Voltage-controlled optical filter based on electrowetting

In this letter, we propose a voltage-controlled optical filter based on electrowetting. The device is made of a transparent cubic cell filled with two immiscible liquids having three indium tin oxide electrodes fabricated on the bottom substrate of the cell. A conductive droplet carrying a color filter is placed on the ITO electrode and the surrounding liquid is density-matched silicone oil. Under zero bias, the droplet is placed in the middle of the substrate and white light passes through the filter and we can see red light on the screen. When a voltage is applied to the device, the filter moves with the liquid based on electrowetting effect, we can see the white light on the screen. Due to the movement of the liquid, our device functions as an optical switcher. The switch time of the device is ~70 ms. The proposed device has a wide application in optical communication, electronic display, and optical switch.     

新型聚合物分散液晶相位光栅的制备

把具有光敏特性的预聚物与向列相液晶按一定比例混合 ,注入表面经过取向处理的液晶盒中。以紫外灯为光源 ,通过光掩膜法 ,使混合物在光场的引发下发生相分离 ,形成液晶 /聚合物相位光栅。由于相分离后液晶在取向膜的作用下沿液晶盒面方向旋转 180° ,克服了传统液晶光栅器件对入射光偏振方向的依赖 ,提高了光的有效利用率。采用光学显微镜和He Ne激光器进行测试 ,结果表明所制样品具有较好的栅结构 ,其衍射效率不受入射光偏振方向的影响且具有电场可调性。该光栅制作方法简便 ,驱动电压低 ,在光通信器件、衍射光学、投影显示、光开关等领域有广泛的应用前景     

Optical switch based on hydraulic actuation

In this paper we demonstrate an optical switch based on hydraulic actuation. Two chambers are filled with dyed oil and water, respectively. The oil–water interface changes as the external pressure is applied to the chamber. A transparent pillar shaped platform with a round dome is fixed on the top substrate and submerged in the oil. When pressure is increased, the shape of the oil–water interface can be changed from concave to convex and the oil is pushed aside. As a result, the water touches the transparent pillar thus forming a light channel which allows the incident light to pass through. Our experiments show that the device can obtain a wide optical attenuation from ∼1 dB to ∼29 dB. The diameter of the aperture can be tuned between 0∼5.1 mm by changing the external pressure. The switchable aperture ratio of the device is ∼39%. By using two immiscible liquids with matched densities, the gravity effect can be overcome. The proposed optical switch has potential applications in variable optical attenuators and adaptive irises.     

利于像差校正的共形整流罩内表面面形设计

共形光学系统中,椭球形等厚度整流罩使入射的平行光线经过整流罩后不再平行,变为发散的光线,进而使系统像差急剧增加,不利于后续像差的校正。通过对等厚度共形整流罩的内表面进行重新设计,打破了共形整流罩的等厚度条件,从而在使用较少校正光学透镜的基础上实现了系统像差的校正。通过分析不同级次非球面分别作为整流罩内表面面形时的像差校正效果,确定了将6次非球面作为共形整流罩内表面面形初始结构。通过对内表面进行优化设计,最终得到整流罩内表面面形。结果表明,该方法有效地减小了共形整流罩引入的像差。最后使用固定校正器对内表面变化后的整流罩进行了像差校正,设计结果表明,内表面的改变有效地减少了光学元件数量,消像差效果良好。     

偏振方向对涡旋光束产生的影响

在利用液晶空间光调制器(LCSLM)产生涡旋光束时,入射光的偏振方向对涡旋的产生有着明显的影响。从液晶空间光调制器的工作原理出发,研究了不同偏振方向的线偏振光在通过LCSLM的相位调制后,涡旋光束产生的变化。通过模拟仿真与实验结果的比较,发现随着线偏振光的偏振方向与液晶分子光轴夹角的增大,液晶空间光调制器的调制误差变大,所产生的涡旋光束的质量变差。当夹角大于4.725°时,涡旋光束的质量明显变差。而随着夹角继续增大,LCSLM对入射光的调制作用减弱,无法产生涡旋光束。     

Improving pattern precision of chromium based black matrix by annealing

Black matrix is a major component of color filter used for blocking light in flat panel industry. Films made of chromium (Cr) and its two oxide/nitride combination layers are commonly used in black matrix for its high optical density and material stability. Each single Cr based layer film of the three multilayer combinations was produced on glass and then annealed in low pressure hydrogen environment. Etching, transmittance of visible light, and microstructure of these films without and with annealing were compared. It was found that annealing can mend the interference between the incident and reflected light for Cr based black matrix. Annealing can also improve the undercut defect and thus pattern precision. The lateral etching rates of Cr based films were found to be much lower and close to one another after annealing. It can be explained the film density and adhesion increase caused by the annealing process. This article provides a potential method in color filter fabrication to improve contrast and color interference issues if Cr based black matrix is used in display application.     

Electro-optical properties of dielectric liquid microlens

We report the electro-optical properties of dielectric liquid droplets based on dielectrophoretic effect. Due to dielectric force, the surface of each droplet can be reshaped which in turn alters its focusing behaviors. Our experimental results show that a deformed droplet can recover to its original shape with a negligible hysteresis. Both amplitude and frequency of the applied voltage play important roles affecting the droplet's shape change. The rise time is mainly governed by the applied voltage: for a given frequency a higher voltage results in a faster rise time. On the other hand, the decay time is jointly determined by the interfacial surface tensions, droplet size, and viscosity of the employed liquids.     

小口径双通道球幕投影镜头的设计

为提高球幕投影成像质量,提出了双通道球幕投影方案,并基于此方案,为3.05 cm(1.2英寸)3DMD芯片技术投影机设计了双通道球幕投影镜头。根据投影方案确定了设计指标,对初始结构的选型做出了合理的分析,阐述了光学设计过程,给出了像差优化及设计结果的评价。为避免镜头口径过大引起的重心不稳,通过合理控制光线入射高度,将镜头首片透镜的口径进行了大幅度的压缩,最终口径仅为102 mm。设计的成像质量高、像质均匀的球幕双拼投影镜头F#为2.5,反远比为6:1,1.0视场在38 lp/mm的Nyquist频率处MTF值为0.5,0.85以内视场的MTF值达到0.65以上,最大横向色差为4.7 μm,小于0.5 pixel。     

聚合物分散液晶光栅的衍射特性的研究

报道了一种由聚合物分散液晶膜与具有周期性条状电极结构板结合的新型光栅器件，借助于聚合物分散液晶膜的电光特性，这种栅对入射光的散射或衍射取决于对其施加的电压，即它是电场可调的，实验结果显示出当驱动电压超过器件器件阈值电压时，衍射光的强度和衍射斑的可见级次被电场调制，而且它能入射光的线性偏振态变为椭圆偏振态。     

Small-angle light scattering symmetry breaking in polymer-dispersed liquid crystal films with inhomogeneous electrically controlled interface anchoring

We have described the method of analyzing and reporting on the results of calculation of the small-angle structure of radiation scattered by a polymer-dispersed liquid crystal film with electrically controlled interfacial anchoring. The method is based on the interference approximation of the wave scattering theory and the hard disk model. Scattering from an individual liquid crystal droplet has been described using the anomalous diffraction approximation extended to the case of droplets with uniform and nonuniform interface anchoring at the droplet–polymer boundary. The director field structure in an individual droplet is determined from the solution of the problem of minimizing the volume density of the free energy. The electrooptical effect of symmetry breaking in the angular distribution of scattered radiation has been analyzed. This effect means that the intensities of radiation scattered within angles +θ _s and–θ _s relative to the direction of illumination in the scattering plane can be different. The effect is of the interference origin and is associated with asymmetry of the phase shift of the wavefront of an incident wave from individual parts of the droplet, which appears due to asymmetry of the director field structure in the droplet, caused by nonuniform anchoring of liquid crystal molecules with the polymer on its surface. This effect is analyzed in the case of normal illumination of the film depending on the interfacial anchoring at the liquid crystal–polymer interface, the orientation of the optical axes of droplets, their concentration, sizes, anisometry, and polydispersity.     

Electro-optical phase shift in polymer dispersed liquid crystals

An anisotropic version of the Maxwell Garnett approximation is applied for studying the electro-optical phase modulation by polymer dispersed liquid crystals (PDLC). The PDLC contain bipolar liquid crystal droplets that can be reoriented by an external field causing a change in the optical birefringence. This approach provides an explicit link between the droplet orientation distribution and the electro-optical phase shift. For aligned droplets we find that the sharpness of the change in the birefringence may be controlled by selecting the initial orientation. For a planar distribution we find sharp transitions with a hysteresis loop whose width depends on the droplet concentration. For a random distribution, the droplet orientation and the optical phase shift change more gradually with the applied field. These results demonstrate that PDLC may be suitable for a wide range of electro-optic applications based on their field-induced phase modulation properties. In addition, it is apparent that the optical phase shift is quite sensitive to changes in droplet orientation. It should therefore be useful for studying reorientation phenomena in PDLC, overcoming the problems due to light scattering in these materials. Received 25 November 1999 and Received in final form 20 January 2000     

Switchable broadband achromatic half-wave plate with nematic liquid crystals

We describe a broadband achromatic half-wave retarder for normally incident light of arbitrary polarization. The device consists of a stack of one nematic liquid-crystal cell with uniform alignment sandwiched between two twisted nematic layers that have identical twist angles (135 degrees) but different orientations of their surface alignment. As a specific application, for light with linear polarization at 45 degrees to the optic axis of the homogeneous cell the stack functions efficiently as an optical switch. The switch rotates the incident linear polarization by 90 degrees in the absence of an electric field. When sufficiently high voltage is applied to all three layers, the device produces a near-zero effect on the incident polarization. An achromatic response in the spectral range 400-700 nm is achieved for both activated and quiescent states.     

一种新的非相干-相干光学转换方法

报道了一种新的非相干-相干光学转换方法,该方法是基于对介质中光致双折射的局部擦除.所用样品为一种含偶氮基侧链聚合物液晶薄膜,该液晶薄膜具有显着的光致双折射和永久光学存储特性.将样品放置在两块相互正交的偏振片之间,用线偏振光在样品中产生稳定的双折射,然后通过入射的非相干图象进行局部地擦除,相干图象由一束He-Ne激光读出.所得相干图象为入射的非相干图象的负片.     

液体透镜的透射波前特性研究

液体透镜是一种新型光学元件,通过改变表面曲率而调整光焦度。液体透镜的透射波前质量会影响成像质量,将液体透镜应用于精密光学系统需要探明其透射波前变化特性。通过理论和仿真分析液体透镜通光孔径内不同高度入射光线的光程差随曲率半径的变化,以及光程差对光焦度的敏感性,以此研究光瞳空间内光程差微变的一致性。分别测量液体透镜在零、正、负光焦度下的透射波前,通过分析实验数据验证液体透镜的光程差微变的一致性。实验结果表明:光程差微变的空间最大差异约为0.22λ～0.36λ,空间分布离散程度约为0.01λ～0.02λ,得出液体透镜随电流微变产生的光程差微变一致性较好,为液体透镜在精密光学系统中的应用和像差补偿提供了技术支撑。     

Optically switchable, polarization-independent holographic polymer dispersed liquid crystal (H-PDLC) gratings

An optically switchable, polarization-independent holographic polymer dispersed liquid crystal (H-PDLC) transmission grating is demonstrated by adding azobenzene-LC and chiral molecules into the H-PDLC formulation. The optical switchable mechanism is from the trans-cis photoisomerization of the doped azobenzene-LC, which modulates the refractive index of the LC rich area. The dependence of the diffraction efficiency of the H-DPLC grating without chiral molecules on light polarization suggests that the orientation of LC directors within the droplet is ellipsoidal and uniaxial. However, the addition of chiral molecules into the H-PDLC formulation helps the formation of isotropic and non-uniaxial LC directors within the droplets. The polarization properties of the grating are investigated and analyzed by the coupled and modified coupled wave theory with a model of sinusoidal dielectric modulation. The results show that the addition of chiral molecules changes the LC phase from nematic to chiral-nematic, where the grating efficiency, which is modulated by the photoinduced phase transition, is independent of the polarization of incident light. Our findings may help improve optical systems that utilize non-polarized light.     

气动光学头罩光传输数值仿真

 气动热环境下光学头罩由于受气动热效应作用,其形状和光学性质都将发生改变,从而影响头罩内的光传输。建立气动光学头罩有限元分析模型,根据热光效应和弹光效应理论,对头罩的折射率场进行数值计算,采用四阶龙格-库塔法编制光线追迹程序对气动光学头罩内红外辐射光线传输进行了数值仿真,得到了头罩光学系统出射波面波像差和调制传递函数。研究结果表明：气动热环境下热光效应对光学头罩光传输的影响远比弹光效应大,且气动光学头罩成像质量受到气动热效应的影响严重下降,为了提高高速飞行器的制导精度,不能忽视气动热对头罩光传输的影响。     

光栅光阀器件的结构改进与制作工艺研究

根据光栅光阀的工作原理,在结构上对传统的光栅光阀器件进行了改进,分析了改进后光栅光阀器件的光学特性、结构特性,以及制作工艺流程.改进后的光栅光阀结构中硅基底上设有二氧化硅隔离层,隔离层上沉积无定形硅作为牺牲层,可动梁的材料是氮化硅,固定梁为蒸镀的金属铝层.通过离子刻蚀的方法刻蚀图形,用化学腐蚀方法掏空牺牲层得到所需桥梁状结构.研究表明改进后的器件黑区范围小,驱动电压较低,光学效率较高,具有潜在的应用前景.     

基于BiFeO_3/ITO复合膜表面钝化的黑硅太阳电池性能研究

采用金属银辅助化学刻蚀法在制绒的硅片表面刻蚀纳米孔形成微纳米双层结构,以期获得高吸收率的太阳能电池用黑硅材料.鉴于微纳米结构会在晶硅表面引入大量的载流子复合中心,利用磁控溅射技术在黑硅太阳电池表面制备了BiFeO_3/ITO复合膜,并对其表面性能和优化效果进行了探索.实验制备的具有微纳米双层结构的黑硅纳米线长约180—320 nm,在300—1000 nm波长范围内入射光反射率均在5%以下.沉积BiFeO_3/ITO复合薄膜后的黑硅太阳能电池反射率略有提高,但仍然具有较强的光吸收性能;采用BiFeO_3/ITO复合膜的黑硅太阳能电池开路电压和短路电流密度分别由最初的0.61 V和28.42 mA/cm~2提升至0.68 V和34.57 mA/cm~2,相应电池的光电转化效率由13.3%上升至16.8%.电池综合性能的改善主要是因为沉积BiFeO_3/ITO复合膜提高了电池光生载流子的有效分离,从而增强了黑硅太阳电池短波区域的光谱响应,表明具有自发极化性能的BiFeO_3薄膜对黑硅太阳能电池的表面性能可起到较好的优化作用.     

Electrically controllable unidirectional transmission in a heterostructure composed of a photonic crystal and a deformable liquid droplet

We propose a new method to realize the tunable unidirectional behavior using a heterostructure composed of a one-dimensional photonic crystal and a deformable liquid droplet. We can control the occurrence of the unidirectional behavior in the heterostructure by adjusting the voltage applied on the liquid system. It is demonstrated that when the voltage is not applied most of incident-wave energy can be transmitted through the heterostructure for backward lights. While the forward lights can’t be transmitted, if the voltage is high enough, the one-way behavior disappears. The applied voltage to control the one-way behavior may be relatively low. Thereby, we can expect that the heterostructure may have potential applications in optical devices.     

Light scattering by a nematic liquid crystal droplet: Wentzel–Kramers–Brillouin approximation

Light scattering by an optically anisotropic liquid crystal (LC) droplet of a nematic in an isotropic polymer matrix is considered in the Wentzel–Kramers–Brillouin (WKB) approximation. General relations are obtained for elements of the amplitude matrix of light scattering by a droplet of arbitrary shape and for the structure of the director field. Analytic expressions for the amplitude matrices are derived for spherical LC droplets with a uniformly oriented structure of local optical axes for strictly forward and strictly backward scattering. The efficiency factors of extinction and backward scattering for a spherical nonabsorbing LC droplet depending on the LC optical anisotropy, refractive index of the polymer, illumination conditions, and orientation of the optical axis of the droplet are analyzed. Verification of the obtained solutions has been performed.