Optical Fiber-Facet Multiplexed Monolithic Silicon Pressure Sensors

This paper describes the design, fabrication, and characterization of the smallest pressure sensors with the required sensitivity, bandwidth, and robustness for turbulent airflow measurements. These fiber-facet monolithic silicon optical pressure sensors consist of a silicon diaphragm above a sealed cavity contained within a 125~\mu \text{m} wide by 5~\mu \text{m} thick silicon disk mounted directly onto a single-mode optical fiber facet. The fiber-mounted sensors form pressure-sensitive interferometric cavities with 1.6 MHz bandwidth, 4 nm/kPa deflection, and up to 0.07 V/kPa sensitivity. The short length of the optical cavity makes the sensors optically efficient and optically broadband, allowing multiplexing using standard optical communications equipment. This is demonstrated experimentally by optically-multiplexing three fiber-facet sensors with up to 161 kPa dynamic ranges and 2 Pa noise floors. These balanced-detection pressure-sensing arrays provide a small-footprint, high-resolution alternative to traditional turbulence measurement equipment.