Considering the increasing demands of bandwidth and the limited spectrum resources, it is necessary to organize several plans for the upgradation of the Super-PON system. Generally, two schemes have been proposed as the improvement involving the increment of the line-rate per channel up to 25 Gbit/s and using bidirectional transmission on one wavelength. Here, the influence of Cross-Phase Modulation (XPM) in the case of line-rate/ channel increment and Stimulated Raman Scattering (SRS) in the case of bidirectional transmission on one wavelength has been investigated, respectively. For the former, XPM obviously causes degradation impact on 25 Gbit/s non-return-to-zero (NRZ)/4-level pulse amplitude modulation (PAM4) signal transmission, resulting in an unpredictable sensitivity penalty (cannot reach the bit error rate (BER) of 1 x 10-2), which can be counteracted in use of optical duobinary (ODB) modulation format demonstrating a sensitivity penalty of 1-dB under the same condition. For the later, the SRS effect causes a power depletion of 1 dB/0.6 dB for pump frequencies of downstream/upstream during the 10 Gbit/s bidirectional transmission on the same wavelength.
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