September 2007

EEEL researchers demonstrate compact fiber laser with GHz fundamental repetition rate

Stabilized femtosecond lasers are proving to be a valuable tool in a variety of applications including optical clocks, precision measurements of range and velocity, precision spectroscopy and arbitrary waveform generation. In particular, fiber-based systems that operate around the telecommunications band are well-suited for many of these applications because they are eye-safe, compact and can exploit existing fiber-optic telecommunication components and fiber-optic networks. At NIST and elsewhere, stabilized fiber-based femtosecond lasers have been demonstrated that provide a train of pulses in the time domain with sub-femtosecond timing jitter and a frequency comb in the frequency domain with sub-hertz comb linewidths. The one current drawback of these fiber-based stabilized femtosecond lasers is their low repetition rate of about 100 MHz, which is not well-suited for many applications. Higher, gigahertz repetition-rate fiber laser systems exist but they typically employ either harmonic mode-locking or a compact proprietary doped-glass design; none of these higher repetition-rate systems have been stabilized to the same high degree as the lower repetition-rate systems.

As an important first step toward realizing a stabilized femtosecond fiber-laser system at GHz repetition rates, John McFerran in collaboration with EEEL researchers has successfully demonstrated a 2 GHz fundamentally mode-locked fiber laser. The laser is comprised of commercially available highly-doped fiber and a saturable absorber. It produces a clean pulse train that can be tightly phase-locked to either an rf or cw optical reference source. Although the optical bandwidth is limited at present to about 2.6 nm, the laser is a preliminary demonstration of an efficient, compact and cost effective frequency comb with a high repetition rate much better suited to many of the practical applications listed above.

Contact:  Nathan Newbury, phone 303-497-4227