We present measurements and analysis of the currently known relative frequency uncertainty of femtosecond laser frequency combs (FLFCs) based on Kerr-lens mode-locked Ti:sapphire lasers. Broadband frequency combs generated directly from the laser oscillator, as well as octave-spanning combs generated with nonlinear optical fiber are compared. The relative frequency uncertainty introduced by an optically referenced FLFC is measured for both its optical and microwave outputs. We find that the relative frequency uncertainty of the optical and microwave outputs of the FLFC can be as low as 8 × 10-20 and 1.7 × 10-18, with a confidence level of 95%, respectively. Photo-detection of the optical pulse train introduces a small amount of excess noise, which degrades the stability and subsequent relative frequency uncertainty limit of the microwave output to 2.6 × 10-17.
Bibliographical noteFunding Information:
Manuscript received June 14, 2006; revised September 12, 2006. The work at the National Institute of Standards and Technology (NIST) was supported in part by NIST and NASA. The project at ECNU was funded in part by the NSF of China under 60490280, STCSM under 04JC14086, 04DZ14009, and 06JC14026, Shanghai, and in part by MOST of China under 2006B806005.
All Science Journal Classification (ASJC) codes
- Atomic and Molecular Physics, and Optics
- Condensed Matter Physics
- Electrical and Electronic Engineering