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The Photonics Spotlight

Extremely Long Mode-locked Fiber Laser

Posted on 2009-01-05 as a part of the Photonics Spotlight (available as e-mail newsletter!)

Permanent link: https://www.rp-photonics.com/spotlight_2009_01_05.html

Author: Dr. Rüdiger Paschotta, RP Photonics Consulting GmbH

Abstract: The article discusses a recent scientific paper, presenting a mode-locked fiber laser with an extremely long laser resonator.

Dr. Rüdiger Paschotta

Ref.: S. Kobtsev et al., “Ultra-low repetition rate mode-locked fiber laser with high-energy pulses”, Opt. Express 16 (26), 21936 (2008)

The above referenced paper describes mode-locked fiber lasers with a resonator length of several kilometers, leading to a pulse repetition rate as low as 77 kHz and a rather high pulse energy of 3.9 μJ. These characteristics are indeed very usual for a mode-locked fiber laser – they would be much more typical for a Q-switched laser.

The impact of nonlinearities and chromatic dispersion in the very long fiber is of course rather strong. In the normal dispersion regime, such a laser can generate strongly up-chirped pulses, which can often be temporally compressed to obtain high-quality picosecond or femtosecond pulses. In the present paper, however, this was demonstrated only for a short version of that laser, having a much higher repetition rate of 22 MHz, but not for the long laser as described above. A challenge is certainly to make a dispersive compressor with a huge amount of dispersion, related to a group delay variation of several nanoseconds within the spectral width of 0.35 nm. Therefore, this laser is currently not a practical source for high-energy picosecond or femtosecond pulses, and in fact it is not even proven that those could be obtained with a suitable compressor.

Anyway, I think it is a good idea to explore such curious parameter regimes, and there may be further progress.

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

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