Optical waveguides – Optical transmission cable
Patent
1999-03-29
2000-12-26
Font, Frank G.
Optical waveguides
Optical transmission cable
385134, 385 33, 385902, G02B 644, G02B 600
Patent
active
061671770
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber cable which comprises a fiber having a central core and a surrounding cladding and which fiber cable is made for transmitting high optical power, specifically power exceeding 1 kW. At least one of the contact ends of the fiber has cooling means for optical power loss.
Optical fiber cables for transmitting high optical power are frequently used in industrial applications. Specifically they are used in cutting and welding operations by means of high-power laser radiation, but also in other industrial applications such as heating, detection or working operations in high-temperature environments this type of optical fiber cables can be used. One of the main problems in this type of high power applications, however, is the problem how to take care of radiation that falls outside the core of the fiber. The power density is normally very high and specific cooling means are required in order to prevent an uncontrolled heating, especially in case of strong back scattering in for instance welding operations.
Different methods to take care of such undesired power radiation are already known. One example is disclosed in DE 4305313, in which the radiation that falls into the cladding of the fiber is spread in a so-called mode stripper and absorbed by a metal surface. This surface can then be cooled from the outside of the component. A similar method is described in SE 83.07140-7.
An optical fiber cable of the above-mentioned type is also presented in SE 93.01100-5. In said fiber cable at least one of the end surfaces of the fiber core is provided with a rod having a larger diameter than the core diameter. At this end the fiber is provided with a reflector designed to conduct rays entering outside the fiber towards an area where they can be absorbed without causing any damage. In the illustrated embodiment this area is surrounded by a heat-abducting device with cooling fins, but it is also mentioned that water cooling means may be included in this area for cooling off the generated heat. Also in this case the cooling is provided from the outside of the component.
A weakness in all of these methods that now have been described is the fact that the heat first must be absorbed by a metal surface and then conducted through the metal material to the cooled surface either this surface is cooled by means of air or by water.
SUMMARY OF THE INVENTION
The object of this invention is to provide an optical fiber cable with an improved cooling capability so that the fiber can be used for transmitting a very high optical power without causing any damage to the fiber itself or to the housing. The invention is based upon the fact that the power (heat) is absorbed directly in a cooling medium instead of being conducted through a metal material.
According to the invention at least one of the contact ends of the fiber, comprising the core and the surrounding cladding, are located in a cavity filled with a flowing coolant so that radiation falling outside the fiber is entered into and absorbed at least partially by the coolant. The walls of the cavity comprises at least one non-absorbing surface. The other wall surfaces could be absorbing (metal). Radiation passing through the coolant is absorbed by said surfaces. As these surfaces are directly cooled by the flowing medium (liquid coolant) any uncontrolled heating can be avoided. As the optical radiation is passing through the flowing coolant before reaching the metallic surface, only a minor part of the radiation is absorbed by the surface.
According to a preferred embodiment the fiber is directly in contact with the surrounding coolant, for example water.
According to an alternative embodiment the fiber is surrounded by a transparent tube which then is directly in contact with the surrounding coolant.
In the following the invention will be described more in detail with reference to the accompanying drawings which schematically illustrates some examples of the new optical fiber cable.
BRIEF DESCRIPTION OF
REFERENCES:
patent: 4575181 (1986-03-01), Ishikawa
patent: 4678273 (1987-07-01), Vilhelmsson
patent: 4707073 (1987-11-01), Kocher
patent: 5619602 (1997-04-01), Sandstrom et al.
Roos Sven-Olov
Sandstrom Ulf
Torstensson Per-Arne
Font Frank G.
Permanova Lasersystem
Punnoose Roy M.
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