Abstract:
A light injection system includes a radiation source, an optical waveguide, and an optical component. The radiation source emits radiation and is oriented relative to the optical waveguide such that a first portion of radiation emitted from the radiation source couples into the optical waveguide as emitted from the radiation source and a second portion of radiation emitted from the radiation source bypasses the optical waveguide as emitted from the radiation source. The optical component redirects at least some of the second portion of radiation emitted from the radiation source that would otherwise bypass the optical waveguide and enables at least some of the redirected radiation to couple into the optical waveguide instead of bypass the optical waveguide.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Application No. 61/322,792, filed Apr. 9, 2010, which is incorporated herein by reference in its entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to light injection systems and, more particularly, systems that inject light into waveguides of frustrated total internal reflection- (FTIR) based touch sensors. 
     BACKGROUND 
     Touch sensitive systems refer, in general, to systems that detect and respond to multiple simultaneous points of contact on a surface. Typically, a touch sensitive system is incorporated within an electronic device in the form of a touch screen display that allows a user to both view and manipulate objects using one or more inputs that are in contact with the screen. Examples of electronic devices in which a touch sensitive system has been used include computer tablets, personal digital assistants (PDA), and cell-phones, among others. A variety of techniques are available that enable touch sensitive systems. For example, some touch systems identify surface contact by detecting changes in heat, pressure, capacitance or light intensity. 
     SUMMARY 
     Techniques are described for light injection used in, for example, touch-sensitive display devices and frustrated total internal reflection touch sensing technology. 
     Implementations of the described techniques may include hardware, a method or process implemented at least partially in hardware, or a computer-readable storage medium encoded with executable instructions that, when executed by a processor, perform operations. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a top view of an example light injection system. 
         FIG. 2  is a back view of an example light injection system. 
         FIG. 3  is a top view of an example light injection system. 
         FIG. 4  is a top view of an example light injection system. 
         FIG. 5  is a top view of an example light injection system. 
         FIG. 6  is a top view of an example light injection system. 
     
    
    
     DETAILED DESCRIPTION 
     Techniques are described for injecting light from a light source into a waveguide in a manner that causes at least some of the light to undergo total internal reflection within the waveguide. In some implementations, the waveguide may be relatively thin as compared to the light source such that all of the light emitted from the light source cannot directly enter a side of the waveguide. In these implementations, although some light emitted from the light source may directly enter the relatively thin waveguide and undergo total internal reflection, other light from the light source bypasses the waveguide entrance surface and becomes ‘stray light’ which can interfere with the touch interpretation apparatus. To improve efficiency of injection and to reduce the stray light, one or more optical components may be used to redirect the light so that it can properly enter the waveguide. Multiple types of optical components may be used to achieve such light redirection. 
       FIG. 1  illustrates an example light injection system. The example light injection system shown in  FIG. 1  may be part of a touch sensitive device, in which a point of contact with the device is detected based on FTIR. The light injection system includes a waveguide  110 , a light source  120 , a circuit board  130 , a spacer/reflector unit  140 , and a reflective surface  150  positioned at one surface of the spacer/reflector unit  140 . 
     The waveguide  110  may be made from a material that is flexible enough to respond to pressure applied by an input and that has a refractive index that allows light to undergo total internal reflection within the waveguide. For instance, the waveguide  110  may be made from materials such as acrylic/polymethylmethacrylate (PMMA), polycarbonate (PC), or polyethylene terephthalate (PET). The waveguide  110  may be an acrylic waveguide that has a thickness of approximately 0.8 mm (800 microns). Other materials and thicknesses can be used as well. 
     The light source  120  may include multiple light emitting diodes (LEDs), which are arranged directly against an edge of the waveguide  110 . Arranging the LEDs in this manner, may maximize direct coupling of electromagnetic radiation (e.g., light) into total internal reflection angular range within the waveguide  110 . The LEDs may have a thickness (e.g., 2.5 mm) that is approximately twice the thickness of the waveguide  110 . 
     Other sources of light such as, for example, laser diodes, may be used instead. In some implementations, the light source  120  can be selected to emit radiation in the infrared portion of the electromagnetic spectrum such that it does not interfere with visible radiation if the touch sensor device is integrated into a display. 
     Some light (e.g., infrared radiation) emitted from light source  120  is directly coupled into the waveguide  110 . Due to the refractive index difference between the waveguide  110  and the medium surrounding the waveguide  110 , at least some of the coupled light undergoes TIR and proceeds to travel down the waveguide  110 . For example, the waveguide  110  may be a thin layer of compliant acrylic surrounded by air. Given the refractive index difference between acrylic (n=1.49) and air (n=1.0), infrared light directly introduced by the light source  120  into the waveguide  110  at any angle of incidence propagates within and along the acrylic layer by TIR. 
     Although about half of the light emitted from the light source  120  directly enters and couples into the waveguide  110 , the other half of the light emitted from the light source  120  does not directly enter the side of the waveguide  110  because the light source is thicker than the waveguide  110 . Accordingly, this other half of light would not enter the waveguide  110  and would be wasted, unless it is otherwise redirected back to the waveguide  110 . 
     The spacer/reflector unit  140  includes a reflective surface  150  that reflects at least some of the lower half of light from the light source  120  back into the light source  120 . This causes at least some of the reflected light to reflect toward the waveguide  110 , enter the side of the waveguide  110 , and couple into the waveguide  110 . Specifically, in the example shown in  FIG. 1 , the light source  120  is an LED that includes an LED chip positioned inside of a reflective parabolic cup. As such, when light (e.g., infrared radiation) reflects off the reflective surface  150  and back into the reflective parabolic cup, the reflective parabolic cup causes at least some of the light to reflect toward the side of the waveguide  110  and couple into the waveguide  110 . In this regard, the reflective surface  150  reduces the amount of light wasted and increases the efficiency of coupling light emitted from the light source  120  into the waveguide  110 . 
     The reflective surface  150  may be a silver or aluminum mirror, a mylar mirror, a diffuse reflector, or any other type of reflector. The higher the reflectivity of the reflective surface  150  the better the recycled light efficiency achieved. 
     The reflective surface  150  may be attached or deposited on the spacer/reflector unit  140 . For example, a body of the spacer/reflector unit  140  may be an opaque material that absorbs stray light that is not being coupled into the waveguide. In this example, the spacer/reflector unit  140  may be made of opaque plastic and the reflective surface  150  may be attached to the appropriate surface of the spacer/reflector unit  140  to reflect light back toward the light source  120 . 
     The reflective surface  150  also may be an integral part of the spacer/reflector unit  140 . For instance, the spacer/reflector unit  140  may be made entirely of a reflective material and the reflective surface  150  may be a surface of the reflective material. 
     In some implementations, the spacer/reflector unit  140  may not be needed to support the waveguide  110 . In these implementations, the reflective surface  150  may be included alone without the body portion of the spacer/reflector unit  140 . For instance, the reflective surface  150  may be a thin film layer glued directly onto the light source  120  for support. 
     The circuit board  130  is a printed circuit board to which the light source  120  is mounted. The circuit board  130  provides electrical signals to the light source  120  to control the light source  120 . The spacer/reflector unit  140  also is attached to the circuit board  130  and supports the waveguide  110  in a manner that is spaced apart from the circuit board  130 . 
     In some examples, the waveguide  110  may be adhered directly to the circuit board  130  and the spacer/reflector unit  140  with the reflective surface  150  may be simply a reflective surface positioned above the waveguide  110 . In these examples, the waveguide  110  would be positioned below the center of the light source  120 , instead of above the center of the light source  120  as shown in  FIG. 1 . This type of configuration may ease manufacturing and reduce costs because the spacer is not needed. However, this type of configuration may not be able to yield as flush of a top surface as the configuration shown in  FIG. 1  because the waveguide  110  would be positioned below the center of the light source  120 . 
       FIG. 2  illustrates the example light injection system shown in  FIG. 1  from a top or bottom view. The example light injection system includes the waveguide  110 , the light source  120 , the circuit board  130 , the spacer/reflector unit  140 , the reflective surface  150 , an adhesive  160 , and thru-holes  170 . As shown, the adhesive  160  (e.g., glue or double stick tape) is placed at gaps between the light sources  120  (e.g., gaps between the LEDs) where no light is being injected into the waveguide  110 . The spacer/reflector unit  140  itself is adhered (e.g., glued or taped) to the circuit board  130 , so the pieces become a rugged and semi-rigid assembly. A thin piece of double stick adhesive may extend along the length of the spacer/reflector unit  140 , so the spacer/reflector unit  140  is tightly secured to the circuit board  130 . The same double stick adhesive may be used between the spacer/reflector unit  140  and the waveguide  110  to affix the waveguide  110  to the spacer/reflector unit  140 . The thru-holes  170  in the circuit board facilitate solid mounting to the device frame. 
     The example light injection system shown in  FIGS. 1 and 2  may provide a flush top surface, with high efficiency light coupling, and ease of manufacture. In this regard, thinner waveguides may be used with high efficiency light coupling and relatively low cost. The use of thinner waveguides may provide a more pleasing user experience and reduce a thickness of touch-screen displays. 
       FIG. 3  illustrates another example light injection system. As shown, the light injection system includes a waveguide  310 , a light source  320 , a reflective cup  330 , a first spacer/reflector unit  340 , and a second spacer/reflector unit  350 . The waveguide  310  may be similar to the waveguide  110  discussed above with respect to  FIG. 1  and the light source  320  may be similar to the light source  120  discussed above with respect to  FIG. 1 . The reflective cup  330  is included in the light source  320  and causes light to reflect back out of a front opening of the light source  320 . As shown, the reflective cup  330  has a parabolic shape. 
     The first spacer/reflector unit  340  and the second spacer/reflector unit  350 , each may be similar to the spacer/reflector unit  140  discussed above with respect to  FIG. 1 . In the example shown in  FIG. 3 , the first spacer/reflector unit  340  and the second spacer/reflector unit  350  sandwich the waveguide  310  and reflect light that would otherwise escape above and below the waveguide  310  back into the light source  320  and, ultimately, into the waveguide  310 . Ray traces  360  illustrate rays of light being reflected off the first spacer/reflector unit  340  and the second spacer/reflector unit  350 , back to the reflective cup  330 , and into the waveguide  310 . The example light injection system shown in  FIG. 1  may have a similar ray tracing pattern, but only for one half of the waveguide  110 . 
     The example light injection system shown in  FIG. 3  may experience higher light coupling efficiency than the example light injection system shown in  FIG. 1  because the central portion of light source  320  is positioned at the input face of the waveguide  310 . However, the example light injection system shown in  FIG. 3  may have increased manufacturing costs as compared to the example light injection system shown in  FIG. 1  because two spacer/reflector units are needed and the waveguide  310  is positioned between the two spacer/reflector units. In addition, the example light injection system shown in  FIG. 3  may have not have as flush of a top surface as the example light injection system shown in  FIG. 1  because a spacer/reflector unit is needed on top of the waveguide  310 . 
       FIG. 4  illustrates another example light injection system. As shown, the light injection system includes a waveguide  410 , a light source  420 , a circuit board  430 , a recycling funnel  440 , and a support plate  450 . The waveguide  410 , the light source  420 , and the circuit board  430  may be similar to the waveguide  110 , the light source  120 , and the circuit board  130  discussed above with respect to  FIG. 1 . The recycling funnel  440  reflects light that would not enter the face of the waveguide  410  back to the light source  420 . Specifically, light hitting a first sloped portion of the recycling funnel  440  undergoes TIR and is directed ninety degrees toward to a second sloped portion of the recycling funnel  440 . When the redirected light reaches the second sloped portion of the recycling funnel  440 , it undergoes TIR again and is directed back into the light source  420 . 
     In the example shown in  FIG. 4 , the light source  420  is an LED that includes an LED chip positioned inside of a reflective parabolic cup. As such, when light (e.g., infrared radiation) returns to the light source  420 , the reflective parabolic cup causes at least some of the light to reflect back toward the side of the waveguide  410  and couple into the waveguide  410 . In this regard, the recycling funnel  440  reduces the amount of stray light and increases the efficiency of coupling light emitted from the light source  420  into the waveguide  410 . 
     The recycling funnel  440  may be made of molded acrylic, polycarbonate, or any other suitable material that has an appropriate index of refraction. The support plate  450  may be an opaque material (e.g., an opaque plastic) that absorbs stray light that is not being coupled into the waveguide. The support plate  450  supports the waveguide  410  and the recycling funnel  440  at an interface where the waveguide  410  and the recycling funnel  440  meet. 
       FIG. 5  illustrates another example light injection system. As shown, the light injection system includes a waveguide  510 , a light source  520 , a circuit board  530 , and a recycling box  540  with reflective surfaces  550  and  560 . The waveguide  510 , the light source  520 , and the circuit board  530  may be similar to the waveguide  110 , the light source  120 , and the circuit board  130  discussed above with respect to  FIG. 1 . The recycling box  540  reflects light that would not enter the face of the waveguide  510  back to the light source  520 . Specifically, light hitting a first reflective surface  550  of the recycling box  540  is reflected ninety degrees toward to a second reflective surface  560  of the recycling box  540 . When the reflected light reaches the second reflective surface  560  of the recycling box  540 , it is reflected again and is directed back into the light source  520 . For light hitting the second reflective surface  560  first, the light would be reflected to the first reflective surface  550  and then reflected by the first reflective surface  550  back into the light source  520 . 
     In the example shown in  FIG. 5 , the light source  520  is an LED that includes an LED chip positioned inside of a reflective parabolic cup. As such, when light (e.g., infrared radiation) returns to the light source  520 , the reflective parabolic cup causes at least some of the light to reflect back toward the side of the waveguide  510  and couple into the waveguide  510 . In this regard, the recycling box  540  reduces the amount of stray light and increases the efficiency of coupling light emitted from the light source  520  into the waveguide  510 . 
     The recycling box  540  may be made of molded acrylic, polycarbonate, or any other suitable material that has an appropriate index of refraction and accommodates reflective surfaces. The reflective surfaces  550  and  560  may be polished and mirrored faces that reflect light emitted by the light source  520 . 
       FIG. 6  illustrates another example light injection system. As shown, the light injection system includes a waveguide  610 , a light source  620 , a circuit board  630 , and a recycling box  640  that includes retroreflecting prism structures. The waveguide  610 , the light source  620 , and the circuit board  630  may be similar to the waveguide  110 , the light source  120 , and the circuit board  130  discussed above with respect to  FIG. 1 . The recycling box  640  reflects light that would not enter the face of the waveguide  610  back to the light source  620 . Specifically, the recycling box  640  includes retroreflecting prism structures that sandwich the waveguide  610  and cover areas where light emitted by the light source  620  does not directly enter the face of the waveguide  610 . By this configuration, light hitting one of the retroreflecting prism structures is reflected back into the light source  620 . 
     In the example shown in  FIG. 6 , the light source  620  is an LED that includes an LED chip positioned inside of a reflective parabolic cup. As such, when light (e.g., infrared radiation) returns to the light source  620 , the reflective parabolic cup causes at least some of the light to reflect back toward the side of the waveguide  610  and couple into the waveguide  610 . In this regard, the recycling box  640  reduces the amount of stray light and increases the efficiency of coupling light emitted from the light source  620  into the waveguide  610 . 
     The recycling box  640  may be made of molded acrylic, polycarbonate, or any other suitable material that has an appropriate index of refraction and accommodates retroreflecting prism structures. 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. 
     In some of the disclosed implementations, frustrated total internal reflection-(FTIR) based touch sensors may be used, and touch events may be registered based on changes in light observed by one or more image sensors that result from light escaping from the FTIR-based touch sensors as a consequence of contact being made with the waveguide by appropriate input mechanisms, such as, for example, fingers. Any type of FTIR-based touch sensor that would benefit from a thin waveguide may be used. For example, the light injection systems and technology described throughout this disclosure may be applied to the FTIR-based touch sensors described in co-pending, commonly owned U.S. Provisional Patent Application Ser. No. 61/182,992 and the corresponding utility patent application, entitled “Touch Sensing,” filed Apr. 9, 2010, and assigned U.S. patent application Ser. No. 12/757,693, both of which are incorporated herein by reference in their entireties. In addition, the light injection systems and technology described throughout this disclosure may be applied to the FTIR-based touch sensors described in co-pending, commonly owned U.S. Provisional Patent Application Ser. No. 61/182,984 and the corresponding utility patent application, entitled “Touch Sensing,” filed Apr. 9, 2010, and assigned U.S. patent application Ser. No. 12/757,937, both of which are incorporated herein by reference in their entireties. 
     It will be understood that various modifications may be made. For example, other useful implementations could be achieved if components in the disclosed systems were combined in a different manner and/or replaced or supplemented by other components. Accordingly, other implementations are within the scope of the disclosure.