Patent ID: 8467637

Claim:
A waveguide path coupling-type photodiode having a semiconductor light absorption layer and an optical waveguide path core formed adjacently to each other: wherein a pair of electrodes facing each other are formed in a boundary portion between said semiconductor light absorption layer and said optical waveguide path core, said electrodes being comprised of at least one layer; wherein said electrodes are formed at an interval of (1/100)λ to λ, (where λ: a wavelength of light that propagates through said optical waveguide path core); wherein at least one part of said electrodes is buried into said semiconductor light absorption layer; wherein at least one layer of said electrodes is configured of a material capable of inducing a surface plasmon; and wherein a clad layer is formed for said optical waveguide path core, wherein said clad layer is configured so that a thickness L 1 and a thickness L 2 thereof meet a thickness L 1 <a thickness L 2 (where the thickness L 1 : a thickness of said clad layer at a position in which said clad layer faces said electrodes, with said optical waveguide path core put between said clad layer and said electrode, and the thickness L 2 : a thickness of said clad layer at a position in which said clad layer is laminated on said optical waveguide path core through which the light propagates).