Touch sensing

Touch Sensing

TECHNICAL FIELD

This disclosure relates to touch sensing

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 m heat, pressure, capacitance or light intensity

SUMMARY

This specification descπbes technologies relating to touch sensing In general, one aspect of the subject matter descπbed in this specification can be embodied in a touch-screen device that includes a radiation source, a pliable waveguide configured to receive radiation emitted by the radiation source and to cause at least some of the received radiation to undergo total internal reflection within the pliable waveguide, a frustrating layer disposed relative to the pliable waveguide so as to enable the frustrating layer to physically contact the pliable waveguide when the pliable waveguide is physically deformed, and an imaging sensor configured to detect at least some radiation that escapes from the pliable waveguide The frustrating layer is configured to cause frustration of the total internal reflection of the received radiation within the pliable waveguide at a contact point between the frustrating layer and the pliable waveguide when the pliable waveguide is physically deformed to contact the frustrating layer such that some of the received radiation undergoing total internal reflection within the pliable waveguide escapes from the pliable waveguide at the contact point This and other implementations may optionally include one or more of the following features In some implementations, the frustrating layer may include a structure configured to steer at least a portion of the radiation that escapes from the pliable waveguide toward the imaging sensor For example, the structure may include a light diffusing surface and/or a volume diffusing structure integral to the frustrating layer In another example, the structure may include a diffraction pattern that corresponds to a grating structure In some cases, the diffraction pattern may be formed by employing an interference pattern that is transferred to the structure, in which a seπes of fringes representing intensity minima or maxima of the transferred interference pattern correspond to the grating structure The grating structure may include a blazed grating profile, a square-wave profile, a sinusoidal profile, and/or a half-sinusoidal profile The square-wave profile may include a 1-bit binary diffraction grating profile Alternatively, or m addition, the square-wave profile may include a multiple-bit modulated binary profile In another example, the structure may include an apeπodic diffraction pattern, in which a seπes of fringes representing intensity minima or maxima of an interference pattern transferred to the structure are arranged in an apeπodic pattern Alternatively, or in addition, the fringes of an interference pattern correspond to planes of refractive index vaπation that are aligned substantially parallel with a surface of the frustrating layer on which the radiation is incident

In some cases, the structure is on a surface of the frustrating layer that is nearest to the pliable waveguide and/or on a surface of the frustrating layer that is furthest from the pliable waveguide The structure may be configured to steer by diffraction at least a portion of the radiation that escapes from the pliable waveguide toward the imaging sensor The structure may be configured to steer by refraction at least a portion of the radiation that escapes from the pliable waveguide toward the imaging sensor In an example, the structure may include an array of pnsms

In certain instances, the structure is divided into sub-structures and each substructure is configured to steer radiation that escapes from the pliable waveguide toward the imaging sensor In some implementations, the device includes a pliable frustrating layer disposed relative to the pliable waveguide so as to enable the pliable frustrating layer to contact the pliable waveguide when the pliable frustrating layer is physically deformed The pliable frustrating layer maybe configured to cause frustration of the total internal reflection of the received radiation withm the pliable waveguide at a contact point between the pliable frustrating layer and the pliable waveguide when the pliable frustrating layer is physically deformed to contact the pliable waveguide layer such that some of the received radiation undergoing total internal reflection withm the pliable waveguide escapes from the pliable waveguide at the contact point between the pliable frustrating layer and the pliable waveguide In some implementations, the frustrating layer is disposed on a first side of the pliable waveguide layer and the pliable frustrating layer is disposed on a second opposite side of the pliable waveguide layer The pliable frustrating layer may include a structure configured to steer at least a portion of the radiation that escapes from the pliable waveguide toward the imaging sensor In some implementations, the touch-screen device includes a display device adjacent to the frustrating layer The display device may include a liquid crystal device, a light emitting diode device or an organic light emitting diode device The frustrating layer may be fixed to the display device The frustrating layer may be in optical contact with the display device In some cases, the touch-screen device includes a coupling layer, in which the coupling layer is in contact with a side of the display device that is furthest from the frustrating layer and in which the coupling layer is configured to couple radiation out of the display device The display device may include the imaging sensor The imaging sensor may be embedded in the display device In some implementations, the touch screen device also includes a screen projection layer, in which the screen projection layer includes a structure configured to diffuse at least a portion of light emitted from the display device In certain implementations, the touch-screen device includes a screen projection layer and a structure configured to diffuse at least a portion of light emitted from the display device on to the screen projection layer

The display device may include a structure configured to steer at least a portion of the radiation that escapes from the pliable waveguide toward the imaging sensor The structure may include a polarizer or substrate of the display device The structure may include a light diffusing structure The light diffusing structure may include a surface diffusive layer or a volumetπc diffusing structure

In some implementations, the touch-screen device includes a cladding layer on a surface of the pliable waveguide Alternatively, or in addition, the touch-screen device includes a cladding layer on the structure Portions of the cladding layer may be located within grooves defined by the structure

Another aspect of the subject matter described in this specification may be embodied in a touch-screen device that includes a radiation source, a pliable waveguide configured to receive radiation emitted by the radiation source and to cause at least some of the received radiation to undergo total internal reflection within the pliable waveguide, a frustrating layer disposed relative to the pliable waveguide so as to enable a top surface of frustrating layer to contact the pliable waveguide when the pliable waveguide is physically deformed, an image generating layer disposed adjacent to a bottom surface of the frustrating layer that is opposite to the top surface of the frustrating layer, in which the image generating layer has a top surface facing the bottom surface of the frustrating layer and a bottom surface that is opposite from the top surface of the image generating layer, an imaging sensor configured to detect at least some of the radiation that escapes from the pliable waveguide, and a hght-steeπng structure disposed adjacent to the bottom surface of the image generating layer, in which the hght-steermg structure is configured to steer at least a portion of the radiation that escapes from the pliable waveguide toward the imaging sensor The frustrating layer is configured to cause frustration of the total internal reflection of the received radiation within the pliable waveguide at a contact point between the top surface of the frustrating layer and the pliable waveguide when the pliable waveguide is physically deformed to contact the top surface of the frustrating layer such that some of the received radiation undergoing total internal reflection within the pliable waveguide escapes from the pliable waveguide at the contact point The image generating layer is configured to emit output images towards the frustrating layer and pliable waveguide and to be transmissive to radiation emitted by the radiation source This and other implementations may optionally include one or more of the following features For example, in some implementations, the hght-steeπng structure may be bonded to the bottom surface of the image generating layer In other implementations, the top surface of the image generating layer is bonded to the bottom surface of the frustrating layer The top surface of the image generating layer may be in optical contact with the bottom surface of the frustrating layer The top surface of the image generating layer may be fixed to the bottom surface of the frustrating layer In some implementations, the image generating layer includes a liquid crystal device and/or a light emitting diode The light emitting diode may include an organic light emitting diode In some implementations, the image generating layer also includes integrated image sensing

In some cases, the hght-steenng structure includes a light diffusing structure The light diffusing structure may include a surface diffusive layer and/or a volumetric diffusive layer

In some implementations, the hght-steenng structure includes a diffraction pattern corresponding to a grating structure The structure can include an apenodic diffraction pattern, in which fringes of the diffraction pattern correspond to planes of refractive index variation that are aligned substantially parallel with a surface of the frustrating layer on which the radiation is incident

In certain implementations, the hght-steenng structure is configured to steer by diffraction at least a portion of the radiation that escapes from the pliable waveguide toward the imaging sensor In some cases, the hght-steenng structure is configured to steer by refraction at least a portion of the radiation that escapes from the pliable waveguide toward the imaging sensor

In certain implementations, the touch-screen device includes a cladding layer on a surface of the pliable waveguide Alternatively, or in addition, the touch-screen device includes a cladding layer on a surface of the hght-steenng structure

In some implementations, the touch-screen device includes multiple imaging sensors, each imaging sensor being configured to detect at least some of the radiation that escapes from the pliable waveguide

The details of one or more implementations are set forth in the accompanying drawings and the descnption below Other features will be apparent from the descnption and drawings, and from the claims The technology described herein can be employed in various implementations including single touch or multi-touch sensitive devices

DESCRIPTION OF DRAWINGS

FIGS 1 A-ID are diagrams of a user interacting with a touch sensitive device FIGS 2 A and 2B are schematic cross-sectional diagrams of examples of different touch sensitive devices

FIG 2C is a schematic cross-sectional diagram of an example of a cladding layer FIGS 3-13 are schematic cross-sectional diagrams of examples of different configurations of waveguides and frustrating layers for incorporation within a touch sensitive device

FIG 14 is a schematic cross-sectional diagram of an example of a touch sensitive device

DETAILED DESCRIPTION A touch-sensitive system can receive an input from various sources of contact which include, for example, a human finger, a stylus, and/or a mechanical object FIGS 1A-1D are diagrams of a user interacting with a multi-touch sensitive device 100 As illustrated m FIGS 1 A-ID, when a user contacts a touch-screen 102 of device 100 using one or more fingers, the device 100 detects the contact made by the user's finger(s) with the touch-screen 102 and tracks movements) made by the user's finger(s) along the surface of the touch-screen 102 Based on a detected path or paths traced by the user's finger(s) on touch-screen 102, device 100 can manipulate information in a corresponding display, whether the display is separate from touch-screen 102 or is integrated as part of touch-screen 102 Given that device 100 can detect contact from multiple mputs, many users may operate device 100 concurrently

One approach for sensing the contact of one or more objects on a surface of a touch sensitive device involves sensing contact points on a waveguide by detecting points along the waveguide from which light is escaping the waveguide due to frustrated total internal reflectance (FTIR) occurring as a consequence of the contact bemg made on the waveguide When light traveling in a first medium (e g , a waveguide) encounters an interface with a second medium having a lower refractive index (e g , air), the light traveling m the first medium may, depending on its angle of incidence with the interface, refract as it passes through the interface If the angle of incidence is greater than a cntical angle, on the other hand, the light will undergo total internal reflection (TIR) within the first medium For example, waveguides such as fiber optic cables employ TIR to transport light efficiently with very little loss In some cases, however, such total internal reflection of light can be frustrated by replacing the medium having the lower refractive index with another material that allows the light to escape from the waveguide By sensing the escaped light, it may be possible to detect the location at which the new mateπal was introduced

Implementations of a touch sensitive device disclosed herein include a pliable waveguide that is configured to deform responsive to surface manipulation (e g , pressure from a finger interacting with a display), which causes a portion of the waveguide at the location of the surface manipulation to physically contact a frustrating layer therebeneath Light that travels along the waveguide, e g , via total internal reflection, escapes at the point of contact to yield a detectable position of waveguide deformation, and hence surface manipulation (i e , total internal reflection of light in the waveguide is frustrated at the point of contact between the waveguide and the frustrating layer) FIG 2 A is a schematic cross-sectional diagram of an example of a touch sensitive device 200, in which a point of contact with device 200 is detected based on FTIR As shown m FIG 2A, device 200 includes a radiation source 202, a pliable waveguide 204, a frustrating layer 206 adjacent to waveguide 204 and an imaging sensor 208 Frustrating layer 206 is positioned relative to the pliable waveguide 204 such that a small gap 212 exists between frustrating layer 206 and pliable waveguide 204 In some implementations, protrusions 214 may be formed on or as part of frustrating layer 206 to maintain the gap 212 between the pliable waveguide 204 and the frustrating layer 206 In such implementations, protrusions 214 (e g , surface roughness) can be formed integrally with frustrating layer 206, i e , protrusions 214, together with frustrating layer 206, form a single mass of seamless, contiguous mateπal In some implementations, a micro- roughness layer having randomly (or semi-randomly) spaced protrusions may be formed on the surface of the frustrating layer 206, which function substantially as protrusions 214 In some cases, protrusions 214 are formed from mateπal distinct from frustrating layer 206 and/or waveguide 204 For example, glass spacers could be used to separate an acrylic waveguide from a polycarbonate frustrating layer The spacing between protrusions 214 can be random, pseudo-random or penodic

Electromagnetic radiation (e g , infrared (IR) radiation) is emitted from radiation source 202 and coupled into pliable waveguide 204 Due to the refractive index difference between pliable waveguide 204 and the medium surrounding waveguide 204, at least some of the coupled radiation then undergoes TIR and proceeds to travel down pliable waveguide 204 For example, waveguide 204 could be formed from a thm layer of compliant acrylic surrounded by air Given the refractive index difference between acrylic (n=l 49) and air (n=l 0), radiation introduced by radiation source 202 into waveguide 204 at an appropriate angle of incidence propagates within and along the acrylic layer by TIR Waveguide 204 is formed from a mateπal that is flexible enough to respond to pressure applied by an input such that sufficient contact can be made with frustrating layer 206 For example, waveguide 204 can be formed from mateπals such as acrylic/polymethylmethacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate (PET) or transparent polyurethane (TPU) Other mateπals can be used as well

In order to frustrate TIR of radiation propagating in waveguide 204, frustrating layer 206 is formed from mateπal that has a refractive index comparable to or higher than compliant waveguide 204 Thus, when compliant waveguide 204 comes into contact with frustrating layer 206, at least a portion of the radiation propagating down waveguide 204 due to TIR is "frustrated" and escapes from waveguide 204 In some cases, at least a portion of radiation 210 continues to propagate by TIR in waveguide 204, as shown in FIG 2A Either a πgid or non-πgid matenal can be used to form frustrating layer 206 In addition, when integrated as part of a display, frustrating layer 206 may be formed from a mateπal that is transparent (or at least transmissive) to the range of wavelengths emitted by a display light source For example, frustrating layer 206 may be formed from glass or from PMMA, both of which are generally transmissive in both the visible and near- infrared regions of the spectrum Alternatively, frustrating layer 206 can be formed from relatively pliable mateπals such as polyvinyl chloride (PVC), polyvinyl butyral (PVB), TPU, or from more rigid matenals such as PET or PC Other mateπals can be used as well Locally depressing waveguide 204 may cause substantial local deformation of frustrating layer 206 as waveguide 204 comes mto contact with frustrating layer 206 hi contrast, portions of frustrating layer 206 far from the region of contact between waveguide 204 and frustrating layer 206 may expenence little or no deformation Such pronounced local deformation may lead to an increase in the area of physical contact between compliant waveguide 204 and frustrating layer 206, thereby causing an increased amount of IR to escape from compliant waveguide 204 in the region of the point of contact m some implementations, frustrating layer 206 may be configured to have a substantially uniform thickness that is within a range of approximately 100 μm through 300 μm In selecting an appropπate thickness for frustrating layer 206, the following considerations may be taken into account If frustrating layer 206 is too thin, it may be difficult to manipulate and handle, for example, during manufacturing On the other hand, if frustrating layer 206 is too thick, it may cause a parallax issue, where a user perceives a point of contact to be displaced (e g , by the thickness of frustrating layer 206) from the actual displayed object with which the user is attempting to interact In alternative implementations, frustrating layer 206 may be configured to be thinner than 100 μm (e g , about 10 μm or about 30 μm) or thicker than 300 μm (e g , about 1 mm or about 2 mm)

Due to the presence of air gap 212 between frustrating layer 206 and pliable waveguide 204, little or no frustration of TIR within waveguide 204 occurs absent some external stimulus However, when pliable waveguide 204 is depressed by, for example, a user's finger 220, a portion of pliable waveguide 204 contacts frustrating layer 206 in a region 201 (identified by dashed line circle) corresponding to the point of depression As descπbed above, in some implementations, the contact between pliable waveguide 204 and frustrating layer 206 may cause local deformation of frustrating layer 206 When frustrating layer 206 contacts waveguide 204, total internal reflection within waveguide 204 is frustrated within region 201 causing at least some radiation to escape from the pliable waveguide 204 It should be noted that although protrusions 214 also contact waveguide 204, the area of contact between protrusions 214 and waveguide 204, when no pressure is applied to pliable waveguide 204, is relatively small compared to the area of contact between frustrating layer 206 and pliable waveguide 204 when pliable waveguide 204 is depressed Accordingly, frustration of TIR that might occur m the regions of contact between protrusions 214 and waveguide 204 is negligible when no pressure is applied to pliable waveguide 204

As shown m FIG 2 A, some of the radiation, represented by arrows "A," escapes from surface 204a of pliable waveguide 204 and travels in a direction towards imaging sensor 208 Imaging sensor 208 images the radiation that escapes from surface 204a As a result, imaging sensor 208 can discnmmately sense, for successive instants of time, points of contact that are sufficiently forceful to deform pliable waveguide 204 such that it contacts a substantial portion of frustrating layer 206 relative to the portion of frustrating layer 206 contacted by waveguide 204 when no pressure is applied That is, for a "single" point of contact on waveguide 204, such as contact by finger 220 shown in FIG 2A, a single "area" of contact corresponding to the portion of frustrating layer 206 that contacts waveguide 204 is discnmmately sensed by imaging sensor 208 Likewise, when two or more objects (e g , two or more fingers of a user) contact and depress waveguide 204 concurrently, multiple areas of contact are discnmmately (and concurrently) sensed by imaging sensor 208 For ease of discussion, the term "a point of contact" may be used throughout this disclosure to refer more generally to any region or area at which contact is made

Various detectors may be used as imaging sensor 208 including, for example, charge-coupled devices (CCDs), photo-diodes or complimentary metal-oxide- semiconductor (CMOS) sensors In some cases, a lens is placed in front of imaging sensor 208 to focus light on sensor 208 Alternatively, or m addition the imaging sensor 208 may include one or more waveguides and/or lenses to assist guiding the incident radiation towards a detection area of a sensing device The output of imaging sensor 208 is supplied to a suitable computer (not shown) or other electronic device capable of handling image-processing operations, such as rectification, background subtraction, noise removal, and analysis for each video frame Machine vision tracking techniques then may be employed by the computer or other electronic device to translate the captured images into discrete touch events and strokes Such processing may be earned out by any suitable computing system In some implementations, touch sensitive device 200 also is combined with a rear- projection source 230 (e g , a video projector) that is capable of displaying visible images Accordingly, touch sensitive device 200 can function as both a sensing and display device at the same time Li implementations where a rear-projection source 230 is used to generate output images, frustrating layer 206 may be configured to be diffusive m the visible spectrum such that frustrating layer 206 may operate as a screen onto which the output images projected by rear-projection source 230 are projected Alternatively, device 200 may be configured to include a separate screen that includes a diffusive mateπal or layer, which is diffusive m the visible spectrum such that the diffusive matenal or layer may operate as a screen onto which the output images projected by rear- projection source 230 are projected The diffusive material/layer of the projection screen can be combined either alone or in combination with another diffuser film

Although FIG 2A shows projection source 230 arranged alongside imaging sensor 208, projection source 230 also can be disposed at other locations and/or away from imaging sensor 208, generally with the aid of suitable optics devices As illustrated rn FIG 2A, device 200 may include a single imaging sensor 208 and a single projection source 230 In certain implementations, the distance between imaging sensor 208 and pliable waveguide 204 is large enough such that a field of view of sensor 208 is capable of imaging/detecting radiation escaping from waveguide 204 at substantially any point of contact along the surface of waveguide 204 However, in other implementations, multiple projectors can be employed so that different images/videos can be projected onto different respective portions of a display Alternatively, or in addition, multiple imaging sensors can be employed so that each image sensor has a field of view capable of imaging/detecting radiation escaping from different portions of waveguide 204 For instance, FIG 2B illustrates one example of the use of multiple imaging sensors 208 within an FTIR-based touch sensitive device Given the relatively small corresponding field of view, each imaging sensor 208 may be located closer to pliable waveguide 204 Accordingly, in some cases, thinner FTIR-based touch sensitive devices may be manufactured In implementations of FTIR-based touch sensitive devices containing multiple imaging sensors, the imaging sensors and projectors may be spaced apart from one another along a single axis, multiple axes, along a grid system, or in other suitable manners For example, the imaging sensors can be arranged such that there is no overlap between the field of view of adjacent sensors 208 Alternatively, the imaging sensors can be arranged such that the field of view of at least one sensor 208 overlaps with the field of view of one or more adjacent sensors 208 The output generated by each sensor then may be supplied to a suitable computer (not shown) or other electronic device capable of handling image-processing operations, and modified to form a composite image/data map corresponding to all or substantially all of the area over which points of contact with pliable waveguide 204 can be made The composite image/data map then may be used to determine where along waveguide 204 points of contact occur Radiation source 202 can include multiple light emitting diodes (LEDs), which are arranged directly against an edge of waveguide 204 so as to maximize coupling of electromagnetic radiation into total internal reflection Other sources of electromagnetic radiation, such as, for example, laser diodes, may be used instead In some implementations, source 202 can be selected to emit radiation in the infrared (IR) portion of the electromagnetic spectrum such that its emissions do not interfere with visible light if device 200 is integrated into a display

In some implementations, pliable waveguide 204 is formed from mateπals that support TIR of infrared light In addition, when integrated as part of a display, pliable waveguide 204 may be selected so as to be transparent (or at least transmissive) to the range of wavelengths emitted by a display light source so as to minimize interference with the display In some cases, the edges of pliable waveguide 204 are polished to maximize TfR coupling of radiation from source 202

In some implementations, waveguide 204 may be configured to have a substantially uniform thickness that is within a range of approximately 0 50 mm through 2 mm In selecting an appropnate thickness for waveguide 204, the following considerations may be taken into account If waveguide 204 is too thm, an insufficient amount of radiation may be coupled into waveguide 204 from source 202 In implementations that utilize one or more lasers for light source 202, however, it may be possible to use a thinner waveguide 204 and still have a sufficient amount of radiation couple into the waveguide 204 than in implementations that utilize one or more LEDs as light source 202 Alternatively, if waveguide 204 is too thick, the waveguide may degrade the quality of output images displayed by the device

In some cases, contacting waveguide 204 with a finger, stylus or other object can cause inadvertent frustration of total internal reflection within waveguide 204 even if waveguide 204 is not depressed enough to come into contact with frustrating layer 206 In addition, such objects may damage waveguide 204 Accordingly, in some implementations, a cladding layer 205 is positioned on top of pliable waveguide 204, either in optical contact with waveguide 204 or layered with a thm air gap between cladding layer 205 and waveguide 204 If the cladding layer is in optical contact with the waveguide, cladding layer 205 is formed of a mateπal that has a refractive index lower than waveguide 204 to maintain total internal reflection of radiation within waveguide

204 Cladding layer 205 may prevent the occurrence of inadvertent FTIR and serves as a barrier between waveguide 204 and a contacting object In addition, cladding layer 205 protects waveguide 204 from damage and/or contamination when waveguide 204 is contacted by an object such as a finger or stylus When integrated as part of a display, cladding layer 205 also is transparent (or at least transmissive) to the range of wavelengths emitted by a display light source For example, cladding layer can be formed of polytetrafluoroethylene (PTFE) or acrylic film

In some implementations, the cladding layer includes multiple layers FIG 2C is a cross-sectional schematic of an example of a cladding layer 205 positioned above a waveguide 204, in which cladding layer 205 includes an anti-glare layer 205a, an infrared (IR) filter 205b and a non-wetting layer 205c IR filter layer 205b functions to filter out ambient IR light incident on touch-sensitive device 200 so as to reduce (e g , prevent) occurrences in which image sensors 208 detect the ambient IR light and erroneously detect contact with device 200 An example of mateπal that can be used in an IR filter layer includes ClearAS, commercially available from Sumitomo Osaka Cement Co , Ltd Anti-glare layer 205a is a scratch-resistant, low friction film disposed on a top surface of IR filter layer 205b A film that can be used as an anti-glare layer includes, for example, a textured polyester film such as Autotex, which is commercially available from MacDermid Inc

In some cases, substantial regions of cladding layer 205 may contact the pliable waveguide such that cladding layer 205 appears to "wet" the pliable waveguide Such regions of "wetting" may inadvertently induce frustration of total internal reflection within the waveguide 204 Furthermore, the wetting regions may alter the amount of visible light that is reflected between waveguide and cladding layer resulting in portions of touch-sensitive device 200 that appear as blotches when dark images are displayed By forming anti-wetting layer 205c on a bottom surface of IR filter layer 205b, however, the size and number of wetting regions may be reduced Similar to anti-glare layer 205a, anti-wettmg layer 205c also may be a polyester film, such as Autotex

The films in cladding layer 205 may be bonded together using, for example, an optical adhesive In the example of FIG 2C, an air gap exists between cladding layer 205 and pliable waveguide 204 The air gap between cladding layer 205 and pliable waveguide 204 may be maintained using, for example, the surface roughness of the bottom surface of cladding layer 205 (e g , surface roughness of the non-wetting layer 205c)

In some implementations, liquid crystal display (LCD) technology or light emitting diode (LED) display technology, which includes organic light emitting diode (OLED) display technology, may be used to generate output display images instead of rear projection technology Employing LCD or LED display technology instead of rear projection technology enables a touch-sensitive device that has reduced volume and thickness compared to a device which utilizes projector technology Using either LEDs, OLEDs or LCD panels also may increase portability Such "thm-panel" touch-sensitive systems can be used in laptop screens, flat-panel displays, PDA's and cell phones, among other devices LCD panels, LED and OLED arrays can be used as the light source in any of the examples and implementations descπbed herein

For example, FIG 2B is a schematic diagram of a cross-section of a touch sensitive device 270 that employs an LCD panel 240 and backlight 250 to generate a visible display As illustrated in FIG 2B, the LCD panel 240 and backlight 250 are disposed beneath frustrating layer 206 In the particular implementation shown in FIG 2B, LCD panel 240 is arranged so that it is fixed to a bottom surface of frustrating layer 206 Although not shown, LCD panel 240 may include one or more components or layers such as, for example, a liquid crystal layer, a color filter layer, one or more polarizer layers, one or more electrode layers, and a substrate layer (e g , a glass substrate) Other layers or components can be included as well Similarly, LED and OLED panels can include, but are not limited to, one or more layers or components, such as a light emitting diode layer, an electrode layer, an adhesive/encapsulant layer and a substrate layer (e g , a glass substrate) In some implementations, frustrating layer 206 is directly bonded to LCD panel

240 using, for example, optical adhesive (not shown) having an index of refraction substantially close in value, e g , withm about 0 1, to the index of refraction of both frustrating layer 206 and LCD panel 240 to provide an optical contact between frustrating layer 206 and LCD panel 240 Optical adhesives, for example, may be optically clear pressure sensitive acrylics or silicones In addition to adhering frustrating layer 206 to LCD panel 240, the presence of the optical adhesive can, in some instances, reduce reflections and/or interference that would otherwise occur due to the refractive index contrast at the surfaces of LCD panel 240 and frustrating layer 206 In particular, air gaps, which have a relatively low refractive index (n = 1), are replaced with optical adhesive havmg a higher refractive index (n > 1) Moreover, in some cases, the optical adhesive fills in roughness between the facing surfaces of panel 240 and layer 206, which would otherwise lead to additional light scattering By reducing the amount of light reflected back toward the viewer, the image contrast provided by touch sensitive device 270 can be improved Although frustrating layer 206 is shown fixed to LCD panel 240, frustrating layer 206 can, in some cases, be arranged in the FTIR-based touch sensitive device such that it does not adhere to the LCD panel 240

Individual pixel portions within LCD panel 240 can be configured to block or transmit visible light, represented by arrows "C," emitted by backlight 250 in order to display an image Furthermore, LCD panel 240 may be transparent to infrared light so that infrared light that escapes from surface 204a of pliable waveguide 204 passes through LCD panel 240 and can be imaged by imaging sensor 208 In some implementations, LEDs (or OLEDs) can be used as the light source in FTIR-based touch sensitive devices Because LEDs (OLEDs) themselves are emissive elements, in implementations m which LEDs (OLEDs) are used to generate output images, there may be no need for a backlight (e g , backlight 250) Similar to LCD panel 240, such LEDs (OLEDs) may be transparent to infrared light and may be arranged in a layer that is bonded to frustrating layer 206

In some implementations, the display device can include one or more image sensors 208 as part of the display device (e g , image sensors 208 may be embedded on or within the display device) In some cases, LCD panel 240 may include photosensors alternating with thin film transistors that drive the liquid crystal cells of LCD panel 240 The photosensors may be made of photodiodes that are sensitive to IR light such as, for example, amorphous hydrogenated silicon germanium, a-SiGe H photodiodes The bandgap of such sensors is about 1 45 eV and could be used to detect light having a wavelength of approximately 850 nm Alternatively, the photodiode mateπal may have a bandgap tuned to match the wavelength of the source radiation Given that the thm film transistors may also use an amorphous semiconductor, the photosensors can, in some implementations, be located on the same substrate that is used to support the thm film transistors In order to detect primarily IR light as opposed to visible light, the photosensors may be covered with a filter that passes light in the IR wavelength range while reflecting or absorbing light having different wavelengths An advantage of the foregoing implementation is that it enables touch sensitive devices that are thinner than devices that use discrete cameras situated beneath and apart from the display device Other display devices also may include embedded photosensors For example, an active matπx OLED device may include IR photodiodes alternating with OLED cells As illustrated in FIGS 2A and 2B, radiation that escapes compliant waveguide

204 due to FTIR when the compliant waveguide 204 contacts frustrating layer 206 may travel m many different directions due to, for example, the surface texture of frustrating layer 206, bulk scatteπng withm frustrating layer 206 or incomplete contact between compliant waveguide 204 and frustrating layer 206 For instance, some of the radiation that escapes from compliant waveguide 204 may travel in a direction away from frustrating layer 206, while some of the escaped radiation may travel towards frustrating layer 206 As a result, a portion of the escaped radiation, as shown by arrows "B" in FIG 2B (and FIG 2A), may never reach imaging sensor 208 One approach to enable capture of a sufficient amount of light from the frustrated TIR to yield position, despite the escaped radiation that never is imaged by imaging sensor 208, may be to increase the intensity of the radiation injected into the pliable waveguide 204 This approach, however, may cause operating efficiency to be diminished Therefore, an alternative approach may be to configure frustrating layer 206 to collect and/or steer radiation that escapes compliant waveguide 204 and that is incident on frustrating layer 206 toward imaging sensor 208 An additional alternative approach is to incorporate a hght-steeπng layer 260 within the touch sensitive display device (see, e g , FIG 2B) Light-steeπng layer 260 may be configured to collect radiation that escapes from pliable waveguide 204 due to FTIR and modify the direction of the collected radiation hi some implementations, hght-steenng layer 260 may be a diffusive layer (e g , a surface diffuser or a volumetπc diffuser) Additionally or alternatively, light-steeπng layer 260 may be configured to steer incident light in one or more specific directions (e g , toward imaging sensor 208)

Similar to frustrating layer 206, light-steeπng layer 260 maybe formed of either a πgid or non-πgid material In addition, when integrated as part of a display, light- steeπng layer 260 may be formed from a mateπal that is transparent (or at least transmissive) to the range of wavelengths emitted by a display light source For example, hght-steenng layer 260 may be formed from PMMA, TPU, PVC, PVB, PET, tπacetate cellulose (TAC) or PC Other mateπals can be used as well In some implementations, a light diffuser, which is typically incorporated in the LCD backlight, also can function as the light-steeπng layer In some implementations, light-steeπng layer 260 can be bonded to a bottom surface of LCD panel 240 Light-steeπng layer 260 can be bonded to a bottom surface of LCD panel 240 using optical adhesive to provide an optical contact between light-steeπng layer 260 and LCD panel 240 Alternatively, if LED (OLED) display technology is employed in place of LCD display technology, hght-steenng layer 260 can be bonded to a bottom surface of the LEDs (OLEDs) using, for example, optical adhesive to provide an optical contact In implementations in which frustrating layer 206 is configured to collect and/or steer radiation that escapes compliant waveguide 204 and that is incident on layer 206 toward imaging sensor 208, frustrating layer 206 may be configured to steer escaped radiation to within a range of angles such that the escaped radiation is steered towards a position on the imaging sensor 208 that is substantially beneath the point of contact between compliant waveguide 204 and frustrating layer 206 By collecting and steeπng radiation towards the optimal area of imaging sensor 208, the operating efficiency of touch sensitive devices 200 and 270 may be increased As a result, less powerful radiation sources 202 may be used, and stray light issues may be reduced Furthermore, by steeπng more of the FTIR escaped radiation towards imaging sensor 208, the probability of failing to sense contact with devices 200 and 270 may be reduced The frustrating layer may be formed from an engineered mateπal having light-steermg microstructures formed withm or on a surface of the engineered mateπal, with the hght- steeπng microstructures being configured to steer radiation/light in one or more particular directions

Similarly, in implementations in which hght-steeπng layer 260 is configured to collect and/or steer radiation that escapes from compliant waveguide 204, light-steeπng layer 260 may be configured to steer escaped radiation to within a range of angles such that the escaped radiation is steered towards a position at least one of the imaging sensors 208 that is substantially beneath the point of contact between compliant waveguide 204 and frustrating layer 206, as shown by arrows "A" in FIGS 2A and 2B Light-steenng layer 260 may be formed from an engineered mateπal having light-steeπng microstructures formed within or on a surface of the engineered mateπal, with the light- steeπng microstructures being configured to steer radiation/light in one or more particular directions Such light-steeπng microstructures may be adhered to or formed within or on the back surface of LCD panel 240, such that radiation/light is steered in one or more particular directions after passing through LCD panel 240 Similarly, engineered matenals having light-steeπng microstructures may be adhered to or formed within or on the back surface of other light sources such as LED devices and OLED devices Vanous implementations of such engineered matenals and light-steeπng microstructure(s) for re- directing radiation that escapes from waveguide 204 may be employed within or on the frustrating layer 206 or light-steermg layer 260

Light-steeπng layer 260 may include, in addition to or as an alternative to hght- steeπng microstructures, a difϊiiser layer The diffuser layer can be configured to collect and/or steer radiation escaping compliant waveguide 204 and incident on the hght- steeπng layer 260 toward imaging sensor 208 In particular, the diffuser layer may cause incident radiation to propagate in a direction generally beneath a point at which the radiation escapes compliant waveguide 204 or to generally spread in a broad range of directions instead of very limited or specific directions The diffuser layer may be formed of material including, but not limited to, PET, PVC, PVB, PMMA or PC The diffuser layer may have a substantially uniform thickness of about 100 microns, although other thicknesses may be used as well

In some implementations, diffuser layer can include surface diffusing structures that are formed on or withm a surface of a mateπal such as LCD panel 240 In some cases, the surface diffusing structures are formed by roughening a surface of a mateπal in LCD panel 240 For example, surface diffusing structures may be formed by roughening a surface of a glass substrate or polaπzer layer of LCD panel 240 to form a surface that diffuses radiation that has escaped from compliant waveguide 204 and is incident on LCD panel 240 Similarly, if an LED or OLED device is used in place of LCD panel 240, a surface of a mateπal in the LED or OLED device such as, for example, a glass substrate can be roughened to form a surface that diffuses radiation that has escaped from compliant waveguide 204 and is incident on LCD panel 240

The surface of components within or fixed to LCD panel 240 can be roughened using one or more methods For example, in some implementations, a roughened "master surface" can be used as a mold for forming a rough surface on the matenal on or within LCD panel 240 Initially, the master surface may be a smooth surface (e g , a smooth glass or metal surface) that is roughened using abrasives including, for example, sandpaper, sandblasting, or hard powders The roughened surface may also be created by treating the oπgmally smooth master surface with an etchant (e g , an acid) to create random pits in the smooth surface For example, clear glass may be roughened by etching the surface with hydro fluoπc acid Other methods for roughening can be used as well The roughened master surface then may be used to emboss the rough pattern mto a plastic film, such as a polaπzer of LCD panel 240 Instead of using a master surface for embossing, the mateπal withm or on LCD panel 240 may be roughened directly using the same techniques as descπbed above m some implementations, the roughened surface, whether as a part of a polaπzer, glass substrate or other component within or on LCD panel 240, has a level of average roughness (i e , the arithmetic average of a surface deviation from average depth) in the range of about 02 to 50 microns Ra In some cases, the roughened surface also has a root mean squared roughness of about 0 2 to 50 microns A level of diffusion for light incident on a roughened surface may be measured m terms of light spreading angle (i e , the approximate angular distribution of incident collimated light after it passes through the diffuser) In some implementations, diffusers with the foregoing levels of roughness have diffusion angles over approximately 160 degrees

Alternatively, or in addition to surface diffusing structures, a diffuser layer can include volume diffusing structures that are formed integrally through at least a portion of the material bulk In some implementations, the engineered microstructures may be employed withm or on a surface of the diffuser layer

In some implementations, radiation that escapes from pliable waveguide 204 due to FTIR may become trapped within LCD panel 240 (or LED device) after being received by LCD panel 240 (or LED device) In such cases, hght-steermg layer 260 may, when placed in contact with or formed on or withm a surface of LCD panel 240 (or LED device), function as a coupling layer to couple the trapped radiation out of LCD panel 240 (or LED device) In some implementations, LCD panel 240 (or LED device) can be placed in optical contact with light-steeπng layer 260 using, for example, an optical adhesive having an index of refraction substantially close in value to a bottom surface of LCD panel 240 (or LED device) and light-steeπng layer 260 to enhance out-coupling of trapped radiation In addition to adhering LCD panel 240 to hght-steermg layer 260, the presence of the optical adhesive can, m some instances, reduce reflections that would otherwise occur due to the refractive index mismatch and surface roughness at the surfaces of LCD panel 240 and light-steeπng layer 260 In some cases, the engineered microstructures which are employed on or within frustrating layer and/or light-steermg layer include diffractive optical elements (DOEs) In general, a DOE structure is a structure that includes a pattern of refractive index variations on the order of a wavelength of light and which pπmaπly diffracts incident radiation A DOE structure can be generated digitally or recorded optically as an mterference pattern between two wavefronts of coherent light hi some implementations, the patterns of refractive index variations in the DOEs may be formed by transferring an interference pattern to mateπal such that a seπes of fringes representing intensity minima and maxima of the interference pattern correspond to the patterns of refractive index vaπation For example, mterference patterns can be transferred to a recording mateπal using techniques such as interference lithography The pattern can be represented by a peπodic, random, semi-random, or mathematically complex, deterministic vaπation of refractive index or thickness across one or more different mateπals hi some cases, the fringes of the transferred interference pattern correspond to a grating structure Depending on the design and construction, a DOE structure transmits or reflects incident radiation m one or more directions DOE structures can include surface diffusing structures that are formed on or within a surface of a mateπal, or volume diffusing structures that are formed integrally through at least a portion of the mateπal bulk

DOE structures include a class of structures called holographic optical elements (HOE) that may be considered to fall within two categoπes thin hologram structures and thick (volume) hologram structures In general, thin hologram structures include surface structures or planes of refractive index vaπation that vary substantially perpendicularly to the surface on which the radiation is incident and are generally used to transmissively steer a range of wavelengths mto one or more particular directions They can be used m conjunction with a separate reflective means, such as a mirror, to operate reflectively Thick hologram structures, on the other hand, can include planes of refractive index vaπations that run substantially parallel to the surface on which radiation is incident, and generally use Bragg selectivity to reflect or transmit a narrow range of wavelengths incident at one or more specific incident angles into one or more particular directions In some implementations, the planes of refractive index vaπations in the HOEs may be formed by transferπng an interference pattern to mateπal such that a seπes of fringes representing intensity minima and maxima of the interference pattern correspond to the planes of refractive index vaπation For example, interference patterns can be transferred to a recording material using techniques such as interference lithography In some cases, the fringes of the transferred interference pattern correspond to a grating structure

Optical modeling software packages are available to facilitate the design of thin or thick hologram structures to direct radiation in a desired direction Code V® is one example of such an optical modeling software package that can be used to design thin or thick hologram structures to direct radiation in a desired direction Other optical modeling software packages also are available

Examples of frustrating layers having several different types of thin hologram structures for steeπng escaped radiation are illustrated in FIGS 3-8 The various different frustrating layers illustrated m FIGS 3-8 can be incorporated withm touch sensitive devices, such as, for example, the touch sensitive devices 200 and 270 illustrated in FIGS 2A and 2B

FIG 3 is a schematic diagram of a cross-section of a pliable waveguide 304 that includes cladding layer 305 and a frustrating layer 306 that includes a thm hologram structure 309 As illustrated in FIG 3, thm hologram structure 309 is formed on a surface of substrate 303 and comes into contact with compliant waveguide 304 Thin hologram structure 309 has a 1-bit binary (or more generally square-wave) diffraction grating profile Grating 309 may be formed from the same mateπal as frustrating layer 306 or from a different matenal Grating 309 may be formed from a series of regularly spaced structures 311 having thicknesses h and widths w that are spaced apart from one another by a distance d Furthermore, the length of structures 311 extends uniformly across the surface of frustrating layer 306 (z e , into and out of the page) The direction of radiation transmitted by grating layer 309 is a function of the periodicity, 77= w + d, of grating structures 311 and the radiation wavelength

In some cases, grating layer 309 may include a cladding layer 313 In such implementations, the cladding layer 313 protects grating structures 311 of grating layer 309 from damage and may fill the spaces between grating structures 311 Grating structures 311 and cladding layer 313 may be formed from mateπal that is transmissive to radiation having a wavelength equal to the wavelength of radiation 310 traveling through waveguide 304 If the touch sensitive device incorporates a display, grating structures 311 and cladding layer 313 also may be transparent (or at least transmissive) to the wavelengths of radiation (e g , visible light) used to generate the display The cladding 313 can be formed of a material that has a refractive index comparable to or greater than the refractive index of waveguide 304 to allow FTIR to occur upon contact with waveguide 304 In addition, cladding layer 313 can be formed to have a thickness t that is greater than thickness h of grating structures 311

Protrusions 314 maintain a small gap 312 between frustrating layer 306 and compliant waveguide 304 when an external stimulus is not present When pressure is applied by an input (not shown) to a portion of pliable waveguide 304, pliable waveguide 304 is deformed and a surface 304a of pliable waveguide 304 comes into contact with frustrating layer 306 As a result, a portion of radiation 310 traveling through pliable waveguide 304 undergoes FTIR The portion of radiation 310 which undergoes FTIR then escapes from compliant waveguide 304 in multiple directions

As illustrated m FIG 3, transmissive thm hologram structure 309 steers radiation that escapes from pliable waveguide 304 m a direction generally perpendicular to a surface of frustrating layer 306 that is in contact with waveguide 304, so that the escaped radiation is aligned with the point of contact between compliant waveguide 304 and frustrating layer 306

Although FIG 3 illustrates thm hologram structure 309 being formed on a surface 306a of frustrating layer 306 that comes into contact with waveguide 304, a thin hologram structure additionally or alternatively can be formed on a surface of a frustrating layer that does not come into contact with waveguide 304 Accordingly, in some implementations, interference between visible light, emitted from an LCD panel or display source, and the hologram structure can be reduced For example, FIG 4 is a schematic diagram of a cross-section of a pliable waveguide 404 that includes cladding layer 405 and a frustrating layer 406 that includes a transmissive diffraction grating 409 formed on a surface 406b of frustrating layer 406 that is opposite from the surface 406a that makes contact with pliable waveguide 404 Similar to grating 309, grating 409 may include a seπes of regularly spaced grating structures 411 A portion of radiation that escapes from waveguide 404 travels through frustrating layer 406 and then is re-directed by gratmg 409 m a direction that is generally perpendicular to a surface 406a of frustrating layer 406 and that is aligned with the point of contact between compliant waveguide 404 and frustrating layer 406 Other variations of thin hologram structures having surface-relief profiles also may be incorporated withm or added to a frustrating layer to steer radiation in a desired direction For example, FIG 5 shows a grating structure 509 formed on a surface of a frustrating layer 506 m which the depth h of the surface-relief does not extend all the way to the surface of frustrating layer 506 That is to say, gratmg structure 509 is offset from a surface of frustrating layer 509 As in previous examples, at least a portion of radiation propagating by TIR in waveguide 504 may escape when waveguide 504 is depressed so as to come into contact with frustrating layer 509 FIG 6 shows another example of a frustrating layer 606 which can be used to frustrate TIR in a waveguide 604 Frustrating layer 606 includes a grating layer 609 having a multi-level or multiple-bit modulated binary profile As illustrated m FIG 6, the multiple-bit modulated binary profile includes ndges 611 and grooves 613 separated by shelves 615

In addition to merely steering radiation in a desired direction, thm film hologram structures also can be used to improve the efficiency with which radiation is transmitted in a particular direction For example, FIG 7 shows a frustrating layer 706 for frustrating TIR in a waveguide 704, in which a blazed grating structure 709 is formed on a surface of frustrating layer 706 As illustrated in FIG 7, the grooves of the diffraction grating 709 form a tπangle profile with a blaze angle, α The blaze angle α is a measure of the blaze slope with respect to a normal to the plane on which the blaze structure 709 is formed Changing the spacing between the blazed ndges determines the output direction (the separation between diffractive orders) of the transmitted radiation while changing the blaze angle α affects the efficiency in which incident radiation is transmitted in a particular diffractive order

Grating structures formed within or on frustrating layers can have other profile shapes besides binary and blazed profiles For example, gratmg structures can be formed to have a sinusoidal profile (i e , symmetrical, sine-wave shaped grooves) or semi- smusoidal (i e , symmetrical, half sme-wave shaped grooves) profile A wide range of profiles can be fabπcated using diamond-turning machines to generate master structures, which can then be replicated Holographic optical elements can be considered as a generalized case of gratings, where the structure can be peπodic, aperiodic, random or noisy, or some combination of these In addition, they can also vary continuously or discretely (piecewise) across their aperture

Although the thm hologram structures illustrated in FIGS 3-7 are peπodic, thin film holograms having apeπodic grating structures also can be formed withm or on a frustrating layer to control radiation received by the frustrating layer In some cases, the thm film hologram structure compπses a diffraction pattern in which fringes of the diffraction pattern are arranged m an apenodic pattern The fringes of the diffraction pattern may correspond to regions in which an intensity of light transmitted or reflected by the diffraction pattern is a minima or maxima Alternatively, or in addition, the fringes may correspond to planes of refractive index variation Such non-periodic hologram structures may further increase efficiency and/or wavelength selectivity In some implementations, an aperiodic hologram structure designed to transmit a large portion of escaped radiation in a particular direction may include profiles that are semi-random or random For example, FIG 8 shows a frustrating layer 806 for frustrating TIR in a waveguide 804, in which frustrating layer 806 includes a thm hologram structure 809 having a random/aperiodic profile 809a As illustrated in FIG 8, the height of structure 809 varies over frustrating layer 806, thus acting as a difϊuser or noise grating with air or other cladding in which incident radiation is exposed to a variation in refractive index Furthermore, a semi-random difruser pattern can be designed to diffract the light into a desired range of angles Two examples of such designed diffusers are the Light Shaping Diffusers® made by Luminit™ Corporation of Torrence, CA and Tailored Microdifϊusers® by Wavefront Technology of Paramount, CA

The thm firm hologram structures descπbed in connection with FIGS 3-8 can be formed from the same or a different mateπal than the frustrating layer For example, diffusers, thin holograms, and gratings can be embossed onto a substrate formed of PET, PMMA or PC The embossing shims are made from diamond-turned, digitally or optically generated masters Another common means of replication is to photo-cure impressions of the structures in resin on a PET or other substrate mateπal Additionally or alternatively, in some implementations, a cladding layer (not shown) having approximately uniform thickness throughout may be disposed on a surface of the than film hologram structures descnbed m connection with FIGS 3-8 The cladding layer may be formed from a material that is transparent (or at least transmissive) to visible light emitted by the display source and can protect the thin film hologram structures from damage

As discussed above, thick hologram structures are another type of DOE structure that can be formed within or on a frustrating layer to steer radiation that escapes a waveguide due to FTIR when the waveguide comes into contact with the frustrating layer One characteristic of thick holograms is that the hologram is made up of layers corresponding to a peπodic variation of transmittance or refractive index that is, to at least some extent, parallel to the hologram surface on which the radiation is incident In thick holograms, light is transmitted by means of Bragg diffraction, i e , light havmg the correct wavelength and beam shape (e g , beam direction, wavefront profile) will be preferentially transmitted by the thick hologram whereas other light will be reflected or absorbed Thus, in contrast to thin hologram structures, a thick hologram structure serves to transmit a relatively small range of wavelengths across a narrow range of incident angles into a relatively small range of output angles For example, radiation having a wavelength of 850 nm undergoing FTIR may be transmitted by a thick hologram structure towards a normal of the waveguide in which the radiation travels, whereas visible light can travel unaffected through the thick hologram structure

Thick hologram structures lead to generally higher diffraction efficiency than in thm hologram structures Diffraction efficiency corresponds to the amount of light diffracted by the hologram relative to the total amount of light incident on the hologram Thick holograms can be replicated from optically generated masters into photopolymer by contact copying

FIG 9 is a schematic diagram of a cross-section of an example frustrating layer 906 for frustrating TIR m a waveguide 904, in which the frustrating layer 906 includes a thick hologram structure 909 Thick hologram structure 909 includes layers of mateπal having a variation m refractive index Due to the refractive index variation, the layers of mateπal form a seπes of fringe planes 930 Fringe planes 930 control either the reflection or transmission of incident radiation m a manner similar to a multilayer dielectric film The material and dimensions of the layers of refractive index modulated material in a thick hologram structure are configured to transmit radiation received by frustrating layer 906 within a particular range of angles Example mateπals for a thick hologram structure include photopolymer and bleached silver hahde In some implementations, thick hologram structures are formed integrally with frustrating layer 906, i e , thick hologram structures, together with frustrating layer 906, form a single mass of seamless, contiguous material For example, as illustrated in FIG 9, thick hologram structure 909 occupies the entire thickness of frustrating layer 906 In some cases, however, thick hologram 909 can be formed separate from and on a surface of frustrating layer 909 instead of being incorporated within frustrating layer 909

FIGS 3-9 illustrate different hologram structures for steering radiation that escapes from the pliable waveguide As illustrated in FIGS 3-9, these hologram structures are formed either on the surface of or within the volume of a frustrating layer As an alternative (or in addition) to forming these hologram structures on the surface of or withm the volume of the frustrating layer, each of these hologram structures may be formed on the bottom surface of an LCD layer (similarly to how light-steering layer 260 is formed on the bottom surface of LCD layer 240 in FIG 2B), within the volume of a diffusive layer (e g , hght-steeπng layer 260 in FIG 2B) that is adhered to the bottom surface of an LCD layer (e g , LCD layer 240 in FIG 2B), or on the bottom surface of a diffusive layer (e g , light-steeπng layer 260 in FIG 2B) Locating the hologram structures beneath the LCD layer may result m less interference with output images generated by the LCD layer than locating the hologram structures on a surface of or within the frustrating layer because, when the hologram structures are located beneath the LCD layer, they are not m the optical path between the LCD layer and a viewer

FIG 1OA is a schematic cross-sectional diagram of an example of a frustrating layer 1006, a hologram structure 1009, and a LCD layer 1040 for incorporation within a touch sensitive device Hologram structure 1009 is formed on a top surface of an LCD panel 1040 and is configured to re-direct radiation towards an imaging sensor Similar to hologram structure 909 shown in FIG 9, structure 1009 is a thick hologram and includes layers of mateπal having a variation in refractive index Due to the refractive index variation, the layers of mateπal form a seπes of fringe planes 1030 Other diffractive optical elements may be formed on LCD panel 1040, as well

In contrast to the implementation illustrated in FIG 1OA, in some implementations, thick hologram structure 1009 is formed on a bottom surface of LCD panel 1040 (i e , on a surface of LCD panel 1040 that is opposite from frustrating layer 1006), as illustrated m FIG 1OB Locating the hologram structure 1009 beneath LCD panel 1040 may reduce interference with output images emitted by LCD panel 1040 As shown in the examples of FIGS 10A-10B, radiation undergoing TIR in waveguide 1004 having cladding layer 1005 is frustrated upon contact with frustrating layer 1006 The frustrated radiation propagates through frustrating layer 1006 Upon reaching hologram structure 1009 bonded to either the front or the rear surface of LCD panel 1040, the radiation then is steered by the hologram structure 1009 within a narrow range of angles that are substantially orthogonal to the plane 1006a of frustrating layer 1006 Accordingly, the radiation then proceeds towards a position on an imaging sensor that is substantially beneath the point of contact between compliant waveguide 1004 and frustrating layer 1006

When frustrating layer 1006 is laminated to LCD panel 1040, for example, as illustrated in FIG 1OB, radiation that escapes from pliable waveguide 1004 due to FTIR may become trapped within LCD panel 1040 (e g , by TIR) after being received by LCD panel 1040 However, when hologram structure 1009 is placed in optical contact with a bottom surface of LCD panel 1040 as shown in FIG 1OB, hologram structure 1009 can, in some implementations, serve to couple the trapped radiation out of LCD panel 1040 Alternatively, if hologram structure 1009 is on a top surface of LCD panel 1040, a coupling layer may be placed in contact with the bottom surface of LCD panel 1040 to couple trapped radiation out of LCD panel 1040 In some implementations, hologram structure 1009 on a top surface of LCD panel 1040 is configured to steer radiation that escapes from pliable waveguide 1004 along angles that are less than a cntical angle of LCD panel 1040, as measured with respect to a normal to a bottom surface of LCD panel 1040 Accordingly, the radiation can escape LCD panel 1040 without becoming trapped In such implementations, a coupling layer such as, for example, a PET based diffiiser, may still be placed in contact with LCD panel 1040 to supplement the light steenng of hologram structure 1009

In both examples illustrated in FIGS 10A-10B, hologram structure 1009 can be bonded to LCD panel 1040 using optical adhesive In addition to adheπng LCD panel 1040 to hologram structure 1009, the presence of the optical adhesive can, in some instances, reduce reflections that would otherwise occur due to the refractive index mismatch (which may occur, for example, at an air gap at the interface between LCD panel 1040 and hologram structure 1009) and surface roughness at the surfaces of LCD panel 1040 and the hologram structure 1009 Similarly, hologram structure 1009 and/or LCD panel 1040 can be bonded to frustrating layer 1006, depending on the configuration employed By reducing the amount of light reflected back toward a viewer, the image contrast provided by touch sensitive device can be improved As an alternative to bonding hologram structure 1009 to LCD panel 1040, m some implementations, hologram structure 1009 may be formed as a separate layer that is not in optical and/or physical contact with the frustrating layer 1006 or the LCD panel 1040

By dividing the thick hologram into a number of sub-holograms, each of which directs light of the desired wavelength into a different direction, it is possible to efficiently "position encode" the light impinging upon the frustrating layer according to its position at the point of incidence on the hologram Thus, light incident from a given point of contact can be directed toward a camera or into a waveguide with a direction corresponding to the point of contact

FIG 11 is a schematic cross-sectional diagram of an example frustrating layer 1106 for incorporation within a touch sensitive device As shown in the example, a thick hologram structure 1109 is positioned on a surface of frustrating layer 1106 and hologram structure 1109 is divided into multiple sub-holograms 1119 Each sub-hologram 1119 can steer incident radiation that escapes from waveguide 1104, due to FTIR, m a direction (indicated by dashed arrows) towards a center of the device where, for example, an imaging sensor 1108 may be located Accordingly, each sub-hologram 1119 can be configured to a have a different respective angle of transmission for a particular wavelength of radiation incident on its surface As an alternative (or in addition) to forming hologram structure 1109 (including sub-holograms 1119) on the bottom surface of frustrating layer 1106, m some implementations, hologram structure 1109 (including sub-holograms 1119) may be formed on the bottom surface of an LCD layer (similarly to how hght-steermg layer 260 is formed on the bottom surface of LCD layer 240 in FIG 2B) or on the bottom surface of a diffusive layer (e g , hght-steeπng layer 260 in FIG 2B) that is adhered to the bottom surface of an LCD layer (e g , LCD layer 240 in FIG 2B)

In addition to, or as an alternative to, reflective layers and DOE structures, refractive optical elements (ROE) also may be employed as engineered microstructures on or within frustrating layer and/or hght-steeπng layer to re-direct radiation that escapes from the waveguide when the frustrating layer contacts the waveguide In general, ROE structures include a seπes of elements that are significantly larger than the wavelength(s) of incident radiation and direct radiation primarily by refraction In some cases, the relatively small amount of diffraction that can occur in ROE structures may compensate for the dispersive properties of the mateπal which forms the frustrating layer Depending on the design and construction, an ROE structure can re-direct incident radiation in one or more directions

FIG 12Ais a schematic cross-sectional diagram of an example frustrating layer 1206 for frustrating TIR in a waveguide 1204 As shown m the example of FIG 12 A, an ROE structure 1209, such as, for example, a Fresnel pπsm array that includes individual Fresnel pπsm elements 1211 is formed on a surface of frustrating layer 1206 Fresnel pπsm elements 1211 are similar to the blazed grating structures illustrated in FIG 7, except that elements 1211 are formed to have dimensions significantly greater than the wavelength of radiation for which re-direction is desired For example, in the present implementation, the pitch between pnsm elements 1211 can be on the order of tens of microns to millimeters in size The πdges of the Fresnel pπsm elements 1211 can form a tπangle profile with an angle, β, that is a measure of the pπsm slope with respect to a normal to the plane on which the elements 1211 are formed Changing β can alter the direction of radiation refracted from the structure 1209 for a particular incident angle Although the example of FIG 12A illustrates a Fresnel pπsm structure having a blazed profile, other profiles including, but not limited to, sinusoidal or saw-tooth shapes, also can be implemented

In some implementations, an encapsulant 1213 may fill the spacing between the Fresnel elements 1211 or other ROE structures The encapsulant 1213 can be formed of transparent (or at least transmissive) mateπals including, for example, BPMA (p- bromophenacyl methacrylate), polycarbonate, polystyrene, silicones, as well as other resms In certain implementations, the encapsulant matenal may be selected to have a high or low refractive index In these implementations, the index of refraction may be sufficiently different from the ROE itself such that refraction can occur Additionally or alternatively, in some implementations, a cladding layer (not shown) having approximately uniform thickness throughout may be disposed on a surface of the prism elements 1211 or on the encapsulant 1213 The cladding layer may be formed of a matenal that is transparent (or at least transmissive) to visible light emitted by the display source and can protect the Fresnel elements 1211 from damage As an alternative (or in addition) to forming ROE structure 1209 (e g , Fresnel pπsm elements 1211 ) on the bottom surface of frustrating layer 1206 as illustrated in FIG 12A, in some implementations, ROE structure 1209 (e g , Fresnel pπsm elements 1211) may be formed on the bottom surface of an LCD layer (similarly to how hght-steeπng layer 260 is formed on the bottom surface of LCD layer 240 in FIG 2B) or on the bottom surface of a diffusive layer (e g , hght-steenng layer 260 in FIG 2B) that is adhered to the bottom surface of an LCD layer (e g , LCD layer 240 in FIG 2B)

FIG 12B illustrates a schematic cross-sectional diagram of an example frustrating layer 1206 that includes an ROE structure 1209, in which the ROE structure 1209 has a truncated pyramid profile That is, ROE structure 1209 includes a seπes of truncated pyramid structures 1221 separated by gaps 1223 In the present implementation, air fills the gap regions, although gaps 1223 may be filled with other matenal having a refractive index lower than the matenal that forms pyramid structures 1221 Radiation (indicated by arrow "B") that escapes a waveguide 1204, due to FTIR, proceeds through frustrating layer 1206 and into the ROE structure 1209 In some cases, the ROE structure 1209 and frustrating layer 1206 have comparable refractive indices such that there is minimal refraction of the radiation as it passes into ROE structure 1209 The radiation then is incident on one of the sloped surfaces of pyramid structures 1221 Depending on the incident angle, the incident radiation can reflect one or more times off the surface of structure 1221 due to total internal reflection and return (as indicated by arrow "D") back toward the device As an alternative (or m addition) to forming ROE structure 1209 on the bottom surface of frustrating layer 1206 as illustrated m FIG 12B, in some implementations, ROE structure 1209 may be formed on the bottom surface of an LCD layer (similarly to how hght-steeπng layer 260 is formed on the bottom surface of LCD layer 240 in FIG 2B) or on the bottom surface of a diffusive layer (e g , hght-steenng layer 260 m FIG 2B) that is adhered to the bottom surface of an LCD layer (e g , LCD layer 240 in FIG 2B)

ROE structures can be formed integrally with the frustrating layer (or LCD), i e , as a single mass of seamless contiguous material or, alternatively, separate from the frustrating layer (or LCD layer) hi some cases, ROE structures can be laminated to the frustrating layer (or LCD layer) or adhered to the frustrating layer using an adhesive ROE structures can be formed using mateπals that include, but are not limited to acrylic, PET, PMMA, TPU or PC substrate Examples of pre-fabncated ROE structures include Vikuiti™ Thm Brightness Enhancement Films (TBEF) and Vikuiti™ Transmissive Right Angle Films (TRAF), both of which can be purchased from 3M (St Paul, MN)

In some implementations, a frustrating layer can be formed both above and beneath the pliable waveguide so that FTIR can be induced at a minimum of two separate regions on the pliable waveguide when an input applies pressure to the device By increasing the number of regions along the waveguide where FTIR occurs, the amount of radiation that escapes can be increased If the additional radiation is detected by an image sensor, the device sensitivity can be increased FIG 13 is a schematic cross-sectional diagram of example frustrating layers 1306 and 1307 for incorporation within a touch sensitive device Frustrating layer 1306 is positioned beneath waveguide 1304 whereas pliable frustrating layer 1307 is positioned above waveguide 1304

In some implementations, protrusions 1315 may be formed on or as part of pliable frustrating layer 1307 to maintain a gap between the pliable waveguide 1304 and the pliable frustrating layer 1307 In such implementations, protrusions 1315 can be formed integrally with pliable frustrating layer 1304, ; e , protrusions 1315, together with pliable frustrating layer 1307, form a single mass of seamless, contiguous mateπal In some implementations, a micro-roughness layer having randomly (or semi-randomly) spaced protrusions maybe formed on the surface of the pliable frustrating layer 1307, in which the micro-roughness functions substantially as protrusions 1315 hi some cases, protrusions 1315 are formed from matenal distinct from pliable frustrating layer 1307 and/or pliable waveguide 1304 For example, glass spacers could be used to separate an acrylic waveguide from a polycarbonate frustrating layer The spacing between protrusions 1315 can be random, pseudo-random or peπodic When input pressure is applied by an object (not shown) to the device, the pliable frustrating layer 1307 is deformed such that it comes into contact with pliable waveguide 1304 hi some cases, further application of pressure to the device will also cause waveguide 1304 to deform such that waveguide 1304 comes into contact with frustrating layer 1306 while maintaining contact with pliable frustrating layer 1307 As a result, at least two regions of contact may be made with the pliable waveguide 1304 that induce FTIR of radiation 1310 that travels through waveguide 1304

At a first region of contact 1380, between waveguide 1304 and frustrating layer 1306, radiation 1310 escapes due to FTIR and travels m a direction toward frustrating layer 1306 At a second region of contact 1382, between waveguide 1304 and pliable frustrating layer 1307, radiation 1310 also escapes due to FTIR and travels in a direction toward pliable frustrating layer 1307 Both frustrating layer 1306 and frustrating layer 1307 can include a DOE structure and/or a ROE structure to re-direct the radiation towards an imaging sensor of the touch sensitive device For example, frustrating layer 1306 includes a first thick hologram structure 1309 disposed on its bottom surface to re- direct radiation that escapes from the first region of contact 1380, in which the re-directed ray is indicated by arrow "A " Similarly, pliable frustrating layer 1307 includes a second thick hologram structure 1329 disposed on its top surface to re-direct radiation that escapes from the second region of contact 1382, in which the re-directed ray is indicated by arrow "B " Ray B then is re-directed again by first thick hologram structure 1309 after passing through waveguide 1304 and frustrating layer 1306 Because light that is redirected by thick hologram structure 1329 eventually may be redirected again by thick hologram structure 1309, thick hologram structure 1329 maybe designed intentionally to account for any change in angle to light that it redirects (e g , arrow "B" m FIG 13) caused by thick hologram structure 1309 In some cases, the DOE and/or ROE structures can be designed to compensate for refraction and/or diffraction that may occur with other structures in the touch-sensitive device

Although rays A and B, as shown in FIG 13, are laterally separated due to the different positions along waveguide 1304 from which they escape, it is possible, in some implementations, to determine that the rays are a result of a single point of contact with the touch-sensitive device For example, in some cases, the separation between rays A and B is small enough that both rays are incident on the same imaging sensor such that the two rays are indistinguishable to the imaging sensor Alternatively, if the rays are incident on separate imaging sensors, a suitable computer (not shown) or other electronic device capable of handling image-processing operations can perform averaging algorithms to identify an averaged location between the separate rays that corresponds to the single point of contact

As an alternative (or in addition) to forming DOE and/or ROE structure 1309 on the bottom surface of frustrating layer 1306 as illustrated in FIG 13, in some implementations, ROE structure 1309 may be formed on the bottom surface of an LCD layer (similarly to how hght-steeπng layer 260 is formed on the bottom surface of LCD layer 240 in FIG 2B) or on the bottom surface of a diffusive layer (e g , hght-steermg layer 260 in FIG 2B) that is adhered to the bottom surface of an LCD layer (e g , LCD layer 240 in FIG 2B)

As an alternative or in addition to the foregoing implementations, the touch sensitive device may include a screen projection layer onto which light from a display device is imaged For example, FIG 14 is a schematic cross-section diagram of a touch- sensitive device 1400 that includes a pliable waveguide layer 1404 through which radiation 1410 is traveling by TIR, a frustrating layer 1406, a display device 1430 and a screen projection layer 1490 Screen projection layer 1490 may include a diffuser layer (e g , surface diffusing structures or volumetric diffusing structures), DOE structures or ROE structures (e g , a fresnel lens) Screen projection layer 1490 may be formed of materials including, but not limited to glass, PMMA, PET, PC, PVC, TPU, or TAC In some implementations, touch sensitive device 1400 also may include, but does not require, a hght-steenng layer 1460 adjacent to screen projection layer 1490 for steeπng or redirecting radiation that has escaped from pliable waveguide 1404 due to FTIR upon contact with frustrating layer 1406 Light-steermg layer 1460 may include DOE structures or ROE structures (e g , a fresnel lens) Light-steeπng layer 1460 may be formed of materials including, but not limited to glass, PMMA, PET, PC, PVC, TPU, or TAC Both light-steeπng layer 1460 and screen projection layer 1490 may be films such as Alpha and Beta screens, which are commercially available from DNP Denmark AS As shown in the example of FIG 14, visible light (indicated by arrow "B") emitted from display device 1430 (e g , a projection source such as a video projector) is emitted towards a top surface of touch sensitive device 1400 (i e , toward frustrating layer 1406 and pliable waveguide 1404) and is incident on hght-steenng layer 1460 Due to the diffusive properties of screen projection layer 1490, the visible light is diffused and imaged onto screen projection layer 1490 forming an image visible to a user viewing device 1400 hi some cases, the light-steeπng structures, which are incorporated in hght- steenng layer 1460, maybe configured to redirect radiation (e g , IR radiation) that has escaped from waveguide 1404 due to FTER upon contact with frustrating layer 1406 For example, as shown in FIQ 14, radiation (indicated by arrow "A") which escapes waveguide 1404 passes through screen projection layer 1490 and is incident on hght- steenng layer 1460 Light-steenng layer 1460, which includes hght-steenng structures, then redirects the incident radiation toward one or more imaging sensors 1408

Alternatively, hght-steenng layer 1460 may include two alternative types of hght-steenng structures a first set of hght-steenng structures configured to diffuse visible light and a second set of hght-steenng structures configured to redirect the radiation which has escaped from waveguide 1404 hi some implementations, hght- steenng layer 1460 does not include hght-steenng structures configured to redirect radiation that has escaped waveguide 1404 Instead, such hght-steenng structures may be formed on or within frustrating layer 1406

Alternatively, in implementations in which hght-steenng layer 1460 is not included in the touch-sensitive device, hght-steenng structures employed on or within screen projection layer 1490 also may be configured to diffuse radiation (e g , IR radiation) that has escaped from waveguide 1404 due to FTIR upon contact with frustrating layer 1406 For example, screen projection layer 1490 may include two alternative types of light-steeπng structures a first set of light-steermg structures configured to diffuse visible light and a second set of hght-steenng structures configured to redirect the radiation which has escaped from waveguide 1404

In some implementations, screen projection layer 1490 and light-steeπng layer 1460 are bonded or laminated together The bondmg/lamination can be performed using an adhesive, such as an optical adhesive, to provide optical contact between screen projection layer 1490 and light-steeπng layer 1460 Alternatively, or in addition, screen projection layer 1490 may be bonded to frustrating layer 1406 using an adhesive such as, for example, an optical adhesive In some cases, an air gap may be present between frustrating layer 1406 and screen projection layer 1490 and/or between screen projection layer 1490 and light-steeπng layer 1460

A number of implementations have been descnbed Nevertheless, various modifications may be made For example, although many of the implementations disclosed herein are descnbed as employing LCD technology to generate output images, OLED or LED technology could be substituted for the LCD technology employed in each of these disclosed implementations to generate the output images OLEDs and LEDs both generally are emissive elements Therefore, in implementations that employ OLED or LED technology to generate output images, there may be no need for a backlight Accordingly, other implementations are within the scope of the following claims