Abstract: A light receiving element includes a substrate including a silicon layer and a photodiode formed of a III-V group compound semiconductor and bonded to the silicon layer. The silicon layer includes a waveguide, the photodiode includes a first semiconductor layer, a light absorbing layer, and a second semiconductor layer, the first semiconductor layer is in contact with the silicon layer, the light absorbing layer and the second semiconductor layer are stacked in this order on a surface of the first semiconductor layer opposite to a surface of the first semiconductor layer in contact with the silicon layer, the first semiconductor layer has a first conductivity type, the second semiconductor layer has a second conductivity type, the first semiconductor layer includes a projecting portion and a first slab portion, and the projecting portion is connected to the first slab portion and projects from the first slab portion.

Abstract: An optical device includes a substrate having a first region and a second region in a surface thereof, a first waveguide for inputting light, and at least one second waveguide for outputting light. The second region surrounds the first region. The first waveguide and the second waveguide are optically coupled to the first region. The substrate includes a first layer and a second layer sequentially stacked one on top of the other in the first region. The second layer has a plurality of holes. A depth of each of the holes is half of a thickness of the second layer or smaller. The substrate does not have the second layer and has the first layer in the second region.

Abstract: A method according to the present disclosure is a method of manufacturing a multiplexer/demultiplexer including a substrate, a first port for inputting light, and a second port for outputting light, the first port and the second port being provided in the substrate. The method includes designing positions of a plurality of holes such that three adjacent holes among the plurality of holes are arranged in a triangle lattice, and forming the plurality of holes in a surface of the substrate.

Abstract: A light receiving device includes a semiconductor substrate having a first major surface and a second major surface opposite to the first major surface, and a metal pattern layer provided on the second major surface. The first major surface is provided with a first input port configured to receive an input of signal light, a second input port configured to receive an input of local oscillation light, a first light receiving element optically coupled to the first input port, an optical 90 degree hybrid element optically coupled to the first input port and the second input port, and a second light receiving element optically coupled to the optical 90 degree hybrid element. The metal pattern layer contains at least one of titanium or chromium.

Abstract: A light receiving device includes a semiconductor substrate having a first major surface and a second major surface opposite to the first major surface, and a metal pattern layer provided on the second major surface. The first major surface is provided with a first input port configured to receive an input of signal light, a second input port configured to receive an input of local oscillation light, a first light receiving element optically coupled to the first input port, an optical 90 degree hybrid element optically coupled to the first input port and the second input port, and a second light receiving element optically coupled to the optical 90 degree hybrid element. The metal pattern layer contains at least one of titanium or chromium.