Quasi-phasematched waveguides periodically poled by applying an external field for efficient SHG

Abstract

The realization of a compact and low cost blue coherent light source is essential for high-density optical data storage, laser printing, and color display applications. So far laser-diode-based second-harmonic-generation (SHG) devices seems to be the most convenient way of making a violet or blue light sources. The conversion efficiency of quasi-phasematching (QPM) SHG is highest when the periodic reversal of the sign of the nonlinear coefficient d of the material occurs in the phasematching period[1]. The QPM-SHG allows the use of any component of the nonlinear susceptibility tensor, and by selecting the period of the sign inversion of the d coefficient, light with arbitrary wavelengths within the transparency range of the nonlinear materials can be generated. A high conversion efficiency QPM-SHG device has the following requirements: 1) it should be composed of materials with large nonlinear coefficients and good transparency, 2) its waveguide should have low loss with strong mode confinement, 3) a good overlap between the fundamental and the second harmonic field, and 4) the periodically inverted domain structure should be obtainable at any depth in the waveguide suitable for first order QPM. The last requirement, in particular, is most important for taking full advantage of the materials.