Suppression of phase noises with residual-spectra eliminator in circulator-free fiber-grating optical code-division multiple-access network coder/decoder

In this work, transmissive spectral characteristics of fiber Bragg gratings (FBGs) are applied to construct a circulator-free scheme of an optical code-division multiple-access (OCDMA) network coder/decoder (codec). The unnecessary spectra would accompany the coding chips to arrive at the photodetectors (PDs) to induce higher phase-induced intensity noise (PIIN) and multiple-access interference (MAI). A residual-spectra eliminator (RSE) between OCDMA encoder and decoder modules is employed to remove the unnecessary spectral parts of data so that the PIIN and MAI can be reduced. A simple experiment performed on the basis of transmissive spectral characteristics of FBGs together with RSE is demonstrated to verify the capability of suppressing residual-spectra noise at the PDs. Performance evaluations indicate that using RSE between network codecs can remarkably lower the PIIN effects in the receiver PDs.