Phase-locked, all-fiber supercontinuum source for
frequency metrology and molecular spectroscopy

Brian Richard Washburn
National Institute of Standards of Technology
29 October 2003

The use of mode-locked femtosecond lasers for optical frequency measurements has spurred a renaissance in the field of frequency metrology. Since the initial demonstration using a Ti:sapphire laser-based frequency comb in 1999, unprecedented precision in measuring optical frequencies over a large optical bandwidth (>1000 nm) can now be accomplished. While Ti:sapphire laser-based systems are excellent laboratory tools, they are not robust enough for field applications and consumer use. A fiber laser?based system, however, holds a number potential advantages over Ti:sapphire laser-based systems in terms of size and cost. Importantly, a fiber laser-based system would require fewer adjustments, consume much less power, and exploit the large range of available telecommunication technologies.

This seminar will introduce the next generation source for stabilized infrared frequency combs: a mode-locked fiber laser whose output is amplified and spectrally broadened in a highly nonlinear optical fiber. The resulting supercontinuum from this source consists of a frequency comb spanning from 1100 nm to 2300 nm, where the comb spacing and offset frequency are phase-locked to a stable RF source. The seminar will begin by discussing the theory and operation of passively mode-locked Erbium-doped fiber lasers. This will involve discussing the aspects of dispersion management and optical nonlinearities in the design of fiber lasers. Then, I will illustrate how a mode-locked fiber laser can be used for precision frequency metrology. This will followed by a description of the all-fiber based supercontinuum source, focusing on the stability and performance of the system. The talk will conclude by detailing the precision spectroscopy of molecular gases that we will perform using the supercontinuum source.

Biography:

Brian Washburn received his B.S degree in physics (summa cum laude) from the University of Wisconsin-Parkside, Kenosha, WI in 1994. As physics undergraduate he spent one year at Argonne National Laboratory researching vortex pinning in high-temperature superconductors. From there, he moved to Emory University and then to Georgia Institute of Technology in Atlanta, GA to complete his Ph.D. in Physics. His graduate career began by conducting ultrafast laser spectroscopy of III?V semiconductors, which included experiments using terahertz generation and time-resolved photoluminescence. His graduate thesis focused on measuring and simulating the nonlinear processes that occur during supercontinuum generation in photonic crystal optical fibers. While at Georgia Tech, Brian was also a member of the Georgia Tech Ultrafast Optical Communications Consortium, which was an association between Georgia Tech, Bell South, Nortel Networks, and Corning Incorporated to develop a 160 Gbit/s optical time division multiplexed communication system. After completing his Ph.D. in 2002, Brian started a postdoctoral position at the National Institute of Standards and Technology (NIST), Boulder CO studying noise properties of supercontinuum generation. This work at NIST has lead to developing the first phase-locked, all-fiber based supercontinuum source for infrared frequency metrology.