Methods and apparatus are disclosed for the nonlinear generation of sum and difference frequencies of electromagnetic radiation propagating in a nonlinear material. A waveguide having a waveguide cavity contains the nonlinear material. Phase matching of the nonlinear generation is obtained by adjusting...http://www.google.co.uk/patents/US6151155?utm_source=gb-gplus-sharePatent US6151155 - Guided wave methods and apparatus for nonlinear frequency generation
