To reconstruct three-dimensional (3D) information perfectly, phase and amplitude of incident waves must be controlled simultaneously. However, since the conventional spatial light modulation techniques could control only one component of phase or amplitude, it has very low quality of reconstructed image of its noise. So, the bulky optical filter system is required. We propose novel pixel design for a complex light modulation that can overcome these limitations. This design is based on the principle of the complex value of each pixel by dividing it into three fixed phases and controllable amplitudes. It is implemented to combination of rotated rods and is modulated to a cross polarized component for an incident wave. It has a concept that each amplitude can be controlled by width or length of each rod. In this research, we present the characteristics of the complex spatial light modulation for the proposed metasurface structure by Fourier modal method (FMM) simulation based on the rigorous coupled wave analysis (RCWA) and verify that the proposed design can control the complex light modulation on the higher-order diffraction component. Also, noise-free hologram is verified by the results of reconstructed diffraction patterns using wave optical based simulations to analyze the distribution of complex modulated waves in free space.
Many architectures of near eye display (NED) using a holographic optical element (HOE) come on the market. HOE has already been successfully industrialized due to its easy manufacturing process and small form factor. However, many studies are being conducted to solve degradation effect by the eye glow that the visibility of the user decreases occurred to external light. HOE is generally used as an element of NED for its good angular and wavelength selectivity characteristics. The parameters controlling those characteristics are the refractive index change and the thickness of HOE. Although the selectivity characteristics are optimized by regulating the two parameters, the eye glow occurs because the HOE reacts in parts other than the desired characteristics for sunlight and white light sources. For a fundamental reason, eye glow is further caused by a sudden refractive index change in boundary condition when incident into the HOE from the air. In this study, we figure out that the boundary condition changes continuously by apodization of the refractive index of HOE for eye glow reduction. Also, we calculate the angular and wavelength selectivity efficiency using scalar Fourier modal method (sFMM) based on rigorous coupled-wave analysis (RCWA) according to the thickness and refractive index change, and investigate the relationship between those parameters.
In our previous work, a meta-surface was designed using adjoint-based topology optimization for high-efficiency. However, since the design pattern was complicated and the size of element was small, it was hard to maintain in the actual process and was not appropriate for commercialization. To solve this problem, we use the adjoint inverse design method by applying the local curvature filter algorithm and curvature flow technique in this study. The meta-surface design was conducted using Fourier modal method, based on rigorous coupled-wave analysis. It is assumed that the meta-surface is composed of pixels having a relative dielectric constant of the dielectric material. The dielectric constant distribution in the meta-lattice region is a design variable for optimization, and the dielectric constant of the air layer is converted over the duration. Traditionally, Gaussian filter was used to change to a processable pattern. However, since it does not maintain high efficiency characteristics, we used the local curvature filter (LCF) method. As a result, the results of efficiently finding and filtering small and complex patterns while maintaining characteristics were acquired. The LCF detects it as a local area according to the degree of curvature. The detected area is filtered using a Bernstein filter, and then combined with the global pattern again. In addition, we re-progress filtering for smooth patterns using the curve flow to adjust the curve threshold value to design the meta-surface. Consequently, we propose the method and theory of novel algorithm as a way of maintaining the high efficiency properties of the meta-surface in practice.
This Conference Presentation, Design of wide-viewing angle, full-color, high-definition, computer-generated holograms with off-axis illumination was recorded at SPIE Photonics West 2022 held in San Francisco, California, United States.
Metrology and inspection (MI) processes are established at critical points of the semiconductor manufacturing process in order to maintain a certain yield and also provide information needed for future processes improvements. Typically, the inspection consists of dark-field (DF) inspection and SEM review/classification processes. An optical DF microscopy system (or inspection tool) first detects particles or pattern defects on wafers and obtains their position coordinates. However, due to its limited optical resolution, the DF system is not widely applied in the review process, which requires higher resolution images of the detected defects such as those provided by scanning electron microscopy (SEM) but with a sacrifice of throughput. We propose an innovative idea of applying two (or three) dark-field microscopy images for intermediate defect classification and size estimation under optical resolution. The proposed method utilizes the angular scattering distribution from a defect that is in the Mie scattering domain, which varies depending on both the beam and defect properties (wavelength, polarization, incident angle; shape, size, complex refractive index). It captures three darkfield images of the same wafer by three inter-changeable objectives with different magnification and numerical aperture (NA) values under identical side illumination conditions. We estimate the defect types and sizes simply by investing three measurements. We demonstrated this proposed method to classify and estimate the defect size down to ~ 80nm by an existing UV inspection tool with three DF imaging modes; 1) M15 mode, sampling stance = 150 nm, NA =0.6, 2) M25 mode, sampling distance = 250 nm, NA=0.36, and 3) M40 mode, sampling distance =400 nm, and NA =0.23. We demonstrated its feasibility by an independent SEM measurement of the detected defects.
We describe a novel system named TRVCT (Translating and Rotating Volume Computed Tomography), developed for computed tomography image from large object with simple method and low price. Tomogram images can be acquired when the object is translating and rotating simultaneously with vertical linear array detector. This method is different from the normal X-ray CT completely. We used fan-beam X-ray, and the direction of the detector and rotating axis are in parallel. Because a hundred or thousand tomograms with Z-axis from just one scanning, it has excellent Z-axis resolution and has an advantage that can improve the resolution in X-Y plane with changing translating speed and frequency of data acquisition. There is no ring artifact that is generated frequently in the third generation CT scanner. So, we can have high resolution tomograms from this TRVCT system. The TRVCT can be used to acquire images for large object like tire, engine, or whole car, and it can remove the scattering from X-ray for high resolution images.
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