Tunable Liquid Crystal Photonic Devices

In addition to displays, liquid crystals have also been used extensively in tunable photonic devices, such as optical phased array for laser beam steering, variable optical attenuator (VOA) for telecommunications, tunable-focus lens for camera zoom lens, LC-infiltrated photonic crystal fibers [1,2], diode laser-pumped dye-doped LC laser, just to mention a few. 

In this chapter, we only select four topics to illustrate the potential appUcations of liquid crystals in photonics and their technical challenges. The four representative subjects selected are (1) laser beam steering, (2) variable optical attenuator, (3) tunable-focus lens, and (4) polarization-independent LC devices. 

Fundamentals of Liquid Crystal Devices, Second Edition. Deng-Ke Yang and Shin-Tson Wu. 2015 John Wiley Sons, Ltd. Published 2015 by John Wiley Sons, Ltd. 

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With each chapter is designed to be self-contained, the first chapters cover the basic physics of liquid crystals, their interaction with light and electric fields, and the means by which they can be modelled. Next arc described the majority of the ways in which liquid crystals can be used in displays, and Chapter 12, the final chapter of the first edition, deals with photonic devices such as beam steerers, tunable-focus lenses and polarisation-independent devices. In this second edition, four new chapters have been added two on blue phase and polymer stabilised blue phase hquid crystals, which are emerging from the realm of academic research to show promise for very fast response display and photonic devices, a chapter which discusses LCD componentry, and a final chapter on the use of LCDs in 3D display systems. 

The Fredericks transition plays a fundamental role in the operation of many liquid crystal displays because the director orientation can be controlled easily by applying an external magnetic or electric field. One striking feature is that the magnitude of the Fredericks threshold voltage is essential to the operation of many liquid-crystal devices. If the Fredericks threshold voltage could be reduced reliably, this would make it possible for the manufacture of very low-power liquid crystal displays and other liquid-crystalline devices. The Fredericks transition can also be employed to achieve tunable all-optical switching and diode operation in the photonic devices (Miroshnichenko et al. 2006). 

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