Study of Electro-optic and Electrostrictive Effects on Polarization in Single Mode Fiber

If the rotational symmetry of single mode (S.M.) fiber is disturbed, either during manufacturing or through some external perturbation the polarization modes have different propagation constant. Due to this generated birefringence, the linear polarized light through S.M. fiber is distributed in two orthogonal eigenmodes. As a result, the state of polarization (SOP) is changed at the exit end of the fiber. In the present paper, electro-optic effect on S.M. fiber has been induced by placing the fiber coil under electric field. Investigation shows that the developed birefringence in fiber arises mainly due to bending and electrostriction/Kerr effect. So, by varying the electric field, the developed anisotropy or birefringence ultimately can be utilized to control the state of polarization (SOP) at the output. Experimental study has been carried out on 40m. and 48m. coiled fiber under D.C. voltage (0 to 280 volts). Results show that SOP of two prototype polarization controllers, become circular i.e. λ/4 plate at 235 volts and 143 volts respectively. The external effect acting upon SM fiber is directly calibrated with respect to phase and ellipticity of light. The correction in calibration equation in particular case where ellipticity change is considerable, has been reported in the present paper. Experiment has been performed to verify the theoretical studies and error has been computed.