Liu Shu-Tian

Finite-difference time-domain analysis of optical bistability with low threshold in one-dimensional nonlinear photonic crystal with Kerr medium

Abstract We present a nonlinear finite-difference time-domain (NFDTD) analysis of optical bistability (OB) in a one-dimensional nonlinear photonic crystal (1D-NPC) with Kerr medium under Debye relaxation. The properties of the defect modes in a symmetrical structure 1D-NPC and the way to obtain low threshold of OB is discussed in detail. The OB threshold depends on the optical thickness and refractive index of defect layer and the number of symmetrical layers. When the half-width of defect mode is small enough and frequency of incident light and linear refractive index are selected carefully, the low threshold OB is able to be obtained. By numerical simulation threshold ∼ 130 KW / m 2 is obtained, correspond refractive index change is only about 0.04.

Low Threshold Bistable Switching by the Nonlinear One-Dimensional Photonic Crystal

In the approximation of the fast Debye relaxation of a nonlinear Kerr medium, the nonlinear finite-difference time-domain method is derived to simulate numerically the one-dimensional nonlinear photonic crystal sandwiched by the Kerr medium. Bistable switching with a low threshold intensity of 0.01kW/cm2 is obtained, and the corresponding refractive index change of the Kerr media is about 0.038.

Superposition of orbital angular momentum of photons by a combined computer-generated hologram fabricated in silica glass with femtosecond laser pulses

This paper introduces a novel method to realize the superposition of orbital angular momentum of photons by combined computer-generated hologram (CCGH) fabricated in silica glass with femtosecond laser pulses. Firstly, the two computer-generated holograms (CGH) of optical vortex were obtained and combined as a CCGH according to the design. Then the CCGH was directly written inside glass by femtosecond laser pulses induced microexplosion without any pre-or post-treatment of the material. The vortex beams with different vortex topological charges (including new topological charges) have been restructured using a collimated He-Ne laser beam incidence to the CCGH normally. A theoretical and experimental explanation has been presented for the generations of the new topological charges.

Nonclassical Properties of Superposition of Two Coherent States Shifted in Phase by 3π/2

We consider the quantum superposition of two coherent states shifted in phase by 3π/2, |α and |−iα, as well as special states that are characterized solely with respect to amplitude α. According to analysis of nonclassical properties such as oscillatory and sub-Poissonian distribution of photon numbers, photon antibunching, quadrature squeezing, and negativity of Wigner function, it is concluded that the considered superposition state is a nonclassical state. Also, the special state is found to exhibit even stronger nonclassical features when relative phase of the superposition is equal to the average photon number |α|2.

Entangled States Based on Two Coherent States 3π/2 out of Phase

Entangled states based on two coherent states 3π/2 out of phase with each other, i.e. |α and ei|−iα, as well as on a special state with a relative phase = |α|2, are constructed. By analysing the amount of entanglement it is evident that entangled states based on this special state can be used as an excellent resource for quantum teleportation. It is also revealed that these entangled states possess some nonclassical features.

Control of the Entanglement between Two Josephson Charge Qubits

We consider a model which consists of two coupled superconducting charge qubits by sharing a large Josephson junction. The time evolution of entanglement between two Josephson charge qubits is investigated by employing the concurrence. We examine the influence of the initial mean photon number, the relative phase and the amplitude of the two qubits on the time evolution of entanglement. The results show that the initial mean photon number, the relative phase and the amplitude of the two qubits play an important role in the evolution of entanglement.

Numerical analysis of surface plasmon nanocavities formed in thickness-modulated metal–insulator–metal waveguides

The enhancement characteristics of the local field in the surface plasmon nanocavities are investigated numerically. The cavity is constructed by placing a defect structure in the thickness-modulated metal–insulator–metal waveguide Bragg gratings. The characteristic impedance based transfer matrix method is used to calculate the transmission spectra and the resonant wavelength of the cavities with various geometric parameters. The finite-difference time-domain method is used to obtain the field pattern of the resonant mode and validate the results of the transfer matrix method. The calculation and simulation results reveal the existence of resonant wavelength shift and intensity variation with structural parameters, such as the modulation period of the gratings, the length and the width of the defect structure. Both numerical analysis and theoretical interpretation on these phenomena are given in details.

Localization and Threshold of Bistable Switching by Gap-Edge Shifting

We numerically investigate the localization behaviour of light propagation in a one-dimensional nonlinear photonic crystal (1D-NPC). It is found that the localization of a high gap-edge mode is better than that of a low one, so that the switching threshold of the 1D-NPC with plus Kerr L-layers is much lower than that with minus Kerr H-layers. For a structure of 16 periods, the threshold of the structure with nonlinear L-layers is about 1/10 of that with nonlinear H-layers in the same level of nonlinear refractive coefficient.

Enhanced Excited-State Optical Nonlinearities in a Novel Metallophthalocyanine Compound (C12H25O)8PcPb

Nonlinear absorption in a novel metallophthalocynine compound (C12H25O)8PcPb was investigated by the Z-scan technique with the irradiation of 8 ns laser pulses at the wavelength of 532 nm. The large optical limiting response was observed. The nonlinear absorption cross section was obtained by the simulation with a simplified rate equation model in which excited triplet-triplet state absorption is dominant. The excited-state absorption cross section and its effective ratio to the ground-state absorption cross section are larger than those of C60. The attenuation factor for (C12H25O)8PcPb is 2.5 times larger than that of C60, which is induced by the heavy atom lead interposition.

Properties of Linear Entropy in k-Photon Jaynes–Cummings Model with Stark Shift and Kerr-Like Medium

The time evolution of the linear entropy of an atom in k-photon Jaynes–Cummings model is investigated taking into consideration Stark shift and Kerr-like medium. The effect of both the Stark shift and Kerr-like medium on the linear entropy is analyzed using a numerical technique for the field initially in coherent state and in even coherent state. The results show that the presence of the Kerr-like medium and Stark shift has an important effect on the properties of the entropy and entanglement. It is also shown that the setting of the initial state plays a significant role in the evolution of the linear entropy and entanglement.