All-Optical Switching With Dye-doped Liquid Crystals
Open Access
- Author:
- Liou, Justin Dianhuan
- Graduate Program:
- Electrical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 01, 2010
- Committee Members:
- Iam Choon Khoo, Dissertation Advisor/Co-Advisor
Iam Choon Khoo, Committee Chair/Co-Chair
Douglas Henry Werner, Committee Member
Shizhuo Yin, Committee Member
Tom Mallouk, Committee Member - Keywords:
- passive optical switching
liquid crystals
optical limiting - Abstract:
- A passive all-optical limiter to clamp high-power incident lasers or intense lights to protect human eyes or optical sensors from being damaged is being investigated. Here we present a dye-doped liquid crystal limiter based on a twist-nematic alignment configuration that switches off a high-power incident beam but allows a low-power beam to get through. Detailed theoretical analysis and experimental investigation of twist-nematic liquid crystal (TNLC) cell switching behaviors under various conditions are presented. Two main mechanisms that contribute to liquid crystal switching include: (1) laser-induced birefringence change and (2) photo-chemical molecular confirmation change. Both will disorder the liquid crystal alignment and destroy the light polarization guidance in the sample. A 90-degrees twist alignment nematic liquid crystal doped with suitable dye could impart the required photonic absorption and order parameter modulation. The Jones matrix and Landau-de Gennes theory are introduced and used for the simulation of light propagation within the liquid crystal samples. Experimentally, we have demonstrated ultrafast all-optical liquid crystal switching operation for lasers spanning the visible to near-infrared spectral region (532nm; 750nm; 1064nm; 1550nm). With increasing intensity, the switching time decreases from microseconds to the nanoseconds regime, in such a manner that the transmitted light energy/intensity is clamped to below the eye- or sensor-safe levels. We also present the simulation models for steady-state and transient TNLC switching behaviors. The simulation starts from solving temperature distribution and then order parameter profiles. Refractive index anisotropy is then evaluated and the light transmission response is calculated and discussed. The theory, simulation, and experiment results are in good accordance.