Electric field induced and natural second order nonlinearity in amorphous dielectric films: From chalcogenide glasses to (ultra) silicon-rich SiNx and SiOx

Applying a dc electric field to dielectric films of arsenic sulfide, silicon rich nitride and silicon rich oxide the symmetry of these amorphous materials is broken and as a result electric field induced second harmonic generation is observed. In addition a natural field free susceptibility contribution is detected. From the quadratic field dependence of the second harmonic signal the field dependent second order susceptibilities are experimentally determined exhibiting values rivalling traditional nonlinear crystals. From the results also the basic third order susceptibility is derived which shows a strong dependence on the Si content of the SiNx and SiOx films. Finally a quasi bound state in continuum in an extended square 2D array of pillars on a SiNx-waveguide is used to enhance the TM-polarised second harmonic signal.