In-band crosstalk due to Rayleigh backscattering (RB) can be avoided in bidirectional wavelength-division multiplexed (WDM) transmission systems when using two identical sets of wavelengths in opposite directions over a single fiber. We describe this by using such sets in a disjoint manner and eliminating the RB crosstalk with the help of simple optical edge filters instead of the WDM comb filters previously employed in interleaved bidirectional systems. We also provide a practical application example and describe the power penalty due to the interferometric RB crosstalk, taking into account recent polarized optical noise research because RB light is partially polarized. Numerical results for externally modulated intensity-modulation/direct-detection (IM/DD) optical systems show that the power penalty can be kept less than 0.5 dB with moderate edge filters, even for more than several tens of optically amplified repeater segments.
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