Wavelength conversion by quasi phase matching and the manufacture and use of optical articles therefor

An optical article for use in a wavelength conversion system, said optical article comprising at least one optical conversion segment consisting of a single crystal containing a series of aligned sections of optical materials selected from (a) materials having the formula K.sub.1-X Rb.sub.X TiOMO.sub.4 where x is from 0 to 1 and M is selected from P and As and (b) materials of said formula wherein the cations of said formula have been partially replaced by at least one of Rb.sup.+, Tl.sup.+ and Cs.sup.+, and at least one of Ba.sup.++, Sr.sup.++ and Ca.sup.++, with the provisos that at least one section is of optical materials selected from (b) and that for optical materials selected from (b) wherein x is greater than 0.8, the cations of said formula are partially replaced by at least one of Tl.sup.+ and CS.sup.+ and at least one of Ba.sup.++, Sr.sup.++ and Ca.sup.++, wherein said sections are selected so that the sum of the product of the length of each section in the direction of alignment and the .DELTA.k for that section is equal to about 2.pi.N where N is an integer other than zero, and so that the nonlinear optical coefficient of at least one section is changed relative to the nonlinear optical coefficient of at least one adjacent section;

• wherein the .DELTA.k for each section is the difference between the sum of the propagation constants for the incident waves for the wavelength conversion system in that section and the sum of the propagation constants for the generated waves for the wavelength conversion system in that section.

A process for preparing a channel waveguide for a wavelength conversion system comprising the steps of:

• (1) providing the z-cut surface of a z-cut substrate of single crystal material having the formula K.sub.1-X Rb.sub.X TiOMO.sub.4 wherein x is from zero to one and M is P or As with an optically smooth surface;
• (2) providing a molten salt containing cations selected from the group consisting of Rb.sup.+, Cs.sup.+ and Tl.sup.+ and cations selected from the group consisting of Ba.sup.++, Sr.sup.++ and Ca.sup.++ with the proviso that when x is greater than 0.8, the molten salt contains cations selected from Tl.sup.+ and Cs.sup.+, in an amount effective to provide upon exposure to said optically smooth surface at a selected temperature for a selected time, sufficient cation replacement to change the index of refraction with respect to the index of refraction of said substrate and to provide a nonlinear optical coefficient which is changed with respect to the nonlinear optical coefficient of the substrate;
• (3) applying a masking material on said substrate to provide a pattern of aligned areas along a portion of said optically smooth surface which are alternately masked with a material resistant to said molten salt and unmasked;
• (4) immersing said masked substrate in said molten salt at said selected temperature for said selected time, thereby providing cation replacement in said unmasked areas;
• and
• (5) removing the masking material from said substrate;
• wherein the length of said masked and unmasked areas being selected such that after said cation replacement in the unmasked areas, a channel waveguide is provided at said portion of the optically smooth surface which comprises at least one optical conversion segment consisting of a series of aligned sections of nonlinear optical materials within a crystal;
• and such that the sum for the series of sections of the product of the length of each section and the .DELTA.k for that section is equal to about 2.pi.N where N is an integer other than zero;
• wherein the .DELTA.k for each section is the difference between the sum of the propagation constants for incident waves for the wavelength conversion system in that section and the sum of the propagation constants for generated waves for said wavelength conversion system in that section.

A method for producing a channel waveguide for a wavelength conversion system, the channel waveguide having at least one optically smooth surface which comprises at least one optical conversion segment consisting of a series of aligned sections of nonlinear optical materials within a crystal such that the sum for the series of sections of the product of the length of each section in the direction of optical propagation and the .DELTA.k for that section is equal to about 2.pi.N, where N is an integer other than zero, wherein the .DELTA.k for each section is the difference between the sum of the propagation constants for incident waves for the wavelength conversion system in that section and the sum of the propagation constants for the generated waves for said wavelength conversion system in that section, said method comprising the steps of:

• providing the z-cut surface of a z-cut substrate of single crystal material, said material having the formula K.sub.1-X Rb.sub.X TiOMO.sub.4 wherein x is from zero to one and M is P or As, with an optically smooth surface, said optically smooth surface having a masking material applied so as to provide a pattern of aligned areas along a portion of said optically smooth surface which are alternately masked with a material resistant to a molten salt and unmasked so as to provide at least one masked area and at least one unmasked area;
• immersing said substrate in said molten salt at a selected temperature for a selected time so as to promote cation replacement in said at least one unmasked area;
• wherein said molten salt contains cations selected from the group consisting of Rb.sup.+, Cs.sup.+ and Tl.sup.+ and cations selected from the group consisting of Ba.sup.++, Sr.sup.++ and Ca.sup.++ with the proviso that when x is greater than 0.8, the molten salt contains cations selected from Tl.sup.+ and Cs.sup.+, in an amount effective to provide, upon exposure to said optically smooth surface at said selected temperature for said selected time, sufficient cation replacement to change the index of refraction of said at least one unmasked area with respect to the index of refraction of said substrate and to provide a nonlinear optical coefficient in said at least one unmasked area which is changed with respect to the nonlinear optical coefficient of the substrate.