A Simple Relative Humidity Sensor Employing Optical Fiber Coated with Lithium Chloride

A simple optical fiber relative humidity sensor was fabricated using a lithium chloride film coated on the distal end of sensing fiber. The sensing element, lithium chloride film whose refractive index is sensitive to moisture, thereby changes the reflected light intensity of the sensing end. By monitoring the change of reflected light intensity under different RH levels, the information about RH of the environment can be obtained. A difference of up to 0.64uW of the reflected optical power is observed when RH changes from 11 to 75%. The LiCl-based sensor has a sensitivity of about 0.01uW/%RH with a slope linearity of more than 99.8%. The experimental setup is simple and easy to handle. The results demonstrate that LiCl-based optical fiber sensor is sensitive, economical, flexible, and fast response, has the potential of remote on-line monitoring humidity.