Abstract: Method and apparatus for the tunable generation of new wavelengths of optical radiation from input sources of predetermined wavelength. Optical radiation from a source (20), or sources, is launched into both the fast and slow axis of a birefringent optical waveguide (12) as pump waves. The pump waves generate new Stokes and anti-Stokes waves through enhanced four photon mixing processes. The Stokes wave is wavelength or frequency shifted from the pump wave by a small amount and exits the end of the optical waveguide (12) where it can be interfaced to various apparatus for utilization. The apparatus preferably employs polarization control means for controlling the polarization of optical radiation launched into the birefringent optical waveguide. The waveguide can also be an optical fiber or planar waveguide structure. The wavelength or radiation generated and output can be tuned by altering the birefringence of the waveguide.