The technique involves firing a laser pulse into a tiny ring that traps light at a set of equally spaced frequencies called a frequency comb. This microring resonator is made from a material with nonlinear optical properties, which allows two photons of the laser light to combine to create two photons with frequencies that are distributed across the frequency comb.

Photon upconversion (UC) is a process in which the sequential absorption of two or more photons leads to the emission of light at shorter wavelength than the excitation wavelength.