# Compact all-fiber polarization-independent up-conversion single-photon detector

## TL;DR

This paper presents a compact, all-fiber, polarization-independent up-conversion single-photon detector operating at 1.55 μm, with high efficiency and low polarization-dependent loss, suitable for quantum communication applications.

## Contribution

The work introduces a novel integrated fiber-based design for polarization-independent single-photon detection with high efficiency and robustness, advancing practical quantum key distribution technology.

## Key findings

- Detection efficiency of 29.3% at 1.55 μm
- Dark count rate of 1600 counts per second
- Polarization dependent loss of 0.1 dB

## Abstract

We demonstrate a compact all-fiber polarization-independent up-conversion single-photon detector based on integrated reverse proton exchanged periodically poled lithium niobate waveguides. The horizontally and vertically polarized components of randomly polarized signals are separated with a fiber-coupled polarization beam splitter, launched into two orthogonally polarized polarization maintaining fibers and fetched into two adjacent independent waveguides on the same device. The up-converted outputs from both waveguide channels are then combined with a multi-mode fiber combiner and detected by a silicon detector. With this configuration, the polarization-independent single-photon counting at 1.55 um is achieved with a system detection efficiency of 29.3%, a dark count rate of 1600 counts per second, and a polarization dependent loss of 0.1dB. This compact all-fiber system is robust and has great application potential in practical quantum key distribution systems.

---
Source: https://tomesphere.com/paper/1903.05814