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Widely tunable coherent sources are desirable in nanophotonics for a multitude of applications ranging from communications to sensing. The mid-infrared spectral region (wavelengths beyond 2 μm) is particularly important for applications relying on molecular spectroscopy. Among tunable sources, optical parametric oscillators typically offer some of the broadest tuning ranges; however, their implementations in nanophotonics have been limited to narrow tuning ranges in the infrared or to visible wavelengths. Here, we surpass these limits in dispersion-engineered periodically poled lithium niobate nanophotonics and demonstrate ultrawidely tunable optical parametric oscillators. Using 100 ns pulses near 1 μm, we generate output wavelengths tunable from 1.53 μm to 3.25 μm in a single chip with output powers as high as tens of milliwatts. Our results represent the first octave-spanning tunable source in nanophotonics extending into the mid-infrared, which can be useful for numerous integrated photonic applications. 

Abstract Optical frequency comb is an enabling technology for a multitude of applications from metrology to ranging and communications. The tremendous progress in sources of optical frequency combs has mostly been centered around the near-infrared spectral region, while many applications demand sources in the visible and mid-infrared, which have so far been challenging to achieve, especially in nanophotonics. Here, we report widely tunable frequency comb generation using optical parametric oscillators in lithium niobate nanophotonics. We demonstrate sub-picosecond frequency combs tunable beyond an octave extending from 1.5 up to 3.3 μm with femtojoule-level thresholds on a single chip. We utilize the up-conversion of the infrared combs to generate visible frequency combs reaching 620 nm on the same chip. The ultra-broadband tunability and visible-to-mid-infrared spectral coverage of our source highlight a practical and universal path for the realization of efficient frequency comb sources in nanophotonics, overcoming their spectral sparsity. 

We demonstrate broadly-tunable synchronously-pumped optical parametric oscillators in nanophotonic lithium niobate. A picosecond 1-µm pump generates subpicosecond signal/idler frequency combs tunable between 1.5 and 3.3µm with up-conversion to the visible on the same chip. 

We demonstrate mid-infrared frequency combs from synchronously-pumped optical parametric oscillators in nanophotonic lithium niobate at 19 GHz. With a picosecond pump at ~1µm, the output can be tuned between 1.5 and 3.3µm supporting sub-picosecond pulses.