Optical system for a virtual retinal display

Abstract

The invention relates to an optical system (10a) for a virtual retinal display with an illumination device (12). The illumination device (12) has a first laser diode (7) for emitting a first light beam (8) within a first wavelength range. The first wavelength range shifts towards a second wavelength range depending on the temperature of the first laser diode (7). Furthermore, the optical system (10a) has a first controllable deflection unit (9) for the first light beam (8) for scanning and projecting the image content. In addition, the optical system (10a) has a holographic optical element (5) for deflecting the first light beam (8) onto an eye (3).The holographic optical element (5) is formed from liquid crystals and has a first holographic function with a first diffraction efficiency range and a second holographic function with a second diffraction efficiency range. The first wavelength range overlaps at least partially with the first diffraction efficiency range, and the second wavelength range overlaps at least partially with the second diffraction efficiency range.Furthermore, the optical system (10a) has a control unit (11) which serves to control the holographic optical element (5) or a polarization switch in such a way that the first light ray (8) incident on the holographic optical element (5) at a first time with a first angle of incidence (15) with the first wavelength and the first light ray (8) incident on the holographic optical element (5) at a second time following the first time with the first angle of incidence (15) with the second wavelength is deflected to the eye (3).

Description

The invention relates to an optical system for a virtual retinal display (retinal scan display). In addition, the invention relates to a method for driving a holographic optical element or a polarization switch of an optical system for a virtual retinal display (retinal scan display).Prior ArtSmart glasses (smart glasses) with retinal scan displays and holographic optical elements for deflecting the light beams onto the eye are already known.It is an object of the present invention to develop an optical system for a virtual retinal display having a holographic optical element for deflecting the light beams onto the eye, the function of which optical system remains always fulfilled even in the event of temperature fluctuations of the laser diode of the optical system.Disclosure of the InventionTo achieve the object, an optical system for a virtual retinal scan display (retinal scan display) according to claim 1 is proposed. Furthermore, a method for driving a holographic optical element or a polarization switch of an optical system for a virtual retinal scan display (retinal scan display) according to claim 10 is proposed.The optical system for a virtual retinal display (retinal scan display) has at least one illumination device which is designed in particular as a projector unit, such as a micro projector unit. The illumination device has at least one first laser diode for emitting a first light beam within a first wavelength range. In this case, the first wavelength range shifts as a function of a temperature of the first laser diode, in particular the temperature of at least one first laser cavity of the first laser diode, toward a second wavelength range. For example, the laser diode can heat up during operation, in particular by the laser power. Furthermore, the optical system has a first controllable deflection unit for the first light beam for scanning projection of the image content. In addition, the optical system has a holographic optical element, in particular designed as a layer, for deflecting the first light beam incident on the holographic optical element by the controllable deflection unit onto an eye. The eye is in particular the eye of a user of the optical system. The holographic optical element is formed of liquid crystals. In this connection, the holographic optical element is used in particular as an LCD hologram. Such liquid crystals are distinguished by the fact that their refractive index is anisotropic. The holographic optical element has a first holographic function having a first diffraction efficiency range and a second holographic function having a second diffraction efficiency range. In this case, the first wavelength range overlaps at least partially with the first diffraction efficiency range and the second wavelength range overlaps at least partially with the second diffraction efficiency range. In particular, the first wavelength range completely overlaps with the first diffraction efficiency range and the second wavelength range completely overlaps with the second diffraction efficiency range. The holographic optical element is preferably embedded in a lens, in particular a spectacle lens, of the optical system. In addition, the optical system comprises a sensor for detecting at least one item of information about the, in particular current, first or second wavelength range of the emitted first light beam. The first sensor is preferably designed as a temperature sensor. The optical system also has a control unit. In this context, the control unit serves to actuate the holographic optical element as a function of the detected information about the, in particular current, first or second wavelength range of the emitted first light beam in such a way that the first light beam having the first wavelength incident on the holographic optical element at a first point in time with a first angle of incidence and the first light beam having the second wavelength incident on the holographic optical element at a second point in time following the first point in time with the first angle of incidence are deflected to the eye. In particular, the light beam is deflected here at the first and second points in time to the same positions of the eye. The angle of incidence selectivity of the first and second holographic functions is thus the same for both wavelengths. Alternatively or additionally, the optical system has a polarization switch for switching over the first light beam in a first or a second polarization direction. The first light beam having the first polarization direction is assigned to the first diffraction efficiency range and the first light beam having the second polarization direction is assigned to the second diffraction efficiency range of the holographic optical element. This means that only first light beams having the first polarization direction are deflected within the first diffraction efficiency range and only first light beams having the second polarization direction are deflected within the second diffraction efficiency range. The polarization switch is preferably formed from a liquid crystal and a polarization filter. In this context, the control unit is designed to actuate the polarization switch as a function of the acquired information about the, in particular current, first or second wavelength range of the emitted first light beam in such a way that the first light beam having the first wavelength incident on the holographic optical element at the first point in time with the first angle of incidence and the first light beam having the second wavelength incident on the holographic optical element at the second point in time following the first point in time with the first angle of incidence are deflected toward the eye, in particular at the same positions of the eye. In both cases, the anisotropy of the holographic optical element is used to enable the functioning of the optical system even in the case of temperature fluctuations of the laser diode.The control unit is preferably designed to determine the first or second wavelength range associated with the current temperature of the first laser diode by means of a look-up table. Alternatively, the first sensor is designed as a first optical spectrometer. The spectral data acquired thereby can be used directly by the control unit in order to determine the, in particular current, first or second wavelength range.The holographic optical element is preferably designed as an, in particular static, holographic optical element which has the first and the second diffraction efficiency range at the first and at the second point in time. Such a holographic optical element having an anisotropic refractive index always has different diffraction efficiency ranges in the three spatial directions x, y and z of the liquid crystals. The holographic optical element has different holographic functions, in particular for x- and for y-polarized light. Thus, the diffraction efficiency (for a specific angle of incidence / angle of diffraction configuration) can be set or recorded to different wavelengths depending on the polarization of the incident light. Alternatively, the holographic optical element is designed as rotatable, in particular rotatable, liquid crystals. In this case, each state, in particular angle of rotation, of the liquid crystals is assigned a different diffraction efficiency range of the holographic optical element. In this context, the control unit is designed to drive the liquid crystals in such a way that the holographic optical element has only the first diffraction efficiency range at the first point in time and only the second diffraction efficiency range at the second point in time. This could allow continuous tracking of the holographic optical element to the shift of the laser wavelength.The optical system preferably additionally has a second laser diode for emitting a second light beam having a second wavelength and having the second polarization direction. In this context, the first laser diode is designed to emit the first light beam having the first polarization direction. The control unit is designed to switch off the first laser diode and switch on the second laser diode, in particular at the second point in time, as a function of the acquired information about the, in particular current, first or second wavelength range of the emitted first light beam. In this case, in particular, the first light beam having the first polarization direction is assigned to the first diffraction efficiency range and the second light beam having the second polarization direction is assigned to the second diffraction efficiency range of the holographic optical element. The polarization switch can thus be dispensed with and the control unit decides, depending on the acquired information, which of the two laser diodes light beams is switched on and off, in particular the current first or second wavelength range.The polarization switch is preferably formed from a liquid crystal and a polarization filter.The polarization switch is preferably arranged in the beam direction of the first light beam between the first laser diode and further optical components, in particular lenses, of the optical system.The optical system is preferably designed as smart glasses, in particular as augmented reality glasses or virtual reality glasses.The present invention further relates to a method for driving a holographic optical element or a polarization switch of an optical system for a virtual retinal display (retinal scan display). The optical system for virtual retinal display has been described above. In the method, a laser diode of the optical system first emits a first light beam within a first wavelength range. The first wavelength range shifts here depending on a temperature of the first laser diode, in particular the temperature of at least one first laser cavity of the first laser diode, to a second wavelength range. In a further method step, the information about the, in particular current, first or second wavelength range of the emitted first light beam is captured by means of the control unit. In addition, the holographic optical element or the polarization filter of the optical system is controlled by the control unit as a function of the detected information about the, in particular current, first or second wavelength range of the emitted first light beam in such a way that the first light beam having the first wavelength incident on the holographic optical element at a first point in time with a first angle of incidence and the first light beam having the second wavelength incident on the holographic optical element at a second point in time following the first point in time with the first angle of incidence are deflected toward the eye, in particular at the same positions of the eye. The method thus enables the mode of operation of the optical system to be guaranteed even in the event of temperature fluctuations of the laser diode.Preferably, the temperature of the first laser diode, in particular the temperature of at least the first laser cavity of the first laser diode, represents the information about the, in particular current, first or second wavelength range of the emitted first light beam.The first wavelength range and the second wavelength range preferably differ from one another in their maxima at least 2 nm, in particular at least 5 nm. The maxima are understood to mean, in particular, the centroids or peaks of the respective wavelength ranges.Preferably, the first and second diffraction efficiency ranges partially overlap. This ensures that no gaps arise between the diffraction efficiency ranges and thus ranges with incorrect or no deflection of the light beams onto the eye.Preferably, the first polarization direction of the first light beam and the second polarization direction of the first light beam are arranged orthogonally to one another. In particular, the polarization switch is designed to polarize the first light beam having the first wavelength in the X direction and the first light beam having the second wavelength in the Y direction. Alternatively, the polarization switch is designed to form the first light beam with the first wavelength to be left-circular and the first light beam with the second wavelength to be right-circular.Preferably, a second laser diode for emitting a second light beam having a second wavelength and having the second polarization direction is also connected by means of the control unit, in particular at the second point in time, as a function of the acquired information about the, in particular current, first or second wavelength range of the emitted first light beam. Furthermore, the first laser diode is switched off by means of the control unit, in particular at the second point in time. The first laser diode serves here for emitting the first light beam having the first polarization direction. The correspondingly different polarization of the light beam thus takes place independently of the polarization switch.DESCRIPTION OF THE DRAWINGSFIG. 1 shows a first embodiment of an optical system for a virtual retinal display (retinal scan display). FIG. 2 shows a second embodiment of the optical system for virtual retinal display (retinal scan display). FIG. 3 shows a third embodiment of the optical system for the retinal viral scan display (retinal scan display). Fig. 4 shows the overlap of wavelength ranges of the first light beam with the corresponding diffraction efficiency ranges of the holographic optical element. FIG. 5 shows a method for driving a holographic optical element of an optical system for a virtual retinal display (retinal scan display). FIG. 6 shows a method for driving a polarization switch of an optical system for a virtual retinal display (retinal scan display).DESCRIPTION OF THE EMBODIMENTSFIG. 1 schematically shows an optical system 10 afor a virtual retinal display (retinal scan display). The optical system 10 ais embodied here as smart glasses with a spectacle frame 19 and a spectacle lens 18. The optical system 10 aincludes an illumination device 12 which is designed in this case as a projector unit of the optical system 10 a. The illumination device 12 in turn has a first laser diode 7 for emitting a first light beam 8 within a first wavelength range. The first wavelength range shifts here depending on a temperature of the first laser diode 7, in particular the temperature of at least one first laser cavity of the first laser diode 7, toward a second wavelength range. Furthermore, the optical system 10 aincludes a first controllable deflection unit 9 for the first light beam 8 for scanning projection of the image content. The controllable deflection unit 9 is designed in particular as a two-dimensionally rotatably mounted micromirror. Alternatively, the controllable deflection unit is formed from two micromirrors which are each rotatably mounted one-dimensionally. The optical system 10a further comprises a holographic optical element 5 for deflecting the first light beam 8 incident on the holographic optical element 5 by the controllable deflection unit 9 onto an eye 3. The eye 3 is the eye 3 of a user of the smart glasses as an optical system 10 a. The holographic optical element 5 is formed of liquid crystals and has a first holographic function having a first diffraction efficiency range and a second holographic function having a second diffraction efficiency range. The first wavelength range overlaps here at least partially with the first diffraction efficiency range and the second wavelength range overlaps at least partially with the second diffraction efficiency range. In this exemplary embodiment, the holographic optical element 5 is integrated, in particular embedded, in a lens 18. The lens 18 is formed here as a spectacle lens of the optical system 10 a. Furthermore, the optical system 10 aincludes a sensor 13 for detecting at least one piece of information about the, in particular current, first or second wavelength range of the emitted first light beam 8. In this embodiment, the sensor 13 is designed as a temperature sensor. In addition, the optical system 10 aincludes a control unit 11. In the illustrated embodiment of the optical system 10 a, the projector unit 12, the controllable deflection unit 9 and the control unit 11 are integrated into the eyeglass frame 19. In this context, the control unit 11 is designed to actuate the holographic optical element 5 as a function of the detected information about the, in particular current, first or second wavelength range of the emitted first light beam 8, in such a way that the first light beam 8 with the first wavelength incident on the holographic optical element 5 at a first point in time with a first angle of incidence 15 and the first light beam 8 with the second wavelength incident on the holographic optical element 5 at a second point in time following the first point in time with the first angle of incidence 15 are deflected toward the eye 3. In particular, the first light beams 8 are deflected at the first and second points in time to the same positions 4 of the eye 3.The control unit 11 is designed, in particular, to determine the first or second wavelength range associated with the current temperature of the first laser diode by means of a look-up table. Alternatively, the first sensor 13 is configured as a first optical spectrometer. The spectral data acquired thereby can be used directly by the control unit 11 in order to determine the, in particular current, first or second wavelength range.In this first embodiment, the holographic optical element 5 is embodied as liquid crystals embodied rotatably, in particular rotatably. In this case, each state, in particular angle of rotation, of the liquid crystals is assigned a different diffraction efficiency range of the holographic optical element 5. The control unit 11 is used here to drive the liquid crystals in such a way that the holographic optical element 5 has only the first diffraction efficiency range at the first point in time and only the second diffraction efficiency range at the second point in time.FIG. 2 schematically shows a second embodiment of an optical system 10 b. In contrast to the first embodiment, the optical system 10 bherein additionally comprises a polarization switch 6. The polarization switch 6 is designed here for switching over the first light beam 8 in a first or a second polarization direction. Optionally, the first polarization direction of the first light beam and the second polarization direction of the first light beam are arranged orthogonally to one another in this case. The first light beam 8 with the first polarization direction is assigned to the first diffraction efficiency range and the first light beam with the second polarization direction is assigned to the second diffraction efficiency range of the holographic optical element 16. In this context, the control unit 11 serves to actuate the polarization switch 6 as a function of the acquired information about the, in particular current, first or second wavelength range of the emitted first light beam 8, in such a way that the first light beam 8 with the first wavelength and the first polarization direction, which is incident on the holographic optical element 16 at a first point in time with the first angle of incidence 15, and the first light beam 8 with the second wavelength and the second polarization direction, which is incident on the holographic optical element 16 at a second point in time, which is subsequent to the first point in time, with the first angle of incidence 15, are deflected toward the eye. In particular, the first light beams 8 are deflected at the first and second points in time to the same positions 4 of the eye 3.In contrast to the first embodiment of the optical system 10 a, the holographic optical element 16 is formed here as a holographic optical element 16 which has both the first and the second diffraction efficiency range at the first and the second point in time. Such a holographic optical element 16 can also be referred to as a static holographic optical element 16.The polarization switch 6 in the embodiment shown is formed from a liquid crystal and a polarization filter. The polarization switch 6 is arranged in the beam direction of the first light beam 8 between the first laser diode 7 and, here for the sake of simplicity, further optical components, in particular lenses, of the optical system 10 b.FIG. 3 schematically shows a third embodiment of an optical system 10 c. In contrast to the first embodiment, the optical system 10 cherein additionally comprises a second laser diode 17 for emitting a second light beam 26 having the second wavelength and having the second polarization direction. In this context, the first laser diode 7 is designed to emit the first light beam 8 with a first polarization direction. The control unit 11 serves to switch off the first laser diode 7 and switch on the second laser diode 17, in particular at the second point in time, as a function of the acquired information about the, in particular current, first or second wavelength range of the emitted first light beam 8.FIG. 4 shows, on the basis of a diagram, the assignment of the first wavelength range 25 ato the first diffraction efficiency range 21 a, and of the second wavelength range 25 bto the second diffraction efficiency range 21 b. Here, the laser power of the first laser diode is plotted on the first Y axis 20 a. The wavelength is plotted on the X axis 20 b. The first wavelength range 25 aof the first light beam of the first laser diode shifts in the direction of the arrow 23 from the first point in time to the second point in time by a temperature increase of the first laser diode toward the higher, second wavelength range 25 b. The different diffraction efficiency ranges 21 aand 21 bof the holographic optical element ensure that the first light beams are always correctly deflected onto the eye of the user of the optical system.Optionally, the first diffraction efficiency region 21 ais assigned a first polarization direction of the first light beam and the second diffraction efficiency region 21 bis assigned a second polarization direction of the first light beam.In the case shown, the first wavelength range 25 aand the second wavelength range 25 bdiffer from one another substantially 2 nm in their maxima 22 aand 22 b. Further, the first diffraction efficiency region 21 aand the second diffraction efficiency region 21 bpartially overlap each other.FIG. 5 shows a method for driving a holographic optical element of an optical system for a virtual retinal display (retinal scan display). The optical system is in particular the optical system shown in FIG. 1. In the method, first in method step 100, a laser diode of the optical system emits a first light beam within a first wavelength range. The first wavelength range shifts here depending on a temperature of the first laser diode, in particular the temperature of at least one first laser cavity of the first laser diode, to a second wavelength range. In a further method step 110, information about the, in particular current, first or second wavelength range of the emitted first light beam is captured by means of the control unit of the optical system. Furthermore, in a method step 140, the holographic optical element of the optical system is controlled by the control unit as a function of the detected information about the, in particular current, first or second wavelength range of the emitted first light beam in such a way that the first light beam having the first wavelength incident on the holographic optical element at a first point in time with a first angle of incidence and the first light beam having the second wavelength incident on the holographic optical element at a second point in time following the first point in time with the first angle of incidence are deflected toward the eye, in particular at the same positions of the eye. The method is then ended.Optionally, the temperature of the first laser diode represents the information about the, in particular current, first or second wavelength range of the emitted first light beam. In particular, this is the temperature of at least the first laser cavity of the first laser diode. In order to determine the currently present first or second wavelength of the first light beam, the control unit optionally resorts to a look-up table on which the temperatures of the first laser diode and the associated first or second wavelength of the emitted first light beam are stored. Alternatively, the first sensor is designed as a first optical spectrometer. The spectral data acquired thereby can be used directly by the control unit in order to determine the, in particular current, first or second wavelength range.FIG. 6 shows a method for driving a polarization switch of an optical system for a virtual retinal display (retinal scan display). In contrast to the method in FIG. 5, in a method step 150 following the method step 110, the polarization filter of the optical system is actuated by the control unit as a function of the acquired information about the, in particular current, first or second wavelength range of the emitted first light beam in such a way that the first light beam having the first wavelength incident on the holographic optical element at a first point in time with a first angle of incidence and the first light beam having the second wavelength incident on the first point in time with the first angle of incidence are deflected toward the eye, in particular at the same positions of the eye. The polarization switch is designed to switch the first light beam having the first wavelength into a first polarization direction at the first point in time and to switch the first light beam having the second wavelength into a second polarization direction at the second point in time. The first polarization direction is assigned to the first diffraction efficiency range of the holographic optical element and the second polarization direction is assigned to the second diffraction efficiency range of the holographic optical element.

Claims

Optical system (10a, 10b, 10c) for a virtual retinal display (retinal scan display), having at least - an illumination device (12), in particular a projector unit, of the optical system (10a, 10b, 10c), wherein the illumination device (12) has at least one first laser diode (7) for emitting a first light beam (8) within a first wavelength range (25a), wherein the first wavelength range (25a) shifts (23) as a function of a temperature of the first laser diode (7), in particular the temperature of at least one first laser cavity of the first laser diode (7), toward a second wavelength range (25b), and - a first drivable deflection unit (9) for the first light beam (8) for scanning projection of the image content, and - a holographic optical element (5, 16) for deflecting the first light beam (8) incident from the controllable deflection unit (9) on the holographic optical element (5, 16) onto an eye (3), in particular of a user of the optical system (10a, 10b, 10c), wherein the holographic optical element (5, 16) is formed from liquid crystals, and the holographic optical element (5, 16) has a first holographic function having a first diffraction efficiency range (21a) and a second holographic function having a second diffraction efficiency range (21b), wherein the first wavelength range (25a) at least partially overlaps the first diffraction efficiency range (21a) and the second wavelength range (25b) at least partially overlaps the second diffraction efficiency range (21b), and - a sensor (13) for detecting at least one item of information about the, in particular current, first (25a) or second wavelength range (25b) of the emitted first light beam (8), and - a control unit (11), and / or - a polarization switch (6) for switching over the first light beam (8) in a first or a second polarization direction, wherein the first light beam (8) with the first polarization direction is assigned to the first diffraction efficiency range (21a) and the first light beam (8) with the second polarization direction is assigned to the second diffraction efficiency range (21b) of the holographic optical element (5, 16), and the control unit (11) is designed to actuate the holographic optical element (5, 16) or the polarization switch (6) in such a way as a function of the detected information about the, in particular current, first (25a) or second wavelength range (25b) of the emitted first light beam (8), the first light beam (8) having the first wavelength (25a) incident on the holographic optical element (5, 16) at a first point in time at a first angle of incidence (15) and the first light beam (8) having the second wavelength (25b) incident on the first point in time at the first angle of incidence (15) are deflected toward the eye (3), in particular identical positions (4) of the eye (3).Optical system (10a, 10b, 10c) according to Claim 1, characterized in that the holographic optical element (5, 16) is formed as a, in particular static, holographic optical element (5, 16) which has the first (21a) and the second diffraction efficiency range (21b) at the first and the second point in time.Optical system (10a, 10b, 10c) according to Claim 1, characterized in that the holographic optical element (5, 16) is designed as liquid crystals which are designed to be rotatable, in particular rotatable, wherein each state, in particular angle of rotation, of the liquid crystals is assigned a different diffraction efficiency range (21, 21b) of the holographic optical element (5, 16), wherein the control unit (11) is designed to drive the liquid crystals in such a way that the holographic optical element (5, 16) has only the first diffraction efficiency range (21a) at the first point in time and only the second diffraction efficiency range (21b) at the second point in time.Optical system (10a, 10b, 10c) according to one of Claims 1 to 3, characterized in that the first sensor (13) is designed as a temperature sensor.Optical system (10a, 10b, 10c) according to one of Claims 1, 2 or 4, characterized in that the optical system (10a, 10b, 10c) additionally has a second laser diode (17) for emitting a second light beam (26) having the second wavelength (25b) and having the second polarization direction, wherein the first laser diode (7) is designed to emit the first light beam (8) having the first polarization direction, wherein the control unit (11) is designed to switch off the first laser diode (7) and switch on the second laser diode (17), in particular at the second point in time, as a function of the detected information about the, in particular current, first (25a) or second wavelength range (25b) of the emitted first light beam (8).Optical system (10a, 10b, 10c) according to one of Claims 1 to 5, characterized in that the holographic optical element (5, 16) is embedded in a lens (18), in particular a spectacle lens, of the optical system (10a, 10b, 10c).The optical system (10a, 10b, 10c) according to any one of claims 1 to 6, characterized in that the polarization switch (6) is formed of a liquid crystal and a polarization filter.Optical system (10a, 10b, 10c) according to one of Claims 1 to 7, characterized in that the polarization switch (6) is arranged in the beam direction of the first light beam (8) between the first laser diode (7) and further optical components, in particular lenses, of the optical system (10a, 10b, 10c).Optical system (10a, 10b, 10c) according to one of Claims 1 to 8, characterized in that the optical system (10a, 10b, 10c) is designed as smart glasses.Method for controlling a holographic optical element (5, 16) or a polarization switch (6) of an optical system (10a, 10b, 10c) for a virtual retinal display (retinal scan display), in particular an optical system (10a, 10b, 10c) according to one of Claims 1 to 9, the optical system (10a, 10b, 10c) at least comprising - an illumination device (12), in particular a projector unit, of the optical system (10a, 10b, 10c), wherein the illumination device (12) has at least one first laser diode (7) for emitting a first light beam (8) within a first wavelength range (25a), wherein the first wavelength range (25a) is dependent on a temperature of the first laser diode (7), in particular the temperature of at least one first laser cavity of the first laser diode (7), a first controllable deflection unit (9) for the first light beam (8) for scanning projection of the image content, and the holographic optical element (5, 16) for deflecting the first light beam (8) incident on the holographic optical element (5, 16) from the controllable deflection unit (9) onto an eye (3), in particular a user of the optical system (10a, 10b, 10c), wherein the holographic optical element (5, 16) is formed from liquid crystals, and the holographic optical element (5, 16) has a first holographic function having a first diffraction efficiency range (21a) and a second holographic function having a second diffraction efficiency range (21b), wherein the first wavelength range (25a) overlaps at least partially with the first diffraction efficiency range (21a) and the second wavelength range (25b) overlaps at least partially with the second diffraction efficiency range (21b), and - a sensor (13) for detecting at least one item of information about the, in particular current, first (25a) or second wavelength range (25b) of the emitted first light beam (8), and - a control unit (11), and / or - the polarization switch (6) for switching the first light beam (8) in a first or a second polarization direction, wherein the first light beam (8) with the first polarization direction is assigned to the first diffraction efficiency range (21a) and the first light beam (8) with the second polarization direction is assigned to the second diffraction efficiency range (21b) of the holographic optical element (5, 16), wherein the method comprises the following method steps: - emitting (100) the first light beam (8) by means of the first laser diode (7), and - detecting (110) the information about the, in particular current, first (25a) or second wavelength range (25b) of the emitted first light beam (8) by means of the control unit (11), and - driving (140, 150) the holographic optical element (5, 16) or the polarization filter (6) of the optical system (10a, 10b, 10c) as a function of the detected information about the, in particular current, first (25a) or second wavelength range (25b) of the emitted first light beam (8) by means of the control unit (11) in such a way that the optical element (5, at a first point in time, has a first angle of incidence (15) on the holographic optical element (5, The first light beam (8) incident at the first wavelength (25a) and the first light beam (8) incident at the second wavelength (25b) at the first angle of incidence (15) at a second point of time following the first point of time are deflected towards the eye (3), in particular at the same positions (4) of the eye (3).Method according to Claim 10, characterized in that the temperature of the first laser diode (7), in particular the temperature of at least the first laser cavity of the first laser diode (7), represents the information about the, in particular current, first (25a) or second wavelength range (25b) of the emitted first light beam (8).Method according to either of Claims 10 and 11, characterized in that the first wavelength range (25a) and the second wavelength range (25b) differ from one another in terms of their maxima, in particular their centroid, at least 2 nm, in particular at least 5 nm.Method according to one of claims 10 to 12, characterised in that the first (25a) and second diffraction efficiency ranges (25b) partially overlap.Method according to one of Claims 10 to 13, characterized in that the first polarization direction of the first light beam (8) and the second polarization direction of the first light beam (8) are arranged orthogonally with respect to one another.Method according to one of Claims 10 or 14, characterized in that the method has the following additional method steps: - switching on a second laser diode (17) for emitting a second light beam (26) having the second wavelength (25b) and having the second polarization direction by means of the control unit (11), in particular at the second point in time, as a function of the detected information about the, in particular current, first (25a) or second wavelength range (25b) of the emitted first light beam (8), and - switching off the first laser diode (7) by means of the control unit (11), in particular at the second point in time, wherein the first laser diode (7) is designed to emit the first light beam (8) having the first polarization direction.

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