KEYWORDS: Holography, Polarization, Dielectric polarization, Multiplexing, Camera shutters, Diffraction, Photonics, Dielectrics, Wavelength division multiplexing, Signal to noise ratio
The null reconstruction can be used to realize multi-channel recording, thereby improves the storage capacity. In this work, phenanthrenequinone-doped poly(methyl methacrylate) photopolymer (PQ/PMMA) that is sensitive to the polarized wave, is used as the recording medium. To better reach the null reconstruction, we need to control exposure time and intensity in the recording stage. By adopting the suitable experimental parameters, the crosstalk between the two holograms is negligible. The analysis of the experimental results shows that the ratio of optical powers of the signal wave to that of reference wave is 1:8-1:10, the exposure time is about 12 minutes, and the optimal signal-to-noise ratio can reach 21:1.
In this letter, we employ vector wave polarization holography theory based on the dielectric tensor description. Newly developed vector wave polarized holography theory breaks up the limitation of paraxial approximation in polarization holograms. Various interesting phenomena have been investigated, the faithful reconstruction is of particular significance. The faithful reconstruction (FR) effect indicates that the polarization state of the reconstruction wave is identical to that of the signal wave, it can be achieved process when the intensity and polarization holographic grating attained a balance during after exposure. The FR property related to the linearly, circularly and elliptically polarization is investigated in our previous work. In our experiment, the recording medium we use is the bulk polarization holographic recording material of phenanthrenequinone-doped polymethyl methacrylate photopolymer (PQ-PMMA). The mixed mass ratio of methyl methacrylate (MMA), azobisisobutyronitrile (AIBN) and phenanthrenequinone (PQ) are 100:1:1. Under the cross-angle of π/2 inside the recording media, the polarized holographic reconstruction of the circular polarization recorded by a horizontal linear polarization wave is calculated. It is found that the circularly polarized signal can be faithful reconstruction by arbitrarily polarized reading waves. However, when the polarization of the reading wave is orthogonal to the polarization of the reference wave, it will occur the null reconstruction (NR). The FR technology will provide a simpler and more effective method for a circular polarization generator. At the same time, the NR technology can quickly detect that the polarized wave is vertical polarization.
Based on tensor polarization holography, the variation of exposure response coefficient with the increase of exposure energy under different recording process is introduced in this paper. We find that different recording processes have different effects on the exposure response coefficient. However, at the beginning of exposure, there is an initial value of the exposure response coefficient independent of the holographic recording process. With this special phenomenon, polarization modulation of reconstructed wave can be easily realized at low exposure energy, such as faithful reconstruction, orthogonal reconstruction and null reconstruction.
Polarization holography has great potential in Ultra-high-definition (UHD) information diplay and data storage. Due to the faithful reconstruction in polarization holography, the storage capacity is further improved easily. In this paper, a device for generating vector vortex beam is demonstrated using the faithful reconstruction characteristics. Through the analysis of the experimental results, it is found that the helical phase order corresponding to different polarization states is different in the transmission process. It shows the independence of vector vortex beam propagation. This method has a certain research space in optical storage, and application prospect in optical micromanipulation optical tweezers.
Based on polarization holography theory, the plane bifocal vector lens is studied. In previous studies, the bifocal vector lens were limited to cross-angle π/2 and bulk materials. However, when the two waves are orthogonal circularly polarized state, the plane bifocal vector lens can be realized, and the limitation of cross-angle π/2 and bulk materials can be broken. The lens produces corresponding focus output through the reading wave with different polarization states, which can be used for large-area optical element research.
Collinear holography data storage (CHDS) is a promising solution for “cold data” storage in the big data age. Studies adopt “amplitude type” and “phase type” orthogonal reference have been sequentially reported for the performance improvement of CHDS. Data from different users can be storage and readout separately by different orthogonal reference, which is meaningful for the application of security data storage. In this paper, a newly “phase type” orthogonal reference specified by a Hadamard orthogonal matrix is proposed for identity information storage. Each one Hadamard vector on behalf of a “phase type” reference, and the symbols “1” and “-1” in Hadamard matrix stands for the phase of 0 and pi of the reference pixel. Several different data pages are recorded using different orthogonal reference in advance, and there is only the specific data page which is matched to the orthogonal reference can be reproduced in the process of reconstruction. The action mechanism of orthogonal reference is analyzed, and the feasibility of the system is verified by numerical simulations and primary experiments.
A single-shot non-interferometric phase retrieval method in holographic data storage is proposed to solve the problems that undetectability for phase by detector directly and unstability caused by interferometric detection. Embedded data are inserted in iterative Fourier transform algorithm to shorten iterations sharply. For avoiding embedded data occupying the code rate, we propose a collinear system to refer to the reference beam, which is always known, as the embedded data. Finally, fast stable phase information reading is realized because of single-shot non-interferometric detection and fast phase retrieval within only several iterations.
In this paper, we propose a frequency expanded method based on non-interferometric phase retrieval which can retrieve complex multi-level phase image by using only 1 times Nyquist frequency. Our proposed method utilizes the property of frequency spectrum periodicity and is the unique method with non-interferometry due to the intensity detection directly on the Fourier domain. For a regular phase image, same spacial frequency means same spectrum width. We choose a rectangular window with the same spacial frequency to the phase image and consider normalized Fourier intensity distribution of the rectangular window as the envelope of that of the phase image. After normalizing the spectrum of the phase image, we can expand its Fourier frequency with 1 times Nyquist size to other higher order frequency positions. Therefore, we can generate high-order frequencies artificially from low-order frequency which help us to retrieve phase image accurately and quickly.
Non-interferometric phase retrieval is a fundamental technique for phase-modulated holographic data storage due to its advantages of easy implementation, simple system setup, and robust noise tolerance. Usually, the iterative algorithm of non-interferometry needs hundreds of iteration numbers to retrieve phase accurately, which decreased the data transfer rate severely. Strong constraint conditions, such as embedded data, can be used on the phase data page to reduce the iteration numbers. However, introducing embedded data will reduce the code rate of the system. We proposed a method that combined the single-shot interferometric method with the non-interferometric iterative Fourier transform algorithm method. We used the phase decoding result by single-shot interferometry as the embedded data in the process of non-interferometry. Therefore, no extra embedded data are needed in the signal code. We realized the code rate improvement as well as keeping fast data transfer rate. In the demonstration, we recorded a four-level phase pattern and retrieved the phase correctly. The bit error rate of phase retrieval is less than 1% within 20 iterations, which proves our approach is practical. In our case, the code rate is increased by two times.
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