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The Photonics Spotlight

New Scientific Paper: Timing Jitter and Phase Noise of Mode-locked Fiber Lasers

Ref.: R. Paschotta, “Timing jitter and phase noise of mode-locked fiber lasers”, Opt. Express 18 (5), 5041 (2010)

(See also: spotlight article of 2009-08-22)

Dr. Rüdiger Paschotta

My latest scientific paper just appeared in the open-access journal Optics Express. I believe that this work will get a lot of attention, as it significantly expands the knowledge on the noise properties of mode-locked fiber lasers.

The noise performance of simple soliton mode-locked fiber lasers has been well understood for many years already; it has been investigated in 1993 (H. A. Haus and A. Mecozzi, “Noise of mode-locked lasers”, IEEE J. Quantum Electron. 29 (3), 983 (1993)), using soliton perturbation theory. Unfortunately, soliton fiber lasers have a fairly limited pulse energy, and mainly for that reason their quantum-noise limited timing jitter is much higher than for bulk lasers, for example. The achievable performance is still quite good, but clearly not the last word.

In recent years, several schemes for mode-locked fiber lasers with substantially higher pulse energies have been developed – most notably, stretched-pulse lasers and wavebreaking-free lasers, the latter often realized with all-normal chromatic dispersion in the resonator. The Haus/Mecozzi analysis is clearly not applicable here, as the assumptions of soliton perturbation theory are not fulfilled. I myself have developed a much more general theoretical treatment (R. Paschotta, Appl. Phys. B 79, 163 (2004)), which can be applied to various mode-locked lasers including most bulk lasers. Still, for the fairly complicated pulse-forming mechanisms in the stretched-pulse and wavebreaking-free fiber lasers, it was not clear whether the application of these results would be valid. Therefore, I decided to investigate several cases using a numerical model as described in R. Paschotta, 79, 153 (2004). The main results are:

A main conclusion from this work is that in order to improve the noise performance of mode-locked fiber lasers, it is not sufficient to raise the pulse energy with any means available. One also has to be careful to avoid regimes where substantial excess noise is introduced. Besides, there is a chance that we discover something interesting and useful by further investigating the discovered anomaly.

Those interested in such topics are advised also to look at the following earlier papers of mine:

This article is a posting of the Photonics Spotlight, authored by Dr. Rüdiger Paschotta. You may link to this page, because its location is permanent. See also the Encyclopedia of Laser Physics and Technology.

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