Rib-Waveguide-Based Optical Path Design for Integrated Photonic Crystal Optomechanical Accelerometers

To prevent the collapse of strip waveguides caused by complete undercut during hydrofluoric acid (HF) release in SOI-based cavity optomechanical accelerometers, we propose using rib waveguides as the on-chip optical transmission medium. Based on a 250-nm-thick SOI wafer, we systematically analyze the photonic crystal (PhC) microcavity, rib waveguide transmission, edge coupling, mode conversion to the PhC waveguide, and evanescent coupling. The PhC microcavity has a quality factor of 2.26 × 105 at 1549.15 nm. The optimized rib waveguide (rib width 500 nm, rib height 220 nm) shows a transmission loss of 0.16 dB over 5000 μm. The rib-to-PhC waveguide coupling efficiency is 94.3% (0.25 dB loss), and a 90-μm-long tapered edge coupler achieves 65% efficiency (1.9 dB loss). The total optical path loss (including two edge couplers, rib waveguide transmission, and rib-to-PhC taper) is 4.21 dB. While maintaining optical performance comparable to strip waveguides, the rib waveguide design significantly improves post-release structural integrity at the design level. This work provides a viable optical circuit design foundation for reliable monolithically integrated cavity optomechanical accelerometers, with device fabrication and full system-level characterization planned as future work.