Patent ID: 6919985

Claim:
An optical wavelength converting apparatus comprising first and second light sources and a nonlinear optical material so that beams from the two light sources are allowed to be incident on the nonlinear optical material to generate sum frequency light of these beams, wherein the nonlinear optical material is provided with a periodic structure that matches phases of the beams from the two light sources with a phase of the sum frequency light of these beams, and wherein wavelengths of the beams from the two light sources and of the sum frequency light of these beams, polarization directions of these three beams in the nonlinear optical material, and propagation directions of these three beams in the nonlinear optical material are determined such that an efficiency of conversion into sum frequency light does not change even with a change in at least one of the parameters defining the efficiency of conversion into sum frequency light, wherein wavelengths of the beams from the two light sources and of the sum frequency light of these beams, polarization directions of these three beams in the nonlinear optical material, and propagation directions of these three beams in the nonlinear optical material are determined such that an efficiency of conversion into sum frequency light does not change even with a change in at least one of an oscillation wavelength of the second light source and the temperature of the nonlinear optical material, and wherein when wavelengths of a beam from the first light source, a beam from the second light source, and a sum frequency light of these beams are defined as λ 1 , λ 2 , and λ 3 , refractive indices of the nonlinear optical material for the beams and light (or refractive indices averaged along the light propagation direction) are defined as n 1 , n 2 , and n 3 , respectively, and a phase mismatch amount Δk is defined as follows: Δ k=n 3 (2π/λ 3 )− n 1 (2π/λ 1 )− n 2 (2π/λ 2 ), the periodic structure has a period Λ given by: Λ=2π/|Δ k |=1 /|n 3 /λ 3 −n 1 /λ 1 −n 2 /λ 2 |, and the wavelengths of beams from the first and second light sources and of the sum frequency light of these beams, polarization directions of these three beams in the nonlinear optical material, and propagation directions of these three beams in the nonlinear optical material are determined so as to be: |∂Δ k/∂λ 2 |≦0.05(μm −2 ).