IPS with positive and negative a. films

The required positive a film s phase retardation Fa+ is equal to the spherical angle ZEAT, thus from Equations (8.17) and (8.27) the required positive a film s thickness da+ can be expressed as  

In the derivation of Equation (8.28), we substitute (f = -45 and f o=21(f into Equation (8.17) because the positive a film s optical axis is oriented at -45° direction, as Figme 8.17(a) shows, and the viewing direction is from (po = 270° azimuthal angle. 

Similarly, the negative a film s phase retardation Fa is equal to the negative spherical angle ZETA, i.e. Fa- = -ZETA. Here the minus sign denotes that the phase retardation of the negative a film is negative and the rotation around PO axis from point E to point A is counterclockwise. Thus, from Equations (8.17) and (8.27) we can obtain the negative a film s thickness da- as 

From Equations (8.23), (8.28), and (8.29), the required film thicknesses depend on the incident angle Oq, the film s refractive indices a+,e a+,o. a-,e. and na-o, and the polarizer s average real refractive index tip. Therefore, once we know the refractive indices of both the films and the polarizer, as well as the intended viewing angle for LCD optimization, we can determine the required film thickness from Equations (8.23), (8.28), and (8.29). By using the parameters listed in Table 8.2 and choosing 0o = 70°, the required film thicknesses as 

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