Optical Fiber Sensor for Measuring Refractive Index

An optical fiber sensor for measuring a liquid refractive index is proposed. When an optical fiber is bent and part of its cladding is stripped off, the light energy ( E ) emerging from the fiber depends on the refractive index of the surrounding medium ( n m ). The change in n m can be found from E . The light output energy and the measuring sensitivity are calculated numerically as a function of n m for several values of the bending radius R . The fundamental characteristics of the sensor, made of a plastic fiber, are investigated using lamp oil and light oil as specimens, and a measurement accuracy of n m to the third decimal place is easily obtained. As applications of this sensor, measurement of liquid density and detection of oil are described.