A hyperfine-transition-referenced vector spectrum analyzer for visible-light integrated photonics

Integrated photonics has been successfully established in the near-infrared (NIR) telecommunication bands. With the soaring demand in biosensing, quantum information and transportable atomic clocks, extensive endeavors have been stacked on translating integrated photonics into the visible spectrum. Demonstrations of visible-light lasers, frequency combs, and atom traps highlight the prospect of creating chip-based optical atomic clocks that can make timing and metrology ubiquitous. A pillar to the development of visible-light integrated photonics is characterization techniques featuring high frequency resolution and wide spectral coverage, which however remain elusive. Here, we demonstrate a vector spectrum analyzer (VSA) for visible-light integrated photonics, offering spectral bandwidth of 766-795 and 518-541 nm. The VSA is rooted in widely chirping, high-power, narrow-linewidth, mode-hop-free lasers that are frequency-doubled from the near-infrared via efficient, broadband CPLN waveguides. The VSA is further referenced to hyperfine structures of alkaline atoms and iodine molecules, enabling megahertz frequency accuracy. We apply our VSA to showcase the characterization of loss, dispersion and phase response of passive integrated devices, as well as densely spaced spectra of mode-locked lasers. Leveraging individual operations at 518-541, 766-795, 1020-1098, and 1260-1640 nm bands, our VSA achieves an aggregate characterization bandwidth exceeding one octave. This capability establishes the VSA as an invaluable diagnostic tool for spectroscopy, nonlinear optical processing, imaging, and quantum interfaces with atomic systems.