DQPSK Directly Phase Modulated DFB for Flexible Coherent UDWDM-PONs

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 {BER}=10 -3 . Negligible penalty was observed when adding a second user at 5-GHz channel separation.