Temperature-tunable photon-pair source for multiplexed time-resolved fluorescence on a nanophotonic platform.

Compact, scalable, and multiplexed fluorescence lifetime sensors are of great interest for point-of-care diagnostics. However, current solutions either lack broad-range wavelength-tuning capabilities or involve complex optical setups that hinder miniaturization. On-chip entangled photon sources offer a promising alternative for time-resolved spectroscopy with their strong temporal correlations, tunable spectral characteristics, and small footprints. Here, we develop a temperature-tunable, visible quantum light source on thin-film lithium niobate (TFLN) with a continuous tuning range greater than one octave, spanning 564.5 nm to 1.494 $\mu$m using only one waveguide. The tunability is enabled by utilizing type-I phase matching. We measured an on-chip efficiency of $(3.88\pm 0.20)\times 10^{9}$ pairs/s/mW, comparable to the most efficient type-0 bulk lithium niobate sources. These results show that the TFLN platform is ideal for on-chip integrated photonic and multiplexed lifetime imaging and sensing.