Abstract:
Backlighting methods and apparatuses to backlight a device. The backlighting apparatus includes a flexible light guide, a light source, and a housing. The light source is disposed adjacent to a transmission interface of the flexible light guide to illuminate the flexible light guide. The housing at least partially encloses the flexible light guide and the light source. A surface area of the flexible light guide is visible through the housing. By using a flexible light guide to backlight the device, the size of the device is reduced compared to conventional devices. Alternatively, the device may accommodate additional components. Other advantages also may be achieved.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Keypad backlighting is currently used in many electronic devices such as mobile phones and personal digital assistants. While current keypad backlighting technologies enhance the visible recognition of individual keys, the current keypad backlighting technologies negatively impact the size and functionality of the devices in which they are used. 
         [0002]      FIG. 1  depicts a cross-sectional view of a conventional backlighting system  10  using top-emitting light emitting diodes (LEDs)  12 . Specifically, the LEDs  12  are wide-angle, top-emitting, component LEDs  12 . The LEDs  12  illuminate a stiff light guide panel  14 . The LEDs  12  and light guide panel  14  are disposed within a housing having a top plate  16  and a bottom plate  18 . Typically, the light guide panel  14  is punched with holes so that keypad plungers  22  can extend through the light guide panel  14 . The keypad plungers  22  are coupled to a plunger layer  20  that is a low optical grade material. When a user pushes a button (not shown) on the keypad, the plunger layer  20  and keypad plunger  22  transfer the tactile contact to a switch  24  within the housing. One type of switch  24  is a metal dome of the type known in the art. Unfortunately, this conventional backlighting system  10  has a disadvantage of creating poor brightness uniformity due to noticeable hot spots from the LEDs  12 . Also, the thickness of the top-emitting LEDs ranges between 0.35 to 0.60 mm, thereby adding to the thickness of the backlighting system. 
         [0003]      FIG. 2  depicts a cross-sectional view of a conventional backlighting system  30  using side-emitting LEDs  32 . This backlighting system  30  includes many of the same components as the backlighting system shown in  FIG. 1  and described above. In particular, the backlighting system  30  includes a stiff light guide panel  14 , a housing having a top plate  16  and a bottom plate  18 , a plunger layer  20 , a keypad plunger  22 , and a switch  24 . The light guide panel  14  of this backlighting system  30  is illuminated by side-emitting LEDs  32 . Unfortunately, this conventional backlighting system  30  also has a disadvantage of hot spots from the holes  34  in the light guide panel  14  to accommodate the keypad plungers  22 . The holes  34  result in localized hot spots and deteriorate the brightness uniformity performance of the light guide panel. The holes  34  also reduce the tactility of the keypad buttons. 
         [0004]    A third type of conventional backlighting system (not shown) uses electroluminescent (EL) lighting. EL lighting systems emit light in response to an electrical current passed through an electroluminescent material. However, the rectifier circuitry in EL backlighting systems generates noise which negatively interferes with other electronic circuitry within the backlit device. 
         [0005]    In view of this, what is needed is a backlighting solution to overcome the problems of hotspots, thickness, and noise associated with conventional backlighting technologies. 
       SUMMARY OF THE INVENTION 
       [0006]    A backlighting apparatus is described. One embodiment of the backlighting apparatus includes a flexible light guide, a light source, and a housing. The light source is disposed adjacent to a transmission interface of the flexible light guide to illuminate the flexible light guide. The housing at least partially encloses the flexible light guide and the light source. A surface area of the flexible light guide is visible through the housing. By using a flexible light guide to backlight the device, the size of the device is reduced compared to conventional devices. Alternatively, the device may accommodate additional components. Other advantages also may be achieved. 
         [0007]    A method for backlighting is also described. One embodiment of the method includes providing a flexible light guide, providing a light source to illuminate the flexible light guide, and disposing the flexible light guide and the light source within a housing of a backlit device, wherein a surface area of the flexible light guide is visible through the housing. Some embodiments of the method also may include applying a micro-lens coating or a pattern-lens coating to the visible surface area of the flexible light guide, disposing a reflective layer on at least one edge of the flexible light guide, or disposing a diffusion material between the visible surface area of the flexible light guide and an opening in the housing. Some embodiments of the method also may include disposing a plunger on the flexible light guide approximately at the visible surface area to transfer pressure from a tactile contact to a switch disposed within the housing. 
         [0008]    Another embodiment of an apparatus to backlight a device is described. One embodiment of the apparatus includes means for illuminating a flexible light guide at a side transmission interface of the flexible light guide and means for providing illumination uniformity within the flexible light guide. 
         [0009]    Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrated by way of example of the principles of the invention. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  depicts a cross-sectional view of a conventional backlighting system using top-emitting light emitting diodes. 
           [0011]      FIG. 2  depicts a cross-sectional view of a conventional backlighting system using side-emitting light emitting diodes. 
           [0012]      FIG. 3  depicts an embodiment of a backlighting system using a flexible light guide. 
           [0013]      FIG. 4  depicts an embodiment of a micro-lens coating assembly. 
           [0014]      FIG. 5  depicts an embodiment of a pattern-lens coating. 
           [0015]      FIG. 6  depicts a cross-sectional view of an embodiment of a backlighting system using a flexible light guide. 
           [0016]      FIG. 7  depicts a cross-sectional view of another embodiment of a backlighting system using a flexible light guide. 
           [0017]      FIG. 8  is a process flow diagram of a backlighting method which may be used in conjunction with the flexible light guide of the backlighting system. 
       
    
    
       [0018]    Throughout the description, similar reference numbers may be used to identify similar elements. 
       DETAILED DESCRIPTION 
       [0019]      FIG. 3  depicts an embodiment of a backlighting system  100  using a flexible light guide  106 . The depicted backlighting system  100  is representative of many different types of electronic devices which use or might benefit from a backlit keypad, backlit buttons, or other backlit components. One exemplary electronic device is a mobile telephone having backlit buttons. Another exemplary electronic device is a personal digital assistant (PDA) having a backlit keypad. Other types of electronic devices also my employ the flexible light guide  106  described herein. 
         [0020]    The illustrated backlighting system  100  includes a light source  102  to illuminate the flexible light guide  106 . In one embodiment, the light source  102  includes multiple light emitting diodes (LEDs)  104 . The LEDs  104  may be surface mount technology (SMT) LEDs or another type of LED. Alternatively, the light source  102  may be another type of light source other than LEDs  104 . In the depicted embodiment, the LEDs  104  are disposed adjacent to a transmission interface  108  of the flexible light guide  106 . Light from the LEDs  104  propagates into the light guide  106  to illuminate one or more backlit components  110  such as a keypad or other buttons. In order to enhance the backlighting of the buttons  110 , a micro-lens coating or pattern-lens coating may be applied to the flexible light guide  106 . Additional details of micro-lens coatings and pattern-lens coatings are shown and described with reference to  FIGS. 4 and 5 . 
         [0021]    In one embodiment, the flexible light guide  106  is fabricated using an elastomer material such as an ultra-thin elastomer. For example, the flexible light guide  106  may be fabricated using polyurethane. However, other flexible materials may be used in conjunction with or instead of an elastomer material. Additionally, the flexible light guide  106  may be fabricated using a high optical grade material or, alternatively, a low optical grade material. A high optical grade material transmits the light with less loss than a low optical grade material. Also, the light uniformity and brightness may be affected by the optical transmission quality of the flexible light guide  106 . In another embodiment, the flexible light guide  106  may be fabricated using a material or coating which is waterproof or water-resistant. For example, one type of waterproof material that may be used to fabricate a flexible light guide  106  is fluorocarbon. Where a waterproof or water-resistant material is used, the flexible light guide  106  may provide structural and environmental protection for the backlighting system  100 . 
         [0022]    In another embodiment, a reflective layer  112  may be coupled to or integrated with the flexible light guide  106 . For example, the reflective layer  112  may be applied to one or more surfaces of the flexible light guide  106  using an adhesive material. In another example, the reflective layer  112  may be integrated with the adhesive applied to the flexible light guide  106 . In another embodiment, the reflective layer  112  may be integrated with the elastomer of the flexible light guide  106 . Although the reflective layer  112  is shown on the outer edges of the flexible light guide  106 , other embodiments may include the reflective layer on more or less surfaces of the flexible light guide  106 . For example, the reflective layer may be applied to the front surface (except for the buttons) of the flexible light guide. 
         [0023]      FIG. 4  depicts an embodiment of a micro-lens coating assembly  120 . The illustrated micro-lens coating assembly  120  includes the flexible light guide  106 . In one embodiment, the flexible light guide  106  includes embedded diffusion particles  122  to diffuse the light as it transmits through the flexible light guide  106 . Alternatively, a separate diffusion layer which is independent of the flexible light guide  106  may be provided. A micro-lens  124  is coupled to the flexible light guide  106 . In one embodiment, a coating resin  126  may be used to couple the micro-lens  124  to the flexible light guide  106 . The coating resin  126  may include reflection pigment  128  to enhance the light propagation associated with the micro-lens  124  and the flexible light guide  106 . 
         [0024]      FIG. 5  depicts an embodiment of a pattern-lens coating  130 . The term pattern lens coating  130  may refer to the pattern of micro-lens assemblies  120  used to demarcate an individual buttons  110  or other components. Additionally, the term pattern lens coating  130  may refer to the overall pattern of localized micro-lens assemblies  120  and components laid out on the flexible light guide  106 . The illustrated pattern lens coating  130  includes six localized groups of micro-lens assemblies  120 . In some embodiments, the distinct groups of micro-lens assemblies  120  may be distributed more or less densely than other groups of micro-lens assemblies  120 . Additionally, the pattern lens coating  130  of individual buttons  110  may include micro-lens assemblies  120  distributed in evenly spaced patterns, randomly spaced patterns, or other types of distributions. 
         [0025]    One exemplary micro-lens coating  120  and pattern-lens coating  130  is manufactured by Toyo Condenser Co., LTD., of Shizuoka, Japan. In one embodiment, the micro-lens coating  120  and the pattern-lens coating  130  are applied to an underside of the flexible light guide  106  to facilitate uniform light distribution within the flexible light guide  106 . In another embodiment, the micro-lens coating  120  is localized at the locations of the individual buttons  110 . In another embodiment, the micro-lens coating  120  has a variable distribution with a different distribution of density according to where the LEDs  104  of the light source  102  are disposed. 
         [0026]      FIG. 6  depicts a cross-sectional view of an embodiment of a backlighting system  140  using a flexible light guide  106 . The illustrated backlighting system  140  includes a light source  102  such as a plurality of LEDs  104 . The light source  102  is disposed adjacent to the flexible light guide  106  to illuminate the flexible light guide  106  through the transmission interface  108  of the flexible light guide  106 . The flexible light guide  106  is disposed within a housing having a back plate  142  and a front plate  144 . The terms “back” and “front” are used in a non-limiting manner to merely designate the button-side (front) and the non-button-side (back) of the flexible light guide  106 . Thus the use of the terms “back” and “front” are not intended to imply or require any specific orientation of the backlighting system  140  during manufacturing, use, or other handling of the backlighting system  140 . In one embodiment, the light source  102  is mounted to the back plate  142  of the housing. 
         [0027]    In the illustrated backlighting system  140 , the flexible light guide  106  includes one or more integrated plungers  146 . The integrated plungers  146  are also referred to as keypad plungers  146 . In one embodiment, the integrated plungers  146  are integrally formed with the flexible light guide  106 . The integrated plungers  146  may be fabricated, for example, by adding a specific hardness material to the elastomer of the flexible light guide  106 . One example of a specific hardness material is peroxide crosslinking agent. In one embodiment, the specific hardness material may be added to the elastomer of the flexible light guide  106  after the micro-lens coating  120  and pattern-lens coating  130  are applied to the flexible light guide  106 . The integrated plungers  146  protrude from the flexible light guide  106  to contact corresponding switches  148 . In one embodiment, the switches  148  are metal domes of the type known in the art. Alternatively, the switches  148  may be another type of switch. 
         [0028]    In one embodiment, the flexible light guide  106  also includes a tapered section or portion  150  near the transmission interface  108 . The tapered section  150  facilitates enhanced light coupling from the light source  102  to the flexible light guide  106 . In particular, the tapered section  150  may use total internal reflection to limit or eliminate light loss from the flexible light guide  106 . In this way, the brightness of the buttons  110  may be increased or maximized. 
         [0029]      FIG. 7  depicts a cross-sectional view of another embodiment of a backlighting system  160  using a flexible light guide  106 . The illustrated backlighting system  160  is substantially similar to the backlighting system  140  of  FIG. 6 . However, the backlighting system  160  of  FIG. 7  includes a diffusion layer  162  interposed between the flexible light guide  106  and the front plate  144 . The diffusion layer  162  facilitates diffusion of the light from the flexible light guide  106 . The diffusion layer  162  also helps to improve light output uniformity to the front plate  144 . Additionally, the diffusion layer  162  may obscure components such as the switches  148  underneath the diffusion layer  162  so that they are not visible through the diffusion layer  162 . 
         [0030]      FIG. 8  is a process flow diagram of a backlighting method  200  which may be used in conjunction with the flexible light guide  106  of the backlighting system  100 . Similarly, the backlighting method  200  may be used in conjunction with other backlighting systems such as the backlighting systems  140  and  160 . At block  202 , an elastomer light guide is provided. The elastomer light guide is one type of flexible light guide  106 . In other embodiments, other types of flexible light guides  106  may be provided. 
         [0031]    At block  204 , an LED  104  is provided to illuminate the elastomer light guide. Alternatively, other types of light sources  102  may be used to illuminate the flexible light guide  106 . At block  206 , the elastomer light guide and the LED  104  are disposed within a backlit device. As one example, the flexible light guide  106  and the light source  102  are disposed within the backlighting system  140 . 
         [0032]    Although the operations of the method(s) herein are shown and described in a particular order, the order of the operations of each method may be altered so that certain operations may be performed in an inverse order or so that certain operations may be performed, at least in part, concurrently with other operations. In another embodiment, instructions or sub-operations of distinct operations may be implemented in an intermittent and/or alternating manner. 
         [0033]    The embodiments described herein present one or more advantages compared to conventional backlighting systems. However, some of the embodiments may have other advantages or less than all of the advantages described herein. Some embodiments produce good light uniformity so that hot spots are not present within the flexible light guide  106 . Some embodiments use a light source  102  that does not produce noise (e.g., noise from rectifier circuitry). Some embodiments facilitate a reduced thickness of the electronic device by using a relatively thin flexible light guide  106 . For example, the flexible light guide  106  may be approximately 2 millimeters (mm), and the plunger height may be approximately 2 mm, so that the total distance between the back plate  142  and the front plate  144  is about 4 mm. Other embodiments may be thinner or less thin than this example. Some embodiments implement integrated plungers  146  to facilitate contact with the corresponding switches  148 . Some embodiments implement a flexible light guide  106  that also serves as a waterproof or water resistant barrier for the electronic device. 
         [0034]    Although specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The scope of the invention is to be defined by the appended claims and their equivalents.