Optical fibers 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 fibers can be used. By means of the optical fibers it is possible to design flexible manufacturing systems for transmitting the laser beam from the high power laser source to the workpiece. An optical fiber typically has an inner glass core and a transparent, surrounding layer, a so-called cladding, having a lower refractive index than the glass core. The function of the cladding is to keep the optical beam confined to the core.
For a long period of time CO2-lasers were the main player on the market for high power industrial lasers. However, at the beginning of the 90s, the Nd:YAG laser started to be a tool for high power applications and the development of fiber optic technology for these type of lasers has become a hot topic.
When designing optical fiber systems for high power laser radiation it is important that the fiber is not damaged in any way because the radiation from a “leaking” or damaged fiber might cause serious personal injuries. Therefore it is previously known to check the status of the fiber by means of specific monitoring systems. See for instance U.S. Pat. No. 4,812,641, DE 4032967, DE 3246290, DE 3031589 and U.S. Pat. No. 5,497,442.
However, it is important to detect damage in the optical fiber not only for security reasons but also for preventing secondary damage in other parts of the system due to said damages or imperfections in the fiber. A weakness in the detecting systems referred to above is the fact that the detection of damage comes too late. When the radiation from the damaged fiber is detected, secondary damage in the optical system might already have occurred.
In WO 03/016854 a device is described in which a detector for sensing substantially radially spread radiation from incident optical radiation is arranged in connection with the entrance and/or exit parts of the fiber. If this substantially radially spread radiation exceeds a certain level this is used as an indication of a damage in the entrance and/or exit zone of the fiber. The detector is arranged in connection with or at a distance from the entrance or exit end of the fiber and the radially spread radiation is then arranged to be transmitted to the detector via optics.
However, in industrial applications using high brilliance lasers at power levels up to and exceeding 20 kW and similarly diode lasers exceeding 10 kW, there is an increasing demand to continuously monitor component status even in passive components such as fiber-optic cables. With fiber-optic cables designed according to the European Automotive Industry fiber standard interface there is a demand to monitor and handle extreme levels of power losses. There is also a demand to provide a more rugged and flexible connector without having detectors and optics arranged at a distance from the entrance or exit end of the fiber as described in WO 03/016854.