Optical solder effects of self-written waveguides in optical circuit devices coupling

"Optical solder" effects of self-written waveguides are systematically studied throughout coupling experiment of conventional multi-mode optical fiber for communication use (core diameter = 50 μm). The waveguide easily connects two optical fibers under significant longitudinal and lateral misalignment. The results clearly show that the present coupling method is very effective. Under 1000 μm longitudinal misalignment, the coupling loss significantly decreases after the waveguide formation even when lateral misalignment exists to some extent. With 30 μm lateral misalignment, the coupling loss is only 1 dB; 40 μm lateral misalignment still gives rather low loss value, 2 dB. The method is also successfully applied to connect two fibers whose edges are non-cleaved (fractured). The coupling loss is fully comparable with that of cleaved fiber coupling. Though the refractive index similarity simply explains this interesting phenomenon, the result can be regarded as another remarkable feature of this unique coupling method; i.e., very commonly required edge treatment of optical waveguides is not necessary for the optical coupling. Some analysis of all-solid type self-written waveguides is also described.