| 摘要 |
PURPOSE:To reduce insertion loss by using a mask pattern which has plural stripes in parallel to the propagation direction of light as the mask pattern for a mixing part. CONSTITUTION:A part corresponding to waveguides nearby the mixing part A of the mask pattern is so shaped that slit openings parallel to the axial direction of a waveguide bundle part C are formed, and the end parts of mask parts where the slits are formed become gradually thinner. This mask pattern is used to make an ion exchange for the formation of waveguides as high- refractive-index parts in a substrate. In this case, slight refractive index variation is caused in a stripe shape in a high-refraction area formed at the mixing part, but the direction of the stripes is parallel to the light propagation direction, so as increase in loss due to the variation becomes extremely small. Consequently, the start coupler which has low loss and has the improved uniformity of branch characteristics is obtained. |
