Dark reaction is a common phenomenon in holographic recording of photoinduced polymer materials, which has some influence on the recording effect of materials. Now we design an experiment to prepare polymethyl methacrylate materials doped with different phenanthrene quinone (PQ) concentrations, and observe their changes in bit error rate, signal-to-noise ratio and diffraction intensity after dark reaction. The results show that the higher the concentration of PQ doping, the higher the diffraction intensity after dark reaction, but too high concentration will lead to the increase of bit error rate and signal-to-noise ratio decrease. It is proved that the material with 1wt% of PQ doping concentration also has lower bit error rate, higher signal-to-noise ratio and relatively higher diffraction intensity after dark reaction.
KEYWORDS: Phase reconstruction, Holography, Data storage, Image processing, Phase shift keying, Image compression, Diffraction, Deep learning, Photonics, Education and training
Holographic data storage systems are candidates for information recording due to their large storage capacity and high transmission rate. In this paper, a phase modulation holographic storage technology with three-grayscale encoding is proposed and implemented. According to the experimental results, if two phase codes in the three-grayscale encoding are relatively close, the performance of phase reconstruction would be degenerated.
The modulation of light is important in phase holographic data storage, and different spatial light modulators have different modulation capabilities for light. In this study, a lens less non-interference phase reconstruction system based on deep learning is applied to evaluate the performance differences of different spatial light modulators in holographic data storage. The performance differences are evaluated, which include the deep learning results versus pixel crosstalk results for phased holographic optical storage.
KEYWORDS: Bragg cells, High speed cameras, Digital micromirror devices, Holography, Data storage, Cameras, Holographic data storage systems, Signal generators, Imaging systems, Digital recording
The frame frequency matching of the Digital Micro-mirror Device (DMD), the acousto-optic modulator (AOM) and high-speed camera can realize the holographic high-speed reading under the reference light changing scene, which greatly improves the data reading speed. In this work, the frame frequency matching to achieve high-speed reading is related to four factors: the resolution and exposure time of the high-speed camera, the duty ratio of AOM, and the phase difference between the signals sent by AOM and DMD. Through the research of the exposure time and resolution of high-speed cameras, the maximum synchronous frame rate of DMD and high-speed cameras can achieve 18KHZ. By synchronizing the frame frequency of both DMD and AOM trigger signals with the signal generator, controlling the duty ratio of AOM and the phase difference of the trigger signals sent to DMD and AOM can enable the high-speed camera to read the reproduction data page near the data recording point, avoiding the waste of storage space. The analysis of the experimental results shows that the camera can read clear information under the conditions of the incident optical power density is 32μw, the AOM duty ratio is larger than 10%, and the phase difference between AOM and DMD is 26°. The realization of DMD, high-speed camera and AOM frequency matching will effectively ensure the reading speed and decoding accuracy of holographic stored data
Displacement multiplexing can improve the storage density of collinear holographic data storage systems and is an essential multiplexing method. This article introduces the use of dark reaction phenomena in recording media to improve the displacement multiplexing effect of collinear holographic data storage systems, and achieves a multiplexing distance of 5 μm.
Exposure intensity affects the diffraction intensity and bit error rate of holographic materials. Now we design the experiment, unify the exposure amount, adjust the intensity of the information light and the recording time, and observe the bit error rate and diffraction intensity after the dark reaction for 1 minute. We verify that holograms with high intensity and short exposure time and dark reaction after 1 minute have lower bit error rate and higher diffraction intensity
KEYWORDS: Data storage, Holography, Deep learning, Tunable filters, Phase retrieval, Education and training, Optical filters, Linear filtering, Data modeling, Signal to noise ratio
Holographic data storage is a powerful potential technology to solve the problem of mass data long-term storage. To increase the storage capacity, the information to be stored is encoded into a complex amplitude. Fast and accurate retrieval of amplitude and phase from the reconstructed beam is necessary during data readout. In this talk, we propose a complex amplitude demodulation method based on deep learning from a single-shot diffraction intensity image and verified it by a non-interferometric lensless experiment demodulating four-level amplitude and four-level phase. By analyzing the correlation between the diffraction intensity features and the amplitude and phase encoding data pages, the inverse problem is decomposed into two backward operators denoted by two convolutional neural networks to demodulate amplitude and phase respectively. The stable and simple complex amplitude demodulation and strong anti-noise performance from the deep learning provide an important guarantee for the practicality of holographic data storage.
KEYWORDS: Deep learning, Crosstalk, Spatial light modulators, Phase retrieval, Phase reconstruction, Diffraction, Data storage, Near field diffraction, Image restoration, Photonics
In the holographic data storage system, we can use deep learning method to learn the relationship between phase patterns and their near-field diffraction intensity images. In the practice, pixel crosstalk always exists. We found the pixel crosstalk between adjacent variable phase pixels was benefit for quick and accurate phase retrieval based on deep learning. We validated our idea by the simulation of adding phase disturbance between pixels on the spatial light modulator.
Compared with traditional iterative methods, deep learning phase reconstruction has lower bit error rate and higher data transfer rate. We found the efficiency of training mainly was from the edges of the phase patterns due to their stronger intensity changes between adjacent phase distribution. According to this characteristic, we proposed a method to only record and use the high frequency component of the phase patterns and to do the deep learning training. This method can improve the storage density due to reducing the material consumption.
The phase retrieval method based on deep learning can be used to solve the iterative problem in holographic data storage. The key of the deep learning method is to build the relationship between the phase data pages and the corresponding near-field diffraction intensity patterns. However, to build the correct relationship, thousands of samples of the training dataset are usually required. In this paper, according to the coding characteristics of phase data pages, we proposed an image segmentation method to greatly reduce the number of original training dataset. The innovation proposed by this new method lies in the special segmentation of the original samples to expand the number of samples.
This paper analyzed the security of random phase encryption holographic storage technology. Taking binary random phase as an example, the recorded hologram is continually readout by series guessing reference. The experiment showed that the correlation coefficient between readout information and the recorded information was firstly decreased and then increased when the phase correct ratio of guessing reference is increased from 0% to 100%. The recorded information can’t be readout at all when the phase correct ratio of guessing reference range from 40% to 60%. Since the guessing reference with phase correct ratio between 40% and 60% has occupied majority guessing cases, the recorded information can’t be cracked in most cases. This indicates the high security of the random phase encryption storage technique.
Research of holographic storage security is of great significance to the development of holographic storage technology. To ensure the difficulty of cracking, the data reconstructed by the wrong key should present a statistically independent random noise distribution as far as possible. This paper studies collinear holographic encryption storage based on the orthogonal Hadamard matrix and random phase. After storing data with a particular key A in a regular ring shape, the secret key A can reconstruct the data. However, some other keys can also reconstruct partial data (crosstalk noise), and this crosstalk greatly reduced the security of the data storage system. Here, random orthogonal phase coding is proposed to solve the crosstalk problem, and the reference light was equally divided into 64 pieces. Each one consists of the same number of pixels at random positions in the circular reference light. The randomness of each reference pixel ensures the consistency of the reconstructed data light intensity, and the data can be completely eliminated due to the orthogonality of the reference light. The orthogonal reconstructed data presents a nearly statistical independent noise distribution, which has effectively reduced the similarity between the original data and the reconstructed data by a wrong key, avoided data leakage, and improved the security of holographic encryption storage.
KEYWORDS: Phase retrieval, Data storage, Holography, Fourier transforms, Computer programming, Solids, Data conversion, Reconstruction algorithms, Interferometry, Holographic data storage systems
Phase-modulation holographic data storage is imaging on the Fourier plane, and the imaging quality has a great influence on
phase retrieval. The iterative Fourier transform algorithm in the non-interference phase retrieval algorithm is widely used
because of its simple and stable system. By adding embedded data to the phase encoding method, the number of iterations can be
effectively reduced. However, the intensity of high-frequency information in Fourier intensity is weaker and more susceptible to
noise. To solve this problem, this paper proposes to use embedded data to improve the intensity of high-frequency information in
the Fourier intensity distribution, thereby improving noise immunity. In simulation, the convergence speed of BER (the bit error
rate) is faster under the same number of iterations.
A method for collinear non-interferometric phase retrieval holographic data storage using a single reference pixel is
proposed. The known embedded data of the signal beam in the traditional off-axis holographic data storage system is
placed in the reference beam through the collinear holographic data storage system, which greatly improves the material
utilization rate. And increasing the intensity of the reference beam can achieve phase retrieval using only one reference
pixel. As the intensity of the reference beam becomes stronger within a certain range, the number of iterations gradually
decreases. With this method, the phase retrieval can be achieved even when the total energy of the reference beam is less
than the signal beam. In the simulation, the four-level phase pattern was recorded and the phase was restored correctly.
The phase holographic storage system is different from the traditional object -image corresponding imaging. Because
of the particularity of phase, it is not easy to be captured by the traditional detector. Therefore, the Fourier lens is used
for Fourier transform to image it on the Fourier plane. The Fourier intensity is detected and the phase is recovered
iteratively by using the iterative Fourier transform algorithm. Due to the existence of aberrations, the wavefront phase
will be affected and the phase will be distorted.In this paper, we mainly study the influence of spherical aberration on
phase transformation. By establishing the light field with wavefront aberration, we study the influence of wavefront
aberration on phase recovery and propose the image restoration algorithm for aberration compensation .The feasibility
of the theory is proved.
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.
Soft x-ray varied line spacing grating (VLSG), which is a vital optical element for laser plasma diagnosis and spectrometry analysis, is conventionally fabricated by holographic lithography or mechanical ruling. In order to overcome the issues of the above fabrication methods, a method based on electron beam lithography-near field lithography (EBL-NFH) is proposed to make good use of the flexibility of EBL and the high throughput of NFH. In this paper, we showed a newly designed soft x-ray VLSG with a central groove density of 3600 lines/mm, which is to be realized based on EBL-NFH. First, the optimization of the spatial distribution of line density and groove profile of the VLSG was shown. As an important element in NFH, a fused silica mask plays a key role during NFH in order to obtain a required line density of VLSG. Therefore, second, the transfer relationship of spatial distribution of line densities between fused silica mask and resist grating was investigated in different exposure modes during NFH. We proposed a formulation about the transfer of line density to design of the groove density distribution of a fused silica grating mask. Finally, the spatial distribution of line densities between the fused silica mask, which is to be fabrication by using EBL, was demonstrated.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.