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[Electrically Controlled Birefringence (ECB) mode]

The ECB mode uses the applied voltage to change the tilt of the liquid crystal molecules, as a result, the birefringence is changed as a function of the tilt angle θ, which is also called as the polar angle, the one between the substrate normal and the molecule's long axis, shown in figure below, which also shows the tilt change under an electric field, when a LC with Δε>0 is present.

Figure 1. A cell configuration of ECB cell at field-off and field-on states.

and the birefringence Δn is defined in the equation below:

In the TN mode, the transmission maxima will be reached when the condition is met:

If we use applied voltage to change the tilt angle to change Δn, we are able to shift the wavelength of the maxima, i.e. we can shift the transmission color. In general, ECB can be used to generate color to replace the color filter, by applying different voltages on each pixel corresponding the desired color. However the color obtained from ECB are not fully saturated because the spectrum curve are not sharp (narrow) enough, with some overlapping with neighbor colors. Therefore, it is not used often in practical applications for color generations.

Further Readings and References:

Yeh, P. and Gu, C., "Optics of Liquid Crystal Displays", John Wiley & Sons, Chichester (1999).


Last update: April, 2006
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