High power injection of laser light into optical fibers is problematic for a many applications.
Alignment, focal adjustment or poor spot quality can quickly destroy the fiber or the connector. For this reason, standard connectors and termination procedures are not adapted to this type of applications.
Besides careful fiber selection and protection is mandatory.
For power delivery applications, a crucial point is to select the proper fiber considering the wavelength, the numerical aperture, the core size as well as the material of the core, cladding, coating and protection. The quality of the laser delivery system will heavily depend on all these parameters.
Most of the time the fibers will be silica / silica type. A polyimide coating will increase temperature resistance and consequently their survival to “injection accident”.
Optical fibers materials are optimized for their transmission of a given wavelength range. As an example, multimode step index all silica fibers usually have a pure silica core and doped silica cladding. The OH ions content will determine the wavelength range transmitted. “High OH” fibers will better transmit UV and visible while a “Low OH” fiber will be selected for transmission of visible and near IR.
The maximum power that can be injected into an optical fiber is highly dependent of many parameters and particularly of the mechanical conditions.
Fiber preparation, optical end face quality, stripping and connector termination procedure have a direct impact on performances. Fiber retention obtained by gluing (to be avoided) or poor crimping can induce fatal stress into the silica of the fiber.
Perfect optical end faces mandatory for most fiber applications can be obtained by polishing or cleaving. With high power applications results are better with cleaved end faces because even with careful polishing abrasion scratches can reduce transparency. Light absorption will increase temperature with a risk of destruction.
High transparency end faces can be obtained by cleaving. The principle is to create a small diamond scratch on the fiber and to apply a stress by traction. The initial flaw will propagate through the molecular structure of the silica thus creating a higly transparent perpendicular optical face without any other preparation.
SEDI-ATI has developed two cleaving tools “Infocut” and “I-Cleave” (see product documentation)
Metallic structures are particularly adapted to power delivery systems which deserve specific protections for security issues. Such structures can avoid the risk of outgoing laser emission in case of fiber breakage and also limit too sharp bending radius.
Different constructions are proposed according to conditions such as bending, flexibility, crush resistance, temperature, etc. (see product documentation). An additional colored PVC extrusion can be made as well as a special marking to differentiate the patchcord.
Simpler protections such as Teflon or PEEK tubes, silicone tubes or cable structures can also be used to protect the fiber in these applications.
See product documentation