CN109031765A - 一种基于双层向列相液晶的光开关 - Google Patents

一种基于双层向列相液晶的光开关 Download PDF

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CN109031765A
CN109031765A CN201811035817.7A CN201811035817A CN109031765A CN 109031765 A CN109031765 A CN 109031765A CN 201811035817 A CN201811035817 A CN 201811035817A CN 109031765 A CN109031765 A CN 109031765A
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郭琦
闫可心
杨小倩
赵慧洁
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Beihang University
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    • 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
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    • G02F1/139—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 characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent
    • G02F1/1393—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 characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent the birefringence of the liquid crystal being electrically controlled, e.g. ECB-, DAP-, HAN-, PI-LC cells
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    • 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
    • G02F1/133528—Polarisers
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Abstract

一种基于双层向列相液晶的快响应光开关，该发明将入射光信号进行电控导通或切断，实现了毫秒级电控响应，可用于光通讯、精密测量、光电探测、图像编码等。所述双层向列相液晶光开关主要包括前置偏振片、两片完全相同的平行取向向列相液晶片、后置偏振片及驱动系统。该器件基于向列相液晶的电控折射率原理，通过合理的结构设计和电驱动匹配使得两向列相液晶片的相位延迟互补，实现该光开关的在截止态与导通态之间的快速切换。

Description

一种基于双层向列相液晶的光开关
技术领域
本发明涉及的双层向列相液晶光开关，是基于向列相液晶的电控折射率效应，通过合理的结构设计和电压驱动匹配使得两向列相液晶片的相位延迟互补，实现该光开关在明暗状态之间的快速切换。
背景技术
光开关是光网络中用以对光信号实现动态控制的核心器件。光开关按照工作媒介不同，主要可分为自由空间型和波导型两大类。自由空间型按照工作原理又可分为机械类和液晶类。目前工业化最普及的光开关是机械光开关，它的原理是用机械技术对光开关的微光学光路进行控制。机械光开关的特点就是不受光波长的影响，介质损耗小，不受偏振的影响等。其缺点就是响应速度慢，体积较大，并且有机械损耗。
利用液晶材料来制备光开关，它的可靠性好，没有机械结构损耗，其最大的优势是电可调谐性，可以使用外场的改变来调节液晶光开关的状态。对于传统的液晶光开关，使用的通常是单向列相液晶，通常，通过施加电场改变向列相液晶盒中液晶分子的排布状态。施加电场后，液晶分子从场截止态(关)转换为场导通态(开)，去除电场后，液晶分子又转换为场截止态(关)。在这个过程中，开和关的时间是体现液晶性能的重要参数。然而，开的时间可以通过施加的电场来控制，关闭时间不能由电场控制。向列相液晶的关闭时间很大程度上取决于液晶材料的参数，如粘度和弹性常数。它还取决于液晶盒特性，例如液晶盒间隙d和锚定强度w，就关闭时间而言，在常规液晶器件中实现这种快速切换是非常困难和复杂的任务。
一种减少关闭时间的方法是通过增加液晶材料和固体表面之间的接触面积，从而加速在关闭所施加的电场之后发生在液晶中的弛豫过程。通常这是通过在液晶体内形成聚合物网络来实现的，该聚合物网络将这些相互作用扩展到液晶体中，从而强烈地影响弛豫过程。然而，在液晶本体中产生的这种聚合物网络可能引起几种不希望的效应，例如光散射，对比度的劣化和驱动电压的增加。
在本文中，我们提出了另一种减少液晶光开关的关的时间的方法。该装置由两个平行取向的向列单元组成，其取向方向对称的分布在起偏器透偏方向两侧，将这两个平行的向列相液晶插入两个正交偏振器之间。通过合理的结构设计和电压驱动匹配使得两个平行的向列相液晶进行相位延迟互补，使该光开关的上升和下降时间分别对应于两个向列相液晶从场截止态到场导通态的开关上升时间，从而实现了明暗状态的快速切换。
发明内容
本发明的技术解决的问题是：利用双层向列相液晶，弥补向列相液晶关闭时间太长的缺点，提供一种快响应的双层向列相液晶光开关，实现2毫秒内的开和关响应时间。
本发明的技术解决方案是：一种基于双层向列相液晶的快响应光开关，其包括：前置偏振片、均具有平行排列的两个平行的单向列相液晶、后置偏振片及驱动系统，如图1所示。
前置偏振片及后置偏振片：前置偏振片位于双层向列相液晶光开关最前端，将入射光束转换为线偏振光，并使其偏振方向与两片向列相液晶长轴方向均呈45°，后置偏振片透偏方向与前置偏振片呈正交方向放置。
覆盖氧化铟锡导电膜的光学玻璃及驱动系统：为向列相液晶层提供外置驱动电场，使向列相液晶分子在不同极性的电场驱动下进行均匀排布。
向列相液晶层：两个平行取向液晶片的层间隙相同，将双层向列相液晶(PA1和PA2)插入两个偏振方向垂直的偏振器之间。其中，两片向列相液晶在场截止态(关)下的指向矢方向正交，并且相对于起偏器的偏振方向为45°,如图2所示。
其中，在没有加电场之前，PA1和PA2都为场截止态(关)。此时， PA1中的双折射Δn＝ΔnPA1≠0,PA2中的双折射Δn＝ΔnPA2≠0。当加到两片液晶上的驱动电压超过阈值电压并达到饱和时，驱动电压将PA1和 PA2中液晶分子的排列从平行切换到垂直。在切换场导通态(开)下， PA1中的双折射将从ΔnPA1≠0切换到ΔnPA1*＝0。同理，PA2中的双折射将从ΔnPA2≠0切换到ΔnPA2*＝0。可以通过合理的选择PA1和PA2的参数和驱动电压来使ΔnPA1＝ΔnPA2。
其中，图3为电压驱动双层向列相液晶快响应光开关的原理示意图，以30Hz频率,10V电压为例。上面两条曲线分别为加载到PA1和PA2上的驱动信号VPA1和VPA2。下面坐标系中a为PA1在驱动信号 VPA1下的光电响应曲线，实验装置设计如图4。b为PA2在驱动驱动 VPA2下的光电响应曲线，实验装置设计如图5。最下面的曲线c为同时加PA1和PA2以及它们的驱动电压VPA1和VPA2的响应曲线，实验装置设计如图3。
在t0时刻，当两片液晶均处于场截止态时，入射光经PA1后偏振态发生变化，再经PA2偏振态又发生变化，经PA1和PA2后相当于偏振态不变，为暗态。在t1时刻，PA1上所施加的驱动电压由0V变为VPA1， PA1中液晶分子由平行排布变为垂直排布，此时PA2上施加驱动电压为0V。在切换状态下，PA1的双折射将从ΔnPA1≠0切换到ΔnPA1*＝0，此时入射光通过PA1后偏振态不变。PA2的双折射ΔnPA2≠0，入射光通过PA2后偏振态发生变化。该器件将从暗态切换到亮态，对应器件上升时间tON。在t2时刻，PA2上所施加的驱动电压由0V变为VPA2，PA1 上的驱动电压维持不变，PA2的双折射将从ΔnPA2≠0切换到ΔnPA2*＝0，此时，入射光经PA1后偏振态不变，经PA2后偏振态仍不变，该器件将从亮态切换到暗态，对应器件的关闭时间tOFF。在t3时刻，在PA1和 PA2上所施加的驱动信号同时变为0V，PA1的双折射将从ΔnPA1*＝0切换到ΔnPA1≠0，PA2的双折射将ΔnPA2*＝0从切换到ΔnPA2≠0，且由于两液晶片完全相同，相位延迟变化量互补，等效于总相位延迟量为零，该器件保持在暗态。
本发明与现有向列相液晶光开关相比优点在于：该双层向列相液晶光开关的开启和关闭时间分别对应于两个向列相液晶片从场截止态到场导通态的的上升时间，均可随驱动电压幅值的增加而降低。克服了单个向列相液晶光开关的关闭时间无法利用驱动优化的缺点。
附图说明
图1为本发明的组成图；
图2为本发明的结构图；
图3为本发明的驱动波形及响应波形图；
图4为本发明的测单向列相液晶PA1响应曲线的结构图；
图5为本发明的测单向列相液晶PA2响应曲线的结构图；
图6中表1为单个向列相液晶和双层向列相液晶开关时间对比表；
具体实施方式
在这里将详细介绍双层向列相液晶光开关的原理与实验结果。正如我们所知道的那样，分子均匀排列的向列相液晶在光学上表现为单轴(双折射)光学板，其光轴与液晶分子在盒中的优选方向一致。插入两个正交偏振器之间时，当液晶的光轴方向相对于偏振器的偏振方向成45°时，透过偏振器和液晶的光的强度I为：
其中δ＝2πdΔn/λ表示由双折射为Δn＝ne-no的液晶材料引起的相位延迟。(ne为非寻常光，n0为寻常光)。λ为入射光的波长，d 为液晶的厚度。有两个这样的液晶盒，他们的双折射和盒厚分别为Δn1＝ne1-no1，Δn2＝ne2-no2和d1，d2。将两个这样的液晶平行放置，使他们的光轴相互垂直，总的相位延迟将是
δtotal＝δ1+δ2＝2π(d1Δn1+d2Δn2)/λ (2)
从上式中可以看出，当液晶盒的厚度d为常数时，只有通过施加电场来改变液晶的双折射。因此，我们可以通过合理的选择PA1和PA2，然后施加电场来控制透过的总光强。
实验结果
按照上文所设计的方案，搭建实验平台，实验结果如图3，上面两条曲线分别为PA1的驱动信号和PA2的驱动信号，其中加载电压幅值为10V频率为30HZ。下面a曲线为PA1的光电响应曲线，b为 PA2的光电响应曲线，c为双层向列相液晶的光电响应曲线。对于PA1，液晶盒的开和关时间分别为1.8ms和4ms；PA2液晶盒的开和关时间分别为1.8ms和5.5ms；双层向列相液晶，开和关的时间分别为1.0ms和 1.8ms，如表1所示。双层向列相液晶的开时间对应PA1的开时间，但比PA1的开时间稍短。双层向列相液晶的关时间对应PA2的开时间，与PA2的关的时间相等。通过适当选择液晶材料，液晶盒的厚度、驱动电压，可以进一步缩短双层向列相液晶的开关时间。分别在 PA1中发生的弛豫过程与在PA2中发生的弛豫过程之间的微小失配可能导致在暗态下透射光的强度略微变化，这里在图3上用红色圆圈标出。这个小的光强变化，不会对观察者造成影响。通过适当选择液晶参数和驱动电压可降低这个小的光强波动。
本发明说明书中未作详细描述的内容属于本领域专业技术人员公知的现有技术。

Claims (6)

1.一种基于双层向列相液晶的光开关，其特征在于，该液晶光开关在外加电场驱动下，对入射光信号实现导通和切断的快速切换；所述的双层向列相液晶光开关是基于向列相液晶的电控折射率效应实现的，其响应时间在2毫秒以内，且随驱动电压幅值的增加而下降；所述的向列相液晶光开关，起偏器与检偏器的透偏方向互相垂直，向列相液晶PA1的指向矢与起偏器透偏方向呈45°角放置，相液晶PA2指向矢与起偏器透偏方向呈-45°角放置。
2.如权利要求1所述向列相液晶光开关，其特征在于，向列相液晶PA1和PA2的指向矢与起偏器透偏方向均呈45°角，该液晶光开关使用的向列相液晶在外加电场下，分子的指向矢发生偏转，沿电场方向排列，此时，入射光经液晶分子后偏振态不变。未加电场时，所有分子指向矢平行于基板排列，并与起偏器透偏方向呈45°角，入射光透过液晶分子后，偏振态改变。通过合理的结构设计和电压驱动匹配，使得两向列相液晶片的相位延迟互补，实现该光开关下降时间的缩短。
3.如权利要求1所述双层相列相液晶光开关，其特征在于，PA1和PA2都不加驱动电压时，入射光通过PA1液晶偏振态发生变化，再通过PA2液晶偏振态再一次发生变化，经PA1和PA2后相当于入射光偏振态没有发生变化，与检偏器透偏方向垂直，是为暗态。
4.如权利要求1所述双层相列相液晶光开关，其特征在于，若给PA1液晶加驱动电压VPA1，PA2液晶不加驱动电压，此时入射光经过PA1液晶层后偏振态不变，再经PA2液晶层后偏振态发生变化，与检偏器透偏方向平行，是为亮态。
5.如权利要求1所述，给PA1和PA2同时施加驱动电压VPA1和VPA2，入射光经PA1偏振态不变，再经PA2偏振态仍不变，与检偏器透射方向垂直，是为暗态。
6.如权利要求1所述双层相列相液晶光开关，其特征在于，该光开关选用完全相同的两片平行取向向列相进行相位互补，其响应时间可通过适当选择液晶的层间隙、增加驱动电压幅值而进一步减小。
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CN112261324A (zh) * 2020-10-21 2021-01-22 中国兵器工业集团第二一四研究所苏州研发中心 一种消除帧转移型EMCCD Smear效应的方法
CN115712211A (zh) * 2022-11-11 2023-02-24 南京邮电大学 一种各向同性相下正性液晶中纳秒电光响应的增强方法

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112261324A (zh) * 2020-10-21 2021-01-22 中国兵器工业集团第二一四研究所苏州研发中心 一种消除帧转移型EMCCD Smear效应的方法
CN115712211A (zh) * 2022-11-11 2023-02-24 南京邮电大学 一种各向同性相下正性液晶中纳秒电光响应的增强方法

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