Wen Shuang-Chun

Controllable Raman soliton self-frequency shift in nonlinear metamaterials

Controllable and dispersive magnetic permeability in the metamaterials (MMs) provides us more freedom to harness the propagation of ultrashort electromagnetic pulses at will. Here we discuss the controllability of the Raman soliton self-frequency shift (SSFS) in the MMs with a nonlinear electric polarization. First, we derive a generalized nonlinear Schroedinger equation suitable for few-cycle pulse propagation in the MMs with delayed Raman response, and demonstrate the Raman effect, high-order Raman-related nonlinearity, and high-order nonlinear dispersion terms occurring in this equation. Second, we present a theoretical investigation on the controllability of the Raman SSFS in the MMs. In particular, we identify the combined effects of the anomalous self-steepening (SS), third-order dispersion (TOD), and Raman effect on SSFS. It is shown that the positive SS effect suppresses SSFS; however, the negative SS effect enhances SSFS, and the positive TOD leads to the deceleration of SSFS. Finally, the effects of SS on the SSFS of the second-order soliton are also discussed.

MODULATION INSTABILITY OF FEMTOSECOND OPTICAL PULSES IN LONG OPTICAL FIBERS WITH MINIMUM GROUP-VELOCITY DISPERSION

A new region where modulation stability occurs in the fibers with minimum group-velocity was found due to the fourth-order dispersion effect. The spectral extent of the region is analyzed and found to be affected by initial input power and the dispersion parameter.

Orbit-orbit interaction and photonic orbital Hall effect in reflection of a light beam

We examine the orbit—orbit interaction when a paraxial beam with intrinsic orbital angular momentum (IOAM) reflects at an air—glass interface. The orbital-dependent splitting of the beam intensity distribution arises due to the interaction between IOAM and extrinsic orbital angular momentum (EOAM). In addition, we find that the beam centroid shows an orbital-dependent rotation when seen along the propagation axis. However, the motion of the beam centroid related to the orbit—orbit interaction undergoes a straight line trajectory with a small angle inclining from the propagation axis. Similar to a previously developed spin-dependent splitting in the photonic spin Hall effect, the orbital-dependent splitting could lead to the photonic orbital Hall effect.

Spatiotemporal Instability of Ultrashort Pulses in Dispersive Self-Focusing Media

Spatiotemporal instability in dispersive self-focusing media is investigated on the basis of a modified nonlinear Schrodinger equation (NLSE) beyond the slowly varying envelope approximation. It is found that, for both normal and anomalous dispersions, space-time focusing may lead to the appearance of new temporal instability regions for some range of spatial frequencies. The physical origin of the new instability regions lies in the part of space-time coupling related to the fourth-order dispersion. Furthermore, space-time focusing shrinks the instability regions and slightly reduces the maximum growth rates of the original spatiotemporal instability gain spectra obtained from the standard NLSE.

Filamentation instability of laser beams in nonlocal nonlinear media

The filamentation instability of laser beams propagating in nonlocal nonlinear media is investigated. It is shown that the filamentation instability can occur in weakly nonlocal self-focusing media for any degree of nonlocality and in defocusing media for the input light intensity exceeding a threshold related to the degree of nonlocality. A linear stability analysis is used to predict the initial growth rate of the instability. It is found that the nonlocality tends to suppress filamentation instability in self-focusing media and to stimulate filamentation instability in self-defocusing media. Numerical simulations confirm the results of the linear stability analysis and disclose a recurrence phenomenon in nonlocal self-focusing media analogous to the Fermi-Pasta-Ulam problem.

Small-Scale Self-Focusing of Intense Laser Beams In the Presence of Vector Effect

We extend Bespalov-Talanov (B-T) theory on small-scale self-focusing (SSSF) to include vector effect of a very narrow intense laser beam with application of the vector self-focusing model. The gain spectrum for perturbations is obtained by using the standard linear instability analysis. It is shown that the influence on SSSF of vector effect is closely related to the beam width. For a very narrow beam, the role played by vector effect becomes significant, it reduces the fastest growing frequency and the maximum growth rate, and shortens the frequency range for perturbation growing, and thus deviates the gain spectrum from that of B-T theory.

Switching the direction of spin accumulation in the spin Hall effect of light by adjusting the optical axis of an uniaxial crystal

We theoretically and experimentally investigate a switchable spin Hall effect (SHE) of light in reflection near the Brewster angle at an air-uniaxial crystal interface. We find a large transverse spin splitting near the Brewster angle, whose sign can be altered by rotating the optical axis. As an analogy of the SHE in an electronic system, a switchable spin accumulation in the SHE of light is detected. We are able to switch the direction of the spin accumulation by adjusting the optical axis angle of the uniaxial crystal. These findings may give opportunities for photon spin manipulating and developing a new generation of nano-photonic devices.

Spin Hall effect of a light beam in anisotropic metamaterials

We theoretically investigate a switchable spin Hall effect of light (SHEL) in reflection for three specific dispersion relations at an air-anisotropic metamaterial interface. The displacements of horizontal and vertical polarization components vary with the incident angle at different dispersion relations. The transverse displacements can be obtained with the relevant metamaterial whose refractive index can be arbitrarily tailed. The results of the SHEL in the metamaterial provide a new way for manipulating the transverse displacements of a specific polarization component.

Focusing and phase compensation of paraxial Hermite-Gaussian and Laguerre-Gaussian beams by a negative refractive index material slab

According to angular spectrum representation, formalisms describing paraxial Hermite-Gaussian and Laguerre-Gaussian beams propagating through an isotropic negative refractive index material (NIM) slab are presented. Focusing and phase compensation of paraxial Hermite-Gaussian and Laguerre-Gaussian beams by the slab are investigated. The phase difference of beams caused by Gouy phase shift in air can be compensated by the inverse Gouy phase shift in NIM, thus the phase difference between the object plane and the image equals to zero in certain matching conditions. If conditions of focusing and phase compensation are satisfied simultaneously, intensity and phase distribution at object plane can be reconstructed at the image plane.

Evaluate the Dispersion Parameters for Ultrashort Pulses Propagating in Photonic Crystals

Using the least-squares spline approximation to analyze the photonic band structure,the dispersion parameters of a two-dimensional photonic crystal are quantitatively calculated.Considering the large bandwidth of an ultrashort pulse,average group velocity and average group velocity dispersion are achieved by introducing a weighting factor,which reveals the share of different frequency components.So the pulse evolution can be predicted theoretically.Propagation of ultrashort pulses through the photonic crystals is simulated by using the finite-difference time-domain method.The results of numerical simulations are well consistent with the theoretical predictions.This process for achieving dispersion parameters is valuable for designing photonic-crystal dispersion devices such as dispersion compensator,pulse compressor and pulse stretcher.