Eye tracking system

Abstract

An eye tracking system (1) comprising a radiation source (2) configured to emit a radiation (7), a waveguide (3), and a volume phase hologram (4) is specified, wherein - the waveguide (3) provides a propagation medium between the radiation source (2) and the volume phase hologram (3); - the volume phase hologram (4) is configured to deflect the radiation towards a user's eye (9); and - the eye tracking system (1) is configured to provide a self-mixing interferometry signal in response to the radiation reflected off or scattered at a part of the user's eye (9) and coupled back into the radiation source (2).

Description

[0001] Description

[0002] EYE TRACKING SYSTEM

[0003] The present application relates to an eye tracking system .

[0004] Most of the current eye-tracking systems are camera-based . Although they are good at capturing the gaze angle , they suf fer from a relatively low frame rate and a comparably high power consumption .

[0005] It is an obj ect to provide an improved eye tracking system .

[0006] This obj ect is achieved, inter alia, by an eye tracking system according to claim 1 . Developments and expediencies are subj ect of the further claims .

[0007] An eye tracking system is speci fied .

[0008] According to at least one embodiment of the eye tracking system, the eye tracking system comprises a radiation source configured to emit a radiation .

[0009] For example , the radiation source comprises a laser source with a cavity configured to emit coherent radiation to irradiate at least part of an eye of the user, for example a cornea, a sclera, or a retina of the user' s eye . For example , the laser source comprises one or more laser diodes to produce one or more laser beams . For example , the laser source comprises a vertical cavity surface-emitting laser (VCSEL ) or an array of VCSELs . VCSELs have a low threshold current and thus have a comparably low power consumption . Further, they can have small dimensions and are available at low cost . However, other laser diodes may also be used, such as edge-emitting lasers , for example distributed feedback ( DFB ) lasers or distributed Bragg reflector ( DBR) lasers .

[0010] For example , the radiation source is configured to emit radiation with a peak wavelength in the infrared or near infrared spectral range . For example , the radiation source is configured to emit radiation with a peak wavelength in a range from 800 nm to 1500 nm . Alternatively or in addition, the radiation source may be configured to emit radiation in the visible spectral range .

[0011] According to at least one embodiment of the eye tracking system, the eye tracking system comprises a waveguide . In particular, the waveguide is arranged in a beam path between the radiation source and the user' s eye . For example , the waveguide extends between a user side and a world side opposite the user side . For example , the waveguide has a thickness in a range from 0 . 1 mm to 10 mm .

[0012] In particular, the waveguide is transparent to the wavelength of the radiation to propagate along a predetermined path through the waveguide due to total internal reflection ( TIR) . In particular, a material of the waveguide may have a refractive index which is higher than that of an environment such as air . For example , the waveguide comprises a glass , a crystal , or a plastics material such as a polymer .

[0013] According to at least one embodiment of the eye tracking system, the eye tracking system comprises a volume phase hologram (VPH) . Using a VPH, radiation impinging onto the VPH at a predefined angle may be deflected into a direction enclosing a speci fic angle with the VPH, wherein the speci fic angle can be defined during production of the VPH, for example . The VPH may ful fil one or more one optical functions . For example , the optical function includes at least one of : deflecting, focussing, converging, collimating, diverging .

[0014] According to at least one embodiment of the eye tracking system, the waveguide provides a propagation medium between the radiation source and the volume phase hologram . Thus , the radiation emitted by the radiation source during operation of the eye tracking system and coupled into the waveguide may travel within the waveguide towards the volume phase hologram .

[0015] According to at least one embodiment of the eye tracking system, the volume phase hologram is configured to deflect the radiation towards a user' s eye . In particular, the radiation propagating in the waveguide may be deflected such that it is coupled out from the waveguide to irradiate at least a region of the user' s eye . Likewise , radiation returning from the eye may be deflected by means of the volume phase hologram on its way back to the radiation source . For example , a volume phase hologram or a combination of volume phase holograms can be configured to provide di f ferent optical trans formations , for example a point to point trans formation, a point to plane wave trans formation, a plane wave to plane wave trans formation or a plane wave to point trans formation, or a sequence of such optical trans formations .

[0016] According to at least one embodiment of the eye tracking system, the eye tracking system is configured to provide a sel f-mixing interferometry ( SMI ) signal in response to the radiation reflected of f or scattered at a part of the user' s eye and coupled back into the radiation source .

[0017] In particular, sel f-mixing interference occurs as a portion of the radiation irradiating the eye is reflected or scattered back from a surface of the eye into a cavity ( or resonator ) of the radiation source . For example , the surface is a cornea or a sclera or an internal surface of the eye such as a retina or an inner surface of the lens . An interference of this portion with the original radiation of the radiation source leads to an SMI signal providing information on a movement of the user' s eye such as a rotation or a velocity or a distance of the eye from the eye tracking system modulation . For example , a frequency or a number of interference fringes of the SMI signal may provide the information . For example , the interferences cause modulations of a laser output intensity that may be detected by a detector such as a photodiode .

[0018] For example , the detector is integrated in the radiation source and configured to obtain a sel f-mixing interference signal . For example , the detector comprises a photodiode arranged behind or within the laser cavity in order to measure the output intensity of the laser .

[0019] For example , the photodiode and an active region of a semiconductor laser as radiation source are integrated in a common semiconductor body comprising semiconductor layers formed by epitaxial growth .

[0020] Alternatively, the photodiode may be located behind a back mirror of the laser cavity arranged opposite to a front mirror . Most of the radiation is emitted during operation of the radiation source through the front mirror .

[0021] Alternatively or in addition, modulations of an electrical operation parameter of the radiation source may be used, for example a laser operation voltage or a laser operation current . Changes in these parameters likewise allow information on the eye movement to be obtained, as these parameters are af fected by sel f-mixing interferometry ef fects as well .

[0022] In at least one embodiment of the eye tracking system, the eye tracking system comprises a radiation source configured to emit a radiation, a waveguide , and a volume phase hologram, wherein the waveguide provides a propagation medium between the radiation source and the volume phase hologram . The volume phase hologram is configured to deflect the radiation towards a user' s eye . The eye tracking system is configured to provide a sel f-mixing interferometry signal in response to the radiation reflected of f or scattered at a part of the user' s eye and coupled back into the radiation source .

[0023] Thus , the user' s eye may provide a surface that reflects or scatters the radiation impinging onto the eye back into the cavity of the radiation source via the waveguide .

[0024] In particular, the eye tracking system allows to obtain information on the eye movement in a very reliable and ef ficient manner . For example , the eye velocity and / or an eye distance change may be derived from the SMI signal . Compared to traditional camera-based eye-tracking systems , a higher repetition rate and a lower power consumption can be obtained .

[0025] During operation of the eye tracking system the radiation may propagate through the waveguide from the radiation source to the volume phase hologram . In particular, total internal reflection may force the radiation to follow a certain path within the waveguide .

[0026] Compared to free space propagation from the radiation source to the VPH, low optical losses can be obtained . Further, the risk that the radiation may be blocked by the user' s body elements such as hair is avoided or at least strongly reduced .

[0027] Further, the waveguide is part of an optical path for the radiation returning from the eye between the volume phase hologram and a sensing module .

[0028] The volume phase hologram may provide an optical function appropriate for determining the sel f-mixing interferometry SMI signal to perform eye tracking . For example , the volume phase hologram is the last beam shaping element in a beam path from the radiation source to the eye . In particular, the volume phase hologram is arranged in a beam path from the eye back to the radiation source . In particular, the waveguide may be used for a back-and- forth-path of the radiation, wherein the radiation goes two times the same path through the waveguide .

[0029] The optical function of the volume phase hologram may be adapted to the way the radiation propagates within the waveguide . For example , the radiation propagating within the waveguide may be collimated, divergent , convergent or focused .

[0030] Alternatively, or in addition, the optical function of the volume phase hologram may be adapted to the region of the eye that is to be irradiated . For example , the radiation may be convergent or focused on its way from the volume phase hologram to the eye i f the sclera or the cornea is used as reflecting and / or scattering surface of the eye . For example , it has been found that an eye movement signature using the cornea can be obtained with the highest signature i f the radiation is focused onto the cornea .

[0031] Collimated radiation may be used, for example , i f the retina is to be irradiated . In this case , the lens of the user' s eye may act as a converging or focussing element .

[0032] Further, the characteristics of the reflected or scattered radiation may be considered for the parameters of the eye tracking system . For example , mostly di f fuse reflection occurs at the sclera, whereas specular reflection may dominate at the cornea .

[0033] According to at least one embodiment of the eye tracking system, the volume phase hologram comprises at least two multiplexed optical functions . During the recording of the volume phase hologram the two or more optical functions can be formed within the same holographic film . Thus , a holographic pattern within the volume phase hologram is configured to ful fil two or more optical functions .

[0034] For example , the volume phase hologram with multiplexed optical functions is configured to direct the radiation onto di f ferent regions of the user ' s eye . Alternatively or in addition, the optical functions may be configured to perform di f ferent optical trans formations .

[0035] According to at least one embodiment of the eye tracking system, the eye tracking system comprises a further volume phase hologram . For example , the further volume phase hologram is configured to deflect radiation propagating within the waveguide towards the user' s eye . In particular, the volume phase hologram and the further volume phase hologram may provide di f ferent beam paths towards the eye . In other words , the volume phase hologram and the further volume phase hologram may represent the last di f fractive optical element within the respective beam path before the radiation impinges onto the eye . Thus , both the volume phase hologram and the further volume phase hologram may act as outcoupling elements for the radiation propagating within the waveguide . On its way back from the eye , the radiation may be coupled into the waveguide via the volume phase hologram and the further volume phase hologram .

[0036] Alternatively, the volume phase hologram and the further volume phase hologram may be arranged in a common beam path . For example , the further volume phase hologram is in a beam path between the radiation source and the volume phase hologram or vice versa .

[0037] Features described in connection with the volume phase hologram may also apply for the further volume phase hologram .

[0038] According to at least one embodiment of the eye tracking system, the volume phase hologram and the further volume phase hologram are configured to irradiate the user ' s eye at di f ferent regions and / or with di f ferent optical functions . In particular the di f ferent regions may be located on di f ferent surfaces of the eye . For example , a first region is located on the cornea or the sclera and a second region is located within the eye , for instance on the retina .

[0039] According to at least one embodiment of the eye tracking system, at least a part of the volume phase hologram is laterally spaced from the further volume phase hologram . Thus , the volume phase hologram and the further volume phase hologram do not overlap completely . The volume phase hologram and the further volume phase hologram may also be spaced apart from one another completely .

[0040] According to at least one embodiment of the eye tracking system, the volume phase hologram and the further volume phase hologram are formed in separate holographic films . Thus , the volume phase hologram and the further volume phase hologram may be produced independently from one another .

[0041] According to at least one embodiment of the eye tracking system, the volume phase hologram and the further volume phase hologram are formed in a common holographic film . In a view onto the waveguide , the volume phase hologram and the further volume phase hologram may overlap at least in regions or be spaced apart from one another . Thus , the same holographic film may be exposed during production such that multiplexed optical functions are provided within the holographic film .

[0042] According to at least one embodiment of the eye tracking system, the eye tracking system comprises a further radiation source configured to provide a further radiation . Features described in connection with the radiation source may also apply for the further radiation source . The radiation and the further radiation may have the same peak emission wavelength or di f ferent peak emission wavelengths .

[0043] According to at least one embodiment of the eye tracking system, the further volume phase hologram is configured to deflect the further radiation towards the user ' s eye . For example , the further volume phase hologram is the last di f fractive optical element in the beam path before the further radiation impinges onto the user ' s eye .

[0044] According to at least one embodiment of the eye tracking system, the eye tracking system comprises an incoupling optical element for coupling the radiation of the radiation source into the waveguide . The incoupling optical element may be located on any side of the waveguide . For example , the incoupling optical element is a prism, a lens , a grating or an additional volume phase hologram . For example , the incoupling optical element is connected to the waveguide in a mechanically stable manner . For example , the incoupling optical element is attached to the waveguide . Alternatively, the incoupling optical element and the waveguide may be formed in one piece .

[0045] The eye tracking system may comprise a further incoupling optical element to couple the further radiation of the further radiation source into the waveguide . Alternatively, the same incoupling element may be used to couple the radiation and the further radiation into the waveguide . For example , the waveguide is used for a back and forth path of the radiation . Thus , the incoupling optical element can also be used to couple out the radiation returning from the eye on its way back to the cavity of the radiation source .

[0046] Thus , the beam path from the eye back to the radiation source does not require any optical elements in addition to those provided for the beam path from the radiation source to the eye . In particular, the volume phase hologram may also be used to couple the radiation returning from the eye into the waveguide . Thus , there is no need for an additional optical element , such as a volume phase hologram, to couple the radiation coming back from the eye into the waveguide towards the radiation source .

[0047] In a similar manner, the waveguide may be used for a back and forth path of the further radiation .

[0048] According to at least one embodiment of the eye tracking system, a beam shaping optics is arranged between the radiation source and the volume phase hologram . In particular, the beam shaping optics may be arranged between the radiation source and the incoupling optical element . For example , the beam shaping optics is a refractive optical element such as a lens . Alternatively or in addition, the beam shaping optics may comprise or consist of a di f fractive optical element such as a grating or a volume phase hologram .

[0049] For example , the beam shaping optics is configured to control the propagation of the radiation within the waveguide . For example , the beam shaping optics may collimate , converge , focus , or diverge the radiation propagating within the waveguide . According to at least one embodiment of the eye tracking system, a main irradiation axis of the radiation irradiating the user ' s eye is tilted with respect to a normal of a surface of the user ' s eye . For example , an angle between the main irradiation axis and the normal to the surface of the user ' s eye is at least 5 ° or at least 10 ° and / or at most 70 ° or at most 60 ° , in particular in a range from 10 ° to 60 ° . In particular, the angle may be chosen depending on the region of the eye to be irradiated .

[0050] Alternatively, the main irradiation axis may extend parallel with respect to the normal of the surface of the user' s eye .

[0051] The main irradiation axis of the radiation and a further main irradiation axis of the further radiation may extend parallel or obliquely with respect to one another .

[0052] According to at least one embodiment of the eye tracking system, the volume phase hologram is a transmission volume phase hologram arranged on a user side of the waveguide or a reflection volume phase hologram arranged on a world side of the waveguide . In both cases the volume phase hologram may be combined with one or more further volume phase holograms arranged on the world side and / or the user side of the waveguide .

[0053] According to at least one embodiment of the eye tracking system, the eye tracking system further comprises a camera configured to image the user' s eye . In particular, the radiation source may be used to generate glint to be detected by the camera . Thus , additional glint generating LEDs used in conventional camera-based systems may be dispensed with . The additional information provided by the camera may help to further increase the eye tracking reliability .

[0054] According to at least one embodiment of the eye tracking system, the eye tracking system is configured to be integrated in a wearable device for mounting to the user ' s head . For example , the wearable device is a headset , glasses , smart glasses or a helmet .

[0055] For example , the eye tracking system may be used for augmented reality (AR) , virtual reality (VR) , mixed reality (MR) or extended reality (XR) applications .

[0056] For example , the volume phase hologram and the further volume phase hologram are reflection volume phase holograms . The reflection volume phase holograms may be arranged in the same optical beam path from the radiation source to the eye . Alternatively, the reflection volume phase hologram and the further reflection volume phase hologram may provide di f ferent optical beam paths from the radiation source or the further radiation source to the eye and back to the respective radiation source .

[0057] According to at least one embodiment of the eye tracking system, the volume phase hologram and the radiation source are fixed together with the waveguide . In particular, the radiation source may be mechanically stably connected to the waveguide during production of the eye tracking system . Thus , the spatial relationship between these elements and the beam path from the radiation source to the volume phase hologram may be defined during production . During operation of the eye tracking system an unintended displacement of the volume phase hologram with respect to the radiation source can be avoided or at least greatly reduced .

[0058] In particular, the eye tracking system may be designed such that the waveguide and all optical elements located within a field of view of the user, for instance one or more volume phase holograms , are transparent so that the user ' s vision is not , or at least not signi ficantly, disturbed . Thus , the eye tracking system may also be used for augmented or mixed reality applications .

[0059] Features described above in connection with at least one embodiment of the eye tracking system can be combined with other features described in connection with at least one embodiment of the eye tracking system unless they are contradictory .

[0060] Further features and configurations will become apparent from the subsequent description of the exemplary embodiments in connection with the figures .

[0061] In the exemplary embodiments and figures similar or similarly acting constituent parts are provided with the same reference signs . Generally, only the di f ferences with respect to the individual exemplary embodiments are described . Unless speci fied otherwise , the description of a part or aspect in one exemplary embodiment applies to a corresponding part or aspect in another exemplary embodiment as well .

[0062] In the Figures :

[0063] Figure 1A shows an exemplary embodiment of the eye tracking system; Figure IB shows an example of a detail of the eye tracking system;

[0064] Figure 1C shows an example of a detail of the eye tracking system;

[0065] Figure ID shows an example of a detail of the eye tracking system;

[0066] Figure IE shows an example of a detail of the eye tracking system;

[0067] Figure 2 shows an exemplary embodiment of the eye tracking system;

[0068] Figure 3 shows an exemplary embodiment of the eye tracking system;

[0069] Figure 4 shows an exemplary embodiment of the eye tracking system;

[0070] Figure 5 shows an exemplary embodiment of the eye tracking system;

[0071] Figure 6 shows an exemplary embodiment of the eye tracking system;

[0072] Figure 7 shows an exemplary embodiment of the eye tracking system;

[0073] Figures 8A to 8C show di f ferent examples of shapes of a waveguide . The figures are schematic representations . The elements illustrated in the figures and their si ze relationships among one another are not necessarily true to scale . Rather, individual elements may be represented with a si ze exaggerated in at least one dimension for the sake of better representability and / or for the sake of better understanding .

[0074] An exemplary embodiment of an eye tracking system 1 is schematically illustrated in Figure 1A.

[0075] The eye tracking system 1 comprises a radiation source 2 configured to provide a radiation 7 , a waveguide 3 and a volume phase hologram 4 . The waveguide 3 provides a propagation medium between the radiation source 2 and the volume phase hologram 4 . Radiation guided within the waveguide 3 from the radiation source 2 to the volume phase hologram 4 due to total internal reflection is deflected by volume phase hologram 4 and exits the waveguide 3 at an output surface region 35 of the waveguide 3 to irradiate a user' s eye 9 .

[0076] Radiation reflected of f or scattered at a part of the user' s eye 9 and coupled back into the radiation source 2 causes an optical interference with the original radiation within a cavity 21 of the radiation source 2 resulting in a sel fmixing interferometry signal . The sel f-mixing interferometry signal provides information on an eye movement , for example , on an eye rotation and / or an eye velocity and / or on a distance between the eye 9 and the waveguide 3 .

[0077] Thus , the eye tracking system 1 provides a sel f-mixing interferometry signal that can be used for performing eye tracking . For example , the SMI signal reports on a change of optical path di f ference over time of the cornea 92 . This can be measured with a high signal to noise ratio and exploited for eye tracking, in particular because of the large numerical aperture provided by the volume phase hologram 4 and minimal losses of the radiation within the waveguide 3 on its way back to the radiation source 2 .

[0078] For example , the radiation source 2 comprises a single VCSEL or a VCSEL array .

[0079] In the exemplary embodiment of Figure 1A, the volume phase hologram 4 deflects and for example converges or focuses the radiation 7 propagating in the waveguide 3 onto the user' s eye 9 . However, another optical function of the volume phase hologram 4 may be appropriate for determining the sel f-mixing interferometry signal to perform eye tracking . This will be described in more detail in connection with the subsequent figures .

[0080] The waveguide 3 extends between a user side 31 and a world side 32 opposite the user side 31 . At the user side 31 and at the world side 32 , total internal reflection occurs so that the radiation 7 is guided from the radiation source 2 to the volume phase hologram 4 . At the volume phase hologram 4 the radiation propagating in the waveguide 3 and impinging onto the volume phase hologram 4 may be deflected with a high ef ficiency, so that almost the complete impinging radiation may be coupled out from the waveguide 3 towards the user' s eye 9 .

[0081] For example , the waveguide 3 may have a thickness in a range from 0 . 1 mm to 10 mm . For example , the waveguide 3 comprises a glass or a plastics material transparent to the radiation 7 of the radiation source 2 .

[0082] In the exemplary embodiment shown in Figure 1A, the radiation 7 is coupled into the waveguide 3 at the user side 31 of the waveguide 3 . However, the radiation may also be coupled into the waveguide 3 at the world side 32 or at a side face of the waveguide 3 .

[0083] The waveguide 3 is also part of an optical path for the radiation returning from the eye 9 , in particular between the volume phase hologram 4 and the radiation source 2 . In particular the waveguide 3 can be used for a back-and- forth path of the radiation, wherein the radiation 7 goes two times the same path through the waveguide 3 . Consequently, the optical path from the eye 9 back to the radiation source 2 does not require any optical elements in addition to those optical elements used for the optical path from the radiation source 2 towards the eye 9 .

[0084] As illustrated in the detail of Figure IB, the eye tracking system 1 , in particular the radiation source 2 may comprise a sensing module 22 to obtain the sel f-mixing interferometry signal .

[0085] The radiation source 2 further comprises a cavity 21 representing a resonator of a laser such as a VCSEL .

[0086] For easier representation, the resonator 21 and the sensing module 22 are not explicitly reproduced in all Figures .

[0087] The sensing module 22 is configured to provide the signal correlated to radiation of the radiation returning from the eye 9 . This radiation, which is scattered at or reflected of f the cornea or the sclera or another surface of the eye , and interferes with the radiation within the cavity 21 of the radiation source 2 causes a sel f-mixing interference providing information on the eye movement .

[0088] For example , the sensing module 22 may comprise a photodiode to detect an output intensity of the radiation 7 . The photodiode may be integrated into the laser chip or be provided as a separate component . The sel f-mixing interference causes a modulation of the output intensity . A number or a frequency of interference fringes detectable in the output intensity of the radiation 7 may be used to derive information on the eye movement .

[0089] Alternatively, the sensing module 22 may be configured to derive the sel f-mixing interferometry signal by monitoring an electrical operation parameter such as a current or a voltage of the radiation source 2 . These electrical operation parameters are likewise modulated due to sel f-mixing interference ef fects within the cavity 21 .

[0090] During operation of the eye tracking system 1 , the optical path of the radiation from the radiation source 2 to the eye 9 and back extends completely within solid material except for the space between the output surface region 35 and the eye 9 .

[0091] Consequently, the risk that human elements such as hair may block the beam path from the radiation source 2 to the volume phase hologram 4 can be avoided or at least reduced compared to a free space configuration where a volume phase hologram is directly irradiated by a radiation source without using a waveguide 3 .

[0092] Furthermore , the beam path between the radiation source 2 and the volume phase hologram 4 can be precisely defined during the production of the eye tracking system 1 by an appropriate alignment of the radiation source 2 with respect to the waveguide 3 and the volume phase hologram 4 .

[0093] Further, the eye tracking system 1 can be configured such that the eye tracking system can be used for individuals having di f ferent eye reliefs . For example , the eye tracking system 1 is configured to be operable in a range from 5 mm to 25 mm .

[0094] The optical function to be performed by the volume phase hologram 4 can be defined in a highly precise manner during production of the volume phase hologram 4 . A thickness of the volume phase hologram 4 , i . e . an extension of the volume phase hologram along a normal to the waveguide 3 , is large compared to the wavelength of the radiation 7 emitted by the radiation source 2 during operation . For example , the thickness is at least by a factor of 2 or at least by a factor of 10 larger than the wavelength of the radiation of the radiation source 2 .

[0095] The eye tracking system 1 may further include an incoupling optical element 5 arranged in the beam path from the radiation source 2 to the waveguide 3 .

[0096] Figures IB and 1C illustrate two examples of an incoupling optical element 5 . In the exemplary embodiment shown in Figure IB, the incoupling optical element 5 is a prism . The incoupling optical element 5 is configured such that the radiation from the radiation source 2 is coupled into the waveguide 3 at an incoupling angle with respect to a normal to the waveguide at this position of the waveguide 3 , which is equal to or larger than the critical angle for total internal reflection .

[0097] The waveguide 3 and the incoupling optical element 5 are configured such that the radiation coupled into the waveguide 3 impinges onto the volume phase hologram 4 after a predetermined number of total internal reflections at the user side 31 and the world side 32 . This can be obtained, for example , by appropriately selecting waveguide parameters such as the thickness or the refractive index and / or the angle at which the radiation is coupled into the waveguide 3 and / or a distance between the radiation source 2 and the volume phase hologram 4 . Thus , the radiation 7 propagates within the waveguide 3 along a predetermined beam path .

[0098] In the exemplary embodiment of Figure 1C, the incoupling optical element 5 comprises an additional volume phase hologram configured as a transmission volume phase hologram 43 . Alternatively, a di f fractive optical element such as a di f fraction grating may be used .

[0099] Further, a beam shaping optics 6 is arranged between the radiation source 2 and the incoupling optical element 5 in the example of Figure 1C . For example , the beam shaping optics 6 is a lens that collimates the radiation 7 .

[0100] Such a beam shaping optics 6 may also be used in connection with other incoupling optical elements 5 . Further, the beam shaping optics 6 may ful fil other optical functions . For example , the beam shaping optics 6 may converge or focus or diverge the radiation 7 .

[0101] In the exemplary embodiment of Figure 1A, the radiation 7 diverges in the waveguide 3 on its way to the volume phase hologram 4 . The volume phase hologram 4 deflects the impinging radiation, wherein focused radiation 701 impinges onto a surface of the eye 9 such as a sclera 91 or a cornea 92 . Thus , the volume phase hologram 4 is configured to perform a point to point trans formation . However, other optical trans formations may also be used .

[0102] Further, a main irradiation axis of the radiation impinging onto the eye 9 extends parallel to a normal of the surface . However, a perpendicular incidence is not required .

[0103] In the examples of Figures ID and IE , a main irradiation axis 45 of the radiation 7 extends obliquely with respect to the surface 97 of the eye . For example , an angle 49 between a normal 99 to the surface 97 and the main irradiation axis 45 is at least 5 ° or at least 10 ° and / or at most 70 ° or at most 60 ° .

[0104] Such an oblique incidence onto the surface 97 of the eye 9 may also be appropriate for collimated radiation 7 or divergent radiation 7 .

[0105] Further, the examples of Figure ID and IE di f fer from one another with respect to the configuration of the volume phase hologram 4 . In the example of Figure ID, the volume phase hologram 4 is a reflection volume phase hologram 42 arranged on the world side 32 of the waveguide 3 . The radiation propagating in the waveguide 7 is deflected by the reflection volume phase hologram 4 such that it exits from the user side 31 of the waveguide 3 .

[0106] In the example of Figure IE , the volume phase hologram 4 is a transmission volume phase hologram 43 arranged on the user side 31 of the waveguide 3 . A transmission volume phase hologram 43 may also be used for all other exemplary embodiments .

[0107] In the exemplary embodiments of Figure 1A to 7 , the waveguide 3 is flat . However, other shapes may also be used for the waveguide 3 .

[0108] Examples of waveguide shapes are illustrated in Figures 8A to 8C . In Figure 8A the waveguide 3 is curved . In the example of Figure 8B, the waveguide has a wedge shape .

[0109] In the example of Figure 8C, the waveguide 3 comprises a plurality of parts , for example a first waveguide part 33 and a second waveguide part 34 . For example , the first waveguide part 33 has a lens shape and the second waveguide part 34 has a wedge shape . These and other shapes of the waveguide 3 may apply to all exemplary embodiments of the eye tracking system 1 .

[0110] The exemplary embodiment of Figure 2 essentially corresponds to the exemplary embodiment of Figure 1A.

[0111] In contrast , the volume phase hologram 4 is configured to irradiate the eye 9 with a collimated radiation 704 . The collimated radiation 704 passes through a pupil 93 of the eye 9 and is focused by a lens 94 of the eye 9 onto a retina 95 of the eye 9 . Thus , the lens 94 of the eye 9 is used as a last optical element within the optical beam path from the radiation source 2 to the surface of the eye to be used as reflecting or scattering surface . A di f fuse reflection occurs at the retina 95 , so that a part of the radiation is coupled back to the cavity 21 of the radiation source 2 .

[0112] In this exemplary embodiment , the volume phase hologram 4 is configured to perform a point to plane wave trans formation . Instead of the retina 95 , another surface of the eye behind the pupil 93 may also be used .

[0113] The SMI signal obtained is mostly influenced by the radial velocity of the eye rotation on the retina, the latter being directly related to the eye movement . As in the previous exemplary embodiment a high signal to noise ratio can be obtained .

[0114] The exemplary embodiment of Figure 3 substantially corresponds to the exemplary embodiment of Figure 1A.

[0115] In contrast , the volume phase hologram 4 is configured to provide a divergent radiation 705 to irradiate the eye 9 . Thus , the radiation spot on the eye 9 may be larger than a lateral extent of the volume phase hologram 4 along the waveguide 3 .

[0116] Using this approach, a large surface , or even the full eye surface , may be irradiated by the radiation 7 . In this exemplary embodiment , the volume phase hologram 4 is configured to perform a point to diverging rays trans formation .

[0117] As in the previous exemplary embodiments , the reflected radiation may contribute to the SMI signal used for eye tracking . In addition the radiation can also serve as illumination for an optional external camera 8 . This can be used to get a contrasted image and / or to produce glints at the eye surface to be used for eye tracking . In this case , the high versability of volume phase holograms allows the radiation source to ful fill two di f ferent tasks at once . This may help to improve the eye tracking system performances . In particular, the eye tracking system may rely both on an SMI signal and on camera data .

[0118] The exemplary embodiment of Figure 4 essentially corresponds to the exemplary embodiment of Figure 1A.

[0119] In contrast , the eye tracking system 1 comprises a further volume phase hologram 41 in addition to the volume phase hologram 4 . For example , the volume phase hologram 4 and the further volume phase hologram 41 are formed in the same holographic film 40 . The volume phase hologram 4 and the further volume phase hologram 41 may spatially overlap at least in regions or be spaced apart from one another .

[0120] In the exemplary embodiment of Figure 4 , the volume phase hologram 4 and the further volume phase hologram 41 are configured to provide di f ferent optical functions and to irradiate di f ferent regions of the eye 9 . The volume phase hologram 4 provides focused radiation 701 irradiating a sclera 91 of the eye 9 . The further volume phase hologram 41 is configured to provide collimated radiation 704 passing through a pupil 93 . This radiation is focused onto a retina 95 of the eye 9 .

[0121] The eye tracking system 1 further comprises a further radiation source 25 in addition to the radiation source 2 . The radiation source 2 is configured to irradiate the volume phase hologram 4 . The further radiation source 25 is configured to irradiate the further volume phase hologram 41 .

[0122] The radiation source 2 and the further radiation source 25 may use separate incoupling optical elements or a common incoupling optical element wherein the incoupling optical element ( s ) may be configured as described in connection with Figures IB or 1C, for instance .

[0123] In this exemplary embodiment the radiation 7 and the further radiation 75 use di f ferent volume phase holograms to irradiate di f ferent regions of the eye . The further volume phase hologram 41 has no , or at least no signi ficant , impact on the radiation 7 of the radiation source 2 on its way to the eye and back . Likewise the volume phase hologram 4 has no , or at least no signi ficant , impact on the further radiation 75 of the further radiation source 25 on its way to the eye and back . The radiation source 2 and the further radiation source 25 may emit radiation with the same peak emission wavelength or with di f ferent peak emission wavelengths .

[0124] Alternatively or in addition, the radiation 7 may be provided by a single radiation source 2 and be split into two or more beams irradiating the volume phase hologram 4 and the further volume phase hologram 41 .

[0125] Further, a small collimated beam may be combined with a diverging beam to irradiate the volume phase hologram 4 and the further volume phase hologram 41 .

[0126] The exemplary embodiment illustrated in Figure 5 essentially corresponds to the exemplary embodiment of Figure 4 . In contrast , the volume phase hologram 4 and the further volume phase hologram 41 are formed from separate holographic films 40 . Consequently, the volume phase hologram 4 and the further volume phase hologram 41 can be produced independently from one another .

[0127] The exemplary embodiment of Figure 6 essentially corresponds to the exemplary embodiment of Figure 1A.

[0128] In contrast , a beam shaping optics 6 is arranged in a beam path from the radiation source 2 to the volume phase hologram 4 . For example , the beam shaping optics 6 is configured to collimate the radiation 7 . The volume phase hologram 4 may perform a plane wave to plane wave trans formation, for instance . Thus , the volume phase hologram 4 may di f fract the radiation 7 and redirect the collimated onto the eye 9 as described in connection with Figure 2 , for instance .

[0129] Alternatively, the volume phase hologram 4 may perform a plane wave to point trans formation to focus the collimated radiation onto the eye 9 as described in connection with Figure 1A, for instance . For example , the beam shaping optics 6 may be arranged between the radiation source 2 and the incoupling optical element 5 , as described in connection with Figure 1C .

[0130] For example , the beam shaping optics 6 may be configured as a refractive optical element such as a lens .

[0131] I f more than one radiation source 2 is present , each radiation source may be provided with an individual beam shaping optics 6 . Alternatively, two or more radiation sources may share a common beam shaping optics . In both cases , each radiation source may experience a di f ferent optical function .

[0132] The exemplary embodiment of Figure 7 essentially corresponds to the exemplary embodiment of Figure 6 .

[0133] In contrast , the beam shaping optics 6 is configured as a further volume phase hologram 41 acting as a lens to collimate the radiation 7 propagating within the waveguide 3 . In this case , the further volume phase hologram 41 is arranged in the beam path from the radiation source 2 to the volume phase hologram 4 . Thus , the desired final optical output can be obtained by splitting up the optical function between two or more optical elements such as the volume phase hologram 4 and the further volume phase hologram 41 . For example , the position of the beam shaping optics 6 allows for adj usting the final beam waist of the radiation 7 . In Figure 7 , the beam shaping optics 6 is a reflection volume phase hologram on the world side of the waveguide . However, a transmission volume phase hologram or a reflection volume phase hologram located on the user side 31 of the waveguide 3 may also be used . The volume phase hologram 4 may be configured to perform a plane wave to plane wave trans formation as described in connection with Figure 6 . Alternatively, the volume phase hologram 4 may be configured to perform a plane wave to point trans formation or a plane wave to diverging rays trans formation to provide an irradiation of the eye 9 as described in connection with Figure 1A or Figure 3 respectively .

[0134] In the exemplary embodiments described above , parameters of the waveguide , the volume phase hologram, the beam waist of the radiation or the angle of incidence onto the eye may be speci fically adapted to the region of the eye that is to be used as reflecting or scattering surface . In particular, two or more volume phase holograms may be used to irradiate the eye with di f ferent optical functions and / or at di f ferent regions of the eye .

[0135] In particular due to the described combination of a waveguide with at least one volume phase hologram, eye tracking can be performed with a high reliability based on sel f-mixing interferometry . Compared to a system using free space propagation between the radiation source and the volume phase hologram, a similar signal to noise ratio may be obtained, but with a reduced risk of interference by human elements such as eyelashes , hair, or skin and with a higher robustness to misalignment over time .

[0136] This patent application claims the priority of German patent application 10 2024 121 932 . 7 , the disclosure content of which is hereby incorporated by reference . The invention described herein is not restricted by the description given with reference to the exemplary embodiments . Rather, the invention encompasses any novel feature and any combination of features , including in particular any combination of features in the claims , even i f this feature or this combination is not itsel f explicitly indicated in the claims or exemplary embodiments .

[0137] References

[0138] 1 eye tracking system

[0139] 2 radiation source

[0140] 21 cavity

[0141] 22 sensing module

[0142] 25 further radiation source

[0143] 3 waveguide

[0144] 31 user side

[0145] 32 world side

[0146] 33 first waveguide part

[0147] 34 second waveguide part

[0148] 35 output surface region

[0149] 4 volume phase hologram

[0150] 41 further volume phase hologram

[0151] 42 reflection volume phase hologram

[0152] 43 transmission volume phase hologram

[0153] 45 main irradiation axis

[0154] 49 angle

[0155] 5 incoupling optical element

[0156] 6 beam shaping optics

[0157] 7 radiation

[0158] 701 focused radiation

[0159] 704 collimated radiation

[0160] 705 divergent radiation

[0161] 706 asymmetric radiation

[0162] 75 further radiation

[0163] 8 camera

[0164] 9 eye

[0165] 91 sclera

[0166] 92 cornea

[0167] 93 pupil

[0168] 94 lens retina surface normal

Claims

Claims1. An eye tracking system (1) , comprising a radiation source (2) configured to emit a radiation (7) ; a waveguide (3) ; and a volume phase hologram (4) ; wherein the waveguide (3) provides a propagation medium between the radiation source (2) and the volume phase hologram (3) ; the volume phase hologram (4) is configured to deflect the radiation towards a user's eye (9) ; and the eye tracking system (1) is configured to provide a self-mixing interferometry signal in response to the radiation reflected off or scattered at a part of the user's eye (9) and coupled back into the radiation source (2) .

2. The eye tracking system according to claim 1, wherein the volume phase hologram (4) comprises at least two multiplexed optical functions.

3. The eye tracking system according to claim 1 or 2, wherein the eye tracking system (1) comprises a further volume phase hologram (41) .

4. The eye tracking system according to claim 3, wherein the further volume phase hologram (41) is arranged in a beam path from the radiation source (2) to the volume phase hologram ( 4 ) .

5. The eye tracking system according to claim 3 or 4, wherein the volume phase hologram (4) and the further volume phase hologram (41) are configured to irradiate the user'seye (9) at different regions and / or with different optical functions .

6. The eye tracking system according to any one of claims 3 to 5, wherein at least a part of the volume phase hologram (4) is laterally spaced from the further volume phase hologram (41) .

7. The eye tracking system according to any one of claims 3 to 6, wherein the volume phase hologram (4) and the further volume phase hologram (41) are formed in a common holographic film (40) .

8. The eye tracking system according to any one of the preceding claims, wherein the eye tracking system (1) comprises a further radiation source (25) configured to provide a further radiation (75) .

9. The eye tracking system according to claim 8 with reference to any one of claims 3 to 7, wherein the further volume phase hologram (41) is configured to deflect the further radiation (75) towards the user's eye (9) .

10. The eye tracking system according to any one of the preceding claims, wherein the eye tracking system (1) comprises an incoupling optical element (5) for coupling the radiation of the radiation source (2) into the waveguide (3) .

11. The eye tracking system according to claim 10,wherein a beam shaping optics (6) is arranged between the radiation source (2) and the volume phase hologram (4) .

12. The eye tracking system according to claim 10 and 11, wherein the beam shaping optics (6) is arranged between the radiation source (2) and the incoupling optical element (5) .

13. The eye tracking system according to any one of the preceding claims, wherein a main irradiation axis (45) of the radiation (7) irradiating the user's eye (9) is tilted with respect to a normal of a surface (97) of the user's eye (9) .

14. The eye tracking system according to any of the preceding claims , wherein the eye tracking system further comprises a camera(8) configured to image the user's eye (9) .

15. The eye tracking system according to any of the preceding claims , wherein the volume phase hologram (4) is a transmission volume phase hologram (43) arranged on a user side (31) of the waveguide (3) or a reflection volume phase hologram (42) arranged on a world side (32) of the waveguide (3) .

16. The eye tracking system according to any of the preceding claims , wherein the eye tracking device (1) is configured to be integrated in a wearable device for mounting to the user' s head .

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