Modeling and simulation of a one-dimensional photonic crystal with a twisted nematic defect layer

• Main Authors: Aaron Archibald, 艾倫
• Other Authors: Wei Lee
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/58824998534522282735

碩士 === 中原大學 === 奈米科技碩士學位學程 === 100 === Liquid crystals flow like liquids yet possess either or both positional and orientational order, such as a solid crystalline material would. They exhibit both dielectric anisotropy, allowing their orientation to be controlled by an applied external field, and optical anisotropy, allowing them to change the polarization of light transmitting through them. Many stable organizations of liquid-crystal (LC) molecules are realized with the assistance of polymer alignment layers, anchoring the orientation of LC molecules at the domain boundaries. These properties are utilized to create high quality LC displays widely available in the market today. However, the development and application of LC materials for display devices is a well-established and maturing field, leading researchers to investigate other possible applications of this versatile state of matter. This work is a result of the ongoing search for tomorrow’s LC technology, exploring the use of a LC material in a twisted-nematic (TN) configuration as a field-controllable defect layer within a onedimensional (1D) photonic crystal (PC). The 1D PC structure is a stack of alternating layers of two dielectric materials. Reflections at each interface of the PC structure create interference patterns based on the thickness and refractive index of each layer of the device. These parameters are designed accordingly to yield a desired overall transmission through the multilayer structure. The inclusion of a LC layer adds new functionality to this structure, providing a method for tuning the spectral properties of the device and contributing an ability to rotate the polarization ofpropagating light. These new features of the hybrid PC/LC device are attractive for application where control of the intensity or polarization of light is required, opening the door for a possible new application of LC materials. Many configurations of a twisted-nematic (TN) defect layer within a 1D PC are yet unexplored. In the same way the TN configuration developed over time for display application, the twisted-nematic layer within a PC must be investigated. This study develops models for calculating the transmission of light through layered isotropic materials, such as the PC structure, as well as through the TN layer. The transmission through the composite device may then be predicted though simulation. The transmission of each component of the device is modeled by calculating the thickness of each material layer, fitting the transmission curve of each component. It is shown that this technique can be used to estimate the thickness of the LC layer within the PC structure as well as provide accurate predictions for the transmission of light through a hybrid PC/TN device having arbitrary twist angle and input polarization. Further experimental data collected from test cells demonstrate the optical properties of several PC/TN schemes. It is found that simulation results closely match experimentally obtained data, and the devices may serve well as wavelength selectors, filters or intensity modulators.