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. 2023 Oct 17;14:6549. doi: 10.1038/s41467-023-42289-0

Fig. 1. Ultra-widely tunable frequency combs from nanophotonic parametric oscillators.

Fig. 1

a Schematic of a doubly resonant optical parametric oscillator fabricated on an X-cut thin-film lithium niobate consisting of a periodically poled region for efficient parametric nonlinear interaction. The waveguides (dimensions: width of 2.5 μm, etch depth of 250 nm) support guided-modes in the mid-infrared corresponding to the idler wave. b Quasi-phase matched parametric gain tuning from visible-to-mid-IR. Phase-matching curves leading to tunable mid-infrared idler emission enabled by optical parametric oscillator devices with slightly different poling periods (Λ) integrated on the same chip. The same chip is capable of producing tunable visible frequency combs thanks to the sum-frequency generation (SFG) process between the pump with the signal and idler waves. Other accompanying up-conversion processes include the second-harmonic (SH) of the signal and the idler. The phase-matching curves for the up-conversion processes are plotted (dotted lines) according to the energy conservation relations and do not strictly satisfy quasi-phase-matching. Some second-harmonic phase-matching curves have been omitted for better clarity. c The emission from the chip overlaps with strong molecular absorption lines in the mid-infrared, covering a spectral window important for molecular spectroscopy. The spectral coverage in the visible includes atomic transition wavelengths corresponding to commonly used trapped ions/ neutral atoms/color centers.