Simultaneous second-harmonic generation and third-harmonic generation in one-dimensional photonic crystal slabs consisting of centrosymmetric materials

We report simultaneous second-harmonic generation (SHG) and third-harmonic generation (THG) in photonic crystals slabs (PCS) by strongly coupling fundamental light into waveguide modes. The spectra of the SHG and THG signals are investigated as a function of both the wavelength and the polarization state of the fundamental beam. The second-order nonlinearity obtained in the PCS can be comparable with that of asymmetric materials, although the PCS consists of centrosymmetric materials. The phase matched results show that the THG is ascribed to the third-order nonlinearity, as well as to the cascading of second-order nonlinearity. The experiment demonstrates a way to obtain multiwavelength coherent sources in nanostructures.