- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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An optical asymmetric encryption scheme with biometric keys
摘要： In this paper, an asymmetric cryptosystem for optical image encryption using biometric keys is proposed based on the phase retrieval algorithm and the phase-truncated Fourier transforms (PTFT) scheme which addresses the issue of key distribution with enhanced security in the optical encryption process. In the proposed system, the encryption keys include optically generated biometric keys and the random phase mask keys of the PTFT scheme, while the decryption keys are kept as the private key in terms of the binary key and the generated phase-only mask of the PTFT scheme. If a person is authorized to retrieve the biometric keys by providing the fingerprint hologram and reconstruction parameters at the receiver stage, then the proposed system satisfies the criteria of asymmetric cryptography with information authentication approach. The biometric key features, by using the digital holography are kept secure and is utilized in both the encryption and decryption operations so that the authenticity of the ciphertext by using the biometric keys can be verified during the decryption process. Numerical simulations are carried out to test the effectiveness and validity of the proposed system.
关键词： Authentication,Fingerprint biometric key,Asymmetric cryptosystem,Digital holography,Optical encryption and decryption
更新于2025-09-23 15:23:52
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Speckle-free common-path quantitative phase imaging with high temporal phase stability using a partially spatially coherent multi-spectral light source
摘要： Quantitative phase imaging (QPI) has been an important technique for the determination of various biophysical parameters, such as the refractive index and morphology of biological cells and tissues. The technique has been implemented using off-axis and common path digital holographic microscopy (DHM). Off-axis DHM, though being ideal for QPI, offers lower temporal phase stability compared to common path techniques. Common path DHM offers a higher temporal phase stability but, being a coherent imaging technique, suffers from speckle artefacts and spurious interference fringes due to the high coherence of the light source. Both artefacts not only degrade the image quality, but also affect the phase measurement results. In this paper, we report the implementation of common path QPI set-up using a partially spatially coherent multi-spectral light source. The spatial coherence of the red and green color lasers is reduced by using a rotating diffuser. Also, a speckle free QPI was implemented using common path Fresnel biprism interferometer. A Fresnel biprism is used in the self-referencing mode, thus offering the advantage of no optical power loss in addition to high temporal stability and the least speckle artefacts. Furthermore, it is very easy to implement, as the system completely replaces the need for spatial filtering at the source end as well as for the reference beam generation. The experiments have been carried out on industrial and biological samples to prove the effect.
关键词： phase measurement,Fresnel biprism interferometer,digital holography,coherence
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - Hangzhou (2018.8.13-2018.8.17)] 2018 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - Optimization of Phase Noise in Digital Holographic Microscopy
摘要： A phase noise optimizing method was proposed in this paper to improve the imaging quality of digital microscopic holography (DHM). In this method, bidimensional empirical mode decomposition (BEMD) was utilized to decompose the digital hologram. According to the principle of decomposition, the characteristics of first order intrinsic mode function (IMF1) are close to the gray value of ideal interference fringes. Therefore, after using BEMD method the digital hologram was optimized with enhanced interference fringes, from which phase image with reduced noise can be retrieved. The validity of the proposed method on noise reduction was verified by experimental results on a nano-step.
关键词： digital holography,phase,bidimensional empirical mode decomposition,noise
更新于2025-09-23 15:22:29
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Comparative appraisal of global and local thresholding methods for binarisation of off-axis digital holograms
摘要： Binary digital and computer-generated holograms are used in a number of digital micromirror device (DMD) applications, including holographic displays, media characterisation, optical encryption, and others. Binarisation is one of the most simple and e?cient methods of hologram compression. In this paper, 12 local and 18 global thresholding techniques of di?erent groups were analysed and compared based on attribute similarity, clustering, entropy, histogram shape, and local adaptive factors. Optically recorded o?-axis digital holograms of di?erent objects were binarised using these methods. The amplitude quality of the obtained reconstructed images was compared using PSNR and SSIM values. The clustering-based methods achieved the highest quality. The results of binarisation by global and local methods were comparable on average.
关键词： Image binarisation,Hologram compression,Thresholding,Digital holography,Digital image processing,Digital micromirror device
更新于2025-09-23 15:21:21
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Fast reconstruction of two-wavelength off-axis multiplexed holograms using division-multiplexing and critical sampling
摘要： Benefiting from two-wavelength information multiplexed into one hologram, two-wavelength off-axis holography can perform simultaneous quantitative phase imaging in an extended thickness range. However, its present phase processing still adopts the traditional Fourier-based method at the expense of the reconstruction speed. Hence, we propose a fast approach by combining critical sampling with division multiplexing. In our approach, the critical sampling is used to remove the redundant data, and the division multiplexing is developed to eliminate the redundant calculation processes. Experimental results illustrate that our approach can yield faster reconstruction with frame rates up to 46 fps even for one megapixel multiplexed holograms at two wavelengths on a single-core personal computer.
关键词： Critical sampling,Multiplex holography,Dual-wavelength digital holography,Fast phase retrieval
更新于2025-09-23 15:21:01
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Real-time pollen monitoring using digital holography
摘要： We present the ?rst validation of the Swisens Poleno, currently the only operational automatic pollen monitoring system based on digital holography. The device provides in-?ight images of all coarse aerosols, and here we develop a two-step classi?cation algorithm that uses these images to identify a range of pollen taxa. Deterministic criteria based on the shape of the particle are applied to initially distinguish between intact pollen grains and other coarse particulate matter. This ?rst level of discrimination identi?es pollen with an accuracy of 96 %. Thereafter, individual pollen taxa are recognized using supervised learning techniques. The algorithm is trained using data obtained by inserting known pollen types into the device, and out of eight pollen taxa six can be identi?ed with an accuracy of above 90 %. In addition to the ability to correctly identify aerosols, an automatic pollen monitoring system needs to be able to correctly determine particle concentrations. To further verify the device, controlled chamber experiments using polystyrene latex beads were performed. This provided reference aerosols with traceable particle size and number concentrations in order to ensure particle size and sampling volume were correctly characterized.
关键词： Swisens Poleno,pollen monitoring,particle classification,digital holography,automatic pollen monitoring system
更新于2025-09-23 15:21:01
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Image plane interference co-phasing technology for synthetic digital holography
摘要： Synthetic aperture is a high-resolution imaging technique which can extend the resolution Rayleigh limit capability of an aperture, while digital holography is a useful digital imaging tool. When synthetic aperture meets digital holography, a high-resolution image can be digitally achieved without many complex optic path adjust systems. However, because of the position errors and phase errors, the synthesis is always di?cult to realize. In this paper, we analyzed the sources and in?uences of these errors which mainly include the phase errors and the shape and position errors, then proposed a valid image plane interference based digitally co-phasing method. A combination of the SPGD (stochastic parallel gradient descent) algorithm with the KAZE-based registration algorithm was proposed to respectively correct the de-phased errors and the shape and position errors. Experiment demonstrated that a high-resolution synthesized image can be achieved with this method without any adjust of the optical path. The biggest advantage of the proposed method is that it can be applied in short and long distance situations, or one sensor is far away from another, or the sensor is large sized, or the angle among sensors is relatively big.
关键词： SPGD,Synthetic aperture,KAZE based registration,Interference imaging,Digital holography,Speckle
更新于2025-09-23 15:21:01
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Birefringence measurement of biological tissue based on polarization-sensitive digital holographic microscopy
摘要： We present a polarization-sensitive digital holography to measure the birefringence of biological tissues with complex structures. The birefringence measurement system is established by incorporating the modified Mach–Zehnder interferometer and lab-developed software. Normal and cancerous bladder tissue samples are measured by using the proposed experimental system. The polarization-dependent phase-shifted holograms are recorded by rotating the polarizer. Moreover, the hybrid reconstruction and least-square unwrapping algorithms are used to extract phase information of biological tissues at different polarization states. The birefringence of tissue is obtained from the above-phase distributions. The results show that polarization sensitivity exists in the normal bladder tissue and cancerous bladder tissue, and the median birefringence value of the cancerous tissue is significantly higher than that of the normal tissue. These results will provide reference for pathological research and clinic diagnoses.
关键词： Mach–Zehnder interferometer,birefringence,polarization-sensitive digital holography,biological tissue,phase distribution
更新于2025-09-23 15:21:01
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Digital holographic sizer for coal powder size distribution measurement: preliminary simulation and experiment
摘要： On-line and continuous measurements of coal powder size distribution in coal-fired plants remain challenging. A coal powder size measurement system based on digital holography (DH) is developed. The effects of several factors, i.e. pixel size, recording distance, particle size, and concentration, on particle size measurement by the DH method are quantified by simulation, yielding the suitable pixel size, recording distance and particle concentration. The measurement system is implemented based on the simulation results and applied to measure particle size distribution of pulverized coal samples. Results show that the particles are clearly reconstructed from the hologram, and the measured size distributions agree well with those of the samples measured by laser particle size analyzer. This work shows that the digital holographic sizer has great potential in coal powder size distribution measurement in power plant pipes.
关键词： digital holography,particle size distribution,coal powder,on-line measurement
更新于2025-09-23 15:21:01
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Experimental analysis and designing strategies of lens-less microscopy with partially coherent illumination
摘要： Lens-less microscopy can achieve a wide field of view imaging (FOV) through a simple configuration compared to conventional microscopy, and it’s very attractive in resource-limited areas because of its cost-effectiveness and portability. Featuring a small package and cheapness, LEDs and LDs both show the potential to act as a reasonable illumination source for lens-less microscopes, especially for portable ones. However, based on holographic theorem, the complex light-field reconstruction algorithms consider the light source as a highly coherent one, while both LEDs and LDs can only provide partially coherent illumination. In this manuscript, we would systematically and experimentally analyze the imaging performances of lens-less microscopy with partially coherent illumination. The analysis covers autofocusing under LED/LD illumination, imaging performances under different LED spatial coherence and imaging performances under LED/LD illumination. Furthermore, based on the analysis, some conclusions about designing a lens-less microscope are presented. We think that the experiments and conclusions can provide effective guidance to construct a low-cost lens-less microscope with trade-off hardware parameters in practices.
关键词： Computational imaging,Digital holography,Microscopy,Portable imaging device,Phase retrieval
更新于2025-09-23 15:21:01