Patent ID: 7593610

Claim:
A manufacturing method for an optical multimode interference device comprising a multimode waveguide having one or more narrow width single-mode waveguides provided at both ends thereof, wherein light introduced into the one or more single-mode waveguides at an input side of the device is interfered within the multimode waveguide and emitted from the one or more single-mode waveguides at an output side of the device, the manufacturing method comprising: (a) on a crystal substrate which is a lower cladding layer, sequentially forming an optical waveguide layer, an upper cladding layer, and a mask layer for etching; (b) patterning the mask layer to form a mask pattern which corresponds to the multimode waveguide and the one or more single-mode waveguides; (c) selectively wet etching the upper cladding layer, using the mask pattern as a mask, to form the upper cladding layer such that, at both ends of said multimode waveguide, a wall face that is not provided with the one or more single-mode waveguides has a predetermined inclination angle along the crystal plane of the upper cladding layer; and (d) dry etching said upper cladding layer, said optical waveguide layer, and said crystal substrate using the mask pattern as a mask, to remove these layers to a predetermined thickness in a perpendicular direction, with the wall faces of the optical waveguide layer maintaining said predetermined inclination angle.