Optical Waveguide as Amplifier Fibre for High-Performance Operation

Abstract

The invention relates to an optical waveguide (3) as a laser medium or as a gain medium for high-power operation, wherein the optical waveguide (3) is an optical fiber, the light-guiding core of which, at least in sections, is doped with rare earth ions. It is an object of the invention to provide an optical waveguide as a laser or a gain medium, and a laser/amplifier combination realized therewith, in which the output signal of the laser or gain medium is better stabilized. The invention achieves this object by virtue of the maximum small signal gain of the optical waveguide (1) being up to 60 dB, preferably up to 50 dB, more preferably up to 40 dB, even more preferably up to 30 dB, on account of the concentration of the rare earth ions and/or the distribution thereof in the light-guiding core. Moreover, the invention relates to the use of such an optical waveguide as an amplifier fiber (3) in a laser/amplifier combination.

Claims

1. Optical waveguide as a laser medium or a gain medium for high-power operation, wherein the optical waveguide is an optical fiber, the light-guiding core of which, at least in sections, is doped with rare earth ions, wherein the maximum small signal gain of the optical waveguide is up to 60 dB, preferably up to 50 dB, more preferably up to 40 dB, even more preferably up to 30 dB, on account of at least one of the concentration of the rare earth ions and the distribution thereof in the light-guiding core.

2. Laser/amplifier combination comprising a laser, an amplifier fiber and a pump light source, wherein the pump light source optically pumps the amplifier fiber and wherein the amplifier fiber amplifies the radiation of the laser propagating therein, wherein the core of the amplifier fiber guiding the laser radiation, at least in sections, is doped with rare earth ions, wherein the maximum small signal gain of the amplifier fiber is up to 60 dB, preferably up to 50 dB, more preferably up to 40 dB, even more preferably up to 30 dB, on account of at least one of the concentration of the rare earth ions and the distribution thereof in the light-guiding core.

3. Laser/amplifier combination according to claim 2, wherein the mean power of the laser radiation at the output of the amplifier fiber is at least 100 W.

4. Laser/amplifier combination according to claim 2, wherein the wavelength of the laser radiation lies away from the wavelength, at which the wavelength-dependent gain of the amplifier fiber is at maximum.

5. Laser/amplifier combination according to claim 2, wherein the wavelength of the light of the pump light source lies away from the wavelength, at which the absorption of the amplifier fiber is at maximum.

6. Use of an optical waveguide as a laser medium or a gain medium for high-power operation, wherein the optical waveguide is an optical fiber, the light-guiding core of which, at least in sections, is doped with rare earth ions, wherein the mean power of radiation amplified in the optical waveguide is at least 100 W, preferably at least 500 W, more preferably at least 1 kW, particularly preferably at least 10 kW, wherein the maximum small signal gain of the optical waveguide is up to 60 dB, preferably up to 50 dB, more preferably up to 40 dB, even more preferably up to 30 dB, on account of at least one of the concentration of the rare earth ions and the distribution thereof in the light-guiding core.

7. Laser/amplifier combination according to claim 2, wherein the mean power of the laser radiation at the output of the amplifier fiber is at least 500 W.

8. Laser/amplifier combination according to claim 2, wherein the mean power of the laser radiation at the output of the amplifier fiber is at least 1 kW.

9. Laser/amplifier combination according to claim 2, wherein the mean power of the laser radiation at the output of the amplifier fiber is at least 10 kW.

10. Laser/amplifier combination according to claim 2, wherein the wavelength of the laser radiation lies below the wavelength, at which the wavelength-dependent gain of the amplifier fiber is at maximum.

Description

[0021] Further features, details and advantages of the invention emerge from the wording of the claims and the following description of exemplary embodiments on the basis of the figures. In the figures:

[0022] FIG. 1 shows a schematic view of a laser/amplifier combination according to the invention;

[0023] FIG. 2 shows a diagram for elucidating the dependence of the mode instability on the gain.

[0024] The laser/amplifier combination shown in FIG. 1 comprises a laser 1, preferably in the form of a fiber laser which produces laser radiation at a low intensity and outputs said laser radiation to an optical fiber 2 by way of a coupling. The laser 1 can be a continuous wave laser or else a pulsed laser. The radiation produced by the laser 1 propagatespossibly after passing through one or more preamplifier stages (not depicted here)in an amplifier fiber 3 and is amplified in it to the desired power. To this end, the laser-radiation-guiding core of the amplifier fiber 3 is doped with rare earth ions. The amplifier fiber 3 is optically pumped by means of a pump light source 4. The light from the pump light source 4 is coupled in a manner known per se into the amplifier fiber 3 by way of a coupler 5. The pump light then propagates in the amplifier fiber 3 together with the laser radiation to be amplified. The mean power of the laser radiation at the output 6 of the amplifier fiber is more than 100 W, possibly even 10 kW or more. In order to avoid mode instability, the maximum small signal gain of the amplifier fiber 3 is less than 60 dB, possibly even less than 30 dB, as a result of a suitable choice of the concentration of the rare earth ions and/or a suitable geometric distribution in the laser-radiation-guiding core.

[0025] The diagram in FIG. 2 illustrates the dependence of the power threshold, above which mode instability occurs, on the small signal gain of the amplifier fiber and on the length of the amplifier fiber. In the diagram, the power threshold P (in watt), above which mode instability occurs, is plotted as a function of the fiber length (in meters). The solid curve denoted by 7 shows the behavior of a conventional amplifier fiber. In the case where the amplifier fiber has a length of 15 m, mode instability occurs when the power of the amplified radiation is above 3 kW. In the case of a smaller small signal gain, the power threshold P is significantly increased. The curve 8 shows the behavior of an amplifier fiber whose small signal gain is only 35 dB (in this case at a wavelength of 1030 nm). Mode instability only occurs above approximately 9 kW in the case of a fiber length of 15 m. The curve 9 shows the behavior of a fiber whose small signal gain is even only 22 dB (at 1010 nm). In the case where the length of the amplifier fiber is 15 m, the power threshold P already lies at 13 kW.

[0026] All of this shows that, according to the invention, it is possible to obtain a stable operation (without mode instability) by using an optical waveguide as an amplifier fiber for high-power operation, wherein the maximum small signal gain of the optical waveguide is reduced to less than 60 dB, preferably into the region of 30 dB or less.