Ultracompact Optical Fiber Sensor for Inner Diameter Measurement

Abstract

ABSTRACT An ultracompact optical fiber Fabry–Perot interferometric sensor is proposed and demonstrated for inner diameter measurement of a capillary tube. The device is a section of single-mode fiber with an angle-polished end face of 45°. When the device is placed inside the capillary tube and in close contact with its inner wall surface, the reflected light from the angle-polished fiber end face is directed sequentially to the fiber core–cladding, cladding–air, and air–capillary interfaces, respectively, and reflected back, and finally returned to the fiber core after being reflected by the angle-polished fiber end face again. As a result, a cascaded Fabry–Perot interferometer system is constructed, which is well suitable for the inner diameter measurement of the capillary tube. Moreover, the wall thickness of the transparent capillary tube can also be conveniently measured by using the same device in slightly different configuration. The relative error of the measurement is small compared with the data provided by the manufacturer. Such a device is ultracompact, robust, flexible, and convenient in operation and is especially attractive for implementing the measurement in a tight or hard-to-reach spatial environment.