Abstract

Laser frequency combs [1,2] have become enabling tools for a growing tree of applications, from calibration of astrophysical spectrographs to molecular science. Extension of the frequency comb technology to the mid-infrared “molecular fingerprint” region (2-20 µm) proves crucial for spectroscopy, astronomy and optical diagnosis as most of the strong fundamental molecular vibration frequencies are located in this range. So far only a limited number of frequency comb sources produced by frequency conversion of near-infrared radiation through nonlinear processes (e.g. difference frequency generation and optical parametric oscillation) [3, 4] have been demonstrated. Here we demonstrate, for the first time, mid-infrared frequency comb generation from monolithic optical whispering-gallery mode microresonators principally allowing for compact, broadband and widely spaced combs with high power per comb line. Equally spaced frequency markers are produced by the third order Kerr nonlinearity in ultra-high Q whispering-gallery-mode micro-resonators [5, 6].

© 2011 Optical Society of America