Soliton and dispersive wave generation with third-order dispersion and temporal boundary.

We investigate the pulse evolution and energy conservation condition at the temporal boundary under third-order dispersion. When the fundamental soliton crosses the temporal boundary and forms two reflected pulses and one transmitted pulse, the power of the transmitted pulse first increases and then decreases as the incident spectrum shifts toward the blue side. If the transmitted spectrum lies in the anomalous group-velocity dispersion region, second-order soliton is formed and dispersive wave is radiated. We present a modified phase-matching condition to predict the resonance frequencies. The predicted results are in good agreement with the results obtained by numerically solving the nonlinear Schrödinger equation.

Effect of chirp on pulse reflection and refraction at a moving temporal boundary.

The reflection and refraction of chirped Gaussian pulse at a moving step refractive-index boundary are investigated. When a chirped Gaussian pulse crosses a temporal boundary, the shape of the reflected spectra is distorted by adjusting chirp parameters. However, the transmitted spectra retain the Gaussian shape. The shape of the final output spectra is the same if the absolute values of the chirp are the same. By changing the chirp values, we can control the energy of the reflected and transmitted pulses, and the splitting distance of the pulse at the temporal boundary. By adjusting the time-dependent refractive index, chirped Gaussian pulses can experience total internal reflection at the temporal boundary. When pulse splitting occurs in an anomalous dispersion region, the velocity of the transmitted pulse decreases.

Manipulation of dispersive waves emission via quadratic spectral phase.

We investigate the process of dispersive waves (DWs) emitted from Gaussian pulse (GP) with an initial quadratic spectral phase (QSP). We show that the radiation of DWs is strongly affected by the QSP parameter. The conversion efficiency and resonant frequency of DWs are effectively enhanced and controlled by tuning the sign and magnitude of the initial QSP. At variance with the case of pure GP, the DWs emission is first advanced and then delayed for negatively QSP modulated GPs; while it is always delayed for positively QSP modulated GPs. We present a modified phase-matching formula that allows us to predict DWs spectral peaks. The resonant frequencies predicted by the phase-matching condition are in very good agreement with the results obtained from the numerical simulation based on the generalized nonlinear Schrödinger equation. The results presented here can be utilized as a effective tool to manipulate DWs emission for applications such as frequency conversion.

Controlling cosine-Gaussian beams in linear media with quadratic external potential.

We investigate both analytically and numerically the propagation dynamic of on-axis and off-axis cosine-Gaussian (CG) beams in a linear medium with quadratic external potential. CG beam propagation evolves periodically with a period depended on the potential depth (α) and whether the beam shape is symmetrical with respect to optical axis. In each period, the CG beam first splits into two sub-beams with different accelerated direction; they then reverse the accelerated direction owing to the quadratic external potential and finally merge again to reproduce its initial shape, and the whole process repeats periodically. The intensity oscillation period of the off-axis CG beam is double times than that of the on-axis one. At the special position, the beam (or spectral) shape is strongly related to the initial spectral (beam) shape. The corresponding scaled relationship is that the spatial intensity Ix (or spatial frequency axis k) is α times the spectral intensity Ik (or space axis x). The interaction of two spatially separated CG beams still exhibit periodic evolution with complex structure in the regime of focal point. The propagation dynamics of two-dimensional CG beams are also presented. When the propagation distance is exactly an integer multiple of half period, there are four focal points in the diagonal position.

Thermally switchable bifunctional plasmonic metasurface for perfect absorption and polarization conversion based on VO2.

Perfect absorption and polarization conversion of electromagnetic wave (EM) are of significant importance for numerous optical applications. Vanadium dioxide (VO2), which can be converted from insulating state to metallic state by being exposed to different temperatures, is introduced into a metallic square loop to constitute a switchable bifunctional plasmonic metasurface for perfect absorption and polarization conversion. Combined theoretical analyses and numerical simulations, the results show that at temperature T = 356 K, the metasurface acts as a perfect absorber with nearly 91% absorptance at the wavelength of 1547 nm. When the temperature decreases to T = 292 K, the metasurface expresses as a high efficiency (about 94%) polarization converter with the polarization conversion ratio up to 86% around 1550 nm. The designed bifunctional metasurface has plenty of potential applications such as energy harvesting, optical sensing and imaging. Moreover, it can also provide guidance to research tunable, smart and multifunctional devices.