Patent ID: 7940451

Claim:
A wavelength converter for entering incident light of one (λ 1 =λ 2 ) or two (λ 1 and λ 2 , or λ 1 and λ 3 ) wavelengths having a relationship of 1/λ 3 =1/λ 2 +1/λ 1 into a nonlinear optical material to output a converted light of a wavelength λ 3 or λ 2 , wherein the nonlinear material has a periodic structure, the sign of a nonlinear optical constant being alternately inverted in a propagating direction of light with a period Λ 0 , and wherein an initial phase for each period Λ 0 is varied so that a variation of the initial phase is changed for a different period Λ ph , wherein: refractive indexes for the nonlinear material relative to the wavelengths λ 1 , λ 2 and λ 3 are defined as n 1 , n 2 and n 3 respectively, the nonlinear material has a periodic structure obtained by changing a variation curve for the initial phase, wherein a phase mismatch Δβ is represented by Δβ=2π(n 3 /λ 3 −n 2 /λ 2 −n 1 /λ 1 ), and at least three phase matching peaks at unequal intervals within a plurality of phase matching peaks represented by 2π/Λ 0 +2πi/Λ ph (i=m, m+1, . . . , n: where m and n are positive or negative integers) have a highest conversion efficiency so that the smallest value for an evaluation function T is obtained, wherein a spatial change d(z) for the nonlinear optical constant at a location z in the light propagating direction is calculated; a Fourier transform is performed for the spatial change d(z); conversion efficiencies η(i) at individual phase matching peaks are obtained; and a desired conversion efficiency η t (i) is employed to calculate the evaluation function T, as below, T=Σ i=m i=n [η( i )−η i ( i )] 2 .