Wen Shuang-chun

Experimental Demonstration of a Low-Pass Spatial Filter Based on a One-Dimensional Photonic Crystal with a Defect Layer

It is predicted theoretically that a one-dimensional photonic crystal (PC) with a defect layer has an incident-angle dependent transmittance. Growing a multilayer of this PC structure on a BK7 glass substrate by means of thermal vacuum evaporation, we have experimentally measured its transmittance at near-infrared wavelength. The measured transmittance are in good agreement with the theoretical prediction if the influence of random errors in the layer thicknesses resulting from the deposition process is excluded. This work suggests that a one-dimensional PC with a defect layer can be fabricated as a two-dimensional near-field low-pass spatial filter.

Formation of Hot Images in Laser Beams through a Self-defocusing Kerr Medium Slab

A nonlinear hot image is usually thought as of a special case of self-focusing, and thus occurs when a laser beam propagates through a slab of self-focusing medium. Here we show theoretically that a hot image may also be formed by a thin slab of self-defocusing medium. The physical origin for this hot image formation is akin to the in-line volume–phase holographic imaging due to the intensity-dependent refractive-index modulation of the self-defocusing medium. Numerical simulations confirm the theoretical prediction and further identify the dependence of the hot image on the beam power, the modulation depth of obscuration and the thickness of self-defocusing medium. The analysis presented here brings new insight into the physics of hot image formation in the high power laser system.

Defect in photonic crystal with negative index material

The transmission property of the photonic crystal containing negative index material is analyzed by means of transfer matrix method. It is demonstrated that a defect mode appears in the conventional Bragg gap and the defect mode is sensitive to the position of the defect cell. For the first time to our knowledge we introduce two defects into such a structure and discuss the dependence of the transmission on the interval of the two defect cells. It is found that a wide degenerate defect mode appears in the Bragg gap, and this degenerate defect mode splits into two different defect modes when the two defect cells become closer.

Enhanced and Tunable Spin Hall Effect of Light upon Reflection of One-Dimensional Photonic Crystal with a Defect Layer

We show that the spin Hall effect of light upon reflection of one-dimensional photonic crystal with a defect layer can be enhanced significantly with a spin-dependent transverse displacement of the beam centroid of several wavelengths of light which is much larger than those reported previously, for horizontal- and vertical-polarization incidence. Under the condition of abrupt phase changes of reflection coefficients however, the spin Hall effect of light could be completely suppressed. Further, we demonstrate that, by tuning the optical parameters of the defect layer, the spin Hall effect of light upon reflection can be switchable for any incident angle and polarization of incidence.

(3+1)-dimensional nonlinear propagation equation for ultrashort pulsed beam in left-handed material

In this paper a comprehensive framework for treating the nonlinear propagation of ultrashort pulse in metamaterial with dispersive dielectric susceptibility and magnetic permeability is presented. Under the slowly-evolving-wave approximation, a generalized (3+1)-dimensional wave equation first order in the propagation coordinate and suitable for both right-handed material (RHM) and left-handed material (LHM) is derived. By the commonly used Drude dispersive model for LHM, a (3+1)-dimensional nonlinear Schrodinger equation describing ultrashort pulsed beam propagation in LHM is obtained, and its difference from that for conventional RHM is discussed. Particularly, the self-steeping effect of ultrashort pulse is found to be anomalous in LHM.

Focal Shift of Paraxial Gaussian Beams in a Left-Handed Material Slab Lens

Focal shift is inevitable in conventional lens systems due to the Fresnel number and angular aperture. In this Letter, we demonstrate that there is no focal shift when a paraxial Gaussian beam passes through a left-handed material slab lens without absorption or gain. However, the effect is exhibited in the presence of absorption or gain, and becomes larger as the absorption or gain increases. When the absorption is equal to the gain, the phenomenon of the focal shift caused by the gain is more obvious. In addition, the field distribution is not affected by the absorption or gain and always remains Gaussian both in internal and external focus planes.

Generation of Efficient Dispersive Waves in Photonic Crystal Fibers

Based on the generalized nonlinear Schrodinger equation, we investigate efficient dispersive wave (DW) generation in a photonic crystal fiber (PCF) by numerical simulation and discuss a way to control DW generation by using an initial input pulse chirp. It is shown that efficient red-shifted DW generation can be obtained in a PCF with negative dispersion slopes. The energy contained in the DWs is considerably decreased for both positively and negatively chirped pulses at the fiber output. This provides us with an opportunity to conveniently and efficiently manipulate the DW generation by controlling the pre-chirp of the soliton. Moreover, we also show that forth-and higher-order dispersion terms play little part in deciding the evolution of DWs.

Integral Equation Method for Electromagnetic Wave Propagation in Stratified Anisotropic Dielectric-Magnetic Materials

X iv :1 00 4. 46 95 v2 [ ph ys ic s. op tic s] 1 7 M ay 2 01 0 Integral equation method for the electromagnetic wave propagation in stratified anisotropic dielectric-magnetic materials SHU Wei-Xing , FU Na, LV Xiao-Fang, LUO Hai-Lu, WEN Shuang-Chun, and FAN Dian-Yuan Key Laboratory for Micro/Nano Optoelectronic Devices of Ministry of Education, School of Computer and Communications, Hunan University, Changsha 410082, China Abstract We investigate the propagation of electromagnetic waves in stratified anisotropic dielectricmagnetic materials using the integral equation method (IEM). Based on the superposition principle, we use Hertz vector formulations of radiated fields to study the interaction of wave with matter. We derive in a new way the dispersion relation, Snell’s law and reflection/transmission coefficients by self-consistent analyses. Moreover, we find two new forms of the generalized extinction theorem. Applying the IEM, we investigate the wave propagation through a slab and disclose the underlying physics which are further verified by numerical simulations. The results lead to a unified framework of the IEM for the propagation of wave incident either from a medium or vacuum in stratified dielectric-magnetic materials.We investigate the propagation of electromagnetic waves in stratified anisotropic dielectric-magnetic materials using the integral equation method (IEM). Based on the superposition principle, we use Hertz vector formulations of radiated fields to study the interaction of wave with matter. We derive in a new way the dispersion relation, Snells law and reflection/transmission coefficients by self-consistent analyses. Moreover, we find two new forms of the generalized extinction theorem. Applying the IEM, we investigate the wave propagation through a slab and disclose the underlying physics, which are further verified by numerical simulations. The results lead to a unified framework of the IEM for the propagation of wave incident either from a medium or vacuum in stratified dielectric-magnetic materials.

Novel transmitter of dark RZ signal based on external modulator

A novel transmitter to generate a dark RZ signal with tunable duty cycle and extinction ratio is proposed, by modifying the process of precoding, modulating and coding. A dark RZ signal is generated simply by using one dual-arm Mach-Zehnder LiNbO3 modulator. We demonstrate experimentally that this optical dark RZ signal can be directly measured by a conventional binary intensity modulation direct detection (IM-DD) receiver. When different values of duty cycles at 2.5 Gbit/s are adjusted, the experimental results show different BER curves and eye diagrams of the optical dark RZ signal.

Compensation for Self-Focusing of Picosecond Pulses in Nd:Glass by Using Cascaded Quadratic Nonlinearity

One of the obstacles in obtaining high power/energy laser sources is self-focusing, which stems from the nonlinear phase shift (B-integral) accumulated during beam propagation in Kerr media. Phase-mismatched second-harmonic generation may impose a nonlinear phase shift on the fundamental with controllable sign and magnitude, which can be used to compensate for self-focusing with a single-pass configuration. We have demonstrated such a possibility for picosecond pulses theoretically and experimentally, and both configurations of pre- and post-compensation by a β-barium borate crystal have been studied in detail. Cascaded second-order nonlinearity-based compensation for self-focusing may provide an auxiliary means to the conventional B-integral control techniques.