Optical frequency comb generation from a monolithic microresonator

Optical frequency 'combs' are light sources that emit at discrete, equally spaced frequencies, so the spectrum has a characteristic comb-like appearance. Frequency combs have revolutionized the fields of spectroscopy and metrology: clocks using the technology now beat atomic clocks, such as the current caesium standard, for accuracy. But the instrumentation required to generate a frequency comb is cumbersome and complex, usually involving a bulky femtosecond laser. Del'Haye et al. have now developed a radically different approach to comb generation: a tiny disc-like resonator structure on a silicon chip is simply illuminated by a conventional laser diode. The resulting interaction between the laser light and the resonator gives rise to an optical frequency comb emitting in the infrared. The simplicity of the scheme — and the prospects of a reduction in size, cost and power — should enhance the utility of optical frequency combs in a broad number of fields.