Rayleigh Noise Reduction in 10-Gb/s Carrier-Distributed WDM-PONs Using In-Band Optical Filtering

To circumvent the challenging issue of Rayleigh noise reduction in wavelength-division-multiplexed passive optical network (WDM-PON), we provide an insight into the source of Rayleigh noise, and confirm that the suppression of carrier Rayleigh backscattering (RB) should be the primary target in the design of Rayleigh noise-resilient upstream receiver module for a transmission reach up to 60 km. Then we propose and demonstrate a novel scheme to effectively suppress the carrier RB in carrier-distributed WDM-PONs. By simply replacing the upstream modulation format of conventional on-off keying (OOK) with differential phase-shift keying (DPSK), the system tolerance to carrier RB is substantially enhanced by 19 dB, as the carrier RB can be considerably rejected by the notch filter-like destructive port of the delay-interferometer (DI) at the optical line terminal (OLT), which is used simultaneously to demodulate the upstream DPSK signal. The dependence of carrier RB suppression on DI´s extinction ratio (ER) and optical carrier´s line width is also theoretically analyzed. Experimental demonstration of 10-Gb/s upstream signal is achieved with less than 2.5-dB power penalty induced by Rayleigh noise after the transmission in 60-km single mode fiber, without using any amplifier in outside plant. The relation between system margin and the gain of optical network unit (ONU) is also studied.