Temperature-dependent gain and noise in fiber Raman amplifiers

Generation of high-purity telecom-band entangled photon pairs in dispersion-shifted fiber

We study the purity of correlated photon pairs generated in a dispersion-shifted fiber at various temperatures. The ratio of coincidence to accidental-coincidence counts greater than 100 can be obtained as the fiber is cooled to liquid-nitrogen temperature (77 K). We then generate polarization-entangled photon pairs by using a compact counterpropagating scheme. Two-photon interference with visibility >98% and Bell's inequality violation by >8 standard deviations of measurement uncertainty are observed at 77 K, without subtracting the accidental-coincidence counts due to background Raman photons.

Raman gain: pump-wavelength dependence in single-mode fiber

The magnitude of the stimulated Raman gain spectrum will depend on the absolute pump wavelength. Measurements of the pump-wavelength scaling of the stimulated Raman gain of several single-mode fibers are presented. The measurements were obtained by use of two techniques: a brute-force comparison of gain versus pump wavelength and a more elegant comparison of the asymmetry in the Stokes and anti-Stokes Raman gain spectrum at a fixed pump wavelength. This second asymmetry technique has the advantage that it is independent of the uncertainties typically associated with relative measurements of optical power.