Remodulation-induced crosstalk mitigation in WDM-PON using remodulation approach is presented in this paper. Utilizing all-optical signal processing, the proposed method has been able to significantly improve system performance in terms of bit error rate (BER) and bit rate distance product. Moreover, the proposed method could be used for both baseband and modulated downstream electrical signals. 1. Introduction As old copper line has been progressively replaced by optical fiber and coherent optical modulation techniques are being deployed, access networks have also changed from fiber-to-the-X (FTTX) active optical network (AON) systems to passive optical network (PON) systems. In PON, deployment and maintenance costs are greatly reduced with fewer fibers and no active components from optical line terminal (OLT) to optical network unit (ONU). With low fiber’s attenuation and better sensitivity of modern optical receivers, it is possible to send optical signal across nearly 20？km toward up to 64 ONUs using only one single mode fiber and optical power splitter/combiner. Standardized by IEEE and ITU-T, the current PON topologies are E-PON and G-PON using time division multiplexing [1, 2]. However, since optical signal power is equally divided between users and time division multiplexing is used, there are issues in security, synchronization, latency, and laser’s rise-time [2]. Next generation of PON focuses on wavelength division multiplexing (WDM-PON) techniques [3–7]. As each user utilizes a different wavelength, the weaknesses of traditional PON are overcome. WDM in traditional sense, where each downstream and upstream channel occupies a different wavelength, is only suitable for backbone networks. In access networks, where user’s deployment cost is limited, installing a wavelength-specific distributed feedback (DFB) laser diode for each user is impractical. Thus, the ability to send and receive signal across a large bandwidth, or colorless operation at ONU, is highly desired [8–13]. One of the best solutions is to reuse the downstream wavelength as carrier for upstream data by means of reflective semiconductor optical amplifier (RSOA) or semiconductor optical amplifier (SOA) with electroabsorption modulator (EAM) [14, 15]. Drawbacks of this solution include remodulation-induced crosstalk at the ONU and crosstalk causes by Rayleigh backscattering along the fiber. Since Rayleigh backscattering introduces crosstalk to counter-propagation signal of the same wavelength, it can be reduced if the upstream and downstream signal’s spectra are not overlap. As a
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