Nonlinear filtering by use of intensity-dependent polarization rotation in birefringent fibers.

We analyze the transmissivity of a nonlinear filter that is based on intensity-dependent polarization rotation in a birefringent fiber. It is shown that the transmissivity of the element depends not only on the intensity of the incident light but also on the time behavior of its amplitude. Such an element can be used as a derivator, an element that transmits only variations in the input pulse. The filter can also be used for obtaining lasers that generate a train of intense noiselike pulses with a broadband spectrum and a short coherence length.