EMBEDDED FIBEROPTIC FABRY-PEROT ULTRASOUND SENSOR

A novel type of fiber-optic ultrasound sensor is presented. The sensor consists of a continuous length of single mode optical fiber with Fabry-Perot interferometer built into it. The acoustic pressure produces changes in the index of refraction along the interferometer cavity through the strain-optic effect, thus modulating the reflected power of the light propagating in the fiber. The dielectric internal mirrors that form the interferometer are fabricated by joining a fiber coated with a TiO2 film at one end to an uncoated fiber by electric arc fusion splicing. Experimental results have been obtained for sensors embedded in plastic and graphite composite materials, using ultrasound waves in the range from 100 KHz to 5 MHz. Values for the optical phase shift amplitude as large as 0.5 rad were obtained at an acoustic frequency of 200 KHz for a 1.1-cm-long interferometer embedded in plastic. The sensor may prove very useful for in service testing of modern structural composite materials. © 1990 IEEE