Optical system for a virtual retinal display

Abstract

The invention relates to an optical system (10a) for a virtual retinal display, having an illumination device (12). The illumination device (12) comprises a first laser diode (7) for emitting a first light beam (8) within a first wavelength range. The first wavelength range shifts toward a second wavelength range in a manner dependent on a temperature of the first laser diode (7). Furthermore, the optical system (10a) comprises a first controllable deflection unit (9) for the first light beam (8), the first controllable deflection unit serving for the scanning projection of the image content. Moreover, the optical system (10a) comprises a holographic optical element (5) for deflecting the first light beam (8) to an eye (3). In this case, 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 in part with the first diffraction efficiency range, and the second wavelength range overlaps at least in part with the second diffraction efficiency range. Furthermore, the optical system (10a) comprises a control unit (11) serving to control the holographic optical element (5) or a polarization switch in such a way that the first light beam (8) having the first wavelength and incident on the holographic optical element (5) at a first angle of incidence (15) at a first time, and the first light beam (8) having the second wavelength and incident at the first angle of incidence (15) at a second time following the first time are deflected to the eye (3), the control being based on detected information regarding the first or second wavelength range of the emitted first light beam (8).

Description

[0001] Description

[0002] Optical system for a virtual retinal display

[0003] The invention relates to an optical system for a virtual retinal display (retinal scan display). Furthermore, the invention relates to a method for controlling a holographic optical element or a polarization switch of an optical system for a virtual retinal display (retinal scan display).

[0004] State of the art

[0005] Data glasses (smartglasses) with retinal scan displays and holographic optical elements for redirecting light rays to the eye are already known.

[0006] It is an object of the present invention to develop an optical system for a virtual retinal display with a holographic optical element for deflecting the light rays onto the eye, the function of which always remains fulfilled even when the laser diode of the optical system fluctuates in temperature.

[0007] Disclosure of the invention

[0008] To achieve this object, an optical system for a virtual retinal display (retinal scan display) according to claim 1 is proposed. Furthermore, a method for controlling a holographic optical element or a polarization switch of an optical system for a virtual retinal display (retinal scan display) according to claim 10 is proposed.

[0009] 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 microprojector unit. The illumination device has at least one first laser diode for emitting a first light beam within a first wavelength range. The first wavelength range shifts towards a second wavelength range depending on a temperature of the first laser diode, in particular the temperature of at least a first laser cavity of the first laser diode. For example, the laser diode can heat up during operation, in particular due to the laser power. Furthermore, the optical system has a first controllable deflection unit for the first light beam for the scanning projection of the image content.Furthermore, 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 from 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 made of liquid crystals. In this context, the holographic optical element is used in particular as an LCD hologram. Such liquid crystals are characterized by the fact that their refractive index is anisotropic. The holographic optical element has a first holographic function with a first diffraction efficiency range and a second holographic function with a second diffraction efficiency range.Here, the first wavelength range at least partially overlaps with the first diffraction efficiency range, and the second wavelength range at least partially overlaps 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. Preferably, the holographic optical element is embedded in a lens, in particular a spectacle lens, of the optical system. Furthermore, 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. Preferably, the first sensor is designed as a temperature sensor. Furthermore, the optical system has a control unit.In this context, the control unit serves to control the holographic optical element, depending on 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 with 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 with the second wavelength incident at a second point in time following the first point in time with the first angle of incidence, is deflected towards the eye. In particular, the light beam is deflected to the same positions of the eye at the first and second points in time. The angle of incidence selectivity of the first and second holographic function is thus the same for both wavelengths.Alternatively or additionally, the optical system comprises a polarization switch for switching the first light beam into a first or a second polarization direction. The first light beam 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. This means that only first light beams with the first polarization direction are deflected within the first diffraction efficiency range, and only first light beams with 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 control the polarization switch depending on 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 with the first wavelength incident on the holographic optical element at the first time with the first angle of incidence and the first light beam with the second wavelength incident at the second time following the first time with the first angle of incidence are deflected towards the eye, in particular to the same positions of the eye. In both cases, the anisotropy of the holographic optical element is used to enable the optical system to function even in the event of temperature fluctuations of the laser diode.

[0010] 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 lookup table. Alternatively, the first sensor is designed as a first optical spectrometer. The control unit can use the spectral data acquired thereby directly to determine the, in particular current, first or second wavelength range. The holographic optical element is preferably designed as a, in particular static, holographic optical element which has the first and second diffraction efficiency ranges at the first and second points in time. Such a holographic optical element with 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, particularly for x- and y-polarized light. Thus, the diffraction efficiency (for a specific angle of incidence / diffraction angle configuration) can be adjusted or recorded to different wavelengths depending on the polarization of the incident light. Alternatively, the holographic optical element is designed as rotatable, in particular twistable, liquid crystals. 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 control the liquid crystals such that the holographic optical element has only the first diffraction efficiency range at the first time and only the second diffraction efficiency range at the second time.This could enable continuous tracking of the holographic optical element to the shift of the laser wavelength.

[0011] Preferably, the optical system additionally comprises a second laser diode for emitting a second light beam with a second wavelength and with the second polarization direction. In this context, the first laser diode is designed to emit the first light beam with 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 time, depending on the detected 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 with the first polarization direction is assigned to the first diffraction efficiency range and the second light beam with the second polarization direction is assigned to the second diffraction efficiency range of the holographic optical element.Thus, the polarization switch can be dispensed with and the control unit decides, depending on the information acquired about the, in particular current, first or second wavelength range, which of the two laser diode light beams is switched on and off.

[0012] Preferably, the polarization switch is formed from a liquid crystal and a polarization filter.

[0013] Preferably, the polarization switch is 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.

[0014] Preferably, the optical system is designed as data glasses, in particular as augmented reality glasses or virtual reality glasses.

[0015] A further subject matter of the present invention is a method for controlling a holographic optical element or a polarization switch of an optical system for a virtual retinal display (retinal scan display). The optical system for the virtual retinal display has been described above. In the method, a laser diode of the optical system initially emits a first light beam within a first wavelength range. The first wavelength range shifts towards a second wavelength range depending on a temperature of the first laser diode, in particular the temperature of at least a first laser cavity of the first laser diode. In a further method step, the information about the, in particular current, first or second wavelength range of the emitted first light beam is acquired by means of the control unit.Furthermore, the holographic optical element or the polarization filter of the optical system is controlled by the control unit depending on 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 with the first wavelength incident on the holographic optical element at a first time with a first angle of incidence and the first light beam with the second wavelength incident at a second time following the first time with the first angle of incidence are deflected toward the eye, in particular to the same positions of the eye. The method thus ensures that the functionality of the optical system is guaranteed even in the event of temperature fluctuations of the laser diode.

[0016] 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.

[0017] Preferably, the first wavelength range and the second wavelength range differ from each other by at least 2 nm, in particular at least 5 nm, in their maxima. The maximas refer in particular to the focal points or peaks of the respective wavelength ranges.

[0018] Preferably, the first and second diffraction efficiency ranges partially overlap. This ensures that there are no gaps between the diffraction efficiency ranges, thus preventing areas with incorrect or no deflection of the light rays to the eye.

[0019] 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 configured to polarize the first light beam with the first wavelength in the X direction and the first light beam with the second wavelength in the Y direction. Alternatively, the polarization switch is configured to polarize the first light beam with the first wavelength in a left-hand circular direction and the first light beam with the second wavelength in a right-hand circular direction.

[0020] Preferably, a second laser diode is furthermore switched on by the control unit, in particular at the second time, for emitting a second light beam with a second wavelength and with the second polarization direction, depending on 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 the control unit, in particular at the second time. The first laser diode serves to emit the first light beam with the first polarization direction. The correspondingly different polarization of the light beam thus occurs independently of the polarization switch.

[0021] Description of the drawings

[0022] Figure 1 shows a first embodiment of an optical system for a virtual retinal display (retinal scan display).

[0023] Figure 2 shows a second embodiment of the optical system for the virtual retinal display (retinal scan display).

[0024] Figure 3 shows a third embodiment of the optical system for the virtual retinal display (retinal scan display).

[0025] Figure 4 shows the overlap of wavelength ranges of the first light beam with the corresponding diffraction efficiency ranges of the holographic optical element.

[0026] Figure 5 shows a method for controlling a holographic optical element of an optical system for a virtual retinal display (retinal scan display).

[0027] Figure 6 shows a method for controlling a polarization switch of an optical system for a virtual retinal display (retinal scan display).

[0028] Description of the embodiments

[0029] Figure 1 schematically shows an optical system 10a for a virtual retinal display (retinal scan display). The optical system 10a is designed as data glasses with a temple 19 and a spectacle lens 18. The optical system 10a comprises an illumination device 12, which in this case is designed as a projector unit of the optical system 10a. 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 towards a second wavelength range depending on a temperature of the first laser diode 7, in particular the temperature of at least a first laser cavity 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 the 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 designed from two micromirrors, each mounted for one-dimensional rotation. The optical system 10a further comprises a holographic optical element 5 for deflecting the first light beam 8 incident from the controllable deflection unit 9 onto the holographic optical element 5 onto an eye 3. The eye 3 is the eye 3 of a user of the data glasses as the optical system 10a. 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. In this exemplary embodiment, the holographic optical element 5 is integrated, in particular embedded, into a lens 18. The lens 18 is designed as a spectacle lens of the optical system 10a. Furthermore, the optical system 10a has a sensor 13 for detecting at least one item of information about the, in particular current, first or second wavelength range of the emitted first light beam 8. The sensor 13 is designed as a temperature sensor in this embodiment. Furthermore, the optical system 10a has a control unit 11. In the illustrated embodiment of the optical system 10a, the projector unit 12, the controllable deflection unit 9, and the control unit 11 are integrated into the temple piece 19.In this context, the control unit 11 is designed to control the holographic optical element 5 depending on 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 at a second point in time following the first point in time with the first angle of incidence 15 are deflected towards the eye 3. In particular, the first light beams 8 are deflected to the same positions 4 of the eye 3 at the first and second points in time.

[0030] The control unit 11 is particularly designed to use a lookup table to determine the first or second wavelength range associated with the current temperature of the first laser diode. Alternatively, the first sensor 13 is designed as a first optical spectrometer. The control unit 11 can directly use the spectral data acquired thereby to determine the first or second wavelength range, in particular the current one.

[0031] In this first embodiment, the holographic optical element 5 is configured as rotatable, in particular twistable, liquid crystals. 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 serves to control the liquid crystals such that the holographic optical element 5 has only the first diffraction efficiency range at the first time and only the second diffraction efficiency range at the second time.

[0032] Figure 2 schematically shows a second embodiment of an optical system 10b. In contrast to the first embodiment, the optical system 10b additionally has a polarization switch 6. The polarization switch 6 is designed to switch the first light beam 8 into 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. 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 control the polarization switch 6, depending on 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, incident on the holographic optical element 16 at a first point in time with the first angle of incidence 15, with the first wavelength and the first polarization direction, and the first light beam 8, incident at a second point in time following the first point in time with the first angle of incidence 15, with the second wavelength and the second polarization direction, are deflected toward the eye. In particular, the first light beams 8 are deflected to the same positions 4 of the eye 3 at the first and second points in time.

[0033] In contrast to the first embodiment of the optical system 10a, the holographic optical element 16 is embodied as a holographic optical element 16 that has both the first and the second diffraction efficiency ranges at the first and second points in time. Such a holographic optical element 16 can also be referred to as a static holographic optical element 16.

[0034] In the illustrated embodiment, the polarization switch 6 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 other optical components, in particular lenses, of the optical system 10b (not shown here for simplicity).

[0035] Figure 3 schematically shows a third embodiment of an optical system 10c. In contrast to the first embodiment, the optical system 10c additionally has a second laser diode 17 for emitting a second light beam 26 with the second wavelength and with 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 time, depending on the detected information about the, in particular current, first or second wavelength range of the emitted first light beam 8.

[0036] Figure 4 uses a diagram to show the assignment of the first wavelength range 25a to the first diffraction efficiency range 21a, and of the second wavelength range 25b to the second diffraction efficiency range 21b. The laser power of the first laser diode is plotted on the first Y-axis 20a. The wavelength is plotted on the X-axis 20b. The first wavelength range 25a of the first light beam of the first laser diode shifts in the direction of arrow 23 from the first time to the second time due to an increase in the temperature of the first laser diode towards the higher, second wavelength range 25b. The different diffraction efficiency ranges 21a and 21b of the holographic optical element ensure that the first light beams are always correctly redirected onto the eye of the user of the optical system.

[0037] Optionally, a first polarization direction of the first light beam is assigned to the first diffraction efficiency range 21 a and a second polarization direction of the first light beam is assigned to the second diffraction efficiency range 21 b.

[0038] In the illustrated case, the first wavelength range 25a and the second wavelength range 25b differ from each other by essentially 2 nm in their maxima 22a and 22b. Furthermore, the first diffraction efficiency range 21a and the second diffraction efficiency range 21b partially overlap with each other.

[0039] Figure 5 shows a method for controlling 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 Figure 1. In the method, in method step 100, a laser diode of the optical system initially emits a first light beam within a first wavelength range. The first wavelength range shifts towards a second wavelength range depending on a temperature of the first laser diode, in particular the temperature of at least a first laser cavity of the first laser diode. In a further method step 110, information about the, in particular current, first or second wavelength range of the emitted first light beam is detected 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 depending on the acquired information about the, in particular current, first or second wavelength range of the emitted first light beam such that the first light beam with the first wavelength incident on the holographic optical element at a first time with a first angle of incidence and the first light beam with the second wavelength incident at a second time following the first time with the first angle of incidence are redirected to the eye, in particular to the same positions of the eye. The method is then terminated.

[0040] Optionally, the temperature of the first laser diode represents 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. To determine the currently present first or second wavelength of the first light beam, the control unit optionally uses a lookup table in 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 control unit can use the spectral data acquired thereby directly to determine the, in particular current, first or second wavelength range.

[0041] Figure 6 shows a method for controlling a polarization switch of an optical system for a virtual retinal display (retinal scan display). In contrast to the method in Figure 5, in a method step 150 following method step 110, the polarization filter of the optical system is controlled by means of 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 with 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 with the second wavelength incident 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 to the same positions of the eye.The polarization switch is configured to switch the first light beam with the first wavelength into a first polarization direction at the first time and the first light beam with the second wavelength into a second polarization direction at the second 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

Claims 1 . An optical system (10a, 10b, 10c) for a virtual retinal display (retinal scan display), comprising at least one 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) towards a second wavelength range (25b) depending on a temperature of the first laser diode (7), in particular the temperature of at least a first laser cavity of the first laser diode (7), and a first controllable 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 light beam emitted by the controllable deflection unit (9) onto the holographic optical element (5, 16). incident first light beam (8) onto one 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 with a first diffraction efficiency range (21a), and a second holographic function with a second diffraction efficiency range (21b), wherein the first wavelength range (25a) at least partially overlaps with the first diffraction efficiency range (21a) and the second wavelength range (25b) at least partially overlaps 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 a polarization switch (6) for switching the first light beam (8) into a first or a second polarization direction,wherein the first light beam (8) with the first polarization direction corresponds to the first, th diffraction efficiency range (21 a) and the first light beam (8) with the second polarization direction is assigned to the second diffraction efficiency range (21 b) of the holographic optical element (5, 16), and the control unit (11) is designed to control the holographic optical element (5, 16) or the polarization switch (6) 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) in such a way that the first light beam (8) with the first wavelength (25a) incident on the holographic optical element (5, 16) at a first point in time with a first angle of incidence (15) and the first light beam (8) with the second wavelength (25b) incident at a second point in time following the first point in time with the first angle of incidence (15) are deflected to the eye (3), in particular to the same positions (4) of the eye (3).

2. Optical system (10a, 10b, 10c) according to claim 1, characterized in that the holographic optical element (5, 16) is designed 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 second times.

3. Optical system (10a, 10b, 10c) according to claim 1, characterized in that the holographic optical element (5, 16) is designed as rotatable, in particular twistable, liquid crystals, 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 control 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 time and only the second diffraction efficiency range (21b) at the second time.

4. 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.

5. 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) with the second wavelength (25b) and with the second polarization direction, wherein the first laser diode (7) is designed to emit the first light beam (8) with the first polarization direction, wherein the control unit (11) is designed to switch off the first laser diode (7) and to switch on the second laser diode (17), in particular at the second time, depending on the detected information about the, in particular current, first (25a) or second wavelength range (25b) of the emitted first light beam (8).

6. 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).

7. Optical system (10a, 10b, 10c) according to one of claims 1 to 6, characterized in that the polarization switch (6) is formed from a liquid crystal and a polarization filter.

8. 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).

9. 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 data glasses.

10. A 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) comprising at least one 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 towards a second wavelength range (25b) depending on a temperature of the first laser diode (7), in particular the temperature of at least a first laser cavity of the first laser diode (7),and 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 from the controllable deflection unit (9) onto 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 with a first diffraction efficiency range (21a) and a second holographic function with a second diffraction efficiency range (21b), wherein the first wavelength range (25a) at least partially overlaps with the first diffraction efficiency range (21a) and the second wavelength range (25b) at least partially overlaps with the second diffraction efficiency range (21b),and a sensor (13) for detecting at least one piece 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) into 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 (21 a) and the first light beam (8) with the second polarization direction is assigned to the second diffraction efficiency range (21 b) of the holographic optical element (5, 16), the method comprising 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 controlling (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) such that the first light beam (8) incident on the holographic optical element (5, 16) at a first time with a first angle of incidence (15) with the first wavelength (25a) and the first light beam (8) incident at a second time following the first time with the first angle of incidence (15) with the second wavelength (25b) to the eye (3), in particular the same positions (4) of the eye (3).

11. 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).

12. Method according to one of claims 10 or 11, characterized in that the first wavelength range (25a) and the second wavelength range (25b) are at least 2nm, in particular at least 5nm, differ from each other in their maxima, especially their center of gravity.

13. Method according to one of claims 10 to 12, characterized in that the first (25a) and second diffraction efficiency range (25b) partially overlap.

14. 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 to one another.

15. Method according to one of claims 10 or 14, characterized in that the method comprises the following additional method steps: Switching on a second laser diode (17) for emitting a second light beam (26) with the second wavelength (25b) and with the second polarization direction by means of the control unit (11), in particular at the second time, depending on 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 time, wherein the first laser diode (7) is designed to emit the first light beam (8) with the first polarization direction.

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