Application of numerical optimization to the design of InP-based wavelength combiners

We applied a numerical device optimization scheme, where tens of parameters can be optimized simultaneously with multiple target performance criteria that are given. The key items of the design scheme are the selection of the best optimization algorithm, metric, and consideration for fabrication errors. This method was then applied to design an MMI beam combiner with rectangular effective refractive steps with up to 75 parameters, and we obtained a simulated insertion loss of 0.8 dB for a 1.4 mm-long 2×1 wavelength combiner, and a simulated insertion loss of 4.2 dB for a 1.9 mm-long 4×1 wavelength combiner, both with 20 nm wavelength spacing. This methodology could also be applied to other types of optical devices.