| 摘要 |
PURPOSE:To shorten a substrate length and reduce a size, and to obtain the easiness of handling by providing plural couples of parallel optical waveguides of a Mach-Zehnder modulator by folding them back on a substrate end surface. CONSTITUTION:A short linear input-side waveguide 11 is provided at the top surface part of the substrate 1 from one substrate end surface 1A to the other substrate end surface 1B. Its end part is branched in a V shape and turned over on the substrate end surface to form a couple of parallel optical waveguides 12-1A and 12-2A to desired overall length while a direction wherein electrooptic effect is larger is selected, so the substrate length is shortened to about 1/3. A couple of V-shaped projection parts 13-1 and 13-2 are coupled with the ends of the parallel waveguides 12-1A and 12-2A and provided having an angle alpha of incidence larger than the total reflection angle so that the vertex is aligned with the other substrate end surface. Mean waveguides 12-1B and 12-2B having desired length are coupled with the return-path end parts of the projection parts 13-1 and 13-2. An earth electrode 16-2 is formed along other parallel optical waveguides 12-1B and 12-2B coupled through the other projection part 13-2, and a microwave power source 20 is connected to the end part of one of a signal electrode 16-1 and an earth electrode 16-2. |
