It is shown that a transparent birefringent element whose eigenstates are a pair of elliptical polarizations with principalaxes along the x and y axes, sandwiched between a pair of orthogonal halfwave plates with principal axes along directions at 45 deg to the x and y axes, is equivalent to an element with the same eigenstates and eigenvalues but with the fast and the slow eigenstates interchanged. The device thus produces the inverse of the original unitary transformation. A similar result holds for a puredichroic element. With electrically switchable halfwave plates such a device can be used to switch the sign of optical activity or to rotate through 90 deg, without any moving parts, a linear retarder or a linear polarizer.
Implementation of nearly arbitrary spatially-varying polarization transformations: a non-diffractive and non-interferometric approach using spatial light modulators
Polarization Multiplexed Diffractive Computing: All-Optical Implementation of a Group of Linear Transformations Through a Polarization-Encoded Diffractive Network
University of California, Los Angeles（加州大学洛杉矶分校）；California NanoSystems Institute (CNSI)（加州纳米系统研究所（CNSI））
由于机器学习的变革性进展，光学计算的研究最近引起了人们的极大关注。在不同的方法中，由空间工程透射表面组成的衍射光学网络已被证明用于全光学统计推断和使用无源自由空间光学层执行任意线性变换。在这里，我们介绍了一种偏振复用衍射处理器，通过使用深度学习训练的单个衍射网络来全光学地执行多个任意选择的线性变换。在该框架中，预先选择的线性偏振器的阵列被定位在各向同性的可训练透射衍射材料之间，并且不同的目标线性变换（复值）被唯一地分配给输入/输出偏振状态的不同组合。通过使用与分配给不同输入/输出偏振组合的复值线性变换中的每一个对应的输入/输出场的数千个示例，经由深度学习和误差反向传播来训练和优化该偏振复用衍射网络的传输层。我们的结果和分析表明，当可训练的衍射特征/神经元数目（N）接近N_p x N_i x N_o时，单个衍射网络可以成功地逼近并全光学地实现一组任意选择的目标变换，误差可以忽略不计，其中N_i和N_o分别表示输入和输出视场的像素数，N_p是指分配给不同输入/输出偏振组合的唯一线性变换的数目。这种偏振复用全光衍射处理器可以在光学计算和基于偏振的机器视觉任务中找到各种应用。
Universal Polarization Transformations: Spatial programming of polarization scattering matrices using a deep learning-designed diffractive polarization transformer
University of California, Los Angeles（加利福尼亚大学洛杉矶分校）；California NanoSystems Institute (CNSI)（加州纳米系统研究所）
Emergence of Pascal's triangle in cascaded polarization optics: an intuitive framework for field transformation
Center for Optical and Electromagnetic Research, College of Optical Science and Engineering（光学与电磁学研究中心，光电学院）；College of Integrated Circuits and Optoelectronic Chips, Shenzhen Technology University（集成电路与光电子芯片学院，深圳技术大学）；School of Electronics, Electrical Engineering, and Computer Science, Queen’s University Belfast（电子、电气与计算机科学学院，贝尔法斯特女王大学）；Centre for Quantum Materials and Technologies, School of Mathematics and Physics Queen’s University Belfast（量子材料与技术中心，数学与物理学院，贝尔法斯特女王大学）
Quadratic Quantum Polarimetry with Entangled Photon Pairs
ARC Centre of Excellence for Transformative Meta-Optical Systems (TMOS), Department of Electronic Materials Engineering, Research School of Physics, The Australian National University（澳大利亚国立大学）；Institute of Applied Physics, Abbe Center of Photonics, Friedrich Schiller University Jena（耶拿弗里德里希·席勒大学应用物理研究所）；Opto-Electronics and Measurement Techniques, Advanced Electronics Centre, Faculty of Information Technology and Electrical Engineering, University of Oulu（奥卢大学信息技术与电气工程学院高级电子中心光电子与测量技术部门）；Institute of Quantum Precision Measurement, State Key Laboratory of Radio Frequency Heterogeneous Integration, College of Physics and Optoelectronic Engineering, Shenzhen University（深圳大学物理与光电工程学院量子精密测量研究所）；Aston Institute of Photonic Technologies, Aston University（阿斯顿大学光子技术研究所）
