DQPSK Directly Phase Modulated DFB for Flexible Coherent UDWDM-PONs

Abstract

A bandwidth-limited distributed feedback laser directly phase modulated with a 5-Gb/s differential quadrature phase shift keying (DQPSK) signal is demonstrated in a statistical ultra-dense wavelength division multiplexing passive optical network. Optical DQPSK modulation was achieved by simply equalizing a four-level waveform. An intradyne receiver based on a 120° optical hybrid with straightforward differential decoding processing was used to detect and recover the data attaining a sensitivity of −38 dBm at $\textrm {BER}=10^{-3}$ . Negligible penalty was observed when adding a second user at 5-GHz channel separation.