Inverse design of broadband and lossless topological photonic crystal waveguide modes

Eric Nussbaum; Stephen Hughes

doi:10.1117/12.2594365

1 August 2021 Inverse design of broadband and lossless topological photonic crystal waveguide modes

Eric Nussbaum, Stephen Hughes

Proceedings Volume 11796, Active Photonic Platforms XIII; 117961H (2021) https://doi.org/10.1117/12.2594365
Event: SPIE Nanoscience + Engineering, 2021, San Diego, California, United States

Abstract

Photonic crystal slab (PCS) waveguides can be engineered to control the propagation of light, finding a variety of applications in optical sensing, nonlinear optics and quantum optics. However, traditional PCS waveguides suffer from disorder-induced backscattering which is especially severe in the slow-light regime. Topological PCS waveguides can support propagating edge-state modes which are possibly more robust against some defects. Here we apply inverse design techniques to modify a state-of-the-art topological PCS waveguide, to obtain a significant (more than 100%) improvement to the operational bandwidth of a lossless waveguide mode. We then optimize the new design's group velocity curve, obtaining two new designs, one with a group index of 28 over a bandwidth ▵ω/ω=1:5% and in the other a maximum group index greater than 200 away from the mode edge. We use an efficient, semi-analytic, computation method, the guided mode expansion method, to calculate photonic band structures and automatic differentiation to calculate objective function gradients. Combining this with a physically intuitive shape parameterization, the method, while initially constraining the optimization to solutions resembling the initial design, is efficient and flexible. This method can be applied to quickly optimize PCS devices towards a large variety of target figures of merit.

Conference Presentation

Citation Download Citation

Eric Nussbaum and Stephen Hughes "Inverse design of broadband and lossless topological photonic crystal waveguide modes", Proc. SPIE 11796, Active Photonic Platforms XIII, 117961H (1 August 2021); https://doi.org/10.1117/12.2594365

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