Depolarization of a beam under phase conjugation: remarkable properties

Summary form only given. Polarization preserving fibers are actually fibers with reasonably strong birefringence, so that each of x- or y-input polarizations follows adiabatically the local birefringence axes. The phase difference between the field E/sub x/ and E/sub y/ is for +45/spl deg/ polarization, is /spl pi//2 for right circular polarization, etc. This phase walks uncontrollably with time and is generally wavelength-dependent in polarization preserving fibers. Selection of a signal from noise based on the a-priori knowledge of polarization properties of signal and noise is discussed. We discuss also how the measurement of the unusual type of depolarization described here may provide the test of the superposition principle in nonlinear optics (it is violated by the phase conjugation) and in quantum mechanics in general.