Digital Coherent Receiver Employing Photonic Downconversion for Phase Modulated Radio-over-Fibre Links

A digital coherent receiver employing photonic downconversion is presented and experimentally demonstrated for phase-modulated radio-over-fibre optical links. The receiver is capable of operating at frequencies exceeding the bandwidth of electrical analog-to-digital converter by using photonic downconversion to translate the high-frequency input RF signal to the operating frequency range of the analog-to-digital converter. First, using linear digital demodulation scheme we measure SFDR of the link at microwave frequency of 5 GHz. Thereafter, successful signal demodulation of 50 Mbit/s Binary Phase Shift Keying (BPSK) modulated data signal at 5 GHz RF carrier frequency is experimentally demonstrated by using an analog-to-digital converter with only I GHz bandwidth. We successfully demonstrate signal demodulation, using the proposed digital coherent receiver with photonic downconversion, after 40 km of transmission through standard single mode fiber.