Physics / mechanism
A frequency comb is a laser source whose output spectrum consists of hundreds to thousands of equally spaced, phase-coherent spectral lines — a ruler in frequency space. Generated via mode-locked lasers, microresonator-based Kerr combs (microcombs), or electro-optic modulation, the line spacing equals the cavity repetition rate (typically 10 MHz–100 GHz). Key parameters: repetition rate stability, comb tooth SNR, octave span, and carrier-envelope offset (CEO) control. Microcombs on chip — using silicon nitride or lithium niobate resonators with Q > 10⁷ — now achieve sub-milliwatt threshold pump power. NIST and PTB-grade optical clocks use combs for absolute frequency measurement at 10⁻¹⁸ fractional uncertainty. Commercial units (Menlo Systems, Octave Photonics) ship at $50K–$200K; chip-scale versions are in late R&D.
Competitive landscape
Competing approaches for precision metrology: optical atomic clocks without comb readout (limited to single transitions), Fourier-transform infrared spectroscopy (lower resolution, no absolute reference), and tunable diode laser absorption spectroscopy (TDLAS). For ranging/LiDAR, time-of-flight and FMCW LiDAR compete on cost.
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.