Kerr combs with selectable central frequency

Optical frequency combs produced by femtosecond Ti:sapphire lasers have revolutionized many applications across the fields of science and metrology, and have opened new vistas in sensing and spectroscopy1. An alternative approach based on four-wave mixing in solid-state microresonators2-13 has been developed to create compact, high-repetition-rate, optical-frequency comb (Kerr comb) generators. In this Letter, we show that a comb centred at virtually any frequency within the transparency window of the microresonator host material can be generated by appropriate design of the microresonator shape, which controls the group velocity dispersion. We present a theoretical framework supporting this, and demonstrate the first frequency comb centred at 794 nm. © 2011 Macmillan Publishers Limited. All rights reserved.