Experimental investigation of polarization-imbalanced nonlinear loop mirror with double-sense twisted fiber as a filter to clean up solitons

In the present work, we report the implementation of a novel polarization-imbalanced NOLM for soliton cleaning. The NOLM consists of a nearly symmetrical coupler with a 51/49 coupling ratio, and the fiber loop which, in contrast to previously reported results, consists of two 100 m pieces of fibers twisted in opposite directions. The use of the symmetrical coupler and two fiber spans twisted in opposite direction allowed a transmission of low-power radiation of 0.5 × 10−3 in the wavelength range of 1520–1560 nm. The maximum transmission at high power was 45% providing 30 dB contrast between high and low power transmission. We show more than 20 dB suppression of Kelley's side bands of 0.6 ps pulses from the output of the fiber mode-locked laser. The experimental results are supported by the numerical simulation and show that cleanup of solitons is possible using a NOLM as intensity filter without dependence of wavelength.