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An optical wavelength converting apparatus comprising first and second light sources and a nonlinear optical material. Beams from the two light sources, incident on the material, generate sum frequency light of these beams. The nonlinear optical material is provided with a periodic structure that ma

An optical wavelength converting apparatus comprising first and second light sources and a nonlinear optical material. Beams from the two light sources, incident on the material, generate sum frequency light of these beams. 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. Also, 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 material, and propagation directions of these three beams in the material are determined such that an efficiency of conversion into sum frequency light does not change even with a change in one of the defining parameters, thus providing an advantageous pumping light source.

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1. 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

1. 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 λ1, λ2, and λ3, refractive indices of the nonlinear optical material for the beams and light (or refractive indices averaged along the light propagation direction) are defined as n1, n2, and n3, respectively, and a phase mismatch amount Δk is defined as follows: Δk=n3(2π/λ3)?n1(2π/λ1)?n2(2π/λ2), the periodic structure has a period Λ given by:Λ=2π/|Δk|=1/|n3/λ3?n1/λ1?n2/λ2|, 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:|∂Δk/∂λ2|?0.05(μm?2). 2. The optical wavelength converting apparatus according to claim 1, wherein 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:?|∂Δk/∂λ2|?0.01 (μm?2).3. 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 λ1, λ2, and λ3, refractive indices of the nonlinear optical material for the beams and light (or refractive indices averaged along the light propagation direction) are defined as n1, n2, and n3, respectively, and a phase mismatch amount Δk is defined as follows: Δk=n3(2π/λ3)?n1(2π/λ2) the periodic structure has a period Λ given by:Λ=290 /|Δk|=1/|n3/λ3?n1/λ1?n2/λ2|, and when a temperature of the nonlinear optical material is defined as T, 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:|∂Δk/∂T|?0.5 (K?1cm?1). 4. The optical wavelength converting apparatus according to claim 3, wherein 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:|∂Δk/∂T|?0.1 (K?1cm?1). 5. 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 the nonlinear optical material is KTiOPO4(KTP), wherein 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 use a component d24 or d15 or both of a nonlinear optical coefficient tensor dij of the nonlinear optical material, and wherein when x, y, and z axes are set as principal axes in the nonlinear optical material and when an angle with the z axis is defined as θ and an angle with the x axis is defined as φ, the propagation direction of beams from the first and second light sources and of the sum frequency light of these beams are set so as to be 64°?θ?90° and 0°?φ?90°, and when the wavelengths of beams from the first light source, the second light source, and the sum frequency light of these beams are defined as λ1, λ2, λ3, these wavelengths are set so as to be 1,220 nm?λ1?1,745 nm, 701 nm?λ2?1,002 nm and 500nm?λ3?550 nm. 6. The optical wavelength converting apparatus according to claim 5, wherein the propagation direction of beams from the first and second light sources and of the sum frequency light of these beams are θ=90° and φ=0°, the wavelengths of beams from the first and second light sources and of the sum frequency light of these beams are 1,519 nm?λ1?1,745 nm, 701 nm?λ2?862 nm, and 500 nm?λ3?550 nm, and the beam from the first light source is polarized along the y axis, the beam from the second light source is polarized along the z axis, and the sum frequency light is polarized along the y axis.7. The optical wavelength converting apparatus according to claim 5, wherein the propagation direction of beams from the first and second light sources and of the sum frequency light of these beams are θ=90° and φ=90°, the wavelengths of beams from the first and second light sources and of the sum frequency light of these beams are 1,220 nm?λ1?1,421 nm, 772 nm?λ2?1,002 nm, and 500 mn?λ3?550 nm, and the beam from the first light source is polarized along the x axis, the beam from the second light source is polarized along the z axis, and the sum frequency light is polarized along the x axis.8. The optical wavelength converting apparatus according to claim 5, wherein when the x, y, and z axes are set as principal axes in the nonlinear optical material and when an angle with the z axis is defined as θ and an angle with the x axis is defined as φ, the propagation direction of beams from the first and second light sources and of the sum frequency light of these beams are set so as to be 79.1°?θ?90° and 20.4°?φ?27.6°, and the wavelengths of beams from the first and second light sources and of the sum frequency light of these beams are set so as to be 1,460 nm?λ1?1745 nm, 701 nm?λ2?882 nm, and 500 nm?λ3?550 nm.9. An optical wavelength converting method of using first and second light sources and nonlinear optical material to allow beams from the two light sources to impinge against 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 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 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 λ1, λ2, and λ3, refractive indices of the nonlinear optical material for the beams and light (or refractive indices averaged along the light propagation direction) are defined as n1, n2, and n3, respectively, and a phase mismatch amount Δk is defined as follows: Δk=n3(2π/λ3)?n1(2π/λ1)?n2(2π/λ2), the periodic structure has a period Λ given by:Λ=2π/|Λk|=1/|n3/λ3?n1/λ1?n2/λ2|, 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:|∂Δk/∂λ2|?0.05 (μm?2). 10. The optical wavelength converting method according to claim 9, wherein 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:|∂Δk/∂λ2|?0.01 (μm?2). 11. An optical wavelength converting method of using first and second light sources and nonlinear optical material to allow beams from the two light sources to impinge against 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 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 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 λ1, λ2, and λ3, refractive indices of the nonlinear optical material for the beams and light (or refractive indices averaged along the light propagation direction) are defined as n1, n2, and n3, respectively, and a phase mismatch amount Δk is defined as follows: Δk=n3(2π/λ3)?n1(2π/λ1)?n2(2π/λ2), the periodic structure has a period Λ given by:Λ=2π/|Δk|=1/|n3/λ3?n1/λ1?n2/λ2|, and when a temperature of the nonlinear optical material is defined as T, 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:|∂Δk/∂T|?0.5 (K?1cm?1). 12. The optical wavelength converting method according to claim 11, 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:|∂Δk/∂T|?0.1 (K?1cm?1).