Non-linear optical material, method of manufacturing the same and optical wavelength converter

An optical wavelength converter comprising an optical cavity and an optical wavelength conversion crystal of a non-linear optical material inserted in said optical cavity, said non-linear optical material comprising a salt formed from an organic compound and an optically active organic acid selected from the group consisting of phenylsuccinic acid, malic acid, mandelic acid, leucinic acid, lactic acid, tartaric acid, abietic acid, quinic acid, camphoric acid, camphor-10-sulfonic acid, methoxyphenylacetic acid, 2-methoxy-2-trifluoromethylphenylacetic acid and phenylpropionic acid, wherein said organic compound has a conjugated .pi. electron system containing both electron donor and acceptor groups and has at least one substituent group selected from the group consisting of --NH.sub.2, --NH--, and ##STR6## which is located outside of said conjugated .pi. electron system wherein:

• said conjugated .pi. electron system is derived from a material selected from the group consisting of benzene derivatives, pyridine derivatives, pyrimidine derivatives, pyrazine derivatives, triazine derivatives, pyrane derivatives, pyrrole derivatives, pyrroline derivatives, pyrazole derivatives, imidazole derivatives, furan derivatives, thiophene derivatives, thiazole derivatives, naphthalene derivatives, quinoline derivatives, indole derivatives, benzimidazole derivatives, indazole derivatives, benzofuran derivatives, benzothiazole derivatives, vinyl derivatives, and allyl derivatives;
• said electron donor groups are selected from the group consisting of amino groups, monosubstituted amino groups, disubstituted amino groups, hydroxyl groups, and alkoxy groups;
• said electron acceptor groups are selected from the group consisting of nitro groups, cyano groups, and carbonyl groups.