Baldacci L, Zanotto S, Biasiol G, Sorba L, Tredicucci A
Opt Express. 2015 Apr 6;23(7):9202-10. doi: 10.1364/OE.23.009202.
In order to extend the Coherent Perfect Absorption (CPA) phenomenology to broadband operation, the interferometric control of absorption is investigated in two-port systems without port permutation symmetry. Starting from the two-port theory of CPA treated within the Scattering Matrix formalism, we demonstrate that for all linear two-port systems with reciprocity the absorption is represented by an ellipse as function of the relative phase and intensity of the two input beams, and it is uniquely determined by the device single-beam reflectance and transmittance, and by the dephasing of the output beams. The basic properties of the phenomenon in systems without port permutation symmetry show that CPA conditions can still be found in such asymmetric devices, while the asymmetry can be beneficial for broadband operation. As experimental proof, we performed transmission measurements on a metal-semiconductor metamaterial, employing a Mach-Zehnder interferometer. The experimental results clearly evidence the elliptical feature of absorption and trace a route towards broadband operation.
为了将相干完美吸收（CPA）现象学扩展到宽带操作，我们在没有端口置换对称性的双端口系统中研究了吸收的干涉控制。从散射矩阵形式体系中处理的CPA双端口理论出发，我们证明，对于所有具有互易性的线性双端口系统，吸收由一个椭圆表示，该椭圆是两个输入光束的相对相位和强度的函数，并且它由器件的单光束反射率和透射率以及输出光束的相位失配唯一确定。在没有端口置换对称性的系统中，该现象的基本特性表明，在这种不对称器件中仍然可以找到CPA条件，而这种不对称性对于宽带操作可能是有益的。作为实验证明，我们使用马赫-曾德尔干涉仪对金属-半导体超材料进行了透射测量。实验结果清楚地证明了吸收的椭圆特征，并为宽带操作指明了一条途径。
