Theoretical Analysis and Experimental Investigation of Fiber-optic Coupler's Strain Characteristic

The most important characteristic of an optical fiber coupler is that its ratio of output power is sensitive to the length of the coupling zone. This character is used for precision strain sensing in this paper, in which the theory analysis and experimental scheme for such sensing applications were presented. The strain characteristic of fiber-optic coupler is investigated with a spiral micrometer to avoids the uncontrollable disturbances induced by self-weight or self-vibration of a cantilever and enhances the measurement precision effectively. The influences of environmental temperature and transversal strain are described in detail. The behavior of the coupler is compared with the response of a high precision strain gauge in the meantime. The results indicate that the fused biconical-tapered coupler is not only sensitive to strain but also exhibits a broad-ranged linear and monotonous relationship between strain and the output power ratio, with excellent temperature stability and independent of transversal mechanical disturbance, making the fused biconical-tapered coupler an ideal candidate for a simple but highly effective optical fiber strain sensor.