Frustrated total internal reflection fiber-optic small-motion sensor for hydrophone use

Abstract

A method and apparatus for sensing motion relies upon the total light traitted by an optical fiber. The fiber is wound in a spiral coil and cemented to a rigid base and a portion of the fiber's cladding is removed exposing its core. A highly refractive plate is placed closely adjacent the exposed core. When the plate is displaced, it intercepts at least a portion of the evanescent field that is adjacent to the spiral core. The intercepted portion reduces the total amount of light otherwise projected through the coiled optic fiber so that a detector can provide representations of the amplitude and frequency of the plate motion. The plate only penetrates the fiber's evanescent optical field which is associated with the total internal reflection at the glass-to-air interface at the fiber's surface. Adjusting devices and pressure compensation optionally are employed making this device suitable for use has a hydrophone.

Dependencies are inferred from the claim text.