The emergences of silicon-based photonic crystal (PhC) waveguides and two-dimensional (2D) PhC line-defect optical cavities have revolutionized the field of integrated photonics. In this paper, we design and fabricate a high-quality (high-Q) 2D silicon-based PhC optical cavity with integrated waveguides. We employ the 2D finite-difference time-domain (FDTD) method to simulate the cavity, considering two different thicknesses: 0.5 μm and 0.25 μm. By optimizing the line-defect and air-slot widths for the integrated PhC waveguides, we are able to achieve remarkable Q-factors for the PhC optical cavity. With a silicon thickness of 0.5 μm, the high-Q achieves an impressively high value of 8.01 × 10⁶, while at a silicon thickness of 0.25 μm, it achieves 1.91 × 10⁷. This research highlights the importance of design optimization and fabrication techniques in achieving high-Q optical devices using PhC and silicon-based structures.

The integration of modern accelerometers and gyroscopes has led to the development of inertial measurement units (IMUs), which have evolved into inertial navigation systems (INS) and, more recently, into positioning, navigation, and timing (PNT) systems. Furthermore, multi-sensor on-chip technology is advancing, delivering wider bandwidths, heightened precision, and further miniaturization. Optomechanical sensor research reveals significant advantages over conventional accelerometers, particularly in the achievement of low-noise resonant optomechanical transduction, which approaches the thermodynamic limit. In this study, we further present a differential-type optomechanical accelerometer based on the two-dimensional slot-type silicon photonic crystal (PhC) micro-cavity from the low-frequency region to near the fundamental resonance frequency. It is demonstrated that, in the parametric optomechanical oscillation mode, the silicon-on-insulator (SOI) sensor has a measured noise-equivalent acceleration (NEA) of ~20 μg/Hz ^1/2 , nearing the thermal noise limit of ~14 μg/Hz ^1/2 . The sensor, designed for broadband vibration measurements, is engineered with a theoretical bandwidth of ~70 kHz, but can only be measured up to 30 kHz due to instrumentation limitations. This device is suitable for various applications such as vibration detection, inertial navigation, acoustic analysis, or optical sensing collaboration.

To improve the efficiency and stability of the system, this paper proposes a monolithic integrated optical path design for a cavity optomechanical accelerometer based on a 250 nm top silicon thickness silicon-on-insulator (SOI) wafer instead of readout through U-shape fiber coupling. Finite Element Analysis (FEA) and Finite-Difference Time-Domain (FDTD) methods are employed to systematically investigate the performance of key optical structures, including the resonant modes and bandgap characteristics of photonic crystal (PhC) microcavities, transmission loss of strip waveguides, coupling efficiency of tapered-lensed fiber-to-waveguide end-faces, coupling characteristics between strip waveguides and PhC waveguides, and the coupling mechanism between PhC waveguides and microcavities. Simulation results demonstrate that the designed PhC microcavity achieves a quality factor (Q-factor) of 2.26 × 10⁵ at a 1550 nm wavelength while the optimized strip waveguide exhibits a low loss of merely 0.2 dB over a 5000 μm transmission length. The strip waveguide to PhC waveguide coupling achieves 92% transmittance at the resonant frequency, corresponding to a loss below 0.4 dB. The optimized edge coupling structure exhibits a transmittance of 75.8% (loss < 1.2 dB), with a 30 μm coupling length scheme (60% transmittance, ~2.2 dB loss) ultimately selected based on process feasibility trade-offs. The total optical path system loss (input to output) is 5.4 dB. The paper confirms that the PhC waveguide–microcavity evanescent coupling method can effectively excite the target cavity mode, ensuring optomechanical coupling efficiency for the accelerometer. This research provides theoretical foundations and design guidelines for the fabrication of high-precision monolithic integrated cavity optomechanical accelerometers.

In recent years, research on light-matter interactions in silicon-based micro/nano cavity optomechanical systems demonstrates high-resolution sensing capabilities (e.g., sub-fm-level displacement sensitivity). Conventional 2D photonic crystal (PhC) cavity optomechanical sensors face inherent limitations: thin silicon layers (200–300 nm) restrict both the mass block (critical for thermal noise suppression) and optical Q-factor. Enlarging the detection mass in such thin layers exacerbates in-plane height nonuniformity, severely limiting high-precision sensing. This study proposes a 500 nm thick silicon-based 2D slot-type PhC cavity design for advanced sensing applications, fabricated on a silicon-on-insulator (SOI) substrate with optimized air slot structures. Systematic parameter optimization via finite element simulations defines structural parameters for the 1550 nm band, followed by 6 × 6 × 6 combinatorial experiments on lattice constant, air hole radius, and line-defect waveguide width. Experimental results demonstrate a loaded Q-factor of 57,000 at 510 nm lattice constant, 175 nm air hole radius, and 883 nm line-defect waveguide width (measured sidewall angle: 88.4°). The thickened silicon layer delivers dual advantages: enhanced mass block for thermal noise reduction and high Q-factor for optomechanical coupling efficiency, alongside improved ridge waveguide compatibility. This work advances the practical development of CMOS-compatible micro-opto-electromechanical systems (MOEMS).