Broadband Tunable Photon-Pair Generation and Spectrum Measurement Based on Noncritical Lithium Niobate Crystals

Photon pairs play a vital role in modern science, driving extensive research into their generation. Yet, the narrow phase-matching bandwidth of conventional crystals has largely confined studies to specific wavelengths, leaving research on broadband tunable sources underexplored. Here, we employ a non-critical phase-matched lithium niobate (LN) crystal to generate widely tunable photon pairs. The generated near-infrared (NIR) photon pairs exhibit a high coincidence-to-accidental ratio (CAR > 20 dB) and are tunable across the 800-1600 nm range. We further showcase the utility of NIR photon pairs in spectroscopy by detecting carbon monoxide (CO) gas absorption. This approach will facilitate the design of advanced LN-based photonic experiments.

💡 Research Summary

This paper presents a broadband, temperature‑tunable source of photon pairs based on non‑critical phase‑matched (NCPM) spontaneous parametric down‑conversion (SPDC) in an x‑cut lithium niobate (LN) crystal. By pumping a 20 mm LN crystal with a continuous‑wave 532 nm laser and controlling the crystal temperature from 170 °C to 230 °C with sub‑0.01 K stability, the authors achieve continuous tuning of the signal and idler wavelengths across the entire near‑infrared (NIR) window from 800 nm to 1600 nm. The phase‑matching condition Δk(T)=2π