Optical: systems and elements – Prism – With refracting surface
Reexamination Certificate
2001-07-11
2002-08-06
Sikder, Mohammad (Department: 2872)
Optical: systems and elements
Prism
With refracting surface
C359S838000, C359S490020, C359S490020, C359S490020
Reexamination Certificate
active
06429983
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transflector. A transflector is an optical element that when illuminated with light from one direction will reflect a significant proportion of the incident light, and that when illuminated with light from another direction will transmit a significant proportion of the incident light. The present invention also relates to a transflective display device, in particular to a transflective electro-optical display device, for example such as a transflective liquid crystal display device.
2. Description of The Related Art
Reflective display devices are well known. The principle of a reflective display device is illustrated in FIG.
1
. This shows a reflective display device that consists of a light-modulating element
4
and a reflector
6
disposed behind the light-modulating element
4
. The light-modulating element is formed of a layer
1
of electro-optic material, for example such as a liquid crystal material, disposed between a front substrate
2
and a rear substrate
3
. The front substrate
2
is transparent, but the rear substrate
3
need not be transparent. (The term “front” of the display device refers to the side of the display device that is intended to face a viewer when the display is in use.) The display device shown in
FIG. 1
is intended to be illuminated from the front by ambient light. A representative source of ambient light
5
is shown in FIG.
1
.
Light incident on the front of the light-modulating element
4
passes through the light-modulating element, is reflected by the reflector
6
, and passes back through the light-modulating element to a viewer
7
. (In practice, light from the light source
5
will undergo refraction as it passes through the optical modulating element, in particular at the front surface of the front substrate
2
. This refraction is not shown in
FIG. 1
for clarity of explanation.) The image seen by the viewer
7
can be changed by varying the voltage applied across the electro-optic layer. A reflective device has the advantage that, under suitable illumination conditions, it can utilise ambient light and does not require its own light source. As a result the power consumption of the display device is reduced, and this is advantageous for a battery-powered device.
For such a reflective display to operate effectively, it is necessary that sufficient of the ambient light incident on the display is directed towards the viewer so that a sufficiently bright display is produced. Blazed reflectors can be used to redirect ambient light impinging on a reflective display at an oblique angle so that, after reflection, it exits the display substantially at normal incidence. This is advantageous since viewers of a display generally view the display from the normal direction, or from a near-normal direction, and the use of a blazed reflector creates a higher reflectance of the display towards such a viewer.
Conventional reflective display devices are generally provided with a scattering reflector. A scattering reflector reflects incident light into a range of angles about the direction of specular reflection. This provides even illumination over the area of the display, and also prevents the viewer from seeing a reflected image of the ambient light source.
Co-pending UK patent application No 9909379.1 and corresponding Japanese patent application No 2000-123 267 disclose a scattering blazed reflector that eliminates diffraction effects.
EP 0 883 015 A1 discloses a scattering reflector for an LC display consisting of a reflector and a light diffusion layer disposed above the reflector. The scattering reflector is used to reflect ambient light back through the LC display. In this reflector, the entire surface of the scattering reflector is covered by a metallic reflective layer that is not transmissive.
In order to improve visibility of images, ambient light is selectively reflected from the scattering reflector into a direction, which is different from the direction of reflection of ambient light from front surfaces of the display. The reflected light intensity therefore depends on the angle under which the reflected light intensity is observed. In order to broaden the range of angles into which light is reflected, a light diffusion layer is provided on the reflector.
The magnitude of the overall reflectivity of this reflector, however, does not depend on the angle at which light is incident on the surface of the reflector.
in practice, the optical modulating element
4
of the display device of
FIG. 1
will require other components to display an image, for example such as electrodes to allow the electro-optic layer
1
to be addressed: the optical modulating element may also comprise one or more polarising or retarding elements. These components have been omitted from
FIG. 1
for clarity.
Reflective display devices have the disadvantage that they cannot operate in conditions of low ambient light, since insufficient light is reflected to form a satisfactory image. Where a display device is required to operate in conditions of low ambient light it is, therefore, necessary for the display device to be provided with an auxiliary light source that can illuminate the light-modulating element in conditions of low ambient light. The auxiliary light source can be disposed either in front of or behind the light-modulating element. A reflective display device in which the auxiliary light source is disposed in front of the light-modulating element is not relevant to the present invention, and will not be described further.
FIG. 2
illustrate the principle of operation of a reflective-type display device in which an auxiliary light source
9
is disposed on the opposite side of the light-modulating element
4
to the viewer
7
. Since the auxiliary light source
9
is disposed behind the light-modulating element, it is generally known as a “back-light”. Moreover, since the auxiliary light source
9
is disposed behind the light-modulating element, the rear substrate
3
is required to be transparent.
In place of the reflector
6
of the display device of
FIG. 1
, the display device of
FIG. 2
is provided with a transflector
8
disposed behind the optical modulating element
4
, between the optical modulating element
4
and the auxiliary light source
9
. As noted above, a transflector is an optical element that when illuminated with light from one direction will reflect a significant proportion of the incident light, and that when illuminated with light from another direction will transmit a significant proportion of the incident light. (The terms “transmit” and “reflect” relate to the intended wavelength range of light with which the device will be used.) The display device of
FIG. 2
is thus known as a transflective display device, since it contains a transflector.
FIG. 2
shows the operation of the transflective display device. When ambient light is incident on the optical modulating element
4
, it passes through the optical modulating element and is reflected by the transflector a back to the viewer
7
(as is the case in
FIG. 1
, the effects of refraction have been ignored in FIG.
2
). Thus, operation in ambient light is the same as for a reflective display device, and the back-light
9
does not need to be illuminated.
In conditions of low ambient light the back-light
9
is illuminated, and light from the back-light
9
passes through the transflector
8
, through the optical modulating element
4
, and reaches the viewer
7
. In this mode of operation the transflector simply serves to transmit light, and it is preferable that the transflector has as great a transmissivity as possible to produce a bright image. In contrast, when the display device is illuminated by the ambient light source
5
the tranoflector
8
acts as a reflector, and it is desirable that the transflector reflects as much as possible of the light from the ambient light source
5
back to the viewer
7
. Thus, in order to obtain a bright image in all lighting conditions, the transfl
Renner Otto Boisselle & Sklar
Sharp Kabushiki Kaisha
Sikder Mohammad
LandOfFree
Transflector, and a transflective display device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Transflector, and a transflective display device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transflector, and a transflective display device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2881000