Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-02-11
2001-10-09
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S098000, C349S115000
Reexamination Certificate
active
06300989
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a technical field of a display device, and more particularly to a technical field of a display device such as a reflective liquid crystal display device or the like which includes a polarized light separator such as a polarizer, a reflective polarizer and so forth, and which reflects external light to effect display, and electronic apparatus such as a portable phone and a watch using the same.
BACKGROUND ART
In a conventional liquid crystal display device utilizing a variable transmission polarization axis optical element for rotating the polarization axis of transmitted light of a TN (Twisted Nematic) liquid crystal, an STN (Super-Twisted Nematic) liquid crystal and the like, a structure is employed in which the variable transmission polarization axis optical element is sandwiched by two sheets of polarizers.
According to such an arrangement, only a polarized light component in a specific direction is transmitted through a first polarizer located on the side of a display screen of liquid crystal, and other polarized light components are absorbed by this first polarizer. The polarization direction of the light transmitted through the first polarizer is selectively changed in response to an alignment state of liquid crystal that changes with respect to a voltage applied to the liquid crystal, and the light is incident on a second polarizer located on the other side of the liquid crystal.
In a normally white mode, for example, regarding each of the pixels, (i) in a state where a voltage is not applied to the liquid crystal, light emitted from this liquid crystal is transmitted through the second polarizer, is reflected by a reflecting plate located at the back thereof and thereafter, is transmitted through the second polarizer, the liquid crystal and the first polarizer again to be emitted as display light from the display screen of a liquid crystal display device, (ii) in a state where a voltage is applied to the liquid crystal, the light emitted from this liquid crystal is absorbed by the second polarizer, and the display light is not emitted from the display screen finally.
In this way, light amounts of the display light emitted from the display screen is controlled for each of the pixels using the liquid crystal, polarizers and so forth arranged on the optical path of the external light while reflecting the external light incident from the display screen by a reflecting film provided inside a device, whereby reflective display is effected.
However, since the polarizer, which is an example of a polarized light separator, effects polarization by absorbing polarized light component in the direction different from a specific polarization axis in the incident light, there is a problem in that usage efficiency of light is bad, thus providing dark reflective display.
SUMMARY OF THE INVENTION
The present invention is made in consideration of the above problem, and an object is to provide, in a display device utilizing a variable transmission polarization axis optical element such as liquid crystal or the like, a display device which can effect bright display at least at the time of reflective display and transmissive display using external light, and an electronic apparatus using the same.
The above object of the present invention is achieved by a display device including: a variable transmission polarization axis means capable of varying a transmission polarization axis; a first polarized light separating means which is placed on one side of the variable transmission polarization axis means, which transmits light of linearly polarized light component in a first direction and which reflects, of the light of linearly polarized light component in a predetermined direction different from the first direction, a component in a wavelength region &Dgr;&lgr; and transmits a component in a predetermined wavelength region −&Dgr;&lgr; different from the wavelength region &Dgr;&lgr;; and a second polarized light separating means which is placed on the other side of the variable transmission polarization axis means, which transmits light of linearly polarized light component in a second direction, and which reflects or absorbs light of linearly polarized light component in a predetermined direction different from the second direction.
According to the display device of the present invention, when effecting reflective display utilizing external light, the external light is incident from the side of the first polarized light separating means. The first polarized light separating means transmits light of linearly polarized light component in the first direction in the incident external light to the side of the variable transmission polarization axis means. Then, the first polarized light separating means reflects light of the component in the wavelength region &Dgr;&lgr; in the linearly polarized light component in a predetermined direction (for example, the direction perpendicular or substantially perpendicular to the first direction) different from the first direction, and transmits light of the component in the wavelength region −&Dgr;&lgr; (for example, all visible light region except the wavelength region &Dgr;&lgr;) different from this wavelength region &Dgr;&lgr;. Next, the second polarized light separating means transmits, of the light incident through the first polarized light separating means and the variable transmission polarization axis means, light of linearly polarized light component in the second direction to the opposite side of the variable transmission polarization axis means, and reflects or absorbs light of linearly polarized light component in a predetermined direction (for example, the direction perpendicular or substantially perpendicular to the second direction) different from the second direction. Here, the light reflected by the second polarized light separating means passes through the variable transmission polarization axis means and the first polarized light separating means in inverse order of the above order. Or, the light separately reflected by a reflecting plate or the like after being transmitted through the second polarized light means passes through the second polarized light separating means, the variable transmission polarization axis means and the first polarized light separating means in inverse order of the above order. As a result of the foregoing, the light of one of the components in the wavelength region −&Dgr;&lgr; and in the all wavelength regions is selectively emitted from the first polarized light separating means in response to the direction of the transmission axis in the variable transmission polarization axis means. Then, together with the light emitted from the inside of the display device, the component in the wavelength region &Dgr;&lgr; in the linearly polarized light component in a predetermined direction of the incident external light is reflected by the first polarized light separating means without entering into the display device, and display becomes bright. However, the light of the component in the wavelength region &Dgr;&lgr; does not contribute to display contrast because it is reflected regardless of the direction of the transmission axis in the variable transmission polarization axis means.
In this way, the first polarized light separating means effects polarization separation by reflecting the component in the wavelength region &Dgr;&lgr; in the linearly polarized light component of the incident external light in the predetermined direction. For this reason, the linearly polarized light component reflected by the polarized light separating means is utilized as display light, as compared with a conventional display device which uses a polarizer for effecting polarization separation by transmitting one linearly polarized light component in one direction and absorbing the other linearly polarized light component perpendicular to the one linearly polarized light component, so that bright reflective display can be obtained. In particular, regarding the first polari
Chowdhury Tarifur R.
Harness & Dickey & Pierce P.L.C.
Seiko Epson Corporation
Sikes William L.
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