This PDF file contains the front matter associated with SPIE Proceedings Volume 11188, including the Title Page, Copyright Information, Table of Contents, Author and Conference Committee lists.

Every physical science existed within our temporal subspace must be temporal (i.e., t>0); otherwise it is a virtual (or fictitious) science as mathematics does. The burden of a scientific postulation is to proof it is existed within our universe and then find the solution. In this article we will show that, there exists a duality between science and mathematics in which any scientific postulation has to be shown it is satisfied all the boundary conditions within our temporal universe, before accepting it as a real physical science. Otherwise their virtual solution is not guarantee it is a physical science. One of the important conditions must be the causality condition (i.e., t>0) for which to confirm a solution is temporal and existed within our universe. Since the entire fundamental laws of science are mathematics, which includes the Maxwell equations, as well the Schrödinger equation, without the imposition of causality condition we are not sure that the solution is a physically real science within our universe. Since we have shown Schrödinger quantum mechanics is timeless, we will show what would happen if his timeless superposition principle is plunging within a temporal space. In which we have found that, timeless space is a virtual-abstract space that only existed in an absolute empty space with zero time (i.e., t = 0). And we have seen that only quantum physicists can implant a physical model into an empty subspace, as Schrödinger did. But empty space and temporal space are mutually excluded.

In this paper, several methods based on a data-centric approach for optical sensing and imaging are summarized and their potential capabilities for miscellaneous problems are presented. At the beginning, the framework of data-centric approach is explained briefly with a generalized formulation of a process of optical sensing and imaging. The essential idea is application of machine learning to estimate the inverse process of the target optical sensing and imaging using mathematical models. Once such an estimation is achieved, the input object and the resultant output signals can be related by the mathematical model. Based on the framework, several problems in optical sensing and imaging are demonstrated. They are single-shot super resolution in diffractive imaging, computer-generated holography based on deep learning, and wavefront sensing using deep learning. These examples are not just simple imaging but sophisticated methods in general optical sensing and imaging. The data-centric approach is expected to be useful in various problems in applied optics.

Digital holographic imaging systems are promising as they provide 3-D information of the object. However, the acquisition of holograms during experiments can be adversely affected by the speckle noise in coherent digital holographic systems. Several different denoising algorithms have been proposed. Traditional denoising algorithms average several holograms under different experimental conditions or use conventional filters to remove the speckle noise. However, these traditional methods require complex holographic experimental conditions. Besides time-consuming, the use of traditional neural networks has been difficult to extract speckle noise characteristics from holograms and the resulting holographic reconstructions have not been ideal. To address tradeoff between speckle noise reduction and efficiency, we analyze holograms in the spectrum domain for fast speckle noise reduction, which can remove multiple-levels speckle noise based on convolutional neural networks using only a single hologram. In order to effectively reduce the speckle noise associated with the hologram, the data set of the neural network training cannot use the current popular image data set. To achieve powerful noise reduction performance, neural networks use multiple-level speckle noise data sets for training. In contrast to existing traditional denoising algorithms, we use convolutional neural networks in spectral denoising for digital hologram. The proposed technique enjoys several desirable properties, including (i) the use of only a single hologram to efficiently handle various speckle noise levels, and (ii) faster speed than traditional approaches without sacrificing denoising performance. Experimental results and holographic reconstruction demonstrate the efficiency of our proposed neural network.

Mass spectrometer is one of the most important instruments in the field of modern analysis. Despite efforts to increase efficiency, it remains a challenge to deploy convolutional neural networks in mass spectrometer due to tight power budgets. In this paper, we propose a hybrid optical-electronic convolutional neural network to achieve fast and accurate classification and identification of mass spectra. The optical convolutional layer is realized by a folded 4f system. Our prototype with one single convolutional layer achieves 96.5% classification accuracy in an experimentally-acquired lipid dataset. A more complicated prototype adding one fully-connected layer achieves 100% accuracy. The proposed hybrid optical-electronic convolutional neural networks might enable non-professionals to avoid the accumulation of experimental experience and complicated calculations.

Optical waves can be described by intensity and phase. However, optical waves oscillate too fast for detectors to measure anything but time-averaged intensities. This is unfortunate since the phase can reveal important information about the object. Therefore, it is necessary to apply the known intensity information to retrieve the phase information, which is called phase retrieval. As a classical phase retrieval algorithm, the Gerchberg-Saxton iteration method has the characteristics of continuous error reduction, but a large number of iterations are needed to obtain high-quality retrieval results. The field of neural network algorithm was initially inspired by the goal of modeling biological neural systems, but then parted ways and became an engineering problem with good results in the field of machine learning. This kind of network relies on the complexity of the system to process information by adjusting the interconnection among a large number of internal nodes. A new algorithm combined the neural network and the Gerchberg-Saxton iterative is proposed. Firstly, the initial phase is obtained by Gerchberg-Saxton iteration method, and then a good training model is obtained by using paired initial phase and precise phase training neural network. For the samples in the test set, the trained model is applied to the phase retrieval results of Gerchberg-Saxton iteration method to obtain more accurate phase results. Experiments proved that the better retrieval results with a few iterations can be acquired.

Conventional head-mounted display for virtual reality, which simply adopts the structure of binocular sets of display and floating lens, may result in visual discomfort for the user such as nausea and double vision as it limits the user's accommodative states which leads to the vergence-accommodation conflict. In this paper, we overview the tomographic near-eye display which achieves a high-resolution, large depth of field and quasi-continuous depth at 60 frames per second for resolving vergence-accommodation conflict. In addition, we investigate several design issues and solutions to implement the specific system in the form of a compact head-mounted display and demonstrate the prototypes and experimental results.

Several recent works for improving the performance of integral imaging based HS are introduced. Firstly, we have proposed a resolution-enhanced integral imaging II-based HS using the moving array lenslet technique (MALT). On this basis, we have proposed two improved methods. Secondly, we have proposed the concept of resolution priority HS (RPHS) for the first time, which is based on the principle of resolution priority II, by adding a quadratic phase term on the conventional Fourier transform. Finally, a simple and fast algorithm for computer-generated hologram (CGH) based on pinhole-type II using a look-up table was proposed.

We proposed a holographic vision system (HVS) based on a hologram acquisition and a hologram classification units, for capturing and identifying holograms of deformable objects. Non-diffractive optical scanning holography (ND-OSH) is used to capture holograms of physical objects, and a deep learning classifier is applied to deduce the identity of the hologram. Our proposed HVS is evaluated with the set of handwritten numerals. Experimental results reveal that with our proposed HVS, holograms of the test samples can be captured, and subsequently classified with accuracy of over 99.5%.

The optical three-dimension measurement methods have been widely used in face recognition, machine vision, biomedical imaging, virtual reality and aerospace with the advantages of fast speed, high precision and non-contact measurement. Recently, the trend of structured light 3D reconstruction tends to be real-time with improving accuracy and reducing the dependence of time domain. The structured light coding is an active measurement method which could provide abundant feature points. The 2D gold matrix is a spatial coding method and it provides a new type of structured light for optical 3D measurement. This scheme provides the dynamic 2D spatial information based on the fast decoding from the encoded projected light. Here, we proposed a binocular stereo vision system based on the structured light encoded by 2D gold matrix. Only a pair of images, which could be captured in real-time by the two cameras, are needed for 3D reconstruction. The experiment shows that the decoding success rate is up to 99.48% for non-planar object. The system is simple in structure and low in cost. It is expected to be applied to real-time 3D measurement fields such as face recognition and biomedical imaging in the future.

The purpose is to create a universal solution for complex structures in this field. Based on the idea of computational imaging, a new imaging system is proposed, which makes full use of global optimization, system reconstruction and control mechanism in actual operation. It overcomes the shortcomings of traditional system construction and control factors, such as complex relationship, large amount of calculation and so on. In the design and implementation of the core optical system, and the scientific of the criterion group, the speed of operation and the operability of the technology are also considered effectively. The results support our theoretical predictions.

Optical diffraction tomography is an important method to obtain the microstructure of biological samples. We present a reconstruction process for the 3D refractive index distribution of samples in optical diffraction tomography. First, obtaining an accurate phase image by preprocessing the interference image is especially important for the reconstruction. The quality oriented method is used to perform phase unwrapping to avoid the influence of residual error. Then, the background phase is eliminated by curve fitting method, which reduces the experimental complexity and requirements. The positional deviation caused by the rotation of the sample is solved by autocorrelation algorithm. We apply a filtered back propagation algorithm based on Fourier diffraction theory to improve the accuracy of reconstruction. Finally, we have carried out experiments on samples such as photonic crystal fiber and pollen, and obtained the detailed internal structure of the samples with satisfactory results.

With the rapid development of precision manufacturing, the optical non-contact three-dimensional measurement method for detecting the morphology of tiny objects has gradually become a hot topic with the advantages of high speed, high precision, large measuring range and high repeatability. When the depth of the microgroove reaches a certain range, the general three-dimensional measurement method cannot be used since the depth of focus is usually not deep enough. In this paper, we proposed a new method of detecting based on the grating projection for detecting phase, which introduced a novel diffractive optical device called Dammann zone plate for measuring three-dimensional shape of tiny objects with an extend of focal length. Dammann grating can produce a finite array of uniform intensity spots in the Fourier transforming plane by modulating the transverse position of the transition points of the binary optical phase. Using this feature, the Dammann zone plate takes advantage of the periodic coding details of the Dammann grating for producing an axial multi-focus system with equal intensity in the focusing system when combined with a focusing lens. This experiment, the depth of focus is greatly extended due to the introduction of Dammann zone plate, which can measure deeper grooves. Therefore, we can collect more three-dimensional information of the tiny object with a CCD camera, and then we can obtain more accurate three-dimensional morphologic profile. This method is simple, accurate and robust for practical applications, so it is highly interesting for detecting deeper grooves of tiny objects.

We proposed a holographic laser processing system with the combination of femtosecond laser and the in-system optimization. Femtosecond laser processing that employ a computer-generated hologram (CGH) displayed on a liquid-crystal-on-silicon spatial light modulator (LCOS-SLM), called holographic femtosecond laser processing (HFLP). Due to the inherent aberrations of the actual optical system, the diffraction peaks of holographic femtosecond laser processing has non-uniformity. To overcome this problem, we demonstrated a method called in-system optimization that optimizing the uniformity of the diffraction peaks while conducting the laser processing simultaneously. By taking advantage of the rewritable capability of the LCOS-SLM, with finite times of iteration perform of the in-system optimization, we obtained uniform peaks of 0.96, when the maximum intensity at the peaks of the diffraction spots was normalized to 1.0. Make use of this system, we realized the high efficiency and uniformity of laser processing, and made compensation for part of the inherent aberration in the optical system. In particular, we believe it can not only effectively avoid the impact of environmental factors on the processing system and will greatly improve the processing efficiency and stability, in the meanwhile, it will be widely applied for precise laser processing in the future.

We are gradually entering the world of picooptics, initiated by developing new holographic facility for fabrication of large-sized grating with picometer measurement techniques. Picometer measurement is at first developed based on the simple two-beam interference, i.e., holography, combined with laser interferometer as a measurement standard. Normally, a laser interferometer could provide nanometer resolution. If we measure over 1000 periods of a high-density grating with nanometer resolution, then for one single period, the resolution might be obtained at picometer resolution. Since we can modulate the holography by changing the angle of two beams slightly, then its period can be measured at picometer accuracy. The difference between two slightly-changed periods can be controlled in picometer accuracy and used as a picometer measurement tool. This means we have the key to open the door of picooptics. Weak chaos principle is realized as one basic characteristics of picometer optical measurement, which is similar but different from the well-known Heisenberg uncertain measurement principle. Picometer measurement is illustrated based on using holographic techniques. Picooptics holography, attosecond (femtosecond) pico-holography and relativistic optics at attosecond time scale and picometer spatial scale are anticipated in the future.

Computer holography is based on advanced computer technology and the basic principle of wave optics, and it is widely employed in many optical fields. In the holographic display, both display systems and encoding methods of computergenerated hologram have effects on the reconstructed image quality. The high coherence of light source causes laser speckle noise that degrades modulation quality severely. The partially temporal coherent light (PTCL) has been applied to holographic reconstruction to reduce speckle noise in display systems, while the encoding methods of computergenerated hologram (CGH) based on PTCL have not been reported. We propose a novel method to encoding CGH, in which a PTCL with a broadband continuous spectrum is used to illuminate the object image.

Depth-added computer-generated holographic stereogram (DA-CGHS) is applied to generate a high-definition (HD) CGH. We have developed a new look-up table (LUT) based technique to compute the diffraction field. In the optimized circumstance, the computing speed of LUT can be twenty-six times faster than that of pixelwise computing. To display the HD-CGH, we have built a hologram printer to fabricate the HD-CGH on a silver halide holographic plate. The size of the printed hologram is about 5 cm square, and the pixel pitch is 0.832 micrometer. Therefore, a hologram with 6×10⁴ by 6×10⁴ pixels can be fabricated by our printer.

Computer-generated holograms are widely used in interferometry for aspherical mirror testing. However, CGH has relatively low numerical aperture, which is limited both by the spatial resolution of the manufacturing process and by the need to do the design in a frame of the rigorous diffraction theory. As a result, the typical minimum period for phase CGH is limited to about 2 μm, if a wavefront error does not exceed λ/20. It limits now f/number at value of f/1.5 for 633 nm wavelength.

In this paper we discuss the technology of direct laser writing on metal films of the titanium group and chromium. It allows one to fabricate microstructures with a period of up to 1 μm at 0.7 μm spot size. Thermochemical effects of laser radiation on the films of various metals have been studied for a long time. The spatial resolution of thermochemical writing on metal films can be significantly improved by through oxidation, which dramatically increases negative feedback at light absorption. The study of laser writing on Zr and Ti films demonstrated their future promise for the technology of creating computer-generated holograms. However, the technology of laser through-oxidation is limited by relatively low scanning speeds of up to 500 mm/s. It limits CGH size when using circular scanning of the laser beam. Reactive ion etching of Ti films through the laser-induced oxide mask can be used to fabricate binary phase structures. The technology is studied for producing diffractive transmission spheres (TS) with an aperture of up to f/0.75.

Computer-generated holograms (CGHs) can be used to reconstruct three-dimensional (3D) images without optical recording of the interference pattern. The conjugate image and zero-order beam have considerable influences on the optical reconstructions in computer-generated holographic display systems based on the amplitude spatial light modulators. Generalized single-sideband method is introduced for suppressing the unwanted terms in computer generated holography. Computer-generated holograms are calculated based on frequency filtering of the object wave, which redistributes the diffraction wave in spatial frequency domain for spectrum filtering during optical reconstruction. When the object wave on the hologram plane of the 3D scene is calculated, the single-sideband filter is addressed numerically after Fourier transform of the object wave. The filtered object wave can be calculated by inverse Fourier transform of the spectrum, and then it can be coded into the amplitude CGH. Different with the overlapped spatial frequency of the unfiltered CGH, the spectrum distributions of the object wave and the conjugate wave are located in the different sides of the spatial frequency domain with help of the single-sideband filter. By placing a single-sideband filter in Fourier plane, the conjugate image and the zero-order beam can be blocked during optical reconstruction. Since the proposed method directly processes the complex amplitude distribution of the object wave, it could be applied to various 3D CGH algorithms. Numerical simulations and optical experiments demonstrate that the proposed method is generally effective for different kinds of CGH algorithms to reconstruct quality three-dimensional scenes that are free of conjugate image and zero-order beam.

An encapsulated metal-dielectric grating is proposed for realization of reflective broadband polarization-independent 1×2 beam splitter under normal incidence. One can quickly choose a grating structure to realize ultrabroad working waveband by using unified designing method for low-dispersion materials based on the diffraction efficiency map versus the normalized period and depth. Moreover, the center wavelength can be flexibly changed. As an example, a reflective ultrabroadband polarization-independent 1×2 beam splitters operating at wavelength of 1550 nm is designed under normal incidence. The simulation results indicated that a bandwidth of 144 nm could be achieved for the total efficiency over 92%. This kind of broadband polarization-independent 1×2 beam splitters could be found in a variety of applications, such as ultrashort pulse splitting, coherent beam combination, complex vector beam shaping, and also high precision displacement measurement.

A 1×5 transmission grating splitter with triangular structure under normal incidence at the wavelength of 1550 nm is presented in this paper. In order to further increase the efficiency, the material of the designed grating is MgF₂. The whole transmitted diffraction efficiency of the gratings is over 99% with uniformity better than 0.3%. The designed parameters of this triangular grating are employed by the rigorous coupled-wave analysis and the simulated annealing algorithm. This grating has a large tolerance for fabrication with better performance, which should be highly interesting for practical applications.

Nowadays, more and more people worldwide suffer from cataracts, an eye disease. The intraocular lens is a precise optical component, which can be implanted into the eyes through the surgery to replace the turbid lens of eyes with the target of providing good vision correction for many cataract patients. Scientists have developed many types of intraocular lenses for correcting vision of cataract patients, but many of them have slightly poor imaging effect because of fewer axial focal points. Dammann zone plate is a very useful optical element, which is formed by introducing the phase modulation of Dammann grating into Fresnel zone plate. The characters of Dammann zone plate enable it to produce a series of axial focal spots distribution with equal intensity in a certain range. In this paper, we introduced Dammann zone plate into the traditional intraocular lens and designed a kind of intraocular lens. And we mainly researched the focusing depth and imaging effect. We find that the intraocular lens with deeper focal depth and better imaging effect can be obtained by the optimal combination of the two parts. This multifocal intraocular lenses enable both the near and far objects to focus on the retina. With the Dammann zone plate, the intraocular lens has deeper focal depth, which allows those cataract patients to get a better visual clarity and can provides better visual quality for them. Therefore, this design has a wide prospect for the treatment of cataract in the future.

Publisher’s Note: This paper, originally published on 18 November 2019, was withdrawn on 25 August 2021 per author request.

In this paper, we propose a two-dimensional metal-dielectric grating with dielectric nanodisks on a thin gold film structure for refractive index sensing due to its near unity absorption at 1050 nm wavelength. The perfect absorption mainly originates from excitation of the horizontal magnetic dipole mode in the metal-dielectric structure. The results show that the sensitivity and full width half maximum are 560 nm/RIU and 11.13 nm over the sensing range of 1.33 to 1.38, respectively. Obviously, the corresponding figure of merit is calculated to be 50.3 RIU^-1, which shows a high sensing performance. Moreover, it also shows excellent performance by measuring the light intensity change in the reflected light at a certain wavelength. The proposed structure has great potential application in biological sensing, integrated photodetectors, chemical applications and so on.

Grating is a very useful diffraction optical element. Highly efficient and broadband gratings are required in current ultrafast femtosecond pulsed lasers. This paper mainly focused on gold-plated reflective gratings. We proposed a rectangular grating with high efficiency and broadband under Littrow incidence at the center wavelength of 800nm for TM polarization. Under Littrow incidence, the duty cycle and the groove depth of the grating determine the diffraction efficiency and bandwidth of the gratings. By the Rigorous Coupled Wave Analysis(RCWA) and simulated annealing algorithm, we analyzed the effects of different grating parameters on grating diffraction efficiency and bandwidth. In this paper, we designed a rectangular grating with duty cycle 0.324, groove depth 1466nm and thickness of connection layer 2146nm, respectively. Its diffraction efficiency of the -1 order approached 98% in broadband. And we analyzed the tolerance of our grating to improve the efficiency of the grating. This kind of grating has very important value in the future application of high power laser.

A novel method based on a grating mode multi-reflection model for designing guided mode resonance gratings under TM polarized incidence is proposed. An effect of near-zero effective refractive index of grating mode is presented. Considering this effect, the design process can be simplified. An example of GMR Brewster grating is designed to verify the design method and a rigorous numerical simulation of the example is given which shows that the design goal is well achieved.

Asymmetrization of fringe profile (the so-called “blazing) of thin phase holograms provides the opportunity to increase their diffraction efficiency to nearly 100%. One of popular applications of thin holograms is generation of the optical vortices. The paper considers advantages and special features of using of digital blazing in such fork-like holograms.

Ptychography is a widely used lensless coherent diffraction imaging approach, in which the complex transmittance function of the object is retrieved from a set of diffraction patterns originating from overlapping sample illumination area. In this paper, we propose a normal-incidence reflection ptychographic system. The sample and detector are located on each side of the beam splitter similarly to Michelson interferometer without reference beam. This system can reveal the topographic structure of reflective samples. Compared with Michelson interferometer based off-axis digital holography, the field-of-view of the proposed reflective ptychography is unlimited by the aperture of the detector.

In this paper, an advanced ray-tracing model for simulating holographic optical element is programmed and demonstrated in Zemax OpticStudio. The model integrates the physical properties of the hologram, such as diffraction direction and efficiency based on incident rays’ wave vector and polarization state, into the standard ray-tracing model. Two different algorithms are implemented and tested. The model also accounts for hologram emulsion shrinkage and refractive index shift. The utility of this new model is demonstrated with a case study of a multi-color holographic imaging system, where the structures of multi-color holograms are built with different methods and the full-color image simulation is performed. Results of different methods are compared and discussed.

Urine analysis (urinalysis) is a critical component to diagnose urinary tract disease. Microscopic evaluation of the urine provides an insight into potential underlying urinary tract disease, which is used for identification and characterization of both common and much less common formed elements in the urine sample. In this paper, the microscopic urinalysis is presented by using single beam digital holographic microscopy (DHM). This is a common path set up wherein both beams (reference and sample) travel through a similar path providing higher temporal stability. In this paper, phasecontrast three - dimensional imaging of red blood cells (erythrocytes), white blood cells (leukocytes), squamous and nonsquamous epithelial cells, casts and various crystals present in the urine samples, have been demonstrated. The proposed imaging modality for the diagnosis of urinary tract disease is simple, non-contact, non-invasive, and provides higher temporal stability due to its common-path geometry.

This paper presents the visual and quantitative investigations on the heat flow performance from plate fin heat sinks using digital holographic interferometry (DHI). In the experiment, double exposure DHI is used to calculate the temperature distribution surrounding the heat sink. First, a digital hologram of ambient air surrounding heat sink is recorded; when no power is applied across the load resistor connected to the bottom of the heat sink. After that, a series of holograms of hot air surrounding the heat sinks are recorded at a constant time interval. The phase difference maps between the heated air and ambient air at different time interval around the heat sink are calculated by numerical method. Visual inspection of reconstructed phase difference maps of air field surrounding the heat sink at a different time provide the qualitative information of temperature variation trend of air field surrounding the heat sink during the heat dissipation process. Quantitative information of temperature distribution surrounding the heat sink is obtained from the relationship between the digitally reconstructed phase difference map of ambient air and heated air. The effect of the number of channels/fin spacing on the heat flow performance of heat sink with equal width and length is also investigated. Experimental data is used to calculate the heat transfer parameters such as local heat flux and convective heat transfer coefficients.

Holographic wavefront sensors are the convenient tool for the fast, cheap and computation lacking wavefront analysis. The use of holographic filters-correlators makes it possible to decompose the wavefront along the basis of Zernike polynomials or to represent it as a set of piston segments. The paper considers possible application of such a technique for beam decomposition along other basis like Hermite-Gauss, Laguerre-Gauss and so on sets.

In this paper, holo-shear lens based interferometer is experimentally demonstrated for the measurement of temperature distribution, and temperature fluctuations inside the wick stabilized micro diffusion flame created from the candle. Holoshear lens based interferometer is a common path interferometer, which is simple, compact, light weight and less vibration sensitive to environmental perturbation. Also, holo-shear lens based interferometer is capable of measuring the temperature profile of a micro sized flame to macro sized flame.

Optical scanning holography (OSH) is a single-pixel holographic recording technique. We will first briefly review OSH. We then show some recent results in pre-processing (such as edge extraction) of holographic information.

A method is proposed for color image encryption by using optical scanning holography together with orthogonal compressive sensing, which can provide distinct keys to different channels of color image, along with synchronous encryption. The theoretical demonstration of orthogonal compressive sensing is prioritized to be narrated, which can produce a preprocessed measurement array for the subsequent sampling. The orthogonal basis matrices may provide an additional key space to guarantee the security of this cryptosystem, and the uncertainty of key is used to make a further illustration. The simulations and discussions are also made on the cyphertext characteristics, the robustness of resisting occlusive attack and some other parameters.

Structured illumination microscopy (SIM) is a well-known super-resolution imaging technique, which exploits moiré patterns created when a sample is illuminated with periodic stripes. Conventional SIM often applies to fluorescent samples, or the samples which have absorption on illumination light. Here we report quantitative phase imaging of transparent samples with a SIM apparatus in transmittance-mode. For this purpose, two sets of fringe patterns, which have two orthogonal orientations and five phase-shifts for each orientation, were generated by a digital micro-mirror device (DMD) and projected on a sample. Under different fringe illuminations slightly-defocused images of the sample were recorded sequentially by a CCD camera, where the object waves along the ±1^st orders of the illumination interfere with each other with a lateral shear in-between. The phase derivatives of the sample along the shear direction can be reconstructed from the phase-shifted intensity patterns. Eventually, the quantitative phase distribution of the sample was obtained by integrating the two phase derivatives. Furthermore, an iterative algorithm was used to enhance the resolution of the phase image, considering the structured illumination synthesizes a larger spectrum in the Fourier domain, similar to oblique illuminations in digital holography. This apparatus can also work in the conventional SIM mode, which images fluorescent samples in an in-focus manner. We believe such simple and versatile apparatus will be widely applied to biological imaging or industrial inspection.

This paper through rigorous mathematical reasoning proves that four-step phase-shifting interference algorithm in phase error caused by nonlinear response inhibition system is better than that of three-step phase-shifting interference algorithm. It makes up the theoretical deficiency of previous relevant studies. And the reconstruction image quality of four-step phaseshifting algorithm is better than that of three-step phase-shifting interference. System simulation and digital holographic experiments have been carried out to prove the correctness and rigor of the above theoretical reasoning. In addition, through the analysis of experimental results, it is found that the experimental error is caused by a large number of high-frequency noise signals.

Though laser repairing can smooth the surfaces of laser damaged optical elements, it is difficult to compensate all the stress in them. Therefore, residual stress detection and compensation are significant as surface smoothing during laser repairing. In order to quantitatively detect the residual stress especially in laser damage detection and laser repairing quality evaluation, we plan to use polarized digital holography to measure and analyze the residual stress distribution inside the target; and we also propose the numerical model of quantitative stress detection using the polarized digital holography. Since the polarized digital holography can reconstruct the residual stress in high resolution, fast speed and high accuracy, the proposed method can be a potential tool in laser damage detection and laser repairing quality evaluation in high power laser fields.

In recent years, 3D display technique is one of the emerging technology and gradually becomes accessible to a broader audience. However, because of the traditional 3D reconstruction method is limited by the number of the feature found in the image, the resolution of the generated 3D model is not high enough for 3D display. A new system is purposed, in which we consider the vertical and horizontal disparity between images, and the optical flow is used to replace the feature matching segment, so that more points can be pushed into the reconstruction process for improving the resolution of the models. Experimental results prove that the resolution of the models can be enhanced effectively. The details of the model are preserved, and the holes in the weak texture region are successfully filled.

Diffractive optical elements (DOE) with an arbitrary topology are widely used in various fields of modern science and technology. Our paper is dedicated to diffractive optics, which is produced by circular laser writing on CLWS-300. In the process of fabrication of diffractive element, a pre-calculated pattern is written on the optical substrate. During this process, writing errors occur that can introduce distortions into the wavefront generated by diffractive optical element. The error of the angular coordinate can make the most significant contribution to the total error. In addition, this type of error is the most difficult to control and correct.
In this paper, we propose a method for measuring the angular coordinate error of the circular laser writing systems based on laser interferometry. The method includes writing special test samples and their subsequent control using a conventional Fizeau interferometer. The angular coordinate error is calculated from the phase map. This method allows detecting errors of the angular coordinates up to 1-2 ang. sec. The test pattern can also be written on the same substrate within a single fabrication process with main pattern. This allows certification and quality control of the fabricated diffractive optical element. In addition, laser writing system can be periodically tested to verify that angular coordinate error is within acceptable limits. The method described in article can be extended to any writing system operating in the polar coordinate system.

Staphylococcus aureus (S. aureus) is a round-shaped, aggressive human pathogen that can grow either by fermentation or by utilizing an elective terminal electron acceptor without oxygen. These bacteria can spread from an infected person to others, and it can enter into the body via the bloodstream and can infect body parts and organs. To avoid spreading infections and life-threatening diseases, a rapid, non-invasive, non-contact expeditious detection system is required. In this paper, a holographic optical element based digital holographic interferometric (DHI) system has been demonstrated for the label-free imaging of S. aureus bacteria. A comparison has been made in the proposed holographic optical element based DHI system and the conventional off-axis Mach–Zehnder configuration based DHI system. The proposed DHI system is an economical, efficient and easy-to-operate interferometric system, and significantly improves the signalto- noise ratio of recorded digital holograms without any spatial filtering.

The optimization of image resolution for digital holographic scanning imaging of biological cells is investigated. Digital holographic scanning imaging experiments on the upper epidermal cells of onions are performed to demonstrate the validity of resolution optimization algorithm. In the experiments, the holograms of the upper epidermal cells of onion are recorded at a certain scanning rate, and then are processed by using the resolution optimization algorithm. As a result, the phase images of the onion epidermal cells with higher contrast and resolution are obtained. According to the synthetic holograms, the changes of cell nucleus and actin microfilament inside onion’s epidermal cells are displayed. In addition, the dehydration process and plasmolysis phenomenon inside onion epidermal cells are also exhibited by recording longterm scanning holograms of living epidermal cells. The experimental results demonstrate that image quality of living onion epidermal cells can be improved by optimizing the algorithms.

Spectral beam combining is an effective method to increase the total output power of a laser system while maintaining a high beam quality. The diffraction grating with high diffraction efficiency and high laser damage threshold is the key component in a spectral-beam-combining laser system. To meet the above requirements, we design a grating on top of a high-reflectivity HfO₂/SiO₂ thin-film stack. The diffraction efficiency of the grating depends mainly on the duty cycle and depth of the grating grooves. The grating was fabricated by using optical interference lithography and reactive ion beam etching. To achieve high efficiency, we controlled the duty cycle by applying an end-point detection technique during development and we controlled the groove depth by adjusting the ion-beam etching time length. In a 50 mm × 50 mm fabricated grating area, the measured diffraction efficiency in TE polarization was 95.8 ± 1.1 % at the center wavelength of 1030 nm. In the wavelength range of 1025 nm to 1035 nm, the measured average diffraction efficiency in TE polarization was 97.7% at center of the grating sample. We describe the details of our work, including design parameters, fabrication processes, and measured diffraction efficiencies.

In this paper, a method based on point source and view-window is proposed that covers the features as full parallax, depth and accurate occlusion cue, shading and lighting, and ensures the computational efficiency in the meantime, to calculate the on-the-fly computer-generated holograms. With the acceleration of graphics processing unit (GPU), a bunch of point data of reconstructed image go through the pipeline of OpenGL and finish with coordinates transformation, fragment interpolation, lighting calculation, occlusion test, calculation and superposition of complex amplitude, and finally hologram are generated and loaded into the spatial light modulator (SLM). The experimental result shows that the lifelike complex full-parallax objects can be reconstructed at a high speed with varying gloss and accurate occlusion when viewed from different perspectives in the view-window.

Nowadays, the monitoring of CO₂ concentration has gradually become the focus of scientists all over the world. In order to study the effects of CO₂ on climate change and global ecosystems, hyperspectral and high spatial resolution CO₂ detectors are necessary. Holographic grating is the core element of that CO₂ detectors, and the immersion holographic grating can greatly improve the resolution of grating and reduce the volume of spectrometer. Therefore, it is necessary to take research on immersion grating. In this paper, we have designed and optimized a quartz immersion grating used in the CO₂ detectors. We have designed and optimized the parameters of the grating, such as the width ratio and groove depth, according to the requirements of the spectrometer used and the actual fabrication errors, we designed and optimized rectangular and trapezoidal groove with different bottom angles to obtain high efficiency and low polarization-dependent immersion gratings. In the 2.04-2.08 μm band, with rectangular groove, the groove depth of the quartz immersion grating is 950 nm, the duty cycle is 0.7, the -1 order diffraction efficiency is over 82%, and the degree of polarization is below 12%. When the groove is trapezoidal and the bottom angle is 85 degrees, the -1 order diffraction efficiency is over 79% and the degree of polarization is below 10% at duty cycle of 0.63 and groove depth of 1050 nm. Then under the trapezoidal groove with a bottom angle of 80 degrees, when the duty cycle is 0.62 and the groove depth is 1100 nm, the -1 order diffraction efficiency is over 81% and the degree of polarization is less than 9%. Finally, we will fabricate a sample of immersion grating with a period of 1117 nm on a quartz substrate by holographic ion beam etching in late 2019.

Weighted iterative algorithm is presented for generating phase holograms with high-quality reconstruction. The reconstruction plane is partitioned into two parts where different constraint strategies are addressed during the iteration process. Signal region of the reconstruction plane is constrained directly according to the amplitude distribution of the target pattern, whereas non-signal region is constrained indirectly by total energy control of the hologram plane based on the energy conservation principle. The weighted iterative algorithm can improve the reconstruction quality by broadening the optimizing space of the calculated phase distribution.

As an important means to obtain three-dimensional depth information of target, optical measurement has been widely used in face recognition, machine manufacturing, aerospace and other related fields in the past decades. Optical three-dimensional imaging and depth measurement is a fast and non-contact method for reconstructing three-dimensional imaging and depth measurement of objects based on optical means and digital image processing analysis. In this paper, a three-dimensional measurement module of transversely rotating combined Dammann grating is proposed, which generates interleaved high-density dot-matrix structured light for three-dimensional imaging and measurement. The measurement module consists of integrated components of laser and beam expander, collimating lens, four transversely rotating combined Dammann gratings with different beam splitting ratios, and objective lens. The laser emits a laser beam which is collimated by a collimating lens. Four Dammann gratings are used to generate four non-staggered dot-matrix by splitting them, and then the high-density staggered projection dot-matrix for three-dimensional measurement and imaging are projected by the objective lens. The measurement module has the advantages of simple structure, high output dot-matrix density, staggered projection dot-matrix edges, and easy integration into mobile devices. This technology may reduce the complexity, number of optical elements, power consumption and cost of structured light projectors in mobile and fixed 3D sensors.

Metasurfaces, a type of metamaterials with ultrathin thickness, have drawn tremendous attention in recent years due to their extraordinary flexibility to manipulate the light at subwavelength scale. It is useful in implementing various optical functions with a set of elements. A typical application of the metasurface is the holographic imaging, and one key parameter for the realization of holographic imaging is its optical efficiency. In this paper, we demonstrate the optimized holographic imaging by using the metasurface coded with a combined phase distribution. Firstly, the phase hologram is generated by Gerchberg-Saxton (GS) algorithm and the blazed grating is formed by introducing a periodic linear phasegradient distribution. Then the phase profile of the hologram is superimposed with the phase of blazed grating to generate a new phase distribution. Benefiting from the advantage of high efficiency for the desired light-manipulation, the metasurface based on the metal-insulator-metal (MIM) structure with different geometric parameters was utilized to cover the phase shift of 0 to 2π for encoding the generated phase distribution. The structure consists of a four-level quantized metallic Au nanorods elements separated by dielectric layers of SiO2 with the Au substrate, so a macro cell of our metasurface consists of 16 (=4× 4) subwavelength meta-atom, which are made of the Au nanorods with different width. The simulated far-filed patterns are calculated by finite-difference time-domain (FDTD) method. Compared to previous metasurface, our structure preferentially steer incident energy into the desired first order diffracted beam with the help of the equivalent of the blazed grating. And the optimized holographic imaging results could be achieved.

At present, scanning electron microscopy (SEM) and atomic force microscopy (AFM) are the main means of measuring grating parameters. When SEM is used, irreversible damage will be caused to the sample. AFM can only detect small areas of samples. AFM is too inefficient for large area diffraction gratings. Therefore, non-destructive testing of grating groove shapes is very necessary. In this paper, the light intensity 、diffraction angle of first-order and diffracted light interferometric fringes are studied and a new method for non-destructive measuring of grating parameter is proposed. We will study the grating parameters based on the rigorous coupled wave theory (RCWA).

A three-dimensional particle image velocimetry (PIV) system is introduced in this paper. Based on camera array light field technology and Tomographic PIV principle, this system is designed for the measurement of instantaneous or continuous three-dimensional velocity of the flow field section or for the measurement of instantaneous three-dimensional velocity within a volume. The camera array light field technology is capable of collecting four-dimensional light field data, and can flexibly adjust the observation field of view, focus position and depth of field through calculation processing. Therefore, combining the camera array light field technology with the Tomo-PIV a 3-dimensional PIV system is achieved. In this paper, the design and development of the system is presented, experimental results and analysis based on this system are discussed.

With the rapid development of augmented reality technology, people can clearly see the superposition of virtual and real world images at the same time. The diffractive optical waveguide has obvious advantages over the geometric optical waveguide because of its high diffraction efficiency, light weight and difficulty in generating ghost images. Therefore, the use of holographic gratings as coupling elements for planar waveguides has been widely used in head-mounted display systems. Because high efficiency grating is required as coupling element in coupling, we use slanted trapezoidal surface relief grating as coupling element of the planar waveguide. In this paper, a slanted trapezoidal surface relief grating has been designed as a high-efficiency coupling element with a grating period of 520 nm and a material of BaK₃ glass with a refractive index of 1.54. By optimizing the structure of the slanted grating, the relationship between the groove parameters and the diffraction efficiency of the slanted rectangular grating and the slanted trapezoidal grating is analyzed in detail. The results show that under the normal incidence of light at 630 nm, the groove depth is 450 nm, and the slant angle θ1 is 40°, when the -1 order diffraction efficiency of the TE polarized light is higher than 80%, the ranges of the slant angle θ₂ and of the maximum diffraction efficiency value would be obtained. This can greatly improve the coupling efficiency of the holographic planar waveguide.

The methods based on spatial and frequency domain processing for resizing the reconstructed image of digital hologram are studied. The first kind of methods for resizing reconstructed image is to resample the hologram. The reconstructed image is reduced by up-sampling or interpolating the hologram and the reconstructed image is magnified by down-sampling hologram. But its viewing angle is reduced. An approach is proposed to preserve the viewing angle. The second kind of method for resizing reconstructed image is to resample selected region in frequency domain of hologram. The reconstructed image is resized by this method without changing its viewing angle.

A noise reduction method based on a shorter synthetic-wavelength in DWDH is proposed in this paper. The unwrapped phase at longer synthetic-wavelength is calculated by using the wrapped phases of two individual wavelengths. By comparing the amplified phase of longer synthetic wavelength, of which magnification is equal to that of wavelengths with the wrapped phase of a single wavelength, the difference of phase noises between the longer synthetic-wavelength phase map and the single-wavelength phase map can be calculated, and then accurate height at single-wavelength can be achieved. The proposed method for calculating phase noise is performed by comparing the phases between the single-wavelength with the shorter synthetic wavelength, and then the height at shorter synthetic-wavelength can be obtained. Compared with the existing method, the proposed method can reduce certain noise and benefit the phase reconstruction of fine structures.

The diffraction characteristics of phase-type soft aperture with super-Gaussian transmittance were studied. It was proved that the phase-type soft aperture with super-Gaussian transmittance can improve the near-field intensity distribution of the beam and suppress the diffraction of the beam. Genetic algorithm was used to design the phase-type soft aperture, and was compared with the error diffusion algorithm. The design results demonstrates that the phase-type soft aperture designed by the genetic algorithm has a smaller RMS error and can suppress the diffraction modulation of the intensity in a large spatial range.