Achromatic birefringence

OPTICAL POLYMER MATERIALS WITH DEFINED ACHROMATIC BIREFRINGENCE... 

Pancharatnam, Achromatic combination of birefringent plates, Proc. Indian Acad. Sci., A41, 137(1955). 

A. M. Title, Improvement of birefringent filters. II Achromatic waveplates, Applied Optics, 14, 229 (1975). 

The only difficulty is, that there do not exist polymers made by radical polymerization with good optical properties and a positive birefnngence. All such polymers as PMMA and polystyrene have substituents perpendicular to the main chain direction and have therefore negative birefringence. If it was possible to direct the aromatic rings of a monomer in the direction of tensile force, the achromatism should be accomplished by copolymerization of such a monomer with PMMA. 

S. Pancharatnam, Achromatic combinations of birefringent plates Part I. An achromatic circular polarizer, Proc. of the Indian Academy of Science, Section A, 41, 130 (1955). 

A coloured backgrormd caused by optical interference is the most serious disadvantage of the STN-LCD because it degrades the colour reproduction of an LCD display. To solve this problem and produce an achromatic black-and-white bacl rormd, the double-layered STN-LCD (D-STN-LCD), which comprises a liquid crystal optical compensator mounted on the STN-LCD, has been developed [4]. Figure 4.3.5 shows the principle of the D-STN-LCD. The compensation layer, which is placed ready fabricated on the driven cell, compensates the optical dispersion caused by the birefringence effect and decolourizes the STN-LCD as long as the following three conditions are met ... 

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