Abstract
Abstract Absolute frequency measurement is of great interest not only for metrology applications but also for high-resolution spectroscopy, optical communications, and physical constant definitions. Frequency standards at optical region based on atomic or molecular absorptions provide high accuracy, but it can’t cover all optical spectrum are limited to some special frequencies. With the progresses of the femtosecond lasers and photonic crystal fibers, the frequency comb from visible to near infrared region is well established. It can accurately measure the absolute frequency of stabilized laser. Mode-locked lasers generate ultrashort optical pulses by establishing a fixed relationship across a broad spectrum of frequency. Mode-locked lasers have resulted in the generation of optical pulse with picosecond or femtosecond duration at time domain. The pulses train generated by a mode-locked laser has a frequency spectrum that consists of a discrete, regular spaced series of sharps lines, known as a frequency comb at frequency domain. The frequency of the nth comb line is nfrep+□□□Establishing an optical frequency comb by simultaneously stabilizes the repetition rate and offset frequency. We used photonic crystal fiber to generate a spectrum that spans an octave. And obtain the offset frequency by self-reference interferometer. We stabilized the repetition rate and offset frequency by controlling the cavity length and the pump power. The frequency fluctuation of the stabilized repetition frequency is 3.63 mHz. The stabilized offset frequency fluctuation is small than 10 mHz. We used the optical frequency comb to measure of a10 component of Iodine R(56) 32-0. The accuracy of our femtosecond comb system is 10-11. The accuracy of rubidium frequency standard is 5x10-11.