A Novel CAP-WDM-PON Employing Multi-Band DFT-Spread DMT Signals Based on Optical Hilbert-Transformed SSB Modulation

We propose and experimentally demonstrate a novel carrier-less amplitude/phase modulation wavelength-division-multiplexing passive optical network (CAP-WDM-PON) with its bandwidth efficiency enhanced by using a multi-band discrete Fourier transform spread (DFT-spread) discrete multi-tone (DMT) signal based on Hilbert-transformed single-sideband (HB-SSB) modulation. The DFT-spread technique is utilized to extend orthogonal subcarriers, which effectively restrain the high-peak signal formation probability, and thereby, it can significantly reduce the high peak-to-average power ratio of the DMT signal. The proposed optical line terminal (OLT) in CAP-WDM-PON suggests five downlink optical subcarriers. For each optical subcarrier, there are as many as $6\times20$ Gb/s SSB digital DMT channels CAP modulated on them, which can be efficiently generated by using only one set of optical transmitter hardware. The experimental results show that the proposed system is capable of accommodating $5\times6$ channels (20 Gb/s per channel) within an optical distribution network (ODN) loss budget of 19.4 dB, and there is a 2.4-dB ODN loss budget improvement by utilizing the DFT-spread scheme. More importantly, the proposed spectral- and bandwidth-efficient CAP-WDM-PON system requires six times less downlink optical transmitters at the OLT, which can be translated into savings in cost, power consumption, and footprint. In addition, key techniques, such as pre-equalization for high-frequency components and digital HB-SSB modulation format for generation of multi-band DMT signals, are also studied.