August 2005

EEEL Researchers Develop and Verify Theory of Fiber Laser-Based Frequency Comb Control

Stabilized optical frequency combs have revolutionized frequency metrology and optical clocks. Optical frequency combs based on fiber optic technology have been developed at NIST and elsewhere over the past two years. These fiber-laser based frequency combs are now commercially available and are even beginning to supplant the original Ti:Sapphire-laser based frequency combs for some work in optical frequency metrology and other applications. Despite the success of fiber laser-based frequency combs, most previous work on these combs has been experimental in nature. The combs from a mode-locked fiber laser have been successfully stabilized through feedback to pump power and cavity length; however there has been no basic understanding of what physical mechanisms in the laser connected these changes, in particular in pump power, to the frequency comb output of the laser. An understanding of the mechanisms and bandwidth governing this feedback is of practical importance for frequency comb design and of basic interest since it provides insight into the rich nonlinear laser dynamics.

Nathan Newbury of the EEEL Optoelectronics Division recently developed a theory for the response of fiber-laser based frequency combs to changes in the pump power, cavity length, and other experimentally-accessible parameters. The theory predicts the comb response in terms of transfer functions. Interestingly, it is quite a complicated system and there are at least five different mechanisms that can play important roles in the laser response. Nathan Newbury, Brian Washburn, and Bill Swann have verified the theory by conducting experimental measurements on frequency combs and showed that the response is consistent with the theory. In addition, they predict that other control parameters could be used to improve the stability of the comb and provide better ultimate performance of the frequency comb.

Contact:

Nathan Newbury, (303) 497-4227