Reflective liquid crystal projection displays with low voltage and high contrast using improved bisector effect
View Patent ↗Methods, systems, devices and apparatus of using a reflective liquid crystal device for projection display operating at a reduced driving voltage and having an increased contrast ratio are disclosed. The reflective liquid crystal device comprises a first substrate, a second substrate with reflector means, and a twisted nematic liquid crystal layer between the first substrate and the second substrate. A polarizing beam splitter is placed outside of the reflective liquid crystal device and adjacent to the first substrate. By setting the entrance polarization direction of the polarizing beam splitter along the azimuthal angle of the linearly polarized eigenmode of the reflective liquid crystal device at the designed driving voltage, a perfect dark state is obtained, which leads to a high contrast ratio at the designed low driving voltage.
1. A reflective liquid crystal projection display device comprising:
a transparent first substrate with a first alignment film and a first alignment direction;
a second substrate with a second alignment film and a second alignment direction;
a liquid crystal layer with positive dielectric constant sandwiched between the first substrate and the second substrate, the liquid crystal layer having a phase retardation value dΔn/λ in the range of approximately 0.4 to approximately 0.8, where d is the thickness of the liquid crystal layer; Δn is the birefringence of liquid crystal materials and λ is the wavelength of incident light; and
a linear polarizer placed outside of the first substrate which is opposite to the liquid crystal layer to linearly polarize an unpolarized light passing through the linear polarizer, the linear polarizer having a first linear polarization direction;
a reflector on an inner side of the second substrate adjacent to the liquid crystal layer to reflect the linearly polarized light,
an analyzer having a second linear polarization direction coupled with the linear polarizer on the outside surface of the first substrate for blocking the reflected linearly polarized light to obtain a dark state, the first linear polarization direction of the linear polarizer is approximately perpendicular to the second linear polarization direction of the analyzer, wherein the liquid crystal layer forms a twist angle φ in the range of approximately 40° to approximately 80° between the second alignment direction on the second substrate and the first alignment direction on the first substrate and the first linear polarization direction of the linear polarizer deviates from the bisector direction of the twist angle of the liquid crystal layer, the liquid crystal layer forming a left-handed twist angle φ and the polarization direction of the linear polarizer forms an angle β with the first alignment polarization of the first substrate, wherein the angle β is larger than φ/2 and less than φ/2+15 degrees.
2. A reflective liquid crystal projection display device comprising:
a transparent first substrate with a first alignment film and a first alignment direction;
a second substrate with a second alignment film and a second alignment direction;
a liquid crystal layer with positive dielectric constant sandwiched between the first substrate and the second substrate, the liquid crystal layer having a phase retardation value dΔn/λ in the range of approximately 0.4 to approximately 0.8, where d is the thickness of the liquid crystal layer; Δn is the birefringence of liquid crystal materials and λ is the wavelength of incident light; and
a linear polarizer placed outside of the first substrate which is opposite to the liquid crystal layer to linearly polarize and not circularly polarize an unpolarized light passing through the linear polarizer, the linear polarizer having a first linear polarization direction;
a reflector on an inner side of the second substrate adjacent to the liquid crystal layer to reflect the linearly polarized light,
an analyzer having a second linear polarization direction coupled with the linear polarizer on the outside surface of the first substrate for blocking the reflected linearly polarized light to obtain a dark state, the first linear polarization direction of the linear polarizer is approximately perpendicular to the second linear polarization direction of the analyzer, wherein the liquid crystal layer forms a twist angle φ in the range of approximately 40° to approximately 80° between the second alignment direction on the second substrate and the first alignment direction on the first substrate and the first linear polarization direction of the linear polarizer deviates from the bisector direction of the twist angle of the liquid crystal layer, the liquid crystal layer forming a left-handed twist angle φ and the polarization direction of the linear polarizer forms an angle β with the first alignment direction on the first substrate, wherein the angle β is larger than φ/2+90 degrees and less than φ/2+105 degrees.