A cantilever beam-based optomechanical inertial sensor in silicon nitride photonics platform

Integrated photonics has emerged as a popular platform for performing a wide range of measurements with high sensitivity. Here, an optical accelerometer in a silicon nitride photonics platform was designed, and the fabricated device’s performance was measured. The device consists of serpentine waveguide loops on the top of a cantilever beam. Light is first split into a reference and sensing arm. When the cantilever is subjected to acceleration, a strain field is generated within the sensing arm that leads to a proportional optical phase change. Light from the reference and sensing arm is combined, and the output has an intensity modulated by the incoming acceleration. These intensity variations are detected at a fiber-coupled photodetector. Low-frequency phase drift from environmental noise has been suppressed by a negative feedback controller connected to an optical fiber stretcher. Because of the high mechanical compliance of the beam, a low noise floor equal to 10.0 ng/√Hz is targeted. The silicon cantilever is thinned to approximately 50 μm, and a bulk silicon proof approximately 500 μm thick resides at the tip. These features are realized with backside etching processes.