Eye tracking sensor and ar / VR glasses and method for eye tracking

Abstract

An eye tracking sensor (10) is specified with - a self-mixing interferometry sensor (1) which is configured to emit a laser radiation (2) for illuminating an eye (3), wherein - the self-mixing interferometry sensor (1) is configured to emit the laser radiation (2) with a divergence (α), and - the self-mixing interferometry sensor (1) is configured to illuminate the eye (3).

Description

[0001] Description

[0002] EYE TRACKING SENSOR AND AR / VR GLASSES AND METHOD FOR EYE TRACKING

[0003] An eye tracking sensor is speci fied .

[0004] Document WO 2020 / 243185 Al describes an eye tracking sensor .

[0005] One obj ect to be solved is to provide an eye tracking sensor which is particularly compact .

[0006] According to at least one aspect of the eye tracking sensor, the eye tracking sensor comprises a sel f-mixing interferometry sensor . For example , the sel f-mixing interferometry sensor comprises or consists of a laser, such as a laser diode , wherein the laser comprises a laser active medium arranged inside an optical resonator . In particular, the laser emits electromagnetic laser radiation during operation . The electromagnetic laser radiation is in the infrared spectral range , for example .

[0007] The sel f-mixing interferometry sensor is configured to emit laser radiation for illuminating an eye . Further, the sel fmixing interferometry sensor is configured to interact with at least a part of the emitted laser radiation which is reflected back to the sensor at the eye .

[0008] For example , during sel f-mixing interferometry at least a part of the electromagnetic laser radiation that is emitted by the laser during operation is at least partially reflected back to the laser by an external obj ect . Speci fically, the external obj ect is an eye whose position, gaze direction, gaze traj ectory, gaze speed, corneal displacement and / or orientation is to be tracked, for example .

[0009] In particular, the reflected electromagnetic radiation is at least partially coupled back into the optical resonator of the laser . For example , the reflected electromagnetic laser radiation undergoes sel f-mixing interference inside the optical resonator, i . e . the reflected electromagnetic laser radiation interferes with the electromagnetic laser radiation that is generated by the laser active medium inside the optical resonator . For example , an amplitude , a phase and / or a frequency of the emitted electromagnetic radiation is altered due to the sel f-mixing interference inside the optical resonator .

[0010] For example , the altered amplitude , phase , and / or frequency of the emitted electromagnetic laser radiation can be detected and comprises information about the external obj ect , such as distance information, position information, speed information, movement information, and / or orientation information . For example resulting output power variations can be monitored by an integrated photodiode or a j unction voltage of the laser diode is monitored which removes the need for such a photodiode . As an example a discernable phase shi ft can be measured using the sel f-mixing interferometry and a cornea displacement can be linked to a fringe frequency .

[0011] For example , the sel f-mixing interferometry sensor provides an electrical signal that comprises a time-series data . For example , the time-series data comprises information about properties of the external obj ect as a function of time . In particular, the time-series data comprises data at a series of discrete time steps , and / or it comprises data that is continuous as a function of time . For example , the timeseries data is digital or analog . Analog time series data can be converted to digital time series data using an analogdigital converter before further processing, for example . The data can, for example , be passed through a speci fically trained neural network to output the angular positon of the eye and / or the gaze direction .

[0012] According to at least one aspect of the eye tracking sensor, the sel f-mixing interferometry sensor is configured to emit the laser radiation with a divergence . That is to say, the laser radiation is not emitted as a confined and focused ray, but a predefinable divergence for the laser radiation is set such that the laser radiation is emitted in a cone with a round or elliptic base .

[0013] According to at least one aspect of the eye tracking sensor, the sel f-mixing interferometry sensor is configured to illuminate the eye . In particular it is possible , that the sel f-mixing interferometry sensor is configured to direct the laser radiation directly at the eye . That is to say, the laser radiation propagates along a straight line from the sel f-mixing interferometry sensor to the eye such that the eye is directly illuminated by the laser radiation . For example , this can mean that a beam path between the sel fmixing interferometry sensor and the eye is free from any reflecting or di f fracting optical element which would change the direction of the laser radiation on its way from the sel f-mixing interferometry sensor to the eye .

[0014] According to at least one aspect of the eye tracking sensor, an eye tracking sensor is speci fied with - a sel f-mixing interferometry sensor which is configured to emit a laser radiation for illuminating an eye , wherein

[0015] - the sel f-mixing interferometry sensor is configured to emit the laser radiation with a divergence , and

[0016] - the sel f-mixing interferometry sensor is configured to illuminate the eye .

[0017] The here-described eye tracking sensor inter alia relies on the following considerations and ideas . For example , eye tracking sensors can be equipped with intermediate optical elements which focus a light beam onto a tiny spot in the eye in order to enhance the signal strength of the reflected light beam or to narrow the frequency peak of the reflected light beam . However, for this additional optical elements have to be used which increase weight and si ze of the eye tracking sensor . Surprisingly it has been found that the use of such often large , additional , for example reflective optical elements between a sel f-mixing interferometry sensor and the eye is not required . It has been found that i f for example the divergence of the emitted laser radiation and / or the distance of the sel f-mixing interferometry sensor and the eye are correctly set , eye movements can be tracked with good accuracy .

[0018] According to at least one aspect of the eye tracking sensor, the sel f-mixing interferometry sensor comprises a laser diode for emitting the laser radiation . For example , the laser diode is a VCSEL (vertical cavity surface emitting laser ) 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.

[0019] For example, the laser source is configured to emit radiation with a peak wavelength in the infrared or near infrared spectral range. For example, the laser source unit is configured to emit radiation with a peak wavelength in a range from 700 nm to 2000 nm.

[0020] According to at least one aspect of the eye tracking sensor, the self-mixing interferometry sensor comprises an optical element which is arranged between the laser diode and the eye. For example, the optical element is or comprises a micro optic which is in direct contact with the laser diode. The optical element fine-tunes the divergence of the laser radiation such that the self-mixing interferometry sensor emits laser radiation with a predefined divergence.

[0021] According to at least one aspect of the eye tracking sensor, the divergence is set between at least 5° and at most 25°, in particular between at least 10° and at most 20°, for example at 16°. With such a divergence, it is possible to create a desired spot size of the laser radiation on the eye. Thereby the divergence (in particular full angle) is e.g. measured at a point where the intensity of the laser radiation has dropped to l / eA2 of its maximum intensity.

[0022] According to at least one aspect of the eye tracking sensor, a distance between the self-mixing interferometry sensor and the eye is between at least 1 cm and at most 10 cm, in paricular between 2 cm and 4 cm, for example 3 cm. Again, with such a distance in combination with an adjusted divergence, a predefined beam size of the laser radiation on the eye can be reached.

[0023] According to at least one aspect of the eye tracking sensor, the laser radiation produces a beam, e.g. a spot, on the eye with a diameter of at least 0.5 cm and at most 2 cm, for example 1 cm. Thereby the diameter is measured at the eye plane. For example, the laser radiation can produce a circular or elliptic beam on the eye. In the case of an elliptic beam, the diameter is measured along the major axis of the ellipse. With such a beam size on the eye, different regions of the eye are illuminated. For example, such a beam covers a part of the cornea and a part of the remaining eyeball. Due to the different reflections of radiation at the different parts of the eye, information can be deduced, for example about the movement of the eye.

[0024] According to at least one aspect of the eye tracking sensor, the sensor is configured for integrating into another device. In particular, the eye tracking device is configured to be integrated in the wearable device for mounting to a user' s head. For example the wearable device is an AR headset, a VR headset, AR / VR glasses, smart glasses or a helmet.

[0025] Thereby, it is possible that the eye tracking sensor is integrated into a lens, for example into a lens of AR or VR glasses or a frame of AR or VR glasses.

[0026] According to at least one aspect of the eye tracking sensor, the eye tracking sensor further comprises a processing unit for processing a signal from the self-mixing interferometry sensor. Thereby it is possible that the processing unit is arranged at a distance to the self-mixing interferometry sensor of the eye tracking sensor . As an example , the processing unit can be integrated into the AR / VR glasses or the VR mask of which the eye tracking sensor is part . Further, it is possible that the processing unit is integrated into a device which is coupled with the sel fmixing interferometry sensor, like for example a cell phone or a computer

[0027] According to at least one aspect of the eye tracking sensor, the eye tracking sensor comprises two or more sel f-mixing interferometry sensors . In particular, the eye tracking sensor then comprises two or more here-described sel f-mixing interferometry sensors which directly illuminate the eye at di f ferent locations with a divergent beam each . For example , the eye tracking sensor comprises two or more sel f-mixing interferometry sensors per eye such that each eye is illuminated by two or more sel f-mixing interferometry sensors in the described way .

[0028] Further, AR / VR glasses are speci fied . According to at least one aspect , the glasses comprise a frame , temples and lenses and a here-described eye tracking sensor or here-described eye tracking sensors are integrated into the frame and / or at least one of the temples and / or at least one of the lenses . For example , two or more eye tracking sensors can be integrated into di f ferent parts of the frame , the temples and the lenses .

[0029] Further am method for eye tracking is speci fied . The here described method can be performed with a here described eye tracking sensor . That is to say all features described for the sensor are described for the method and vice versa . According to at least one aspect of the method, a sel f-mixing interferometry sensor emits laser radiation and illuminates an eye . Further, the sel f-mixing interferometry sensor e . g . absorbs at least a part of the emitted laser radiation which is reflected back to the sensor at the eye .

[0030] According to at least one aspect of the method, the sel fmixing interferometry sensor emits the laser radiation with a divergence . That is to say, the laser radiation is not emitted as a confined and focused ray, but a predefinable divergence for the laser radiation is set such that the laser radiation is emitted in a cone with a round or elliptic base .

[0031] According to at least one aspect of method, the sel f-mixing interferometry sensor illuminates the eye . For example , the sel f-mixing interferometry sensor directs the laser radiation directly at the eye . That is to say, the laser radiation propagates along a straight line from the sel f-mixing interferometry sensor to the eye such that the eye is directly illuminated by the laser radiation . For example , this can mean that a beam path between the sel f-mixing interferometry sensor and the eye is free from any reflecting or di f fracting optical element which would change the direction of the laser radiation on its way from the sel fmixing interferometry sensor to the eye .

[0032] According to at least one aspect of method, the method comprises

[0033] - a sel f-mixing interferometry sensor which emits a laser radiation and illuminates an eye , wherein

[0034] - the sel f-mixing interferometry sensor is emits the laser radiation with a divergence , and the sel f-mixing interferometry sensor illuminates the eye .

[0035] Further advantageous embodiments and further embodiments of the herein described eye tracking sensor, the herein described AR / VR glasses and the herein described method for eye tracking become apparent from the following exemplary embodiments described in connection with the figures .

[0036] Figure 1 shows a schematic drawing of an exemplary embodiment of a here-described eye tracking sensor and a here-described method;

[0037] Figure 2 shows a further exemplary embodiment of a here- described eye tracking sensor and a here-described method;

[0038] Figure 3 compares a here-described eye tracking sensor and a here-described method with an alternative solution in a schematic drawing; and

[0039] Figure 4 shows a schematic drawing of here-described AR / VR glasses .

[0040] In the exemplary embodiments and figures , identical , similar or identically acting elements are provided in each case with the same reference numerals . The elements illustrated and their si ze ratios to one another should not be regarded as being to scale , but rather individual elements , such as for example elements , components , devices and regions , may have been made exaggeratedly large to illustrate them better and / or to aid comprehension . In accordance with the schematic drawing of Figure 1, a first embodiment of a here-described eye tracking sensor and a here-described method is explained.

[0041] The eye tracking sensor 10 comprises two self-mixing interferometry sensors 1. Each of the self-mixing interferometry sensors 1 is configured to emit laser radiation 2 for illuminating an eye 3. That is to say, during operation the interferometry sensors 1 emits laser radiation

[0042] 2 and illuminates an eye 3

[0043] Thereby, each self-mixing interferometry sensor 1 is configured to emit the laser radiation 2 with a divergence d, for example of about 16°. The distance D between the eye 3 and the self-mixing interferometry sensor 1 is, for example,

[0044] 3 cm. In operation the each self-mixing interferometry sensor emits the laser radiation 2 with the divergence d.

[0045] As can be seen from Figure 1, a beam path 5 between the selfmixing interferometry sensor 1 and the eye 3 is free of any reflecting or diffractive optical element 6 (see also Figure 3) for both self-mixing interferometry sensors 1. That is to say, the laser radiation 2 is directly directed to the eye 3.

[0046] As illustrated in Figure 1, when considering specular reflection of the laser radiation 2 at the eye 3, the beam can be decomposed into multiple rays 2a, 2b, 2c which reach the eye 3 at different locations.

[0047] For example, the first part of the radiation 2a is perpendicular to the cornea 32 of the eye 3. In this case, the reflected light reaches the self-mixing interferometry sensor 1 and contributes to the interferometry signal. This contribution contains information related to the eye movement via the cornea' s displacement and therefore can be used for the eye tracking .

[0048] A second part of radiation 2b is perpendicular to the eyeball 31 . In this case the reflected layer also contributes to the sel f-mixing interferometry signal but may contain less meaningful information regarding the eye movement .

[0049] A third part of radiation 2c is neither perpendicular to the eyeball nor to the cornea and the reflected light is not rej ected into the sel f-mixing interferometry sensor 1 . Therefore the contribution for eye tracking of this radiation may be small compared to the contribution of the first part of radiation 2a and the second part of radiation 2b .

[0050] These considerations only take specular reflection into account . However, in practice di f fuse reflection also occurs , even i f the surface of the eye is optically smooth . This contribution also contains valid information on the eye movement or the position of the eye and can also be used for eye tracking purposes .

[0051] Due to the fact that the laser radiation 2 is emitted with a divergence a at a distance D to the eye 3 , a beam 33 with a diameter a is formed on the eye . Due to this beam, a rather large part of the eye 3 is illuminated by radiation 3 and contributions from the di f ferent parts 2a, 2b, 2c of the laser radiation 2 can be considered which enhance the accuracy of the eye tracking .

[0052] For example , the diameter a of the beam 33 is 1 cm at the plane of the eye . As shown in Figure 1 , the eye 3 is directly illuminated in this way by two sel f-mixing interferometry sensors 1 and thus a particularly accurate tracking of the eye movement is possible .

[0053] In the embodiment of Figure 1 , the eye tracking sensor 10 is for example part of AR glasses 4 and one of the sel f-mixing interferometry sensors 1 is integrated into a temple 42 and one of the sel f-mixing interferometry sensors 1 is integrated into a frame 41 of the glasses 4 .

[0054] Figure 2 shows a schematic sectional view of a here-described eye tracking sensor 10 . The eye tracking sensor 10 comprises the sel f-mixing interferometry sensor 1 which comprises a laser diode 11 and an optical element 12 . The laser diode 11 is , for example , a VCSEL .

[0055] The laser diode comprises inter alia an active region I la for producing the laser radiation 2 . Further, the laser diode 11 comprises an optical resonator formed by the mirrors 11b . Current is supplied to the laser diode 11 by contacts 11c .

[0056] The optical element 12 , for example , comprising micro optics , can be used to sense the divergence a of the laser radiation 2 . The sel f-mixing interferometry sensor signal can be processed by processing unit 13 e . g . from measurements of the j unction voltage of the laser diode 11 .

[0057] Figure 3 shows a comparison between the here-described eye tracking sensor 10 and an alternative approach .

[0058] The alternative approach on the left side shows an eye tracking sensor 10 where the laser radiation 2 is reflected by a reflecting or di f fracting optical element 6 which, for example , can be a reflection grating, a volume phase hologram, a mirror or the like . With this , only a small beam illuminates the eye 3 and a plurality of such eye tracking sensors with bulky optics 6 is necessary for tracking the eye movement .

[0059] By way of contrast , the here-described eye tracking sensor 10 on the right-hand side comprises a sel f-mixing interferometry sensor 1 which directly illuminates the eye 3 with a divergent laser radiation 2 forming a beam 33 with a diameter a and thus illuminating a larger part of the eye 3 .

[0060] With this it is possible , for example , that the eye tracking sensor 10 comprises only a single sel f-mixing interferometry sensor 1 per eye .

[0061] Further, only divergence control of the emitted laser radiation 2 is necessary, which relaxes the optical system .

[0062] The wavelength of the laser radiation 2 can be freely chosen, which reduces eye safety concerns by allowing long wavelengths as the laser radiation does not have to be adapted to the properties of the optical element 6 . For example for the here described eye tracking sensor it is possible to use a laser diode 11 which emits laser radiation with a peak wavelength of 900 nm or greater, in particular of 1000 nm or greater .

[0063] Further, the low component count of the here-described eye tracking sensor 10 allows for a rather simple and lightweight system . This makes the here-described eye tracking sensor more robust regarding system stability . Costs are reduced by avoiding the manuf cturing of intermediate optical elements

[0064] 6 , like for example holographic elements .

[0065] The schematic spatial view of Figure 4 shows the here- described AR / VR glasses where the interferometry sensors 1 are integrated into the frame 41 of the glasses 4 . From this position each sel f-mixing interferometry sensor 1 directs its laser radiation 2 directly at one of the eye 3 . That is to say, the laser radiation 2 propagates along a straight line from the sel f-mixing interferometry sensors 1 to the respective eye such that the eye is directly illuminated by the laser radiation 2 . This means that a beam path 5 between the sel f-mixing interferometry sensor 1 and the respective eye 3 is free from any reflecting or di f fracting optical element 6 which would change the direction of the laser radiation on its way from the sel f-mixing interferometry sensor to the eye .

[0066] Alternatively or additionally to the features described in connection with the figures , the exemplary embodiments shown in the figures can comprise further features described in the general part of the description . Moreover, features and embodiments of the figures can be combined with each other, even i f such combination is not explicitly described .

[0067] This patent application claims the priority of German patent application 102023126619 . 5 , the disclosure content of which is hereby incorporated by reference .

[0068] The invention is not restricted to the exemplary embodiments by the description on the basis of said exemplary embodiments . Rather, the invention encompasses any new feature and also any combination of features , which in particular comprises any combination of features in the patent claims and any combination of features in the exemplary embodiments , even i f this feature or this combination itsel f is not explicitly speci fied in the patent claims or exemplary embodiments .

[0069] References

[0070] 1 sel f-mixing interferometry sensor

[0071] 11 laser diode

[0072] I la active region

[0073] 11b mirror

[0074] 11c contact

[0075] 12 optical element

[0076] 13 processing unit

[0077] 2 laser radiation

[0078] 2a first part of radiation

[0079] 2b second part of radiation

[0080] 2c third part of radiation

[0081] 3 eye

[0082] 31 eye ball

[0083] 32 cornea

[0084] 33 beam

[0085] 4 glasses

[0086] 41 frame

[0087] 42 t emp 1 e

[0088] 43 lens

[0089] 5 beam path

[0090] 6 reflecting optical element a divergence

[0091] D distance

Claims

Claims1. An eye tracking sensor (10) with- a self-mixing interferometry sensor (1) which is configured to emit a laser radiation (2) for illuminating an eye (3) , wherein- the self-mixing interferometry sensor (1) is configured to emit the laser radiation (2) with a divergence (a) ,- the self-mixing interferometry sensor (1) is configured to illuminate the eye (3) , and- the laser radiation (2) produces a beam (33) on the eye (3) with a diameter (a) of at least 0.5 cm and at most 2 cm.

2. The eye tracking sensor according to the previous claim, wherein a beam path (5) between the self-mixing interferometry sensor (1) and the eye (3) is free of any reflecting or diffractive optical element (6) .

3. The eye tracking sensor according to at least one of the previous claims, wherein the self-mixing interferometry sensor (1) comprises a laser diode (11) .

4. The eye tracking sensor according to the previous claim, wherein the self-mixing interferometry sensor (1) comprises an optical element (12) between the laser diode (11) and the eye ( 3 ) .

5. The eye tracking sensor according to at least one of the previous claims, wherein the divergence (a) is set between at least 5° and at most 25°, in particular between at least 10° and at most 20°.

6. The eye tracking sensor according to at least one of the previous claims, wherein a distance (D) between the selfmixing interferometry sensor (1) and the eye (3) is between at least 1 cm and at most 10 cm.

7. The eye tracking sensor according to at least one of the previous claims, wherein the beam (33) on the eye (3) is configured to cover a part of the cornea and a part of the remaining eyeball of the eye (3) .

8. The eye tracking sensor according to at least one of the previous claims which is configured for integrating into a wearable device for mounting to a user's head.

9. The eye tracking sensor according to at least one of the previous claims which is configured for integrating into a lens ( 43 ) .

10. The eye tracking sensor according to at least one of the previous claims further comprising a processing unit (13) for processing a signal from the self-mixing interferometry sensor .

11. The eye tracking sensor according to at least one of the previous claims with two or more self-mixing interferometry sensors ( 1 ) .

12. AR / VR glasses comprising- a frame (41) , temples (42) and lenses (43) and- the eye tracking sensor (10) according to at least one of the previous claims, wherein the at least one self-mixing interferometry sensor (1) is integrated in the frame (41)and / or at least one of the temples (42) and / or at least one of the lenses (43) .

13. A method for eye tracking, wherein - a self-mixing interferometry sensor (1) emits a laser radiation (2) and illuminates an eye (3) , wherein- the self-mixing interferometry sensor (1) emits the laser radiation (2) with a divergence (a) , and- the self-mixing interferometry sensor (1) illuminates the eye ( 3 ) .

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