The Interaction Of Electro-optic And Nonlinear Optic Effects In Dielectric Superlattice

The electro-optic and nonlinear effects in LiNbO3optical superlattice are studied. Firstly, the four-section periodically poled lithium niobate is designed to realize polarization insensitive nonlinear frequency conversion, including second harmonic generation and sum frequency generation. And then we discuss the electro-optic effect in periodically poled LiNbO3with a defect, and realize an electromagnetic induced transparency-like transmission. A low-voltage electro-optic modulator is proposed based on this structure. At the end, Raman scattering is discussed in an ionic-type phononic crystal.1. Polarization insensitive second harmonic generation is proposed in the periodically poled lithium niobate. The sample consists of three sections. External electric field could be selectively applied to them to regulate the polarization states of fundamental wave. Y-polarized and z-polarized fundamental wave both generates z-polarized second harmonic. And so when fundamental wave containing both y-polarized and z-polarized components is propagated through the sample, the generated second harmonic will interfere with each other and the sample cannot realize polarization insensitive frequency doubled. And then we design a four-section periodically poled lithium niobate to realize polarization insensitive second harmonic generation. The sample consists of four sections. External electric field could be selectively applied to them to regulate the polarization states of fundamental wave and second harmonic. In a case, a y-polarized pumping fundamental wave generates a z-polarized second harmonic and a z-polarized fundamental wave generates a z-polarized second harmonic. If the domain structure is well designed, the fundamental wave with an arbitrary polarization state could realize efficient frequency doubled.2. Polarization independent sum frequency generation is proposed in the periodically poled lithium niobate. The sample consists of four sections. External electric field could be selectively applied to them to induce polarization rotation between the ordinary and extraordinary waves. The sum frequency generation dependency on the signal wave’s polarization states are investigated, which exhibits great polarization-insensitivity. The light intensity of the converted sum frequency wave keeps at the same level with arbitrary signal wave’s polarization states. The structure could be used in single photon detection and optical communication system.3. We study the electro-optic effect in periodically poled lithium niobate with a central defect, and electromagnetically induced transparency-like transmission is observed. With an electric field applied, light satisfying the phase matching condition experiences polarization rotation then turns back. The output light keeps its original polarization. If a polarizer is placed at the outlet end, the corresponding light always may pass through freely with phase variation. On the other hand, light with a neighboring wavelength is blocked. Then we obtain an electromagnetically induced transparency-like spectrum and realize tunable group delay meanwhile. A low-voltage electro-optic modulator is proposed on the basis of this structure.4. We study the long-wavelength optical properties such as polariton excitation resulting from the coupling between lattice vibrations and electro-magnetic waves in an ionic-type phononic crystal, which is similar to the ionic crystals. The fundamental equations of the coupled motion are similar to the Huangkun equations in form. The dispersion relation of polariton excitation could be calculated according to the equations. And then Raman scattering is discussed in the microwave band because of the similarity to the real ionic crystal in an ionic-type phononic crystal.