Visible dual-comb spectroscopy across more than 100 THz with lithium niobate nanophotonic waveguides

TL;DR

This paper presents a compact dual-comb spectrometer using lithium niobate nanophotonic waveguides that achieves over 100 THz of visible spectrum coverage with high resolution, enabling advanced spectroscopic measurements.

Contribution

The work introduces a simple, efficient method to convert near-infrared frequency combs to visible wavelengths using TFLN nanophotonics, achieving broad bandwidth and high resolution in a compact device.

Findings

Achieved nearly 120 THz bandwidth in visible spectrum

Demonstrated broadband absorption measurement of molecular iodine

Showcased high-resolution spectroscopy of NO2, rubidium, and sodium

Abstract

Broadband and high-resolution spectroscopy in the visible and ultraviolet is central to advances in multiple fields, including fundamental quantum physics, biology, atmospheric science and astronomy. Traditionally, these measurements are performed with grating or Fourier-transform spectrometers using incoherent light sources. Leveraging coherent light enables powerful frequency-comb-based techniques, but is limited by the technical complexity of efficiently generating broad spectral bandwidths from relatively narrowband and spectrally distant laser sources. Current visible dual-comb spectrometers require implicit compromises between optical bandwidth, experimental simplicity, and acquisition speed. In this work, we introduce a simple and efficient dual-comb spectrometer that converts robust Er:fiber frequency combs from the near-infrared to the ultraviolet and visible with thin-film lithium niobate (TFLN) nanophotonic waveguides. Using real-time signal processing, we retrieve coherently averaged dual-comb spectra over nearly 120 THz of simultaneous bandwidth in the visible with 100 MHz spectral resolution. With these capabilities, we measure the broadband absorption spectrum of molecular iodine (I2), demonstrating the broadest visible spectral coverage of a dual-comb spectrometer to date. Additional measurements of NO2, atomic rubidium, and atomic sodium further illustrate the achievable combination of spectroscopic bandwidth, resolution, and intrinsic frequency accuracy. Our results demonstrate the powerful integration of low-power frequency combs, nonlinear nanophotonics, and digital signal processing to enable a compact, efficient and versatile approach to high-resolution mapping of complex absorption spectra across 500 THz in the UV-visible and near-infrared spectral regions for multiple applications beyond the research lab