100  km Coherent Nyquist Ultradense Wavelength Division Multiplexed Passive Optical Network Using a Tunable Gain-Switched Comb Source

We propose and experimentally demonstrate a long-reach Nyquist ultradense wavelength division multiplexed passive optical network using a tunable optical frequency comb source and a digital coherent receiver. Each of the six comb tones on a 12.5 GHz grid is modulated with a 12 Gbaud Nyquist polarization division multiplexed quadrature phase shift keyed signal which includes a 20% overhead for forward error correction. Unrepeated downlink transmission of 100 km is demonstrated at three different operating wavelengths across the C-band. A worst-case channel sensitivity of −35.3  dBm (59 photons/bit) is achieved at a bit error rate of 1.5×10−2, yielding a system loss budget of 35.7 dB.