Abstract:
According to an embodiment of the invention, an optical element is provided. The optical element includes: a substrate having a birefringence characteristic and having a first surface and a second surface; a first transflective optical film disposed on the first surface of the substrate; and a second transflective optical film disposed on the second surface of the substrate. According to an embodiment of the invention, a display system including the optical element is also provided.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of Taiwan Patent Application No. 101108242, filed on Mar. 12, 2012, the entirety of which is incorporated by reference herein. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The invention relates to an optical element and a display system, and in particular relates to a display system including a touch panel and a display panel. 
         [0004]    2. Description of the Related Art 
         [0005]    The projected capacitive technology has been widely applied in the touch panel technology. The projected capacitive touch panel may include a glass-type touch panel or a film-type touch panel. 
         [0006]    Typically, a touch panel operates with a display panel. A commonly used display panel may be a liquid crystal display panel. Making the touch panel and the display panel fit the desire of the users, have become an important issue. 
         [0007]      FIG. 1  is a perspective view showing a conventional display system. As shown in  FIG. 1 , a display system  100  includes a display panel  102 , a touch panel  104 , and a backlight source  106 . In  FIG. 1 , the touch panel  104  is, for example, a film-type touch panel which includes, for example, a polyethylene terephthalate (PET) substrate having a birefringence characteristic. The display panel  102  is, for example, a liquid crystal display panel which may includes a polarization layer  102 P 1 , a polarization layer  102 P 2 , and a liquid crystal unit  102 C sandwiched therebetween. The inventor of this application found that if the film-type touch panel  104  operates together with the display panel  102 , light coming from the light exit surface is not a linearly polarized light but an elliptically polarized light. In this case, if a user who wears polarized sunglasses watches the display system  100 , a mura phenomenon is observed, which negatively affects the display quality. 
         [0008]    In the following, the mechanism which may result in the mura phenomenon is illustrated in accompany with  FIG. 1 . As shown in  FIG. 1 , the non-polarized light L emitted from the backlight source  106  becomes a linearly polarized light after penetrating the polarization layer  102 P  1  of the display panel  102 . When the liquid crystal panel is in the bright state, the linearly polarized light which rotates by an angle after penetrating the liquid crystal unit  102 C may penetrate through the polarization layer  102 P 2  and continue to enter the touch panel  104 . However, in  FIG. 1 , the touch panel  104  is a film-type touch panel which includes, for example, a PET substrate having a birefringence characteristic. When the linearly polarized light passes the PET substrate having a birefringence characteristic, two components of the linearly polarized light encounter different retardations such that the linearly polarized light becomes an elliptically polarized light. Because light having different wavelengths (i.e., light with different colors) encounter different elliptical polarization degrees, the amount of light with different colors penetrating through the polarized sunglasses are also different if an observer who wears the polarized sunglasses observes the display system  100 . 
         [0009]    As shown in  FIG. 1 , the elliptically polarized light with different colors encounter different elliptical polarization degrees after passing through the touch panel  104 . Thus, after the elliptically polarized light with different colors penetrate through a polarization layer  108  (simulating the polarized sunglasses), they are transformed into linearly polarized light having different intensities, thus resulting in the mura phenomenon. 
         [0010]    Besides the situations mentioned above, if an anti-reflection film or an anti-scattering film is disposed in the display system, the mura phenomenon may also occur similarly. 
       SUMMARY 
       [0011]    According to an embodiment of the invention, an optical element is provided. The optical element includes: a substrate having a birefringence characteristic and having a first surface and a second surface; a first transflective optical film disposed on the first surface of the substrate; and a second transflective optical film disposed on the second surface of the substrate. 
         [0012]    According to an embodiment of the invention, a display system is provided. The display system includes: a display panel; and a touch panel disposed on the display panel, wherein the touch panel includes: a substrate having a birefringence characteristic and having a first surface and a second surface; a first transflective optical film disposed on the first surface of the substrate; and a second transflective optical film disposed on the second surface of the substrate. 
         [0013]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0015]      FIG. 1  is a perspective view showing a conventional display system; 
           [0016]      FIG. 2  is a cross-sectional view showing an optical element according to an embodiment of the present invention; 
           [0017]      FIGS. 3A-3B  are cross-sectional views respectively showing optical elements according to embodiments of the present invention; and 
           [0018]      FIGS. 4A-4C  are three-dimensional views respectively showing display systems according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0020]    The manufacturing method and method for use of the embodiment of the invention are illustrated in detail as follows. It is understood, that the following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numbers and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Furthermore, descriptions of a first layer “on,” “overlying,” (and like descriptions) a second layer, include embodiments where the first and second layers are in direct contact and those where one or more layers are interposing the first and second layers. 
         [0021]    In order to reduce and/or resolve the mura problem mentioned above, the inventor of the application provides an optical element.  FIG. 2  is a cross-sectional view showing an optical element  200  according to an embodiment of the present invention. The optical element  200  may be used to transform an elliptically polarized light into a non-polarized light or a substantially not polarized light. 
         [0022]    As shown in  FIG. 2 , the optical element  200  includes a substrate  202  and an optical film  204 T 1  and an optical film  204 T 2  disposed on two sides of the substrate  202 . In one embodiment, the substrate  202  is a substrate having a birefringence characteristic, which is, for example, a polymer substrate. In one embodiment, the substrate  202  is a PET (polyethylene terephthalate) substrate, a PEN (polyethylene naphthalate) substrate, a PI (polyimide) substrate, or combinations thereof. In one embodiment, the optical films  204 T 1  and  204 T 2  directly contact with the two sides of the substrate  202 , respectively. The optical films  204 T 1  and  204 T 2  may be transflective layers which allow a portion of light to penetrate therethrough and let another portion of light be reflected. 
         [0023]    As shown in  FIG. 2 , when the linearly polarized light L enters the optical element  200 , the linearly polarized light L may penetrate through the optical film  204 T 1  to enter the substrate  202 . In one embodiment, because the substrate  202  has a birefringence characteristic, the linearly polarized light L is transformed into an elliptically polarized light. Because there are optical films  204 T 1  and  204 T 2  disposed on two sides of the substrate  202 , portions of the elliptically polarized light undergo a plurality of reflections or transmissions between the two optical films  204 T 1  and  204 T 2 . The phases of these portions of the elliptically polarized light change during each of the reflections. Thus, the elliptically polarized light finally transmitted from the optical element  200  has a variety of different phases. For example, although light L 1  and lights L 2 , L 3 , or L 4  may still be elliptically polarized light, the phases thereof are different from each other. These elliptically polarized light having different phases together form a non-polarized light (or substantially not polarized light) L′. 
         [0024]    In one embodiment, the optical element  200  illustrated in the embodiment shown in  FIG. 2  may be integrated with the display system illustrated in  FIG. 1 . The optical element  200  may be used to, for example, turn the elliptically polarized light into the non-polarized light. After the non-polarized light passes through a polarization layer or a polarized sunglasses, the non-polarized light becomes a linearly polarized light having a variety of colored lights with substantially the same intensity. There is substantially no problem due to the mura phenomenon. 
         [0025]      FIGS. 3A-3B  are cross-sectional views respectively showing optical elements according to embodiments of the present invention. As shown in  FIG. 3A , in one embodiment, the optical element may include a substrate  300  and transflective optical films  302   a  and  302   b  disposed on two sides of the substrate  300 . The substrate  300  may be a substrate having a birefringence characteristic. The transflective optical films  302   a  and  302   b  may be transflective layers such as aluminum films, silver films, copper film, gold films, platinum film, chromium films, nickel films, or combination thereof. In one embodiment, the material of the transflective optical films  302   a  and the material of the transflective optical films  302   b  are the same. In another embodiment, the material of the transflective optical films  302   a  is different from the material of transflective optical films  302   b . In one embodiment, the visible transmittance of the transflective optical film  302   a  or  302   b  is larger than the visible reflectance of the transflective optical film  302   a  or  302   b . For example, the visible transmittance of the transflective optical film  302   a  or  302   b  may be about 60%, and the reflectance thereof may be about 40%. In a preferable embodiment, the visible reflectance of the transflective optical film  302   a  or  302   b  is larger than the visible transmittance of the transflective optical film  302   a  or  302   b . For example, the visible transmittance of the transflective optical film  302   a  or  302   b  may be about 30%, and the reflectance thereof may be about 70%. It should be appreciated that the visible reflectance of the transflective optical film  302   a  or  302   b  ranging from 40%-70% is sufficient for reducing the problem due to the mura phenomenon. In one embodiment, the substrate  300  may be (but is not limited to) a PET substrate with a thickness of about 180 μm, and both the transflective optical films  302   a  and  302   b  are (but is not limited to) aluminum films with a thickness of about 3 nm. 
         [0026]    In another embodiment, the transflective optical film may be a stacked structure of a plurality of material layers. As shown in  FIG. 3B , transflective optical films disposed on the two sides of the substrate  300  may be stacked layers of transflective optical films  302   a   1 ,  302   a   2 ,  302   a   3 , and  302   a   4  and stacked layers of transflective optical films  302   b   1 ,  302   b   2 ,  302   b   3 , and  302   b   4 , respectively. In one embodiment, these stacked layers of the transflective optical films are stacked layers having transflective optical films with higher refractive indices and transflective optical films with smaller refractive indices disposed alternately. For example, the refractive index of the transflective optical film  302   a   1  may be larger than the refractive index of the transflective optical film  302   a   2 . The refractive index of the transflective optical film  302   a   2  may be smaller than the refractive index of the transflective optical film  302   a   3 . In one embodiment, the substrate  300  may be (but is not limited to) a PET substrate with a thickness of about 180 μm, and both the transflective optical films disposed on the two sides of the substrate  300  may be stacked layers of a Nb 2 O 5  film with a thickness of about 91 nm, a SiO 2  film with a thickness of about 78 nm, and a Nb 2 O 5  film with a thickness of about 45 nm. In one embodiment, a suitable transflective optical film with a higher refractive index may include a TiO 2  film, a Nb 2 O 5  film, a Ta 2 O 5  film, a SnO 2  film, or combinations thereof, and a suitable transflective optical film with a smaller refractive index may include a SiO 2  film, a MgF 2  film, a Na 3 AlF 6  film, or combinations thereof. 
         [0027]      FIGS. 4A-4C  are three-dimensional views respectively showing display systems according to embodiments of the present invention, which illustrate that an optical element is introduced into a display system composed of a liquid crystal display panel and a touch panel for reducing and/or preventing the problem due to the mora phenomenon. 
         [0028]    As shown in  FIG. 4A , the display system includes a backlight source  406 , a display panel  402 , a touch panel  404 , and an adhesion layer or air gap  403  therebetween. In one embodiment, the display panel  402  may include a stacked structure of a polarization layer  402 P 1 , a glass substrate  402 G 1 , a thin film transistor array  402 T, an ITO layer  402 I 1 , an alignment layer  402 A 1 , a liquid crystal unit  402 C, an alignment layer  402 A 2 , an ITO layer  402 I 2 , a color filter layer array  402   f , a glass substrate  402 G 2 , and a polarization layer  402 P 2 . In one embodiment, the touch panel  404  may include an electrode layer  404 X, a transflective optical film  404 T 1 , a plastic substrate  404 P 1  (which may have a birefringence characteristic), a transflective optical film  404 T 2 , an adhesion layer  404 A, an electrode layer  404 Y, and a plastic substrate  404 P 2 , wherein an optical element composed of the transflective optical film  404 T 1 , the plastic substrate  404 P 1  (which may have a birefringence characteristic), and the transflective optical film  404 T 2  may transform an elliptically polarized light into a non-polarized light. 
         [0029]    As shown in  FIG. 4A , after the non-polarized light coming from the backlight source  406  passes the display panel  402  to be transformed into a linearly polarized light and then passes through the optical element composed of the transflective optical film  404 T 1 , the plastic substrate  404 P 1 , and the transflective optical film  404 T 2 , it is transformed into a non-polarized light. Thus, even if the non-polarized light passes through the plastic substrate  404 P 2 , it is still a non-polarized light. Even if a user wearing polarized sunglasses or an anti-reflection layer or anti-spreading film is additionally disposed on the display system, the problem due to the mora phenomenon is substantially not encountered. 
         [0030]    In another embodiment, as shown in  FIG. 4B , the display system includes a backlight source  406 , a display panel  402 , a touch panel  404 , and an adhesion layer or air gap  403  therebetween. The display panel  402  may be substantially the same with the display panel  402  shown in  FIG. 4A . The touch panel  404  may include a stacked structure of an electrode layer  404 X, a plastic substrate  404 P 1 , an adhesion layer  404 A, an electrode layer  404 Y, a transflective optical film  404 T 1 , a plastic substrate  404 P 2 , and a transflective optical film  404 T 2 . 
         [0031]    In this case, a non-polarized light coming from the backlight source  406  is transformed into a linearly polarized light after passing through the display panel  402 , which is then transformed into an elliptically polarized light after passing through the plastic substrate  404 P  1  having a birefringence characteristic. Even so, the elliptically polarized light may be transformed into a non-polarized light after passing through the optical element composed of the transflective optical film  404 T 1 , the plastic substrate  404 P 2 , and the transflective optical film  404 T 2 . Thus, even if a user wearing polarized sunglasses or an anti-reflection layer or anti-spreading film is additionally disposed on the display system, the problem due to the mura phenomenon is substantially not encountered. 
         [0032]    In yet another embodiment, as shown in  FIG. 4C , the display system includes a backlight source  406 , a display panel  402 , a touch panel  404 , and an adhesion layer or air gap  403  therebetween. The display panel  402  may be substantially the same with the display panel  402  shown in  FIG. 4A . The touch panel  404  may include a stacked structure of a transflective optical film  404 T 1 , a plastic substrate  404 P, a transflective optical film  404 T 2 , an adhesion layer  404 A, an electrode layer  404 X, an insulating layer  404 I, an electrode layer  404 Y, and a glass substrate  404 G. 
         [0033]    In this case, the linearly polarized light penetrating the display panel  402  may be transformed into a non-polarized light after passing through the optical element composed of the transflective optical film  404 T 1 , the plastic substrate  404 P (which is, for example, an anti-spreading film), and the transflective optical film  404 T 2 . Thus, even if a user wearing polarized sunglasses or an anti-reflection layer is additionally disposed on the display system, the problem due to the mura phenomenon is substantially not encountered. 
         [0034]    While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.