Analysis of the temporal coherence function of a femtosecond optical frequency comb

Abstract

The temporal coherence function of the femtosecond pulse train from femtosecond optical frequency comb (FOFC) has been studied. The theoretical derivation, which is based on the electric field equations of a pulse train, has been used to model the temporal coherence function of the FOFC and shows good agreement with experimental measurements which are taken with a modified Michelson interferometer. The theoretical and experimental points of view provide useful information for applications of FOFC in imaging and metrology.

Demonstration of optical correlation domain reflectometry based on coherence synchronization for long-range measurement

“…An optical frequency comb is promising for use as the laser source. Although the autocorrelation of an optical frequency comb has multiple correlation peaks whose spacing is the reciprocal of the frequency spacing between the spectral lines 6 , coherence synchronization can select one arbitrary correlation peak. For this, the spectrum of the phase modulation must be broader than the frequency spacing of the optical frequency comb.…”

Synthetic adjacent pulse repetition interval length method to solve integer ambiguity problem: theoretical analysis

“…Length measurement using an FOFC source has distinct measurement characteristics [3,4] and applications [5]- [7]. Many special techniques [8]- [11] have been developed to exploit these distinct characteristics (especially the temporal coherence) of FOFC light.…”

“…Generally, however, these methods suffers from the integer ambiguity (IA) problem. We have previously [3] used shutters set in front of the reflecting surfaces to turn the reflected light on and off in order to distinguish different reflecting surfaces. This paper presents a new approach to solve this IA problem for an absolute and arbitrary long-distance measurement.…”

Sub-ppm absolute distance measurements using an optical frequency comb generated by a conventional dual-drive Mach-Zehnder modulator

“…In [9], the synthesizing of the mode-locked condition of the comb has been proposed, simultaneously with the time-of-flight technique, in order to achieve nonambiguity lengths from a few meters to 10 6 m. In [10], they use the combination of synthetic wavelength interferometry (SWI), time of flight (TOF) and spectrally-resolved interferometry (SRI) using the optical comb of femtosecond laser in order to achieve non-ambiguity lengths up to the coherence length of the modes. Nevertheless, optical frequency combs that are generated by mode-locked lasers can produce an interferometric pattern only at a multiple of c/2f R [11], where c is the speed of light and f R the repetition frequency of the mode-locked laser: no information is provided for distances between two interferometric patterns. Hence, in order to develop a laser ruler, it would be necessary to modulate the repetition frequency of the mode-locked laser, but this possibility is only limited to a very small frequency variation and the needed frequency span (about 1% or more) is not achievable on a mode-locked laser.…”