October, 2003

Fiber Laser-Based Frequency Comb for Frequency Metrology in the Infrared
Developed by EEEL, OFS and PL Collaboration

Staff of EEEL's Optoelectronics Division, in collaboration with researchers at OFS Laboratories and staff of PL's Time and Frequency Division, have recently developed a phase-locked "frequency comb" in the 1100 to 2200 nm wavelength region using fiber optic technology. This novel frequency comb should enable high-precision frequency metrology experiments in the near infrared, and, in particular, across the telecommunications region of 1300 to 1600 nm. Indeed, over the past several years stabilized frequency combs have revolutionized frequency metrology and optical clocks. However, prior to this present work, all self-referenced, phase-locked frequency combs used bulk-optic solid-state lasers and covered only the visible and very near infrared. This fiber laser-based comb extends this wavelength coverage 1000 nm further into the infrared. In addition, the fiber laser-based system can be much more compact, robust, power-efficient and lighter than a bulk optic solid state laser system, and can require less alignment. Finally, it can be easily integrated into a telecommunication system

The phase-locked frequency comb is based on a mode-locked, erbium-doped, fiber laser whose output is amplified and spectrally broadened in novel dispersion-flattened, highly nonlinear optical fiber to span from 1100 to 2200 nm. This supercontinuum actually comprises a comb of frequency lines, separated by the laser repetition rate and with an arbitrary frequency offset. Borrowing the now standard techniques used with Ti:sapphire laser-based systems, the researchers phase-locked both the comb spacing and offset to an RF oscillator. If the RF oscillator is phase-locked to an atomic frequency standard, the comb will form an accurate frequency ruler covering the entire near infrared region from 1100 to 2200 nm. Any unknown optical frequency can then be measured by simply comparing its frequency to that of the nearest tooth of the stabilized frequency comb.

Contact:

Nathan Newbury, (303) 497-4227