Up–conversion detectors at 1550 nm for quantum communication: review and recent advances

Abstract

2 Title : will be set by the publisher Abstract. Up-conversion, or hybrid, detectors have been investigated in quantum communication experiments to replace Indium-GalliumArsenide avalanche photodiodes (InGaAs-APD) for the detection of infrared and telecom single photons. Those detectors are based on the supposedly noise-free process of frequency up-conversion, also called sum-frequency generation (SFG), using a second order (χ 2 ) non-linear crystal. Powered by an intense pump laser, this process permits transposing with a certain probability the single photons at telecom wavelengths to the visible range where silicon APDs (Si-APD) operate with a much better performance than InGaAs detectors. To date, the literature reports up-conversion detectors having efficiency and noise figures comparable to that of the best commercially available IngaAs-APDs. However, in all of these previous realizations, a pump-induced noise is always observed which was initially expected to be as low as the dark count level of the Si-APDs. Although this additional noise represents a problem for the detection, up-conversion detectors have advantageously replaced InGaAs-APDs in various long-distance quantum cryptography schemes since they offer a continuous regime operation mode instead of a gated mode necessary for InGaAs-APDs, and the possibility of much higher counting rates. Despite attempted explanations, no detailed nor conclusive study of this noise has been reported.The aim of this paper is to offer a definitive explanation for this noise. We first give a review of the state of the art by describing already demonstrated up-conversion detectors. We discuss these realizations especially regarding the choices made for the material, in bulk or guided configurations, the single photon wavelengths, and the pump scheme. Then we describe an original device made of waveguides integrated on periodically poled lithium niobate (PPLN)or on single-domain lithium niobate aimed at investigating the origin of the additional pump-induced noise. The poled waveguides are designed to up-convert single photons at 1550 nm to 600 nm when a 980 nm diode laser is used as pump. We obtain an overall efficiency of about 0.6% for a noise level of about 8·10 3 counts/s. This overall efficiency includes both insertion and propagation losses, and internal up-conversion and quantum detection (Si-APD) efficiencies. Despite a low efficiency value compared to what has been obtained so far by other groups, the efficiency/noise ratio is still comparable which still allows us investigating the noise issue.From the spectrum obtained in both poled and non-poled waveguides we conclude that the noise comes from an alternative phasematching scheme which permits creating paired photons at 1550 and 2700 nm wavelength by down-conversion of the 980 nm pump laser. Knowing that 1550 nm corresponds to the input signal wavelength, upconversion of actual signal or pump-induced photons at this particular wavelength cannot be discriminated, therefore contributing to the noise at the fi...

On the genesis and evolution of Integrated Quantum Optics

“…Increasing quantum communication distances therefore amounts to improving the detection process, especially reducing the noise figure, since optical fiber technology has reached its theoretical limits in terms of propagation losses. Quantum communication scientists had the idea of hybrid up-conversion detection which seems to be a good alternative since it allows, at least theoretically, to translate photons from the telecom range to photons in the visible range via the association of the SFG process and permit the use of high performance Si-APDs [144][145][146][147][148][149][150][151][152][153][154].…”

“…Many hybrid detectors for quantum communication experiments operating at the telecom wavelengths of 1310 and 1550 nm have been reported in the literature. A detailed review on the recent advances in the field is given in [154]. These detectors are based on various pump schemes and different nonlinear crystals.…”

“…As in [147], the pump wavelength was around 1550 nm while the signal photons were at 1310 nm. [154], in which a systematic study of this noise has been carried out using a PPLN waveguide and a pump at 980 nm wavelength, showed that the process of SPDC was responsible for this background noise. This process involves one pump photon at 980 nm that splits into energy-correlated photons, with one at 1550 nm which corresponds to the signal, and one at 2660 nm.…”

“…In particular, we will consider sum and difference frequency generation (SFG -DFG) processes. SFG, or up-conversion, has been employed for converting single photon wavelengths from the telecommunication bands (1310 and 1550 nm) to the visible band (below 800 nm), making it possible to use Silicon avalanche photodiodes (Si-APDs) that are not sensitive at telecom wavelengths [146][147][148][149][150][151][152][153][154][155][156]. In this case, advantages are multiple since Si-APDs show much better performance than Indium-Gallium-Arsenide (InGaAs) APDs usually employed for telecom detection [157][158][159].…”

“…A detailed review on the recent advances in the field is given in Ref. [156]. These detectors are based on various pump schemes and different nonlinear crystals.…”