Light-induced Self-written Waveguides for Large Core Optical Fiber Modules

A fabrication technique for producing lightinduced self-written (LISW) waveguides for large-core optical fibers is proposed. The proposed technique employs a photopolymerizable resin consisting of two kinds of photopolymerizable monomers that differ from each other in terms of both refractive index and polymerization mechanism. The core portion is formed by virtue of a self-trapping effect, in which visible light is irradiated to the resin through an optical fiber that is inserted into the resin. Only the low refractive index monomer can be radically polymerized to form the LISW waveguide, which is generated from one end of the fiber. After the irradiation is stopped, the concentration gradient induced by the comsumption of the low refractive index monomer initiates a counter-diffusion phenomenon between the residual monomers. The low refractive index radically polymerizable monomer diffuses into the core region, while the high refractive index cationic polymerizable monomer diffuses out of the core region. The residual monomers are subsequently cured by exposure to UV light, and the region with decreased concentration of high refractive index monomer becomes a cladding layer. The resultant refractive index profiles of the waveguides were experimentally confirmed to be "W-shaped". The measured propagation loss of the waveguide was 1.7 dB/cm at 680 nm wavelength.