Researchers in the Optoelectronics Division of EEEL have demonstrated an all-fiber photon-pair source with the highest coincidence-to-accidental ratio (CAR) reported to date in the fiber-optic telecommunications C-band (wavelengths near 1550 nm). Shellee Dyer, Sae Woo Nam, Burm Baek, and Marty Stevens achieved this through careful optimization of pair-production efficiency as well as detailed characterization and minimization of all sources of background photons, including Raman generation in the nonlinear fiber and in the single-mode fiber, and leakage of pump photons. They cooled the nonlinear fiber to 4 K to eliminate most of the Raman scattering and reduced other noise photon counts with thorough system design. This yields a CAR of 1300 at a pair generation rate of 2 kHz. This CAR, a measure of the ratio of the desired photon pairs compared to other noise photons such as Raman photons and dark counts in the output signal, is a factor of 12 higher than previously reported results in the C-band. Measured data and theoretical predictions showed good agreement. Additionally, the researchers demonstrated that by pumping the fiber system with a continuous-wave laser instead of the conventional pulsed laser, a photon pair generation rate as high as 40 MHz can be achieved. This is comparable to the brightest of fiber-based and free-space crystal photon pair sources available, which typically have maximum photon pair generation rates on the order of 10 MHz, while it maintains the advantage of the fiber's single mode operation.
The demonstrations eliminate the two main barriers for practical applications of all-fiber photon pair sources: the noise created by Raman scattering in the fiber and the low photon pair rate arising from the weak nonlinear coefficient of the fiber. This all-fiber source generating photon pairs in the important fiber-optic telecommunications C-band is essential for long-distance distribution of quantum information. The source is expected to have a broad range of applications, including quantum communications and quantum computing.
Contact: sdyer [at] boulder.nist.gov (Shellee Dyer), phone x303-497-7463 (Boulder)