A wavelength conversion optical element using a nonlinear optical effect of a device structure in which wavelength conversion efficiency rises as targeted when the length of a waveguide is increased is provided. The element adopts a waveguide structure using lithium niobate of a second-order nonlinear optical material. Wavelength conversion regions are formed to correspond to two linear waveguides extending in parallel to each other on a plane of the planar structure and correspond to the lengths of the two linear waveguides. One end side of the linear waveguide is an incident side of excitation light and one end side of the linear waveguide is an emission side of wavelength converted light. The linear waveguides excluding the incident side and the emission side are joined by a bent waveguide. Second-order nonlinear optical media forming the linear waveguides have polarization inversion structures in which directions of spontaneous polarization are periodically inverted with respect to a propagation direction of light.

A method, apparatus, and system for non-linear optical process. A first light of a first wavelength is routed in a first loop in a main nonlinear optical waveguide. The first loop has a first length for the first light of the first wavelength. A second light of a second wavelength is routed in a second loop that includes portions of the main nonlinear optical waveguide and a first extension optical waveguide. The second loop has a second length for the second light of the second wavelength. A third light of a third wavelength is routed in a third loop that include portions of the main nonlinear optical waveguide and a second extension optical waveguide. The third loop has a third length for the third light of the third wavelength.

A method, apparatus, and system for non-linear optical process. A first light of a first wavelength is routed in a first loop in a main nonlinear optical waveguide. The first loop has a first length for the first light of the first wavelength. A second light of a second wavelength is routed in a second loop that includes portions of the main nonlinear optical waveguide and a first extension optical waveguide. The second loop has a second length for the second light of the second wavelength. A third light of a third wavelength is routed in a third loop that include portions of the main nonlinear optical waveguide and a second extension optical waveguide. The third loop has a third length for the third light of the third wavelength.

An optical waveguide structure comprises a first coupler and a second coupler that, in combination, direct a first-wavelength light to travel through a nonlinear-optical waveguide, the two couplers and an extension waveguide but not a secondary waveguide, a first resonator loop is defined for which the first-wavelength light is resonant. The two couplers, in combination, also direct a second-wavelength light to travel through the nonlinear-optical waveguide, the two couplers and the secondary waveguide but not the extension waveguide, wherein a different second resonator loop is defined for which the second-wavelength light is resonant.

An optical waveguide structure comprises a first coupler and a second coupler that, in combination, direct a first-wavelength light to travel through a nonlinear-optical waveguide, the two couplers and an extension waveguide but not a secondary waveguide, a first resonator loop is defined for which the first-wavelength light is resonant. The two couplers, in combination, also direct a second-wavelength light to travel through the nonlinear-optical waveguide, the two couplers and the secondary waveguide but not the extension waveguide, wherein a different second resonator loop is defined for which the second-wavelength light is resonant.

An optical waveguide structure comprises a nonlinear optical waveguide comprising a nonlinear optical material having a second order nonlinear coefficient that changes with a direction of light propagation. A first portion of the nonlinear optical waveguide in which a light propagating through the first portion is affected by a positive value of a second order nonlinear coefficient. A second portion of the nonlinear optical waveguide in which the light propagating through the first portion is affected by a negative value of a second order nonlinear coefficient, wherein a set of dimensions in the nonlinear optical waveguide in the first portion and the second portion is selected to cause the light to have a phase walk-off that is an odd multiple of 180 degrees.

An optical waveguide structure comprises a nonlinear optical waveguide comprising a nonlinear optical material having a second order nonlinear coefficient that changes with a direction of light propagation. A first portion of the nonlinear optical waveguide in which a light propagating through the first portion is affected by a positive value of a second order nonlinear coefficient. A second portion of the nonlinear optical waveguide in which the light propagating through the first portion is affected by a negative value of a second order nonlinear coefficient, wherein a set of dimensions in the nonlinear optical waveguide in the first portion and the second portion is selected to cause the light to have a phase walk-off that is an odd multiple of 180 degrees.

Improved efficiency for nonlinear optical interactions is provided by using strongly confining waveguides for simultaneous imposition of dispersion design constraints at two or more dispersion orders. Quasi-phase-matching allows for phase-matching to be accomplished independently of the waveguide design, which helps provide sufficient design freedom for the dispersion design.

A method for fabricating an optical waveguide comprises: providing a sample of lithium niobate doped with magnesium oxide and having at least one grating of periodic domain inversion defined therein; applying a layer of metallic zinc to a surface of the sample over the at least one grating using sputter deposition; heating the sample in an atmosphere of pure oxygen to cause the zinc to indiffuse into the lithium niobate to form a waveguiding layer of increased refractive index under the surface of the sample; and using a dicing blade to cut two substantially parallel channels along a length direction of the at least one grating, to define a ridge waveguide between the two channels.

With a wavelength conversion device based on a nonlinear optical effect, when arrayed waveguides including an intended nonlinear waveguide are fabricated, unwanted slab waveguides are inevitably formed. The slab waveguides can cause an erroneous measurement in the selection of a waveguide having desired characteristics from the arrayed waveguides. The erroneous measurement can lead to redoing steps for fabricating the wavelength conversion device and a decrease in the yield and inhibit the evaluation of the characteristics in selection of the waveguide and the subsequent fabrication of the wavelength conversion device from being efficiently performed. A wavelength conversion device according to the present invention includes a plurality of waveguides formed on a substrate, and a plurality of slab waveguides that are arranged substantially in parallel with and spaced apart from the plurality of waveguides, and a guided light attenuator is formed in each of the slab waveguides. The guided light attenuators allow efficient selection of a waveguide having desired optical characteristics from the plurality of waveguides. The light attenuation by the guided light attenuators can be changed in steps for fabricating the wavelength conversion device.