| 主权项 |
1. A rib waveguide type high-order mode filter, comprising:
a plate-like slab region; a projection portion formed in a stripe along a waveguiding direction of light on the slab region; and a mesa region having a bottom surface positioned at the same level as that of the bottom surface of the slab region and a top surface positioned at a higher level than that of the top surface of the slab region, on at least one side of the slab region in a transverse direction parallel to at least one of the bottom surface of the mesa region and the top surface of the mesa region, wherein the projection portion, the slab region, and the mesa region are made of the same material; the mesa region comprises a doped area in which an optical-absorption function is added by impurity doping into the material; a refraction index in the doped area is decreased due to the impurity doping as compared to the material located around the doped area; and the mesa region comprises a non-doped area located on at least one of a side above the doped area, a side below the doped area, a right side of the doped area, and a left side of the doped area. |
