5.4: Improvement of Fast Response LC Materials by Bent‐Core Dopants in Optical Compensated Bend (OCB) Mode Liquid Crystal Displays

Wang, Ling Yung; Tsai, Shin Yi; Lin, Hong‐Cheu; Chen, Szu Fen Fenny; Lyu, Robert; Mo, Chi Neng

doi:10.1889/1.3069684

Cited by 1 publication

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“…Methods have been developed for faster response including polymer-stabilized LC, [1][2][3] polymer-dispersed LC, 4 and π-cells. [5][6][7][8] However, the transition time of all of these devices are still in the range of several milliseconds and not sufficient for the high-frame rates needed for multifield sequential displays.…”

Section: Introductionmentioning

confidence: 99%

Fast-response liquid crystal variable optical retarder and multilevel attenuator

2013

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Abstract. We propose and demonstrate a fast-response liquid crystal (LC) variable optical retarder or attenuator with several transmission levels. The fast-response LC optical device consists of dual π-cells. The device is designed so that the transition between any two states is controlled by the application of an increased voltage level rather than by applying a lower level. This design offers transition times in the range of tens of microseconds between any transmission states. A limitation of the device is that the time between transitions cannot be arbitrarily short and is typically milliseconds. 1 Introduction A fast-response liquid crystal (LC) optical retarder or an attenuator with multilevel transmission is needed for many applications, where LC devices are considered to be too slow [e.g., in the field of optical communications or for field sequential three-dimensional (3-D) displays of the future].The response time of conventional nematic LC devices is usually in the range of milliseconds. Methods have been developed for faster response including polymer-stabilized LC, 1-3 polymer-dispersed LC, 4 and π-cells. 5-8 However, the transition time of all of these devices are still in the range of several milliseconds and not sufficient for the high-frame rates needed for multifield sequential displays.To understand why many previous approaches have not been sufficient in decreasing the response time of LC devices, it is helpful to consider what governs that time. In most LC devices, the director orientation results from the competition between torques exerted by an applied electric field, and the elastic torques resulting from the director are not being uniformly aligned with the surface-imposed orientation. The response time of the device is different for the case of the transition to a more distorted director field with the application of a higher voltage (call this, the voltage-applied transition) than it is to the less distorted director field with the application of a lower voltage (call this, the voltage-removed transition). If we would like to decrease the response time for the first case, an approach is just to apply a higher voltage during the transition, but the response time of the second case is limited by the material properties of the LC material that cannot be chosen at will. Therefore, it is typical that the total response time of a LC device is limited by the time required for transition to the less distorted state when the applied voltage is lowered (or removed).Therefore, it has been the focus of a great deal of research to modify the material properties of LC materials to decrease the response time. But for many applications, the results of this work have not been sufficient.

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