Mode locking based on the temporal Talbot effect

Thomas Udem,Akira Ozawa

doi:10.1007/s00340-017-6676-0

Abstract

We propose a new laser mode locking state in which the pulse disperses quickly and then revives after a certain time. This mechanism is based on the temporal Talbot effect and requires a large amount of intra-cavity group velocity dispersion. Similar to the usual mode locking it should be possible to employ the Kerr effect to force the laser into this mode, even when the cold cavity dispersion is not exactly matched. We show that the mode spectrum of such a laser is not equidistant but increases linearly with very high precision. This Talbot frequency comb can be self referenced. The beating with the adjacent modes uniquely defines the optical mode frequency, which means that the optical spectrum is directly mapped into the radio frequency domain. This is similar to the dual frequency comb technique, albeit without the limiting relative jitter between two combs.

Highlights

The Talbot effect has been described for the first time in 1836 as a peculiar phenomenon observed in the near field of an optical grating
These radio frequency (RF) components are the result of beating between adjacent optical modes and can be seen in the power spectrum of the laser output
To estimate the order of magnitude of the required length of the fiber Bragg grating (FBG) Δz we calculate the difference of the round trip phase delay for the two ends of the spectrum using (7): Δ = ( 0 + Δ ∕2) − ( 0 − Δ ∕2)

Summary

Introduction

The Talbot effect has been described for the first time in 1836 as a peculiar phenomenon observed in the near field of an optical grating. Summing over contributions of the individual rulings to the total field in the Fresnel approximation, a term of the form exp(−ikl2a2∕2z) appears with the wave number k, the rulings numbered by l and spaced. This article is part of the topical collection “Enlightening the World with the Laser” - Honoring T. W. Hänsch guest edited by Tilman Esslinger, Nathalie Picqué, and Thomas Udem

Talbot Comb

Self‐referencing

Non‐linear interactions

Example design

Conclusions