Transport performance in optical path cross-connect system employing unequally spaced channel allocation

The transmission performance of an optical path cross-connect (OPXC) system employing unequally spaced channel allocation is evaluated. Four-wave mixing (FWM) light is generated at a different wavelength from all other signal lights when unequally spaced channel allocation is employed in the OPXC system. This evaluation shows that FWM light degrades the transmission performance because the received FWM light power is added to the signal and closes the eye aperture of the signal. The FWM light is rejected by the employed demultiplexer when the full-width at the half maximum (FWHM) of the demultiplexer is reduced. The FWHM of the demultiplexer should be designed in order to minimize the transmission performance degradation caused by the FWM crosstalk. The FWHM of the arrayed-waveguide-grating (AWG) demultiplexer that is developed for the OPXC system is 0.6 nm, and a 400 km transmission with optical path cross-connections is successfully completed in a 4×4 OPXC system test-bed employing unequal channel spacing with a 10 GHz frequency slot, i.e., the minimum frequency separation between signal light and FWM light. Further reduction in the FWM crosstalk is required for the OPXC system in order to support longer distances between nodes. The distance of 120 km ×5 requires that the frequency slot is increased to 30 GHz and the FWHM of the AWG demultiplexer is 0.3 nm