| 摘要 |
PURPOSE:To enhance the optical insulating characteristic of an above-mentioned waveguide and to increase the density and integration scale of circuits by determining the thickness direction of a substrate at the X-axis or Y-axis direction of a crystal and decreasing the refractive index in the required parts adjacent to the optical waveguide in the substrate region outside the above-mantioned waveguide by hydrogen atom substitution. CONSTITUTION:The substrate 1 consists of an LiNbO3 crystal and is so formed that the X-axis or Y-axis direction of the crystal is made to coincide with the thickness direction. Ti is diffused from the region of a prescribed circuit pattern to form the optical waveguide 2 having the high refractive index within the substrate. The lower refractive index regions 3A, 3B are provided to a belt shape of a specified width adjacently to the outer peripheral side of both curved paths 2B, 2C over the length from nearly the beginning point of the curve up to the end point. The regions 3A, 3B are formed by substituting Li in the LiNbO3 crystal with H over the regions of the specified depth and width. A transmission loss is thereby greatly decreased and the radius of curvature can be decreased simultaneously in the case of including the curved parts in the waveguide and, therefore, the density ad integration scale of the circuit are increased and the size of the element is reduced. |
