Optical filters with different configurations based on cholesteric liquid crystals （CLCs） are designed. The central wavelength from CLCs can be tuned by the electric field or temperature. For the electric field tuni...Optical filters with different configurations based on cholesteric liquid crystals （CLCs） are designed. The central wavelength from CLCs can be tuned by the electric field or temperature. For the electric field tuning, the ITO is designed with circular patterns, which can make the tunable range 18 nm. For the temperature tuning, two-layer- CLC configurations are used. The experimental results indicate that a deepened or broadened bandgap from the CLC can be achieved by different handedness or concentrations of chiral dopants. The spectrum study is carried out.展开更多
We propose and demonstrate a pseudo Fabry–Pérot filter in the terahertz frequency range of 0.1–0.5 THz. It consists of alternative liquid crystal layers and metallic slats. Separate sharp resonant peaks are sho...We propose and demonstrate a pseudo Fabry–Pérot filter in the terahertz frequency range of 0.1–0.5 THz. It consists of alternative liquid crystal layers and metallic slats. Separate sharp resonant peaks are shown in the simulated transmission spectra, and their positions shift toward higher frequencies when the refractive index of liquid crystal decreases. The measured transmission spectra are consistent with corresponding simulations. Via thermally tuning the refractive index of the filled liquid crystal, the resonant transmission frequencies shift accordingly. The work supplies a novel design for tunable terahertz filters, which would play important roles in terahertz imaging, sensing, high speed communication, and security applications.展开更多
Applicability of guided mode resonant structures to tunable optical filtering and sensing is demonstrated using nematic liquid crystals. As a sensor, a minimum refractive index detectivity of 10^-5 is demonstrated whi...Applicability of guided mode resonant structures to tunable optical filtering and sensing is demonstrated using nematic liquid crystals. As a sensor, a minimum refractive index detectivity of 10^-5 is demonstrated while as a tunable filter, tunability range of few tens of nanometers with 2-nm bandwidth is presented. The optimum design is achieved by maximizing the evanescent field region in the analyte which maximizes the overlap integral. The device can be operated in reflection or transmission modes at normal incidence. It can also be operated at a single wavelength by measuring the angular profile of the light beam.展开更多
基于液晶调谐滤光片(LCTF)的光谱相机由于体积小、功耗低、集成方便,适合多种搭载平台,同时通过光谱反射率来识别目标物,可以有效解决同色异谱的问题,在伪装识别、精细农产品产值估计等方面有很好的应用前景。比较测量法因其能有效排除...基于液晶调谐滤光片(LCTF)的光谱相机由于体积小、功耗低、集成方便,适合多种搭载平台,同时通过光谱反射率来识别目标物,可以有效解决同色异谱的问题,在伪装识别、精细农产品产值估计等方面有很好的应用前景。比较测量法因其能有效排除光照条件和场景背景条件的影响,重建效率较高,在光谱相机的光谱反射率重建中被普遍采用。比较测量法通常采用标准白板作为参考物,但实际应用中,经常会遇到目标场景空间位置不便放置标准白板的情况。针对这种情况,研究采用LCTF光谱相机采集的目标场景中亮度高的颜色作为参考的比较测量法进行目标物的光谱反射率重建来解决上述问题。实验以美国X-Rite的Gretg Macbeth Color Checker(MCC)色卡作为目标物,分别参考亮度高的五个不同色块,运用比较测量法完成红、绿、蓝三个色块的光谱反射率重建。将重建后三个色块的光谱反射率与采用台式分光光度计(X-Rite Color Eye7000A)测量的标准光谱反射比进行比较。结果显示,重建后的红、绿、蓝三个色块的光谱反射率曲线与用分光光度计测量的标准光谱反射率曲线的形状基本相似,每组曲线的均方根误差均小于0.05;重建的蓝色色块的光谱反射率以参考与其光谱反射比接近的蓝绿色重建的效果最好;重建的红色和绿色色块的光谱反射率以除白色外亮度最高的黄色为参考重建的效果最好;二者均比参考标准白板的反射率重建效果好。实验结果说明采用目标场景中亮度高目视效果明显的色块作为参考对象可被用来进行LCTF光谱相机的光谱反射率重建。该方法有效扩大了比较测量法以及液晶调谐光谱成像系统的应用效率。展开更多
基于液晶可调滤波器（LCTF）和CM O S组合的多光谱成像系统,在435-720 n m 波段范围内,以每隔5 n m 波段对小白菜叶片进行灰度值信息的提取,然后求出各个波段的灰度值平均值、标准差以及相关系数,并采用自适应波段选择法（ABS）提取出...基于液晶可调滤波器（LCTF）和CM O S组合的多光谱成像系统,在435-720 n m 波段范围内,以每隔5 n m 波段对小白菜叶片进行灰度值信息的提取,然后求出各个波段的灰度值平均值、标准差以及相关系数,并采用自适应波段选择法（ABS）提取出小白菜叶片的波段指数,最后通过波段指数的排序选取出小白菜叶片的有效特征波段.实验结果表明,用A B S 的特征波段提取的算法,能够快速有效地获取小白菜叶片的光谱信息,在445 nm 、450 nm 、455 nm 、680 nm 、685 nm 、690 nm 、695nm 和710nm 波段具有较理想的波段指数值,有较大的光谱信息量.因此,这些波段可以很好地作为识别小白菜叶片的有效特征信息波段.展开更多
可调带通滤波器是物联网、卫星通信、智能天线等系统中不可缺少的关键器件之一。针对目前对可调带通滤波器小型化、低成本和高集成度等特点的应用需求,提出了一种基于液晶材料的可调带通滤波器设计方法。通过微带传输线结构实现了近零...可调带通滤波器是物联网、卫星通信、智能天线等系统中不可缺少的关键器件之一。针对目前对可调带通滤波器小型化、低成本和高集成度等特点的应用需求,提出了一种基于液晶材料的可调带通滤波器设计方法。通过微带传输线结构实现了近零介电常数(epsilon near zero,ENZ)超材料单元结构的设计,并利用ENZ超材料的窄通道隧穿效应有效实现了窄带滤波功能,通过将3个ENZ超材料单元结构串联从而完成了带通滤波器基本结构的设计。在此基础上,将微波液晶材料引入ENZ超材料的隧穿通道中,利用液晶材料在外部驱动电压作用下介电参数可变的特性,最终实现了对带通滤波特性的有效调控。全波数值仿真结果表明,所提出的基于ENZ超材料的液晶带通滤波器能够实现中心频率15.88~16.73 GHz的调控,从而验证了设计方法的有效性。展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 61107059,61308052 and 61077047the Fundamental Research Funds for the Central Universitiesthe 111 Project of the Harbin Engineering University under Grant No B13015
文摘Optical filters with different configurations based on cholesteric liquid crystals （CLCs） are designed. The central wavelength from CLCs can be tuned by the electric field or temperature. For the electric field tuning, the ITO is designed with circular patterns, which can make the tunable range 18 nm. For the temperature tuning, two-layer- CLC configurations are used. The experimental results indicate that a deepened or broadened bandgap from the CLC can be achieved by different handedness or concentrations of chiral dopants. The spectrum study is carried out.
基金supported by the National Natural Science Foundation of China(Nos.11304151,61490714,61435008,and 61575093)the Ph.D.Programs Foundation of the Ministry of Education of China(No.20120091120020)the Fundamental Research Funds for the Central Universities(Nos.021314380020 and 021314380023)
文摘We propose and demonstrate a pseudo Fabry–Pérot filter in the terahertz frequency range of 0.1–0.5 THz. It consists of alternative liquid crystal layers and metallic slats. Separate sharp resonant peaks are shown in the simulated transmission spectra, and their positions shift toward higher frequencies when the refractive index of liquid crystal decreases. The measured transmission spectra are consistent with corresponding simulations. Via thermally tuning the refractive index of the filled liquid crystal, the resonant transmission frequencies shift accordingly. The work supplies a novel design for tunable terahertz filters, which would play important roles in terahertz imaging, sensing, high speed communication, and security applications.
基金supported by the Ministry of Scienceunder Tashtiot Project
文摘Applicability of guided mode resonant structures to tunable optical filtering and sensing is demonstrated using nematic liquid crystals. As a sensor, a minimum refractive index detectivity of 10^-5 is demonstrated while as a tunable filter, tunability range of few tens of nanometers with 2-nm bandwidth is presented. The optimum design is achieved by maximizing the evanescent field region in the analyte which maximizes the overlap integral. The device can be operated in reflection or transmission modes at normal incidence. It can also be operated at a single wavelength by measuring the angular profile of the light beam.
文摘基于液晶调谐滤光片(LCTF)的光谱相机由于体积小、功耗低、集成方便,适合多种搭载平台,同时通过光谱反射率来识别目标物,可以有效解决同色异谱的问题,在伪装识别、精细农产品产值估计等方面有很好的应用前景。比较测量法因其能有效排除光照条件和场景背景条件的影响,重建效率较高,在光谱相机的光谱反射率重建中被普遍采用。比较测量法通常采用标准白板作为参考物,但实际应用中,经常会遇到目标场景空间位置不便放置标准白板的情况。针对这种情况,研究采用LCTF光谱相机采集的目标场景中亮度高的颜色作为参考的比较测量法进行目标物的光谱反射率重建来解决上述问题。实验以美国X-Rite的Gretg Macbeth Color Checker(MCC)色卡作为目标物,分别参考亮度高的五个不同色块,运用比较测量法完成红、绿、蓝三个色块的光谱反射率重建。将重建后三个色块的光谱反射率与采用台式分光光度计(X-Rite Color Eye7000A)测量的标准光谱反射比进行比较。结果显示,重建后的红、绿、蓝三个色块的光谱反射率曲线与用分光光度计测量的标准光谱反射率曲线的形状基本相似,每组曲线的均方根误差均小于0.05;重建的蓝色色块的光谱反射率以参考与其光谱反射比接近的蓝绿色重建的效果最好;重建的红色和绿色色块的光谱反射率以除白色外亮度最高的黄色为参考重建的效果最好;二者均比参考标准白板的反射率重建效果好。实验结果说明采用目标场景中亮度高目视效果明显的色块作为参考对象可被用来进行LCTF光谱相机的光谱反射率重建。该方法有效扩大了比较测量法以及液晶调谐光谱成像系统的应用效率。
文摘基于液晶可调滤波器（LCTF）和CM O S组合的多光谱成像系统,在435-720 n m 波段范围内,以每隔5 n m 波段对小白菜叶片进行灰度值信息的提取,然后求出各个波段的灰度值平均值、标准差以及相关系数,并采用自适应波段选择法（ABS）提取出小白菜叶片的波段指数,最后通过波段指数的排序选取出小白菜叶片的有效特征波段.实验结果表明,用A B S 的特征波段提取的算法,能够快速有效地获取小白菜叶片的光谱信息,在445 nm 、450 nm 、455 nm 、680 nm 、685 nm 、690 nm 、695nm 和710nm 波段具有较理想的波段指数值,有较大的光谱信息量.因此,这些波段可以很好地作为识别小白菜叶片的有效特征信息波段.
文摘可调带通滤波器是物联网、卫星通信、智能天线等系统中不可缺少的关键器件之一。针对目前对可调带通滤波器小型化、低成本和高集成度等特点的应用需求,提出了一种基于液晶材料的可调带通滤波器设计方法。通过微带传输线结构实现了近零介电常数(epsilon near zero,ENZ)超材料单元结构的设计,并利用ENZ超材料的窄通道隧穿效应有效实现了窄带滤波功能,通过将3个ENZ超材料单元结构串联从而完成了带通滤波器基本结构的设计。在此基础上,将微波液晶材料引入ENZ超材料的隧穿通道中,利用液晶材料在外部驱动电压作用下介电参数可变的特性,最终实现了对带通滤波特性的有效调控。全波数值仿真结果表明,所提出的基于ENZ超材料的液晶带通滤波器能够实现中心频率15.88~16.73 GHz的调控,从而验证了设计方法的有效性。
