Highly selective terahertz optical frequency comb generator.

Using a 10.5-GHz resonant electro-optic modulator placed inside a resonant optical cavity, we generated an optical frequency comb with a span wider than 3 THz. The optical resonator consists of three mirrors, with the output coupler being a thin Fabry-Perot cavity with a free spectral range of 2 THz and a finesse of 400. Tuning this filter cavity onto resonance with a particular high-order sideband permits efficient output coupling of the desired sideband power from the comb generator, while keeping all other sidebands inside for continued comb generation. This spectrally pure output light was then heterodyne detected by another laser with a frequency offset of the order of 1 THz.