Patent ID: 8358460

Claim:
A method of preventing a back conversion process occurring during generation of a conversion wave by coupling a second harmonic wave of a pump wave with a signal wave in a waveguide that includes an optical substrate that is periodically poled and that has a waveguide part extending along a wave propagation direction, the method comprising: launching the pump and signal waves into the waveguide part to generate the second harmonic wave from the pump wave and the conversion wave from an interaction of the second harmonic wave with the signal wave; determining a location, in terms of a propagation distance, where the energy of the conversion wave starts to decline due to destructive interference between the signal wave and the conversion wave; sectioning the optical substrate at the location so that the optical substrate is divided into at least two sections that are oriented along the wave propagation direction, each of the sections having a wave input facet and a wave output facet, the wave output facet of an upstream one of the sections facing the wave input facet of a downstream one of the sections; and disposing a band-pass filter layer at the location and between the wave output facet of the upstream one of the sections and the wave input facet of the downstream one of the sections to filter out the signal wave to prevent the signal wave from destructively interfering with the conversion wave, thereby preventing the back conversion process.