Third-order optical nonlinearity in silicon nitride films prepared using magnetron sputtering and application for optical bistability

We investigate the third-order optical nonlinearity in silicon nitride (SiN) films prepared using magnetron sputtering. The large nonlinear refractive index n₂ in SiN prepared at room temperature of a value of -2.00 × 10^-16 m²/W and the nonlinear absorption coefficient β of 1.44 × 10^-9 m/W are determined by the Z-scan method at a wavelength of 1064 nm and a pulse duration of 25 ps. The n₂ is three orders of magnitude larger than that in SiN films prepared by the chemical vapor deposition method and at a wavelength of 1.55 μm. The enhanced n₂ up to -6.27 × 10^-16 m²/W and the slightly changed β, indicating an enhanced ratio of |Reχ⁽³⁾|/|Imχ⁽³⁾|, are further obtained in the annealed samples. Such a change is probably due to the crystallization of the films. The optical bistability in SiN resonant waveguide grating (RWG) is numerically studied. The low threshold intensity around 300 MW/cm² in the RWG is obtained.