Phase-locking transition in Raman combs generated with whispering gallery mode resonators
GUOPING LIN1,2,* AND YANNE K. CHEMBO1
1Optics Department, FEMTO-ST Institute, CNRS & Université Bourgogne-Franche-Comté, 15B Avenue des Montboucons,
25030 Besançon cedex, France
2MOE Key Laboratory of Fundamental Physical Quantities Measurement, School of Physics, Huazhong University of Science and
Technology, 1037 Luoyu Road, Wuhan 430074, China
*Corresponding author: guoping_lin@hust.edu.cn
We investigate the mechanisms leading to phase locking in Raman optical frequency combs generated with ultrahigh Q crystalline whispering gallery mode disk resonators. We show that several regimes can be triggered depending on the pumping conditions, such as single-frequency Raman lasing, multimode operation involving more than one family of cavity eigenmodes, and Kerr-assisted Raman frequency comb generation. The phase locking and coherence of the combs are experimentally monitored through the measurement of beat signal spectra. These phase-locked combs, which feature high coherence and wide spectral spans, are obtained with pump powers in the range of a few tens of mW. In particular, Raman frequency combs with multiple free-spectral range spacings are reported, and the measured beat signal in the microwave domain features a 3 dB linewidth smaller than 50 Hz, thereby indicating phase locking.
Opt. Lett. 41, 3718 (2016).
