According to tensor polarization holography theory, changes in material properties induced by exposure can be characterized by two coefficients, denoted as A and B. These coefficients represent the scalar and tensor components of the photoinduced change in the dielectric tensor, respectively. The A/B is defined as the exposure response coefficient, which plays a crucial role in determining the controllability of the optical field. Gauging the value of A/B of a polarization-sensitive medium in advance is essential for realizing distinctive experimental phenomena and designing holograms with specific functions. The precision of this coefficient affects whether experimental work using polarization holography produces the anticipated results. In this work, we propose an improved method for accurately measuring A/B. Both A/B-independent and A/B-dependent hologram designs are analyzed. Experimental results demonstrate that the proposed method significantly enhances the measurement accuracy of A/B.

High-density storage of big data in the information age calls for higher data transmission rates. Holographic data storage technology, based on the principles of three-dimensional volume holographic recording and two-dimensional planar transmission, delivers an extremely high data transmission rate. Given the need for encoding two-dimensional data pages, spatial light modulators (SLMs) are employed for information encoding, and the modulation region of SLMs has become a key limiting factor for the data transmission rate of holographic data storage systems. However, to overcome the limitation that the limited imaging area of SLMs in holographic data storage fails to fully exploit the potential of this technology, this paper proposes an ultra-high-speed holographic data storage system based on extending data page size. The signal beams modulated by two digital micromirror devices (DMDs) are stitched and aligned through an optical system to achieve an expanded data page size. The reference beam is modulated using a mask to conserve the limited pixel resources of DMDs. Coupled with the 5:16 amplitude data encoding rule, the proposed system achieves an ultra-high data transmission rate of 20.06 Gb/s.

Current holographic data storage (HDS) systems mainly use amplitude and phase modulation for data encoding, while polarization is limited to multi-channel multiplexing, often causing operational difficulties and system complexity. To solve this, we propose a new, to the best of our knowledge, method that combines multiple polarization states into a single data page. Using polarization holography theory, we developed a reconstruction method capable of accurately reconstructing data pages with different polarization information. This method encodes data directly through multiple polarization states on one page. Decoding is simplified using a single 45° linear polarizer before the camera, enabling efficient distinction between different polarization states. Experiments show zero-error decoding for 2-, 3-, and 4-level polarization data pages. This research simplifies system design, reduces operation complexity, and expands HDS encoding dimensions, offering a new technical approach for practical high-density holographic storage.

A collinear holographic data storage system stores two-dimensional information in the three-dimensional spatial domain of the medium, offering features such as high speed, high density, and long lifespan, making it a promising technology for the future of data storage. However, a collinear holographic data storage system is limited by the alignment error of the optical system and is also sensitive to environmental noise and external interference, which increases the reading error. When recording and reading holographic storage materials, synchronous marks are used for positioning to correct data misalignment. Therefore, optimizing synchronous mark design of data pages is crucial for improving storage stability and reading accuracy. In this paper, we propose a star-shaped synchronous mark to replace the square-shaped synchronous mark, which improves the holographic grating coupling efficiency. Experimental results show that this method enhances reconstruction strength and reduces reading errors caused by external factors. The star-shaped synchronous mark achieves a better spectral match with the reference pattern, yielding a stronger diffracted signal. Experimental results show that this method reduces the bit error rate by approximately 25% compared to square-shaped synchronous marks under displacement multiplexing.

Neural networks significantly outperform traditional methods in both decoding amplitude-, phase-, and polarization-encoded data pages and suppressing noise within them. However, the mechanism behind neural networks’ denoising capability remains not fully understood. We discover that zeroing channels can improve the reconstruction effect of the model. Consequently, this paper presents a method to locate the noise feature objectively from γ, the weights of the Batch Normalization (BN) layer. γ stands for the importance of the channel in the model and γ < 1 means the channel may contain noise feature. Through experiments, removing the channels that contained a higher proportion of these noisy features, the reconstructed data pages showed a ~2% improvement in Peak Signal-to-Noise Ratio (PSNR) compared to results obtained by directly outputting data without removing the noisy channels. It indicates that neural networks achieve efficient denoising of encoded data pages by adjusting the weight parameters of BN layers, thereby suppressing or enhancing specific channels.

We present a hybrid multiplexing method for holographic optical storage that combines complex-amplitude encoding with polarization- and angle-based multiplexing to enhance storage density and capacity significantly beyond conventional approaches. By leveraging polarization holography, complex-amplitude data can be selectively recorded into orthogonal polarization channels. Furthermore, angular multiplexing is also applied to co-record multiple holograms at the same spatial location. During the reading process, each hologram can be selectively reconstructed under its specific Bragg and polarization conditions. Remarkably, despite exploiting these degrees, the reconstruction fidelity remains exceptionally high, with negligible degradation or crosstalk. This demonstrates a scalable route to high‑capacity, high‑fidelity holographic memories for next‑generation data‑intensive applications.

With the advent of the big data era, traditional storage technologies struggle to meet the demands for long-term, secure, and cost-effective preservation of massive amounts of information. Collinear holographic storage technology has emerged as a strong contender for next-generation optical storage due to its high storage density, rapid parallel transmission, and exceptional reliability. Among various storage materials, phenanthraquinone-doped poly(methyl methacrylate) (PQ/PMMA) photopolymer has garnered significant attention for its negligible photo-induced volume shrinkage, low cost, controllable thickness, and polarization-sensitive holographic response properties. However, the material’s limited photosensitivity, low polarization response, and poor optical uniformity severely constrain its application in high-speed recording and multidimensional multiplexing holographic systems. This paper reviews the primary methods and strategies employed over the past five years to enhance the holographic performance of PQ/PMMA photopolymer materials, based on the microscopic physicochemical mechanisms underlying traditional and polarization holography, including chemical modification, nanoscale doping, mechanical control, etc. Through a systematic review of these research advances, this paper aims to provide theoretical foundations and technical references for developing high-performance PQ/PMMA photopolymer materials suitable for collinear holographic storage.

To address the key issues of uneven distribution of functional groups, large dispersion of holographic storage performance across different regions, and poor consistency of storage capacity in traditional PQ/PMMA holographic storage photopolymers, this paper introduces a low-viscosity reactive diluent, tripropylene glycol diacrylate (TPGDA), to modify the matrix. Leveraging the viscosity-reducing and double-bond crosslinking properties of TPGDA, the molecular diffusion behavior of the system was regulated. The effects of TPGDA doping ratio, the ratio of photosensitizer PQ to thermal initiator AIBN, and post-curing process on the holographic performance uniformity of the material were systematically investigated. The uniformity was quantitatively evaluated by the variance of diffraction efficiency at different points. Visible light absorption spectra and Fourier-transform infrared (FT-IR) spectroscopy were employed to reveal the modification mechanism from the perspective of functional group distribution. Actual-data read/write tests were conducted using a collinear holographic storage system. The experimental results show that the optimal TPGDA doping concentration is 40 wt%. For the optimized formulation TPGDA:MMA:AIBN:PQ = 8 g:12 g:0.20 g:0.18 g, the modified material achieves an average diffraction efficiency of 76.58%, and the diffraction efficiency variance decreases from 23.49 (pristine matrix) to 1.64, indicating a significant improvement in performance uniformity. Compared with pure PQ/PMMA, the modified material exhibits an approximately 1.95-fold increase in maximum diffraction efficiency, a 2-fold increase in recording rate, and a 1.6-1.75-fold increase in refractive index modulation. FT-IR spectroscopy confirms that TPGDA optimizes the spatial distribution uniformity of C=C and C=O functional groups. In collinear holographic measurements, the bit error rate (BER) variance of the modified sample is reduced by 40% relative to the pristine matrix, achieving homogeneous storage performance across the entire area while maintaining comparable signal-to-noise ratio (SNR) and BER. Additional short-time UV post-curing can further enhance the diffraction efficiency and refractive index modulation, and a thinner substrate can avoid performance fluctuations caused by incomplete thermal curing of thick samples. This study achieves directional optimization of the holographic uniformity of PQ/PMMA through reactive diluent viscosity reduction modification, providing a new strategy for the formulation design and engineering preparation of high-consistency holographic storage photopolymers.

Multidimensional holographic data storage that exploits the amplitude, phase, and polarization degrees of freedom of light offers a promising route for increasing storage density and capacity. However, polarization-multichannel recording has mainly been demonstrated in off-axis configurations, and its applicability to collinear holographic storage remains unclear. In collinear systems, the signal and reference fields are focused through a common optical path, producing a paraxial small-angle interference condition that may introduce polarization-channel crosstalk. Here, we investigate dual orthogonal circular-polarization-channel complex-amplitude recording under a paraxial approximation focused-recording geometry, enabling three-dimensional data storage leveraging amplitude, phase, and polarization. Based on tensor polarization holography, we analyze the channel reconstruction relation and verify experimentally that the residual crosstalk remains sufficiently weak to support independent recording and reconstruction of two complex-amplitude data pages. To address the resulting complex-amplitude coupling in intensity-only detection, separate U-net decoders are employed for amplitude and phase recovery, achieving high-precision decoding. This work demonstrates the feasibility of extending polarization-assisted multidimensional encoding from off-axis holography to paraxial approximation recording, and provides a basis for its incorporation into collinear holographic data storage.

In phase-modulated holographic storage, unequal interval phase encoding provides distinct diffraction intensity distributions between adjacent phases, which offers more discriminative features for convolutional neural networks. Numerous combinations of unequal-interval encoding schemes exist, and there is a lack of effective guidelines for their optimization. To address this, we propose an encoding design method based on phase difference interval optimization, which systematically regulates the distribution of phase differences to improve reconstruction performance. Simulation and experimental results demonstrate that the designed three-level and four-level encoding methods achieve the lowest phase reconstruction errors. Compared to the equal-interval encoding, the BER of the optimal three-level phase encoding (0, 43, 128) decreased by about 59%, while the BER of the optimal four-level phase encoding (0, 21, 85, 127) decreased by about 38%, validating the effectiveness and superiority of the proposed method. Furthermore, this approach has the potential to be extended to higher-level encoding, providing new insights for the encoding design of high-capacity holographic storage systems.

Holographic data storage (HDS) offers high capacity and throughput, making it a promising candidate for next-generation storage technologies. However, it is susceptible to increased bit error rate (BER) due to optical/electronic non-idealities and media inhomogeneity. To address this challenge, we propose an implicit neural representation (INR)-based data representation method with a dropout training strategy for robust HDS. In this framework, image information is encoded into compact network parameters, which are subsequently written to and read from the storage medium using an off-the-shelf HDS technique. The retrieved parameters are then loaded for inference to reconstruct the image. Compared with conventional pixel-wise image storage, the global representation enhances robustness by allowing the network to compensate for partial parameter errors. Moreover, it reduces the number of required data pages, providing compression benefits for sparse images. Both simulations and experiments demonstrate consistent gains under noisy conditions, with peak signal-to-noise ratio (PSNR) improved by over 50%, structural similarity index measure (SSIM) above 0.95, and a compression ratio of 2.92 for sparse images. These results demonstrate the effectiveness of the proposed approach for reliable HDS under high BER conditions.

Holographic data storage (HDS) offers a promising route toward high-capacity and high-throughput optical information storage. However, its achievable storage density is often limited by the dimensionality of the encoded optical field. Light inherently possesses multiple physical degrees of freedom, including amplitude, phase, and polarization, which provide an opportunity to substantially increase the information capacity of a single data page if they can be efficiently and reliably exploited. In this work, we investigate multidimensional information encoding and decoding in the HDS by fully utilizing these three fundamental properties of light. For encoding, a full three-dimensional modulation scheme is established by controlling the complex amplitude distributions of two orthogonal polarization states and employing a double-phase hologram strategy, which allows a single phase-only spatial light modulator to jointly encode amplitude, phase, and polarization information within the optical field. For decoding, a convolutional neural network, named TriDecode-Net, is designed to simultaneously retrieve three-dimensional information directly from diffraction intensity images. This approach enables synchronous recording and retrieval of multidimensional optical information, significantly increasing the information content of a single holographic data page compared with conventional holographic encoding approaches. Beyond data storage, the proposed multidimensional modulation and reconstruction framework also provides opportunities for optical encryption, anti-counterfeiting, high-capacity optical communication, and the generation and control of structured light fields. (c) 2026 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

After several centuries of development, photosensitive materials are being widely used in photography and videography. However, a material that possesses low shrinkage and can ensure high sensitivity is still elusive. Therefore, we have developed and designed a photosensitive material that maintains high sensitivity while exhibiting low shrinkage and excellent stability to address the growing demand for high-speed holographic data storage system in the big data era. A novel material, thiol-ene-phenanthrenequinone (PQ)-doped poly(methyl methacrylate) (PMMA), was developed by incorporating pentaerythritol tetra(3-mercaptopropionate) (PETMP) into a cross-linked PMMA network. Compared with traditional PQ/PMMA (similar to 0.55 cm & centerdot;J(-1)), the improved formulation demonstrated a four-fold increase in photosensitivity (similar to 2.54 cm & centerdot;J(-1)) and a drastically reduced response time (from similar to 70.93 s to similar to 7.57 s). More importantly, the material maintained a low photo-induced shrinkage factor of similar to 6.6 parts per thousand. Practical testing in a collinear holographic storage system confirmed the capability of the material to record a single holographic data page within 1 s and maintain a bit error rate below 1%. Microscopic characterization revealed that the enhancement mechanisms involved the thiol-ene anti-Markovnikov addition reaction during exposure and a retardation effect during thermal polymerization, which increased the residual monomer concentration (from similar to 5% to similar to 11%) available for photochemical reactions. Furthermore, the cross-linked network improved the thermal stability of the PMMA matrix, evidenced by the increased decomposition temperature and glass transition temperature (T-g), without adversely affecting the volume stability. These findings indicate that the thiol-ene-PQ/PMMA material is a highly promising candidate for enabling fast high-density holographic data storage, potentially meeting the requirements of future servo-based collinear storage systems.

We propose a precise reconstruction, with crosstalk-free switching, of two holograms. Our approach utilizes orthogonal polarizations that illuminate the holograms to modulate both amplitude/phase and polarization, effectively mitigating crosstalk between the hologram data streams. Furthermore, the incorporation of a 90° interference angle facilitates the recording of multiple holograms. Experimental results have demonstrated the high-precision decoding of amplitude,phase, and polarization data for two reconstructed holograms. The integration of orthogonally polarized light with a 90°interference angle sets the stage for achieving multi-dimensional polarization modulation in systems with more than two channels.

In amplitude-modulated holographic storage, due to material inhomogeneity, optical system aberrations, and environmental interference, the recorded and read amplitude data pages often contain a large amount of random noise, leading to a decrease in the image signal-to-noise ratio (SNR). However, the traditional U-Net has a limited ability to handle random noise, particularly for low-SNR data pages, making it difficult to effectively enhance SNR. This paper proposes an improved U-Net named DRAMCU-Net (dilated residual attention and multi-scale convolution U-Net) for enhancing the SNR of holographic data storage images. DRAMCU-Net achieves multi-level feature extraction and attention focusing by introducing dilated residual attention blocks (DRABs) and utilizing multi-scale convolutional blocks (MS-Conv) instead of traditional convolutional blocks to efficiently capture feature information at different scales. Additionally, a dropout layer is employed to enhance the model's global robustness. Experimental results demonstrate that compared to the U-Net, the low-SNR data pages reconstructed by DRAMCU-Net achieve approximately 30% higher SNR.

Photopolymer PQ/PMMA, as a pivotal material in the field of holographic storage, demonstrates significant application potential owing to its advantages, such as straightforward preparation processes, cost-effectiveness, and tunable thickness. However, its practical application is still constrained by the need for further enhancement in key performance indicators, including diffraction efficiency, photosensitivity, and anti-aging properties. In this study, N-vinylpyrrolidone (NVP) is employed as a comonomer. By precisely controlling the doping ratio, we systematically investigate the influence mechanism of different NVP doping concentrations on the holographic performance of NVP-PQ/PMMA materials. Research indicates that the introduction of NVP effectively increases the vinyl concentration in the PQ/PMMA matrix, thereby directly generating photoproducts with PQ during the photoreaction process and further enhancing the photopolymerization process. Consequently, the holographic performance of the novel NVP-PQ/PMMA material is improved in a multi-faceted manner compared to ordinary PQ/PMMA. Specifically, the diffraction efficiency is enhanced by 1.93 times, the photosensitivity is increased by 1.64 times, the material uniformity is improved by 38%, and the light-induced shrinkage rate is reduced by 39%. Additionally, NVP-PQ/PMMA materials exhibit excellent stability and aging resistance in high-temperature accelerated aging experiments. Doping with a monomer of specific structure enhances the optical properties, providing broad adaptability for further research on PQ/PMMA photopolymer materials.