OCB模式液晶光栅的光学特性研究.docx

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Introduction
OCB (Optically Compensated Bend) mode is a liquid crystal display (LCD) technology that is widely used in various applications, especially in high-speed displays. OCB mode is a twisted nematic (TN) cell that requires a specific optical alignment to achieve high contrast and fast response time. This paper presents a study on the optical properties of OCB mode, specifically the liquid crystal (LC) optical axis and the LC director distribution.
Liquid Crystal Optical Axis
The OCB mode uses a TN cell with a bend in the liquid crystal layer. This bend creates a specific optical axis orientation along the liquid crystal layer. The optical axis direction is perpendicular to the LC director at the two electrodes, and it is parallel to the LC director close to the center of the cell. The optical axis is defined as the direction where the LC refractive index is highest.
The optical axis orientation determines the polarization of light that can pass through the OCB cell. When the polarization direction of light is perpendicular to the optical axis, no light can pass through the cell. When the polarization direction is parallel to the optical axis, the light can pass through the cell unhindered. This feature is critical for high contrast displays.
LC Director Distribution
The LC director distribution is another critical factor that affects the optical properties of OCB mode. The director distribution describes how the LC molecules are oriented in the cell. In an OCB cell, the LC director tilts from the top electrode to the bottom electrode due to the bend in the liquid crystal layer. The tilt angle is zero at the top electrode and increases to the maximum at the bottom electrode.
The director distribution affects the response time of the OCB cell. The tilt angle gradient creates a torque on the LC molecules that causes them to twist and align with the electric field. This torque is stronger near the top electrode, where the tilt angle gradient is steeper, and weaker near the bottom electrode, where the tilt angle gradient is shallower. The response time of the OCB cell is faster near the top electrode and slower near the bottom electrode.
Conclusion
In conclusion, the optical properties of OCB mode are determined by the LC optical axis orientation and the director distribution. The LC optical axis is perpendicular to the LC director at the two electrodes and parallel to the LC director in the center of the cell. The director distribution tilts from the top electrode to the bottom electrode due to the bend in the liquid crystal layer. Both the LC optical axis and the director distribution affect the polarization of light passing through the cell and the response time of the cell. Understanding these properties is crucial for designing high-speed OCB mode displays.