CN108761891A - A kind of wide range polarization grating optimization method based on compensation of refractive index - Google Patents

A kind of wide range polarization grating optimization method based on compensation of refractive index Download PDF

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CN108761891A
CN108761891A CN201810630409.XA CN201810630409A CN108761891A CN 108761891 A CN108761891 A CN 108761891A CN 201810630409 A CN201810630409 A CN 201810630409A CN 108761891 A CN108761891 A CN 108761891A
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polarization grating
wide range
refractive index
liquid crystal
polarization
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郭琦
陈达
张天颢
赵慧洁
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Beihang University
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Beihang University
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/133502—Antiglare, refractive index matching layers

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Mathematical Physics (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Diffracting Gratings Or Hologram Optical Elements (AREA)

Abstract

A kind of wide range polarization grating optimization method based on compensation of refractive index is to transmit the optimization method that perturbation of spectrum is proposed for elimination wide range polarization grating (Broadband Polarization Grating).The present invention increases one layer of glass structure on the basis of wide range polarization grating structure, by refractive index difference between reducing medium to weaken the interference that film interference is brought, has effectively contained the disturbance of transmissivity, has improved the homogeneity of wide range polarization grating transmitance.

Description

一种基于折射率补偿的宽谱偏振光栅优化方法A wide-spectrum polarization grating optimization method based on refractive index compensation

技术领域technical field

本发明涉及的宽谱液晶偏振光栅，可以在较宽的谱段内实现高衍射效率的偏振转换。本发明通过增加一层补偿介质，有效抑制了光栅的薄膜干涉效应，实现了宽谱段内稳定的高透过率。The wide-spectrum liquid crystal polarization grating involved in the invention can realize polarization conversion with high diffraction efficiency in a wide spectral range. The invention effectively suppresses the film interference effect of the grating by adding a layer of compensation medium, and realizes stable high transmittance in a wide spectrum.

背景技术Background technique

液晶偏振光栅是一种微纳光学器件，它可以以极高的转换效率(近100％)将一束非偏振光转换为两束椭圆偏振光。改进后的宽谱偏振光栅还能够实现较宽波段内的高效转换，可用于制作100％偏振片等高效偏振器件。Liquid crystal polarization grating is a kind of micro-nano optical device, which can convert one beam of unpolarized light into two beams of elliptically polarized light with extremely high conversion efficiency (nearly 100%). The improved wide-spectrum polarization grating can also realize high-efficiency conversion in a wider wavelength band, and can be used to make high-efficiency polarization devices such as 100% polarizers.

然而，在液晶偏振光栅的仿真和制造过程中，由于薄膜干涉的存在，如图1所示，使得宽谱段偏振光栅的透射谱存在着较大的扰动，会降低偏振光栅的透过率，影响器件的偏振转换效果。如图2所示，在偏振光栅镀在SiO2基底上，直接与空气接触时，不同波长对应的透过率扰动比较剧烈，不仅造成了一定的能量损失，不同波长光的透过率差异也会造成一定的颜色失真。需要一种方法来解决透过率扰动的问题。However, in the simulation and manufacturing process of the liquid crystal polarization grating, due to the existence of thin film interference, as shown in Figure 1, there is a large disturbance in the transmission spectrum of the wide-band polarization grating, which will reduce the transmittance of the polarization grating. Affect the polarization conversion effect of the device. As shown in Figure 2, when the polarization grating is plated on the SiO2 substrate and directly in contact with the air, the transmittance perturbation corresponding to different wavelengths is relatively severe, which not only causes a certain energy loss, but also causes differences in the transmittance of different wavelengths of light. Cause some color distortion. A method is needed to address the problem of transmittance perturbations.

薄膜干涉是导致透过率扰动的主要原因，所以优化目标就是消除薄膜干涉。薄膜干涉是由膜层与其他介质交界处的反射引起的。消除薄膜干涉的一般思路是控制膜层厚度，达到减弱或者消除某一波长薄膜干涉的效果。但是由于改变偏振光栅厚度时，其中心波长也会发生改变，且宽谱偏振光栅需要对所有波长都有良好的透过效果，所以无法通过改变厚度的方法解决薄膜干涉问题。Thin film interference is the main cause of transmittance disturbance, so the optimization goal is to eliminate thin film interference. Thin-film interference is caused by reflections at the interface between the film and other media. The general idea of eliminating thin-film interference is to control the thickness of the film layer to reduce or eliminate the effect of thin-film interference at a certain wavelength. However, when the thickness of the polarization grating is changed, its central wavelength will also change, and the wide-spectrum polarization grating needs to have a good transmission effect for all wavelengths, so the thin-film interference problem cannot be solved by changing the thickness.

解决薄膜干涉的另一种方法是使用折射率补偿，即，采用一种与偏振光栅材料折射率相近的材料与其相接触，可以显著减弱介质交界处的反射，从而抑制薄膜干涉。对于液晶偏振光栅而言，使用折射率补偿的方法更可行。Another way to solve thin-film interference is to use refractive index compensation, that is, using a material with a similar refractive index to the polarizing grating material to contact it can significantly reduce the reflection at the interface of the medium, thereby suppressing thin-film interference. For liquid crystal polarization gratings, the method of using refractive index compensation is more feasible.

发明内容Contents of the invention

本发明所要技术解决问题是：提供一种优化结构，以减弱宽谱偏振光栅的透过率扰动问题。The technical problem to be solved by the present invention is to provide an optimized structure to reduce the disturbance of the transmittance of the wide-spectrum polarization grating.

本发明的技术解决方案是：在宽谱偏振光栅与空气接触的表面蒸镀一层与其材料折射率相近的补偿膜层。The technical solution of the present invention is: on the surface of the wide-spectrum polarization grating in contact with the air, a compensation film layer with a refractive index close to that of the material is evaporated.

补偿膜层：用来进行折射率补偿以减弱薄膜干涉。其材料的选择应该符合以下3点要求：Compensation film layer: used for refractive index compensation to reduce thin film interference. The selection of its material should meet the following three requirements:

●折射率与偏振光栅材料折射率相近The refractive index is similar to that of the polarizing grating material

●色散小，尽量减少材料色差的引入。●Small dispersion, minimize the introduction of material chromatic aberration.

●尽量选择成本低，制备工艺成熟的材料●Try to choose materials with low cost and mature preparation technology

如选择SiO2(n＝1.47)作为补偿膜层的材料，符合上述要求。增加补偿膜层减小了折射率差值，从而减弱了偏振光栅的薄膜干涉。其原理如公式1所示，薄膜干涉中上下两层界面处反射光的光程差If SiO2 (n=1.47) is selected as the material of the compensation film layer, it meets the above requirements. Increasing the compensation film layer reduces the refractive index difference, thereby weakening the film interference of the polarization grating. The principle is shown in formula 1, the optical path difference of the reflected light at the interface of the upper and lower layers in thin film interference

d为晶体膜层的厚度，n1,n2分别为介质和晶体的折射率，i为入射光与界面夹角，在正入射时取90°，λ为入射光波长。由于半波损失的存在，当n1≈n2时，对于任意波长的光而言，反射最弱，透射最强，薄膜干涉被大大减弱。这样，就解决了透过率扰动的问题。此外，补偿膜层还可以防尘防水，起到保护偏振光栅的作用，延长器件的使用寿命。d is the thickness of the crystal film, n 1 and n 2 are the refractive indices of the medium and the crystal, respectively, i is the angle between the incident light and the interface, which is 90° at normal incidence, and λ is the wavelength of the incident light. Due to the existence of half-wave loss, when n1≈n2, for any wavelength of light, the reflection is the weakest, the transmission is the strongest, and the thin-film interference is greatly weakened. In this way, the problem of transmittance disturbance is solved. In addition, the compensation film layer can also prevent dust and water, play a role in protecting the polarization grating, and prolong the service life of the device.

使用优化后的结构，可以达到很好的降低透过率扰动的效果，如图3所示。在增加补偿膜层与增透膜之后，各波长的透过率均有了明显提升(超过99.5％)，且扰动明显减小(扰动在±0.5％范围内)，达到了很好的优化效果。Using the optimized structure can achieve a very good effect of reducing the transmittance disturbance, as shown in Figure 3. After adding the compensation film and anti-reflection film, the transmittance of each wavelength has been significantly improved (more than 99.5%), and the disturbance has been significantly reduced (the disturbance is within ±0.5%), achieving a very good optimization effect .

附图说明Description of drawings

图1薄膜干涉原理示意图Figure 1 Schematic diagram of thin film interference principle

图2优化后宽谱偏振光栅结构示意图Figure 2 Schematic diagram of optimized broadband polarization grating structure

图3衍射效率扰动示意图Figure 3 Schematic diagram of diffraction efficiency perturbation

图4增加补偿膜层后衍射效率图Figure 4 Diffraction efficiency diagram after adding compensation film layer

Claims (5)

1. a kind of wide range polarization grating optimization method based on compensation of refractive index, which is characterized in that the wide range polarization grating uses The encapsulating structure of upper layer and lower layer medium.By matching the refractive index of polarization grating and encapsulation medium, wide range is on the one hand reduced On the one hand the transmitance perturbed problem of polarization grating has protection polarization grating, the advantage of dustproof and waterproof.
2. wide range polarization grating optimization structure as described in claim 1 is followed successively by (1) compensation film layer from top to bottom, (2) are chiral Polarization grating, (3) opposite-handed polarization grating, (4) substrate of glass.Wherein compensation film layer is compensation of refractive index and device protection Nuclear structure.
3. wide range polarization grating optimization method as described in claim 1 is using the liquid crystal material refractive index with polarization grating Similar material is covered in the surface of polarization grating as compensation film layer.Such structure significantly reduces thin film interference effects Influence to transmitance.
4. liquid crystal polarization gratings as described in claim 1 are a kind of diffraction grating based on liquid crystal, liquid crystal molecule main shaft square Change in sinusoidal rule to space coordinate, characteristic is non-polarized incident light being beamed into several with different polarization states Sub-light wave.Liquid crystal polarization gratings are operated under the conditions of half-wave, i.e., meet best match to single wavelength, are presented close to 100% Diffraction efficiency.
5. wide spectrum polarizing liquid crystal grating as described in claim 1 widens polarised light using the method for multilayer chiral liquid crystal superposition The effective bandwidth of grid, two layers of chiral layers superposition is with Δ λ/λ~56%, and theoretical diffraction efficiency is in 85% -93% range.
CN201810630409.XA 2018-06-19 2018-06-19 A kind of wide range polarization grating optimization method based on compensation of refractive index Pending CN108761891A (en)

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Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1391662A (en) * 1999-11-19 2003-01-15 康宁股份有限公司 Lateral field based liquid crystal gratings
US20040239869A1 (en) * 2003-06-02 2004-12-02 Cavanaugh Shanti A. Narrow band tunable filter with integrated detector
CN1965250A (en) * 2004-06-25 2007-05-16 诺思罗普格鲁曼公司 Optical compensation of cover glass-air gap-display stack for high ambient lighting
CN101657741A (en) * 2007-04-16 2010-02-24 北卡罗莱纳州立大学 Multilayer achromatic liquid crystal polarization grating and related manufacturing method
CN202210190U (en) * 2011-07-26 2012-05-02 信利半导体有限公司 3d display module and mobile phone
JP2013007781A (en) * 2011-06-22 2013-01-10 Citizen Holdings Co Ltd Liquid crystal device
CN103472521A (en) * 2007-04-16 2013-12-25 北卡罗莱纳州立大学 Low-twist chiral liquid crystal polarization gratings and related fabrication methods
CN106575007A (en) * 2014-07-31 2017-04-19 北卡罗莱纳州立大学 Bragg liquid crystal polarization gratings
CN106918932A (en) * 2017-03-09 2017-07-04 苏州晶萃光学科技有限公司 A kind of optically controlled liquid crystal spatial light modulator and its application

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1391662A (en) * 1999-11-19 2003-01-15 康宁股份有限公司 Lateral field based liquid crystal gratings
US20040239869A1 (en) * 2003-06-02 2004-12-02 Cavanaugh Shanti A. Narrow band tunable filter with integrated detector
CN1965250A (en) * 2004-06-25 2007-05-16 诺思罗普格鲁曼公司 Optical compensation of cover glass-air gap-display stack for high ambient lighting
CN101657741A (en) * 2007-04-16 2010-02-24 北卡罗莱纳州立大学 Multilayer achromatic liquid crystal polarization grating and related manufacturing method
CN103472521A (en) * 2007-04-16 2013-12-25 北卡罗莱纳州立大学 Low-twist chiral liquid crystal polarization gratings and related fabrication methods
JP2013007781A (en) * 2011-06-22 2013-01-10 Citizen Holdings Co Ltd Liquid crystal device
CN202210190U (en) * 2011-07-26 2012-05-02 信利半导体有限公司 3d display module and mobile phone
CN106575007A (en) * 2014-07-31 2017-04-19 北卡罗莱纳州立大学 Bragg liquid crystal polarization gratings
CN106918932A (en) * 2017-03-09 2017-07-04 苏州晶萃光学科技有限公司 A kind of optically controlled liquid crystal spatial light modulator and its application

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