Performance Implications of Cascaded Wavelength Selective Switches on a Probabilistically Shaped 64-QAM System

The effect of bandwidth narrowing originating from the cascading of wavelength selective switches (WSSs) on the generalized mutual information is assessed for probabilistically shaped, 28 Gbaud, 64-ary quadrature amplitude modulation (QAM) constellations. The system simulation includes the generation of shaped symbol sequences based on the Maxwell-Boltzmann distribution, cascaded WSS filters, simplified detection, and calculation of the bit-wise achievable information rate (BW-AIR). Results are compared for a noise loading configuration and a more practical distributed noise configuration. The statistical variations in the filter responses are addressed by considering 1000 realizations that result from randomly selected parameters for each of the individual WSS filter responses. Experimental results for a noise loading configuration and emulation of the overall frequency response for a filter cascade exhibit good agreement with corresponding simulation results.