Self-written waveguide structure in photosensitive polyimide resin fabricated by exposure and thermosetting process

A new fabrication technique of self-written waveguide was developed by using a photosensitive polyimide (PSPI) resin. The PSPI resin enables us to fabricate a solidified cladding portion of the self-written waveguide only by a thermosetting process after writing of the waveguide core. In the PSPI resin, a self-focusing effect of the exposing laser light, induced by difference in refractive index between exposed and unexposed portions, was observed. The coupling loss between two multimode fibers, which were placed with 0.5-mm gap, was decreased to 0.7 dB by insertion of the PSPI all-solid self-written waveguide. This simple fabrication method of the self-written waveguide structure is applicable to a convenient alignment technique of optical components.