Reflectance-adjustable reflector and reflectance-adjustable display device

A reflectance-adjustable reflector including a phase modulation element and a first polarizer is provided. The phase modulation element includes a first substrate, a second substrate opposite to the first substrate, a phase modulation layer located between the first substrate and the second substrate, a first electrode layer located between the first substrate and the phase modulation layer, and a second electrode layer located between the second substrate and the phase modulation layer. Thicknesses of the first substrate and the second substrate are between 0.01 mm and 0.5 mm. The first polarizer is disposed on the first substrate. The first substrate is located between the first polarizer and the first electrode layer. A total thickness of the phase modulation element and the first polarizer is less than 1 mm. A reflectance-adjustable display device is also provided.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a reflector and a display device and more particularly relates to a reflectance-adjustable reflector and a reflectance-adjustable display device.

Description of Related Art

In the conventional art, reflectance of a reflector or a display device is a fixed value. Namely, the reflectance of the reflector or the display device does not change with the intensity of light incident on the reflector or the display device. Since the reflectance of the reflector is generally quite high, the user often suffers the impact of glare when the reflector or the display device using the same is subject to strong light. For example, when driving at night, the rearview mirror is often subject to strong light emitted from the vehicle in the back, such that the driver suffers from the impact of glare, which often poses a threat to road safety. Therefore, how to produce a reflector or a display device that has adjustable reflectance to adapt to the environment is a target to be achieved by researchers of ordinary skill in the art.

SUMMARY OF THE INVENTION

The invention provides a reflectance-adjustable reflector and a reflectance-adjustable display device that have adjustable reflectance.

Other objects and advantages of the invention can be further illustrated by the technical features broadly embodied and described as follows.

In order to achieve one or a portion of or all of the objects or other objects, an embodiment of the invention provides a reflectance-adjustable reflector that includes a phase modulation element and a first polarizer. The phase modulation element includes a first substrate, a second substrate, a phase modulation layer, a first electrode layer, and a second electrode layer. The second substrate is opposite to the first substrate, wherein thicknesses of the first substrate and the second substrate are between 0.01 mm and 0.5 mm. The phase modulation layer is located between the first substrate and the second substrate. The first electrode layer is located between the first substrate and the phase modulation layer. The second electrode layer is located between the second substrate and the phase modulation layer. The first polarizer is disposed on the first substrate, wherein the first substrate is located between the first polarizer and the first electrode layer, and a total thickness of the phase modulation element and the first polarizer is less than 1 mm.

In order to achieve one or a portion of or all of the objects or other objects, an embodiment of the invention provides a reflectance-adjustable display device that includes a display device and a reflectance-adjustable reflector. The display device has a display surface. The reflectance-adjustable reflector is located on the display surface and includes a phase modulation element and a first polarizer. The phase modulation element includes a first substrate, a second substrate, a phase modulation layer, a first electrode layer, and a second electrode layer. The second substrate is located between the display device and the first substrate, wherein thicknesses of the first substrate and the second substrate are between 0.01 mm and 0.5 mm. The phase modulation layer is located between the first substrate and the second substrate. The first electrode layer is located between the first substrate and the phase modulation layer. The second electrode layer is located between the second substrate and the phase modulation layer. The first polarizer is disposed on the first substrate, wherein the first substrate is located between the first polarizer and the first electrode layer, and a total thickness of the phase modulation element and the first polarizer is less than 1 mm.

Based on the above, the embodiments of the invention have at least one of the following advantages or effects. In the reflectance-adjustable reflector according to the embodiments of the invention, the phase retardation provided by the phase modulation layer may be controlled by modulating the electric potential difference between the first electrode layer and the second electrode layer. Thus, with the collaboration of the first polarizer, the amount of light reflected by the reflectance-adjustable reflector may be adjusted. Accordingly, the reflectance-adjustable reflector of the invention and the reflectance-adjustable display device using the same may render ideal reflectance to adapt to the environment. Moreover, since the thicknesses of the first substrate and the second substrate are between 0.01 mm and 0.5 mm, and the total thickness of the phase modulation element and the first polarizer is less than 1 mm, ghost image phenomenon can be avoided, and thereby improving the quality of a displayed image of the reflectance-adjustable reflector and the reflectance-adjustable display device.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1AandFIG. 1Bare schematic diagrams illustrating a reflectance-adjustable reflector according to a first embodiment of the invention in a high reflectance mode and a low reflectance mode respectively.FIG. 2Apresents a displayed image of the reflectance-adjustable reflector inFIG. 1Aunder the condition that thicknesses of the first substrate and the second substrate are greater than 0.5 mm.FIG. 2Bpresents a displayed image of the reflectance-adjustable reflector inFIG. 1Aunder the condition that thicknesses of the first substrate and the second substrate are less than 0.5 mm.

Referring toFIG. 1AandFIG. 1B, a reflectance-adjustable reflector100includes a phase modulation element110and a first polarizer120. The phase modulation element110includes a first substrate SUB1, a second substrate SUB2, a phase modulation layer PM, a first electrode layer E1, and a second electrode layer E2. The second substrate SUB2is opposite to the first substrate SUB1, wherein thicknesses (HSUB1and HSUB2) of the first substrate SUB1and the second substrate SUB2are between 0.01 mm and 0.5 mm. The phase modulation layer PM is located between the first substrate SUB1and the second substrate SUB2. The first electrode layer E1is located between the first substrate SUB1and the phase modulation layer PM. The second electrode layer E2is located between the second substrate SUB2and the phase modulation layer PM. The first polarizer120is disposed on the first substrate SUB1, wherein the first substrate SUB1is located between the first polarizer120and the first electrode layer E1, and a total thickness of the phase modulation element110and the first polarizer120, i.e. the sum of the thickness H110of the phase modulation element110and the thickness H120of the first polarizer120, is less than 1 mm.

In the embodiment, the reflectance-adjustable reflector100further includes a second polarizer130disposed under the second substrate SUB2, wherein the second substrate SUB2is located between the second polarizer130and the second electrode layer E2.

In detail, the first electrode layer E1may be disposed on the first substrate SUB1, and the second electrode layer E2may be disposed on the second substrate SUB2. The first substrate SUB1and the second substrate SUB2are then sealed under the condition that the first electrode layer E1and the second electrode layer E2are located between the first substrate SUB1and the second substrate SUB2. After the first substrate SUB1and the second substrate SUB2are sealed, a space is kept between the first electrode layer E1and the second electrode layer E2to fill in the phase modulation layer PM. In the embodiment, the reflectance-adjustable reflector100may further includes a first alignment layer and a second alignment layer (not shown), wherein the first alignment layer is located between the first electrode layer E1and the phase modulation layer PM, and the second alignment layer is located between the second electrode layer E2and the phase modulation layer PM. The first polarizer120may be adhered to an outer surface of the first substrate SUB1, and the second polarizer130may be adhered to an outer surface of the second substrate SUB2. However, the manufacturing methods and steps of the reflectance-adjustable reflector100are not limited to the above.

In the embodiment, the first polarizer120and the second polarizer130are reflection-type polarizing films, wherein reflection axes (A120and A130) of the first polarizer120and the second polarizer130are vertical to each other. In detail, the reflection axis A130of the second polarizer130is parallel to a first direction D1, and the reflection axis A120of the first polarizer120is parallel to a second direction D2that is vertical to the first direction D1. However, the invention is not limited to the above. Alternatively, extension directions of the reflection axis A120and the reflection axis A130may be switched. In another embodiment, the reflection axis A120may be parallel to the reflection axis A130. In yet another embodiment, the first polarizer120may be an absorption-type polarizing film and an absorption axis thereof is parallel or vertical to the reflection axis A130.

The first substrate SUB1and the second substrate SUB2may be transparent substrates to avoid blocking the transmission of light. For example, the first substrate SUB1and the second substrate SUB2are respectively a thin glass substrate or a polymer transparent substrate. Compared to the thin glass substrate, the polymer transparent substrate has a higher mechanical strength under the same thickness. Therefore, the first substrate SUB1and the second substrate SUB2preferably use the polymer transparent substrates, but the invention is not limited thereto.

The polymer transparent substrates may possess a low birefringence. For example, a material of the polymer transparent substrates may include polymethylmethacrylate (PMMA), cyclo olefin copolymer (COC), cyclo olefin polymer (COP), polycarbonate (PC), or triacetyl cellulose (TAC). Alternatively, the polymer transparent substrates may possess birefringence. Besides, the optical axes (slow axes) of the polymer transparent substrates may be parallel or vertical to the reflection axes of the reflection-type polarizing films so as to avoid the generation of Mura phenomenon and to reduce reflectance or transmittance. For example, a material of the polymer transparent substrates may include polyethylene terephthalate (PET) or polycarbonate (PC), but the invention is not limited thereto.

The phase modulation layer PM is adapted to provide a phase difference based on an electric potential difference between the first electrode layer E1and the second electrode layer E2. For example, the phase modulation layer PM is a liquid crystal layer, the first alignment layer and the second alignment layer (not shown) are respectively located at opposite sides of the phase modulation layer PM to align the direction of liquid crystal molecules of the liquid crystal layer, and the first electrode layer E1and the second electrode layer E2are transparent electrode layers, but the invention is not limited to the above.

A polarization state of the light entering the phase modulation element110may be changed depending on the phase difference provided by the phase modulation layer PM. Thereby, with the collaboration of the first polarizer120and the second polarizer130, reflectance of the reflectance-adjustable reflector100may be controlled by modulating the electric potential difference between the first electrode E1and the second electrode E2. For example, the reflectance of the reflectance-adjustable reflector100may be switched between a high reflectance mode and a low reflectance mode.

In detail, in the high reflectance mode, as shown inFIG. 1A, light B incident on the reflectance-adjustable reflector100may be a non-polarized light. Namely, the light B includes P polarized light (marked as a double arrow) and S polarized light (marked as a circle with an X in the middle). Since a polarization direction of the P polarized light is parallel to the reflection axis A120of the first polarizer120, and a polarization direction of the S polarized light is vertical to the reflection axis A120of the first polarizer120, the P polarized light is reflected by the first polarizer120(the light reflected by the first polarizer120is marked as B1) while the S polarized light passes the first polarizer120(the light passes the first polarizer120is marked as B2). Under the condition that the reflection axis A120of the first polarizer120is vertical to the reflection axis A130of the second polarizer130, no phase difference is provided by the phase modulation layer PM in the high reflectance mode, thus the S polarized light passes the phase modulation layer PM without change in polarization direction. Since the polarization direction of the S polarized light is parallel to the reflection axis A130of the second polarizer130, the S polarized light is then reflected by the second polarizer130and transmitted back to the phase modulation element110. The S polarized light passes the phase modulation layer PM again without change in polarization direction and then passes the first polarizer120. In the high reflectance mode, the sum of the light reflected by the reflectance-adjustable reflector100(including the light B1reflected by the first polarizer120and the light B2reflected by the second polarizer130and output from the reflectance-adjustable reflector100) is about 95% of the light B incident on the reflectance-adjustable reflector100, wherein 5% loss is mainly because the reflectance of the second polarizer130does not reach 100% in general.

On the other hand, as shown inFIG. 1B, under the condition that the reflection axis A120of the first polarizer120is vertical to the reflection axis A130of the second polarizer130, a half wavelength phase difference is provided by the phase modulation layer PM in the low reflectance mode, thus the S polarized light passing the first polarizer120is turned into the P polarized light after passing the phase modulation layer PM. Since the polarization direction of the P polarized light is vertical to the reflection axis A130of the second polarizer130, the P polarized light then passes the second polarizer130. In the low reflectance mode, the sum of the light beam reflected by the reflectance-adjustable reflector100(i.e. the light B1reflected by the first polarizer120) is about 50% of the light B incident on the reflectance-adjustable reflector100.

Based on the above, the reflectance of the reflectance-adjustable reflector100of the embodiment may be switched between the high reflectance mode (95% reflectance) and the low reflectance mode (50% reflectance). Since liquid crystal molecules of the liquid crystal layer (the phase modulation layer PM) have fast response time, the reflectance-adjustable reflector100may quickly render ideal reflectance to adapt to the environment. Take the reflectance-adjustable reflector100being applied as a rearview mirror as an example, the reflectance-adjustable reflector100may be quickly switched to the high reflectance mode when driving at daytime or to serve as a makeup mirror. On the other hand, the reflectance-adjustable reflector100may be quickly switched to the low reflectance mode when driving at night, to prevent the driver from suffering the impact of glare owning to the reflectance-adjustable reflector100being subject to the strong light from the vehicle in the back.

It is noted that the high reflectance mode and the low reflectance mode can be switched manually or automatically. For example, a switching button may be made to allow the user to switch between the high reflectance mode and the low reflectance mode manually. Alternatively, a light sensor electrically connected to a controller (not shown) of the reflectance-adjustable reflector100may be provided to sense the intensity of light incident on the reflectance-adjustable reflector100, such that the high reflectance mode and the low reflectance mode may be switched automatically.

Moreover, since the thicknesses (HSUB1and HSUB2) of the first substrate SUB1and the second substrate SUB2are between 0.01 mm and 0.5 mm, and a total thickness of the phase modulation element110and the first polarizer120is less than 1 mm, a lateral distance between the light B1reflected by the first polarizer120and the light B2reflected by the second polarizer130and output from the reflectance-adjustable reflector100inFIG. 1Ais reduced. Therefore, ghost image phenomenon can be avoided, and thereby improving the quality of the displayed image. Specifically, when the light B obliquely incident on the reflectance-adjustable reflector100, the lateral distance between the light B1reflected by the first polarizer120and the light B2reflected by the second polarizer130and output from the reflectance-adjustable reflector100is proportional to a longitudinal distance between reflection surfaces of the light B1and the light B2. The longitudinal distance between reflection surfaces of the light B1and the light B2refers to the longitudinal distance between the top surface of the first polarizer120and the top surface of the second polarizer130, which is also the total thickness of the phase modulation element110and the first polarizer120.

InFIG. 2AandFIG. 2B, the reflectance-adjustable reflector100is placed next to an object (a grid pattern P on the top ofFIG. 2AandFIG. 2B) to observe whether a ghost image exists in the displayed image RI (i.e. the image reflected by the reflectance-adjustable reflector100) or not. In the reflectance-adjustable reflector100ofFIG. 2A, the thicknesses (HSUB1and HSUB2) of the first substrate SUB1and the second substrate SUB2are greater than 0.5 mm, thus a total thickness of the phase modulation element110and the first polarizer120is greater than 1 mm. In the reflectance-adjustable reflector100ofFIG. 2B, the thicknesses (HSUB1and HSUB2) of the first substrate SUB1and the second substrate SUB2are less than 0.5 mm, and a total thickness of the phase modulation element110and the first polarizer120is less than 1 mm. Theoretically, the pattern of the displayed image RI and the grid pattern P shall be the same; however, it is very clear that there are a plurality of pale thin lines (the ghost image GI) respectively located next to the thick solid line (the reflection of the grid pattern P) in the displayed image RI of the reflectance-adjustable reflector100inFIG. 2A. This is because the thicker the substrates (the first substrate SUB1and the second substrate SUB2), the bigger the lateral distance between the light B1reflected by the first polarizer120and the light B2reflected by the second polarizer130and output from the reflectance-adjustable reflector100, thereby results in the ghost image GI visible to human eyes. On the contrary, by controlling the thickness HSUB1of the first substrate SUB1, the thickness HSUB2of the second substrate SUB2, and the total thickness of the phase modulation element110and the first polarizer120, the ghost image phenomenon can be avoided in the displayed image RI of the reflectance-adjustable reflector100inFIG. 2B.

Hereinafter, other embodiments of the reflectance-adjustable reflector are described with reference toFIG. 3AtoFIG. 7B, wherein the same components are labeled with the same reference numerals. Thus, description of the materials, relative configuration, and effects thereof are not repeated hereinafter.

FIG. 3AandFIG. 3Bare schematic diagrams illustrating a reflectance-adjustable reflector according to a second embodiment of the invention in a high reflectance mode and a low reflectance mode respectively.FIG. 4is a schematic diagram illustrating a reflectance-adjustable reflector according to a third embodiment of the invention.FIG. 5is a schematic diagram illustrating a reflectance-adjustable reflector according to a fourth embodiment of the invention.FIG. 6AandFIG. 6Bare schematic diagrams illustrating a reflectance-adjustable reflector according to a fifth embodiment of the invention in a high reflectance mode and a low reflectance mode respectively.FIG. 7AandFIG. 7Bare schematic diagrams illustrating a reflectance-adjustable reflector according to a sixth embodiment of the invention in a high reflectance mode and a low reflectance mode respectively.

Referring toFIG. 3AandFIG. 3B, the main difference between the reflectance-adjustable reflector200and the reflectance-adjustable reflector100inFIG. 1AandFIG. 1Bis as follow. In the reflectance-adjustable reflector200, the reflection axis A120of the first polarizer120is parallel to the reflection axis A130of the second polarizer130, wherein extension directions of the reflection axis A120and the reflection axis A130are both parallel to the first direction D1, but the invention is not limited thereto. Alternatively, extension directions of the reflection axis A120and the reflection axis A130may both parallel to the second direction D2.

In the high reflectance mode, as shown inFIG. 3A, since the polarization direction of the S polarized light (marked as a circle with an X in the middle) is parallel to the reflection axis A120of the first polarizer120, and the polarization direction of the P polarized light (marked as a double arrow) is vertical to the reflection axis A120of the first polarizer120, the S polarized light is reflected by the first polarizer120(the light reflected by the first polarizer120is marked as B1) while the P polarized light passes the first polarizer120(the light passes the first polarizer120is marked as B2). Under the condition that the reflection axis A120of the first polarizer120is parallel to the reflection axis A130of the second polarizer130, a half wavelength phase difference is provided by the phase modulation layer PM in the high reflectance mode, thus the P polarized light passing the first polarizer120is turned into the S polarized light after passing the phase modulation layer PM. Since the polarization direction of the S polarized light is parallel to the reflection axis A130of the second polarizer130, the S polarized light is then reflected by the second polarizer130and transmitted back to the phase modulation element110. The S polarized light reflected by the second polarizer130is turned into the P polarized light after passing the phase modulation layer PM, and the P polarized light then passes the first polarizer120. In the high reflectance mode, the sum of the light reflected by the reflectance-adjustable reflector200(including the light B1reflected by the first polarizer120and the light B2reflected by the second polarizer130and output from the reflectance-adjustable reflector200) is about 95% of the light B incident on the reflectance-adjustable reflector200.

On the other hand, as shown inFIG. 3B, under the condition that the reflection axis A120of the first polarizer120is parallel to the reflection axis A130of the second polarizer130, no phase difference is provided by the phase modulation layer PM in the low reflectance mode, thus the P polarized light passing the first polarizer120passes the phase modulation layer PM without change in polarization direction. Since the polarization direction of the P polarized light is vertical to the reflection axis A130of the second polarizer130, the P polarized light passing the phase modulation layer PM then passes the second polarizer130. In the low reflectance mode, the sum of the light reflected by the reflectance-adjustable reflector200(i.e. the light B1reflected by the first polarizer120) is about 50% of the light B incident on the reflectance-adjustable reflector200.

Referring toFIG. 4, the main difference between the reflectance-adjustable reflector300and the reflectance-adjustable reflector100inFIG. 1AandFIG. 1Bis as follow. In the reflectance-adjustable reflector300, the reflectance-adjustable reflector300further includes a first phase compensation layer140and a second phase compensation layer150. The first phase compensation layer140is located between the first polarizer120and the first substrate SUB1. The second phase compensation layer150is disposed under the second substrate SUB2, wherein the second substrate SUB2is located between the second phase compensation layer150and the second electrode layer E2, and the second phase compensation layer150is located between the second polarizer130and the second substrate SUB2. Since liquid crystal molecules of the liquid crystal layer (the phase modulation layer PM) are not isotropic, reflectance at different viewing angles vary in accordance with different orientations of liquid crystal molecules. Since the first phase compensation layer140and the second phase compensation layer150are adapted to compensate the reflectance difference between different viewing angles, consistency of the reflectance of the reflectance-adjustable reflector300at each of the viewing angles may be enhanced.

Besides, a total thickness of the phase modulation element110, the first polarizer120, the first phase compensation layer140, and the second phase compensation layer150(i.e. the sum of the thickness H110of the phase modulation element110, the thickness and H120of the first polarizer120, a thickness H140of the first phase compensation layer140, and a thickness H150of the second phase compensation layer150) is less than 1 mm, so as to reduce the lateral distance between the light reflected by the first polarizer120and the light reflected by the second polarizer130and output from the reflectance-adjustable reflector300. Therefore, ghost image phenomenon can be avoided, and thereby improving the quality of the displayed image.

In the embodiment, the reflection axes (not shown) of the first polarizer120and the second polarizer130may be vertical or parallel to each other. Alternatively, the first polarizer120may be an absorption-type polarizing film and an absorption axis thereof is parallel or vertical to the reflection axis A130.

Referring toFIG. 5, the main difference between the reflectance-adjustable reflector400and the reflectance-adjustable reflector100inFIG. 1AandFIG. 1Bis as follow. In the reflectance-adjustable reflector400, the reflectance-adjustable reflector400further includes a light absorbing layer160disposed on the first polarizer120, wherein the first polarizer120is located between the light absorbing layer160and the first substrate SUB1. Since the light absorbing layer160is adapted to absorb the light incident on the reflectance-adjustable reflector400, the reflectance of the reflectance-adjustable reflector400may be reduced, and thus the anti-glare effect may be enhanced. The light absorbing layer160may have 10% absorption rate, but the invention is not limited thereto. For example, a material of the light absorbing layer160includes dye, ink, etc. In another embodiment, the light absorbing layer160may be replaced by a light absorption-adjustable layer. The light absorption-adjustable layer may include a photochromic layer or an electrochromic layer, but the invention is not limited thereto.

In the embodiment, the reflection axes (not shown) of the first polarizer120and the second polarizer130may be vertical or parallel to each other. Alternatively, the first polarizer120may be an absorption-type polarizing film and an absorption axis thereof is parallel or vertical to the reflection axis A130.

Referring toFIG. 6AandFIG. 6B, the main differences between the reflectance-adjustable reflector500and the reflectance-adjustable reflector100inFIG. 1AandFIG. 1Bare as follow. In the reflectance-adjustable reflector500, the first polarizer120is a reflection-type polarizing film, and the reflectance-adjustable reflector500further includes an absorption-type polarizing film170located between the first polarizer120and the first substrate SUB1. The absorption-type polarizing film170has an absorption axis A170parallel to the reflection axis A120of the first polarizer120. Moreover, the reflectance-adjustable reflector500may further include a reflective layer180disposed under the second substrate SUB2, wherein the second substrate SUB2is located between the reflective layer180and the second electrode layer E2.

In the high reflectance mode, as shown inFIG. 6A, since the polarization direction of the P polarized light (marked as a double arrow) is parallel to the reflection axis A120of the first polarizer120, and the polarization direction of the S polarized light (marked as a circle with an X in the middle) is vertical to the reflection axis A120of the first polarizer120and the absorption axis A170of the absorption-type polarizing film170, the P polarized light is reflected by the first polarizer120(the light reflected by the first polarizer120is marked as B1) while the S polarized light sequentially passes the first polarizer120and the absorption-type polarizing film170(the light passes the first polarizer120and the absorption-type polarizing film170is marked as B2). Under the condition that the second polarizer130inFIG. 1AandFIG. 1Bis replaced by the reflective layer180, no phase difference is provided by the phase modulation layer PM in the high reflectance mode, thus the P polarized light passes the phase modulation layer PM without change in polarization direction. After reflected by the reflective layer180, the P polarized light then sequentially passes the phase modulation element110, the absorption-type polarizing film170, and the first polarizer120. In the high reflectance mode, the sum of the light reflected by the reflectance-adjustable reflector500(including the light B1reflected by the first polarizer120and the light B2reflected by the reflective layer180and output from the reflectance-adjustable reflector500) is about 95% of the light B incident on the reflectance-adjustable reflector500.

On the other hand, as shown inFIG. 6B, under the condition that the second polarizer130inFIG. 1AandFIG. 1Bis replaced by the reflective layer180, a quarter wavelength phase difference is provided by the phase modulation layer PM in the low reflectance mode, thus the S polarized light passing the absorption-type polarizing film170is turned into dextrorotation light after passing the phase modulation layer PM. After reflected by the reflective layer180, the dextrorotation light is turned into laevorotatory light, and the laevorotatory light is turned into the P polarized light after passing the phase modulation layer PM. Since the polarization direction of the P polarized light is parallel to the absorption axis A170of the absorption-type polarizing film170, the P polarized light is then absorbed by the absorption-type polarizing film170. In the low reflectance mode, the sum of the light reflected by the reflectance-adjustable reflector500(i.e. the light B1reflected by the first polarizer120) is about 50% of the light B incident on the reflectance-adjustable reflector500.

Besides, a total thickness of the phase modulation element110, the first polarizer120, and the absorption-type polarizing film170(i.e. the sum of the thickness H110of the phase modulation element110, the thickness and H120of the first polarizer120, and a thickness H170of the absorption-type polarizing film170) is less than 1 mm, so as to reduce the lateral distance between the light B1reflected by the first polarizer120and the light B2reflected by the reflective layer180and output from the reflectance-adjustable reflector500inFIG. 6A. Therefore, ghost image phenomenon can be avoided, and thereby improving the quality of the displayed image.

Referring toFIG. 7AandFIG. 7B, the main differences between the reflectance-adjustable reflector600and the reflectance-adjustable reflector500inFIG. 6AandFIG. 6Bare as follow. In the reflectance-adjustable reflector600, the second electrode layer E2is a reflective electrode layer which is adapted to reflect the light beam B2entering the phase modulation element110. Thus, the reflective layer180inFIG. 6AandFIG. 6Bis omitted. Namely, compared to the reflectance-adjustable reflector500inFIG. 6AandFIG. 6B, the cost of the reflectance-adjustable reflector600may be lower.

In the high reflectance mode, as shown inFIG. 7A, under the condition that the second electrode layer E2is a reflective electrode layer, no phase difference is provided by the phase modulation layer PM in the high reflectance mode, thus the S polarized light passing the absorption-type polarizing film170passes the phase modulation layer PM without change in polarization direction. After reflected by the second electrode layer E2, the S polarized light then passes the phase modulation layer PM again without change in polarization direction. Since the polarization direction of the S polarized light is vertical to the absorption axis A170of the absorption-type polarizing film170and the reflection axis A120of the first polarizer120, the S polarized light sequentially passes the absorption-type polarizing film170and the first polarizer120. In the high reflectance mode, the sum of the light reflected by the reflectance-adjustable reflector600(including the light B1reflected by the first polarizer120and the light B2reflected by the second electrode layer E2and output from the reflectance-adjustable reflector600) is about 95% of the light B incident on the reflectance-adjustable reflector600.

On the other hand, as shown inFIG. 7B, under the condition that the second electrode layer E2is a reflective electrode layer, a quarter wavelength phase difference is provided by the phase modulation layer PM in the low reflectance mode, thus the S polarized light passing the absorption-type polarizing film170is turned into dextrorotation light after passing the phase modulation layer PM. After reflected by the second electrode layer E2, the dextrorotation light is turned into laevorotatory light, and the laevorotatory light is turned into the P polarized light after passing the phase modulation layer PM. Since the polarization direction of the P polarized light is parallel to the absorption axis A170of the absorption-type polarizing film170, the P polarized light is then absorbed by the absorption-type polarizing film170. In the low reflectance mode, the sum of the light reflected by the reflectance-adjustable reflector600(i.e. the light B1reflected by the first polarizer120) is about 50% of the light B incident on the reflectance-adjustable reflector600.

Since the longitudinal distance between the reflection surfaces of the light B1and the light B2(i.e. the longitudinal distance between the top surface of the first polarizer120and the top surface of the second electrode layer E2) is reduced (compared to the reflectance-adjustable reflector500inFIG. 6AandFIG. 6B), the lateral distance between the light B1reflected by the first polarizer120and the light B2reflected by the second electrode layer E2and output from the reflectance-adjustable reflector600is reduced accordingly. Therefore, the ghost image phenomenon can be avoided, and thereby improving the quality of the displayed image.

FIG. 8AandFIG. 8Bare schematic diagrams illustrating a reflectance-adjustable display device according to a first embodiment of the invention in a high reflectance mode and a low reflectance mode respectively. Referring toFIG. 8AandFIG. 8B, a reflectance-adjustable display device10includes a display device12and a reflectance-adjustable reflector14.

The display device12is, for example, a liquid crystal display device and comprises a backlight module BL and a display panel DP located between the reflectance-adjustable reflector14and the backlight module BL. The display panel DP may include a top polarizer P1and a bottom polarizer P2. The top polarizer P1and the bottom polarizer P2may be absorption-type polarizing films, wherein absorption axes (AP1and AP2) of the top polarizer P1and the bottom polarizer P2may be vertical to each other. For example, the absorption axis AP1of the top polarizer P1is parallel to the first direction D1, and the absorption axis AP2of the bottom polarizer P2is parallel to the second direction D2. However, the invention is not limited thereto. Alternatively, extension directions of the absorption axis AP1and the absorption axis AP2may be switched. In another embodiment, the absorption axis AP1may be parallel to the absorption axis AP2, and extension directions of the absorption axis AP1and the absorption axis AP2may be parallel to the first direction D1or the second direction D2. The display device12has a display surface DS. The display surface DS of the display device12is, for example, a top surface of the top polarizer P1, but the invention is not limited thereto.

The reflectance-adjustable reflector14is located on the display surface DS. In the embodiment, the reflectance-adjustable reflector14adopts the configuration of the reflectance-adjustable reflector100inFIG. 1Aand FIB.1B, wherein the second substrate SUB2is located between the display device12and the first substrate SUB1. The same components are labeled with the same reference numerals. Thus, description of the materials, relative configuration, and effects thereof are not repeated hereinafter. In another embodiment, the reflectance-adjustable reflector14may adopt the configuration of the reflectance-adjustable reflector200inFIG. 3Aand FIB.3B, the reflectance-adjustable reflector300inFIG. 4, or the reflectance-adjustable reflector400inFIG. 5. The reflectance-adjustable reflector14in the embodiment ofFIG. 9AandFIG. 9Band the embodiment ofFIG. 10AandFIG. 10Bmay also adopt the configuration of the reflectance-adjustable reflector200inFIG. 3Aand FIB.3B, the reflectance-adjustable reflector300inFIG. 4, or the reflectance-adjustable reflector400inFIG. 5, thus the same description will not be repeated hereinafter.

In the embodiment, the reflection axis A130of the second polarizer130is parallel to the absorption axis AP1of the top polarizer P1, so that the light B′ from the display device12may pass the second polarizer130. In detail, a polarization direction of the light B′ from the top polarizer P1shall be vertical to absorption axis AP1, therefore, the light B′ is P polarized light. Since the P polarized light is vertical to the reflection axis A130of the second polarizer130, the light B′ passes the second polarizer130in both of the high reflectance mode and the low reflectance mode. However, the invention is not limited to the above. In another embodiment, the reflection axis A130of the second polarizer130may be vertical to the absorption axis AP1of the top polarizer P1, and the reflectance-adjustable display device10may further includes a half wave plate (not shown) located between the display device12and the reflectance-adjustable reflector14, so that the light B′ from the display device12may pass the second polarizer130.

In the high reflectance mode, as shown inFIG. 8A, under the condition that the reflection axis A120of the first polarizer120is vertical to the reflection axis A130of the second polarizer130, no phase difference is provided by the phase modulation layer PM in the high reflectance mode, thus the light B′ (P polarized light) passes the phase modulation layer PM without change in polarization direction. Since the polarization direction of the light B′ (P polarized light) is parallel to the reflection axis A120of the first polarizer120, the light B′ is then reflected by the first polarizer120(the light reflected by the first polarizer120is not shown). Namely, the light B′ from the display device12will not be perceived by the user in the high reflectance mode.

On the other hand, as shown inFIG. 8B, under the condition that the reflection axis A120of the first polarizer120is vertical to the reflection axis A130of the second polarizer130, a half wavelength phase difference is provided by the phase modulation layer PM in the low reflectance mode, thus the light B′ (P polarized light) passing the second polarizer130is turned into the S polarized light after passing the phase modulation layer PM. Since the polarization direction of the S polarized light is vertical to the reflection axis A120of the first polarizer120, the light B′ passing the phase modulation layer PM passes the first polarizer120. Namely, the light B′ from the display device12will be perceived by the user in the low reflectance mode.

In the low reflectance mode, it is noted that the light B2passing the second polarizer130and transmitted to the display device12will be absorbed by the bottom polarizer P2or depolarized by the backlight module BL, thus the amount of the light B2output from the reflectance-adjustable display device10from the first polarizer120will be very small and can be neglected.

Hereinafter, other embodiments of the reflectance-adjustable display device are described with reference toFIG. 9AtoFIG. 11B, wherein the same components are labeled with the same reference numerals. Thus, description of the materials, relative configuration, and effects thereof are not repeated hereinafter.FIG. 9AandFIG. 9Bare schematic diagrams illustrating a reflectance-adjustable display device according to a second embodiment of the invention in a high reflectance mode and a low reflectance mode respectively.FIG. 10AandFIG. 10Bare schematic diagrams illustrating a reflectance-adjustable display device according to a third embodiment of the invention in a high reflectance mode and a low reflectance mode respectively.FIG. 11AandFIG. 11Bare schematic diagrams illustrating a reflectance-adjustable display device according to a fourth embodiment of the invention in a high reflectance mode and a low reflectance mode respectively.

Referring toFIG. 9AandFIG. 9B, the main difference between the reflectance-adjustable display device20and the reflectance-adjustable display device10inFIG. 8AandFIG. 8Bis as follow. The same components are labeled with the same reference numerals. Thus, description of the materials, relative configuration, and effects thereof are not repeated hereinafter. In the reflectance-adjustable display device20, the display device22is an organic light emitting display device that comprises a circular polarizer CP adjacent to the reflectance-adjustable reflector14. The circular polarizer CP may comprises a quarter-wave plate and a linear polarizer having an absorption axis ACP.

In the embodiment, the display device22may further include a top substrate SUBT, a bottom substrate SUBB, an anode electrode layer EA, a cathode electrode layer EC, a hole transporting layer HTL, an electron transporting layer ETL, and an organic light-emitting layer OL. The top substrate SUBT is located between the bottom substrate SUBB and the reflectance-adjustable reflector14. The organic light-emitting layer OL is located between the bottom substrate SUBB and the top substrate SUBT. The anode electrode layer EA is located between the organic light-emitting layer OL and the top substrate SUBT. The cathode electrode layer EC is located between the organic light-emitting layer OL and the bottom substrate SUBB. The hole transporting layer HTL is located between the organic light-emitting layer OL and the anode electrode layer EA. The electron transporting layer ETL is located between the organic light-emitting layer OL and the cathode electrode layer EC. The circular polarizer CP is located on the top substrate SUBT, wherein the top substrate SUBT is located between the circular polarizer CP and the anode electrode layer EA. The display surface DS of the display device22is, for example, a top surface of the circular polarizer CP, but the invention is not limited thereto.

In the embodiment, the reflection axis A130of the second polarizer130is parallel to the absorption axis ACP of the circular polarizer CP, so that the light B′ emitted from the display device22may pass the second polarizer130. In detail, a polarization direction of the light B′ output from the circular polarizer CP shall be vertical to the absorption axis ACP, therefore, the light B′ is a P polarized light. Since the P polarized light is vertical to the reflection axis A130of the second polarizer130, the light B′ passes through the second polarizer130in both of the high reflectance mode and the low reflectance mode. However, the invention is not limited to the above. In another embodiment, the reflection axis A130of the second polarizer130may be vertical to the absorption axis ACP of the circular polarizer CP, and the reflectance-adjustable display device20may further includes a half wave plate (not shown) located between the display device22and the reflectance-adjustable reflector14, so that the light B′ from the display device22may pass the second polarizer130.

In the high reflectance mode, as shown inFIG. 9A, under the condition that the reflection axis A120of the first polarizer120is vertical to the reflection axis A130of the second polarizer130, no phase difference is provided by the phase modulation layer PM in the high reflectance mode, thus the light B′ (P polarized light) passes the phase modulation layer PM without change in polarization direction. Since the polarization direction of the light B′ (P polarized light) is parallel to the reflection axis A120of the first polarizer120, the light B′ is then reflected by the first polarizer120(the light reflected by the second polarizer130is not shown). Namely, the light B′ from the display device22will not be perceived by the user in the high reflectance mode.

On the other hand, as shown inFIG. 9B, under the condition that the reflection axis A120of the first polarizer120is vertical to the reflection axis A130of the second polarizer130, a half wavelength phase difference is provided by the phase modulation layer PM in the low reflectance mode, thus the light B′ (P polarized light) passing the second polarizer130is turned into the S polarized light after passing the phase modulation layer PM. Since the polarization direction of the S polarized light is vertical to the reflection axis A120of the first polarizer120, the light B′ passing the phase modulation layer PM passes the first polarizer120. Namely, the light B′ emitted from the display device22will be perceived by the user in the low reflectance mode.

In the low reflectance mode, it is noted that the light B2passing the second polarizer130and transmitted to the display device22is turned into dextrorotation light after passing the circular polarizer CP. Under the condition that the cathode electrode layer EC is a reflective electrode layer, the dextrorotation light is turned into laevorotatory light after being reflected by the cathode electrode layer EC. The laevorotatory light is then absorbed by the circular polarizer CP.

Referring toFIG. 10AandFIG. 10B, the main difference between the reflectance-adjustable display device30and the reflectance-adjustable display device10inFIG. 8AandFIG. 8Bis as follow. In the reflectance-adjustable display device30, the display device32is an electrophoretic display device.

In the embodiment, the display device32may include a top substrate SUBT, a bottom substrate SUBB, a top electrode layer ET, a bottom electrode layer EB, and an electrophoretic layer EP. The top substrate SUBT is located between the bottom substrate SUBB and the reflectance-adjustable reflector14. The electrophoretic layer EP is located between the bottom substrate SUBB and the top substrate SUBT. The top electrode layer ET is located between the electrophoretic layer EP and the top substrate SUBT. The bottom electrode layer EB is located between the electrophoretic layer EP and the bottom substrate SUBB. The display surface DS of the display device32is, for example, a top surface of the top substrate SUBT, but the invention is not limited thereto.

The electrophoretic display device (the display device32) is a reflective display device. Namely, the ambient light serve as the illumination light of the electrophoretic display device. Since the light B2passing the phase modulation layer PM is reflected by the second polarizer130instead of transmitted to the display device32in the high reflectance mode, as shown inFIG. 10A, the user will not perceived the light B′ from the display device32in the high reflectance mode.

On the other hand, as shown inFIG. 10B, under the condition that the reflection axis A120of the first polarizer120is vertical to the reflection axis A130of the second polarizer130, a half wavelength phase difference is provided by the phase modulation layer PM in the low reflectance mode, thus the S polarized light passing the first polarizer120is turned into the P polarized light after passing the phase modulation layer PM. Since the polarization direction of the P polarized light is vertical to the reflection axis A130of the second polarizer130, the P polarized light then passes the second polarizer130and is transmitted to the display device32and serve as the illumination light of the display device32. The P polarized light transmitted to the display device32is then depolarized by the electrophoretic layer EP. Thus, the light B′ (the depolarized light B2with display information) from the display device32includes S polarized light and P polarized light. Since the polarization direction of the S polarized light is parallel to the reflection axis A130of the second polarizer130, and the polarization direction of the P polarized light is vertical to the reflection axis A130of the second polarizer130, the S polarized light is reflected by the second polarizer130(the light reflected by the second polarizer130is not shown) while the P polarized light passes the second polarizer130. The light B′ (the P polarized light) passing the second polarizer130is turned into the S polarized light after passing the phase modulation layer PM. Since the polarization direction of the S polarized light is vertical to the reflection axis A120of the first polarizer120, the light B′ passing the phase modulation layer PM passes the first polarizer120. Namely, the light B′ from the display device32will be perceived by the user in the low reflectance mode.

Referring toFIG. 11AandFIG. 11B, the main difference between the reflectance-adjustable display device40and the reflectance-adjustable display device20inFIG. 9AandFIG. 9Bis as follow. In the reflectance-adjustable display device40, the display device42adopts the configuration of the display device22inFIG. 9Aand FIB.9B but omits the circular polarizer CP inFIG. 9AandFIG. 9B. The reflectance-adjustable reflector44adopts the configuration of the reflectance-adjustable reflector110inFIG. 6Aand FIB.6B but omits the reflective layer180inFIG. 6AandFIG. 6B. However, the invention is not limited to the above. In another embodiment, the absorption-type polarizing film170may be omitted, and the first polarizer120may be a reflection-type polarizing film or an absorption-type polarizing film.

In the high reflectance mode, as shown inFIG. 11A, since the polarization direction of the P polarized light (marked as a double arrow) is parallel to the reflection axis A120of the first polarizer120, and the polarization direction of the S polarized light (marked as a circle with an X in the middle) is vertical to the reflection axis A120of the first polarizer120and the absorption axis A170of the absorption-type polarizing film170, the P polarized light is reflected by the first polarizer120(the light reflected by the first polarizer120is marked as B1) while the S polarized light sequentially passes the first polarizer120and the absorption-type polarizing film170(the light passes the first polarizer120and the absorption-type polarizing film170is marked as B2). No wavelength phase difference is provided by the phase modulation layer PM in the high reflectance mode, thus the S polarized light passing the absorption-type polarizing film170passes the phase modulation layer PM without change in polarization direction and is further transmitted to the display device42. Under the condition that the cathode electrode layer EC is a reflective electrode layer, the S polarized light is reflected by the cathode electrode layer EC and sequentially passes the phase modulation element110, the absorption-type polarizing film170, and the first polarizer120. The light B′ from the display device42includes the P polarized light and the S polarized light. Since the polarization direction of the P polarized light (marked as a double arrow) is parallel to the absorption axis A170of the absorption-type polarizing film170, and the polarization direction of the S polarized light (marked as a circle with an X in the middle) is vertical to the absorption axis A170of the absorption-type polarizing film170and the reflection axis A120of the first polarizer120, the P polarized light is absorbed by the absorption-type polarizing film170while the S polarized light sequentially passes the absorption-type polarizing film170and the first polarizer120. Namely, not only the light B1reflected by the first polarizer120and the light B2reflected by the cathode electrode layer EC and output from the reflectance-adjustable reflector44, but also the light B′ from the display device42can be perceived by the user in the high reflectance mode.

In the low reflectance mode, as shown inFIG. 11B, a quarter wavelength phase difference is provided by the phase modulation layer PM, thus the S polarized light passing the absorption-type polarizing film170is turned into dextrorotation light after passing the phase modulation layer PM. After reflected by the cathode electrode layer EC, the dextrorotation light is turned into laevorotatory light, and the laevorotatory light is turned into the P polarized light after passing the phase modulation layer PM. Since the polarization direction of the P polarized light is parallel to the absorption axis A170of the absorption-type polarizing film170, the P polarized light is then absorbed by the absorption-type polarizing film170. The light B′ from the display device42includes the P polarized light and the S polarized light. Since the polarization direction of the P polarized light (marked as a double arrow) is parallel to the absorption axis A170of the absorption-type polarizing film170, and the polarization direction of the S polarized light (marked as a circle with an X in the middle) is vertical to the absorption axis A170of the absorption-type polarizing film170and the reflection axis A120of the first polarizer120, the P polarized light is absorbed by the absorption-type polarizing film170while the S polarized light sequentially passes the absorption-type polarizing film170and the first polarizer120. Namely, not only the light B1reflected by the first polarizer120, but also the light B′ from the display device22can be perceived by the user in the low reflectance mode.

In conclusion of the above, the embodiments of the invention achieve at least one of the following advantages or effects. In the reflectance-adjustable reflector according to the embodiments of the invention, the phase retardation provided by the phase modulation layer may be modulated by modulating the electric potential difference between the first electrode layer and the second electrode layer. With the collaboration of the first polarizer, the amount of light reflected by the reflectance-adjustable reflector may be adjusted. Therefore, the reflectance-adjustable reflector of the invention and the reflectance-adjustable display device using the same may render ideal reflectance to adapt to the environment. Moreover, since the thicknesses of the first substrate and the second substrate are between 0.01 mm and 0.5 mm, and the total thickness of the phase modulation element and the first polarizer is less than 1 mm, ghost image phenomenon can be avoided, and thereby improving the quality of a displayed image of the reflectance-adjustable reflector and the reflectance-adjustable display device.