Optical devices comprising high performance polarizer package

#The present invention relates to optical devices comprising sheet polarizer packages comprising certain arrangements of compensator plates.

#Flat Panel Displays such as Liquid Crystal Displays typically use sheet polarizers. Most of the sheet polarizers in a commercial scale production are made by a unidirectional alignment of dichroic crystals in a sub-micron size. The crystals are introduced into a polymer material such as Polyvinyl Alcohol (PVA) followed by stretching to introduce an uni-axial alignment of the dichroic crystals. An “O”-type sheet polarizer absorbs the extraordinary ray vibrating in the direction of the stretch while transmitting the ordinary ray. The other type of sheet polarizer, “E”, transmits the extraordinary ray and absorbs the ordinary ray. Most of the sheet polarizers currently in a commercial use are “O” type. Note that there are many other types of polarizers, such as wire grid polarizers described in U.S. Pat. No. 6,122,103 commercially available from Moxtek Inc. of Orem, Utah, or prismatic polarizers as disclosed in U.S. Pat. No. 2,403,731, however, in this patent application, “polarizer” shall be understood as sheet polarizers only, such as high efficiency polarizer NPF-G1220DU available from Nitto Denko America, Inc. of San Jose, Calif.. An ideal sheet polarizer would absorb 100% of light polarized in the absorbing axis and transmit 100% of light polarized in the transmission axis. However, a practical sheet polarizer generally transmits less than 50% of incoming un-polarized light. Usually, a sheet polarizer comprises an absorbing layer and two protective layers, and sometimes also includes compensators. For this reason, a polarizer will also be referred to as a polarizer package in this application.

#In a typical transmissive LCD such as Twisted Nematic (TN) LCD, a liquid crystal cell is positioned between two crossed polarizer packages with their absorbing axes (or equally, transmission axes) orthogonal to each other. With continuous development of LCDs modes and their compensators, the apparent quality of LCDs can be limited by the performance of the polarizer package. N particular, the apparent performance of an LCD is much affected by the amount of light leakage traveling through the two crossed polarizer packages when the liquid crystal is not placed between the two crossed polarizers. It is desirable to have as little light leakage as possible. Actually, very little light can go through two crossed polarizer packages provided the light is impinged in the direction normal to the plane of the sheet polarizers. As is well known in the art, however, when the light propagation direction deviates from the normal, there occurs a significant amount of light leakage with the maximum leakage occurring at a large polar angle and 45 degrees of azimuthal angle relative to the transmission axis of the polarizer. In order to prevent this, the combination of two types of polarizers “O” type and “E” type has been suggested by Lazarev et al. (“Low-leakage off-angle in E-polarizers”, Journal of the SID, pp. 101-105 (2001)). Theoretically, a matched combination of the two transmits little light in all directions. Yet, actual materialization of the “E”-type sheet polarizer is in its beginning state and its performance, by no means, is satisfactory. Thus, other methods of prevention of the leakage are desirable for practical applications. In what follows, a polarizer may be either an “O” or “E” type, although the specific examples provided actually are “O” type sheet polarizers.

#FIG. 1A is a cross sectional view of a prior art polarizer package.

#FIG. 1B is a perspective view of a transmissive optical device formed by a pair of crossed prior art polarizer packages.

#FIG. 1C is an iso-transmission plot of crossed prior art polarizer packages.

#It is one of our objects to provide a high performance polarizer package, which has a large tolerance of alignment of the compensators relative to their preferred orientation, and therefore can be fabricated with a simpler process.

#It is another of our objects to provide a high performance polarizer package, which can be used in conjunction with another identical polarizer package.

#It is yet another of our objects to provide a high performance polarizer package which can be used in conjunction with a reflective plate and a quarter-wave plate.