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arXiv 1207.2091nlin.PSphysics.optics
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嵌入$χ^{(2)}$-非线性格点对的线性晶格中的对称和非对称局域模

Symmetric and asymmetric localized modes in linear lattices with an embedded pair of $χ^{(2)}$-nonlinear sites

V. A. Brazhnyi, B. A. Malomed

摘要:

我们构建家庭的对称,反对称,和非对称的孤立模式在一维双色晶格的二次谐波产生($χ^{(2)}$)的非线性集中在一对网站放置在距离$l$。晶格可以被构建为光波导阵列。得到的解决方案在一个隐式的分析形式,这是明确的情况下,相邻的非线性网站,$l=1$。通过计算小扰动的特征值分析了系统的稳定性,并通过直接仿真进行了验证。在级联限制,这对应于大的失配$q$,系统变得相当于最近研究的单组分晶格与两个嵌入网站进行立方非线性。随着$q$的变化,模式发生了质的变化。特别是,在$l\geq 2$,破缺分岔(SBB),从对称的非对称状态,是超临界和亚临界的小和大的$q$值,分别,而分岔总是超临界的$l=1$。在实验中,第二和第一类型之间的相变的相应变化可以通过经由输入光束的波长改变失配来实现。对称模的存在阈值(最小总功率)恰好在$q=0$处为零,这表明使用低功率光束创建孤立模的可能性。解族的稳定性也随着$q$的变化而变化。

英文摘要:

We construct families of symmetric, antisymmetric, and asymmetric solitary modes in one-dimensional bichromatic lattices with the second-harmonic-generating ($χ^{(2)}$) nonlinearity concentrated at a pair of sites placed at distance $l$. The lattice can be built as an array of optical waveguides. Solutions are obtained in an implicit analytical form, which is made explicit in the case of adjacent nonlinear sites, $l=1$. The stability is analyzed through the computation of eigenvalues for small perturbations, and verified by direct simulations. In the cascading limit, which corresponds to large mismatch $q$, the system becomes tantamount to the recently studied single-component lattice with two embedded sites carrying the cubic nonlinearity. The modes undergo qualitative changes with the variation of $q$. In particular, at $l\geq 2$, the symmetry-breaking bifurcation (SBB), which creates asymmetric states from symmetric ones, is supercritical and subcritical for small and large values of $q$, respectively, while the bifurcation is always supercritical at $l=1$. In the experiment, the corresponding change of the phase transition between the second and first kinds may be implemented by varying the mismatch, via the wavelength of the input beam. The existence threshold (minimum total power) for the symmetric modes vanishes exactly at $q=0$, which suggests a possibility to create the solitary mode using low-power beams. The stability of solution families also changes with $q$.

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