Self-calibrating measurement setup for fiber-optic polarimetric sensors

Optical fiber sensors can be categorized into amplitude, phase (interferometric) or polarimetric devices. In the former case the measurand directly modulates the intensity of light propagating through the fiber. Simplicity of construction is one of the chief advantages but sensitivity is rather low. Interferometric sensors offer highest sensitivity but the required components are quite complicated. Fiber optic polarimetric sensors are based on changes in the propagation constants of the two linearly polarized eigenmodes of birefringent single-mode fiber. For maximum sensitivity in standard measurement setups both eigenmodes of the sensing fiber have to be excited equally. This requires a tedious tuning procedure and can lead to an unknown sensitivity if the leading fiber experiences external stress due to bending. Although fiber-optic polarimetric sensors offer very high sensitivity and there is no need for a reference fiber, they are not used due to the above mentioned reasons. In the following a measurement setup with which these drawbacks are solved is described