Visible-to-mid-IR tunable frequency comb in nanophotonics

TL;DR

This paper demonstrates a chip-based, tunable frequency comb source in nanophotonics that covers visible to mid-infrared wavelengths, enabling versatile applications in spectroscopy and communications.

Contribution

It introduces a novel ultra-widely tunable optical parametric oscillator in lithium niobate nanophotonics capable of generating broad, tunable frequency combs from visible to mid-infrared on a single chip.

Findings

Tunable frequency combs from 1.5 to 3.3 μm with femtojoule thresholds.

Visible frequency combs reaching 620 nm generated on-chip.

Broad spectral coverage achieved in nanophotonics.

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 frequency combs tunable from visible to mid-infrared on a single chip based on ultra-widely tunable optical parametric oscillators in lithium niobate nanophotonics. Using picosecond-long pump pulses around 1 $\mu$m and tuning of the quasi-phase matching, we show sub-picosecond frequency combs tunable beyond an octave extending from 1.5 $\mu$m up to 3.3 $\mu$m with femtojoule-level thresholds. 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 nanophotonic source can be combined with an on-chip picosecond source as its pump, as well as pulse shortening and spectral broadening mechanisms at its output, all of which are readily available in lithium niobate nanophotonics. Our results highlight a practical and universal path for the realization of efficient frequency comb sources in nanophotonics overcoming their spectral sparsity.