Patent ID: 7855787
Filing Date: 2010-12-21
Classification: G02F

Abstract:
1. A method of determining a pretilt angle θ tilt in a liquid-crystal cell, said cell including a cavity between two substrates containing liquid-crystal molecules, each face of the substrates inside the cavity including an alignment layer such that the liquid-crystal molecules are each inclined to the plane of the substrates by said pretilt angle, said liquid crystal being of the twisted nematic type with a defined twist angle θ twist , and said cell having a top position and a bottom position which define a vertical mid-axis when viewed from the front, the method comprising: using contrast meter for establishing a transmission measurement curve, along said vertical axis of the cell, for transmission of a light beam at a defined wavelength λ of said cell as a function of the angle of incidence α of a light beam on said cell, and comparing said measurement curve with a plurality of simulation curves for the transmission of said cell at the same wavelength λ as a function of the angle of incidence of the light beam along said vertical axis of the cell, each of said plurality of simulation curves being calculated for a defined pretilt value and said plurality of simulation curves being calculated by taking apparent values of the thickness d of the liquid-crystal cavity between the two substrates, of the extraordinary index ne of the liquid crystals and of the twist angle θ in which γ is the transmission angle of the light beam in the liquid crystal, which depends on the angle of incidence α, no is the ordinary index of the liquid crystals, d is the thickness of the cavity and ne is the extraordinary index at normal incidence.