We demonstrate a fiber-based correlated-photon source, wherein the two daughter photons are degenerate in frequency. A coincidence-to-accidental-coincidence ratio >100 is obtained when the fiber is cooled to liquid nitrogen temperature
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.
Abstract : SEE REPORTWe generate high-purity correlated and entangled photon-pairs at the telecom wavelengths in a cooled 10-meter highly nonlinear fiber (HNLF). In our previous project (contract no: FA8750-12-1-0136), we were able to generate correlated/entangled photon-pair using the highly nonlinear fiber in a counter-propagating scheme (CPS). With the HNLF at room temperature, we obtain coincidence-to-accidental ratio (CAR) 26-30 and two-photon interference with visibility 92%-93%. This is the best performance compared to the reported results in the literature on HNLF and Photonic Crystal Fiber (PCF) at telecom wavelengths. Unlike the PCF or microstructure fiber, the HNLF can be cooled at liquid nitrogen temperatures (77K) to suppress Raman photons. By cooling the HNLF, we expect to obtain a CAR 130 and two-photon interference with visibility 98%. We will verify the non-local behavior of high-purity HNLF-based entangled photon-pairs by making Bell s Inequalities measurements. We investigate the effect of multiple scattering on the telecom wavelength photon-pair. Our findings show that quantum correlation of polarization-entangled photon-pairs is better preserved than polarization-correlated photon-pairs in multiple scattering processes.