Nonlinear Optical Responses of Blue-Phase Liquid Crystals and Their Applications

Open Access
- Author:
- Ho, Tsung Jui
- Graduate Program:
- Electrical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 27, 2018
- Committee Members:
- Iam-Choon Khoo, Dissertation Advisor/Co-Advisor
Iam-Choon Khoo, Committee Chair/Co-Chair
Victor Pasko, Committee Member
Zhiwen Liu, Committee Member
Thomas E. Mallouk, Outside Member - Keywords:
- optic
optical
liquid crystals
blue-phase liquid crystals
laser
bragg grating
bragg diffraction
wave mixing
optical materials
photorefractive
optical limiting
optical switching
nonlinear optic - Abstract:
- “Are they called ’blue phases’ because they are in blue color?” This is the most common question asked by many people. The answer is yes but no. The name was given by the scientist who first observed the special liquid crystalline phase reflecting the color blue, however, the reflection color does not represent the phases. The major difference of blue-phase liquid crystal from other phases is their self-assembly three-dimensional photonic crystalline structure with a lattice constant typically around hundreds of nanometers, and their ability to show Bragg reflection over the visible spectrum. At first, blue-phases were not popular because they are optically isotropic, i.e. no birefringence. However, they attracted wide attention over academic or industrial studies owing to their unique optical properties, such as a fast response time, being polarization- free, possessing no restriction on thickness, and having a self-assembly 3-D structure. Nowadays, scientists in chemistry are able to expand the temperature range from 1 K to almost 100 K and cover the room temperature. Therefore, blue phases are shown to be a promising material to overcome the disadvantage of typical liquid crystal materials. In this dissertation, I will present a comprehensive study of nonlinear optical properties in blue-phase liquid crystal as well as their applications. First, ultrafast optical response of BPLC will be introduced. The results showed that pure transparent BPLC is capable of significantly attenuating a picosecond laser pulse with very high intensity. The mechanism is Maxwell stress-induced flow-reorientation effect. Owing to its tightly bounded structure, BPLC is a promising material for optical switching or optical limiter devices. Furthermore, a detailed study of all-optical image processing with dye-doped BPLC will be revealed. Unlike typical nematic liquid crystals, blue phases are not restricted to sample thickness, and, therefore, Bragg grating condition can be applied to BPLC. The results showed that the diffraction efficiency of BPLC under holographic setup can provide results nearly one hundred times greater than that of the case with nematic liquid crystal. The high diffraction efficiency makes BPLC capable of many different applications, such as hologram reconstruction, phase conjugation, or photorefractive effect. Moreover, an interesting and simple way to prolong the grating memory is discovered, and the detail dynamical studies are shown in the dissertation.