| 摘要 |
PROBLEM TO BE SOLVED: To obtain high dispersion of birefringence in a wide wavelength range by forming a plurality of cores each having a higher refractive index than that of a clad on a dielectric substrate to be used as the clad so as to obtain the distribution of the refractive index showing a plurality of maxima. SOLUTION: When a Ti diffusion method is used, for example, a patterned Ti metal film is deposited on a LiNbO3 substrate 111 and diffused into the substrate by heat treatment to form a plurality of cores 112 having a high refractive index near the surface. During the heat treatment, external diffusion of Li2O is caused to decrease the trapping effect for light. To prevent that, the treatment is performed in Li2O or LiNbO3 powder. For example, in a proton exchange method, LiNbO3 is dipped in a fused liquid of benzoic acid (C6 H5COOH) at about 210 to 250 deg.C for several ten minutes to exchange Li+ and H+ so that a region having a high refractive index can be obtained. Thus, the distribution of the refractive index shows two peaks n1 corresponding to the two cores 112 formed by the Ti diffusion method on the LiNbO3 substrate 111. |
