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.

中文翻译：

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使用非局部前向布里渊相互作用塑造非线性光学响应

我们已经习惯了这样一种观念，即光敏度可以被视为介质的局部特性。在非线性光学的背景下，克尔过程和拉曼过程都被认为是局部的，这意味着一个位置的光场不会在空间的不同位置产生非线性响应。这是因为材料内产生的电子和声子干扰被限制在一个小于光波长的区域。相比之下，布里渊相互作用会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空间中远大于光波长的区域。可以利用这些相互作用的非局部性来设计新型过程，其中高度离域的声子模式作为可设计的通道，在不同的光波导中传播的光波之间调解散射过程。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，但此类系统的重要动力学尚未得到探索。在这项工作中，我们展示了由空间扩展的布里渊有源声子模式产生的三阶非线性过程涉及来自空间分离、光学解耦波导的混合产物，产生非局部“联合敏感性”。我们进一步探索了多种声学模式的耦合，并表明多模式声学干扰可实现可定制的非局部非线性磁化率，表现出多极频率响应。