利用非局域前向布里渊相互作用整形非线性光学响应
Shaping nonlinear optical response using nonlocal forward Brillouin interactions
摘要：
我们逐渐习惯了这样一种观念，即光学折射率可以被看作是介质的一种局部性质。在非线性光学的背景下，克尔和拉曼过程都被认为是局部的，这意味着在一个位置的光场不会在空间中的不同位置产生非线性响应。这是因为在材料内产生的电子和声子扰动被限制在小于光波长的区域内。相比之下，布里渊相互作用可以导致高度非局部非线性响应，因为通过布里渊过程产生的弹性波可以占据比光波长大得多的空间区域。这些相互作用的非定域性可以用来设计新型的过程，其中高度离域的声子模式作为一个可工程化的通道，介导在不同的光波导中传播的光波之间的散射过程。这些类型的非局部光机械响应最近已被证明是信息转导的基础，但这种系统的非平凡动力学尚未被探索。在这项工作中，我们表明，三阶非线性过程中产生的空间扩展布里渊有源声子模式涉及混合产品从空间分离，光去耦波导，产生一个非本地的“联合可解释性”。我们进一步探讨了多个声学模式的耦合，并表明，多模声干扰使一个可定制的非局部非线性敏感性，表现出多极频率响应。
英文摘要：
We grow accustomed to the notion that optical susceptibilities can be treated as a local property of a medium. In the context of nonlinear optics, both Kerr and Raman processes are considered local, meaning that optical fields at one location do not produce a nonlinear response at distinct locations in space. This is because the electronic and phononic disturbances produced within the material are confined to a region that is smaller than an optical wavelength. By comparison, Brillouin interactions can result in a highly nonlocal nonlinear response, as the elastic waves generated through the Brillouin process can occupy a region in space much larger than an optical wavelength. The nonlocality of these interactions can be exploited to engineer new types of processes, where highly delocalized phonon modes serve as an engineerable channel that mediates scattering processes between light waves propagating in distinct optical waveguides. These types of nonlocal optomechanical responses have been recently demonstrated as the basis for information transduction, however the nontrivial dynamics of such systems has yet to be explored. In this work, we show that the third-order nonlinear process resulting from spatially extended Brillouin-active phonon modes involves mixing products from spatially separated, optically decoupled waveguides, yielding a nonlocal 'joint-susceptibility'. We further explore the coupling of multiple acoustic modes and show that multi-mode acoustic interference enables a tailorable nonlocal-nonlinear susceptibility, exhibiting a multi-pole frequency response.
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