Full-duplex hybrid optical link with 40 Gbit/s 16-QAM signal for wired or wireless selective access based on polarization division multiplexing

Abstract

A full-duplex hybrid optical link with 40 Gbit/s 16-ary quadrature amplitude modulation (16-QAM) signal based on polarization division multiplexing (PDM) is proposed, which can provide wired or wireless selective access for the user terminals. The 16-QAM downlink signal for wired and wireless accesses is only modulated onto one of the polarization states of the light wave. Then the generated data-bearing optical tone orthogonally combines with the other polarization state to constitute the downlink optical signal. At the hybrid optical network unit (HONU), an ordinary laser with the fixed wavelength is not only used to provide the optical local oscillator (OLO) for downlink wireless access but also the optical carrier for its uplink, while the OLO and uplink optical carrier for wired access are extracted from the downlink optical signal. Moreover, since the downlink optical signal is a baseband one with two orthogonal polarization states, the spectrum efficiency of our proposed scheme is high. The obtained constellations and eye diagrams of the demodulated 16-QAM downlink and uplink signals for wired and wireless accesses show that our proposed full-duplex hybrid optical link can still maintain a good transmission performance after being transmitted over 20 km standard single mode fiber (SSMF).