METHOD FOR DETECTING A GAZE DIRECTION OF AN EYE

Abstract

A method for detecting a gaze direction of an eye includes the steps of irradiating at least one wavelength-modulated laser beam onto an eye, detecting an optical path length of the emitted laser beam based on laser feedback interferometry of the emitted laser radiation with a backscattered radiation from the eye, detecting a Doppler shift of the emitted radiation and the backscattered radiation based on the laser feedback interferometry, detecting an eye velocity based on the Doppler shift, and detecting an eye movement of the eye based on the optical path length and the eye velocity.

Claims

1. A method for detecting a gaze direction of an eye, comprising the steps of: irradiating at least one wavelength-modulated laser beam onto an eye, detecting an optical path length of the irradiated laser beam based on laser feedback interferometry of the irradiated laser beam and the portion of the beam backscattered from the eye, detecting a Doppler shift of the irradiated laser beam and the backscattered portion based on laser feedback interferometry, detecting an eye velocity based on the Doppler shift, and detecting an eye movement of the eye based on the optical path length and the eye velocity.

2. The method according to claim 1, further comprising the steps of: detecting a reflectivity of the eye depending on the amplitude and phase position of the portion of the laser beam backscattered from the eye, and detecting an absolute eye position based on the reflectivity and the optical path length.

3. The method according to claim 2, wherein the absolute eye position detection is performed at predefined points of time, and wherein an eye movement between the predefined points of time is detected based on the eye velocity.

4. The method according to claim 1, wherein eye velocity detection is based on the following equation:
F.sub.D=2v cos(α)/λ, wherein: v is the eye velocity; F.sub.D is a Doppler frequency corresponding to the Doppler shift of the irradiated laser beam and the backscattered part of the emitted laser beam, α is an angle between a direction of the irradiated laser beam and a tangent to an ocular surface which contacts the ocular surface at an impingement point at which the laser beam impinges on the eye and which also is located in the plane spanned by a wave vector and a surface normal at the impingement point; and λ is a wavelength of the irradiated laser beam.

5. The method according to claim 4, further comprising the steps of: detecting a rotation rate of the eye; and calibrating to determine the angle α, wherein the calibration is based on the optical path length, the eye velocity, and the rotation rate of the eye.

6. The method according to claim 5, wherein the rotation rate of the eye is detected depending on a rotation rate of a head of the user detected by means of a rotation rate sensor.

7. The method according to claim 1, further comprising the steps of: detecting a maximum eye velocity during an eye movement, and predicting an eye movement end position based on the maximum velocity.

8. The method according to claim 1, wherein at least two laser beams are irradiated onto the eye, and wherein the two irradiated laser beams are aligned such that an angle and/or a distance between a wave vector of each irradiated laser beam and at least one of two mutually orthogonal rotational axes of the eye, respectively, is not zero.

9. A gaze detection arrangement for detecting a gaze direction, comprising: a laser device which is configured to irradiate at least one laser beam onto an eye, and a control device which is configured to operate the laser device and: irradiate the at least one laser beam onto an eye, detect an optical path length of the irradiated laser beam based on laser feedback interferometry of the irradiated laser beam and the portion of the beam backscattered from the eye, detect a Doppler shift of the irradiated laser beam and the backscattered portion based on laser feedback interferometry, detect an eye velocity based on the Doppler shift, and detect an eye movement of the eye based on the optical path length and the eye velocity.

10. The gaze detection arrangement according to claim 9, wherein the laser device comprises at least one surface emitter with integrated photodiode.

11. The gaze detection arrangement according to claim 9, wherein the laser device comprises a beam splitting element which is configured to split a single laser beam into at least two laser beams.

12. The gaze detection arrangement according to claim 9, wherein the at least one laser beam is directed directly onto the eye, and/or wherein the gaze detection arrangement further comprises a deflection element which is configured to deflect the at least one laser beam irradiated by the laser device onto the eye.

13. A pair of smart glasses comprising a gaze detection arrangement according to claim 9, wherein the laser device comprises at least one laser source which is arranged on a spectacle frame, which especially surrounds a spectacle lens, and/or on a spectacle temple and/or is arranged in a spectacle lens.

14. The pair of smart glasses according to claim 13, further comprising a rotation rate sensor, which is configured to detect a rotation of the user's head.

15. The pair of smart glasses according to claim 13, further comprising an input and/or output device which is configured to receive an input from the user and/or to output an output to the user.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In the following, the invention will be described by means of example embodiments in connection with the figures. In the figures, functionally identical components are each indicated by the same reference numbers, wherein:

[0031] FIG. 1 is a simplified schematic view of a pair of smart glasses according to a first embodiment of the invention,

[0032] FIG. 2 is a simplified schematic detailed view of a gaze detection procedure using the smart glasses of FIG. 1,

[0033] FIG. 3 is another simplified schematic detailed view of the implementation of gaze detection using the smart glasses of FIG. 1,

[0034] FIG. 4 is a simplified schematic representation of measurement data from the smart glasses of FIG. 1 when performing gaze detection,

[0035] FIG. 5 is another simplified schematic view of a pair of smart glasses according to a second embodiment of the invention, and

[0036] FIG. 6 is a simplified schematic view of a pair of smart glasses according to a third embodiment of the invention.

PREFERRED EMBODIMENTS OF THE INVENTION

[0037] FIG. 1 shows a simplified schematic view of a pair of smart glasses 50 according to a first embodiment of the invention. The smart glasses 50 comprise a spectacle lens 52, a spectacle frame 51 in which the spectacle lens 52 is received, and a spectacle temple 53 for holding the smart glasses 50 on a users head. The smart glasses 50 are thus configured to be worn on a users head.

[0038] The smart glasses 50 comprise a gaze detection arrangement 20, by which a gaze direction of an eye 10 of the user may be detected. For this purpose, the gaze detection arrangement 20 comprises a laser device 3 and a control device 4, which is configured to operate the laser device 4 to perform a respective method for detecting the gaze direction of the eye 10. The control device 4 is arranged in the spectacle temple 53 of the smart glasses 50 for compact design.

[0039] The laser device 3 includes a total of five surface emitters 3a, 3b, 3c, 3d, 3e as laser sources. Four of the five surface emitters 3a, 3b, 3c, 3d are distributedly arranged on the spectacle frame 51 around the spectacle lens 52. A fifth surface emitter 3e is arranged on the spectacle temple 53. Each of the surface emitters 3a, 3b, 3c, 3d, 3e is configured to irradiate a wavelength-modulated laser beam 1 onto the eye 10. In this case, triangle-modulated laser light is emitted as the laser beam 1 within the wavelength. For the reason of clarity, only one single laser beam 1 emitted by the first surface emitter 3a is shown in the figures. Each laser beam 1 is directed in a separate laser spot 30a, 30b, 30c, 30d, 30e onto an ocular surface 11 of the eye 10.

[0040] FIG. 2 shows the laser spots 30a, 30b, 30c, 30d of the first four surface emitters 3a, 3b, 3c, 3d arranged on the spectacle frame 51. In FIG. 3, the fifth laser spot 30e generated by the fifth surface emitter 3e is shown on the side of the eye 10.

[0041] As can be seen in FIGS. 2 and 3, the laser spots 30a, 30b, 30c, 30d, 30e are preferably located within a region of the iris 12 of the eye 10, or in the vicinity of that region. As a result, when the eye 10 is moved, the pupil 13 of the eye 10 is often moved close to or through the laser spots 1, so that the position and movement of the pupil 13 may be detected with high accuracy to determine the gaze direction of the eye with high accuracy.

[0042] Realization of the method for detecting the gaze direction of the eye 10 is described in detail below, the description being based on a single laser beam 1 only.

[0043] The laser beam 1 is initially irradiated onto the eye 10. At the eye surface 11, the laser beam 1 will at least partially be backscattered. As a result, overlap of the irradiated laser beam 1 with the portion of the backscattered radiation propagating back in parallel in the direction of the surface emitter 3a occurs. By means of the photodiode integrated in the surface emitter 3a, a laser feedback interferometry is performed to detect the resulting interference radiation, as an overlap of irradiated laser radiation 1 and radiation backscattered in the opposite direction. As the photodiode is integrated directly into the laser cavity of the surface emitter 3a, detection of the resulting interference radiation is performed by the so-called self-mixing effect.

[0044] An exemplary frequency spectrum 25 of the resulting interference radiation, which can be detected by means of the integrated photodiode of the surface emitter 3a, is shown schematically in FIG. 4. The axis 25a corresponds to the frequency and the axis 25b to the amplitude. The reference number 26 indicates the peak frequency of the detected interference radiation, detected for example by means of a Fourier analysis. As a result of the triangular modulation of the wavelength of the emitted laser beam 1, the peak frequency 26 is dependent on an optical path length 2. The optical path length 2 (cf. FIG. 1), corresponds to a distance covered by the laser beam 1 between the surface emitter 3a and the ocular surface 11. As the laser beam 1 is irradiated directly onto the eye 10, in the first embodiment of FIG. 1, the optical path length 2 corresponds to the shortest distance between the surface emitter 3a and the eye surface 11. Thus, with a wavelength of the emitted laser beam 1 being known, the optical path length 2 may be detected based on laser feedback interferometry for a specific eye position, i.e. for a specific gaze direction.

[0045] FIG. 4 shows an exemplary frequency spectrum 25, which is being recorded during constant movement of the eye surface 11 in relation to the laser beam 1, i.e. during rotation of the eye 10. During that movement, a shift 27 of the peak frequency 26 occurs towards a shifted peak frequency 26′ shown as a dashed line, as a result of the Doppler effect. The Doppler shift of the emitted and the backscattered laser radiation resulting therefrom can thus be detected based on the frequency spectrum 25. Based on this Doppler shift, the instantaneous eye velocity of a movement of the eye 10 as well as a direction of the movement can be detected.

[0046] To calculate the eye velocity using the Doppler shift, an angle α between the eye surface 11 and the laser beam 1 is detected and taken to compensate for any oblique position of the irradiated laser radiation 1 in relation to the eye surface 11. In detail, the angle α describes the smallest angle between the laser beam 1 and a plane 35 configured at the corresponding laser spot 30b tangential to the ocular surface 11 (cf. FIG. 3).

[0047] Calibration can be performed depending on a rotation rate of the eye 10 to determine the angle α. The rotation rate of the eye 10 is detected depending on a rotation rate of the users head, wherein the rotation rate of the head during rotating is detected using a rotation rate sensor 6, which is integrated in the spectacle temple 53, while simultaneously a stationary point in space is focused with the eye 10. The rotation rate of the eye 10 is estimated under the assumption that the eye performs a movement opposite to the head movement.

[0048] In addition to detecting the frequencies of the irradiated and backscattered laser radiation, a signal-to-noise ratio of the backscattered radiation is detected, wherefrom a reflectivity of the eye 10 is detected. The reflectivity is different for different region of the eye 10. Particularly, the reflectivity which has been detected changes when the laser beam 1 passes anatomical boundaries of the eye 10, such as the iris 12 or the pupil 13. Thus, the reflectivity of the eye 10 can be used to estimate which region of the eye 10 is currently irradiated by the laser beam 1. An instantaneous absolute eye position of the eye 10 can thus be detected in combination with the detected optical path length 2.

[0049] Thus, any eye movement can be detected using the eye tracking arrangement 20 based on the laser feedback interferometry, wherein any eye movement of the eye 10 can be detected and tracked. In combination with the determination of the absolute eye position, which, for example, will only be executed at predetermined times, and additionally based on the reflectivity, the instantaneous gaze direction of the eye 10 can thereby be detected. Using the components required to perform determination of the gaze direction, particularly high temporal resolution of gaze direction determination can be achieved with low energy requirements. In addition, particularly low-cost components can be used.

[0050] FIG. 5 shows a simplified schematic view of a pair of smart glasses 50 according to a second embodiment of the invention. The second embodiment essentially corresponds to the first embodiment of FIG. 1 but with the difference of the laser device 3 being alternatively configured. In the second embodiment of FIG. 5, the laser device 3 of the eye tracking arrangement 20 comprises four surface emitters 3a, 3b, 3c, 3d with integrated photodiode, all of which are arranged on the spectacle temple 53. The laser beams 1 emitted by the surface emitters 3a, 3b, 3c, 3d will thus be indirectly irradiated onto the eye 10. Specifically, the laser beams 1 are irradiated onto the spectacle lens 52, exemplified by a focusing point 1′ on the spectacle lens 52. A deflection element 54 in the form of a holographic optical element is integrated into the spectacle lens 52, which deflects the laser beams 1 towards the eye 10. In this way, an alternative arrangement of the laser device 3 may be provided, by which the method for detecting the gaze may also be performed.

[0051] Furthermore, the smart glasses 50 of the second embodiment of FIG. 5 additionally comprise an input and/or output device 7 which is configured to output an output to the user. The input and/or output device 7 comprises a projection unit, which is configured to project an image onto a retina of the eye 10. The projection unit can be used, for example, to display an augmented reality or virtual reality. Preferably, the projection unit is coupled to the control device 4, wherein the control device 4 is configured to operate the projection unit in response to the detected gaze direction. For example, the projected image can be adapted depending on the gaze direction.

[0052] FIG. 6 shows a simplified schematic view of a pair of smart glasses 50 according to a third embodiment example of the invention. The third embodiment example essentially corresponds to the second embodiment example of FIG. 5 but having an alternative embodiment of the laser device 3.

[0053] In the third embodiment example, the laser device 3 only comprises a single surface emitter 3a as a laser source. The single laser beam 1 emitted from the single surface emitter 3a is split into two or more laser beams 1a, 1 b using a beam splitting element 30. The two laser beams 1a, 1 b will indirectly be irradiated onto the eye 10 via a deflection element 54 in the spectacle lens 52, similar to the second embodiment example of FIG. 5. For example, the two laser beams 1a, 1b can be focused on a common point on the eye 10, as shown in FIG. 6. By splitting the beams according to the third embodiment example, another particularly advantageous configuration and arrangement of the smart glasses 50 can be provided.