This PDF file contains the front matter associated with SPIE Proceedings Volume 10818 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

In this article we based on the laws of physics to illustrate the enigma of time in creating our physical space (i.e., the universe). We have shown that without time there would be no physical substances, no space and no life. In reference to Einstein’s energy equation, we see that energy and mass can be traded, and every mass can be treated as an Energy Reservoir. We have further shown that physical space cannot be embedded in absolute empty space and cannot have absolute empty subspace in it. Since all physical substances existed with time, our cosmos is created in the context of time and every substance including our universe coexists with time. Although time initiates the creation, it is the physical substances which indicate to us the existence of time. We are not alone is almost an absolute certainty. Someday we may find a right planet, once upon a time, had harbored a civilization for a short period of light years.

Computer-generated hologram (CGH) is a key technology in electro-holography systems. However, the huge computational complexity is a challenge for practical demands. In this paper, we propose an improved algorithm to accelerate CGH computation based on symmetric compressed LUT (SC-LUT) algorithm. In LUT calculation, the horizontal and vertical modulation factors is reduced to one-dimension arrays instead of dual one-dimension arrays. In hologram calculation, we introduce a one-time generation of color holograms method which is accelerated by matrix convolution operation. Numerical simulation results also show at least 13 times faster than existing algorithms without sacrificing the computation precision. The proposed algorithm accelerated by the graphic processing unit (GPU) is an effective method for fast calculation of CGH in color holographic display.

Wavefront distortions or phase aberrations usually degrade the performance of imaging systems, thus limit the imaging resolution and image quality. Adaptive optics (AO) is proposed and developed in order to remove the effect of optical aberrations. Traditional AO systems use wavefront sensors (such as the Shaker-Hartmann sensor) to measure wavefront errors. Development of wavefront-sensorless adaptive optics in recent years eliminates the need for wavefront sensors, which simplifies system structure, reduces the cost and overcomes some limitations of traditional adaptive optics. In this paper, we focus on the implementation of Image-based wavefront-sensorless adaptive optics in Fresnel Incoherent Correlation Digital Holography (FINCH) to improve the imaging quality. Zernike polynomials are introduced to describe aberrations, sharpness and intensity are employed to evaluate the imaging quality dynamically, and the measurement and compensation are implemented combining with curve fitting algorithm. We implemented this method in FINCH system, which can achieve incoherent holograms by using the correlation between the object information and the image of a pinhole. A phase mask is mounted on a SLM to split the beam and shift phase to suppress the twin images in the reconstruction. Both the aberration and the phase mask were introduced by SLM. The image-based wavefront-sensorless adaptive optics is investigated experimentally in a FINCH imaging system.

Detection of the particle especially the nanoparticle attracts much attention in various fields from analysis of various biological materials to environmental monitoring. Microring resonator coated with high refractive index film provides a structure supporting whispering-gallery-modes (WGMs) due to the contrast of the refractive index. This structure can be used as a microfluidic detection and indication of the binding of nanoparticles. In this work, we numerically investigated and optimized this microring resonator, pursuing high quality factors 10⁶, yielding the intense light and analyte interactions, as well as extremely high sensitivity and low detection limit. For a single particle adhered to the inner surface of the microring, the eigenmode were investigated. The symmetric and asymmetric modes located the particle at the antinode and node due to the backscattered light coupling between the clockwise and counter-clockwise propagation the WGMs. This leads to the original degenerate resonance mode splitting in frequency. The electric-field intensity distributions along the radius direction near to the film for the fundamental mode and higher order mode were simulated with and without particles. We found that the significant of splitting for the fundamental mode (~ 0.010 THz) due to the scatter of the particles was very different with the separation between fundamental mode and high order mode (~ 1 THz). In addition, the splitting in changed with the size and number of the particle were obtained and the sizes of the particles were estimated which consistent with those in design

Using a metasurface comprising an array of dielectric nanobricks and a backreflector, a ultracompact, broadband and high efficiency (nearly 100%) half-waveplate can be obtained which covers the whole fiber telecommunications windows (S, C, and L bands).

Three-dimensional human face identification card using micro lens array is proposed based on the introduction of integrated imaging technology into three-dimensional human face identification cards. The traditional ID card is a two-dimensional plane photograph. With the development of integrated imaging technology, each unit lens in the integrated imaging technology can record relative parts of information from various directions, combining a lenticular lens array and a concave lens array to realize naked eye in natural light you can see the three-dimensional photos on the ID card. This technology not only achieves visual three-dimensionality and beauty, but also enhances the security of identity cards, and can be widely applied to various situations requiring authentication.

Grating theory is normally designed for nano/microoptics applications. If we consider the further smaller size, we might enter the area of picometer optics. Although it seems picometer optics might be the frontier of developing nanooptics devices into the next step, it is hard to make picometer optical devices previously. We will report a series of three works that can lead us into the picometer scale. The first is to fabricate high-density gratings whose periods can be controlled to be slightly different in picometer range, which is done by rotating Dammann grating in a microrad angle for achieving the grating period continuously tuned in picometer scale. The second is to propose carrier pico-grating array for measuring the distances of the moving grating, which can be done in picometer accuracy. The third is to measure the wavefront of two-beam interferences in picometer accuracy, which is far beyond the current normal laser interferometer. Initial experimental results demonstrated that the wavefront has been measured with 250pm linear phase difference, which is impossible to obtain with the traditional laser interferometer. Taking consideration of these picometer works together, we believe that picometer optics should come with these picometer optical tools further extended in the near future.

With the release of IphoneX, compact 3D optical measurement has become a popular technology. An important application of compact 3D optical measurement is to realize 3D imaging of targets. A compact three-dimensional optical measuring instrument can project a coded or structured light pattern onto an object to achieve the purpose of three-dimensional imaging. Apple's solution is to design diffractive optical elements using algorithms (such as the Gerchberg-Saxton algorithm) to produce a fan-out staggered dot matrix projection pattern in which some dot matrix produce a lateral offset from adjacent dot matrix. In this paper, a new method is proposed to generate the interlaced lattice projection pattern, i. e. the transverse odd-even combinational Dammann grating method. This method produces the above pattern by two Dammann gratings placed perpendicular to the optical axis, which is different from the scheme proposed by Apple. The advantage of this scheme is that the overal structure is simple and the design cost is reduced, so it is easy to mass-produce, and its lateral combinational structure is conducive to the miniaturization and integration of devices, so it is convenient to integrate in various interconnected devices. For example, mobile phones with 3D face recognition using this technology are not only easy to use, but also highly secure.

That paper focuses on indirect measurements of the diffraction gratings by analyzing their scattered distribution. The method is based on pre-calculated numerical dependencies of the energy characteristics. The comparison of measured diffraction efficiency values with numerical simulations provide the inverse measurements of the profile height. Presented research belongs to the field of scatterometry of high-resolution diffraction optical elements. The concept is tested with polymeric sinusoidal relief. Considered phase diffraction gratings have interest in field of linear displacement encoders.

Directional backlight has lots of potential applications, including dual view display, anti-spy display, and 3D display. The traditional backlight module illuminates the LCD panel with an angular divergence of around ±60°, while the required angular divergence of directional backlight for anti-spy display is less than ±30°. In this paper, the proposed backlight module is consisted of a LED linear array, a coupling prism and a backlight plate. The wavelength of the gratings are such designed that the angular divergence of the emitting light from the backlight module is limited within ±6.6°. Furthermore, the depth of the gratings is well tuned over the backlight plate so that the diffraction efficiency of the nano-gratings increases as the distance from the LED light sources increases. As a result, a uniform illumination can be achieved over an area of 5.5-inch.

To meet the increasing demand for the dynamic naked-eye 3D display, we proposed a new method to realize the dynamic effect of hologram by using the holographic printing technology. We used a convergent light as the object beam to print out a holographic plate through point-by-point exposure inside a photopolymer material. In reproduction, an image processed by two view images of a 3D object was directly projected to the holographic plate as reconstruction beam, and two images were observed from different directions. That is, when we project an image containing several views of a 3D object, based on multi-view principle, we can observe the reconstructed 3D effect. Since the display plate doesn’t carry amplitude information, the content of reproduced 3D image depends on that of the projected image. Thus, a dynamic stereo effect can be achieved by projecting each image processed from a frame of dynamic stereo continuously

As an important feature of image, color can be used to achieve binocular vision. However, different colors may have different contributions. In this experiment, we designed a stimulus in which luminance is incongruent and color could be manipulated. Color variations were based on opponent color space, where seventeen color points distributing in red-green and blue-yellow directions were selected. The stimulus consisted of an array of asymmetric patches uniformly distributed in a constant sized volume. Subjects were required to indicate the amount of perceived depth patches in the 3D displays. Our results demonstrate that the amount of perceived depth patches was influenced by color information, and indicate that colors have different contributions to binocular matching.

This paper proposes an optimized method of three-dimensional measurement based on three measuring triangles. The three measuring triangles are made up of the left camera, the right camera, the projector and the object to be measured. After projecting N binary band limited patterns on the surface of the object to be measured, the object can be divided into three parts to be measured using the temporal correlation based on Hamming distance. The three parts of the measuring data complement each other without overlapping each other and thus changing the useless data measured in original binocular measurement system into effective data. In this way, the missing data of binocular measurement system is made up and the integrity of the measurement results are improved. The experimental results verify that the integrity of the reconstructed point cloud using the three measuring triangles method is higher than that of the original binocular 3D measurement method, which proves that the proposed optimized method is a convenient solution for solving the problem of partial point cloud missing in the binocular structure measurement.

In this paper, a non-contact, fast and high-precision optical 3D measurement method is proposed to provide a detection scheme for the processing of optical rough glass in the grinding stage. We first use a planar calibration board to map the phase-height of the optical rough glass in a certain spatial range, then use the phase-shifting method to obtain the heightmodulated phase distribution of the rough glass. Finally, the 3D profile of the whole rough glass is obtained based on the phase-height mapping. The whole detection process can be completed in a few minutes, and the accuracy is less than 100 microns.

In this paper, we used an algorithm for the synthesis of binary computer generated holograms Fourier, applying pseudo-random phase masks to increase the intensity of high-frequency components of holograms. A feature of such a computer generated hologram is that the generated symbolic information is an axis-symmetrical picture, which is determined by the mathematical description of the Fourier transformation. The holograms are recorded in a collimated beam with the help of a spatial light modulator in a projection mode. The hologram is recorded with a decrease in linear dimensions to reduce the distortions introduced by spatial light modulator. The progress of computer-synthesized holograms has fallen on the progress of computer technology. In this article, the key issue is the photochemical procedure of processing holograms after their exposure. This processing allows to increase the transmittance of the hologram up to 96%, which enables to install computer generated holograms directly in the field of view of a person. A positive effect of the photochemical treatment process is also an increase in the overall diffraction efficiency of the hologram and redistribution of the intensity from the central point (radiation that did not diffract on the structure and passed through the hologram) to the image that was formed as a result of diffraction of radiation.

Digital holography based sound propagation imaging works on phase change characteristics of a medium where sound wave propagates. Spatial and temporal distribution of sound field can be obtained by measuring phase modulation of light caused by sound field. In this technique, object wave passes near to vibrating object and the interference patterns are recorded in digital holograms as a function of time. After using numerical reconstruction by angular spectrum method and acousto-optic data processing, sound field can be visualized. This technique has been tested for vibration frequency measurement and can also visualize the human voice by optical means. It has also been used for optical voice encryption, which can secure voice. For vibration frequency measurement, Fourier analysis is used and for voice encryption, optical image encryption techniques have been utilized. In this paper, we present our proposed sound wave imaging scheme and its applications in frequency estimation and voice encryption. In the support of sound imaging scheme and its applications, we present detailed theory and experimental results.

One important aspect of our universe is that one cannot get something from nothing; there is always a price to pay. In this article we show that every bit of information is limited by a quantum unit. Since we are communicating within a temporal subspace, this unit can be equivalently described as a quantum limited subspace (QLS), as imposed by the Heisenberg Principle. We show that communication can be exploited within and outside the QLS. The size of a QLS is determined by carrier signal bandwidth; that is narrower the bandwidth the larger the size of the QLS. By manipulating the size of a QLS, more efficient information transmission strategies can be developed. Examples for inside and outside QLS communication are given. Extension to relativistic communication has also demonstrated. We remark that, a new era of communication is anticipated to immerge and it will change our way in communicating, observation and computing, we used to use, forever!

Mode division multiplexing provides mutually orthogonal communication channels to break the capacity-per-fiber limit given by the Shannon theorem. Cylindrical vector beams (CVBs) as a set of orthogonal eigen modes in optical fiber have the potential application in high capacity optical communication. However, there is still no efficient multiplexing/demultiplexing scheme for coaxial multiple CVBs generation and detection. In this work, we propose and demonstrate the efficient sorting of coaxial multiple CVBs based on the anisotropic geometric optical transformation approach using the Pancharatnam-Berry optical element (PBOE) device. The device is fabricated by the photo-alignment liquid crystal (LC) in a thin film with a total pixel number of 768×768 and a pixel size of 11.7 μm. Since the PBOE has the circular polarizations selective property, the device can independently modulate the left-handed circular polarized and right-handed circular polarized light components of CVB. The anisotropic geometric optical transformation is capable of transforming the ring-shape intensity distribution of CVB to two straight lines. Through the phase correction and fourier transform, the CVB is finally converted to a spot with a lateral displacement proportional to the input CVB orders. In the proof of concept experiment, we demonstrated CVB sorting with a large dynamic sorting range of 20 different orders of CVBs with efficiency up to 61.7%. The coaxial multiple CVBs with a minimal order interval of 3 are separated in the experiment. We also implement the CVB sorting approach in optical fiber communication system as a demultiplexer after 2.8 km signals transmission.

We offer a convenient and dynamic method for the measurement of the orbital angular momentum of light using its distinct Fraunhofer diffraction patterns(FDPs) after passing through programmable apertures generated by a digital micromirror device (DMD). The DMD allows for a practical way of testing and centering several apertures, while minimizing movements in the setup in between measurements. We show how to extract the topological charge value, polarity, and parity from the resulting patterns, along with the limitations of each polygon shape, such as the symmetry and uniqueness issues. An experimental demonstration is also provided, confirming the expected patterns simulated using the far-field diffraction integral. This study establishes the potential speed and accuracy brought by the use of a DMD for the challenging task of characterizing the orbital angular momentum of light.

Orthogonal crossed gratings, or two-dimensional (2D) gratings are key optical elements in plane optical encoders. In this paper, Scanning Dammann lithography (SDL) was implemented to fabricate gold-coated 2D gratings by stepping and scanning a 2D air-bearing stage and rotating Dammann gratings. A displacement measurement interferometer (DMI) was applied to monitor the 2D stage which ensured the positioning accuracy of exposing. A series of experiments by varying the exposure dose were conducted. The atomic force microscope (AFM) results indicted the duty cycle changed with the exposure dose. A 2D gold-coated grating with a size 100*100mm was also fabricated. Since it is straightforward to extend the size of the substrate up to hundreds of millimeters, SDL is a promising method to fabricate large-sized 2D gratings with controllable duty cycle.

Different methods of optical vortex detection were investigated. The method of generating optical beams with a nonzero orbital angular momentum using a liquid-crystal HoloEye LC-2002 light modulator was demonstrated, and various methods for detecting optical vortices were tested. The distance at which the structure of the vortex beam decays for the technically possible aperture of the receiving interference system was determined. The results of experimental studies of beam size at different distances were presented. Calculations of the beam and the singularity of the optical vortex divergence angle are performed as a function of the length of the atmospheric path. Additional method for vortices detection based on data from the output of the Shack-Hartmann wavefront sensor using a machine learning system was also presented.

This article considers the use of holographic interferometer to overwrite the holograms for distortion correction. Each optical system contains some deviations of the beam path, called aberrations of the optical system. They are considered in the resulting interference figure as a distortion of the bands. While increasing the sensitivity of the interference pattern, new aberrations caused by re-registration of the installation in addition to the aberrations already presented on the interferogram caused by the initial record, also multiplied by N times, are introduced N times. In this experiment we decided to use a modified setup with spatially combined interferograms with use of reflective SLM (spatial light modulator) LETO and digital image handling of the interferograms recorded by CCD or CMOS camera.

Diffraction grating is widely used in a variety of applications, and the grating must have good quality. In various methods of making large-sized gratings, laser direct writing has obvious advantages. Our research group uses the parallel direct laser writing technology to produce a sinusoidal grating with a size of 100×100mm and line number of 1780 per millimeter. Firstly, the grating is analyzed theoretically to find a groove depth where the sinusoidal grating can reach its highest efficiency, then the grating is produced by laser direct writing and finally coated with a layer of gold. In this paper, we introduce the fabrication and efficiency measurement of grating, and estimate its uniformity. We get 16×16 data points which is divided into 4×3 area from the measurement. For each small area, the efficiency is measured and processed by software, obtaining the efficiency distribution diagram. Most efficiencies are around 90%, which is close to the theoretical calculation. Meanwhile, the efficiency distribution is uniform. Experimental results demonstrated that the developed parallel direct laser writing technology is feasible for writing large-size grating.

A wide-band two-port polarization-independent beam splitter is designed and analyzed at the incident wavelength of 1550nm. Diffraction efficiencies are 49.67%/49.57% and 48.69%/48.88% for TE and TM polarizations in the 0th and the -1st, respectively. Usually, it’s difficult for two-port beam splitter to achieve wide bandwidth for both polarizations. In this paper, the presented grating has advantages of wide incident wavelength range of 110nm and angular bandwidth of 8.8° with good splitting ratio uniformity for both polarizations, particularly TE polarization. Moreover, the aspect ratio of the grating depth to the ridge width is low, which can be etched relatively easily and effectively. This wide-band splitter should be highly interesting for practical applications.

A single-groove grating for four-port TE-polarization beam splitting under normal incidence at the wavelength of 632.8nm is presented. The total efficiency of the beam splitter is over 77% with beam split uniformity better than 5%. Rigorous coupled-wave analysis (RCWA) and the simulated annealing (SA) algorithm are employed to design this beam splitter grating. The tolerance of fabrication errors of the grating is analyzed.

In this paper, we propose a method for measuring the micro-angle based on the 2D grating Talbot effect to generate the moiré fringe period. Firstly, the measurement principle of the micro rotation angle of the 2D grating and the characteristics of the 2D grating Talbot imaging are analyzed. And then the 2D grating is measured by the Moiré fringe generated by the Talbot image. Based on this, we derive the calculation formula of the angle, and analyze the accuracy of this method of measuring angle. The method of generating moiré fringes by Talbot imaging has the advantages of higher precision, more flexibility and convenience in measuring the rotation angle than stacking two directly.

Measurement of parameters of test blazed gratings made on a substrate together with the manufactured element makes possible to avoid measuring and identification of complicated structure in the working area of the multilevel diffractive optical elements or the energy characteristics of the wavefront transformed by the element. This approach allows one to make the inspection process less dependable on the element type. In this case, the profile shape, depth, and period of the test gratings can be optimized to specific task of technological inspection. Measurement of diffraction efficiency of the test blazed gratings in reflected light with visible wavelength makes possible to define parameters of multilevel diffractive optical elements designed for operation in transmission mode for DUV range. The wavelength of probe laser beam and incidence angle should provide a 2π phase jump at diffractive zones boundaries in the test grating structure at measurement in reflection mode. Elimination of disturbing laser radiation reflected from the back side of the substrate during the measurement is carried out by installing the test element on a layer of immersion liquid dropped on surface of a support substrate, which can be made as wedged or single-side polished with ground back side. The problem of the influence of the backward slopes of the blazed test gratings on the measurement of the characteristic curve of the technological process is proposed to be solved by using the sinusoidal form of the test grating profile. In this paper, a method for processing profilograms of such a profile is considered and experimental results obtained at fabrication of conformal correctors by means of proximity half-tone lithography are discussed.

The direct laser writing lithography technology is an efficient way to make the large-sized diffraction gratings. It has the advantages of high efficiency, low cost and high flexibility. For further improvement the performance of the direct laser writing technology, we introduced the two-dimensional Dammann grating into the direct laser writing system. The Dammann grating can create a finite array of uniform intensity spots so that the efficiency of the writing can be increased. In addition, we also proposed a way of rotating the two-dimensional Dammann grating. By the geometric relationship, the expressions of the rotation angle can be derived. Considering the efficiency, the uniformity and the price of the 1D Dammann, we proposed the rotating 2D Dammann grating technology based on the 1D Dammann grating. While the rotation angles of 1D Dammann grating and the 2D Dammann grating are different. The efficiency of laser writing based on 2D Dammann is quite higher than the 1D-Dammann laser writing. We can use this method to fabricate the large-sized diffraction gratings efficiently.

In this paper, we discuss some light diffraction phenomena with a simple quantum theory. Firstly, the wave function of the free particle in quantum mechanics is used to explain Fraunhofer diffraction of the light at a rectangular aperture, and the result is consistent with the Huygens-Fresnel principle. Secondly, probabilistic wave method is used to analyze the Talbot effect of a two-dimensional grating. The results show that the photons at the Talbot distance and incident photons are described by the same probability wave. Finally, Talbot effect is used to measure the wavelength of incident light.

Spectrum plays an essential role in spectral imaging technology. To obtain the spectral information of image, two high - density diffraction gratings which substitute the prism are introduced in the Sagnac loop to form the polarization Sagnac interferometer (PSI). Usually, it’s difficult for prism to achieve wider angle of spectral line and higher resolution, the presented Sagnac loop with high-density gratings has advantages of wide spectral and high resolution. Meanwhile, the dispersion generated by grating is more uniformed than the prism. The two parallel beams exit from the Sagnac loop and the pass through the linear polarizer and finally polymerized on the focal plane array (FPA) by an imaging lens. This compact Sagnac loop with two high-density diffraction gratings is a new way to obtain the spectral-resolved image, which should be interesting for practical applications.

Currently rainbow and volume holograms are the most used protective holograms. The production technology of such holograms allows to replicate them at the industrial level without deteriorating their protective properties. However, new methods of obtaining protective holograms have been recently studied. Previously has been repeatedly demonstrated the possibility of applying computer-generated Fourier holograms (CGHs) to scattering, non-photosensitive media. We want to study the possibilities of obtaining Fourier holograms on such media and discover protective properties of such holograms. We consider the possibility to obtain binary and halftone CGHs on various mediums in mass-production, including metallized films, self-adhesive labels on paper basis, paper and laser film. For the application we used technologies of thermal transfer and laser printing, as well as direct laser recording. The reconstruction was carried out both optically and using a smartphone. This paper presents experiments and results of mass-production holograms on the selected mediums. We have simulated the distortions that may occur after manufacturing of CGHs, analyzed the quality of the image being reconstructed under various application methods. We show that such holograms can be used as security elements in specific cases. Still, there are the possibilities of improving the quality of deposition of protective hologram elements depending on the used technology, as well as the possibility of taking into account potential distortions during the synthesis of holograms.

An alternative holographic wavefront analiser scheme based on the light guide plate with computer-generated holograms and diffractive optical element is proposed. Advantages of the scheme are the absence of a maximum of zero order of diffraction in the photodetector plane and potentially better recognition of aberrations.

Optical position encoders working according to the interference method consists of a measurement scale and a measuring head moving along each other. The scale has a reflection diffraction grating on its surface and the measuring head has a transmission diffraction grating with same period inside. Laser light passing and diffracting through these two gratings creates an interference signal on an optical detector. Decoding of the interference signal phase allows to determinate current position. Known optical position encoders use complex optical schemes and some phase optical elements to form several quadrature signals with different phase for higher encoder accuracy. Previously we researched such kind of schemes [1, 2]. In this paper we propose to use a common optical scheme without phase elements but with a complex structured measuring head grating for this purpose to simplify an optical scheme and alignment requirements. The optical scheme of position encoder based on measuring head grating with specific structure is research and described in this paper.

Optically variable devices (OVD), otherwise called security holograms are widely used to protect IDs and other sensitive documents against counterfeiting. That being said, the problem of quick authenticity verification and quality control remain to be of utmost importance. This paper presents a prototype of the automated optical-electronic device for OVD authentication and quality control, as a complex solution. Developed device allows to conduct both quick preliminary hologram inspection, which is based on photometric image analysis, and in-depth hologram analysis. In-depth analysis implies microrelief parameters, like spatial frequency, relief depth, grating orientation measurements, using light intensity distribution in diffraction orders and the formed pattern of diffraction orders.

Speckle fields contain many random dark and bright spots. In traditional speckle interference measurement technique, the information of the bright areas is fully utilized, and the speckle vortices that exit in the dark areas are often overlooked. The generation of speckle vortices by using phase-only liquid crystal spatial light modulator (LC-SLM) combined with the double Archimedes’ spiral micro-holes array is experimentally and theoretically studied. In the experiment, the gray image of double Archimedes’ spiral micro-holes array is displayed on the screen of LC-SLM, and the output optical field is captured by a CCD camera. The numerical simulations and experimental results show that speckle vortices can be generated by using this method.

Publisher’s Note: This manuscript, originally published on 2 November 2018, has been withdrawn by the publisher for editorial reasons.

Publisher’s Note: This manuscript, originally published on 2 November 2018, has been withdrawn by the publisher for editorial reasons.

Since it was discovered that hippocampus plays a vital role in human memory, enormous investigations on brain memory have been carried out in the last a few decades. However, so far, there has been no report demonstrating how and in what form that the memory is encoded, stored and retrieved. In this paper, we propose a holographic model with theoretical analysis to describe the mechanism of memory encoding, storage and retrieval in brain. The model suggests that memory encoding in brain is achieved through the process of hologram generation in synapses via the interference of the signal wave carrying the outside information and the energy wave emitted by neurons of hippocampus. The holograms are formed by modulated synapses with the structures of the interference patterns. In memory retrieval process, hippocampus emits the same energy wave as that used for encoding with consciousness to induce the reconstruction of the signal wave from the hologram. Experiment was carried out to simulate hologram encoding and retrieval. The discussion presented in the paper shows that the proposed model can reasonably explain some phenomena related to brain memory.

Since target information can be extracted from the light scattering distributions, light scattering from randomly rough surface has been studied in details. As numerical light scattering computation methods can provide precise information avoiding complicated operations and expensive experimental setups, various numerical methods have been widely used. However, most of them require ensemble average computation to obtain the stable results, inevitably decreasing the calculation efficiency. In order to further accelerate the processing speed by avoiding the ensemble average calculation, a high speed method based on surface slope probability density function is designed in this paper, which using the statistical parameters of randomly rough surfaces for direct light scattering calculation. With numerical simulations proving its high accuracy and rapid speed in light scattering computation, the slope probability density function based method is a potential tool for light scattering computation and analysis.

Evolution of phase singularities is studied when a laser beam propagates through an inhomogeneous turbulent atmosphere. The simulation results reveal that, when the laser beam propagates along an uplink turbulent atmosphere path, the density of phase singularities (DPS) stars at zero and then grows rapidly with the increasing of the propagating height. When the beam propagates to a certain height, the DPS reaches its maximum and then begins to decrease. When the laser beam propagates along a downlink turbulent atmosphere path, the functional form of the DPS has a shape of monotone increasing cure with the decrease of the propagation height and reaches its maximum near the ground.

In order to measure optical element surface defects accurately, we proposed a fast and nondestructive microscopic observation method based on lensless digital holography technology. The basic principle of lensless digital holographic microscopy imaging technology based on spherical wave is introduced. CCD was adapted as photoelectric converter and almost-perfect spherical reference wave can be acquired by using optical fiber of high numerical aperture. The wave aberration induced by the defects is effectively recorded and then the accurate reconstruction result of the defect structure is obtained. This method will have potential application in the quantitative measurement for the defects on optical surface and is helpful for the further research and understanding the influence of surface defects on high-power laser system.

Digital holographic diffraction tomography combines digital holography with optical diffraction tomography. According to the Fourier diffraction theory, the spectrum information is unevenly distributed on a Ewald sphere, and most of these data cannot exactly locate on the 3D matrix points. To solve this problem, a single assignment based nearest neighbor interpolation method is proposed. Firstly, the points to be interpolated are chosen on the 3D matrix. For each angle, a search scope is confirmed by two spheres with a radius R (k₀-0.5< R <k₀+0.5), where k0 is the radius of Ewald sphere. Then, the point on the 3D matrix is assigned by the value of the nearest neighbor point within this scope. After the assignment of the frequency information for all the angles, the object function is obtained by 3D inverse Fourier transform. In order to verify the feasibility of this method, a digital holographic diffraction tomography system is built. The 3D refractive index (RI) distribution of a microsphere with known RI 1.4607 is measured. Comparing with the conventional nearest neighbor interpolation algorithm, the relative error is reduced from 0.51% to 0.36%. It is demonstrated that the proposed algorithm can improve the reconstruction accuracy for diffraction tomography.

With the development of optical communication, especially the wide applications of dense wavelength division multiplexing (DWDM) technology, all-optical communication is attracting more and more attention. Wavelength selective switch (WSS) is a new technology, which has the advantage of free switching of individual wavelength. The wavelength division devices play an important role in above mentioned optical communication system. Holographic gratings is one kind of DWDM device, which are characterized by dispersion, high diffraction efficiency and polarization-insensitive. Nowadays, holographic gratings have been widely used in optical communication systems. However, the polarization-insensitive transmission gratings have high aspect ratio structure, which are very hard to transfer the pattern from photoresist mask to substrate (fused silicon). In this paper, the aspect ratio is effectively reduced by adopting LaK9 as substrate with a high index of refraction relatively. The structure parameters of polarization-insensitive gratings should be designed and optimized, such as period, duty cycle and depth. The diffraction efficiency under TE polarization mode and TM polarization mode was discussed respectively in detail in this paper. At the same time, the bandwidth of the designed gratings is discussed. As a result, a proper gratings were designed with high diffraction efficiency (>90%) under TE polarization mode and TM polarization mode, which could be applied in optical communication. The ion etching difficulty is eased by reducing the aspect ratio.

In order to solve the problem of slow computation of point source model, we designed a real-time computer holographic generation system based on a multi-core CPUs and graphics processing unit (GPU). This system makes full use of the GPU's powerful parallel computing capabilities and CPU logic computing capabilities. It has been verified through experiments that the system is effective and feasible. At the same time, we use the Compute Unified Device Architecture (CUDA) platform to program an algorithm for the parallel computation of holograms in a graphics processing unit. In this paper, we have implemented a point source model to generate compute-generated holograms. We also compared computational performance in CPUs, GPUs, multi-core CPUs and GPUs. Among them, the multi-core CPU and GPU systems have the fastest computational holograms, which can at least increase the hologram calculation speed by 120 times compared with the equivalent CPU system, and also can increase the speed of calculation by 2 to 10 times compared with the GPU system. Therefore, the system which we designed provides a new method for real-time calculation of holograms.

In this paper, we propose a high-density grating interferometry system, which can be applied to measure displacement on the nanometer precision. We make use of the optical subdivision module to improve the measurement resolution which is better than the traditional one. The core part of the whole system is a grating with high-density of 1780 lines/mm and long-range of 100mm*100mm. The apparatus adopts a symmetrical structure to reduce the error resulting from environmental disturbance. The system provides a novel measurement technique to improve the grating interferometry. The experimental results show that the grating interferometer system has good stability, and the in-situ measurement error is within ±5 nm for a long time. The grating interferometer can measure the short distance displacement of 30 nm and can control the error within ±2 nm. The measurement of the distance of 10 mm can control the error within ±20 nm. The results proves the feasibility of our proposed improved.

In this paper, we propose a dielectric cavity enhanced high reflective multiband waveplate based on nano-grating structure, which exhibits quarter waveplate at two wavelengths (λ=810nm and λ=1530nm) and half waveplate at another wavelength (λ=1100nm). The simulation results show that at the working wavelengths (i.e., 810nm, 1100nm and 1531nm) of the device, the reflections are larger than 94% and the average value is about 95% with polarization orientation at 45° . As compare with the traditional metal nanograting waveplate, it has large phase difference with the same geometrical parameters (period, aspect ratio and thickness), and it also does not need to rotate the polarization orientation of the incident light when it work at different wavelengths. It provides a great potential for applications in advanced nanophotonic devices and integrated photonic systems.

A method of automatic focus searching is present that calculates the similarity degree of the two amplitude terms reconstructed with a fixed interval. It is based on the optical field distribution characteristics in a diffraction-limited system, as which a digital holography imaging can be described. The supportive theory is briefed in this paper, and then several typical similarity algorithms are introduced that are used as the focus degree measurement. The autofocus procedure and precisely focus searching of this proposed autofocusing method are given. Each similarity algorithm based autofocusing is validated in simulation. The results demonstrate their applicability and reliability.

The Talbot effect of a one dimensional (1D) grating in the focal region of a lens illuminated by a suitable spherical wavefront was analyzed based on the Fresnel diffraction theory. The condition of the self-imaging in the focal plane was also deduced. We found that the integer and fractional self-imaging phenomena can be produced with different distance between the point source and the grating. In addition, some formulas about a magnification, the period and the slitswidth of the diffracted images of the grating in the focal region were also given. Furthermore, the different parameters influencing the self-image are also discussed by some simulations. A grating was used for an example to test the validity of this theory. The agreement between the numerical and experimental results suggests the practicability of this theory to realize different Talbot imaging with various structures of the periodic objects, which can open a new door to achieve various potential uses related to optical trapping, super-resolution nano-processing and lithography of multifocal spots array.

This paper presents new high-performance optical-electronic scanner for security holograms authentication. Scanning speed is increased due to the use of sophisticated modern scanning systems, high-speed sensors and specifically designed and manufactured optical system components. Correlation filters used in the information processing decrease total processing time and increase resulting reliability of the authentication process.

Full-color holographic waveguide display usually adopts a single-plate display structure, and although the structure is simple and light, the field of view is small. As to this problem, a full-color holographic waveguide display with double-layer grating and double-plate structure is proposed. This configuration consists of four gratings to realize the light input and output, and expension of the exit pupil.To display the RGB color with a better uniformity in the wider field of view, with the Rigorous Coupled-wave Analysis(RCWA), the shape of grating and grating films are designed and optimized.

Various manufacturing techniques are used to minimize the number of micro--relief steps and consequently the time and volume of processed substance for large scale production of diffractive phase elements (DPEs) such that to approximate the desired field distribution in terms of mean squared error, uniformity, and efficiency in the lower domain of quantized phase levels. The paper presents a method to optimize DPE manufacturing using unequal imprinted phase steps by direct laser writing via two photon polymerization. The algorithm is implemented with Python software and contains two feedback loops of analysis: one at the optical image level, the other at the DPE level. The unequal sizes of phase steps are optimal with respect to the particular DPE subjected to fabrication. DPEs and the corresponding optical images are presented in simulated and experimental versions, respectively. The results are evidencing the advantage of unequal steps versus the equal ones. The method is an acceptable compromise between preserving relevant micro-relief details and accurate image reconstruction under the constraint of limited number of imprinted steps and lower processing time.

The work is devoted to the calculation of the optimal parameters of diffraction gratings for input and output of radiation from the holographic lightguides for augmented reality glasses. Two main stages can be distinguished, namely: the calculation of the grating’s period in each of the optical lightguides to obtain a multicolor image in a large field of view, and the calculation of the height of the relief profile (to maximize the diffraction efficiency).

A new type of plane optical lens, the Fresnel-grating lens with variable-line-space grating surface based on dual pointsource holographic technique, is demonstrated, optimized and fabricated in this research. The Fresnel-grating lens integrates the function of a diffraction grating and a Fresnel lens, and provides collimation, focusing as well as dispersion effects at the same time, which simplifies the optical structure and fits perfectly for a miniature spectrometer. The variable-line-space grating surface can enhance the modulation ability of the spectrometer system A mathematical model is established based on the least wave-change principle and the system parameters are optimized using optics simulation software ZEMAX. The fabrication procedures for the Fresnel-grating lens with soft lithography are illustrated in detail, and a dual-point holographic exposure optical path to form the grating surface as well as a mold to cast the Fresnel-grating lens are constructed. Samples of Fresnel-grating lens with the size of 16mm×16mm×5mm are fabricated and preliminarily tested. The period on the central part of fabricated grating surface is 926±2nm and the results show great consistency with the simulation. With further testing in the spectrometer system, the Fresnel-grating lens with a variable-line-space grating surface holds considerable potential in the miniature spectrometer area.

Guided mode resonance (GMR) gratings are used as filters due to the narrow bandwidth and high efficiency at the resonance wavelength. In this paper, a two-dimensional gradient-period GMR grating with rectangular array structure is proposed. Ta₂O₅, HfO₂ and SiO₂ are selected as grating materials. Double reflection peaks are obtained by matching the guide modes in two orthogonal planes of diffraction to different wavelengths. The rigorous coupled wave analysis (RCWA) are used to analyze the resonance characteristics of two-dimensional GMR grating. By comparing the resonance behavior, the resonance wavelengths of two-dimensional GMR grating can be approximated as the superposition of two one-dimensional GMR gratings, the periods of the two one-dimensional gratings are respectively equal to those of the two-dimensional GMR grating along x and y direction (Λ_x and Λ_y). Thus, we can control the two resonance wavelengths by changing the periods of Λ_x, Λ_y. According to the result of design, when the two resonance peaks are both in the spectrum range of 850nm-1050nm, the efficiencies of the two peaks are greater than 90%, and full width at half-maximum (FWHM) less than 1.5nm. This two-wavelength tunable filter will be a good two-dimensional displacement sensor. The effects of duty cycle, groove depth and other parameters on the resonance wavelength are also studied.

Crossed-grating, as the standard element for metrology in two-dimensional precision positioning system, has been widely used in precision machine tools, highly sophisticated manufacturing and machining system. The technical indicators of crossed-grating, such as its diffraction efficiency and the efficiency equilibrium of the TE or TM polarized light are relevant to the microstructure of crossed-grating. While the structure of crossed-grating is determined by the microstructure of holographic photoresist grating. For exploring the evolution of microstructure of crossed holographic photoresist grating. In this paper, a new method for obtaining the variation curve of groove depth with exposure volume （the contrast curve of photoresist）is proposed, this method does not need a series of repeated experiments and is easy to operate compared with previous step experiments. The contrast curve of photoresist under different developing conditions (such as developer concentration and developing time) are analyzed. In addition, the top-view groove profile of crossed holographic photoresist grating under different process conditions are revealed too. The above research results provides a theoretical basis for the process parameters in holographic recording and developing of crossed holographic photoresist grating.

Phase information of coherent light is difficult to obtain directly through the Imaging optical system. At present, the more advanced method is to use coherent diffraction imaging method for phase recovery, but its imaging field of view is relatively small, and it is easy to appear the phenomenon of image reconstruction stagnation for objects with slightly complicated structure. Therefore, the effect of boundary conditions on coherent diffraction imaging method is studied in this paper. On the basis of the traditional coherent diffraction imaging method, this paper focuses on the transformation of the iterative conversion algorithm according to the different combination of the hybrid input and output method and the extrapolation method, and forms three new iterative conversion algorithms. The contrast experiment of coherent diffraction imaging method based on three new iterative transformation algorithms is designed by using interferometric test method. The experimental results show that the RMS value of the estimated phase deviation and ideal phase deviation is only 0.0096λ for the phase recovery method with single boundary condition, and the detection deviation RMS value is less than 0.0012λ for a phase recovery method with dual boundary conditions. This method has very important application value for phase recovery of coherent light.

In this paper, the method of recognition and superposition of sub-pixel shifting in digital holograms is investigated. A group of non-scanning holograms is recognized and superposed by using sub-pixel shifting algorithm. Further, spatio-temporal scanning holograms with sub-pixel displacement are recognized and superposed to further improve imaging resolution by combining spatio-temporal scanning digital holography with sub-pixel shifting algorithm. The experimental results verify the feasibility of improving resolution with sub-pixel displacement.

In this paper, a voxel-based algorithm for calculating phase-only three-dimensional (3D) computer generated holograms (CGHs) with occlusion effect is proposed. The 3D object can be firstly decomposed into a number of self-luminous voxels, which is the minimum imaging unit of the object. According to occlusion relationship, the 3D position and propagation direction of each voxel can be determined, where the axial position, lateral position and the propagation direction are precisely controlled by digital Fresnel lens, digital grating and hologram segmentation, respectively. Then, in order to reconstruct the 3D object composed of multiple voxels, the pre-calculated holograms for all of the voxels are synthesized with the interweaving arrangement method. Moreover, the look-up-table (LUT) method is used in the hologram generation process to improve the calculating speed. An experimental verification system for the proposed algorithm is constructed using a single SLM. The optical reconstruction results demonstrate that the CGHs generated by the proposed algorithm can successfully provide 3D sensation with occlusion effect.

Currently, diffractive optical elements with light guide substrates are used in miniature display systems especially in systems for vehicles, aircraft, and systems, where the observed image overlaps with the real scene. It is possible to get rid of the double image and zero order (this feature is inherent in computer generated hologram Fourier) as a result of synthesis of complex Fresnel hologram. As a result, we can synthesize a complex hologram that is free of the twin image and the zero-order light using a single spatial light modulator. The holograms are recorded with a spatial light modulator in a projection mode. This configuration consists of glass substrate with computer generated holograms Fresnel and diffraction gratings, as a diffractive optical element, for input and output of radiation. Reconstructing beam is incident on the computer generated holograms Fresnel, and then through diffraction grating 1 radiation is introduced into the plate at an angle of TIR and spread in it. When the light reaches the surface of the substrate with a diffraction grating 2, part of the light emerges from it. diffraction gratings are two diffraction gratings, which should have different diffraction to ensure uniform brightness of the observed image. It should be noted that to ensure the non-uniform diffraction efficiency of diffraction grating exit area was divided into multiple zones. Thus, the zonal diffraction grating was recorded with its exposure value. Light beams diffracted on computer generated holograms Fresnel enter and then multiple output from substrate, thus forming for observer an increased image of the test object.

This paper proposes a method for implementing off-axis reflective digital holography using a single diffraction grating element. The typical off-axis digital holography uses a beam splitter to form interference beams, and obtain off-axis interference patterns by tilting a mirror. We use a diffraction grating to replace the mirror and beam splitter with one element. The grating element separates the incident beam into +1 and -1 orders, and the separated beams are used as the reference beam and the signal beam, respectively. The signal beam reflects off the tilted specimen and returns to the grating element. The diffraction grating acts as a beam combiner to diffract the tilted signal beam again to interfere the signal beam with the reference beam. Therefore, the diffraction grating device acts as a multi-functional device that simultaneously performs the functions of the beam splitter and mirror. We set the image sensor plane at an angle perpendicular to the tilted signal beam. As a result, the reference beam can be incident on the image sensor plane in the form of off-axis. Since the two devices required in the conventional off-axis digital holography can be implemented as a single grating component, a cost effective and compact system can be realized.

Reflective liquid crystal spatial light modulator (SLM) is a widely used optical instrument because of its brilliant and high precision wavefront modulation ability. However, as mentioned by the producer and other researchers, the plane of SLM is not ideally flat but distorted during the manufacturing process. Here, we presented an automatic procedure for aberration correction based on interference. After the aberrations being measured with a wavefront sensor, the correction wavefront is automatically obtained by analyzing these aberrations. Then, the correction wavefront can be used to compensate the inherent distortion of SLM. This method is simple, user friendly and effective.

Stereoacuity, or named stereoscopic acuity, is the minimum disparity that can be perceived by someone with two eyes and normal brain functions. It is extremely relevant to human stereopsis and considerable individual variability. Due to the contribution of color information to stereopsis is controversial, this study is focused on designing and conducting a stereoacuity test for different colors. In particular, the effect of color variations on stereoacuity was evaluated by using 3D displays to present color random-dot stereogram (RDS) stimuli. Seventeen color points sampled from the CIELAB color space were selected for the test. All sample color points are averagely distributed in red-green and yellow-blue directions at isoluminance. The stimuli had the same dot density of 50% and black background, with different colors and disparities. Then the minimum disparity was obtained as the stereoacuity of subject. The results of experiment show that the stereoacuities are not significantly different in red-green direction and blue-yellow directions. These results support the view that color does not contribute to the stereoacuity.

High-speed and high-precision human face 3D shape measurement plays a very important role in diverse applications such as human-computer interaction, 3D face recognition, Virtual Reality. This paper introduces a structured light system based on VCSEL(Vertical Cavity Surface Emitting Laser) with one simulated projectors and two camera for human face 3D shape measurement. Large-scale production cost of VCSEL is low, because of the manufacturing process compatible with LED. VCSEL has the advantages of projecting a large area of diffractive structure light and easy to integrate into lens array internally. The process of VCSEL projecting the structural light that changes over time to human face is simulated by computer. The ICP algorithm is used to match the image of single frame structure light from the right camera to the left camera. A single frame image of three-dimensional face point cloud is obtained by using binocular stereo vision principle. The multi-frame images of point cloud that change along time series are superposed to obtain higher density point cloud data and improve the measurement accuracy. This 3D measurement based on VCSEL has advantages of low cost, high precision, and small size and should be useful for practical applications.

We propose a multi-fiber holographic interferometry for fabricate double-periodic Graded Photonic Crystal (GPC) structures over large areas. This experimental system consists of an ultraviolet laser, Single-Mode Optical Fiber Splitters (SMOFS), fiber holder and focus lens. This method simplifies the system configuration by leaving out the spatial light modulator. Holographic GPC structures have been designed by using multi-fiber interference in this paper. The interference pattern is controlled by the number and position of the beams. The simulation results show that the gradient trend in the interference graph can be accurately adjusted through the above method. Experiment results were obtained and recorded for multi-fiber interfering system. The simulated interference patterns are verified experimentally through a microscopic camera. A good consistence has been observed between the theoretical and experimental results. This proposed method is possible to develop a new technique for fabrication of GPC lens or lens array.

The problem of the reconstructed of different scene depth was analyzed in single-step holographic stereogram printing based on effective perspective images’ segmentation and mosaicking (EPISM). The reconstructed quality of short scene depth is bad. the causes of flipping effect in holographic stereogram are studied in detail, and the influence of flipping effect on image quality is alleviated by reducing the size of holographic element (Hogel). The curvature distortion of holographic stereogram is analyzed. The effect of curvature distortion on the reconstructed quality of holographic stereogram is verified by changing the distance of object protruding sampling plane. The theoretical analysis was verified experimentally with different scene depth. The reconstructed image of high quality and short scene depth was obtained, and the practicability of EPISM was improved.