A time-to-digital converter with steady calibration through single-photon detection

TL;DR

This paper presents an FPGA-based time-to-digital converter with steady calibration using single-photon detection, suitable for quantum communication, demonstrating high precision, continuous operation, and temperature robustness.

Contribution

The novel calibration method leverages single-photon detection for continuous, accurate calibration without interrupting data acquisition in FPGA-based TDCs.

Findings

Residual FWHM jitter of 27 ps achieved

Continuous streaming at 12 M events/sec for a week

Calibration effective across 5°C to 80°C

Abstract

Time-to-Digital Converters (TDCs) are a crucial tool in a wide array of fields, in particular for quantum communication, where time taggers performance can severely affect the quality of the entire application. Nowadays, FPGA-based TDCs present a viable alternative to ASIC ones, once the non-linear behavior due to the intrinsic nature of the device is properly mitigated. To compensate for said nonlinearities, a calibration procedure is required, which should be maintained throughout its runtime. Here we present the design and the demonstration of a TDC that is FPGA-based showing a residual FWHM jitter of 27 ps, that is scalable for multichannel operation. The target application in Quantum Key Distribution (QKD) is discussed with a calibration method based on the exploitation of single-photon detection that does not require stopping the data acquisition or using any estimation methods, thus increasing accuracy and removing data loss. The calibration was tested in a relevant environment, investigating the behavior of the device between 5 {\deg}C and 80 {\deg}C. Moreover, our design is capable of continuously streaming up to 12 Mevents/s for up to ~1 week without the TDC overflowing making it ready for a real-life scenario deployment.