Numerical investigation of slow solitons in Bragg gratings with a hyperbolic tangent apodization

This paper numerically and analytically investigates the formation and propagation motion of optical soliton in the Bragg grating.We choose the fibre Bragg grating with hyperbolic tangent apodization in the middle section in order to obtain slower solitons.Optical fibre soliton but not Bragg grating soliton is used as input pulse in the discussion,which is much more approximate to the light source for the practical purpose.We discuss in detail the effects of the soliton’s velocity with some parameters in the process of transmission.The results show that by choosing special parameters,one can make the soliton slow-down with a little distortion and energy decay and obtain tunable time-delay on a small scale.     

Two-soliton interaction in the vicinity of a defect inside a fiber Bragg grating and its application for obtaining an all-optical memory

We study the interaction between two Bragg solitons in the vicinity of a defect inside a fiber Bragg grating. A soliton that is trapped in the defect can be released by launching a second soliton. The effect can be used to obtain an all-optical memory that is not strongly sensitive to the phase and the timing arrival of the solitons.     

Holographic solitons

We propose a new kind of an optical spatial soliton: the holographic soliton. This soliton consists of two mutually coherent field components that interfere, induce a periodic change in the refractive index, and simultaneously are Bragg diffracted from the grating. Holographic solitons are formed when the broadening tendency of diffraction is balanced by phase modulation that is due to Bragg diffraction from the induced grating. Holographic solitons are solely supported by cross-phase modulation arising from the induced grating, not involving self-phase modulation at all.     

有限宽度布拉格原子层中光子囚禁与移动孤子的研究

研究二能级原子层宽度对一维共振吸收布拉格反射镜中自感应透明光孤子形成的影响.结果表明：在有限宽度的二能级原子层中仍可激发稳定的移动孤子，其激发条件对原子层宽度依赖不大；然而静止孤子的存在条件却敏感地依赖于原子层的宽度，二能级原子层宽度只有小于某一特定值时，光脉冲才能演化成静止孤子. 关键词： 有限宽度 周期结构 移动孤子 静止孤子     

Kerr类非线性介质周期结构中的慢Bragg孤子

在耦合模理论的基础上,给出了一维无限大Kerr类非线性介质周期结构中的孤波解,并且指出,孤波的振幅依赖于入射频率以及脉宽两个参量.同时也证明,在布拉格共振极限条件下,孤波解可以简化成所谓的“隙孤子”解或是“慢布拉格孤子”解 关键词： 孤波 慢布拉格孤子 隙孤子 耦合模理论     

光纤布拉格光栅中的隙孤子存在条件

提出光纤布拉格光栅中产生隙孤子的条件和参量制约关系。利用非线性耦合模式方程建立光纤布拉格光栅中孤子的传播方程,通过扰动方法建立了参量的微分方程,计算得到参量近似解。以周期非线性光学介质中隙孤子存在的条件为依据,数学计算分析得到两组参量关系不等式。最终通过数值计算说明了这些参量之间存在制约关系和物理意义。从而理论上说明了在光纤布拉格光栅中隙孤子存在需要选择适当参量。为光纤布拉格光栅中产生隙孤子的实验和进一步的工程应用提供了理论基础。     

Creating very slow optical gap solitons with a grating-assisted coupler

We show that optical gap solitons can be produced with velocities down to 4% of the group velocity of light using a grating-assisted coupler, i.e., a fiber Bragg grating that is linearly coupled to a non-Bragg fiber over a finite domain. Forward- and backward-moving light pulses in the non-Bragg fiber(s) that reach the coupling region simultaneously couple into the Bragg fiber and form a moving soliton, which then propagates beyond the coupling region. Two of these solitons can collide to create an even slower or stopped soliton.     

Dissipative soliton in an amplifier with a Bragg grating

A dissipative soliton in an amplifier with a Bragg grating is numerically investigated by direct simulation of Maxwell-Bloch equations. The result of the simulation indicates that a solitary wave can exist in such a medium. However, the pulse shape of the dissipative soliton is asymmetrical because of the gain saturation effect. This gain saturation effect results from the high power of the ultrashort dissipative soliton. The influence of amplifier gain on the solitary wave is also investigated.     

Raman gap solitons

We show that an intense pump pulse, detuned far from the Bragg resonance of a nonlinear periodic structure, can excite a gap soliton at a wavelength within the band gap that corresponds to the Raman shift of the medium. This Raman gap soliton is a stable, long-lived, quasistationary excitation that exists within the grating even after the pump pulse has passed. We find both stationary solitons as well as slow Raman gap solitons with velocities as low as 1% of the speed of light. The predicted phenomena should be observable in fiber Bragg gratings and other nonlinear photonic band gap structures.     

Zero-n gap soliton

Periodic structures consisting of alternating layers of positive-index and negative-index materials have a novel bandgap at the frequency at which the average refractive index is zero. We show that, in the presence of a Kerr nonlinearity, this zero-n gap can switch from low transmission to a perfectly transmitting state, forming a nonlinear resonance or gap soliton in the process. This zero-n gap soliton is omnidirectional, in contrast to the usual Bragg gap soliton of positive-index periodic structures.     

Efficient method for launching in-gap solitons in fiber Bragg gratings using a two-segment apodization profile

We theoretically demonstrate what is a new method for efficient launching of in-gap solitons in fiber Bragg gratings. The method is based on generating a soliton outside the grating bandgap. Then, the soliton is adiabatically coupled into the bandgap by using its particlelike behavior. We compare our method to a previously published launching scheme that is based on generating the soliton directly within the grating bandgap. When using low-intensity incident pulses, the transmission efficiency of our method is three times higher than that of the previously published scheme.     

Observation of discrete gap solitons in binary waveguide arrays

We report an experimental study of discrete gap solitons in binary arrays of optical waveguides. We observe self-focusing indicating soliton generation when the inclination angle of an input beam is slightly above the Bragg angle and show that the propagation direction of the emerging gap soliton is influenced by the effect of interband momentum exchange.     

Nonlinear responses of the periodic structure composed of single negative materials

We investigate the nonlinear responses of the one-dimensional periodic structure containing alternate single negative materials. The transmission property of this nonlinear periodic structure is studied and the bistable behavior is found. Similar as in the linear periodic structure, the transmission property of this nonlinear structure in the zero phase (zero-?) gap region is found to be relatively insensitive to the incident angle from 0° to 30°, in comparison with that in the Bragg gap. Especially, the transmissions associated with the zero-? gap reach the peaks at almost the same input intensity for different incident angles. Another merit of the transmission property in the zero-? gap is that a lower threshold is needed to achieve the bistability than in the Bragg gap. The electric field distribution in the system is further studied. We observe the zero-? gap soliton and compare it with the usual Bragg gap soliton. The differences between these two kinds of solitons are analyzed, and the zero-? gap soliton is shown to be insensitive to the incident angle. In the end, we find that the transmission and the soliton in the zero-? gap are also weakly dependent on the loss and the scaling in contrast to that in the Bragg gap.     

Optical Pulse Compression Schemes That Use Nonlinear Bragg Gratings

Nonlinear optical pulse compression of picosecond pulses typically requires long lengths of optical fiber and multiple components. Periodic structures, such as fiber Bragg gratings, are highly dispersive at wavelengths outside of the photonic bandgap. This implies that such gratings can be used as very short all-fiber compressors. In this paper a number of such compression schemes are reviewed involving uniform and nonuniform fiber Bragg gratings, relying on both soliton and nonsoliton compression principles. Experimental results supporting the corresponding underlying theory are also presented. Finally, an extension of one of the compression schemes is shown, which allows the generation of adjustable high-repetition rate soliton trains.     

Optical Pulse Compression Schemes That Use Nonlinear Bragg Gratings

Nonlinear optical pulse compression of picosecond pulses typically requires long lengths of optical fiber and multiple components. Periodic structures, such as fiber Bragg gratings, are highly dispersive at wavelengths outside of the photonic bandgap. This implies that such gratings can be used as very short all-fiber compressors. In this paper a number of such compression schemes are reviewed involving uniform and nonuniform fiber Bragg gratings, relying on both soliton and nonsoliton compression principles. Experimental results supporting the corresponding underlying theory are also presented. Finally, an extension of one of the compression schemes is shown, which allows the generation of adjustable high-repetition rate soliton trains.     

光纤布拉格光栅中隙孤子的EPP方法分析

提出了利用EPP方法分析光纤布拉格光栅中隙孤子的解。基于非线性耦合模式方程(NLCME)定性地分析了无微扰条件下的隙孤子参数与孤子的其它特性的关系。利用EPP方法分析了隙孤子的能量特性。证明了隙孤子的速度影响形态特性和能量分布。从理论上解释了已观察到的一系列隙孤子的试验现象,对光纤布拉格光栅中产生隙孤子的应用具有理论意义。     

Optical zoomeron as a result of beatings of the internal modes of a Bragg soliton

A new solution of two-wave Maxwell-Bloch equations has been obtained analytically and numerically. It describes the propagation of an oscillating nonlinear optical solitary wave, or optical zoomeron, in a one-dimensional periodic resonant Bragg structure. It has been shown that the appearance of large oscillations in the velocity and total amplitude of Bloch modes of the pulse is caused by beating of internal modes of the perturbed Bragg soliton.     

Optical AND gate based on soliton interaction in a fiber Bragg grating

Using computer simulations, we demonstrate an optical cascadable AND gate based on soliton interaction in a fiber Bragg grating. A single soliton that is launched into the device is backreflected. When two solitons are launched, one of the solitons is transmitted while the other is backreflected. The time delay between the solitons may be few times longer than the duration of the solitons. We show that the interaction causes an increase in the frequency of one of the solitons that enables its transmission through the grating bandgap.     

Creation of solitons and vortices by bragg reflection of Bose-Einstein condensates in an optical lattice

We study the dynamics of Bose-Einstein condensates in an optical lattice and harmonic trap. The condensates are set in motion by displacing the trap and initially follow simple semiclassical paths, shaped by the lowest energy band. Above a critical displacement, the condensate undergoes Bragg reflection. For high atom densities, the first Bragg reflection generates a train of solitons and vortices, which destabilize the condensate and trigger explosive expansion. At lower densities, soliton and vortex formation requires multiple Bragg reflections, and damps the center-of-mass motion.     

Trapping of slowly moving or stationary two-color gap solitons

We address the important problem of excitation of gap solitons of a parametric nature, which are sustained in periodically corrugated frequency-doubling media near Bragg resonance with both the fundamental frequency and its second harmonic. We demonstrate that a zero-velocity soliton can be trapped in a finite Bragg structure by the quiescence of two counterpropagating moving solitons, which in turn might be formed by injection of appropriate light pulses at a single carrier frequency.