Reflectivity characteristics of the fiber loop mirror with a polarization controller

In this paper, reflectivity characteristics of a fiber loop mirror (FLM), which is formed by inserting a fiber polarization controller (PC) into the fiber loop of an ordinary FLM, are investigated in detail. A theoretical model for determining the reflectivity characteristics of the FLM is present by using the equivalent optical path technique, and the reflectivity characteristics of the FLM are then simulated with the model. The simulation results show that, when the FLM is based on a 3 dB optical coupler (OC), the reflectivity of the FLM may be continuously adjusted to any value between 1 and 0 by changing the PC state, i.e. by either changing the fast axis orientation or the birefringence intensity of the PC alone, as well as both of them; the reflectivity spectra of the FLM are wide and flattened for any PC state, mainly limited by the operating bandwidth of the OC used. The reflectivity characteristics of the FLM are further tested experimentally. The results verify that the reflectivity of the FLM may truly be continuously adjusted between its maximum and minimum values by changing the PC state. The obtainable maximum and minimum reflectivities of the FLM are measured to be 93% and 2%, respectively. Moreover, the experimental results are in agreement with those of the simulations.