  We demonstrate an efficient generation of frequency anti-correlated entangled
photon pairs at telecom wavelength. The fundamental laser is a continuous-wave
high-power fiber laser at 1560 nm, through an extracavity frequency doubling
system, a 780-nm pump with a power as high as 742 mW is realized. After single
passing through a periodically poled KTiOPO4 (PPKTP) crystal, degenerate
down-converted photon pairs are generated. With an overall detection efficiency
of 14.8 %, the count rates of the single photons and coincidence of the photon
pairs are measured to be 370 kHz and 22 kHz, respectively. The spectra of the
signal and idler photons are centered at 1560.23 and 1560.04 nm, while their
3-dB bandwidths being 3.22 nm both. The joint spectrum of the photon pair is
observed to be frequency anti correlated and have a spectral bandwidth of 0.52
nm. According to the ratio of the single photon spectral bandwidth to the joint
spectral bandwidth of the photon pairs, the degree of frequency entanglement is
quantified to be 6.19. Based on a Hong Ou Mandel interferometric coincidence
measurement, a frequency indistinguishability of 95 % is demonstrated. The good
agreements with the theoretical estimations show that the inherent extra
intensity noise in fiber lasers has little influence on frequency entanglement
of the generated photon pairs.
