Wavelength conversion device

A wavelength conversion device comprising a second-order nonlinear optical medium with a polarization inversion structure, wherein in a nonlinear optical process in which wavelength conversion is performed through an interaction in which three wavelengths of λ1, λ2, and λ3 have a relationship of 1/λ1=1/λ2+1/λ3, the polarization inversion structure has a polarization inversion period A which satisfies n1/λ1−n2/λ2−n3/λ3−1/Λ=0 where n1 is a refractive index at μ1, n2 is a refractive index at λ2, and n3 is a refractive index at λ3 in the second-order nonlinear optical medium,

• the polarization inversion period Λ is divided into 2a regions (where a is an integer of 2 or more), and
• when the 2a regions divided from the polarization inversion period A each has a width ratio of an inverted region and a non-inverted region of r to 1−r (where 0≤r≤1), a width ratio value r is set such that, when one period in phase of a sine function from 0 to 2π is divided into 2a regions in correspondence with the division of A into 2a regions, a value of the sine function in a center of each divided region is (1−2r)±0.1.