Modified Holographic Exposure to Fabricate Varied Bragg Grating in an Identical Chip

A new fabricating method is demonstrated to realize two different Bragg gratings in an identical chip using traditional holographic exposure. Polyimide is used to protect one Bragg grating during the first period. The technical process of this method is as simple as that of standard holographic exposure.

Dynamic shaping of vectorial optical fields based on two-dimensional blazed holographic grating

We propose a vectorial optical field generation system based on two-dimensional blazed grating to high-efficiently generate structured optical fields with prescribed amplitude,phase,and polarization.In this system,an optimized blazed grating hologram is written on a spatial light modulator(SLM)and can diffract the majority of the incident light into the first-order diffractions of the x and y directions,which then serve as base vectors for synthesizing desired vector beams.Compared with the conventional cosine grating used in the previous work,the proposed two-dimensional,blazed grating has a much higher efficiency.Both computer simulation and optical experiment validate that a conversion efficiency up to 5 times that of the former work is achieved.Our method can facilitate applications of the optical field manipulation.

Electrically tunable holographic polymer templated blue phase liquid crystal grating

In this paper, we demonstrate an alternative approach to fabricating an electrically tunable holographic polymer tem- plated blue phase liquid crystal grating. This grating is obtained by preforming a polymer template comprised of periodic fringes, and then refilling it with a blue phase liquid crystal. Compared with conventional holographic polymer dispersed liquid crystal gratings, our grating can remarkably reduce its switching voltage from 200 V to 43 V while maintaining a sub-millisecond response time. The holographic polymer templated blue phase liquid crystal （HPTBPLC） grating is free from electrode patterning, thus leading to a lower cost and more flexible applications.

Study on holographic grating diffraction for Laguerre–Gaussian beam generation

Laguerre-Gaussian beams, as a special model with spiral phase structure, have been intensively investigated. Holographic grating method is a convenient method of generating Laguerre-Gaussian beams and measuring their orbital angular momenta. But due to some inevitable adverse factors such as lateral displacement, angular deflection and elliptical incident profile of incident beam, the practical effectiveness should be reevaluated. This paper is devoted to the study on the influences of the abovementioned three adverse factors on the holographic grating method. The characteristics of the mode decomposition of diffractive order and the relative powers of the orbital angular momentum eigen-states are also given.

Diffraction of an ultrashort pulsed beam with arbitrary polarization state from a volume holographic grating in LiNbO3 crystals

Based on a modified coupled wave theory of Kogelnik, we have studied the diffraction of an ultrashort pulsed beam with an arbitrary polarization state from a volume holographic grating in photorefractive LiNbO3 crystals. The results indicate that the diffracted intensity distributions in the spectral and temporal domains and the diffraction efficiency of the grating are both changed by the polarization state and spectral bandwidth of the input pulsed beam. A method is given of choosing the grating parameters and input conditions to obtain a large variation range of the spectral bandwidth of the diffracted pulsed beam with an appropriate diffraction efficiency. Our study presents a possibility of using a volume holographic grating recorded in anisotropic materials to shape a broadband ultrashort pulsed beam by modulating its polarization state.

PHOTOINDUCED HOLOGRAPHIC PHASE GRATINGS BURIED IN AZOBENZENE SIDE-CHAIN POLYMER FILMS WITH A CHIRAL GROUP

An optically active polymer (PM1) containing azobenzene moieties with a chiral group (s-2-methyl-butyl) wassynthesized by homopolymerization of monomer, 4-[2-(methacryloyloxy)ethyloxy-4'-(s-2-methyl-1-butyl oxycarbonyl)azobenzene, using the free radical polymerization method. The polymer dissolved in tetrahydrofuran (THF) could be easilyprocessed into high optical quality films. The optical anisotropy of the polymer films was investigated by polarizing opticalmicroscopy (POM). The experimental results showed that irradiation with a circularly polarized beam could align theorientation of the molecules in the polymer films. Moreover, the holographic phase gratings of photo-induced polymer filmswere detected by atomic force microscopy (AFM) and POM. In comparison with polymer containing no chiral group, it wasfound from the preliminary measurement of the photo-induced holographic phase gratings that PM1 containing a chiralgroup could form holographic phase gratings buried in the films.

Self-Enhancement of Scalar and Vector Holographic Gratings in Azobenzene Molecular Glassy Films

Self-enhancement (SE) effect of scalar and vector holographic gratings (HG) recorded in three different azobenzene molecular glassy films is experimentally studied in both transmission and reflection modes at 532 and 633 nm. The maximal SE factor (the ratio of diffraction efficiency to its initial value) SEF = 42 has been achieved. It is shown that the model of complementary HG can be applied also in scalar transmission thin HG case to explain coherent SE. The possibility of vector HG coherent SE in transmission mode is experimentally demonstrated for the first time (SEF = 4.3). The possibility of coherent HG SE in reflection mode is also established for the first time (SEF = 21). HG recording processes as well as coherent SE processes are found to be independent in transmission and reflection modes being determined by volume and surface relief HG, respectively. The permittivity gradient mechanism is proposed to explain the coherent SE of surface relief HG. Both HG recording and coherent SE efficiencies strongly decrease when HG period is decreased from 2 mm to 0.5 mm. No relaxational SE effect is found. Coherent SE effect in molecular glasses is found to be weaker than in inorganic materials.

Analysis of Optical Properties of Off-Axis Reflective Volume Holographic Grating

The coupled wave theory for volume holographic grating with curved interference fringes has been proposed based on the Kogelnik’s coupled wave theory with the plane interference fringes. The formula about the magnitude and directional angle of grating vector in arbitrary position of volume holographic grating with curved grating has been deduced. We found that the wavelength selectivity and angular selectivity may be different in different position of volume holographic curved stripe grating which depend on the angle between the propagation vector of reference beam and signal beam. The larger the angle, the greater the angle and wavelength selectivity, whereas the weaker.

Study on the adaptability of augmented reality smartglasses for astigmatism based on holographic waveguide grating

Background Augmen ted reality(AR)smartglasses are considered as the next generation of smart devices to replace mobile phones,and are widely concerned.But at present,AR smartglasses are usually designed according to the human normal eyes.In order to experience AR smartglasses perfectly,abnormal eye users must first wear diopters.Methods For people with astigmatism to use AR smartglasses without wearing a diopter lens,a cylindrical lens waveguide grating is designed in this study based on the principle of holographic waveguide grating.First,a cylindrical lens waveguide substrate is constructed for external light deflection to satisfy the users'normal viewing of the real world.Further,a variable period grating structure is established based on the cylindrical lens waveguide substrate to normally emit the light from the virtual world in the optical machine to the human eyes.Finally,the structural parameters of grating are optimized to improve the diffraction efficiency.Results The results show that the structure of cylindrical lens waveguide grating allows people with astigmatism to wear AR smartglasses directly.The total light utilization rate reaches 90%with excellent imaging uniformity.The brightness difference is less than 0.92%and the vertical field of view is 10°.Conclusions This research serves as a guide for AR product designs for people with long/short sightedness and promotes the development of such products.

Spectral selective fluorescence molecular imaging with volume holographic imaging system

A compact volume holographic imaging(VHI)method that can detect fluorescence objects located in diffusive medium in spectral selective imaging manner is presented.The enlargement of lateralfield of view of the VHI system is realized by using broadband illumination and demagnification optics.Each target spectrum of°uorescence emitting from a di®usive medium is probed by tuning the inclination angle of the transmission volume holographic grating(VHG).With the use of the single transmission VHG,fluorescence images with different spectrum are obtained sequentially and precise three-dimensional(3D)information of deep fluorescent objects located in a diffusive medium can be reconstructed from these images.The results of phantom experiments demonstrate that two fluorescent objects with a sub-millimeter distance can be resolved by spectral selective imaging.

Multilayer GaAs-Based Heterostructures with Holographic Concentrator for Solar Cells

The present paper studies the issue of forming a diffraction concentrator in the form of relief diffraction gratings. The possibility of their application for solar energy systems based on GaAs heterostructures has been studied. It was shown that the use of diffractive and holographic concentrators proves to be very effective, since they provide for the increased radiant flux onto sensitive surface of the solar cell, whereas no automatic solar tracker is required. This will create novel approaches for a wide range application of gallium arsenide solar cells.

光折变晶体中平面光栅的构建与研究

光折变效应在全息存储和处理方面具有重要的应用价值,光折变晶体中的全息光栅特性直接影响信息处理的质量和速度.本实验通过理论分析,计算得出Raman-Nath平面光栅的制作参量,设计实验系统并测量了LiNbO 3晶体中平面光栅的多级衍射性质,讨论了多级衍射效率和其空间分布特征.实验设计基于学生的光学知识和实验技能,向非线性光学知识和科学思辨创新方法拓展,在可调光分束器、图像处理等方面具有潜在的应用价值.

采用丙烯酸酯双单体的高空间频率透射式体全息H-PDLC光栅的研制

全息聚合物分散液晶(holographic-polymer dispersed liquid crystal, H-PDLC)体全息光栅因其化学状态稳定、制作简单、价格低廉等优势为全息光波导耦合器件提供了一个更优的思路。本文提出了采用复合型丙烯酸酯类高/低折射率匹配调制的H-PDLC透射式体光栅的研制。首先结合耦合波理论及分子扩散理论介绍了H-PDLC光栅的形成机理。然后,通过实验对不同官能度单体的光栅材料进行筛选,并研究其全息衍射特性。在此基础上,进一步采用提高引发剂含量的方式优化了高频体全息H-PDLC光栅性能。实验结果表明,该双单体的H-PDLC配方可实现在可见光波段透过率大于90%,在空间频率为973 lp/mm下,衍射效率达到90%,响应带宽为99 nm;在2 941 lp/mm下,衍射效率为75.4%,响应带宽为29 nm。该H-PDLC光栅作为波导显示系统的耦合器件有可观的应用前景。

大功率808 nm分布反馈激光器阵列研制

为了提高808 nm大功率半导体激光器阵列的波长稳定性,提出了带有二阶布拉格光栅的大功率宽条型808 nm分布反馈激光器阵列。相比于传统的一阶布拉格光栅,其可以显著抑制简并纵模的产生,提高器件的波长锁定范围。借助于金属有机化学气相沉积、全息光刻、干法刻蚀以及湿法腐蚀等工艺,完成了器件的制备,并且在准连续条件(200 A、200μs、20 Hz)下,对所制备的激光器阵列进行了不同温度下的性能测试。测试结果表明:器件峰值输出功率可达到190 W,光电转换效率超过55%,光谱半高宽为0.6 nm,温漂系数为0.06 nm/K,波长锁定范围达到125℃(-35~90℃)。另外,对其进行了老化考评,结果显示,老化2 000 h后峰值功率衰减小于4%。

Seya-Namioka类型真空紫外光谱系统的研制和性能测试

为了满足磁约束核聚变领域的杂质测量要求,研制了一套Seya Namioka真空紫外光谱仪。该光谱仪的主要部件是可调宽度的入射狭缝、凹面光栅和探测器。光谱仪的光通量通过可调节宽度的入射狭缝来调节,入射狭缝宽度可以在10~1000μm范围内调节。分光元件选用线密度为1200 lines·mm^(-1)的凹面全息光栅。光栅表面涂有铝(Al)和氟化镁(MgF2),以提高衍射效率。光栅的可使用波段为50~460 nm,针对其中的50~250 nm波段进行光路优化设计。选用深度制冷背照式电荷耦合器件(CCD)作为光谱仪的探测器。通过转动光栅转台旋转光栅来改变衍射角,实现50~250 nm范围内的光谱观测。基于凹面光栅的参数,确定了具体光路,并分析了波长随光栅旋转角度的变化关系及不同波长处的线色散率。基于凹面光栅成像理论,对系统的光谱分辨率进行了计算分析。通过分析不同出射臂下的光谱分辨率,确定最优出射臂为205 mm。在出射臂为205 mm、入射狭缝为20μm的情况下,分析了入射狭缝宽度、像素大小、像差和衍射极限对光谱分辨率影响。结果表明:衍射极限对光谱分辨率的影响最小,基本上可以忽略不计,出射狭缝的宽度对光谱分辨率有较大贡献,大约为0.09~0.10 nm,且在50~250 nm波长范围内缓慢增加。分析了不同入射狭缝宽度(10~80μm)下光谱分辨率,光谱分辨率随狭缝宽度呈递增趋势,变化范围为0.10~0.32 nm,当狭缝宽度达到80μm时,光谱分辨率已经变的较差,不利于高分辨线辐射光谱测量。在实际测量中,应该综合考虑光通量和光谱分辨率需求。采用低压汞灯和微波等离子体光源进行波长校准和性能测试。基于零阶光谱和汞灯的特征光谱HgⅠ(185 nm)对光谱仪进行了波长标定。通过HgⅠ(185 nm)谱线的高斯拟合分析,得到仪器在185 nm处的光谱分辨率为0.1243 nm,与理论计算值接近。通过实验与理论计算对比不同出射臂下的HgⅠ(185 nm)光谱分辨率,验证了仪器在出射臂为205 mm处获得最佳光谱分辨能力。利用微波等离子体放电光源装置对光谱仪进行了进一步的性能测试,基于光源发射的氮、氧和氦线的测量,验证了光谱仪在50~250 nm波长范围内具有良好的探测能力。

一种基于折衍混合结构的无油墨印刷技术研究

传统印刷技术的视觉效果单一,且普遍使用重污染的重金属和高分子材料的油墨,造成了严重的环境污染。为解决上述问题,本研究探索了一种基于折衍混合结构的无油墨印刷技术。通过微纳结构对光学折射和衍射现象实现了彩色化,并利用莫尔成像原理突破了传统印刷中难以实现三维和动态视觉效果的瓶颈,提供了丰富的视觉效果。采用激光直写和干涉光刻制版,结合压印技术制备的基于微透镜阵列和光栅结构的印刷品,具有高分辨率、低成本和环境友好的优点。本研究所提出的无油墨印刷技术满足了人们对印刷品质的不断追求,具有巨大的应用潜力。

LO-RAY-LIGH@ Diffraction Gratings in UV-VIS Spectroscopy

It has been more than half a century since the release of the first Shimadzu UV-VIS （UV-visible） spectrophotometer QB-50 in 1952, and during this time more than 160,000 UV-VIS spectrometers have been produced and installed in a wide variety of different applications. A lot of technical innovations have been implemented to improve the performance and significantly reduce the stray light levels. The latest innovation during development of sophisticated spectrophotometers is based on a new holographic exposure method and optimized etching process which has made it possible to produce both high-efficient and exceptionally low stray light gratings. These LO-RAY-LIGH~ gratings have guaranteed values of stray light at the intermediate position between zero-order and first-order lights. The values are measured by Shimadzu＇s laser stray-light-measuring system. The latest development in the series of UV-VIS spectrophotometers is the UV-2700 which is a true double beam double monochromator system in a compact design for high-precision spectral analysis of a wide range of samples including organic and inorganic compounds, biological samples, optical materials and photovoltaics. The high performance optical system is designed with ＂LO-RAY-LIGH＂ diffraction gratings, featuring highest efficiency and exceptionally low stray light. The spectrophotometer operates in the wavelength range from 185 nm to 900 nm and allows highly sophisticated applications such as direct measurement of high density samples up to 8 absorbance units without dilution.

基于FOSC型的宽波段高效率中低色散光谱仪设计(特邀)

为实现各类暂现源及暗弱目标的宽波段、高效率光谱后随观测,以1.9 m光学望远镜为例,设计了一种基于Faint Object Spectrograph and Camera型的双通道中低色散光谱仪,可实现三种光谱分辨率(R=500、2000和5500),工作波段覆盖紫外-近红外(310~1000 nm)。根据光栅方程和光谱分辨率等各项指标,确定光谱仪的初始结构参数,针对光谱仪在全波段的高效率需求以及仪器随动的包络限制,确定光学系统采用双通道设计并近似对称分布:准直系统采用了不同于传统Faint Object Spectrograph and Camera型光谱仪的折反射式系统,在提高了系统效率的同时压缩了空间。色散系统根据直视棱栅的不同工艺,通过棱镜材料和角度的调整对工作波段的光栅效率进行优化并得到8种棱栅参数;红蓝通道相机系统在设计过程中优化选取光学材料,同时结合二次非球面和单透镜的主动调焦补偿,实现大动态温度范围(-30℃~20℃)全视场(φ16°)最大弥散斑半径均方根小于5μm的优良像质。该系统结构紧凑、分布对称,设计结果满足各项指标,光谱仪全波段峰值效率优于60%,最低效率优于20%,具有较高的可实现性。基于曲面芯片工艺,以红通道为例,简化的相机系统至少可提高整体光谱效率约4%,可以为未来光谱仪相机系统的设计提供参考。

基于平面反射式全息光栅的激光自混合纳米位移测量研究

纳米位移测量技术是实现高精度纳米制造的基础。激光自混合干涉为精密纳米位移测量提供了一种结构简便、成本低廉,同时测量精度可达纳米量级的精密位移测量方法。区别于传统基于反射镜或散射面为反馈元件的激光自混合干涉测量方案,研究了一种基于平面反射式全息光栅的激光自混合纳米位移测量方法,该方法的位移测量结果以光栅的周期为基准。实验测得了在弱反馈强度条件下的光栅自混合干涉信号,通过阈值设定的方法确定位移方向的反转点,结合反余弦的相位解包裹算法处理光栅自混合信号,获得了对应的位移测量值。最终采用商用激光干涉仪与自组装的光栅自混合干涉仪进行位移测量数据的比对测量,实验结果表明,经过线性修正后,其位移误差不超过0.241%。

等周期变倾角干涉条纹复用法扩展增强现实耦合元件体光栅角度带宽

为了提高光波导近眼显示成像系统的视场角,本文提出了一种等周期变倾角干涉条纹复用方法,用于扩展增强现实眼镜耦合元件体光栅的角度带宽。该方法通过复用等周期变倾角干涉条纹满足了不同入射角的布拉格条件,并且消除了体光栅周期变化对入射光衍射角度的影响,从而提升耦合元件体光栅的角度响应范围,降低光栅衍射引入的杂散光。利用严格耦合波理论对复用三幅等周期变倾角干涉条纹的体光栅进行模拟,在波长为530 nm的TE和TM偏振态下,复用后的体光栅角度带宽分别为3.6°和3.3°,与单幅干涉条纹体光栅相比,角度带宽扩展了1倍。该方法有望打破体光栅角度带宽受光栅材料的限制,用于扩展近眼显示成像系统的视场角,实现轻量化、高效率、大视场、低杂散光的增强现实眼镜。