OPTICAL EVALUATION OF THE COUPLING ZONE BETWEEN CONCENTRATING OPTICS AND A POLYMER OPTICAL FIBER

摘要

For the daylighting system SOLLEKTOR [1] there are different possibilities to realize the interface between concentrating optics and a polymer optical fiber (POF). A recent version of the SOLLEKTOR uses Fresnel lenses to focus the sunlight and to couple it into the POF that is fixed in a special mount to avoid a thermal degeneration. State of the art is connecting POF and mount by adhesive bonding using an optical adhesive that shows a defined polymerization under ultraviolet radiation. Besides the ultraviolet activation spectrum the adhesive shows a small absorption in the blue visible range. This unwanted absorption retains even after the polymerization and influences the natural spectrum of the concentrated sunlight. For this reason it is useful to design a process, where supporting additives can be circumvented. Laser Transmission Welding (LTW) offers the possibility to use only the basic material of the joining partners. The LTW process is already used for welding plastics in industry but not for welding smaller areas requiring very good optical properties. An optical investigation of the welding zone is essential to determine possible losses. Optical power losses can be caused by Fresnel reflection and at air inclusions, absorption or scattering effects of particles in the joining zone. This paper presents an appropriate measurement method that enables a characterization of the joining zone and a comparison between LTW and adhesive bonding.