| 摘要 |
PURPOSE:To obtain an inexpensive modulator superior in temperature characteristic, by providing one channel-type optical waveguide on the surface of an electrooptic crystal, and providing an ion exchange layer, whose thickness is changed cyclically in the light propagation direction, and a voltage applying means around this waveguide. CONSTITUTION:The modulator consists of a Z-cut lithium niobate crystal plate 1, and a titanium diffusion channel waveguide 2 and an ion exchange layer 3 are formed. An electrode 4 for applying an electric field into the waveguide 2 is provided on the upper face of the ion exchange layer. The depth of the ion exchange layer 3 is changed cyclically in the light propagation direction, and its cycle is changed to LAMBDA1-LAMBDA2 (LAMBDA2>LAMBDA1) monotonously. An average thickness (d) of the layer 3 is so determined that an equivalent refractive index nr of the radiation mode is lower than an equivalent refractive index ng of the guided mode. Thus, the difference between ng and nr, namely, the change of the radiation angle due to the temperature change of double refraction is reduced, and the mode conversion is performed with a low voltage. |
