Efficient Harmonic Generation and Frequency Conversion in Multi-Mode Cavities


Efficient harmonic generation and frequency conversion scheme is useful in high-frequency sources, ultra-compact coherent optical sources, imaging, and spectroscopy.

Problem Addressed

In nonlinear frequency conversion, light at one frequency co-propagates with the generated light at the harmonic frequency. Previous experimental and theoretical work on second-harmonic generation in cavities has largely focused on cavities with a single resonant mode at the pump frequency. Such structures require high input power. Second-harmonic generation in a doubly resonant cavity, with a resonance at both the pump and harmonic frequency, has previously been analyzed only in the limit where nonlinear down-conversion can be neglected. Previous work on third-harmonic generation in cavities, similarly, considered only singly resonant cavities; moreover, past work focused on the case of χ(2) materials where 3ω is generated by cascading two nonlinear processes (harmonic generation and frequency summing). Furthermore, the previous theoretical work, with a few exception, focused on one-dimensional Fabry-Perot cavity geometries, in which the problem of obtaining cavity modes with the correct frequency ratio was posed as a problem of phase-matching, and addressed by methods such as using off-normal beams.


This invention is a doubly-resonant cavity structure having a plurality of resonant modes. The invented cavity allows total frequency conversion for second or third-harmonic generation using χ(2) and χ(3) nonlinearities between the cavity structures. The total frequency conversion is efficiently optimized by determining a critical power for the process of the total frequency conversion, and this critical power depends only on parameters of the cavity structure. The invention can achieve 100% frequency conversion with milliwatts of power, and can have intense light in cavity, without the phase-matching problem.


  • No frequency conversion saturation point; frequency conversion peaks at 100%
  • Efficient harmonic generation and frequency conversion