Uniform lying helix(ULH) is a cholesteric LC structure with helical axix lying on the substrate. This structure has a periodic refractive index profile characteristics, so that it can be used as a phase grating. The ULH period can be tuned with different electric fields which provide with various applications.
However, ULH is not a steady state in general, once the electric field shutdown, ULH texture will transform to planar texture. Generally, the ULH exist only under a few conditions: well homogeneous alignment and cell the ratio of gap to pitch smaller than 2 , in case the ratio more than 2, the ULH won¡¦t align well. We use two methods to make ULH align well at large cell gap pitch ratio; cooling down from isotropic temperature under electric field and putting mechanical stress on the sample, therefore we can get a well alignment and more stable ULH.
We discuss the influence of different boundary conditions to the stability of ULH, and we discover that when d/p large than 10, the stability of ULH improved significantly. Then we study the influence in different alignment anchoring, we find stronger anchoring energy makes ULH transform to planar easily. So we use photo alignment to get weaker anchoring energy, and the ULH using photo alignment stable more than 24 hours.
Finally we use a large d/p ULH as tunable phase grating, the pitch length can be tuned about 380nm with low power consumption, and it still have grating function when the field shutdown .
Keyword: cholesteric liquid crystal¡Buniform lying helix¡Bgrating
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0713112-220714 |
| Date | 13 July 2012 |
| Creators | Li, Hsueh-Wen |
| Contributors | Wen-Jun Zheng, Wei Lee, Andy Ying-Guey Fuh, Tsung-Hsien Lin, Shie-Chang Jeng |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0713112-220714 |
| Rights | user_define, Copyright information available at source archive |
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