Passive Fiber Optic Evanescent Wave Sensor for the Measurement of Refractive Index at Various Temperatures Using a Tunable Light Source

Abstract

The study of refractive index of liquids over a range of 10oC to 60oC shows very interesting results to design and develop a highly sensitive passive fiber optic sensor based on a U-shaped glass probe. The depth of penetration of light that escaping from the core of the fiber into the cladding plays a crucial role in the development of a highly sensitive fiber optic evanescent wave sensor. The depth of penetration of an optical fiber striped off its cladding is directly related to the wavelength of the light, the index of refraction of the surrounding medium, the angle of incidence of light, the bending radius and thickness of the U-shaped probe. In the design of the sensor a U-shaped glass probe is used to replace the core of the fiber in the region of sensing, the diameter of which is same as that of the cores of a pair of insensitive fibers which in-turn connected to a tunable light source and an optical detector. The sensor is highly reliable, robust and easy to configure using multimode PCS fibers and the source operating at the wavelengths of 630nm, 660nm, 820nm and 850nm.