Frequency shift detection mechanism in GaAs waveguides with mode-coupled Bragg gratings

Frequency shift detection is crucial for advancing quantum, laser and metrology technologies. Here, we propose a compact design for detecting frequency shift in GaAs waveguides with mode-coupled Bragg gratings, which provides enhanced sensitivity. Our proposed architecture features a main ridge waveguide with a Bragg grating, flanked by two curved ridge waveguides. This configuration exhibits an optical phenomenon characterized by a transmission crossing at the wavelength of the Bragg grating. Using particle swarm optimization and employing efficient figures of merit, we achieve a high transmission crossing. The observed asymmetric transmission crossing not only holds the promise for a compact on-chip laser frequency stabilizer, but also fosters the development of novel sensing platforms with heightened sensitivity.