IdealPhotonics' frequency comb, an "optical ruler" that combines ultra-wide spectral coverage with atomic clock-level stability, uses mode-locked lasers to generate equally spaced optical frequency teeth (e.g., 1 GHz spacing) for absolute frequency measurement and ultra-precise spectral calibration.A series of highly stable and strictly equally spaced optical frequency lines, offering both wide spectral coverage and absolute frequency accuracy, can bridge optical and microwave frequency bands.