# Fully integrated free-running InGaAs/InP single-photon detector for accurate lidar applications

## TL;DR

This paper introduces a fully integrated free-running InGaAs/InP single-photon detector optimized for lidar, demonstrating comparable performance to superconducting detectors after correction algorithms, with advantages in cost and size.

## Contribution

The paper presents a novel integrated InGaAs/InP NFAD-based detector with optimized parameters and correction algorithms, suitable for practical, accurate lidar applications.

## Key findings

- Achieved 1.6 Mcps maximum count rate with 10% PDE and 950 cps dark count rate.
- Performance after correction closely matches that of superconducting detectors, with only ~2% error.
- Demonstrated practical lidar application with comparable results to advanced detectors.

## Abstract

We present a fully integrated InGaAs/InP negative feedback avalanche diode (NFAD) based free-running single-photon detector (SPD) designed for accurate lidar applications. A free-piston Stirling cooler is used to cool down the NFAD with a large temperature range, and an active hold-off circuit implemented in a field programmable gate array is applied to further suppress the afterpulsing contribution. The key parameters of the free-running SPD including photon detection efficiency (PDE), dark count rate (DCR), afterpulse probability, and maximum count rate (MCR) are dedicatedly optimized for lidar application in practice. We then perform a field experiment using a Mie lidar system with 20 kHz pulse repetition frequency to compare the performance between the free-running InGaAs/InP SPD and a commercial superconducting nanowire single-photon detector (SNSPD). Our detector exhibits good performance with 1.6 Mcps MCR (0.6 {\mu}s hold-off time), 10% PDE, 950 cps DCR, and 18% afterpulse probability over 50 {\mu}s period. Such performance is worse than the SNSPD with 60% PDE and 300 cps DCR. However, after performing a specific algorithm that we have developed for afterpulse and count rate corrections, the lidar system performance in terms of range-corrected signal (Pr2) distribution using our SPD agrees very well with the result using the SNSPD, with only a relative error of ~2%. Due to the advantages of low-cost and small size of InGaAs/InP NFADs, such detector provides a practical solution for accurate lidar applications.