Publications by authors named "Jiachen Wu"

8 Publications

  • Page 1 of 1

High-speed computer-generated holography using an autoencoder-based deep neural network.

Opt Lett 2021 Jun;46(12):2908-2911

Learning-based computer-generated holography (CGH) provides a rapid hologram generation approach for holographic displays. Supervised training requires a large-scale dataset with target images and corresponding holograms. We propose an autoencoder-based neural network (holoencoder) for phase-only hologram generation. Physical diffraction propagation was incorporated into the autoencoder's decoding part. The holoencoder can automatically learn the latent encodings of phase-only holograms in an unsupervised manner. The proposed holoencoder was able to generate high-fidelity 4K resolution holograms in 0.15 s. The reconstruction results validate the good generalizability of the holoencoder, and the experiments show fewer speckles in the reconstructed image compared with the existing CGH algorithms.
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http://dx.doi.org/10.1364/OL.425485DOI Listing
June 2021

DNN-FZA camera: a deep learning approach toward broadband FZA lensless imaging.

Opt Lett 2021 Jan;46(1):130-133

In mask-based lensless imaging, iterative reconstruction methods based on the geometric optics model produce artifacts and are computationally expensive. We present a prototype of a lensless camera that uses a deep neural network (DNN) to realize rapid reconstruction for Fresnel zone aperture (FZA) imaging. A deep back-projection network (DBPN) is connected behind a U-Net providing an error feedback mechanism, which realizes the self-correction of features to recover the image detail. A diffraction model generates the training data under conditions of broadband incoherent imaging. In the reconstructed results, blur caused by diffraction is shown to have been ameliorated, while the computing time is 2 orders of magnitude faster than the traditional iterative image reconstruction algorithms. This strategy could drastically reduce the design and assembly costs of cameras, paving the way for integration of portable sensors and systems.
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http://dx.doi.org/10.1364/OL.411228DOI Listing
January 2021

Investigating the Aging Effects of Biochar on Soil C and Si Dissolution and the Interactive Impact on Copper Immobilization.

Molecules 2020 Sep 21;25(18). Epub 2020 Sep 21.

School of the Environment, South China Normal University, Guangzhou 510006, China.

Aging tests were used to investigate the long-term effects of BC on the immobilization of Cu, and the soil silicon dissolution of three types soils (black soil, (BS), vegetable garden soil (VS) and red soil (RS)). Litchi branch biochars (BC) at 10% (/) were incubated with three Cu (400 mg/kg) contaminated soils. The effect on soil properties of pH, soil organic carbon (SOC), dissolved organic carbon (DOC) and available silicon content were investigated, along with the speciation distribution of Cu. The results indicated that SOC, DOC, and available silicon content (except, BC300) increased with the application of BCs. On the other hand, the DTPA (diethylenetriaminepentaacetic acid) extractable Cu content in BS, VS and RS soils were reduced by 4-12%, 18-25%, and 12-19%, respectively. The Cu availability in all soils first increased, and then decreased during the aging process. The sum of the other four fractions, including the carbonate fraction and the inert component increased by 4-4.5% (BS), 1.4-2.1% (VS), and 0.5-1% (RS) respectively, over the long-term process. Moreover, during the whole aging process, the soil properties (such as pH, SOC, DOC and available silicon content) were almost stable. This study demonstrates that BCs, especially those produced at a higher temperature, are superior to those been produced at 300 °C in immobilizing Cu and releasing available silicon in soils. However, the remediation efficiencies were restricted by the soil type contamination status and remediation time.
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http://dx.doi.org/10.3390/molecules25184319DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7570456PMC
September 2020

Assessing biochar application to immobilize Cd and Pb in a contaminated soil: a field experiment under a cucumber-sweet potato-rape rotation.

Environ Geochem Health 2020 Dec 23;42(12):4233-4244. Epub 2020 Apr 23.

School of Environment, South China Normal University, Guangzhou, 510006, China.

Cd and Pb are common toxic contaminants prevailing in agricultural soils contaminated by mining activities. In this study, biochar was used to stabilize Cd and Pb contaminated soil for safe with three crops rotation condition within one year. Field experiments were carried out to investigate the effect of Litchi branch biochar (BC), pyrolyzed at 600 °C and applied at 4 rates [(0 t ha (T0), 10 t ha (T1), 20 t ha (T2) and 30 t ha (T3)]) on remediation of Cd and Pb in agricultural soil near Dabaoshan Mine in South China under a cucumber-sweet potato-rape rotation. The results showed that the application of BC can significantly increase the pH, cation exchange capacity and soil organic matter. After cultivation of crops, the pH values decrease gradually, with the biggest drop of 0.45 pH units in T3 treatment after rape cultivation. BC application increased the yield of three crops up to onefold to twofold in T3 treatment as compared to the control. The uptake of Cd and Pb in all three crops decreases with the increase in BC doses, which is mainly related to the decrease in bioavailable metals in their respective soil treatments. Under 1-year crops rotation, the remediation ability of BC still remains, while Cd and Pb can exhibit different risk to different crops. The data of this study can provide scientific suggestions for the selection of suitable crops and proper BC amount in remediation of heavy metal contaminated soil.
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http://dx.doi.org/10.1007/s10653-020-00564-9DOI Listing
December 2020

Single-shot lensless imaging with fresnel zone aperture and incoherent illumination.

Light Sci Appl 2020 7;9:53. Epub 2020 Apr 7.

2Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 USA.

Lensless imaging eliminates the need for geometric isomorphism between a scene and an image while allowing the construction of compact, lightweight imaging systems. However, a challenging inverse problem remains due to the low reconstructed signal-to-noise ratio. Current implementations require multiple masks or multiple shots to denoise the reconstruction. We propose single-shot lensless imaging with a Fresnel zone aperture and incoherent illumination. By using the Fresnel zone aperture to encode the incoherent rays in wavefront-like form, the captured pattern has the same form as the inline hologram. Since conventional backpropagation reconstruction is troubled by the twin-image problem, we show that the compressive sensing algorithm is effective in removing this twin-image artifact due to the sparsity in natural scenes. The reconstruction with a significantly improved signal-to-noise ratio from a single-shot image promotes a camera architecture that is flat and reliable in its structure and free of the need for strict calibration.
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http://dx.doi.org/10.1038/s41377-020-0289-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7138823PMC
April 2020

Structured light field 3D imaging.

Opt Express 2016 Sep;24(18):20324-34

In this paper, we propose a method by means of light field imaging under structured illumination to deal with high dynamic range 3D imaging. Fringe patterns are projected onto a scene and modulated by the scene depth then a structured light field is detected using light field recording devices. The structured light field contains information about ray direction and phase-encoded depth, via which the scene depth can be estimated from different directions. The multidirectional depth estimation can achieve high dynamic 3D imaging effectively. We analyzed and derived the phase-depth mapping in the structured light field and then proposed a flexible ray-based calibration approach to determine the independent mapping coefficients for each ray. Experimental results demonstrated the validity of the proposed method to perform high-quality 3D imaging for highly and lowly reflective surfaces.
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http://dx.doi.org/10.1364/OE.24.020324DOI Listing
September 2016

Vulnerability to ciphertext-only attack of optical encryption scheme based on double random phase encoding.

Opt Express 2015 Jul;23(15):18955-68

We demonstrate in this paper that the traditional double random phase encoding (DRPE) technique is vulnerable to ciphertext-only attack (COA). In this method, an unauthorized user (or say attacker) is assumed to be able to retrieve the corresponding plaintext from the only ciphertext under some certain condition. The proposed scheme mainly relies on a hybrid iterative phase retrieval (HIPR) algorithm, which combines various phase retrieval algorithms. With an estimation of the number of nonzero pixels (NNP) in the original plaintext, an attacker could recover the plaintext in a large extent. The simulation results show that this method is feasible and validate.
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http://dx.doi.org/10.1364/OE.23.018955DOI Listing
July 2015

Optical cryptosystem based on phase-truncated Fresnel diffraction and transport of intensity equation.

Opt Express 2015 Apr;23(7):8845-54

A novel optical cryptosystem based on phase-truncated Fresnel diffraction (PTFD) and transport of intensity equation (TIE) is proposed. By using the phase truncation technique, a phase-encoded plaintext could be encrypted into a real-valued noise-like intensity distribution by employing a random amplitude mask (RAM) and a random phase mask (RPM), which are regarded as two secret keys. For decryption, a generalized amplitude-phase retrieval (GAPR) algorithm combined with the TIE method are proposed to recover the plaintext with the help of two keys. Different from the current phase-truncated-based optical cryptosystems which need record the truncated phase as decryption keys, our scheme do not need the truncated phase because of the introducing of the TIE method. Moreover, the proposed scheme is expected to against existing attacks. A set of numerical simulation results show the feasibility and security of the proposed method.
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http://dx.doi.org/10.1364/OE.23.008845DOI Listing
April 2015