Holographic Optical Elements (HOEs) have emerged as a pivotal technology in enhancing holographic Augmented Reality (AR) display systems. This paper presents an innovative approach that utilizes an off-axis arrangement with an HOE to secure a wide field of view up to 55°, making significant strides in volumetric reduction compared to conventional 4f filtering systems. However, a challenge arises from Bragg mismatch in the HOE, which creates aberrations. Our work proposes a method for compensating these aberrations on a voxel-by-voxel basis, substantially improving the quality of the holographic display. Limitations such as the 2mm maximum size of the eye box due to the diffraction limit of the spatial light modulator (SLM) are acknowledged, but we suggest potential solutions such as using the HOE substrate glass as a waveguide and incorporating an array of lenses with an eye tracker for pupil tracking. Our findings offer significant contributions to the holographic display technology landscape and suggest promising avenues for future research.
Digital holographic microscopy has been widely adopted in the field of biology because of its ability of quantifying phase information. Unlike those conventional transmission-type phase imaging techniques, reflective digital holographic microscopy can be applied in the field of display industry or semiconductor industry for inspecting unwanted defects in a certain fabrication process. Consequently, it is necessary and required to achieve large field of view and resolution enhancement to meet the demands on the fast and accurate shape measurement. To increase the minimum resolution, we are going to adopt programmable illumination patterns by the use of fast-activating digital micro-mirror devices (DMDs) referring to Fourier ptychographic illumination. In this work, to expand space bandwidth product in reflection-type digital holographic microscopy (RDHM) configuration, we apply a fast-activating digital micro-mirror device for a amplitude-type spatial light modulator and a micro-lens array in the reference arm of a conventional RDHM.
Depth extraction and recovery from the recorded image have been studied and applied in many fields such as biology, robotics, and computer vision. In some researches, the aperture in the imaging system is coded as a particular function in order to distinguish relative distances from the focal plane or recognize sampled points from the recorded image and the image captured through this coded aperture is useful to retrieve blurred images or acquire depth maps. These studies are associated with the shape of point spread function (PSF). In some approaches, diffraction-based engineered PSFs such as double-helix and cubic phase are applied to extract the depth information. In this paper, we propose a depth measurement method based on the optical analysis of the pupil function. It is well known that the PSF is represented as a Fourier transform of the product of pupil function and spherical phase in a coherent imaging system. Also, it is possible to estimate the intensity of the PSF corresponding to the distance of the object in an incoherent imaging system. Then the depth information is extracted from a snapshot image by inverse transform of the image.
To measure object wave in digital holography, the phase-shifting technique is popular by changing the phase of the reference wave. A piezo actuator (PZT) is usually used as a device to shift the phase. In a case to obtain the phase information of color object with multiple wavelengths, four-step phase-shifting algorithm with quarter wavelength shift is not convenient since the amount of the phase shift is difference according to each wavelength. In this paper, the generalized four-step phase-shifting method is proposed and experimentally verified to obtain color digital hologram using an image sensor with a Bayer pattern for capturing interference pattern shifted phase by one PZT.
Recently the technology of hologram receives a lot of interest owing to its advantages and many researches on hologram recordings have been actively studied. In some studies, digital hologram printing methods have lots of applications because of the ability to record large area hologram based on the technique of holographic stereogram. The holographic stereogram printing method records the hologram composed of hogels which are the unit of the hologram recorded at once. This method has advantages in flexibility of the size since it records the hologram hogel by hogel. In addition, the hologram printer records not only wavefront of real objects captured by charge coupled device (CCD) but also hologram patterns of virtual objects calculated by computer-generated hologram (CGH) algorithm. In previous systems, it is difficult to implement the hologram in high resolution because of the low numerical aperture of hogels. In this paper, we suggest the method of recording high-resolution hologram using binary wavefront pattern and discuss the optical modulation properties of the printed binary pattern.
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