Design of an augmented reality display based on polarization grating

A new optical system for an augmented reality(AR) display is proposed in this paper.The optical system mainly includes a ray deflector, coupling input grating, optical waveguide, and coupling output grating.Both the ray deflector and the coupling input grating are designed based on the diffraction characteristics of the polarization grating, and the coupling output grating is the Bragg reflection grating.Compared with other AR schemes, this AR optical system not only reduces the number of projections from two to one, but also improves the efficiency of light coupling into the optical waveguides.The energy loss is reduced by utilizing the single-order diffraction characteristics of the polarization grating in its coupling input structure.The light deflector uses the polarization selectivity of the polarization grating and the characteristics of the rotating light of the twisted nematic liquid crystal layer to realize beam deflection.The working principle of the optical system is experimentally and theoretically demonstrated.     

Airy beam laser

A method to design lasers that emit an arbitrary beam profile is studied. In these lasers, output-coupling is performed by a diffraction grating that imposes a phase and amplitude distribution onto the diffracted light. A solid-state laser emitting beams with a two-dimensional Airy intensity profile is demonstrated both theoretically and experimentally. In this case, the diffraction grating adds a transverse cubic phase to the diffracted light. An Airy beam is obtained by performing optical Fourier transform of the out-coupled light. The laser beam profile and power characteristics are shown to agree with theory.     

方形光阑限制高斯光束的传输变换

对基模高斯光束经方形光阑限制光学系统的光斑传输变换规律进行了论述．对于任一共轴光学系统,在不考虑有效光阑前面元件的衍射和变换时,考察入射光经有效光阑和其后面的元件发生衍射,根据柯林斯公式,对于非成像光学系统,采用稳相法得到出射光场的振幅分布;对于成像光学系统,根据像传递原理得到出射光场的振幅分布,最后得出出射光斑大小由有效光阑边长与光阑处高斯光束腰斑大小比较决定的结论．     

Displacements and deformations of a vortex light beam produced by the diffraction grating with embedded phase singularity

Properties of vortex light beams produced by a diffraction grating with groove bifurcation (“fork” structure) are studied in the case of small diffraction angles. Analytical expressions are derived for the amplitude distribution of a diffracted beam generated from an incident Gaussian beam with arbitrary radius and wavefront curvature, transversely shifted and inclined with respect to the nominal axis (normal to the grating crossing it at the bifurcation point). In such situations, the output beam becomes asymmetric; the optical vortex core and the intensity maximum displace orthogonally to the incident beam shift direction. The nearest vicinity of the vortex core preserves its circular symmetry and the optical vortex remains locally isotropic. The effects of misalignment depend on the incident beam characteristics, the diffraction order and the propagation distance behind the grating. Experimental measurements support the results of calculations.     

Polarization and Color Separator Using Binary Phase Grating with Subwavelength Period

A data projector using three liquid crystal display panels has a complex optical system. The illuminating optics separate the beam from a light source into three primary colors and separate those into opposite polarizations using multi-layer films and prisms. A reflection grating with the period of subwavelength has high diffraction efficiency for p polarized light and high regularly reflectance for s polarized light. The diffraction angle of a grating largely depends on the wavelength, because a diffractive optical element (DOE) has large chromatic dispersion. The grating with the period of subwavelength can separate the unpolarized light into polarization components effectively using its polarization dependency and can separate white light into color components using its chromatic dispersion simultaneously. The grating makes the optical system simpler and smaller than those with conventional devices. In this paper the efficiency of polarization separation for the grating is calculated by a rigorous analytical method. Next, the condition for color separation is calculated by Snell#x0027;s law, and an optical system using a grating that performs polarization and color separation is proposed. Experimental results of the DOE fabricated are well matched with those of this simulation.     

Fabry-Perot interferometer with diffraction-scattered reflection of light

The incorporation of a phase grating into the optical system of a Fabry-Perot interferometer makes it possible to transform the incident beam of light so that the major part of energy in the reflected wave is contained in the side lobes in the far-field diffraction pattern and radiation in the zero order of diffraction along the optical axis is suppressed. Experimental results are presented, which are obtained with a grating produced by evaporating a thin-layer dielectric coating onto the input mirror of the interferometer.     

基于微机电系统光栅平动式光调制器实验和优化设计

基于微机电系统(MEMS)的光栅平动式光调制器(光栅平动式光调制器)调制性能的实验研究关系到其进一步应用。设计了光栅平动式光调制器的相干光学信息处理系统实验方案,He-Ne激光器出射的光束经扩束器和准直透射后成为平行光入射光栅平动式光调制器,被测光栅平动式光调制器放置在相干光学信息处理系统的输入面,滤波器在频谱面上,显微镜放大像面上的信号,经CCD在计算机上记录存储;实验结果和理论分析吻合。对光栅平动式光调制器进行方案优化,将可动光栅边框和悬臂梁表面处理成不反光,使可动光栅和下反射镜构成的整个反射面为光栅周期的整数倍。经理论计算,在光栅周期为8μm,光栅占空比为0.5,光栅边距为2μm,周期数为6的条件下,光栅平动式光调制器图像填充率为74.67%,光学效率为81.06%,衬比度大于5000∶1。     

基于InP的全光高速相机的理论和实验研究

为了评估基于瞬态光栅的全光高速相机系统中激发光强与图像信号之间的对应关系,验证基于磷化铟（InP）建立该相机的可行性。针对InP材料从理论上分析了从光子入射激发载流子,到载流子影响折射率,再到折射率影响衍射效率过程中各物理量值之间的关系;并建立了基于衍射光收集的图像探测系统获取InP内部的瞬态光栅分布图像。理论结果给出了针对InP材料的激发光强与载流子浓度的关系,探针激光为 1064 nm时载流子浓度与折射率之间的关系,以及瞬态光栅为矩形光栅时折射率与衍射效率之间的关系,特别指出在基于InP和1064 nm探针激光的高速相机系统中,若时间分辨为1 ps量级,对于532 nm激发光,系统的灵敏度为1.3105 Wcm-2量级。实验结果证明了基于InP和1064 nm探针光可以建立全光高速相机系统,并根据所获得图像得出系统的空间分辨好于5.04 lp/mm。     

Optical vortices generated by dislocations in a cholesteric liquid crystal

We report the observation of optical vortices in a laser beam propagating through the stripe pattern of a cholesteric liquid crystal. The liquid crystal is confined in a cell with homogeneous boundary conditions and forms a diffraction phase grating. Optical vortices are produced by edge dislocations of the cholesteric grating. The vortices show up as spots of zero light intensity in the diffraction maxima. There is one spot in each +1 and -1 diffraction maximum and two spots in diffraction maxima +2 and -2.     

The compensability between the longitudinal and transverse mismachining tolerance of grating in the optical pick-up head

In this paper numeric analysis is made to the influence of the longitudinal mismachining tolerance (LMT)and the transverse mismachining tolerance (TMT) of the grating in the optical pick-up head (GOPH) of VCD, DVD, and CD-ROM on the transmissivity and the intensity ratio of the auxiliary light beam to the main read-write light beam (IRAM) by using the general expression of diffraction efficiency obtained from the scalar diffraction theory. On solving GOPH problem, the scalar diffraction theory and the vector diffraction theory are coincident, and the scalar diffraction theory is reliable. The result shows that LMT and TMT can compensate for the inverse effect of IRAM, however, at the expense of reducing transmissivity. As far as GOPH is concerned, the goodness that LMT and TMT can be effectively compensated for is very advantageous in manufacturing of the grating.     

Zemax软件在取样光栅对设计中的应用

 光束取样光栅(BSG)是一种重要的用于光束取样诊断的衍射光学元件。以2块取样光栅代替单块光栅作为初始光学结构,运用Zemax光学设计软件采用分步优化的方法设计了具有消像差功能的光栅对结构,此方法比采用Matlab语言编程计算的方法消像差更快捷、更灵活,同时可以验证程序计算结果的正确性。设计结果显示：再现的会聚光经2块光栅衍射后在像平面上点列图中的均方根半径仅为0.506μm,单块取样光栅的均方根半径则为7.284μm,说明2块光栅能够做到像差互相矫正,其像质明显好于单块取样光栅。另外,设计出的双光栅光学系统,可进行远场光斑质量检测,为激光束性能的在线诊断提供了行之有效的技术支持。     

畴腐蚀掺镁铌酸锂可调阵列光分束器的研究

研究了不同畴腐蚀深度的掺镁铌酸锂二维六角可调阵列光分束器的分数Talbot效应.对不同Talbot分数β和不同畴腐蚀深度的阵列光分束器Talbot衍射像进行了数值模拟理论研究.模拟结果表明,Talbot分数β可以改变Talbot衍射像的周期及结构分布,而畴腐蚀深度可有效调制衍射像的光强分布.在理论研究的基础上,设计并制备了具有不同畴腐蚀深度的掺镁铌酸锂二维六角阵列光分束器,对其在不同Talbot分数β条件下的分数Talbot效应进行了通光实验研究,实现了畴腐蚀阵列光分束器对近场Talbot衍射光强分布的调制,实验结果与理论研究结果一致.     

Two-dimensional higher-diffraction-order optical beam splitter based on phenanthrenequinone-doped poly(methyl methacrylate) photopolymer

A two-dimensional optical beam splitter has been realized that uses the higher diffraction orders of a refractive-index grating. Gratings were recorded experimentally with light from a semiconductor laser incident at a small angle on phenanthrenequinone-doped poly(methyl methacrylate) photopolymer. The incident signal beam, which was made up of three different wavelengths (632.8, 532.0, and 488.0 nm), was split by the grating into multiple output beams with nearly equal size and separation. Results are given for when the sample grating was placed behind, in front of, and in the focal plane of a Fourier lens. The properties of higher-order-diffraction images have been discussed. The discussion shows that a two-dimensional higher-diffraction-order optical beam splitter provides a practical method for splitting a signal beam.     

Fourier optics analysis of grating sensors with tilt errors

Dynamic diffraction gratings can be microfabricated with precision and offer extremely sensitive displacement measurements and light intensity modulation. The effect of pure translation of the moving part of the grating on diffracted order intensities is well known. This study focuses on the parameters that limit the intensity and the contrast of the interference. The effects of grating duty cycle, mirror reflectivities, sensor tilt and detector size are investigated using Fourier optics theory and Gaussian beam optics. Analytical findings reveal that fringe visibility becomes <0.3 when the optical path variation exceeds half the wavelength within the grating interferometer. The fringe visibility can be compensated by monitoring the interfering portion of the diffracted order light only through detector size reduction in the expense of optical power. Experiments were conducted with a grating interferometer that resulted in an eightfold increase in fringe visibility with reduced detector size, which is in agreement with theory. Findings show that diffraction grating readout principle is not limited to translating sensors but also can be used for sensors with tilt or other deflection modes.     

Multistate polarization addressing using a single beam in an azo polymer film

Peculiar light-matter interactions can break the rule that a single beam polarization can address only two states in an optical memory device. Multistate storage of a single beam polarization is achieved using self-induced surface diffraction gratings in a photoactive polymer material. The grating orientation follows the incident light beam's polarization direction. The permanent self-induced surface relief grating can be read out in real time using the same laser beam.     

关于利用激光光束偏转法测量热扩散率的研究

本文介绍了激光光束偏转法测量材料热扩散率的原理,从理论上分析了光的粒子性和光的衍射限制了该方法对热扩散率的测量精度,指出了提高测量精度的关键在于提高信号对光束偏转的灵敏度为此给出了一种带有Ronchi光栅的迈克耳孙干涉仪的探测装置,从而使灵敏度提高了约5.3倍.     

甲基红染料掺杂的聚乙烯醇薄膜光存储特性的实验研究

用2倍频小型YAG激光(532nm)作为写入光和擦除光,用He-Ne激光器623.8nm线作为读出光,用CCD作为探测器,研究了不同写入光功率下,甲基红/聚乙烯醇(MR/PVA)薄膜光栅生长的动力学过程和不同擦除光功率下,光栅擦除的动力学过程.结合光栅生长曲线的波动现象,对光存储机制进行了新的探讨.实验发现,两写入光和读出光的功率配比为1:1:1时,可获得最大衍射效率,提出读出光对写入过程具有双重作用的物理模型,对此实验结果给出了合理的解释.     

Diffraction of a narrow laser beam by a thick hologram: Experimental results

Results are reported on an optical effect observed with a thick, two-beam holographic transmission grating. Illumination of the grating with a narrow laser beam (beam waist much smaller than grating thickness) results in the emergence of four diffracted beams at the rear surface of the hologram. The results are in qualitative agreement with the theory of Chu and represent an optical analogue of an X-ray diffraction effect predicted by Kato and observed by Authier.     

Michelson interferometer with multichannel interferogram recording

A schematic diagram of a Michelson interferometer with a diffraction grating for which the length of one arm is a function of the transverse coordinate of the light beam is proposed. The possibility of recording the interferograms without mechanical displacement of optical elements of the interferometer is demonstrated.     

Theory of laser-induced amplitude and phase gratings including photoselection,orientational relaxation and population kinetics

The generation of amplitude and phase gratings in an absorbing medium is discussed, including the effects of light polarization, population kinetics and orientational relaxation. A theory is given which describes light diffraction by a combination of an amplitude and a phase grating. It is shown that the coherent coupling effect in transient absorption measurements is solely due to the amplitude grating. Weak absorption and a low triplet yield favour diffraction of the probing beam by the phase grating in triple-beam experiments. Phase grating experiments can be performed with highly soluble absorber dyes, the absorption maximum of which is far away from the laser wavelength. Due to photoselection, diffraction by an amplitude grating depends on the polarization of the probing beam while phase grating diffraction is insensitive to this. Perpendicular polarization of the two exciting pulses prevents the buildup of a phase grating and results in light diffracted by the amplitude grating that is proportional to the transient dichroism signal as known from the common absorption relaxation.