Experimental investigation of the non-linear optical fiber loop mirror with a symmetrical coupler and a quarter-wave retarder plate in the loop.

We research experimentally the configuration of an, non linear optical fiber loop mirror, with a symmetrical coupler, highly twisted low-birefringence fiber and a quarter-wave retarder plate inserted into the loop as polarization controller. The retarder plate is used to create an asymmetry in polarization and the nonlinear polarization rotation is used to produce a differential phase shift between the counter-propagating beams in the fiber loop. It is possible to change the transmission behavior with the rotation of the retarder plate. Some advantages that we get with this configuration, in comparison with others similar devices are high contrast between the maximun and minimun of the transmission and flexibility in the adjustment of its transmission characteristic curve. With this, we have the possibility to use it to reduce the amplitude fluctuations in a train of optical pulses.