Patent Publication Number: US-2022230473-A1

Title: Apparatus for a Near-Eye Display

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. patent application Ser. No. 17/105,848 filed on Nov. 27, 2020, which is a continuation of U.S. patent application Ser. No. 15/552,897, filed on Aug. 23, 2017, now U.S. Pat. No. 10,878,235, which is a national stage of International Patent Application No. PCT/FI2016/050072, filed on Feb. 5, 2016, which claims priority from European Patent Application No. 15156666.8, filed on Feb. 26, 2015, each of which is incorporated herein by reference in their entirety. 
    
    
     TECHNOLOGICAL FIELD 
     Examples of the present disclosure relate to an apparatus for a near-eye display. Some examples, though without prejudice to the foregoing, relate to an apparatus for providing gaze tracking in a near-eye display. 
     BACKGROUND 
     Gaze tracking, namely the process of determining a point of gaze of a user&#39;s eye so as to determine a line of sight associated with the user&#39;s eye or to determine where the user is looking (and thus determining what the user is looking at), typically relies on capturing video images from a user&#39;s eye(s). Such video based gaze tracking typically uses infrared (IR) LEDs or infrared lasers for illuminating the eye and detecting reflections/glints of the infrared light from the eye (e.g. its cornea/surface). A determination of a user&#39;s gaze may be calculated based on the detected IR reflections and detected eye features such as detected pupil position. Conventional near-eye displays with integrated gaze tracking functionality systems are not always optimal, not least for example in view of the additional components as well as increased complexity, size and weight necessary to incorporate both gaze tracking functionality as well as display functionality in a near-eye display. 
     The listing or discussion of any prior-published document or any background in this specification should not necessarily be taken as an acknowledgement that the document or background is part of the state of the art or is common general knowledge. One or more aspects/examples of the present disclosure may or may not address one or more of the background issues. 
     BRIEF SUMMARY 
     An aspect of the present invention is set out in the claims. 
     According to at least some but not necessarily all examples of the disclosure there is provided an apparatus comprising:
         a light modulator configured to receive light of a first range of wavelengths and generate an image beam therefrom, wherein the light modulator is further configured to receive light of a second range of wavelengths and generate a probe beam therefrom; one or more light guides comprising:
           one or more in-coupling diffractive element areas, and   one or more out-coupling diffractive element areas;   
           wherein the one or more in-coupling diffractive element areas are configured to receive and in-couple the image beam and the probe beam into the one or more light guides; and   wherein the one or more out-coupling diffractive element areas are configured to out-couple, from the one or more light guides:
           the image beam to a user&#39;s eye for user viewing, and   the probe beam to the user&#39;s eye for detection of reflection therefrom.   
               

     According to at least some but not necessarily all examples of the disclosure there is provided an apparatus comprising:
         means configured to receive light of a first range of wavelengths and generate an image beam therefrom, wherein the means is further configured to receive light of a second range of wavelengths and generate a probe beam therefrom;   one or more means for guiding light comprising:
           one or more in-coupling diffractive means, and   one or more out-coupling diffractive means;   
           wherein the one or more in-coupling diffractive means are configured to receive and in-couple the image beam and the probe beam into the one or more means for guiding light; and   wherein the one or more out-coupling diffractive means are configured to out-couple, from the one or more means for guiding light:
           the image beam to a user&#39;s eye for user viewing, and   the probe beam to the user&#39;s eye for detection of reflection therefrom.   
               

     According to at least some but not necessarily all examples of the disclosure there is provided an apparatus comprising:
         means configured to generate an image beam of light at a first range of wavelengths, wherein the means is further configured to generate a probe beam of light of a second range of wavelengths;   one or more means for guiding light comprising:
           one or more in-coupling diffractive means, and   one or more out-coupling diffractive means;   
           wherein the one or more in-coupling diffractive means are configured to receive and in-couple the image beam and the probe beam into the one or more means for guiding light; and   wherein the one or more out-coupling diffractive means are configured to out-couple, from the one or more means for guiding light:
           the image beam to a user&#39;s eye for user viewing, and   the probe beam to the user&#39;s eye for detection of reflection therefrom.   
               

     Certain examples of the apparatus may be provided as a module for a device or as a device itself. The device may be configured for at least one of: portable use, wearable use, head mountable use. Certain examples of the apparatus are configured for use with a Near Eye Display (NED) for providing both display and gaze tracking functionality. 
     The examples of the present disclosure and the accompanying claims may be suitably combined in any manner apparent to one of ordinary skill in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of various examples of the present disclosure that are useful for understanding the detailed description and certain embodiments of the invention, reference will now be made by way of example only to the accompanying drawings in which: 
         FIG. 1  schematically illustrates an example of an apparatus according to the present disclosure; 
         FIG. 2  schematically illustrates a further example of an apparatus according to the present disclosure; 
         FIG. 3  schematically illustrates an example of diffractive light guides suitable for use with examples of the present disclosure; 
         FIG. 4  schematically illustrates a yet further example of an apparatus according to the present disclosure; and 
         FIGS. 5A and 5B  schematically illustrate examples of light modulators suitable for use with examples of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Examples of apparatuses according to the present disclosure will now be described with reference to the Figures. Similar reference numerals are used in the Figures to designate similar features. For clarity, all reference numerals are not necessarily displayed in all figures. 
       FIG. 1  schematically illustrates a block diagram of an apparatus  100  according to an example of the present disclosure.  FIG. 1  focuses on the functional components necessary for describing the operation of the apparatus. 
     The apparatus  100  comprises a light modulator  101  configured to receive light of a first range of wavelengths  102 , and generate an image beam  103  therefrom. The light modulator  101  is further configured so as to receive light of a second range of wavelengths  104  and generate a probe beam  105  therefrom. 
     The apparatus  100  further comprises one or more light guides  106  comprising one or more in-coupling diffractive element areas  107 , and one or more out-coupling diffractive element areas  108 . The one or more in-coupling diffractive element areas  107  are configured to receive and in-couple the image beam  103  and the probe beam  105  into the one or more light guides  106 . The one or more out-coupling diffractive element areas  108  are configured to out-couple, from the one or more light guides  106 :
         the image beam  109  to a user&#39;s eye  110  for user viewing, and   the probe beam  111  to the user&#39;s eye  110  for detection of reflection therefrom.       

     Each of the components described above may be one or more of any element, device, mechanism or means configured to perform the corresponding functions of the respective components as described in greater detail below. The component blocks of  FIG. 1  are functional and the functions described may or may not be performed by a single physical entity for example the light modulator  101  may correspond to an assembly/arrangement of components, not least for example as shown in  FIG. 5A  or  FIG. 5B . Accordingly, the blocks support: combinations of means for performing the specified functions. 
     The light modulator  101  may comprise a light modulating/modifying means configured to modulate/modify the incident light  102 ,  104  of first and second ranges of wavelengths so as to impart an image or pattern thereon and generate one or more collimated beams  103 ,  105  comprising a variable image or pattern. The light modulator  101  may comprise one or more of: an optical engine, a light engine, a micro display, optics (e.g. enlarging optics and collimating optics), a projector, a digital light processing (DLP) system, a liquid crystal on silicone (LCoS), a retinal scan display, a laser scanning system, a microelectromechanical (MEM) system (e.g. for providing scanning/raster scanning). The light modulator  101 , in certain examples, may be: a reflective based display, a transmissive based display or an emissive based display. 
     In some examples, instead of receiving light of a first and a second range of wavelengths and generating an image beam and probe beam therefrom, the light modulator may be configured to be able to generate for itself an image beam of light of a first range of wavelengths and a probe beam of light of a second range of wavelengths. For example the light modulator may comprise one or more display elements which itself creates a pixelated image/probe pattern that is then projected through an optical setup, e.g. an OLED display or an LED array display, for in-coupling to the one or more light guides. 
     The image beam  103  may comprise a collimated beam of light that may be expanded and guided to user&#39;s eye  110  for viewing and perceiving the image which is imparted to the light  102  that forms the image beam  103  by the light modulator  101 . Where the light  102  of the first range of wavelengths comprises one or more colour channels of visible light, e.g. one or more of red (R), green (G) and blue (B), the image beam  103  may correspondingly comprise light within the visible range of the electromagnetic spectrum, e.g. one or more of R, G and B. In certain examples, one or more image beams may be generated corresponding to the image in differing colour channels, e.g. one or more of R, G and B, from light received in the respective colour channels. 
     The probe beam  105  may comprise a collimated beam of light that may be expanded and guided to user&#39;s eye  110  for reflection therefrom. In certain examples (see  FIG. 2 ), such reflection is detected and used in part to determine a gaze or direction of view of the eye  110 . The light modulator  101  may impart a variable pattern, image, shape or size to light  104  that forms the probe beam  105 . Where the light of the second range of wavelengths comprises infrared light the probe beam may correspondingly comprise light within the infrared part of the electromagnetic spectrum. 
     The one or more light guides  106  may comprise light guiding means comprising one or more means for diffracting beams into and out of the light guide, for example a diffractive optical element. The light guides may, for example, be a one or more substantially planar substrates comprising one or more areas or diffractive elements/gratings/grooves that are disposed on lower or upper surfaces of the substrate or even located internally of the substrate. The light guide may be an exit pupil expander configured to expand an incident beam of light  103 ,  105  in one or more directions. The light guides may be transparent and the apparatus may be configured such that the user can see the real world though the apparatus/light guides whilst also seeing a virtual image/world via the apparatus/light guides. 
     Certain examples of the apparatus: may reduce the complexity of a combined display and gaze tracking device, may provide improved integration and require fewer components, and may thus also reduce the weight and size of the apparatus by enabling the sharing/reutilisation of various components. This may enable the provision of a miniaturised and efficient apparatus for integrated NED and Gaze tracking. For example, the light modulator  101  which generates the image beam  103  is also used to generate the probe beam  105 . In other examples, a light source for emitting the light for the image beam  103  is also used to generate the light for the probe beam  105 . 
     The use of the light modulator  101  to generate the probe beam  105  may enable a pattern, shape or size of the probe beam to be dynamically varied. Such control of the probe beam may enable the creation of complex variable shapes, sizes, patterns/images of the probe beam. Moreover, the probe beam could be dynamically adjusted during use so as to achieve optimal detection and measurement results thereby enabling more robust gaze tracking as well as simpler gaze tracking calibration. 
     Furthermore, certain examples (e.g.  FIG. 1 ) provide the ability to share/utilise one or more of in-coupling diffractive elements  107  and/or one or more of the out-coupling diffractive elements  108  to in-couple and/or out-couple both the image beam  103  and the probe beam  105  and may thereby reduce the number of optical components and the complexity of the arrangements of such components that may otherwise have been required to direct each of the image beam and probe beam separately and independently. 
     Furthermore, certain examples (see e.g.  FIG. 5A ) may enable the use of a combined light source  512  which simultaneously generates both the light  102  for the image beam  103  as well as light  104  for the probe beam  105  and may thereby reduce the number of components (and thus the weight, size and complexity) of the apparatus. 
     In the example of  FIG. 1 , the light guide  106  comprises a substrate of an optical material having first and second opposing surfaces. The substrate comprises an area of in-coupling diffractive elements  107  and an area of out-coupling diffractive elements  108  which may be laterally spaced apart from one another on the planar substrate for example at either end of the substrate. The in-coupling diffractive element area is configured to receive one or more input optical beams, i.e. either the image beam  103  (“image display beam”) or the probe beam  105  (“gaze tracking probe beam”), and diffract the input optical beam substantially within the first and second surfaces to provide a diffracted optical beam within the substrate which is coupled via total internal reflection to the out-coupling diffractive element area  108 . The out-coupling diffractive element area is configured to further diffract the diffracted optical beam out of the substrate to provide an output optical beam, namely an output of the image display beam  109  or the output gaze tracking probe beam  111 . 
     The out-coupling diffractive element  108  may be configured so as to not only just output the diffracted optical beam from the substrate but also to expand the diffracted optical beam in one direction. Further diffractive elements may be provided (for example  316   a  as shown in  FIG. 3 ) for expanding the diffracted optical beam in another direction so as to provide an output beam  109 ,  111  that can be expanded beam in two directions. 
     In certain examples, the in-coupling and out-coupling elements may be based on other optical methods than diffraction gratings and groves, for example volume holograms or gratings, or semi-transparent mirror structures. 
     The apparatus of  FIG. 1  shows a schematic illustration of a monocular apparatus. However, it is to be appreciated that the apparatus could be configured in a binocular form. Such a binocular form could correspond to providing two apparatuses  100  one for each of the user&#39;s eyes. For example, providing apparatus  100  shown in  FIG. 1  for a user&#39;s right eye and a mirror image version of the apparatus  100  for the user&#39;s left eye (similar to that of  FIG. 2 ). As an alternative to using two such laterally adjacent light guides, a single light guide could be provided having an in-coupling diffractive element area between two out-coupling diffractive element areas located at either end of the light guide wherein the in-coupling diffractive element area is configured to provide two diffracted input optical beams, one coupled to one of the out-coupling diffractive element areas, for example at a left hand end of the light guide, and the other diffracted input optical beam coupled to the other of the out-coupling diffractive element areas at the other end, e.g. a right hand end of the light guide. 
       FIG. 1  shows a single diffractive light guide  106  provided with one in-coupling diffractive element area  107  which is configured to diffract light at the first range of wavelengths (e.g. in the visible part of the electromagnetic spectrum) as well as light at the second range of wavelengths (e.g. the IR part of the electromagnetic spectrum). Thus, the diffractive element area  107  may be configured to in-couple both the image display beam as well as the gaze tracking probe beam, i.e. the diffractive element may be configured so as to diffract (or at least have an acceptable efficiency for diffracting) each of infrared, red, green and blue colour channels regions of the electromagnetic spectrum or to diffract a portion of a colour channel. It should be appreciated that other colour channels/apportionment of the visible spectrum may also be envisaged. Likewise, the single out-coupling diffractive element  108  may be similarly configured to diffract and out-couple a corresponding wide range of wavelengths. 
     As an alternative to using a single in-coupling diffractive element area for in-coupling a wide range of wavelengths of input beams  103 ,  105 , a plurality of in-coupling diffractive element areas could be provided on a light guide, each area spatially distinct from another and each being configured and optimised to diffract a particular/narrower range of wavelengths, for example one or more colour channels, infrared, red, green or blue, to provide one or more diffractive optical beams of such wavelengths of light within the substrate for out-coupling from the substrate by one or more out-coupling diffractive element areas. 
     Likewise, a plurality of out-coupling diffractive elements could be provided on the light guide each configured and optimised to diffract a particular narrow range of wavelengths of light and out-couple them from the light guide. 
     Yet further alternatively, instead of having a single light guide (with one or more in-coupling diffractive element areas and one or more out-coupling diffractive element areas) a plurality of light guides may be provided, e.g. vertically aligned and stacked on top of each other. Each of the stacked light guides could be provided with one or more in/out-coupling diffractive element areas configured and optimised to in-couple and out-couple one or more particular colour channels. Thus, it is to be appreciated that a variety of possible combinations of: numbers of in- and out-coupling diffractive element areas per light guide, as well as number of stacked light guides are envisaged. 
       FIG. 2  shows an apparatus  200  in a binocular form comprising a right hand side set of stacked light guides  106   a  and  106   a ′ along with a left hand side set of stacked light guides  106   b  and  106   b ′. For the sake of simplicity, the below discussion focuses just on the right hand side components of the apparatus. It is to be appreciated that similar components may be provided on the left hand side of the apparatus (with equivalent reference numerals but designated with a “b” instead of “a”). 
     Of the two stacked light guides  106   a  and  106   a ′, one is configured and optimised to in-couple, expand and out-couple visible light for example in the green and blue parts of the spectrum, whereas the other light guide is configured and optimised to in-couple, expand and out-couple infrared light and red light. 
     It is to be appreciated that other permutations may readily be envisaged, not least for example a plurality of stacked light guides each optimised for one of: blue, green, red and infrared respectively, or, similarly to  FIG. 1 , a single light guide may be provided for in- and out-coupling all of IR, R, G and B wavelengths of light beams. Also, one light guide optimised for RGB could be provided with another optimised for IR. Such an IR optimised light guide could be made to be thinner than an RGB light guide. It could further be configured for other integrated uses, such as: being used as a protective element, or a capacitive measurement surface for face/eye movement detection as well as an LC shutter and hot mirror as discussed in further details below. 
     A single light source  212   a  emits light  102 ,  104  for both the image display beam  103  (i.e. visible light) as well as light for the gaze tracking probe beam  105 , (i.e. infrared light). Such a light source generating simultaneously both visible light and infrared light may correspond to a laser crystal on silicone based light source as discussed further with respect to  FIG. 5A . 
     Alternatively, instead of having a light source that generates simultaneously both the visible and infrared light, separate light sources may be provided which generate independently visible light and infrared, for example separate light sources configured to emit each of visible light and infrared light, not least for example separate red, green, blue and infrared LEDs positioned adjacent to one another which can be separately and independently controlled/switched on such that only visible light is emitted and received by the light modulator when generating the display imaging and likewise only infrared light is emitted and received at the light modulator when generating the gaze tracking probe beam. 
     The light source  212   a  generates the light of the first range of wavelengths  102  and also generates the light of the second range of wavelengths  104 , each of which are incident to a light modulator  201   a  which generates an image display beam  103  and a gaze tracking probe beam  105  from such incident light respectively. Additional optics, e.g. lenses, mirrors or MEM system may be provided as well as other mechanisms for focusing, collimating the source of light into beams of light that may further be scanned/rastered into the in-coupling diffractive element. 
     The image display beam from the light modulator  201   a  is incident to a first in-coupling diffractive element area  107   a  and in-coupled into the first light guide  106   a  and then out-coupled via out-coupling diffractive element  108   a  (propagating through the underlying light guide  106   a ′) so as to be directed towards a user&#39;s eye  110 . The first light guide may be configured and optimised so as to in-couple, expand and out-couple light of the image display beam in green and blue parts of the visible spectrum. The further light guide  106   a ′ may be provided with an in-coupling diffractive element area  107   a ′ and an out-coupling diffractive element area  108   a ′ configured and optimised to in-couple, expand and diffract out visible light of the image display beam in the red part of the spectrum. The second light guide  106   a ′ may further be configured to in-couple, expand and out-couple infrared light to provide an output gaze tracking probe beam  111  which is incident to the user&#39;s eye to be reflected therefrom. 
     A detector  213 , such as an IR detector/sensor or camera, may be provided to detect reflections  214  of the gaze tracking probe beam from the user&#39;s eye, i.e. images/video of the user&#39;s eye in IR. The detection and measurement of such reflections  214  of the infrared gaze tracking probe beam may be used in part by a controller  215  to calculate and determine a user&#39;s gaze. 
     In some examples, other features of the eye are also measured and captured, for example related to a location of the user&#39;s eye pupil. In some examples, the IR detector/eye camera is used to capture and measure not only the reference reflections/glints  214  but is also used to capture and measure a location of the eye pupil. A determination may be made of the detected location of the reference reflection  214  relative to the detected location of the pupil. Differences of the relative movement between the pupil and the reference reflections  214  can be used for detecting changes in the gaze direction. 
     The determination of the gaze may also be dependent on the generated gaze tracking probe beam, i.e. taking into account one or more characteristics of the generated infrared probe beam outputted such as its initial shape, size and intensity prior to being reflected from the user&#39;s eye as compared to the shape, size and intensity of the detected reflected gaze tracking probe beam. 
     Implementation of the controller  215  can be in hardware alone (e.g. circuitry such as processing circuitry comprising one or more processors and memory circuitry comprising one or more memory elements), have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware). 
     The controller  215  may be used to control one or more of the light source  212   a  and the light modulator  201   a  so as to control each of the image display beam and the gaze tracking probe beam. The generated gaze tracking probe beam may be modified, e.g. its size or shape or intensity, depended upon the detected reflected gaze tracking probe beam. Such feedback from the detection of the reflected gaze tracking probe beam can assist in the calibration of the apparatus and enable for the gaze tracking probe beam&#39;s pattern, shape or size to be optimised for the prevailing circumstances of use. 
     Whilst  FIG. 2  shows a single detector  213  for detecting the gaze of one eye, i.e. the user&#39;s right eye, the arrangement could be modified to, alternatively or additionally, determine the gaze of the user&#39;s other eye. Whilst  FIG. 2  shows a single detector  213  for detecting the gaze of one eye, i.e. the user&#39;s right eye, the arrangement could be modified to determine the gaze of the eye using two or more detectors. Whilst  FIG. 2  shows two light sources  212   a  and  212   b,  and two modulators  201   a  and  201   b,  a single light source and/or a single light modulator could be provided for generate image display and probe beams that are incident to each of the two in-coupling diffractive element areas  107   a  and  107   b.    
     In the apparatus of  FIG. 2 , where a combined visible and infrared light source is used, i.e. that simultaneously generates both visible and infrared light (as opposed to separately and independently generating visible and IR light such that the emission of visible and IR light can be separately and independently controlled), the apparatus may further comprise a selectively controllable filter to selectively filter out one of: the visible light (or a sub colour channel thereof) or the infrared light. 
     In some examples, e.g. where the IR optimised light guide is below (and disposed closer to the eye than) the RGB optimised light guide, a passive IR pass filter could be placed between the in-coupling area of the RGB optimised light guide and the in-coupling area of the IR optimised light guide, e.g. so as to reduce in-coupling of RGB light to the IR light guide. Alternatively, in other examples, e.g. where the RGB optimised light guide is below (and placed closer to the eye than) the IR optimised light guide, an IR blocking filter could be placed between the respective in-coupling areas, e.g. so as to reduce in-coupling of IR light to the RBG light guide. 
     In some examples a Liquid Crystal (LC) shutter could be placed between the light guides and the outside environment/world/reality. For example the LC shutter could form part of a selectively transparent part of the external housing of the apparatus which is configured to selectively enable a real world view though the apparatus. Adjusting the shutter&#39;s transmissivity would control how much ambient light gets to the eye through the shutter and through the transparent light guides. The LC shutter could, in some examples, be integrated into an IR optimised light guide, in which case such a light guide may be placed between the RGB optimised light guide(s) and the outside environment/world/reality so that it would not block the RGB light from the light guide reaching the eye. 
     In some examples, the light guide  106   a ′ which in-couples, expands and out-couples the infrared gaze tracking probe beam may be configured so as to selectively filter the transmission of infrared light therethrough. The light guide  106   a ′ may be configured to act as a liquid crystal shutter that can selectively block the transmission of infrared light therethrough whilst still permitting the transmission of visible light therethrough. 
     When an image display beam is being generated and outputted, a selectively controllable filter may be used to block infrared light such that only visible light is incident to the user&#39;s eye during periods of outputting the image display beam output for user viewing. Likewise, in other examples, visible light may be selectively filtered/blocked/switched off such that only infrared gaze tracking light probe beam may be generated and incident to the user&#39;s eye when outputting an infrared gaze tracking probe beam. 
       FIG. 3  schematically illustrates an example of light guides  306   a  and  306   b  suitable for use with examples of the present disclosure. For example, the light guides  306   a  and  306   b  may be configured for use as light guides  106   a  and  106   b,  or  106   a ′ and  106   b ′ of  FIG. 2 . 
     The light guide  306   a  comprises in-coupling diffractive area  307   a  which in-couples an input beam  305   a  to the substrate, which beam is then expanded via diffractive element area  316   a  in a y direction and then expanded in an x direction and out-coupled out of the light guide via an out-coupling diffractive element  308   a  so as to produce output beam  311   a.  The input optical beam  305   a  may correspond to an image display beam (or a component of the image display beam such as a red, green or blue component thereof) or an infrared gaze tracking probe beam. 
     In the apparatus of  FIG. 2 , the reflected gaze tracking probe beam  214  needs to propagate through each of the stacked light guides  106   a ′ and  106   a  to reach the detector for detection.  FIG. 4  schematically shows an apparatus  400  that avoids such issues. 
       FIG. 4  schematically shows an apparatus in the form of glasses/goggles with support members/arms  418  for holding the apparatus in place on a user&#39;s head. In this example, the detector  413  is not disposed on the light guides. Instead, a reflector element  417 , such as a mirror or hot mirror configured to reflect infrared light, is provided e.g. on in the light guide, namely an inner/lower surface of the lower light guide. It is to be appreciated that the reflector element could be located almost anywhere in front of the eye, even on an opposite side of the light guide stack. 
     The reflector is configured to further reflect  419  the reflected gaze tracking beam to a detector  413 , thereby providing increased flexibility as to the location of the detector. In this example, the detector is disposed on a part of a housing of the apparatus such as support arm  418 . The reflector  417  may be further configured so as to provide optical power so as to focus the reflected infrared gaze tracking probe beam  214  towards the detector  413 . 
       FIG. 5A  schematically illustrates an example of an apparatus  500  comprising a combined/highly integrated visible and infrared light source  512  which may be used as a laser projector engine. A laser diode  521  generates infrared light which is focused by lens  522  into a non-linear crystal  523 , such as periodically poled lithium niobate (PPLN), comprising a surface bragg grating whereby the infrared light is converted into red, green and blue visible wavelengths. However, some infrared light will pass through the non-linear crystal without undergoing such conversion. A conventional laser projection engine would typically block such non-converted infrared light deeming it to be an undesired noise signal. However, such non-converted infrared light may advantageously be used in examples of the present application as a source of infrared illumination. Thus, the light source  512  provides the simultaneous generation of both visible light as well as infrared light that can be incident to a light modulator  501 , under control of a controller  515 , so as to sequentially generate an image display beam and a gaze tracking probe beam from the incident visible and infrared beams respectively. A selectively controllable filter or shutter may be used to selectively filter/block IR light when the image display beam is being generated and likewise selectively filter/block visible light when the gaze tracking probe beam is being generated. 
     The light modulator  501  comprises a two axis scanning mirror which can be used to impart an image to the visible light from the light source to generate the image display beam. Also, the light modulator can be used to impart a pattern on the infrared light from the light source to generate the gaze tracking probe beam. 
       FIG. 5B  schematically illustrates an apparatus  530  with an alternative light source  512  and an alternative light modulator  501 . The light source  512  is configured to independently and separately generate visible light (and/or sub component colour channels thereof) and infrared light. The light source  512  may corresponds to one or more separate light sources, e.g. LEDs, such as: red, green, blue and infrared LEDs which are independently operable under control of a controller  515 . Light from the LEDs is directed to a reflective microdisplay  531  via beam splitter  532 . The modulated/modified light reflected from the microdisplay is then guided to a prism  533  and reflected therefrom to an in-coupling diffractive element area  507  of a light guide  506  to be out-coupled to a user&#39;s eye  110  via out-coupling diffractive element area  508 . A detector  513  is provided that is configured to detect the out-coupled light which is reflected from the user&#39;s eye. 
     The apparatuses as variously described above may be provided in a module. As used here ‘module’ refers to a unit or apparatus that excludes certain parts/components that would be added by an end manufacturer or a user. 
     In certain examples, the apparatus may be provided as a device, wherein a device is configured for at least one of portable use, wearable use and head mountable use. The device may also be configured to provide functionality in addition to display and gaze tracking. For example, the device may additionally be configured to provide one or more of: audio/text/video communication functions (e.g. tele-communication, video-communication, and/or text transmission (Short Message Service (SMS)/Multimedia Message Service (MMS)/emailing) functions), interactive/non-interactive viewing functions (e.g. web-browsing, navigation, TV/program viewing functions), music recording/playing functions (e.g. Moving Picture Experts Group-1 Audio Layer 3 (MP3) or other format and/or (frequency modulation/amplitude modulation) radio broadcast recording/playing), downloading/sending of data functions, image capture function (e.g. using a (e.g. in-built) digital camera), and gaming functions. 
     The apparatus may be a part of a NED device, for example, glasses or goggles. It should be understood, however, that glasses or goggles are merely illustrative of an NED device that would benefit from examples of implementations of the present disclosure and, therefore, should not be taken to limit the scope of the present disclosure to the same. For example the apparatus may take other forms such as a visor or helmet or may be implemented in other electronic devices not least hand devices, or portable devices. 
     Although examples of the apparatus have been described above in terms of comprising various components, it should be understood that the components may be embodied as or otherwise controlled by a corresponding processing element, processor or circuitry of the apparatus. 
     As used in this application, the term ‘circuitry’ refers to all of the following:
         (a) hardware-only circuit implementations (such as implementations in only analogue and/or digital circuitry) and   (b) to combinations of circuits and software (and/or firmware), such as (as applicable): (i) to a combination of processor(s) or (ii) to portions of processor(s)/software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and   (c) to circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present.       

     This definition of ‘circuitry’ applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term “circuitry” would also cover an implementation of merely a processor (or multiple processors) or portion of a processor and its (or their) accompanying software and/or firmware. 
     Features described in the preceding description may be used in combinations other than the combinations explicitly described. 
     Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not. Although various examples of the present disclosure have been described in the preceding paragraphs, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as set out in the claims. 
     The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to “comprising only one . . . ” or by using “consisting”. 
     In this description, wording such as ‘couple’, ‘connect’ and ‘communication’ and their derivatives mean operationally coupled/connected/in communication. It should be appreciated that any number or combination of intervening components can exist (including no intervening components). 
     In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some or all other examples. Thus ‘example’, ‘for example’ or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. 
     In this description, references to “a/an/the” [feature, element, component, means . . . ] are to be interpreted as “at least one” [feature, element, component, means . . . ] unless explicitly stated otherwise. 
     The above description describes some examples of the present disclosure however those of ordinary skill in the art will be aware of possible alternative structures and method features which offer equivalent functionality to the specific examples of such structures and features described herein above and which for the sake of brevity and clarity have been omitted from the above description. Nonetheless, the above description should be read as implicitly including reference to such alternative structures and method features which provide equivalent functionality unless such alternative structures or method features are explicitly excluded in the above description of the examples of the present disclosure. 
     Whilst endeavouring in the foregoing specification to draw attention to those features of examples of the present disclosure believed to be of particular importance it should be understood that the applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.