A Genetic-Algorithm Enhanced Design of a Silicon-Photonics Wavelength Multiplexer/Demultiplexer Circuit

This paper proposes a novel design for a wavelength Multiplexer/Demultiplexer circuit based on the complementary-metal-oxide-semiconductor (CMOS) platform. The wavelength-division multiplexing (WDM) specifications for this device include free spectral range of 100 GHz (equivalently $0.8\text{nm}$), channel spacing of 50 GHz, crosstalk less than −23 dB, dispersion less than 30 ps/nm, and preferably shape factor greater than 0.6, alongside minimal insertion loss and device footprint. The new design incorporates four additional ring resonators compared to previous studies, resulting in significant enhancement in crosstalk by 13 and 4 dB for the through port and drop port signals, respectively. Additionally, the transmission shape factor increases by 25% and 50% for the through port and drop port, respectively. The design approach employs a genetic algorithm to achieve optimal coupling coefficients for a multi-objective optimisation problem without a mathematical closed form, significantly reducing the computation time. This proposed algorithm seeks a balanced solution where all performance parameters reach acceptable values rather than optimising each parameter individually. This method proves to be both efficient and expedient, effectively eliminating the trial-and-error approach and the need for visual investigation of the Z-domain of the circuit transmission commonly used in the literature.