AU2007216782A1 - Optical elements for waveguide-based optical touch input devices - Google Patents

Description

-1i- OPTICAL ELEMENTS FOR WAVEGUIDE-BASED OPTICAL TOUCH INPUT DEVICES FIELD OF THE INVENTION 00 5 The invention relates to a simplified construction for waveguide-based optical ID systems and in particular waveguide-based optical touch input devices.

BACKGROUND TO THE INVENTION SAny discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.

Touch input devices or sensors for computers and other consumer electronics devices such as mobile phones, personal digital assistants (PDAs) and hand-held games are highly desirable due to their extreme ease of use. Touch input devices may include a display underlying the input area, in which case they are commonly known as 'touch screens'. However other touch input devices, often known as 'touch panels', do not have a display. In the past, a variety of approaches have been used to provide touch input devices. The most common approach uses a flexible resistive overlay, although the overlay is easily damaged, can cause glare problems, and tends to dim an underlying display, requiring excess power usage to compensate for such dimming. Resistive devices can also be sensitive to humidity, and the cost and drive power consumption of the resistive overlay scale quadratically with perimeter. Another approach is capacitive touch, which also requires an overlay. In this case the overlay is generally more durable, but the glare and dimming problems remain.

In yet another common approach, a matrix of light beams (usually infrared) is established in front of a display, with a touch event detected by the interruption of one or more of the beams. Such "optical" touch input devices have long been known (US 3,478,220; US 3,673,327), with the beams generated by arrays of optical sources such as LEDs or VCSELs and detected by corresponding arrays of detectors (such as phototransistors or photodiodes). This type of optical touch input device has the advantage of being overlay-free and can function in a variety of ambient light conditions (US 4,988,983), but has a major cost problem in that it requires a large number of source -2- Sand detector components, as well as supporting electronics. Since the spatial resolution of such a system depends on the number of sources and detectors, this component cost increases with display size and resolution.

US Patent Nos. 5,914,709, 6,181,842 and 6,351,260, and US Patent Application Nos. 2002/0088930 Al and 2004/0201579 Al, each of which is incorporated herein by ,1reference in its entirety, disclose an improved type of optical touch input device, where 00 r- waveguides are used to distribute and collect the matrix of light beams. As discussed below with reference to Figure 1, this approach requires only a single optical source and a single multi-element detector (for example a linear CCD array or a digital camera 10 chip), representing a substantial cost reduction.

In this optical touch input device, an array 20 of integrated optical waveguides ('transmit' waveguides) 10 conduct light from a single optical source 11 to integrated inplane lenses 16 that collimate the light in the plane of a display/input area 13 and launch an array of light beams 12 across that display/input area 13. The light is collected by a second array 21 of integrated in-plane lenses 17 and integrated optical waveguides ('receive' waveguides) 14 at the other side of the display/input area, and conducted to a position-sensitive multi-element) detector 15. A touch event by a finger or stylus) cuts one or more of the beams of light and is detected as a shadow, with position determined from the particular beam(s) blocked by the touching object. That is, the position of any physical blockage can be identified in each dimension, enabling user feedback to be entered into the device. Preferably, the device also includes external vertical collimating lenses (VCLs) 111, 112 adjacent to the integrated in-plane lenses 16, 17 on each side of the input area 13, to collimate the light beams 12 in the direction perpendicular to the plane of the input area.

As shown in Figure 1, the touch input devices are usually two dimensional and rectangular, with a two axis Y) array 20 of transmit waveguides 10 along adjacent sides of the input area 13, and a corresponding two axis array 21 of receive waveguides 14 along the other two sides. As part of the transmit side, in one embodiment a single optical source 11 (such as an LED or a vertical cavity surface emitting laser (VCSEL)) launches light via some form of optical power splitter 18 into a plurality of waveguides that form the X and Y axes of the transmit array 20. The X and Y transmit waveguides are usually fabricated on an L shaped substrate 19, and likewise for the X and Y receive waveguides, so that a single source and a single position-sensitive detector can be used -3- 0 0 to cover both X and Y dimensions. However in alternative embodiments, a separate source and/or detector may be used for each of the X and Y dimensions. For simplicity, C Figure 1 only shows four waveguides per side of the input area 13; in actual touch input devices there will generally be sufficient waveguides for substantial coverage of the input area.

In the type of optical touch screen sensor described above, each "receive" rwaveguide 14 is in optical communication with at least one individual element of the c, multi-element detector 15. It will be appreciated that for this system to accurately o determine the position of a touch event, it is crucial that the signal from each transmit 0 10 waveguide 10 be faithfully guided to each receive waveguide 14 and subsequently to the multi-element detector Generally, the transmit waveguides 10, optical power splitter 18 and in-plane lenses 16 are fabricated together on a substrate 19 as an integrated whole or "transmit array" 20 by any suitable technique such as mask-based photolithography. Similar comments apply to the "receive array" 21 comprising receive waveguides 14 and inplane lenses 17. VCLs 111 and 112 have cylindrical curvature in the vertical plane, and are unlikely to be formed in the same process as the arrays 20 and 21: those skilled in the art will appreciate that it is extremely difficult to reliably fabricate structures with vertical curvature via photolithographic techniques. Accordingly, vertical collimation is generally provided by external VCLs 111 and 112, fabricated for example by injection moulding. In this case, precise alignment of the VCLs with the waveguide arrays 20 and 21 on both the transmit and receive sides is essential, as a small error in alignment will significantly affect the reliability of signal transmission from the transmit side to the receive side, thereby degrading the ability of the device to determine a touch event.

Similarly, the VCLs will have to be fabricated to a precise shape, which may be beyond the accuracy of injection moulding. In another problem, warping or flexing of the display will disrupt the relative positioning of the transmit and receive arrays, again degrading the ability of the device to determine a touch event.

It is an object of the present invention to ameliorate or at least provide a commercial alternative to the prior art and, at least in the preferred embodiments, improve the performance of optical touch input devices.

-4- DISCLOSURE OF THE INVENTION Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".

,In a first aspect, the present invention provides a method for transmitting an 0 r optical signal between a transmit waveguide array and a receive waveguide array of a touch input device, said device having an input area for receiving user input, said method comprising: providing an optical source; coupling an optical signal from said optical source into said transmit waveguide array; allowing said optical signal emanating from said transmit waveguide array to diverge with a first divergence angle in a direction substantially perpendicular to said input area as it propagates in a substantially unrestricted fashion across said input area towards said receive waveguide array; and setting the power of said optical source such that in the absence of a touch event, a minimum predetermined quantity of said optical signal is captured by said receive waveguide array.

As discussed above, there are difficulties with conventional optical touch systems that use external vertical collimating lenses. Not only are such lenses difficult to produce, their use causes alignment difficulties between the lenses, transmit waveguides and receive waveguides.

The method proposed allows the optical signal emanating from the transmit waveguides to diverge in effectively unrestricted fashion in the vertical plane i.e.

perpendicular to the input area. This divergence is balanced with the power of the signal such that the receive waveguides receive sufficient signal i.e. a minimum predetermined quantity, to confirm reliably the lack of a touch event.

When a touch event occurs the receive waveguide array receives a substantially reduced or zero signal. When there is no touch event the receive waveguide array should receive sufficient quantity of signal to determine the absence of such an event.

In a preferred embodiment there are no components, optical or otherwise between the transmit and waveguide arrays, with the possible exception of a protective 'window' in the bezel enclosing the transmit and receive arrays. This window, if present, is preferably opaque to ambient light, ie light at wavelengths removed from that Sof the signal light. Such features are well known in the art of optical touch input devices.

In another embodiment, at least one aperture means is provided between the transmit waveguide array and receive waveguide array to restrict passage across the input area of at least a portion of the signal not impinging directly on the receive OC) waveguide array.

rP Preferably the aperture means is adapted to restrict the field of view of the receive waveguide array.

In another embodiment, the height of the transmit waveguide array may be 10 controlled to alter the divergence angle of the signal across the input area.

In yet a further embodiment, a weakly converging lens means may be provided between the transmit waveguide array and receive waveguide array, said lens reducing the divergence angle of the optical signal relative to the signal leaving the transmit waveguide array, with the proviso that the optical signal continues to diverge (in the vertical direction) after passing through the lens.

In a second aspect, the present invention provides an optical transmission system for transmitting an optical signal between a transmit waveguide array and a receive waveguide array of a touch input device, said device having an input area for receiving user input, wherein an optical signal from an optical source is coupled into and propagates through said transmit waveguide array, then allowed to diverge in a direction substantially perpendicular to said input area as it propagates in a substantially unrestricted fashion across said input area towards said receive waveguide array, without striking any vertical collimation optical componentry between said transmit waveguide array and said receive waveguide array.

DESCRIPTION OF THE DRAWINGS The present invention will now be described by way of example only with reference to the accompanying figures in which: Figure 1 is a diagrammatic plan view of a prior art touch input device.

Figures 2 and 3 are cross sectional side views through the device of Figure 1.

Figures 4-6 are similar cross sectional side views showing first, second and third embodiments of the present invention.

Figures 7A-7C illustrate the operation of various types of simple lenses.

-6- Figures 8A-8B are cross sectional side views showing details of the waveguide construction that may cause asymmetric divergence of the optical signal.

BEST MODE FOR CARRYING OUT THE INVENTION Referring firstly to Figures 2 and 3 and the coordinate system 23 illustrated ,1therein, these drawings show side views of an input device in the form of a prior art r touch input device with a transmit waveguide array 20 and a receive waveguide array 21. To reduce divergence and loss of power of the output signal 22 emanating from the transmit waveguide array 20, a vertical collimating lens (VCL) 111 is provided to 10 collimate and direct one or more light beams 12 towards a receive waveguide array 21.

A VCL 112 is also provided adjacent to the receive waveguide array to focus and direct the one or more light beams 12 into the receive waveguides of the receive waveguide array 21. As would be appreciated by persons skilled in the art, the construction and positioning of the VCLs 111 and 112 is vital to ensure reliable guiding of the light beams 12 from the transmit waveguide array 20 to the receive waveguide array 21, as shown in the 'ideal' case of Figure 2.

An example ofmisalignment between a VCL and a waveguide array, and its consequences, can be seen in Figure 3. In this instance a transmit waveguide array and a VCL 111 are misaligned in the z-direction such that a light beam 12 is misdirected and does not impinge at all on a receive waveguide array 21. It will be appreciated that since the VCL 111 and transmit waveguide array 20 have considerable length in the xdirection, equal to the length of the respective side of the input area, it is also vital to precisely orient the two components in terms of angle. These requirements of precise translational and rotation alignments present difficulties during assembly of a touch input device, especially if it is to be used in an inexpensive consumer electronics device.

Further, it is also necessary to fabricate the VCLs with a high degree of precision, which may be beyond the capability of inexpensive injection moulding or extrusion techniques.

Finally, even if the various components can be manufactured and assembled at cost with sufficient precision, the touch input device will still be vulnerable to warping, say by mechanical force or thermal expansion, that would move a receive waveguide array 21 relative to a transmit waveguide array 20. Mechanical warping or flexing may be a particular problem for large or flexible displays. Note that since the VCL 111 and transmit waveguide array 20 are generally mounted on a common base, and likewise for -7- Sthe VCL 112 and receive waveguide array 21, the alignment between each VCL and its respective waveguide array is unlikely to be affected by mechanical warping of the touch input device, although thermal expansion may still affect this alignment.

The fundamental cause of these problems in a prior art touch input device of the type shown in Figure 1 is that the distance between a VCL and its respective waveguide 00 array (of order 1mm) is approximately two orders of magnitude smaller than the width r of a typical input area, i.e. the distance between the VCLs 111 and 112. It will be understood by those skilled in the art of optical lens design and of design and assembly of micro-optical elements that this represents a high magnification optical system, and as C, 10 such is extremely sensitive to errors in positioning of the elements. As shown in Figure 3, even a slight misplacement of a VCL 111 relative to a transmit waveguide array renders the receive waveguide array 21 completely blind to a beam 12.

Surprisingly, the Applicants have found that a touch input device can in fact be operated reliably, with sufficient optical signal captured by the receive waveguide array, in the complete absence of VCLs on either the transmit or receive sides.

Turning to Figure 4, operation of an optical touch input device in the absence of VCLs is shown, whereby a transmit waveguide array 20 produces one or more beams 41 which diverge in the z-direction (ie substantially perpendicular to the input area of the touch input device). While significant portions 42 of this signal are not collected by the receive waveguide array 21, a small portion is, and this collected portion is then guided to a detector in a conventional fashion. Provided the power emitted by the optical source and the sensitivity of the detector are sufficient in combination, even the small portion of each beam 41 that is collected by each waveguide in the receive waveguide array 21 can reliably confirm receipt of the beam 41, thereby indicating the absence of a touch event.

It is only when a touch event occurs, preventing all or a significant part of that small portion of a beam 41 from entering one or more waveguides in the receive waveguide array 21, that a touch event would be indicated. It will be appreciated that the divergent nature of each beam 41 makes the touch input device much more robust against relative movement between a receive waveguide array 21 and a transmit waveguide array 20, as could be caused by mechanical force, thermal expansion, flexing or warping etc.

This is quite surprising and contrary to conventional thinking. The method allows a functional optical touch input device to be obtained even if the VCLs are omitted from the configuration. This of course represents a substantial reduction in 1-8-

O

0 component cost, and solves both the VCL-related fabrication and assembly problems mentioned above.

C There are a number of factors that must be balanced to ensure that sufficient signal is collected by the receive waveguides 21 in the absence of a touch event. These factors include optical source power, detector sensitivity, the height of the transmit waveguides (which affects the divergence angle of the beams 41), the distance between r the transmit waveguide array 20 and the receive waveguide array 21, the ambient light intensity, and generally the size of the display/input area. The display size has two o effects. Firstly, a larger display requires more waveguides along each side for the same ,1 10 spatial resolution, so for a given source power there will be less optical power in each beam 41. Secondly, as each beam 41 continues to diverge when traversing a larger display, a smaller fraction will be collected by the receive waveguides. All these factors must be taken into consideration when determining the optical power required to allow unrestrained divergence of each beam 41 while providing a sufficient quantity of optical signal to reach the receive waveguide array 21 in the absence of a touch event. Without wishing to be bound by theory, it is believed that the surprisingly successful operation of an optical touch input device in the absence of VCLs is due primarily to two factors: firstly the extraordinary sensitivity of detectors such as digital camera chips based for example on complementary metal oxide semiconductor (CMOS) technology; and secondly on the limited ability for ambient light (that may manifest itself as noise at the detector) to be collected by the receive waveguides.

A further embodiment of the present invention can be seen in Figure 5. In this embodiment aperture means 51 or 52 are placed proximate to a transmit waveguide array 20 or a receive waveguide array 21. It should be recognised here that it is not necessary for both aperture means to be provided. Either or both aperture means will have some effect on the transmission of an optical signal from a transmit array 20 to a receive array 21, and on the suppression of noise from ambient light.

A transmit aperture means 51 proximate to a transmit waveguide array 20 allows a sector 53 of each diverging beam 41 to pass, while preventing the remainder of each beam from escaping into the environment where it may interfere with other instrumentation (including other receive arrays), cause discomfort to a user (especially if the signal light is visible), or be otherwise detected disadvantageously. Preferably, the -9- Ssector 53 is sufficiently wide to comfortably encompass the height of the receive waveguide array 21.

C/ A receive aperture means 52 proximate to a receive waveguide array 21 serves to restrict the field of view of the receive waveguide array such that only those portions of each beam 41 passing directly into the waveguides of the receive waveguide array will ,1be collected. This serves to prevent ambient light from entering the receive waveguide r- array 21 and interfering with the operation of the touch input device. Although ambient light of wavelengths far removed from the operating wavelength can be blocked by filtering, as is well known in optical touch input systems, ambient light at or around the 10 operating wavelength cannot be so simply removed hence it is preferable to position an aperture 52 close to but not in contact with the receive waveguide array 21.

Another mechanism for controlling the divergence of the beams 41 is to change the height of the transmit waveguides themselves. To explain, it is well known in optics that the diffraction of a beam emitted from a source is dependent upon the dimensions of that source. By increasing the height of the waveguides of a transmit waveguide array the diffraction angle of the emitted light beams 41 can be reduced, although the beams will still diverge in an unrestricted fashion. Increasing the height of the transmit waveguides may also advantageously increase the amount of signal light. Although a similar increase in the height of the receive waveguides would increase the collected fraction of each light beam 41, it would also increase the propensity for the receive waveguides to collect unwanted ambient light.

It is of course inevitable that with increasing display/input area size, there will come a point where the fraction of light collected by the receive waveguides from beams diverging in unrestricted fashion will simply be insufficient for reliable touch detection, especially in high ambient light conditions. In such cases, a third embodiment of the present invention may be applicable. In this embodiment, shown in Figure 6, a weakly converging lens 61, preferably of elongated cylindrical form (ie extended in the xdirection), is provided between a transmit waveguide array 20 and a receive waveguide array 21, in close proximity to the transmit waveguide array 20. In this embodiment, the weakly converging lens 61 reduces the (vertical) divergence angle of a beam 62, although the beam 62 continues to diverge after traversing the weakly converging lens 61. Since the weakly converging lens 61 does not collimate the signal light into substantially parallel rays, it is to be distinguished from the VCLs of the prior art optical input devices. Those skilled in the art of optics will understand that a weakly converging lens 61 produces a virtual image of each signal emanating from a transmit waveguide array 20, not a real image. By way of illustration, the operation of a weakly converging lens 61 is shown in Figure 7A. For the purposes of this specification, a weakly converging lens 61 acts on a real object 70 to produce a virtual image 71 (ie an image on the same side of the lens as the object), wherein the magnitude of the image r distance 72 is greater than the magnitude of the object distance 73. This is to be distinguished from the operation of a 'strongly converging lens': as shown in Figure 7B, a strongly converging lens 74 acts on a real object 70 to produce a real image 75 (ie an image on the opposite side of the lens to the object). A weakly converging lens is also to be distinguished from a diverging lens 76 which, as shown in Figure 7C, acts on a real object 70 to produce a virtual image 71, wherein the magnitude of the image distance 72 is less than the magnitude of the object distance 73.

For the purposes of this specification, a perfectly collimating lens (ie one where the image distance is infinite) is considered to be a strongly converging lens. Those skilled in the art will understand that a perfectly collimating lens is an idealisation, and in reality a collimating lens will still form an image of the object. This image may be either real or virtual, but in any event the magnitude of the image distance will be very much greater than the magnitude of the object distance.

It should be noted that an elongated lens of similar power to the weakly converging lens 61 shown in Figure 6 should in general not be placed in close proximity to a receive waveguide array 21, because it would act to increase the amount of ambient light collected by the receive waveguides.

Since the beam 62 continues to diverge as it passes across the input area of a touch input device, the optical system remains robust to inaccuracies in assembly and lens manufacture, and to display warping. The optimum power of an elongated weakly converging lens 61 is, essentially, determined by a compromise between the sensitivity, robustness and cost of the optical touch input system, and may be dictated by the particular application. In one example embodiment, the power of a weakly converging lens 61 is chosen such that, after a beam 62 passes through the weakly converging lens 61, its divergence angle is from ten to one hundred times larger than the angle subtended by the height of the receive waveguides.

-11- SReturning now to the aperture means 51, 52 shown in Figure 5, each aperture means may be provided separately from or integrated with the respective waveguide array. A convenient method for providing aperture means 51, 52 separately from the waveguide arrays is to incorporate them into the protective bezel that typically encloses the waveguide arrays. Alternatively, the waveguide arrays themselves may provide a 00 useful aperture means, particularly if they are oriented in a preferred fashion.

r For instance we refer to embodiments shown in Figures 8A and 8B, where certain integral parts of a transmit waveguide act as an aperture means. Referring firstly to Figure 8A, a single waveguide 10 of a transmit waveguide array 20, typically 10 comprising a substrate 80, a lower cladding layer 81, a core layer 85 with an in-plane lens 16, and an upper cladding layer 95, emits a divergent signal 100. The lower cladding layer 81, core layer 85 and upper cladding layer 95 may all for example comprise photo-patternable polymer materials, as disclosed for example in US patent application No 11/742,194 entitled 'Methods for fabricating polymer optical waveguides on large area panels', incorporated herein by reference in its entirety. If the upper cladding layer 95 is present, it should be patterned, for example as disclosed in US patent No 7,218,812, incorporated herein by reference in its entirety, so that it does not cover the curved end face 90 of the in-plane lens 16. The substrate 80 may comprise a rigid material such as a silicon wafer, or a flexible material such as a polycarbonate or polyethylene terephthalate (PET). As disclosed in US patent application No 11/552,380 entitled 'Improved optical elements for waveguide-based optical touch screens', incorporated herein by reference in its entirety, if a substrate 80 comprises a material that would otherwise be transparent to signal light, it preferably additionally comprises a material, such as carbon black or a dye, that absorbs signal light. The lower cladding layer 81 and upper cladding layer 95 are both optional, although a lower cladding layer 81 is preferably present for optical and planarisation purposes, and an upper cladding layer 95 is preferably present for optical and protective purposes.

It will be appreciated that after the transmit and receive waveguides have been fabricated, they must be singulated from the substrate sheet, for example by a dicing process, and that to preserve the curved end face 90 of an in-plane lens 16, it should be stepped back a certain distance (say 1 to 50[tm, more realistically 5 to 50[tm) from the substrate end face 91 defined by the singulation process. Recalling that the substrate is preferably highly absorbing at the signal wavelength, this 'stepped back' configuration -12- Scauses a portion of a diverging beam 100 to be blocked by refraction or absorption in the lower cladding 81 and substrate 80, so that the beam 100 diverges asymmetrically about the horizontal axis 101. In the specific embodiment shown in Figure 8A, where a transmit waveguide array 20 is mounted 'substrate side down' on the display, a beam 100 diverges by an angle 104 of only 2' below the horizontal axis 101 compared with an angle 103 of 140 above it.

O In an alternative embodiment shown in Figure 8B, a transmit waveguide array is mounted 'substrate side up' on a display, ie 'upside down'. In other words it is mounted on its upper cladding 95 and is covered by the substrate 80 and lower cladding 10 81. In this instance the diverging beam 100 is again asymmetrical with respect to the horizontal axis 101, but reversed from Figure 8A. Disregarding reflection off the display surface 102 for now, it will be appreciated that the 'upside down' configuration of Figure 8B is to be preferred, since there is less potential for the excess portion of a beam 100 (ie that portion not collected by the receive waveguides) to escape into the environment. Equivalently, on the receive side, there is less potential for ambient light to be collected by the receive waveguides. Reflection of both signal and ambient light off the surface 102 may still occur of course, but the reflected light will always be of lesser intensity than direct light, especially if the display surface has a broadband antireflection coating. It will be appreciated that the 'self aperturing' of the signal, as shown in Figure 8B, is advantageous to the operation of the touch input device.

EXPERIMENT

By way of example, a transmit array of sixty waveguides with integrated in-plane lenses, and a corresponding receive array with integrated in-plane lenses, were fabricated from photo-patternable polymers on silicon substrates, using techniques disclosed in US patent No 7,218,812. The two arrays were placed 6cm apart and facing each other on a cradle, in the 'upside down' fashion shown in Figure 8B, with the output end of the receive array butted against a two-dimensional CMOS detector chip connected to a video monitor. Light from either a red (630 nm) or infrared (850 nm) laser was coupled by an SMF 28 optical fibre into the transmit array. No vertical collimating lenses (VCLs) were installed in the device whatsoever. Each waveguide was 11 tm high, and the divergence angle in the vertical direction was approximately 16' (as shown in Figure 8B) for both wavelengths. Despite the lack of VCLs, the CMOS detector received a -13sufficient signal level; in some cases with the infrared laser source, the position sensitive detector was even saturated. Beam blockages by touch events were easily detected.

This simple experiment has shown a configuration that is capable of being used as a touch sensor in the absence of vertical collimating lenses.

Although the invention has been described with reference to certain specific ,1 examples, it will be appreciated by those skilled in the art that the invention may be r- embodied in many other forms.

INDl 00

Claims (12)

1. 2. A method as claimed in claim 1 wherein at least one aperture means is provided between said transmit waveguide array and said receive waveguide array to restrict passage across said input area of at least a portion of said optical signal not impinging directly on said receive waveguide array.
2. 3. A method as claimed in claim 1 or claim 2 wherein an aperture means is provided proximate to said transmit waveguide array.
3. 4. A method as claimed in any one of the previous claims wherein an aperture means is provided proximate to said receive waveguide array. A method as claimed in any one of claims 2 to 4 wherein at least one of said aperture means is adapted to restrict the field of view of said receive waveguide array.
4. 6. A method as claimed in any one of the preceding claims wherein the height of said transmit waveguide array is controlled to alter said first divergence angle.
5. 7. A method as claimed in any one of the preceding claims wherein a weakly converging lens is provided between said transmit waveguide array and said receive waveguide array, wherein after passing through said weakly converging lens, said optical signal diverges with a second divergence angle, less than said first divergence angle.
6. 8. An optical transmission system for transmitting an optical signal between a transmit waveguide array and a receive waveguide array of a touch input device, said device having an input area for receiving user input, wherein an optical signal from an optical source is coupled into and propagates through said transmit waveguide array, then allowed to diverge in a direction substantially perpendicular to V, said input area as it propagates in a substantially unrestricted fashion across said input area towards said receive waveguide array, without striking any vertical collimation optical componentry between said transmit waveguide array and said receive N, waveguide array. 00
7. 9. An optical transmission system as claimed in claim 8 wherein at least one aperture means is provided between said transmit waveguide array and said rreceive waveguide array to restrict passage across said input area of at least a portion of said optical signal not impinging directly on said receive waveguide array. An optical transmission system as claimed in claim 8 or claim 9 wherein an aperture means is provided proximate to said transmit waveguide array.
8. 11. An optical transmission system as claimed in any one of claims 8 to wherein an aperture means is provided proximate to said receive waveguide array.
9. 12. An optical transmission system as claimed in any one of claims 9 to 11 wherein said aperture means is separate and spaced from said transmit waveguide array and/or said receive waveguide array.
10. 13. An optical transmission system as claimed in any one of claims 9 to 11 wherein said aperture means is integrated with said transmit waveguide array and/or said receive waveguide array.
11. 14. An optical transmission system as claimed in any one of claims 8 to 13 wherein a weakly converging lens is provided between said transmit waveguide array and said receive waveguide array, said weakly converging lens reducing the divergence angle of said optical signal compared to the divergence angle of said optical signal as it leaves said transmit waveguide array. A method for transmitting an optical signal between a transmit waveguide array and a receive waveguide array, substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying Figures 4 to 8B and/or the accompanying examples.
12. 16. An optical transmission system for transmitting an optical signal between a transmit waveguide array and a receive waveguide array of a touch input device, substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying Figures 4 to 8B and/or 00 \,l r- 00, 1^, p.sD t",l