Up-Conversion Devices Demonstrated to Work at Longer Wavelengths and Higher System Data Rates
In collaboration with Stanford University, the NIST quantum communications group demonstrated single photon frequency up-conversion devices with longer wavelengths and higher system data rates than previously reported.
The performances of single-photon detectors play a critical role in quantum communications systems. For example, in quantum key distribution (QKD) systems operated over fiber-optic networks, the maximum reach and data rates are limited by the wavelengths used and the performance of single photon detectors at those wavelengths. For long range systems using silica fibers, the low-loss 1.31 and 1.55 µm wavelengths are desirable. Current commercial detectors at these wavelengths are often based on InGaAs/InP avalanche photodiodes. However, the high noise level and gating requirements limits their applications and data rates. Progress on superconducting single photon detectors is very impressive, but they are of limited practicality for field use due to the need for bulky and expensive cryogenic cooling. Inexpensive silicon based single photon detectors show excellent performance at room temperature, but only work in the visible or near visible wavelengths below 1 µm. Achieving both long distance transmission and high detection data rates are important requirements in quantum communications.
Previously, the NIST Quantum Communications research group developed a frequency up-conversion detector for single photon level light at 1.31 µm. By using a strong pump at 1.55 µm, the single photons at 1.31 µm are converted into the visible region and detected by a silicon- based avalanche photodiode (APD) with an overall detection efficiency, taking all system losses into account, of over 30%. As a follow-on to that research, NIST and Stanford developed an up-conversion detector targeting 1.55 µm, the other low-loss transmission window in silica based fibers. In this case, the single photons at 1.55 µm are pumped at 1.9 µm creating near visible single photons efficiently detectable using a silicon-based APD. The 1.55 µm system achieves a detection efficiency of over 35% with low noise characteristics .
One of the drawbacks of silicon based avalanche detectors is the so-called detection jitter. Once a signal photon enters at surface of the detector, after a certain time delay, an output electrical pulse is generated by the detector. The time delay is not exactly same for individual photons. That causes a detection jitter, which limits the maximum detection rate of the system. To overcome this, NIST quantum communication research team has demonstrated a method to increase the date rate of quantum communication systems equipped with up-conversion detectors. The demonstration is implemented in a one-channel broadband device by using a novel multi-wavelength pumping scheme. (See "System data rate breaks..." below). Based on the demonstrated principle-proving scheme, the NIST and Stanford researchers developed a unique dual-channel up-conversion device. In this device, signal photons at 1.3 µm are pumped by two slightly separated wavelengths near 1.55 µm and converted to two photons at slightly separated visible wavelengths in the two channels. The visible photons are separated using a dispersion element and sent to two distinct silicon based APDs for detection. In each channel, the conversion efficiency is optimized; therefore, the system data rate can be doubled with the maximum detection efficiency . In theory, multiple channels and detectors can be used providing a potentially unlimited detection rate.
 J. S. Pelc, L. Ma, C. R. Phillips, Q. Zhang, C. Langrock, O. Slattery, X. Tang, and M. M. Fejer, "Long-wavelength-pumped upconversion single-photon detector at 1550 nm: performance and noise analysis", Optics Express, Vol. 19, No. 22, Page 21445 (Oct. 17, 2011). PDF: http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-22-21445
 J. S. Pelc, Paulina S. Kuo, Oliver Slattery, Lijun Ma, Xiao Tang, and M. M. Fejer, "Dual-channel, single-photon upconversion detector at 1.3 µm", Optics Express, Vol. 20, No. 17, 19075 (August 13, 2012). PDF: http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-17-19075
CONTACT: Xiao Tang (ITL), ext. 2503