Photonic chip–based optical frequency comb using soliton Cherenkov radiation

• Published in: Science (American Association for the Advancement of Science) Vol. 351; no. 6271; pp. 357 - 360
• Main Authors: Brasch, V., Geiselmann, M., Herr, T., Lihachev, G., Pfeiffer, M. H. P., Gorodetsky, M. L., Kippenberg, T. J.
• Format: Journal Article
• Language: English
• Published: United States American Association for the Advancement of Science 22-01-2016; The American Association for the Advancement of Science
• Subjects: Nonlinear systems; Optics; Radiation; Spectrum analysis
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.aad4811

Optical solitons are propagating pulses of light that retain their shape because nonlinearity and dispersion balance each other. In the presence of higher-order dispersion, optical solitons can emit dispersive waves via the process of soliton Cherenkov radiation. This process underlies supercontinuum generation and is of critical importance in frequency metrology. Using a continuous wave–pumped, dispersion-engineered, integrated silicon nitride microresonator, we generated continuously circulating temporal dissipative Kerr solitons. The presence of higher-order dispersion led to the emission of red-shifted soliton Cherenkov radiation. The output corresponds to a fully coherent optical frequency comb that spans two-thirds of an octave and whose phase we were able to stabilize to the sub-Hertz level. By preserving coherence over a broad spectral bandwidth, our device offers the opportunity to develop compact on-chip frequency combs for frequency metrology or spectroscopy.