Abstract:
An optical touchpad system is disclosed that may be easily integrated into a variety of applications. One feature of the optical touchpad system that may contribute to this versatility may be the ability of the optical touchpad system to function in the same manner independent from a topology and/or opacity of an interface surface of the optical touchpad system. This may enable the interface surface to be composed of any of a variety of materials. This may further enable the interface surface to include various topologies adapted for the application in which the optical touchpad system may be employed.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a optical touchpad system, with a multilayer waveguide that includes at least one total internal reflection mirror, for determining information relating to an engagement between an object and an interface surface of the optical touchpad system. 
       BACKGROUND OF THE INVENTION 
       [0002]    Generally, touchpad systems are implemented for a variety of applications. Some of these applications include, computer interfaces, keypads, keyboards, and other applications. Various types of touch pads are known. Optical touch pads have certain advantages over some other types of touch pads at least for some applications. Various types of optical touchpad systems may be used in some or all of these applications. However, conventional optical touchpad systems may include various drawbacks. For example, conventional optical touchpad systems may be costly, imprecise, temperamental, fragile, energy inefficient, or may have other weaknesses and/or drawbacks. Further, conventional systems may require that an interface surface (e.g. a surface that is engaged by a user) have a generally planar, or otherwise uniform topology. Some conventional optical touchpads may require that light reach the interface surface to enable an object in engagement with the interface surface to interact with the light. Thus some, conventional optical touchpad systems may require that the interface surface be either (i) predominantly transparent, or (ii) predominantly opaque. These limitations on topology and/or opacity may restrict the use of these systems with respect to some of the applications for touchpad systems. Various other drawbacks exist with known touchpads, including optical touchpads. 
       SUMMARY OF THE INVENTION 
       [0003]    One aspect of the invention relates to an optical touchpad system including a waveguide having a plurality of waveguide layers. For example, the waveguide may include an interface layer, an irradiation layer, a signal layer, and/or other layers. The interface layer may be defined by a first surface, a second surface and a relatively rigid material between the first and the second surface of the interface layer. The material between the first and the second surface of the interface layer may be opaque and/or or may be transparent. The material forming the interface layer may have a first index of refraction. The irradiation layer may be defined by a first surface, a second surface and may include a relatively pliable, transparent material having a second index of refraction that is greater than the first index of refraction. The signal layer may be defined by a first surface, a second surface and a transparent material having a third index of refraction that is less than the second index of refraction between the first and the second surface of the signal layer. 
         [0004]    The first surface of the interface layer may comprise an interface surface. The interface surface may be configured to be engaged by a user by use of an animate object (e.g., one or more finger) or an inanimate object (e.g., a stylus or other object). The engagement may include the user depressing a portion of the interface surface. The second surface of the interface layer may be located adjacent to the first surface of the irradiation layer. The second surface of the irradiation layer may be adjacent to the first surface of the signal layer. At the boundary between the interface layer and the irradiation layer a reflective surface may be formed to reflect light incident on the boundary from within the irradiation layer back into the irradiation layer. In some instances, the reflective surface may include a first total internal reflection mirror created by the first and second refractive indices of the materials in the interface layer and the irradiation layer. The first total internal reflection mirror may have a first critical angle. The boundary between the irradiation layer and the signal layer may form a second total internal reflection mirror having a second critical angle. The second total internal reflection mirror may be configured to reflect light incident on the second total internal reflection mirror from within the irradiation layer back into the irradiation layer. 
         [0005]    In some instances, including implementations in which the interface layer includes an opaque material between the first and the second surfaces of the interface layer, the waveguide may be configured to reflect light at the boundary between the interface layer and the irradiation layer by reflection other than total internal reflection. For example, a reflective layer may be disposed between the interface layer and the irradiation layer (e.g., by applying a thin film, by sputtering a coating or film, etc.) that reflects light from with the irradiation layer back into the irradiation layer without substantial variation based on the angle of incidence of the light. As another example, the opaque material between the first and second surfaces of the interface layer may inherently provide reflection at the boundary between the interface layer and the irradiation layer by reflection other than total internal reflection (e.g., the material includes a metal). As yet another example, one or more interference mirrors may be provided at the boundary between the interface layer and the irradiation layer to reflect radiation appropriately. 
         [0006]    At least one of the layers (e.g. the irradiation layer) may be optically coupled to one or more electromagnetic radiation emitters to receive electromagnetic radiation (e.g., light) emitted therefrom. One or more of the layers (e.g., the signal layer) may be optically coupled to one or more sensors. 
         [0007]    In operation, according to one embodiment, light received by the irradiation layer is normally trapped within the irradiation layer at least in part by reflection at the boundary between the interface layer and the irradiation layer (e.g., total internal reflection, etc.) and by total internal reflection at the total internal reflection mirror formed at the boundary between the irradiation layer and the signal layer. Engagement of the interface surface with an object causes the irradiation layer to at least partially deform. This deformation of the irradiation layer may interact (e.g., deflect, scatter, etc.) with the light, or other electromagnetic radiation, in the irradiation layer, such that the angle of incidence of at least a portion of the light incident on the second surface of the irradiation layer, which is normally trapped within the irradiation layer, becomes incident on the second surface of the irradiation layer with an angle of incidence that is less than the critical angle of the total internal reflection mirror formed at the second surface by the boundary between the irradiation layer and the signal layer. Thus, this light is leaked from the irradiation layer to the signal layer. The leaked light is then guided to the one or more sensors at least in part by reflection at the second surface of the signal layer. The one or more sensors may detect one or more properties of the light to determine information about the engagement of the interface surface and the object (e.g., the position of engagement, the force applied to the interface surface by the object, etc.). 
         [0008]    This configuration of optical touchpad provides various advantages over known touchpads. For example, the optical touchpad that may be able to function independent from a topology and/or opacity of an interface surface of the optical touchpad. This may enable the interface surface to be composed of any of a variety of materials (e.g., metal, wood, colored glass, colored polymers, clear glass, clear polymers, etc.). This may further enable the interface surface to include various topologies adapted for different applications in which the optical touchpad may be employed (e.g., appliances, doorbells, remote controls, personal electronics, keyboards, antiglare finishes, camera lenses, scroll buttons, tactile control input, Braille text, joysticks, applicable buttons, etc.). The operation of the optical touchpad may further enable an enhanced frame rate, reduced optical noise in the optical signal(s) guided to the one or more sensors, augment the ruggedness of the optical touchpad, and/or provide other advantages. 
         [0009]    In some implementations, the optical touchpad system comprises one or more emitters, one or more sensors, a waveguide, and one or more processors. The emitters emit electromagnetic radiation, and may be optically coupled with the waveguide so that electromagnetic radiation emitted by the emitters may be directed into the waveguide. The detectors may be configured to monitor one or more properties of electromagnetic radiation. For instance, the one or more properties may include intensity, directionality, frequency, amplitude, amplitude modulation, and/or other properties. The detectors may include one or more photosensitive sensors that receive electromagnetic radiation, and output one or more output signals that are indicative of one or more of the properties of the received electromagnetic radiation. The detectors may be optically coupled to the waveguide to receive electromagnetic radiation from the waveguide, and may output one or more output signals that are indicative of one or more properties of the electromagnetic radiation received from the waveguide. The processor may be operatively coupled with the detectors to receive the one or more output signals generated by the detectors. Based on the received output signals, the processor may determine information about an engagement between an object and an interface surface of the optical touchpad system formed by the waveguide. 
         [0010]    These and other objects, features, benefits, and advantages of the invention will be apparent through the detailed description of the preferred embodiments and the drawings attached hereto. It is also to be understood that both the foregoing general description and the following detailed description are exemplary and not restrictive of the scope of the invention. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  illustrates a side elevation of an optical touchpad system, in accordance with one or more embodiments of the invention. 
           [0012]      FIG. 2  illustrates an arrangement of an emitter within an optical touchpad system, according to one or more embodiments of the invention. 
           [0013]      FIG. 3  illustrates a side elevation of an optical touchpad system being engaged by an object, in accordance with one or more embodiments of the invention. 
           [0014]      FIG. 4  illustrates a aerial view of an optical touchpad system, according to one or more embodiments of the invention. 
           [0015]      FIG. 5  illustrates a side elevation view of an optical touchpad system with an interface surface that has a non-planar topology, in accordance with one or more embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]      FIG. 1  illustrates an optical touchpad system  10  according to one or more embodiments of the invention. Optical touchpad system  10  may include an interface surface  12 , one or more emitters  14 , one or more detectors  16 , and a waveguide  18 . Interface surface  12  is configured such that a user can engage interface surface  12  with an object (e.g., a fingertip, a stylus, etc.). Optical touchpad system  10  detects a position of the engagement between interface surface  12  and the object. 
         [0017]    Emitters  14  emit electromagnetic radiation, and may be optically coupled with waveguide  18  so that electromagnetic radiation emitted by emitters  14  may be directed into waveguide  18 . Emitters  14  may include one or more Organic Light Emitting Devices (“OLEDs”), lasers (e.g., diode lasers or other laser sources), Light Emitting Devices (“LEDs”), Hot Cathode Fluorescent Lamps (“HCFLs”), Cold Cathode Fluorescent Lamps (“CCFLs”) incandescent lamps, halogen bulbs, received ambient light, and/or other electromagnetic radiation sources. In some embodiments, emitters  14  may be disposed at the periphery of waveguide  18  in optical touchpad system  10  (e.g., as illustrated in  FIG. 1 ). However, this is not limiting and alternative configurations exist. For example, emitters  14  may be disposed away from waveguide  18  and electromagnetic radiation produced by emitters  14  may be guided to waveguide  18  by additional optical elements (e.g., one or more optical fibers, etc.). As another example, some or all of emitters  14  may be embedded within waveguide  18  beneath interface layer  12  at locations more central to optical touchpad system than those shown in  FIG. 1 . 
         [0018]    Detectors  16  may monitor one or more properties of electromagnetic radiation. For instance, the one or more properties may include intensity, directionality, frequency, amplitude, amplitude modulation, and/or other properties. Detectors  16  may include one or more photosensitive sensors (e.g., one or more photosensitive diodes, CCD arrays, CMOS arrays, line sensors etc.) that receive electromagnetic radiation, and may output one or more output signals that are indicative of one or more of the properties of the received electromagnetic radiation. As will be discussed further below, detectors  16  may include spatial filters (e.g., one or more apertures, slits, sets of slits, refractive elements, etc.) to filter the electromagnetic radiation before it becomes incident on the photosensitive sensor(s). In some implementations, detectors  16  may be optically coupled to waveguide  18  to receive electromagnetic radiation from waveguide  18 , and may output one or more output signals that are indicative of one or more properties of the electromagnetic radiation received from waveguide  18 . Based on these output signals, information about the engagement between the object and interface surface  12  may be determined (e.g., position, force of engagement, etc.) 
         [0019]    In some implementations, waveguide  18  may include a plurality of waveguide layers. For example, waveguide  18  may include an interface layer  20 , an irradiation layer  22 , a signal layer  24 , and/or other layers. Waveguide  18  may receive electromagnetic radiation from emitters  14  and direct a portion of the received electromagnetic radiation to detectors  16  such that information regarding the engagement between the object and interface surface  12  may be determined. 
         [0020]    As can be seen in  FIG. 1 , interface layer  20  may be defined by a first surface  28 , a second surface  30  and may be formed of a flexible, relatively rigid material disposed between first and second surfaces  28  and  30 . For instance, interface layer  20  may be formed from metal, wood, colored class, colored polymers, ceramics, polyethylene terephthalate (“PET”), polycarbonate, silicone, polyurethane, FEP, and/or other materials. In some implementations, the material forming interface layer  20  may be transparent to enable electromagnetic radiation to pass into and out of waveguide  18  via interface surface  12 . However, this is not always the case, as will be discussed further below. Interface layer  20  may include a material having a first index of refraction. Although interface layer  20  is shown in  FIG. 1  as a single contiguous layer, in some implementations, interface layer  20  may be a composite layer including a plurality of separate layers of the same, or different, materials. For instance, in implementations in which interface layer  20  includes substantially opaque interface surface  12 , interface layer  20  may include a first layer that provides interface surface and a second layer disposed between the first layer and irradiation layer  22  that is formed from a material that is not opaque (e.g., transparent) and has a predetermined index of refraction (e.g., the first index of refraction). 
         [0021]    Irradiation layer  22  may be defined by a first surface  32  and a second surface  34 , and may be formed from a transparent material having a second index of refraction. For example, irradiation layer  22  may be formed from glass, PET, polycarbonate, silicone, PP, ABS, polyurethane, and/or other transparent materials. In some instances, the transparent material that forms irradiation layer  22  may be relatively pliable. In various ones of these instances, the pliability of irradiation layer  22  may be a known value. 
         [0022]    In implementations in which interface layer  20  includes a layer formed from a transparent material, the second index of refraction may be greater than the first index of refraction. Irradiation layer  22  is illustrated in  FIG. 1  as being disposed adjacent to interface layer  20  within waveguide  18  such that second surface  30  of interface layer  20  is near or in contact with first surface  32  of irradiation layer  22 . Irradiation layer  22  may be optically coupled with emitters  14  to receive electromagnetic radiation therefrom. In some instances, additional optical components (not shown) may guide radiation emitted by emitters  14  into irradiation layer  22 . In some other instances, emitters  14  may be integrally formed within, or positioned directly adjacent to, irradiation layer  22 . 
         [0023]    Turning briefly to  FIG. 2 , in some implementations, absorption materials  26  that absorb electromagnetic radiation emitted by emitters  14  at relatively low angles of incidence to the surfaces that bound irradiation layer  22  may be provided within waveguide  18 . In the implementations illustrated in  FIG. 2 , emitter  14  may include a side emitting OLED formed within irradiation layer  22 . Absorption material  26  may be provided adjacent to irradiation layer  22  and may extend out from emitter  14  to a predetermined distance to absorb some of the radiation emitted by emitter  14 . Absorption material  26  may be substantially index matched to one or both of interface layer  20  and signal layer  24 , thereby ensuring that substantially any angles of incident light that would not be totally internally reflected at the boundary between irradiation layer  22  and interface layer  20  and/or the boundary between irradiation layer  22  and signal layer  24  may be absorbed. Absorption material  26  may be applied by print, by paint, by UV cure, by heat cure, or by other methods. Absorption material  26  may include paint, silicone, polymer, emerald, or other materials. 
         [0024]    Returning to  FIG. 1 , in some instances, the difference between the first index of refraction and the second index of refraction may create a total internal reflection mirror at the boundary between interface layer  20  and irradiation layer  22 . The total internal reflection mirror at the boundary between interface layer  20  and irradiation layer  22  may have a predetermined critical angle (illustrated in  FIG. 1  as θ 1 ). Electromagnetic radiation (illustrated in  FIG. 1  as electromagnetic radiation  36 ) that becomes incident on the total internal reflection mirror formed between interface layer  20  and irradiation layer  22  from within irradiation layer  22  with an angle of incidence (illustrated in  FIG. 1  as φ 1 ) greater than critical angle θ 1  may be reflected back into irradiation layer  22  by total internal reflection. 
         [0025]    As shown in  FIG. 1 , signal layer  24  may be defined by a first surface  38 , a second surface  40 , and may be formed from a transparent material having a third index of refraction. In some instances, the third index of refraction is less than the second index of refraction. In instances in which interface layer  20  is formed from a transparent material, the third index of refraction may be less than the second index of refraction but greater than the first index of refraction. Signal layer  24  may be disposed within waveguide  18  adjacent to irradiation layer  22  such that first surface  38  of signal layer  24  is at or near second surface  34  of irradiation layer  22 . The difference between the second index of refraction and the third index of refraction may create a total internal reflection mirror at the boundary between irradiation layer  22  and signal layer  24  with a predetermined critical angle (illustrated in  FIG. 1  as θ 2 ). The total internal reflection mirror formed at the boundary between irradiation layer  22  and signal layer  24  may totally internally reflect electromagnetic radiation (illustrated in  FIG. 1  as electromagnetic radiation  36 ) that is incident on the total internal reflection mirror from within irradiation layer  22  at an angle of incidence (illustrated in  FIG. 2  as φ 2 ) greater than critical angle θ 2 . For various purposes, some of which are discussed below, the material (or materials) used to form signal layer  24  may be relatively rigid. 
         [0026]    In some implementations (not shown), one or more auxiliary and/or boundary layers may be disposed between irradiation layer  22  and signal layer  24 . In these implementations, the additional layers may be transparent, and may be formed with an appropriate index of refraction (or indices of refraction) so as to form one or more total internal reflection mirrors. The one or more total internal reflection mirrors formed by the auxiliary and/or boundary layers may perform some or all of the functionality described herein as being provided by the total internal reflection mirror formed at conjunction of surfaces  34  and  38  in the implementation illustrated in  FIG. 1 . 
         [0027]    Signal layer  24  may be bounded on second side  40  by a base layer  42 . Base layer  42  may be defined by a first surface  44  and a second surface  46 . In some implementations, such as the implementations illustrated in  FIG. 1 , base layer  42  may be included as a layer in waveguide  18 . In these implementations, second surface  46  may comprise a mounting surface configured to be mounted to a base object. The base object may include virtually any object on which touchpad system  10  may be used as a touchpad. For example, the base object may include an electronic display (e.g., a display monitor, a mobile device, a television, etc.), a keypad, a keyboard, a button, an appliance (e.g., a stove, an air conditioner unit, a washing machine, etc.), a control panel (e.g., an automobile control panel, an airplane control panel, etc.), or other base objects. 
         [0028]    In some instances, base layer  42  may be formed from a material with a fourth index of refraction less than the third index of refraction such that a total internal reflection mirror may be formed at the boundary between signal layer  24  and base layer  42 . The total internal reflection mirror formed between signal layer  24  and base layer  42  may have a predetermined critical angle θ 3 . Electromagnetic radiation incident on the total internal reflection mirror from within signal layer  24  at an angle of incidence greater than critical angle θ 3  may be totally internally reflected back into signal layer  24 . 
         [0029]    As was mentioned above, in some implementations, base layer  42  may not be included as a layer in waveguide  18 . In these implementations, base layer  42  may be formed as an integral part of the base object on which waveguide  18  is disposed. For instance, base layer  42  may include a glass (or other suitable material) layer that forms the screen of an electronic or other display. In other implementations (not shown), base layer  42  may be included in waveguide  18  as a composite layer formed from a plurality of sub-layers. 
         [0030]    As is illustrated in  FIG. 1 , signal layer  24  may be optically coupled to detectors  16  to provide electromagnetic radiation thereto, as will be discussed further below. In some implementations, detectors  16  may be integrally formed within, or positioned directly adjacent to, signal layer  24  to receive electromagnetic radiation from signal layer  24 . In some other implementations, additional optical components (not shown) may be provided to direct radiation from signal layer  24  to detectors  16 . For example, the additional optical components may include one or more optical fibers and/or other components capable of guiding electromagnetic radiation. 
         [0031]    As was previously discussed, in some implementations, interface layer  20  and/or base layer  42  may be transparent. This may enable a user of touchpad system  10  to view an image through waveguide  18  (e.g., formed on the base object). For instance, in these implementations the user may view an image formed by an electronic or other display (e.g., backlit display, reflective display, etc.), a printed image formed on the base object beneath waveguide  18 , or other images formed by the base object. As was discussed above with respect to interface layer  20 , in some implementations, interface layer  20  and/or base layer  42  may include a plurality of layers including at least one layer that is substantially opaque. In this implementations, the substantially opaque layer may be bounded by a transparent layer having an index of refraction that enables total internal reflection at the boundary of interface layer  20  and/or base layer  42  as described above. However, in other implementations, all or a portion of one or both of interface layer  20  and base layer  42  may be substantially opaque, and radiation may be reflected within waveguide  18  at the boundary between interface layer  20  and irradiation layer  22  (e.g., first surface  32 ), and/or the boundary between signal layer  24  and base layer  42  by reflection other than total internal reflection. For example, the reflection may be a product of a reflective layer or coating disposed at these boundaries to reflect electromagnetic radiation back into irradiation layer  22  and/or signal layer  24 . As another example, one or more interference mirrors may be provided to reflect radiation appropriately at these boundaries. 
         [0032]      FIG. 3  illustrates one or more aspects of the operation of optical touchpad system  10 , according to one or more implementations of the invention. In  FIG. 3  a user has engaged interface surface  12  with an object  48  (e.g., a stylus, a fingertip, etc.). The force of the engagement between object  48  and interface surface  12  may deform interface layer  20  into waveguide  18 , thereby compressing the relatively pliable irradiation layer  22 , forming an indention  50  in first surface  32 . Due to the irregularity of first surface  32  at indention  50 , a portion of the electromagnetic radiation (illustrated in  FIG. 3  as electromagnetic radiation  52 ) emitted by emitters  14  and trapped within irradiation layer  22  by total internal reflection between irradiation layer  22  and signal layer  24  may be deflected such that it becomes incident on the total internal reflection mirror formed between irradiation layer  22  and signal layer  24  at an angle of incidence (illustrated in  FIG. 2  as  03 ) less than the critical angle θ 2  of this total internal reflection mirror. Rather than remaining trapped within irradiation layer  22  by total internal reflection, electromagnetic radiation  52  may pass through the total internal reflection mirror formed at the boundary of irradiation layer  22  and signal layer  24 , and into signal layer  24 . Electromagnetic radiation  52  that passes into signal layer  24  may be reflected at the boundary between signal layer  24  and base layer  42  back toward irradiation layer  22 . 
         [0033]    As can be seen in  FIG. 3 , electromagnetic radiation  52  may then be guided through waveguide  18  passing back and forth between signal layer  24  and irradiation layer  22  until it becomes incident on detectors  16  via signal layer  24 . Based on the output signals generated by detectors  16  in response to the receipt of electromagnetic radiation  52 , information related to the engagement between object  48  and interface surface  12  may be determined. For instance, the position of the engagement between object  48  and interface surface  12  with respect to interface surface  12  may be determined, the force applied to interface surface  12  by object  48  may be determined, or other information may be determined. 
         [0034]    It should be appreciated that although irradiation layer  22  is illustrated in  FIG. 3  as being pliable, and signal layer  24  is illustrated in  FIG. 3  as being relatively rigid, that this disclosure is not intended to be limiting. For instance, irradiation layer  22  may be formed from a relatively rigid material and signal layer  24  may be formed from a relatively pliable material. In such a configuration, engagement of object  48  with interface surface would deform waveguide  18  such that indention  50  would still be formed in first surface  32  and a corresponding indention would also be formed at the boundary between irradiation layer  22  and signal layer  24 . 
         [0035]    It should further be appreciated that the configuration of waveguide  18  with irradiation layer  22  disposed between signal layer  24  and interface surface  12  is not intended to be limiting. For example, in other implementations, the positions of irradiation layer  22  and signal layer  24  in  FIG. 3  may be switched. In these implementations various aspects of the operation of optical touchpad system  10  may remain unchanged. For instance, in these implementations, an indentation may be formed in irradiation layer  22  as a result of an engagement between interface surface  12  and an object, and the indentation may enable radiation to be leaked from irradiation layer  22  to signal layer  24 . The leaked radiation may then be directed to detectors  16  at least in part by total internal reflection at a boundary of signal layer  24  opposite from irradiation layer  22 . 
         [0036]      FIG. 4  illustrates a top view of optical touchpad system  10 , according to one or more implementations of the invention. In the implementations illustrated in  FIG. 4 , waveguide  18  provides a substantially rectangular interface surface  12  with clusters of emitters  14  and detectors  16  provided at each corner. It should be appreciated that this shape of interface surface  12  and arrangement of emitters  14  and detectors  16  is for illustrative purposes only, and that alternative configurations of these features are contemplated. For instance, in other implementations, arrays of emitters and detectors may be disposed substantially adjacent to each other in a manner that generally surrounds waveguide  18  with emitters and detectors. Other configurations are also contemplated. 
         [0037]    Detectors  16  in the implementations of  FIG. 4  may include directional sensors adapted to determine the direction of a source of radiation. For example, each of detectors  16  may include an optical element and a line sensor, wherein the optical element directs electromagnetic radiation onto the line sensor in such a manner that the direction of the source of the electromagnetic radiation can be determined. For instance, the optical element may include one or more apertures, and/or may incorporate a refractive element. Some implementations of suitable directional sensors are described in U.S. patent application Ser. No. 10/507,018, filed Mar. 12, 2003, and entitled “TOUCH PAD, A STYLUS FOR USE WITH THE TOUCH PAD, AND A METHOD OF OPERATING THE TOUCH PAD”. 
         [0038]    As object  48  is engaged with interface surfaced  12 , indention  50  created by this engagement causes a portion of the electromagnetic radiation emitted into waveguide  18  by emitters  14  to be deflected out of irradiation layer  22  into signal layer  24  (as was illustrated in  FIG. 3 ). In effect, this introduction of electromagnetic radiation into signal layer  24  acts similar to a source of electromagnetic radiation emitting the electromagnetic radiation into signal layer  24 . Thus, as the electromagnetic radiation deflected into signal layer  24  reaches detectors  16 , each of detectors  16  outputs one or more output signals that enable detection of the direction of indention  50  with respect to that detector  16 . Using conventional triangulation techniques, detections of the direction to indention  50  with respect to detectors  16  based on the output signals of detectors  16  may be combined to determine the position of the engagement between object  48  and interface layer  12  (e.g., indentation  50 ). It should be appreciated that although  FIG. 4  illustrates optical touchpad system  10  as including four detectors  16  (which would enable four separate directional detections of indentation  50 ), other implementations may employ triangulation using more or less detectors  16 . 
         [0039]    In some implementations, the emission of electromagnetic radiation from emitters  14  may be modulated so that electromagnetic radiation emitted by one or more of emitters  14  may be differentiated from electromagnetic radiation emitted by others of emitters  14 . For instance, in the implementation illustrated in  FIG. 4 , the emission of electromagnetic radiation by each of emitters  14  may be amplitude modulated at different frequencies. This may enable, based on the output signals of a given one of detectors  16 , determination of a direction from the given detector  16  in which an engagement between object  48  and interface surface  12  as described above, but it may further enable a determination as to the amount of electromagnetic radiation from each of emitters  14  that is being guided from the engagement to the given detector  16 . Implementations including this feature of modulation (e.g., amplitude modulation) of the electromagnetic radiation emitted by emitters  14  may demonstrate an augmented ability to discern information (e.g., position information, pressure information, etc.) related to simultaneous engagements between two or more objects and interface surface  12  at different positions (e.g., information about two separate engagements between two different fingertips of a user and interface surface  12 ). 
         [0040]    It should be appreciated that the implementation described above, in which each of emitters  14  in  FIG. 4  are modulated to enable differentiation between the electromagnetic radiation emitted by each of the various emitters  14  is not intended to be limiting. For example, emitters  14  may be frequency modulated and/or controlled (e.g., modulating or otherwise controlling the color of the light emitted by emitters  14 ) rather than amplitude modulated. As another example, in other implementations groups of emitters may be modulated in a substantially identical manner to enable differentiation between electromagnetic radiation emitted by the different groups of emitters  14 . As an example of this in optical system  10  illustrated in  FIG. 4 , the emitters  14  located at each corner of waveguide  18  may be amplitude modulated at the same frequency, which may be different than the modulation frequency of emitters  14  disposed at the other corners of waveguide  18 . 
         [0041]    As has been mentioned briefly above, information about the engagement between object  48  and interface surface  12  may be determined based on the output signals generated by detectors  16 . For instance, information related to the force applied by object  48  onto interface surface  12  (e.g., the pressure of the engagement) may be determined. Referring back to  FIG. 3 , as the force applied by object  48  on interface surface  12  increases, object  48  may be pressed further into waveguide  18 , thereby increasing the size of indention  50 . As can be seen in  FIG. 3 , as the size of indention  50  increases, the amount of electromagnetic radiation traveling within irradiation layer  22  deflected by indention  50  also increases, which may cause an increase in the amount of electromagnetic radiation introduced into signal layer  24  that will eventually propagate within waveguide  18  to detectors  16  in the manner illustrated by  FIG. 3 . If irradiation layer  22  has a known pliability curve, emitters  14  emit a known quantity of electromagnetic radiation (e.g., a known number of photons), and detectors  16  have a known quantum efficiency, then the force applied to interface surface  12  by object  48  may be determined from a calculation of the amount of electromagnetic radiation guided to detectors  16  based on the output signals generated by detectors  16 . 
         [0042]    In some implementations, emitters  14  and/or detectors  16  may be operatively coupled to one of more processors. The processors may be operable to control the emission of electromagnetic radiation from emitters  14 , receive and process the output signals generated by detectors (e.g., to calculate information about engagements between objects and interface surface  12  as described above), or provide other processing functionality with respect to optical touchpad system  10 . In some instances, the processors may include one or more processors external to optical touchpad system  10  (e.g., a host computer that communicates with optical touchpad system  10 ), one or more processors that are included integrally in optical touchpad system  10 , or both. For example, the processors may include one or more semi-conductive device (e.g., an ASIC, an FPGA, etc.), or other processors, integrated with one or more of detectors  16 . These processors may be operatively connected with one or more external processors. The external processors may, in some cases, provide redundant processing to the processors that are integrated with detectors  16 , and/or the external processor may provide additional processing to determine additional information related to an engagement between interface surface  12  and an object. For instance, the integrated processors may determine a position of the engagement and the external processors may determine a force applied by the object to interface surface  12 . 
         [0043]    Referring to  FIG. 5 , optical touchpad system  10  is illustrated including an alternative interface layer  20 , according to one or more implementations of the invention. As illustrated in  FIG. 5 , interface layer  20  may be of varying thickness such that interface surface  12  is provided with a non-planar topology. This feature may be implemented in instances in which interface layer  20  includes transparent and/or opaque materials. Unlike some other optical touchpad systems, the irregular topology of interface surface  12  may not interfere with determining accurate information related to the engagement between object  48  and interface surface  12  in part because optical touchpad surface  10  may not require electromagnetic radiation to pass into and out of waveguide  18  at interface surface  12  in a regular or predictable manner in order to operate. 
         [0044]    Due to this ability to provide reliable information about the engagement between object  48  and interface surface  12  when interface surface  12  has a non-planar topology and/or is opaque, optical touchpad system  10  may be suitable for a variety of applications where other conventional optical touchpads may not produce reliable results. For example, optical touchpad system  10  may be configured such that clearly formed buttons are formed in interface surface  12  (e.g., as individual raised areas). These buttons may even incorporate raised and/or depressed portions formed on individual buttons (e.g., for Braille markings on the buttons, which may enhance a human/machine interface designed for blind individuals, etc.). In some instances, optical touchpad system  10  may be formed such that interface surface  12  forms an entire keyboard (e.g., a QWERTY keyboard, a Latin keyboard with a different configuration, a keyboard comprising characters other than Latin, etc.) and scroll pad area as a single unit such that optical touchpad system  10  may be incorporated into a laptop computer as the input portion of the computer. Similarly, optical touchpad system  10  may be provided as the keypad in a remote control, a mobile phone, a personal digital assistant, or other wireless client device. In other instances, the topology of interface surface  12  may be shaped into a game controller (e.g., a joystick, etc.) with one or more directional inputs, one or more buttons, and/or one or more other control inputs. 
         [0045]    The ability to provide reliable information about the engagement between object  48  and interface surface  12  when interface surface  12  has a non-planar topology and/or is opaque may further enable users to alter and/or customize interface surface  12 . For example, a user may provide opaque markings on interface surface  12  (e.g., by pen, by sticker, etc.). As another example, a user may provide customized topographic features to interface surface  10 . For instance, a blind user may provide a interface surface  12  with Braille and/or other symbols to facilitate control over an electronic apparatus. As another example, the user may create a customizable interface (e.g., a keyboard) by placing topographical features (e.g., keys, buttons, joysticks, etc.) on interface surface  12 . Other uses of this feature of enabling user alteration and/or customization of interface surface  12  exist. 
         [0046]    In some implementations, one or more of emitters  14 , detectors  16 , electronic circuitry, or other components of optical touchpad system  10  may be integrally formed with waveguide  18 . For example, these components may be printed, laminated, or otherwise integrally formed within one or more of layers  20 ,  22 ,  24 , or  42  prior to, or concurrent with, the combination of layers  20 ,  22 ,  24 , and/or  42  in waveguide  18 . This may reduce an overall cost of manufacturing optical touchpad system  10 , enhance a robustness or ruggedness of optical touchpad system  10 , increase an accuracy of alignment of the components in optical touchpad system  10 , or provide other advantages. In some instances, one or more of emitters,  14 , detectors  16 , electronic circuitry, or other components may be formed integrally into one or more waveguide layers separate from waveguide  18 , and then the one or more separate waveguide layers may be attached to waveguide  18  to optically couple the components formed on the separate waveguide layer(s) with irradiation layer  22  and/or signal layer  24 . 
         [0047]    Other embodiments, uses and advantages of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. The specification should be considered exemplary only, and the scope of the invention is accordingly intended to be limited only by the following claims.