Optical pressure-sensing system using optical resonator cavity

Abstract

An optical pressure-sensing system in which an optical beam splitter couples input light from a light source to an optically resonant pressure sensor and couples output light reflected from the sensor to a light detector. The light detector may divide the output light into bands having different wavelengths and then take the ratio of the light in one band to the light in the other band in order to provide an output that is insensitive to various spurious responses in the system. The optical beam splitter may be formed by two pairs of graded refractive index lenses. A partially reflective, partially transmissive mirror is sandwiched between the lenses of one pair, while a dichroic mirror is sandwiched between the second pair. The pairs of lenses are placed in abutting relationship to each other. The optical beam splitter may also be formed by a block of transparent material having a partially reflective, partially transmissive mirror on one edge. The optical pressure sensor is formed by a transparent substrate having a cylindrical recess and a resilient diaphragm positioned over the recess to form an optically resonant cavity. Differential pressure may be sensed by placing a second substrate having a cylindrical recess over the side of the diaphragm opposite from the first substrate. The optical pressure sensor may be specifically adapted for use as a microphone by utilizing a relatively thick cavity having a pedestal projecting from the substrate close to the diaphragm to form an optically resonant cavity. The optical pressure sensor may also sense gas density by filling the optically resonant cavity with the gas being measured having a pressure at a predetermined density and temperature that matches the pressure of the gas being measured at that same density and temperature.