Patent Description:
Eye-tracking is a term for the process of measuring either the point of gaze or the motion of an eye relative to the head. An eye-tracker is a term for a device for measuring eye positions and eye movement. Eye-trackers are commonly used in several fields of research and development, such as physiologically on the visual system, in psychology, in psycholinguistics, marketing, as an input device for human-computer interaction and in product design. There are presently a number of methods for measuring eye movement. One of the emerging variants thereof uses video images from which the eye position is extracted.

Eye-trackers are generally adapted to measure rotations of the eye in one of several ways, but principally they fall into three main categories: measurement of the movement of an object in contact with the eye, optical tracking without direct contact to the eye and measurement of electric potentials using electrodes placed around the eyes.

The optical tracking category mentioned above uses some of the available non-contact, optical methods for measuring eye motion. Emitted light, typically in the infrared wavelength region, is reflected from the eye and sensed by a video camera or some other specially designed optical sensor. The sensed information is then analysed in real time to extract eye movements from changes in reflections.

In conventional head-worn eye-tracking devices, electro-optical components, such as one or more cameras and/or light sources, are usually mounted on a mechanical support structure. Most convenient and a classic solution is to have at least partly covered the frame of a pair of glasses with the mentioned structure onto which the necessary components have been mounted.

An example of such a solution is disclosed in <CIT>, which describes a portable eye-tracking device including a frame having a glasses lens attached thereon with, so as to, to the greatest possible extent, resemble a traditional pair of eye-glasses or sunglasses. The frame includes a centrepiece to which the glasses lens is attached and from which sidepieces extend. These sidepieces may fit above the ear of a user in the manner of a traditional pair of eye-glasses or sun glasses. A nose piece is provided for comfort and to assist in fitting of the device to a user's nose. A scene camera, which may capture still and/or video images and/or other image data, is disposed in the glasses lens above the nose piece. To record sound, a microphone may also be placed adjacent or near to the scene camera. A control unit is located within one or both arms (sidepieces).

To the frame is attached a mechanical support structure with optics holding members, usually fixated to the frame of the portable eye-tracking device. The mechanical support structure with optics holding members usually constitutes a visibly and physically obstructive element to the user. This support structure may be perceived as disturbing and less attractive both from functional and esthetical points of view. Mounting fragile and sometimes very sensitive optical and/or electronic components on an extending frame structure may also be undesired from the perspective of strength and durability of the lens and its functional elements, all of which are crucial for a robust and reliable function of an eye-tracking device.

Further, <CIT>, discloses a device adapted to be worn by a user, comprising an optical element, a light source and a sensor. The optical element is adapted to be arranged in front of an eye of the user and formed of a light-transmitting material allowing the user to see through the optical element, wherein the light source is arranged on the optical element and adapted to illuminate at least a part of the eye of the user. Further, the sensor is adapted to capture light which has been emitted from the light source and reflected on the eye.

Moreover, at least to date, since eye-tracking technology is now emerging, prior art solutions have not been optimised in terms of cost and efficiency when setting up production facilities for producing eye-tracking devices in a large scale.

An object of the present invention is to at least alleviate one of the problems with the prior art.

Another object of the present invention is to reduce the weight of equipment attached on the outside of the lens.

At least one of these objects is fulfilled with a lens according to an independent claim directed to a lens.

Further advantages are achieved with the features of the dependent claims.

According to a first aspect of the invention a lens is provided for eye tracking applications, the lens comprising a first protective layer with a first surface, arranged to face towards the eye to be tracked when the lens is used for eye tracking. The lens further comprises a supporting layer; and a second protective layer with a second surface, arranged to face away from the eye to be tracked when the lens is used for eye tracking. The supporting layer is arranged between the first protective layer and the second protective layer, and the supporting layer comprises at least a first opening between the first protective layer and the second protective layer. The lens further comprises an electrical component arranged extending through the first opening. The lens further comprises a light source arranged to emit a first light into the first protective layer, which light exits the first protective layer from the first surface and is directed towards the eye to be tracked when the lens is used for eye tracking and even further, the lens comprises a refractive element arranged to face towards the eye in the light path of the light source, the refractive element being an integral part of the first protective layer.

With the lens according to the invention the incorporation of an electrical component into the lens is facilitated. During manufacturing of the lens the electric component may be arranged extending through the supporting layer. The first protective layer and the second protective layer may then be formed on opposite sides of the supporting layer. The electrical component then becomes correctly positioned in the lens.

The lens may be used in devices for augmented reality (AR) as well as in devices for virtual reality (VR). Especially in VR applications it is preferable if the lens is flat as it is to be combined with a display which in most cases is flat. It is however possible to make the lens with a curved surface.

The size of the at least one opening may be arranged to provide support for the electrical component during manufacturing of the lens. According to a preferred embodiment this is achieved by making the opening with slightly larger dimensions than the electrical component, which is to be arranged in the opening. After the arrangement of the electrical device in the opening an optically transmitting material may be arranged between the supporting layer and the electrical component to fix it in relation to the supporting layer. The first protective layer and the second protective layer are then formed on opposite sides of the supporting layer.

As an alternative the first opening may be formed with slightly smaller dimensions than the electrical component. In this way a press fitting is achieved. With a press fitting the forming of the opening must be done with tight tolerances.

Said electrical component is an image capturing device, arranged to receive light from the eye to be tracked when the lens is used for eye tracking. It is advantageous to have the image capturing device incorporated in the lens. In this way as the problem of arranging an image capturing device on the lens is then avoided. The image capturing device may be comprise any suitable image sensor, such as, e.g., a CMOS sensor and a CCD. The image capturing device may also comprise optical elements to form an image on the image sensor.

The image capturing device is in contact with the first protective layer. If no special measures are taken the image capturing device will be in contact with the first protective layer. It is preferred that the image capturing device extends into the first protective layer.

The lens comprises a light source arranged to emit light into the first protective layer, which light exits the first protective layer from the first surface and is directed towards the eye to be tracked when the lens is used for eye tracking. With a light source incorporated into the lens in this way, the problem of arrangement of a light source on the outside of the lens is avoided.

The supporting layer may comprise a second opening between the first protective layer and the second protective layer, wherein the light source is arranged to extend through the second opening. This arrangement may be favourable for some applications and may facilitate the arrangement of the light source in the correct desired angle in relation to the first surface.

The light source is preferably a light emitting diode, LED, or a laser. The light source preferably emits light in a narrow wavelength band. The image capturing device is preferably arranged to detect light in said wavelength band. It is preferred that the wavelength band is in the near infrared wavelength region. With the light in that wavelength region the light does not disturb the user of the lens. The wavelength band in which the light source emits light may typically be in the range <NUM>-<NUM>. By having the image capturing device detecting light only in the wavelength region in which the light source emits light, the quality of the eye tracking is improved.

The light source may be arranged with a predetermined angle in relation to the first surface, so that the light, emitted from the light source, is directed towards the cornea of the eye to be tracked when the lens is used for eye tracking. By such a direction of the light from the light source, the eye tracking may be optimized, as it is favourable to track the cornea of the eye.

The image capturing device may be arranged with a predetermined angle in relation to the first surface, such that the image capturing device is arranged to receive light reflected from the cornea of the eye to be tracked when the lens is used for eye tracking. By having the image capturing device arranged in this way, the eye tracking may be optimized, as it is primarily the cornea that is illuminated.

The lens may comprise a first cable connected to the image capturing device, wherein the cable extends from the image capturing device, between the supporting layer and the first surface or the second surface to the outside of the lens, to enable connection of the image capturing device to a control unit by means of the first cable. With such an arrangement of the first cable it is secured in lens and cannot move in the field of view of the user of the lens.

The first cable may be arranged in contact with the supporting layer. This facilitates the manufacturing of the lens as the first cable is then secured to the supporting layer before formation of the first protective layer and the third protective layer.

The lens may comprise a second cable connected to the light source, wherein the second cable extends from the light source, between the supporting layer and the first surface or the second surface to the outside of the lens, to enable connection of the light source device to a control unit by means of the second cable. The arrangement of also the second cable in this way has the same advantages as the arrangement of the first cable in the same way.

The second cable may be arranged in contact with the supporting layer. This facilitates the manufacturing of the lens as the second cable is then secured to the supporting layer before formation of the first protective layer and the second protective layer. This has the same advantages as mentioned above for the first cable.

The material in the first protective layer and/or the second protective layer may be a polymer. A polymer may be formed on the supporting layer without negatively affecting the electrical component.

The material in the supporting layer may be a polymer. A polymer is favourable for combination with the first and third protective layers of polymer.

At least some of the objectives are according to an aspect of the present disclosure also achieved by a head-worn device according to claim <NUM>. The head-worn device comprises at least one lens for eye-tracking applications according to the present disclosure. The head-worn device has the advantages discussed in relation to the lens.

The head-worn device may be an augmented reality headset, where a transparent display is either integrated into the lens, attached to the lens or arranged in the vicinity of the lens.

The head-worn device may alternatively be a virtual reality headset, comprising a display wherein the lens is either integrated into the display, attached in front of the display or arranged in front of the display.

It should be emphasised that any of the above-described embodiments can be combined according to the appended claims.

Combinations of these embodiments might provide additional advantages. Further advantages might arise when putting the disclosure into practice or when studying the following detailed description.

For a more detailed understanding of the present invention and its objects and advantages, reference is made to the following detailed description, which should be read together with the accompanying drawings. Same reference numbers refer to same components in the different figures.

<FIG> depicts schematically a lens <NUM> according to an example not forming part of the claimed invention.

The lens <NUM> is particularly arranged and intended for eye-tracking applications. The lens comprises a first protective layer <NUM>, arranged to face towards the eye <NUM> to be tracked when the lens <NUM> is used for eye-tracking, wherein the first protective layer comprises a first surface <NUM>, arranged to face towards the eye <NUM> to be tracked when the lens <NUM> is used for eye-tracking. The first surface <NUM> may have the shape of a first non-zero curvature.

The lens <NUM> also comprises a supporting layer <NUM>. The supporting layer <NUM> is arranged to face away from the eye <NUM> to be tracked when the lens is used for eye-tracking. Further, the lens <NUM> may comprise a second protective layer <NUM> with a second surface <NUM> arranged to face away from the eye <NUM> to be tracked when the lens is used for eye-tracking. In this case, the supporting layer <NUM> is arranged between the first protective layer <NUM> and the second protective layer <NUM>.

In one example, the supporting layer comprises a first opening <NUM> between the first protective layer <NUM> and the second protective layer <NUM>. An electrical component in the form of an image capturing device is arranged extending through the first opening <NUM>. The first opening <NUM> may have a larger dimension than the image capturing device <NUM>. This allows the angle of the image capturing device <NUM> to be adjusted during manufacturing of the lens <NUM>. The arrangement of the image capturing device <NUM> is performed before the arrangement of the first protective layer <NUM> and the second protective layer <NUM>. After arrangement of the image capturing device in the first opening <NUM> an optically transmitting adhesive <NUM> may be applied to fill out the remainder of the first opening. A first cable <NUM> is connected to the image capturing device <NUM>. The first cable <NUM> may extend from the imaging device <NUM> in contact with the supporting layer between the supporting layer and the first surface <NUM> to the outside of the lens <NUM>. This enables connection of the image capturing device <NUM> to a control unit <NUM>.

The image capturing device <NUM> comprises an image sensor, such as a CMOS sensor or CCD sensor; RGB colour sensor; infrared sensor or similar. The image capturing device <NUM> also comprises any necessary optical elements for focusing of the incident light from the eye <NUM>.

The first protective layer <NUM> and the second protective layer <NUM> of the lens <NUM> consists of materials such as glass and/or one or several polymers, comprising for example plastic, acrylic glass, polycarbonate, polyethylene terephthalate or polyepoxides. The supporting layer <NUM> may comprise a suitable polymer. Examples of materials for the different layers <NUM>, <NUM>, <NUM>, <NUM>, include: glass and/or one or several polymers, comprising for example plastic, acrylic glass, polycarbonate, polyethylene terephthalate or polyepoxides.

The thickness of the first protective layer <NUM> may be in the range <NUM>-<NUM>, preferably in the range <NUM>-<NUM>, more preferably in the range <NUM>-<NUM>, and most preferred in the range <NUM>-<NUM>.

The lens <NUM> also comprises a light source <NUM>, which in the embodiment shown in <FIG> is attached to the supporting layer <NUM> and is arranged within the first protective layer <NUM>. The light source <NUM> is arranged to emit a first light through the first surface <NUM> towards the eye <NUM>, and most preferably towards the cornea of the eye <NUM>. The image capturing device <NUM> is directed towards the eye <NUM> and most preferably towards the cornea of the eye to capture the first light. In order to achieve a clear signal the light source <NUM> is arranged to emit light in a specific wavelength band, and the image capturing device <NUM> is arranged to capture light in the same wavelength band. The light source <NUM> may be adapted to emit the first light essentially at wavelengths in the wavelength range <NUM>-<NUM>, preferably in the wavelength range <NUM>-<NUM>, more preferably in the wavelength range <NUM>-<NUM>. The image capturing device <NUM> captures images of the eye during movement of the eye in order the track the movement of the eye in a manner known per se from prior art eye-tracking systems.

Due to the higher refractive index of the material in the first protective layer compared to the refractive index of the air on the outside of the first surface <NUM> some of the first light will be subject to total internal reflection as is shown by the line <NUM>. If the first light reaches the image capturing device it will deteriorate the image captured by the image capturing device <NUM>. In order to avoid that some of the first light reaches the image capturing device <NUM> the supporting layer <NUM> may be adapted to be absorptive for the majority of wavelengths of the first light. In other words, if the first light is in a wavelength band, e.g., in the range <NUM>-<NUM>, the absorptive layer should be adapted to be absorptive in the same wavelength band. As an example, if the light source <NUM> emits light at a wavelength around <NUM> the absorptive the supporting layer <NUM> is adapted to be absorptive at least around <NUM>. This will prevent the first light from reaching the image capturing device <NUM>. The supporting layer is preferably transparent at visible wavelengths to enable for a user to look through the lens <NUM>. The supporting layer <NUM> of the lens <NUM> may be provided with an absorbing dye, in order to absorb the first light. As an alternative the second protective layer <NUM>, instead of the supporting layer <NUM>, may function as an absorptive layer. Thus, the second protective layer <NUM> of the lens <NUM> may be provided with an absorbing dye, in order to absorb the first light, while transmitting visible light.

The lens <NUM> also comprises a second cable <NUM> connected to the light source. The second cable <NUM> may extend from the light source <NUM>, between the supporting layer <NUM> and the first surface <NUM> in contact with the supporting layer <NUM>, to the outside of the lens <NUM>. The second cable <NUM> may be connected to the control unit <NUM>.

The control unit <NUM> controls the light source <NUM> and the image capturing device and may be adapted to communicate with other equipment, such as a computer, by wire or wirelessly. The first cable <NUM> and the second cable <NUM> provide data and/or power supply. The data and/or power supply is preferably connected to the potential of the light source and/or the image capturing device, such as a camera.

<FIG> depicts schematically a lens according to an alternative example not forming part of the claimed invention. One difference compared to the lens <NUM> shown in <FIG> is that the lens <NUM> of <FIG> is that the lens in <FIG> comprises a separate absorptive layer <NUM>. The absorptive layer <NUM> is adapted to be absorptive for the wavelengths of the first light emitted by the first light source <NUM>. Both the supporting layer <NUM> and the absorptive layer <NUM> are essentially transparent for visible wavelengths to allow a user to look through the lens. In <FIG> the first cable <NUM> is arranged on the other side of the supporting layer <NUM> compared to the lens <NUM> in <FIG>, i.e., between the supporting layer <NUM> and the second surface <NUM>. The absorptive layer <NUM> is provided with an absorbing dye, in order to absorb the first light, which has been reflected by total internal reflection. It is possible to have the absorptive layer <NUM> and the supporting layer <NUM> in the other order, i.e., to have the supporting layer <NUM> between the absorptive layer <NUM> and the first protective layer <NUM>. The second protective layer <NUM> provides a protection for the back of the image capturing device <NUM>.

<FIG> shows schematically a lens according to an alternative example not forming part of the claimed invention. In <FIG> the lens <NUM> comprises only a first protective layer <NUM> and a supporting layer <NUM>. The supporting layer <NUM> is an absorptive layer adapted to absorb the part of the first light, which is reflected in total internal reflection. The lens in <FIG> may comprise a second opening <NUM>. The light source is arranged to extend through the second opening. The second opening increases the possibility to adjust the direction of the first light. The lens <NUM> may be flat. This embodiment is especially interesting when the invention is used in VR headsets. VR headset may or may not comprise a separate lens. Thus, potentially the lens <NUM> in <FIG> could be the display.

The lens including all of its layers has a thickness in the range of <NUM>-<NUM>, preferably <NUM>-<NUM>. It is possible to have the lens even thicker, but the weight of the lens might become an issue then. It may also be possible to produce the lens thinner than <NUM> if future image capturing devices exhibit smaller dimensions than the present image capturing devices.

<FIG> a and 4b show in an enlarged view a part of the lens <NUM> and the light source <NUM> according to two alternative embodiments. The light source may for example be a light emitting diode, LED, or a laser. Most light emitting diodes LEDs currently available on the market are produced from materials with a refractive index close to the refractive index of the material of the first protective layer in which the light emitting diode is to be arranged. The focussing function provided by the dome shape of the lens gets lost and is therefore in an alternative embodiment replaced by the dome-shaped micro lens, a lens that is attached onto the first surface <NUM> on the first protective layer <NUM>. The lens <NUM> has the dual function of focussing the first light emitted from the light source <NUM> and reducing internal reflection. This is shown in <FIG>. As can be seen in <FIG> where a refractive element <NUM> is arranged in front of the light source <NUM>. The refractive element <NUM> has a curved surface <NUM>. The refractive element <NUM> is integral with the first protective layer <NUM>. The refractive element preferably has the same refractive index as the first protective layer <NUM>. The curved surface <NUM> of the refractive element <NUM> has, seen from the light source <NUM>, a convex shape, such that the emission cone of the first light is emitted onto the curved surface <NUM> with an angle of incidence, which relative to the curved surface <NUM> is smaller than the critical angle at which total internal reflection would occur. Thus, because stray light with large angles of incidence in relation to the inner surface of the lens are reduced, internal reflections are minimised. In other words, less light will fall on the inner surface with an angle of incident larger than the critical angle, due to the curved surface <NUM> of the <NUM> refractive element <NUM>.

<FIG> shows an alternative embodiment with a refractive element that narrows the emission cone from the at least one light source <NUM>. The refractive element <NUM> is integral with the first protective lens <NUM> so that it does not protrude out of the first surface <NUM>. The refractive element <NUM> has a curved surface <NUM>. The refractive element <NUM> may have a refractive index that is <NUM>-<NUM> % higher than the refractive index of the first protective layer <NUM>. Preferably, the refractive element <NUM> may have a refractive index that is <NUM>-<NUM> % higher than the refractive index of the first protective layer <NUM>. The curved surface <NUM> of the refractive element <NUM> has, seen from the light source <NUM>, a convex shape, such that the emission cone of the first light is emitted onto the curved surface <NUM> with an angle of incidence, which relative to the curved surface <NUM> is smaller than the critical angle at which total internal reflection would occur.

<FIG> depicts schematically different embodiments of a head-worn device <NUM> according to an embodiment of the present disclosure. The head-worn device <NUM> can be glasses (<FIG>) for eye-tracking (without display); an augmented reality headset (<FIG>), where a transparent display <NUM> is either integrated into the lens, attached to the lens or arranged in the vicinity of the lens; or a virtual reality headset (<FIG>), comprising a display <NUM> wherein the lens is either integrated into the display, attached in front of the display or arranged in front of the display.

Claim 1:
A lens (<NUM>) for eye tracking applications, the lens (<NUM>) comprising:
a first protective layer (<NUM>) with a first surface (<NUM>), arranged to face towards the eye (<NUM>) to be tracked when the lens (<NUM>) is used for eye tracking;
a supporting layer (<NUM>); and
a second protective layer (<NUM>) with a second surface (<NUM>), arranged to face away from the eye (<NUM>) to be tracked when the lens (<NUM>) is used for eye tracking,
wherein the supporting layer (<NUM>) is arranged between the first protective layer (<NUM>) and the second protective layer (<NUM>), and wherein the supporting layer (<NUM>) comprises at least a first opening (<NUM>) between the first protective layer (<NUM>) and the second protective layer (<NUM>);
the lens (<NUM>) comprises a light source (<NUM>) arranged to emit a first light into the first protective layer (<NUM>), which light exits the first protective layer (<NUM>) from the first surface (<NUM>) and is directed towards the eye (<NUM>) to be tracked when the lens (<NUM>) is used for eye tracking; and
characterised in that an electrical component (<NUM>) is arranged extending through the first opening (<NUM>), wherein said electrical component is an image capturing device (<NUM>), arranged to receive light from the eye (<NUM>) to be tracked when the lens (<NUM>) is used for eye tracking, wherein the image capturing device (<NUM>) is in contact with the first protective layer (<NUM>); wherein
the lens further comprises a refractive element (<NUM>) arranged to face towards the eye (<NUM>) in the light path of the light source (<NUM>), the refractive element (<NUM>) being an integral part of the first protective layer (<NUM>).