Optimizing up-conversion single-photon detectors for quantum key distribution

Abstract

High-performance single-photon detectors (SPDs) at 1550-nm band are critical for fiber-based quantum communications. Among many types of SPDs, the up-conversion SPDs based on periodically poled lithium niobate waveguides are of great interest. Combined with a strong pump laser, the telecom single-photons are converted into short wavelength ones and detected by silicon-based SPDs. However, due to the difficulty of precise controlling waveguide profile, the direct coupling between a single-mode fiber and the waveguide is not efficient. Here by utilizing fiber taper with proper diameter, optimal mode-matching is achieved and coupling efficiency up to 93% is measured. With an optimized design, a system detection efficiency of 36% and noise counting rate of 90 cps are realized. The maximum detection efficiency is characterized as 40% with a noise counting rate of 200 cps. Numerical simulation results indicate that our device can significantly improve the performance of QKD and extend the communication distance longer than 200 km.

Evaluation of Femtosecond Time-bin Qubits Using Frequency Up-conversion Technique

“…In contrast, our UCSPD achieved a femtosecond order temporal resolution and practical detection efficiency using readily available commercial crystals. [10] 300 K 400 ps 40.2 % 200 cps 100 ns UCSPD (pulse) [12,13] 300 K 0.3 ps 16.9 % -UCSPD (this work) 300 K 0.4 ps 3.3 % 700 cps -Using these experimental results, we set optimum measurement conditions as: a crystal length of 2 mm, pump power of 300 mW (in these conditions, temporal resolution of 415 fs, up-conversion efficiency of 10.1 %, and average photon number of the detection limit as 3.3 × 10 −5 /pulse).…”

“…These detectors were initially developed to convert telecommunication wavelength photons to shorter wavelengths that can be more efficiently detected by commercial single-photon detectors such as Si avalanche photodiodes (APD) instead of InGaAs APDs [7]. Currently, UCSPDs that use a CW laser as a pump light, achieve conversion efficiencies of more than 90 % [8][9][10]. In these types of UCSPDs, the temporal resolution and dead time depends on the performance of the Si APDs.…”

Toward Fully‐Fledged Quantum and Classical Communication Over Deployed Fiber with Up‐Conversion Module

“…Nonetheless, state-of-the art systems for up-conversion detectors of single-photon signals in the C band, have demonstrated a very high overall efficiency above 30%, with a dark count rate as low as 100 Hz, thus enabling quantum communication up to 45 dB of channel loss. [39][40][41] Furthermore, it is important to notice that although we have used a bulky and custom home-made system (which requires the prealignment of the free-space silicon detector), the nonlinear crystal could be integrated in photonic platforms for a more efficient and stable solution. [42] Regarding the InGaAs detector, we would like to stress once again that we have used a commercial device, equipped with an off-the-shelf band-pass filter of 100 GHz bandwidth, com-bined with a polarization beam splitter for polarization filtering.…”

“…Nonetheless, state‐of‐the art systems for up‐conversion detectors of single‐photon signals in the C band, have demonstrated a very high overall efficiency above 30%, with a dark count rate as low as 100 Hz, thus enabling quantum communication up to 45 dB of channel loss. [ 39–41 ] Furthermore, it is important to notice that although we have used a bulky and custom home‐made system (which requires the pre‐alignment of the free‐space silicon detector), the nonlinear crystal could be integrated in photonic platforms for a more efficient and stable solution. [ 42 ]…”

Towards fully-fledged quantum and classical communication over deployed fiber with up-conversion module

“…With this setup, our up-conversion receiver can work only for short-distance QKD, below 6 dB channel loss, as shown in Figure 5f). Nonetheless, state-of-the art systems for up-conversion detectors of single-photon signals in the C band, have demonstrated a very high overall efficiency above 30%, with a dark count rate as low as 100 Hz, thus enabling quantum communication up to 45 dB of channel loss [39][40][41]. Furthermore, it is important to notice that although we have used a bulky and custom home-made system (which requires the pre-alignment of the free-space silicon detector), the nonlinear crystal could be integrated in photonic platforms for a more efficient and stable solution [42].…”