Patent ID: 8481945

Claim:
An optical frequency converter comprising: a waveguide including a core made of a nonlinear optical medium having a refractive index n 1,light in a wavelength region of light, and cladding disposed so as to cover the core and made of a material whose refractive index n 2,light in the wavelength region of light is lower than the refractive index n 1,light ; and a coupling section made of a material whose refractive index n 3,THz in a wavelength region of a terahertz wave is higher than the refractive index n 1,light and disposed in contact with the cladding, the coupling section being configured to couple the waveguide with a space in the wavelength region of the terahertz wave, wherein the coupling section covers the cladding, and wherein the cladding has a thickness that is set within a range in which the thickness is larger than or equal to a thickness that allows the intensity of the light propagating through the core to be smaller than or equal to 1/e 2 , e being a base of a natural logarithm, and in which the thickness is smaller than or equal to a thickness that is ½ of an equivalent wavelength of the terahertz wave in the cladding.