Since the inception of holographic technology, its application value has been widely recognized. Among its applications, holographic optical elements have become important optical devices in various research fields due to their compact size, lightweight, and ease of fabrication. As an advanced theory of traditional holography, polarization holography enhances the ability to control the light field by adding the dimension of polarization. Therefore, the holographic optical elements can more comprehensively manipulate the amplitude, phase, and polarization of the light field in the spatial domain. Starting with the principles of polarization holography, we introduce phenomena observable through polarization holography, such as faithful reproduction and zero-order reproduction, which are not seen in traditional holography. Based on these phenomena, we elaborate on the research progress of polarization holography in the fabrication of various light field manipulation and detection devices. Finally, we analyze and forecast the future development trends of polarization holography technology, highlighting key scientific issues worthy of further attention and research.
The event camera is a biomimetic dynamic vision sensor with advantages such as high time resolution, wide dynamic response range, and low power consumption. It can continuously capture changes in light intensity within the field of view. Developing visual measurement solutions based on event cameras is crucial for addressing dynamic problems. However, event-based measurement systems face two significant challenges. Firstly, event cameras output asynchronous event streams, which lose spatial information during transmission, making it difficult to reference traditional vision measurement algorithms. Secondly, event cameras lack reliable filtering algorithms, leading to poor-quality restored event frames, which are insufficient for reliably calculating image features. Our study outlines the development process of event cameras and reviews research on event-based target tracking. We also discuss advancements in event camera calibration, event-based structured light measurement, and event-based autofocus techniques. The 3D measurement scheme based on event cameras encounters issues with the unreliability of event stream data features and low measurement accuracy. By studying spatio-temporal information extraction algorithms, we aim to improve measurement accuracy. Developing high-speed event camera measurement systems and designing efficient solutions with low-bandwidth, low-power, and small computation will further advance the field of high-speed visual measurement.
To achieve higher accuracy in distortion correction with a limited number of marking points, we propose a method for optimal arrangement of marking points and reverse fitting distortion correction based on Zernike polynomials. In this method, we do not directly obtain the distortion distribution by fitting the position errors of marking points in the measurement results. Instead, we first fit the distortion errors based on the true positions of the components and then recover the distortion distribution through a reverse solution, which effectively avoids high-order errors introduced by the distortion itself. Additionally, we establish an algorithm for solving the marking point distribution by minimizing the matrix condition number and obtain the optimal arrangement coordinates for marking points based on Zernike polynomials. Compared with traditional methods, our proposed method improves the correction accuracy by more than 7 times with fewer marking points. This method has been successfully applied in the testing and processing of a Φ150 mm double-curvature elliptical mirror (asphericity of 8.86 mm, maximum distortion of 79 mm), achieving an average correction accuracy of 0.252 mm. The final surface accuracy, represented by the root mean square (RMS) error, reaches 0.029λ, which strongly supports the manufacturing of important optical components.