Abstract

Slow light waveguides in photonic crystals are engineered using a conventional method or a deep learning (DL) method, which is data-intensive and suffers from data inconsistency, and both methods result in overlong computation time with low efficiency. In this paper, we overcome these problems by inversely optimizing the dispersion band of a photonic moiré lattice waveguide using automatic differentiation (AD). The AD framework allows the creation of a definite target band to which a selected band is optimized, and a mean square error (MSE) as an objective function between the selected and the target bands is used to efficiently compute gradients using the autograd backend of the AD library. Using a limited-memory Broyden-Fletcher-Goldfarb-Shanno minimizer algorithm, the optimization converges to the target band, with the lowest MSE value of $9.844 \times {10^{- 7}}$, and a waveguide that produces the exact target band is obtained. The optimized structure supports a slow light mode with a group index of 35.3, a bandwidth of 110 nm, and a normalized-delay-bandwidth-product of 0.805, which is a 140.9% and 178.9% significant improvement if compared to conventional and DL optimization methods, respectively. The waveguide could be utilized in slow light devices for buffering.

© 2023 Optica Publishing Group

Photonic Moiré lattice waveguide with a large slow light bandwidth and delay-bandwidth product

Ibrahim Nasidi, Ran Hao, Jun Chen, Erping Li, and ShangZhong Jin
Appl. Opt. 61(19) 5776-5781 (2022)

Slow light in an alternative row of ellipse-hole photonic crystal waveguide

Yameng Xu, Lei Xiang, Eric Cassan, Dingshan Gao, and Xinliang Zhang
Appl. Opt. 52(6) 1155-1160 (2013)

Wideband slow light with low dispersion in asymmetric slotted photonic crystal waveguides

Bo Liu, Tao Wang, Jian Tang, Xiaoming Li, Chuanbo Dong, and Yu He
Appl. Opt. 52(34) 8394-8401 (2013)

Accurate and efficient prediction of photonic crystal waveguide bandstructures using neural networks

Caspar F. Schwahn and Sebastian A. Schulz
Opt. Continuum 2(6) 1479-1489 (2023)

Wideband slow light in photonic crystal slab waveguide based on geometry adjustment and optofluidic infiltration

Morteza Janfaza and Mohammad Ali Mansouri-Birjandi
Appl. Opt. 52(34) 8184-8189 (2013)