Abstract
Adding a chiral dopant in twisted nematic (TN) liquid crystal cell can stabilize the orientation of liquid crystal molecules, particularly in high TN (HTN) or super TN (STN) liquid crystal cells. The difference in pitches in liquid crystal is induced by the chiral dopant, and these different pitches affect the orientation of liquid crystal director under an external applied voltage and influence the characteristics of microwave modulation. To illustrate this point, the microwave phase shift per unit length (MPSL) versus voltage is calculated on the basis of the elastic theory of liquid crystal and the finite-difference iterative method. Enhancing the pitch induced by the chiral dopant in liquid crystal increases the MPSLs, but the stability of the twisted structures is decreased. Thus, appropriate pitches of 100d, 4d, and 2d can be applied in TN, HTN, and STN cells with cell gap d to enhance the characteristics of microwave modulation and stabilize the structures in twisted cell. This method can improve the characteristics of liquid crystal microwave modulators such that the operating voltage and the size of such phase shifters can be decreased.
Highlights
In recent decades, the application of liquid crystal in displays has matured, and exploring other ways of using liquid crystal is becoming increasingly important
We investigated the microwave modulation characteristics of twisted liquid crystals with chiral dopant
Based on the elastic theory of liquid crystal and the finite-difference iterative method, the dependencies of the microwave phase shift per unit length (MPSL) on the applied voltage with different pitches induced by the chiral dopant in twisted nematic (TN), high TN (HTN), and super TN (STN) cells were obtained
Summary
The application of liquid crystal in displays has matured, and exploring other ways of using liquid crystal is becoming increasingly important. Thereafter, they continued studying TN cell with weak anchoring energy at the boundaries and found that the MPSL induced by a given voltage is strongly increased with the decrease in anchoring energy.[15] Ye et al.[16,17] studied the pre-tilted angles of liquid crystal director at the boundaries of a TN cell filled with E7. We calculated the difference in MPSLs between improved and unimproved states In the former situation, P=100d, P=4d, and P=2d were applied in TN, HTN, and STN cells with pre-tilted angle θ0 = θd = 5◦ and anchoring energy w=5×10 5 J/m2.
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