Duplex Baseband Signal Transmission Over Free Space Optical Link Employing Carrier Reuse

Abstract

With increasing IoT and a plethora of multimedia applications being used, there is an ever-increasing demand for bandwidth-intensive applications. Communication networks employing optical fiber had been the de facto standard for such communication systems. The Optical Fiber network's high cost and man-hours required for laying demand wireless solutions. Therefore, an optimum and cost-effective duplex optical link for two channels baseband signal data transmission has been designed and validated using a single laser source. An optical link for 20 Gbps duplex data transmission is designed based upon single laser source utilization. A cost-efficient and simple design have been accomplished with a transmission distance of 1.5 km by utilizing Differential Quadrature Phase Shift Keying (DQPSK) and On-Off Keying (OOK) modulation techniques. The design allowed us to recycle the downlink signal in uplink transmission over free Space, thus eradicating the requirement for a separate laser at the other end. Each channel's transmission data rate was 10 Gb/sec. At the former end, the DQPSK technique was employed for data modulation and the data was transmitted into free space. The data was then split at the latter end for downlink reception along with reusing the downlink received signal for uplink transmission to the former end utilizing the OOK modulation technique. The received data was compared with the transmitted one to verify and validate the system's accuracy through signal waveforms and BER (Bit Error Rate). The eye diagrams and the Bit error rate (BER) graphs of the received downlink and uplink signals over a duplex Free Space Optical (FSO) transmission link are discussed and presented.