Inverse design of compact silicon photonic waveguide reflectors and their application for Fabry-Perot resonators

Silicon photonic waveguide resonators, such as microring resonators, photonic crystal waveguide cavities, and Fabry-Perot resonators based on the distributed Bragg reflectors, are key device components for silicon-based photonic integrated circuits (Si-PIC). For the Si-PIC with high integration density, the device footprints of the conventional photonic waveguide resonators need to be more compact. Inverse design, which is operated by the design expectation and different from the conventional design methods, has been investigated for reducing the photonic device components nowadays. In this paper, we inversely designed the silicon photonic waveguide reflectors for two target wavelengths: one is 1310 nm and the other is 1550 nm. The silicon photonic waveguide reflectors have reflectance of 0.99993 and 0.9955 for the wavelength of 1310 nm and 1550 nm each with 5-μm-long reflectors. Also, we theoretically investigated Fabry-Perot resonators based on the inversely designed photonic waveguide reflectors. Q factors of the Fabry-Perot resonators have been calculated to be 1.3 × 10⁵ for the wavelength of 1310 nm and 2583 for the wavelength of 1550 nm. We have expected that the inversely designed photonic waveguide reflectors and their applications for the Fabry-Perot resonators can be utilized for compact passive/active device components such as wavelength filters, modulators, and external cavity lasers.