for free-space optical (FSO) communications using a single-photodetector (single-PD) coherent receiver array with quadrature phase shift keying (QPSK) signals in an atmospheric cell. The single-PD based on the Kramers-Kronig relation, which can recover the signal from the detected intensity has the advantages of simple structure and cost-effectiveness, and its performance is close to that of the conventional coherent receiver. The spatial diversity technology is verified using a two-aperture single-PD coherent receiver array and the impact of the atmospheric turbulence is effectively reduced. When the bit error rate (BER) is 1 x 10-3, using the dual single-PD receiver array, the received power of -45.96, -44.88, or -43.87 dBm is achieved when the temperature difference of the atmospheric cell is 0, 100, or 250 degrees C, respectively, which is 2.10, 2.16, or 2.25 dB receiver sensitivity improved compared to a single-PD receiver.