Coherent light generators – Optical fiber laser
Reexamination Certificate
1999-07-09
2001-12-04
Scott, Jr., Leon (Department: 2877)
Coherent light generators
Optical fiber laser
C372S006000, C372S072000, C372S037000, C385S134000, C385S137000, C385S147000
Reexamination Certificate
active
06327279
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a device for and a method of pump light supply for laser active and/or amplifying fibers.
For excitation of a laser light emission of a so-called fiber laser, two different possibilities are known. A so-called pump, or in other words an energy excitation can be provided either by a longitudinal or a transverse supply of excitation lights. For excitation of fiber lasers and fiber amplifiers exclusively longitudinal pumping is known. A basis for this is provided, in addition to other aspects, in the length-diameter ratio of the fibers. Since a fiber core typically is available over a diameter of at least 10 &mgr;m, therefore during a transverse pumping only an exceptionally low fraction of the pumping efficiency can be absorbed. For example a laser core with a diameter of 7 &mgr;m, (single-mode laser or amplifier for a utilization with 1 &mgr;m wave length) absorbs during a single-time passage only substantially between 0.1% and 1% of the pump power, and this fraction depends on an ion doping concentration of the fiber laser or amplifier.
Also, a method of longitudinal coupling of the pump light in the laser core, in particular for high power fiber laser and amplifier, is known with output conductors of several watts. Since the radiation quality of the pump laser diodes for a direct coupling of the pump power in the region doped with a laserion (so-called single-mode region) of the fiber is not sufficient, high light powers must be realized only through fibers with multiple cores.
Patent document WO 95 10868 shows a method for a repeated supply of pump light in so-called double core fibers. The fibers are composed of multiple cores which are arranged coaxially with one another. In one pump core with a typical diameter of 100 &mgr;m-400 &mgr;m, the power of the laser diodes is coupled. The diameter of the pump core has a plurality of diameters of the single mode laser cores, typically between 5 &mgr;m and 10 &mgr;m. Advantageous for the double core fibers when compared with conventional pump technique, is the possibility to realize fiber lasers with only one occurring spacial mode of the irradiated laser light, as well as a very high pump light aperture and pump light coupling surface.
The disadvantage of the known double core method is the expensive and complicated and therefore cost intense manufacture of the multiple core fibers. Since the fibers additionally must be optimized, for example with respect to polarization preservation and a radiation strength, there are limitations with respect to the materials to be used for the fibers. In the pump core the occurring radiation modes which have no spacial overlapping with the laser core must be suppressed. This can be performed by spacial winding technique or pump core geometries. Moreover, the known double core techniques for a beam formation of the laser diodes are technically expensive and have the risk of insufficient reliability, which in many applications, for example for space applications can be problematic. In addition, a simultaneous coupling of signal and pump sources is required in a double core fiber for amplifier applications of a wave-length-selective coupling, whereby typically power losses occur up to 50%.
SUMMARY OF THE INVENTION
Accordingly, it is an object of present invention to provide an arrangement for and a method of a transverse pump light supply for laser active fibers and/or amplified fibers, which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated in a device for loading of a light wave guide formed as a fiber with exciting energy in form of a pump light supply for producing a laser light, which has a fiber selected from a group consisting of a laser fiber and an amplifier fiber which is wound with at least one winding in a coil-like manner for a transverse coupling of exciting pump light.
Another feature of present invention resides in a method of loading of a light wave guide formed as a fiber laser for producing a monochromatic laser light for amplifying a coherent or an incoherent signal light, comprising the steps of providing a coil-like wound fiber, using as an excitation energy a pump light, and regulating the pump light transversely into the coil-like wound fiber.
When the device is designed and a method is performed in accordance with the present invention, they have the advantage of a high power output with the utilization of relatively simple and therefore cost-favorable fibers with simultaneously very low losses. The utilization of relatively expensive and thereby cost-intense double core fibers can be dispensed with. In addition, the inventive device and method have the advantage of a high output power with a low energy consumption and low losses, and thereby a very high efficiency.
Due to the possibility of a redundant coupling of a plurality of laser diodes, which each must have only a relatively low radiation quality, there is a high fault safety and thereby an exceptionally high reliability of a whole system. The laser diode for producing and supplying of the pump light can be coupled therefore in a structurally very simple manner directly to a pump chamber. Thereby there are no difficulties due to a coupling of the jet-shaped laser diodes in the fibers. In addition, an easily available amplifier and laser fibers can be engaged without problems. In contrast to the known longitudinal pump systems, the fiber ends of the laser and/or amplifier fibers are freely accessible, which substantially improves the possibilities for use. The advantage with regard to the known double core fibers is a considerable increase of the surface available for joining in a transversal coupling of the pump light.
It is also advantageous that it is simple to produce an intermediate space between two receiving parts for receiving a tangential supplied fiber, for example by grinding-in. Very low requirements are made to the quality of the surface which is surrounded by the fiber, which is very cost-favorable for manufacture.
In accordance with a preferable embodiment, a fine adjustment of a width of the intermediate space which receives the fiber is possible by an axial displacement of a corresponding conically shaped inner and outer cylinder, which provides an exact adaptation to the diameter of the fiber.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
REFERENCES:
patent: WO 95/10868 (1995-04-01), None
Flores Ruiz Delma R.
Jr. Leon Scott
Robert & Bosch GmbH
Striker Michael J.
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