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Most of the existing metasurfaces are effective for the incident wave with the specific circularly polarized (CP) or linearly polarized (LP) state, that is the polarization-sensitive metasurface. This drawback dramatically hinders the practical use of the metasurface. Herein, this paper presents a strategy of polarization-insensitive transmissive microwave metasurfaces to manipulate the incident wave with arbitrary CP and LP states. The metasurface consists of polarization-insensitive unit cells. For the left circularly polarized (LCP) and right circularly polarized (RCP) incident waves, the same abrupt phase covering 0° to 360° can be realized by combining the Pancharatnam–Berry (PB) and resonant phases. As the arbitrary LP wave can decompose into the LCP and RCP waves, metasurfaces consisting of designed unit cells are valid for any polarization states. The polarization-insensitive transmissive microwave metalens and orbital angular momentum multiplexing metasurface working at 23 GHz are devised for verification. Simulation and measurement results verify the availability of the approach. The proposed method is suitable for designing microwave-transmissive metasurfaces capable of polarization insensitivity.

In this paper, we propose a new kind of circular Airy beam whose spectrum is imposed an initial quadratic phase modulation (QPM). Unlike common abruptly autofocusing beams, we find that such modulated circular Airy beams (MCAB) at image plane, i.e., initial plane, may be morphed into conventional Airy patterns or Bessel-like patterns in spatial regime, depending on the magnitude of QPM. We further investigate the propagation characteristics of the MCAB both analytically and numerically. It is found that the focal intensity, as well as the size of focal spot, do not change with the QPM, but the latter greatly affects the focal trajectory and the focal position of MCAB. In particular, we show that, for the case of Airy pattern, MCAB will exhibit a dual abruptly focusing behaviors having the same focal intensity as well as size of focal spot, where there is one focus behind the image plane, and the another one is in front of it. On the other hand, for the case of Bessel-like pattern, the dual abruptly foci are simultaneously observed behind the image plane for positive QPM but in front of it for negative QPM, thus leading to the formation of an elegant optical bottle with paraboloidal shape. Such novel dual focusing behaviors are expected to be applied in the field of optical trapping and particle acceleration.

In this paper, we put forward a novel method for the management of optical collapse through controlling anomalous nonlinear diffraction (NLD) originating from the vectoral effect in metamaterials with simultaneous cubic electric and magnetic nonlinearity, particularly focusing on the unusual behaviors different from those in ordinary positive-index materials. First, NLD in metamaterials can be positive or negative, which makes it possible for us to offer greatly enhanced design freedom to manipulate the behavior of optical collapse at will. Then, it is further demonstrated that the negative NLD can arrest the catastrophic self-focusing of optical wave; however, the positive NLD will lead to the acceleration of its occurrence, as opposed to the case in ordinary positive-index materials. Our analysis is performed by directly numerically solving the nonlinear Schrödinger equation, as well as by using the modulation theory, both showing consistent results. These findings show that NLD in metamaterials can provide a more powerful tool in controlling the collapse of optical wave when compared with the corresponding case in ordinary positive-index materials.

In this paper, we investigate the dynamical behaviors of the modulation instability (MI) of copropagating optical beams in fractional coupled nonlinear Schrödinger equations (NLSE) with the aim of revealing some novel properties different from those in the conventional coupled NLSE. By applying the standard linear stability method, we first derive an expression for the gain resulting from the instability induced by cross-phase modulation (CPM) in the presence of the Lévy indexes related to fractional effects. It is found that the modulation instability of copropagating optical beams still occurs even in the fractional NLSE with self-defocusing nonlinearity. Then, the analysis of our results further reveals that such Lévy indexes increase the fastest growth frequency and the bandwidth of conventional instability not only for the self-focusing case but also for the self-defocusing case, but do not influence the corresponding maximum gain. Numerical simulations are performed to confirm theoretical predictions. These findings suggest that the novel fractional physical settings may open up new possibilities for the manipulation of MI and nonlinear waves. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the novel behavior of induced focusing in nonlinear metamaterials (MMs) through designing probe-pump configuration, where the coupled waves may simultaneously experience negative refractive index or positive refractive index, or one experiences positive refractive index and another experiences negative refractive index both analytically and numerically. It is shown that cross-phase modulation (XPM) in MM not only brings some new features to the behavior of induced focusing, but also makes it possible in the ordinary positive-index materials (OMs), where it is otherwise impossible. First, we reveal that weak probe beam can be focused by strong pump beam even when their centers are completely overlapping each other. Moreover, it is found that the separated distance between coupled waves has an optimal value, which results in the strongest focusing of probe beam. Finally, another most notable property is that a spatial induced focusing is found to occur for different combinations of the signs of refractive index decided by the probe and pump beams, respectively, implying that a spatial XPM in MMs can be used as a more powerful tool for controlling the inducing focusing, when compared with the corresponding case in OMs. Our findings demonstrate that MMs can provide us unique opportunities unattainable in OMs to manipulate the all-optical control of optical focusing behavior through the new physical mechanism of XPM. [ABSTRACT FROM AUTHOR]

We report on the generation of superbroad spectrum bunched noise-like pulses from a passively mode-locked erbium-doped fiber laser, in which the cavity is made of purely anomalous dispersion fibers. The maximum 3 dB spectral bandwidth of the pulse is about 98 nm. We show numerically that the superbroad spectrum of the pulse is caused by the fiber birefringence. [ABSTRACT FROM AUTHOR]

We present a numerical study of the propagation dynamics of accelerating and decelerating truncated Airy pulses (TAPs) in the anomalous dispersion region of optical fibres, with inclusion of the Raman scattering effects, by analysing their cross-correlation frequency resolved optical gating traces. We identify the differences between the evolution dynamics of a decelerating and accelerating TAP. It is shown that the main lobe of the pulse is capable of shedding solitons, which are delayed due to the Raman effects. For the decelerating pulse, however, the soliton is dragged from the original pulse and never meets the input oscillatory Airy tail due to the deceleration of both the pulse and the soliton. The rest of the decelerating pulse rebuilds a new Airy waveform with a stronger degree of truncation compared with that of the incident pulse. For the accelerating TAP, the soliton collides continuously with the tail of the pulse and thus gains further energy by means of their nonlinear interaction. As a consequence, the remaining pulse cannot develop a new Airy waveform. In addition, under the same conditions, the Raman-induced frequency shift of the accelerating TAP is much larger compared with that of the decelerating one. [ABSTRACT FROM AUTHOR]