WO2024052125A1

WO2024052125A1 - Optical element and method for producing an optical element

Info

Publication number: WO2024052125A1
Application number: PCT/EP2023/073144
Authority: WO
Inventors: Thomas Kippes; Alan Lenef
Original assignee: Ams Osram International GmbH
Current assignee: Ams Osram International GmbH
Priority date: 2022-09-09
Filing date: 2023-08-23
Publication date: 2024-03-14
Anticipated expiration: 2025-03-09

Abstract

An optical element (1) is specified herein, comprising: - a dichroic beam combiner (2) configured for superimposing a first light beam (31) in a first wavelength range onto a second light beam (32) in a second wavelength range different from the first wavelength range, - a first diffractive element (41) arranged on a first light- incoupling region (21) of the dichroic beam combiner (2), the first diffractive element (41) configured for collimating the first light beam (31) before entering the dichroic beam combiner (2), and - a second diffractive element (42) arranged on a second light-incoupling region (22) of the dichroic beam combiner (2), the second diffractive element (42) configured for collimating the second light beam (32) before entering the dichroic beam combiner (2). Further, a method for producing an optical element is specified herein.

Description

OPTICAL ELEMENT AND METHOD FOR PRODUCING AN OPTICAL ELEMENT

An optical element and a method for producing an optical element are speci fied herein .

At least one obj ect of certain embodiments is to speci fy an optical element for combining light beams that is particularly compact , as well as a method for producing such an optical element .

According to at least one aspect , the optical element comprises a dichroic beam combiner configured for superimposing a first light beam in a first wavelength range onto a second light beam in a second wavelength range di f ferent from the first wavelength range . In particular, the dichroic beam combiner superimposes the first light beam onto the second light beam such that the first light beam and the second light beam have identical propagation directions after being coupled out of the optical element . Here and in the following, the first light beam and the second light beam have identical propagation directions , i f their propagation directions deviate by at most 5 ° , preferably by at most 1 ° , and particularly preferably by at most 0 . 2 ° .

Moreover, the dichroic beam combiner preferably superimposes the first light beam onto the second light beam such that the first light beam and the second light beam overlap in a plane perpendicular to the propagation direction . For example , the first light beam and the second light beam overlap completely . In particular, on a light-outcoupling surface of the dichroic beam combiner, a distance between a center of the first light beam and a center of the second light beam is smaller than or equal to one hal f , preferably one tenth, of a beam width of the first light beam or of the second light beam . Here and in the following, the beam width speci fies a full width at hal f maximum ( FWHM) of an intensity distribution of the first or second light beam in a plane perpendicular to the propagation direction . For light beams with an elliptic or non-circular intensity distribution, the beam width corresponds to a maximum beam width within said plane .

The beam width of the first light beam and the beam width of the second light beam may be equal or deviate from one another . For example , the beam width of the first light beam is by at most 50% , preferably by at most 10% , larger or smaller than the beam width of the second light beam .

The first light beam and/or the second light beam preferably comprise electromagnetic laser radiation . Electromagnetic laser radiation is generated by stimulated emission . Compared to electromagnetic radiation generated by spontaneous emission, electromagnetic laser radiation has a larger coherence length, a smaller spectral line width, and/or a higher degree of polari zation . For example , the first light beam and the second light beam are Gaussian beams .

For example , the first light beam and the second light beam comprise electromagnetic laser radiation in a spectral range between infrared light and ultraviolet light . Preferably, the first wavelength range and the second wavelength range do not overlap, such that the first light beam and the second light beam comprise electromagnetic laser radiation in mutually di f ferent wavelength ranges . In other words , the second wavelength range preferably does not comprise wavelengths from within the first wavelength range and vice versa. For example, the first light beam comprises electromagnetic laser radiation in a red spectral range, whereas the second light beam comprises electromagnetic laser radiation in a green spectral range.

According to at least one further aspect, the optical element comprises a first diffractive element arranged on a first light-incoupling region of the dichroic beam combiner and the first diffractive element is configured for collimating the first light beam before entering the dichroic beam combiner. In particular, the first diffractive element is configured to reduce a beam divergence of the first light beam. Here and in the following, the beam divergence is an angular measure of an increase of the beam width along the propagation direction of the light beam. In particular, the beam divergence specifies an opening angle of a cone, wherein the light beam propagates .

For example, after collimation by the first diffractive element, the beam divergence of the first light beam is at most 5°, preferably at most 1°, and particularly preferably at most 0.2°. For example, after collimation by the first diffractive element a beam divergence of the first light beam is reduced by at least 70%, preferably by at least 90%, and particularly preferably by at least 98%. In other words, after collimation by the first diffractive element the beam divergence of the first light beam is at most 30%, preferably at most 10%, and particularly preferably at most 2% of an initial beam divergence of the first light beam emitted by a laser diode, for example. According to at least one further aspect, the optical element comprises a second diffractive element arranged on a second light-incoupling region of the dichroic beam combiner and the second diffractive element is configured for collimating the second light beam before entering the dichroic beam combiner. In particular, the second diffractive element is configured to reduce the beam divergence of the second light beam. For example, after collimation by the second diffractive element, the beam divergence of the second light beam is at most 5°, preferably at most 1°, and particularly preferably at most 0.2°. For example, after collimation by the second diffractive element a beam divergence of the second light beam is reduced by at least 70%, preferably by at least 90%, and particularly by at least 98%. In other words, after collimation by the second diffractive element the beam divergence of the second light beam is at most 30%, preferably at most 10%, and particularly preferably at most 2% of an initial beam divergence of the second light beam emitted by a laser diode, for example.

In particular, the first diffractive element and/or the second diffractive element changes a wave front of electromagnetic radiation passing through said diffractive element due to diffraction. For example, sub-regions of the first diffractive element and/or the second diffractive element may act as an optical diffraction grating. In particular, the first and/or second diffractive element imparts a spatially varying phase shift onto the wave front. The first and/or second diffractive element thus can be used to shape a wave front of the first light beam and/or of the second light beam, respectively. Accordingly, the first diffractive element and/or the second diffractive element can be configured to collimate, focus, and/or change a propagation direction of the first light beam and/or the second light beam, for example .

Preferably, the first di f fractive element is arranged directly on the first light-incoupling region of the dichroic beam combiner and/or the second di f fractive element is arranged directly on the second light-incoupling region of the dichroic beam combiner . For example , the first di f fractive element and/or the second di f fractive element are bonded onto a surface of the dichroic beam combiner . In particular, the first light-incoupling region and the second light-incoupling region are spatially separated regions . In other words , the first light-incoupling region and the second light-incoupling region do not overlap .

According to a preferred embodiment , the optical element comprises :

- a dichroic beam combiner configured for superimposing a first light beam in a first wavelength range onto a second light beam in a second wavelength range di f ferent from the first wavelength range ,

- a first di f fractive element arranged on a first lightincoupling region of the dichroic beam combiner, the first di f fractive element configured for collimating the first light beam before entering the dichroic beam combiner, and

- a second di f fractive element arranged on a second lightincoupling region of the dichroic beam combiner, the second di f fractive element configured for collimating the second light beam before entering the dichroic beam combiner .

The optical element described herein is based on the idea to use nano-structured surfaces for di f f ractively collimating at least two di f ferent laser beams before superimposing these laser beams with a dichroic beam combiner . Compared to a collimation of the laser beams using refractive optical elements , such as lenses , the optical element may be more compact and a complexity in manufacturing may be reduced . In particular, it is not necessary to optically align multiple components during assembly of a laser package including at least two laser diodes and the optical element described herein, for example .

For example , refractive optical elements for fast and slow axis collimation may not have a flat surface that can be mounted directly on a surface of a dichroic beam combiner . Accordingly, the dichroic beam combiner and refractive optical elements for collimation of each laser beam may need to be optically aligned during assembly of the laser package , thereby increasing a complexity and cost of a manufacturing process .

Advantageously, the di f fractive optical elements for collimation of the laser beams described herein can be directly arranged or formed on a surface of the dichroic beam combiner during production of the optical element . Therefore , no optical alignment of refractive optical elements for collimation is necessary during assembly of the laser package . Moreover, the number of optical elements within the laser package can be reduced, as no separate refractive optical elements for collimation of the laser beams are needed .

According to at least one further aspect of the optical element , the first di f fractive element and/or the second di f fractive element comprises a nano-structured surface . In particular, the nano-structured surface imparts a spatially dependent phase shi ft onto the first light beam and/or the second light beam, respectively . In other words , the nanostructured surface is configured to shape a wave front of the first light beam and/or the second light beam . Preferably, a linear dimension of structures within the plane of the nanostructured surface is smaller than or equal to a wavelength in the first wavelength range and/or in the second wavelength range , as determined by a refractive index in a body of the dichroic beam combiner .

According to at least one further aspect of the optical element , the nano-structured surface comprises an aperiodic array of nano-pillars . For example , the nano-pillars are arranged at vertices of a periodic two-dimensional lattice , such as a rectangular lattice or a hexagonal lattice for example , wherein a si ze and/or a shape of the nano-pillars changes across periods of the lattice , such that the aperiodic array is formed . Alternatively or in addition, the nano-pillars may be arranged aperiodically . In other words , the nano-pillars may not be arranged at vertices of a periodic lattice , at least in regions of the aperiodic array .

Preferably, the nano-pillars comprise a dielectric material that is at least partially transparent for electromagnetic radiation in the first wavelength range and/or in the second wavelength range . For example , at visible wavelengths , the nano-pillars comprise titanium dioxide , zinc oxide , silicon nitride , or other known high refractive index, optically transparent thin film oxides and/or nitrides . In particular, the nano-structured surface comprising the aperiodic array of nano-pillars gives rise to an aperiodic modulation of a refractive index across the nano-structured surface of the first di f fractive element and/or the second di f fractive element . Accordingly, the array of nano-pillars can imprint a spatially varying phase shi ft onto the wave front of the first light beam and/or the second light beam, respectively .

For example , a cross section of the nano-pillars in plain view of the nano-structured surface may be circular, semicircular, elliptic, oval , triangular, rectangular, square , pentagonal , hexagonal , or polygonal . Moreover, the cross section of the nano-pillars may change along a direction perpendicular to the nano-structured surface . For example , the nano-pillars may be cylinder-shaped, cone-shaped, pyramid-shaped, or the like . In some embodiments the nanopillars may have an arbitrary shape .

According to at least one further aspect of the optical element , a lateral si ze and/or a vertical si ze of the nanopillars is smaller than or equal to a wavelength in the first wavelength range or in the second wavelength range . Here and in the following " lateral" refers to directions parallel to the nano-structured surface , whereas "vertical" refers to a direction perpendicular to the nano-structured surface . In other words , a width and/or a height of the nano-pillars is smaller than or equal to a wavelength in the first wavelength range or in the second wavelength range . For example , a fraction of the nano-pillars or all of the nano-pillars have a lateral and/or a vertical si ze that is smaller than or equal to a wavelength in the first wavelength range or in the second wavelength range . Moreover, a center-to-center distance between neighboring nano-pillars is preferably smaller than or equal to a wavelength in the first wavelength range or in the second wavelength range . The actual spacing requirements between neighboring nano-pillars depend on the array configuration, in particular to avoid higher order diffraction components.

According to at least one further aspect of the optical element, the first diffractive element is configured to collimate the first light beam with respect to two independent axes perpendicular to the propagation direction of the first light beam and/or the second diffractive element is configured to collimate the second light beam with respect to two independent axes perpendicular to the propagation direction of the second light beam. For example, the first light beam and/or the second light beam has different beam divergences along the two independent axes. For example, the beam divergence is larger across one axis, the fast axis, and smaller across the other axis, the slow axis. In other words, the first diffractive element and/or the second diffractive element is configured for both, a fast axis collimation and a slow axis collimation.

Advantageously, the first diffractive element and/or the second diffractive element allows for a fast axis collimation and for a slow axis collimation while having a particularly compact structure compared to refractive lenses for fast and slow axis collimation. In some cases, by taking advantage of both focusing and off-axis deflection functions that can be generated in a single diffractive element, it is possible to simultaneously collimate both axes as well as reduce a degree of ellipticity in the collimated beams.

According to at least one further aspect of the optical element, the dichroic beam combiner comprises a dichroic element configured for reflecting the first light beam and for transmitting the second light beam. In particular, the dichroic element has a reflectance of at least 90% for the first light beam and a transmittance of at least 90% for the second light beam .

For example , the dichroic element comprises a dielectric layer stack with two or more dielectric layers with di f ferent refractive indices for electromagnetic radiation in the first wavelength range and/or in the second wavelength range . In particular, by adj usting a thickness of each of the two or more layers , a reflectance and/or transmittance of the dichroic element can be adj usted as a function of the wavelength of the electromagnetic radiation .

According to at least one further aspect of the optical element , the dichroic beam combiner comprises a transparent body with a first main surface including the first lightincoupling region and the second light-incoupling region . In particular, the transparent body is at least partially transparent for the first light beam and the second light beam . For example , a transmittance of the transparent body for the first light beam and for the second light beam is at least 90% . For example , the transparent body comprises glass , a semiconductor material , a plastic, or other transparent materials for the desired wavelength ranges , or consists of one of these materials .

According to at least one further aspect of the optical element , the dichroic element is arranged on the second light-incoupling region . In particular, the second light beam incident on the second light-incoupling region is transmitted through the dichroic element , whereas the first light beam, coupled into the transparent body via the first lightincoupling region and propagating therein, is reflected by the dichroic element . In other words , the first light beam and the second light beam are incident on opposite sides of the dichroic element .

Preferably, angles of incidence of the first light beam and of the second light beam onto the dichroic element are adj usted such that the transmitted second light beam and the reflected first light beam are superimposed onto each other . In other words , the first light beam and the second light beam overlap and have the same propagation direction after the first light beam is reflected by the dichroic element and after the second light beam is transmitted through the dichroic element , respectively . As the di f fractive elements can also be used to alter the transmitted beam angles , additional flexibility exits with respect to incident light beam angles .

According to at least one further aspect of the optical element , the transparent body comprises a second main surface opposite to the first main surface , and a reflective element is arranged on the second main surface . In other words , the reflective element is arranged opposite to the first lightincoupling region and the second light-incoupling region . In particular, the reflective element is configured to redirect the first light beam towards the second light-incoupling region after being coupled into the transparent body via the first light-incoupling region . For example , a reflectance of the reflective element for the first light beam is at least 90% , preferably at least 99% .

For example , the reflective element comprises a metallic layer and/or a Bragg mirror, or consists of a metallic layer or a Bragg mirror . Here and in the following, the Bragg mirror is a stack of alternating dielectric layers with di f ferent refractive indices for the first light beam . By adj usting a thickness and/or the refractive index contrast between the alternating layers , a Bragg mirror with a speci fied reflectance for the first light beam can be formed .

According to at least one further aspect of the optical element , the reflective element is a di f fractive element comprising a nano-structured surface . In particular, the nano-structured surface comprises an aperiodic array of nanopillars . For example , the nano-pillars may have a similar shape , form, and/or si ze as the nano-pillars disclosed in connection with the first and/or second refractive elements .

Advantageously, the nano-structured surface of the reflective element may be configured to further collimate the first light beam upon reflection . Moreover, the nano-structured surface of the reflective element may be configured to steer the first light beam upon reflection . In other words , an angle of reflection of the first light beam can be adj usted by configuring the nano-structured surface of the reflective element accordingly . In particular, the nano-structured surface of the reflective element can be used to steer the first light beam towards the dichroic element on the second light-incoupling region of the dichroic beam combiner . Advantageously, a reflective element in the form of a di f fractive element comprising a nano-structured surface gives rise to a more compact package of the optical element .

According to at least one further aspect of the optical element , the first di f fractive element and/or the second di f fractive element are configured to change a propagation direction of the first light beam and/or of the second light beam, respectively. In particular, the first diffractive element is configured to steer the first light beam upon entering the transparent body. Moreover, the second diffractive element may be configured to steer the second light beam upon entering the transparent body. In other words, the first diffractive element and the second diffractive element can be configured to adjust a propagation direction of the first light beam and the second light beam inside the transparent body. Advantageously, the dichroic beam combiner may have a more compact form by adjusting the propagation directions of the light beams within the transparent body.

According to at least one further aspect, the optical element further comprises a third diffractive element configured for collimating a third light beam and the third diffractive element is arranged on a third light-incoupling region of the dichroic beam combiner. The dichroic beam combiner is configured to superimpose the first light beam, the second light beam and the third light beam onto each other. The first light beam comprises electromagnetic laser radiation in a red spectral range, the second light beam comprises electromagnetic laser radiation in a green spectral range, and the third light beam comprises electromagnetic laser radiation in a blue spectral range.

In particular, the third diffractive element may have a similar structure as the first and second diffractive elements. For example, the third diffractive element has a nano-structured surface comprising an aperiodic array of nano-pillars as described above. In particular, the dichroic beam combiner comprises one dichroic element arranged on the second light-incoupling region and configured to reflect the first light beam and to transmit the second light beam . Furthermore , the dichroic beam combiner comprises a further dichroic element configured to reflect both the first light beam and the second light beam, while the third light beam is transmitted through the further dichroic element . The further dichroic element is arranged on the third light-incoupling region .

According to at least one further aspect of the optical element , an outcoupling element is arranged at a light- outcoupling region of the transparent body . In particular, the superimposed first and second light beams are coupled out of the optical element after passing through the outcoupling element . The outcoupling element may be configured for a further collimation of the first and second light beams . For example , the outcoupling element comprises a lens , a microlens , or a nano-structured surface with an aperiodic array of nano-pillars configured for di f fractive scattering of the first and second light beams . Preferably, the outcoupling element is arranged directly on the second main surface of the transparent body .

According to at least one further embodiment , the optical element comprises :

- the transparent body including the first light-incoupling region, the second light-incoupling region and the light- outcoupling region,

- the dichroic element arranged on the second lightincoupling region, - the first di f fractive element arranged on the first lightincoupling region and the second di f fractive element arranged on the dichroic element , wherein

- the dichroic element reflects the first light beam propagating inside the transparent body and coupled into the transparent body via the first light-incoupling region,

- the dichroic element transmits the second light beam coupled into the transparent body via the second lightincoupling region,

- the first di f fractive element collimates the first light beam before entering the transparent body and the second di f fractive element collimates the second light beam before entering the transparent body, and

- the first light beam and the second light beam overlap upon exiting the transparent body via the light-outcoupling region .

Further, a method for producing an optical element is speci fied herein . In particular, an optical element as speci fied above may be produced using this method . All features of the optical element are also disclosed for the method for producing an optical element , and vice versa .

According to at least one aspect , the method for producing an optical element comprises a step of providing a dichroic beam combiner for superimposing a first light beam in a first wavelength range onto a second light beam in a second wavelength range di f ferent from the first wavelength range .

According to at least one further aspect , the method comprises a step of arranging a first di f fractive element on a first light-incoupling region of the dichroic beam combiner and a second di f fractive element on a second light-incoupling region of the dichroic beam combiner .

According to at least one further aspect of the method, the first di f fractive element is configured for collimating the first light beam before entering the dichroic beam combiner and the second di f fractive element is configured for collimating the second light beam before entering the dichroic beam combiner .

According to a preferred embodiment , the method for producing an optical element comprises the steps :

- providing a dichroic beam combiner for superimposing a first light beam in a first wavelength range onto a second light beam in a second wavelength range di f ferent from the first wavelength range ,

- arranging a first di f fractive element on a first lightincoupling region of the dichroic beam combiner and a second di f fractive element on a second light-incoupling region of the dichroic beam combiner, wherein

- the first di f fractive element is configured for collimating the first light beam before entering the dichroic beam combiner and the second di f fractive element is configured for collimating the second light beam before entering the dichroic beam combiner .

According to at least one further aspect of the method, the step of providing a dichroic beam combiner includes providing a transparent body with a first main surface including the first light-incoupling region and the second light-incoupling region . According to at least one further aspect of the method, the step of providing a dichroic beam combiner further includes disposing a dichroic element on the second light-incoupling region of the transparent body . In particular, the dichroic element is configured to reflect the first light beam and to transmit the second light beam . For example , a dielectric layer sequence forming the dichroic element is disposed directly on the first main surface of the transparent body . The dielectric layer sequence may be disposed by chemical vapor deposition, sputtering, or physical vapor deposition, such as ion-assisted electron-beam deposition, for example .

According to at least one further aspect of the method, the step of providing a dichroic beam combiner further includes disposing a reflective element on a second main surface of the transparent body opposite to the first main surface . In particular, the reflective element is configured to redirect the first light beam propagating inside the transparent body towards the second light-incoupling region, where it is further reflected by the dichroic element .

According to at least one further aspect of the method, the first di f fractive element and the second di f fractive element comprise a nano-structured surface formed on a common carrier . In particular, the nano-structured surface comprises an aperiodic array of nano-pillars . Preferably, the common carrier comprises a dielectric material or consists of a dielectric material that is at least partially transparent for the first light beam and for the second light beam . For example , a transmittance of the common carrier for the first light beam and for the second light beam is at least 90% . In particular, the common carrier is a wafer comprising silicone or a di f ferent polymer, for example . The nano-structured surface may be arranged on a fused silica substrate embedded into or arranged on the silicone wafer, for example . The nano-structured surface is formed using photolithography, electron beam lithography, or nanoimprint lithography, for example .

According to at least one further aspect of the method, the common carrier is bonded onto the dichroic beam combiner . In particular, the common carrier is wafer bonded with the first main surface of the transparent body . For example , the common carrier is wafer bonded onto the dichroic beam combiner using a laser welding process or glueing .

According to at least one further aspect of the method, the first di f fractive element and the second di f fractive element are picked and placed onto the first light-incoupling region and onto the second light-incoupling region of the dichroic beam combiner, respectively . In other words , the first di f fractive element and the second di f fractive element are individually arranged on the first light-incoupling region and the second light-incoupling region, respectively .

According to at least one further aspect of the method, a buf fer layer and a surface layer are disposed on the first light-incoupling region and on the second light-incoupling region of the dichroic beam combiner . In particular, the buf fer layer and the surface layer are disposed on the first main surface of the transparent body, after the dichroic element has been arranged on the first main surface . For example , the buf fer layer and/or the surface layer are disposed by sputtering, chemical vapor deposition, or physical vapor deposition . Preferably, the buf fer layer and the surface layer are at least partially transparent for the first light beam and for the second light beam . For example , a reflectance of the buf fer layer and a reflectance of the surface layer for the first light beam and the second light beam is at least 90% .

For example , the buf fer layer is configured to provide a smooth surface for depositing the surface layer . For example , the buf fer layer comprises silicon dioxide or aluminium oxide , whereas the surface layer comprises titanium dioxide , zinc oxide , silicon nitride , or other known high refractive index, optically transparent thin film oxides and/or nitrides , or consists of one of these materials . It is also possible that the surface layer is deposited directly onto the dichroic beam combiner . In other words , no buf fer layer may be needed between the dichroic beam combiner and the surface layer .

According to at least one further aspect of the method, the first di f fractive element is arranged on the first lightincoupling region and the second di f fractive element is arranged on the second light-incoupling region of the beam combiner by forming a nano-structured surface in the surface layer . For example , the nano-structured surface is formed by photolithography, electron beam lithography, or any other method that is suitable for forming an aperiodic array of nano-pillars .

The first di f fractive element may also be formed directly in the material of the transparent body . In other words , a surface of the transparent body may comprise the nanostructure of the first di f fractive element . Accordingly, no surface layer may be needed to form the nano-structured surface of the first di f fractive element therein .

According to at least one further aspect of the method, a plurality of optical elements is produced by forming a plurality of dichroic beam combiners using a common transparent body that is singulated into a plurality of optical elements in a last step of the method . In particular, the first and second di f fractive elements are arranged on the dichroic beam combiner before dicing the transparent body . The singulation step may also include dicing the common carrier wherein the first and second di f fractive elements can be formed .

Further advantageous embodiments and further embodiments of the optical element and the method for producing an optical element may become apparent from the following exemplary embodiments described in connection with the figures .

Figure 1 shows a schematic cross-section of an optical element according to an exemplary embodiment .

Figure 2 shows a schematic cross-section of a di f fractive element of an optical element according to an exemplary embodiment .

Figures 3 to 5 show schematic cross sections of stages of optical elements after a step of a method for producing an optical element according to di f ferent exemplary embodiments .

Elements that are identical , similar or have the same ef fect , are denoted by the same reference signs in the figures . The figures and the proportions of the elements shown in the figures are not to be regarded as true to scale. Rather, individual elements, in particular layer thicknesses, may be shown exaggeratedly large for better representability and/or better understanding.

The optical element 1 according to the exemplary embodiment in Figure 1 comprises a dichroic beam combiner 2 as well as a first diffractive element 41, a second diffractive element 42 and a third diffractive element 43. The dichroic beam combiner 2 is configured to superimpose a first light beam 31 and a second light beam 32 onto a third light beam 33. The first light beam 31 comprises electromagnetic laser radiation in a red spectral range, the second light beam 32 comprises electromagnetic laser radiation in a green spectral range, and the third light beam 33 comprises electromagnetic laser radiation in a blue spectral range. The first, second and third light beams 31, 32, 33 are coupled into the dichroic beam combiner via first, second and third light-incoupling regions 21, 22, 23, respectively. The spectral ranges or colors of the first, second and third light beams 31, 32, 33 may also be interchanged.

The dichroic beam combiner 2 comprises a transparent body 7 with a first main surface 71 including the first, second and third light-incoupling regions 21, 22, 23, as well as two dichroic elements 6 and a reflective element 8. The transparent body comprises or consists of glass. One dichroic element 6 is arranged directly on the first main surface 71 of the transparent body 7 in the second light-incoupling region 22. A further dichroic element 6 is arranged directly on the first main surface 71 of the transparent body 7 in the third light-incoupling region 23. The dichroic element 6 in the second light-incoupling region

22 is configured to reflect the first light beam 31 propagating inside the transparent body 7 and to transmit the second light beam 32 that is coupled into the transparent body 7 via the second light-incoupling region 22 . In particular, angles of incidence of the first light beam 31 and of the second light beam 32 on the dichroic element 6 are adj usted such that the first light beam 31 and the second light 32 beam are superimposed onto each other inside the transparent body 7 after reflection by the dichroic element 6 and transmission through the dichroic element 6 , respectively .

The dichroic element 6 in the third light-incoupling region

23 is configured to reflect the superimposed first and second light beams 31 , 32 propagating inside the transparent body 7 , and to transmit the third light beam 33 that is coupled into the transparent body 7 via the third light-incoupling region 23 . In particular, angles of incidence of the first and second light beam 31 , 32 , as well as of the third light beam 33 on the dichroic element 6 are adj usted such that the first light beam 31 , the second light beam 32 and the third light beam 33 are superimposed onto each other inside the transparent body 7 . The superimposed first , second and third light beams 31 , 32 , 33 are then coupled out of the transparent body 7 via a second main surface 72 opposite to the first main surface 71 .

The dichroic elements 6 comprise di f ferent dielectric layer stacks with di f ferent wavelength dependent reflectances and transmittances . In particular, thicknesses of the dielectric layers in the dielectric layer stacks are adj usted to obtain the desired reflectances and transmittances for the first, second and third light beams 31, 32, 33.

The reflective element 8 is arranged on a region of the second main surface 72 of the transparent body 7. The reflective element 8 is configured to reflect the first light beam 31 and the second light beam 32 that propagate within the transparent body 7. In particular, the reflective element 8 is configured to redirect the first light beam 31 onto the dichroic element 6 in the second light-incoupling region 22, and to redirect the superimposed first and the second light beams 32, 33 onto the dichroic element 6 in the third lightincoupling region 23. The reflective element 8 may comprise a nano-structured surface with an aperiodic array of dielectric nano-pillars configured for a diffractive reflection of the incident first and second light beams 31, 32. The reflective element 8 may be designed to adjust steering angles and/or fine-tune collimation. The nano-structured surface of the reflective element 8 may have different regions with different nano structures corresponding to the different incident light beams 31, 32.

The first, second and third diffractive elements 41, 42, 43 are arranged on the first, second and third light-incoupling regions 21, 22, 23 of the dichroic beam combiner 2. In particular, the first diffractive element 41 is arranged directly on the first main surface 71 of the transparent body 7 in the first light-incoupling region 21, whereas the second and third diffractive elements 42, 43 are disposed directly on the dichroic elements 6 that are arranged in the second and third light-incoupling regions 22, 23, respectively. The first, second and third diffractive elements 41, 42, 43 are configured to collimate the first, second and third light beams 31, 32, 33 upon entering the dichroic beam combiner 2, respectively. In particular, the first, second and third diffractive elements 41, 42, 43 reduce a beam divergence a of the first, second and third light beams 31, 32, 33 respectively. The first second and third diffractive elements 41, 42, 43 each comprise a nano-structured surface with an aperiodic array of dielectric nano-pillars. The aperiodic array of nano-pillars of each diffractive element 41, 42, 43 is tailored to the respective wavelength range of the first, second and third light beam 31, 32, 33.

Furthermore, the optical element 1 comprises an outcoupling element 12 arranged directly on the second main surface 72 of the transparent body 7. The superimposed first, second and third light beams 31, 32, 33 are coupled out of the optical element 1 through the outcoupling element 12. The outcoupling element 12 comprises a lens and is configured to further collimate the superimposed first, second and third light beams 31, 32, 33. The outcoupling element 12 may also comprise or consist of a diffractive element with a nanostructured surface.

The diffractive element 41, 42, 43 in Figure 2 is part of an optical element 1 according to an exemplary embodiment and comprises a dielectric surface layer 11 that is at least partially transparent for the first second and third light beams 31, 32, 33. For example, the dielectric surface layer 11 comprises titanium dioxide, zinc oxide, silicon nitride, or other known high refractive index, optically transparent thin film oxides and/or nitrides. For example, the dielectric surface layer 11 has a thickness between 300 nanometer and 1 micrometer, inclusive . The dielectric surface layer 11 has a nano-structured surface 5 configured for di f fractive scattering of incident electromagnetic radiation . In particular, the dielectric surface layer 11 may be arranged on a buf fer layer 10 (not shown in Fig . 2 ) , or on a substrate , such as a carrier 9 , for example .

The nano-structured surface 5 comprises an aperiodic array of nano-pillars 51 . The nano-pillars 51 have a lateral extension D and/or a vertical extension H that is smaller than or equal to a wavelength of the first , second or third light beam 31 , 32 , 33 , respectively . Moreover, a center-to-center distance P between neighboring nano-pillars 51 is smaller than or equal to the wavelength of the first , second or third light beam

31 , 32 , 33 , respectively . In particular, the wavelength refers to a wavelength of the electromagnetic radiation within the medium with the highest refractive index that bounds the nano-structured surface 5 , such as the buf fer layer 10 or the carrier 9 .

In particular, a sub-wavelength nano-structured surface 5 comprising nano-pillars 51 arranged at vertices of a square lattice with lattice period a should ful fill the condition a < ln, where X denotes the free-space wavelength of the electromagnetic radiation and n is the refractive index of the carrier 9 or of the buf fer layer 10 . Similarly, for a

2 A hexagonal lattice the condition reads a < -.

The nano-structured surface 5 comprising the aperiodic array of nano-pillars 51 is configured to shape a wave front of the first , second or third light beams 31 , 32 , 33 by imparting spatially varying phase onto the respective light beam 31 ,

32 , 33 passing through the nano-structured surface 5 . In particular, the nano-structured surface 5 is configured to collimate the first, second, or third light beam 31, 32, 33, respectively .

Figure 3 shows a stage of a plurality of optical elements 1 after a step of a method for producing an optical element according to an exemplary embodiment. In particular, a plurality of beam combiners 2 are provided that comprise a common transparent body 7. The transparent body 7 has a first light-incoupling region 21 and a second light-incoupling region 22 for each optical element 1. A dichroic element 6 is disposed at each second light-incoupling region 22.

Furthermore, a plurality of first and second diffractive elements 41, 42 is provided, that are formed in the surface of a common carrier 9. The carrier 9 comprises a silicone wafer, or a different polymer wafer, for example. Each first and second diffractive element 41, 42 comprises a nanostructured surface 5. In particular, each diffractive element 41, 42 may comprise a fused silica substrate with a nanostructured surface 5 that is arranged on the common silicone wafer. For example, the nano-structured surface 5 comprises an aperiodic array of nano-pillars formed via photolithography or via electron beam lithography.

The transparent body 7 and the common carrier 9 are aligned, such that each first or second diffractive element 41, 42 is arranged adjacent to a corresponding first or second lightincoupling region 21, 22, respectively. In a following step of the method for producing an optical element, the common carrier 9 is wafer bonded onto the transparent body 7, such that each first diffractive element 41 is arranged directly on the transparent body 7 at a corresponding first light- incoupling region 21 and each second di f fractive element 42 is directly arranged on a corresponding dichroic element 6 . The wafer bonding is performed by a laser welding process or glueing, for example .

In a subsequent step of the method for producing an optical element , the transparent body 7 with the wafer bonded carrier 9 is singulated, for example by sawing, plasma etching, or scribing and breaking the transparent body 7 and the carrier 9 across a singulation line 13 in order to produce a plurality of optical elements 1 .

Figure 4 shows a stage of a plurality of optical elements 1 after a step of a method for producing an optical element according to a further exemplary embodiment . In contrast to the exemplary embodiment described in connection with Figure 3 , the first and second di f fractive elements 41 , 42 are individually picked and placed onto the first and second light-incoupling regions 21 , 22 of the dichroic beam combiner

2 . In particular, the individual first dichroic elements 41 are bonded directly onto the transparent body 7 , whereas the second dichroic elements 42 are bonded directly onto the dichroic elements 6 .

Figure 4 shows a stage of a plurality of optical elements 1 after a step of a method for producing an optical element according to a further exemplary embodiment . In contrast to the exemplary embodiment described in connection with Figure

3 , the first and second di f fractive elements 41 , 42 are formed by first disposing a buf fer layer 10 a surface layer 11 on the dichroic beam splitter 2 . For example , the buf fer layer 10 comprises silicon dioxide or aluminum oxide , whereas the surface layer 11 comprises titanium dioxide or zinc oxide .

The buf fer layer 10 is disposed directly on the first main surface 71 of the transparent body 7 as well as on the dichroic elements 6 and covers the first and second lightincoupling regions 21 , 22 . The buf fer layer 10 provides a smooth surface onto which the surface layer 11 is disposed .

The first and second di f fractive elements 41 , 42 are arranged at the first and second light-incoupling regions 21 , 22 , respectively, by forming nano-structured surfaces 5 in the surface layer 11 . The nano-structured surfaces 5 each comprise an aperiodic array of nano-pillars and are configured for collimating a first and a second light beam 31 32 , respectively (not shown in Figure 5 , see e . g . Figure 1 ) .

This patent application claims the priority of German patent application DE 102022122952 . 1 , the disclosure content of which is hereby incorporated by reference .

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

1 Optical element

2 dichroic beam combiner

21 first light-incoupling region

22 second light-incoupling region

23 third light-incoupling region

31 first light beam

32 second light beam

33 third light beam

41 first di f fractive element

42 second di f fractive element

43 third di f fractive element

5 nano-structured surface

51 nano pillar

6 dichroic element

7 transparent body

71 first main surface

72 second main surface

8 reflective element

9 carrier

10 buf fer layer

11 surface layer

12 outcoupling element

13 singulation line a beam divergence

P distance

D lateral si ze

H vertical si ze

Claims

1. Optical element (1) , comprising

- a dichroic beam combiner (2) configured for superimposing a first light beam (31) in a first wavelength range onto a second light beam (32) in a second wavelength range different from the first wavelength range,

- a first diffractive element (41) arranged on a first lightincoupling region (21) of the dichroic beam combiner (2) , the first diffractive element (41) configured for collimating the first light beam (31) before entering the dichroic beam combiner (2) , and

- a second diffractive element (42) arranged on a second light-incoupling region (22) of the dichroic beam combiner (2) , the second diffractive element (42) configured for collimating the second light beam (32) before entering the dichroic beam combiner (2) , wherein

- the first diffractive element (41) and/or the second diffractive element (42) comprises a nano-structured surface (5) .

2. Optical element (1) according to the previous claim, wherein

- the nano-structured surface (5) comprises an aperiodic array of nano-pillars (51) , and

- a lateral size (D) and/or a vertical size (H) of the nanopillars (51) is smaller than or equal to a wavelength in the first wavelength range or in the second wavelength range.

3. Optical element (1) according to any of the previous claims , wherein the first diffractive element (41) is configured to collimate the first light beam (31) with respect to two independent axes perpendicular to the propagation direction of the first light beam (31) and/or the second diffractive (42) element is configured to collimate the second light beam (32) with respect to two independent axes perpendicular to the propagation direction of the second light beam (32) .

4. Optical element (1) according to any of the previous claims , wherein the dichroic beam combiner (2) comprises a dichroic element (6) configured for reflecting the first light beam (31) and for transmitting the second light beam (32) .

5. Optical element (1) according to the previous claim, wherein

- the dichroic beam combiner (2) comprises a transparent body (7) with a first main surface (71) including the first lightincoupling region (21) and the second light-incoupling region (22) , and

- the dichroic element (6) is arranged on the second lightincoupling region (22) .

6. Optical element (1) according to the previous claim, wherein

- the transparent body (7) comprises a second main surface (72) opposite to the first main surface (71) , and

- a reflective element (8) is arranged on the second main surface ( 72 ) .

7. Optical element (1) according to the previous claim, wherein the reflective element (8) comprises a nano-structured surface (5) configured for a diffractive reflection of the first light beam (31) . 8. Optical element (1) according to any of the previous claims , wherein the first diffractive element (41) and/or the second diffractive element (42) are configured to change a propagation direction of the first light beam (31) and/or the second light beam (32) , respectively.

9. Optical element (1) according to any of the previous claims, further comprising

- a third diffractive element (43) configured for collimating a third light beam (33) , the third diffractive element (43) arranged on a third light-incoupling region (23) of the dichroic beam combiner (2) , wherein

- the dichroic beam combiner (2) is configured to superimpose the first light beam (31) , the second light beam (32) and the third light beam (33) onto each other,

- the first light beam (31) comprises electromagnetic laser radiation in a red spectral range,

- the second light beam (32) comprises electromagnetic laser radiation in a green spectral range, and

- the third light beam (33) comprises electromagnetic laser radiation in a blue spectral range.

10. Method for producing an optical element (1) comprising the steps:

- providing a dichroic beam combiner (2) for superimposing a first light beam (31) in a first wavelength range onto a second light beam (32) in a second wavelength range different from the first wavelength range,

- arranging a first diffractive element (41) on a first light-incoupling region (21) of the dichroic beam combiner (2) and a second diffractive element (42) on a second light- incoupling region (22) of the dichroic beam combiner (2) , wherein

- the first diffractive element (41) is configured for collimating the first light beam (31) before entering the dichroic beam combiner (2) and the second diffractive element (42) is configured for collimating the second light beam (32) before entering the dichroic beam combiner (2) , and

11. Method according to the previous claim, wherein the step of providing a dichroic beam combiner (2) includes:

- providing a transparent body (7) with a first main surface

(71) including the first light-incoupling region (21) and the second light-incoupling region (22) ,

- disposing a dichroic element (6) on the second lightincoupling region (22) of the transparent body (2) ,

- disposing a reflective element (8) on a second main surface

(72) of the transparent body (7) opposite to the first main surface (71) .

12. Method according to any of claims 10 or 11, wherein

- the first diffractive element (41) and the second diffractive element (42) comprise a nano-structured surface (5) formed on a common carrier (9) , and

- the common carrier (9) is bonded onto the beam combiner (2) .

13. Method according to any of claims 10 or 11, wherein the first diffractive element (41) and the second diffractive element (42) are picked and placed onto the first light- incoupling region (21) and the second light-incoupling region (22) , respectively.

14. Method according to any of claims 10 or 11, wherein - a buffer layer (10) and a surface layer (11) are disposed on the first light-incoupling region (21) and on the second light-incoupling region (22) of the dichroic beam combiner ( 2 ) , and

- the first diffractive element (41) is arranged on the first light-incoupling region (21) and the second diffractive element (42) is arranged on the second light-incoupling region (22) of the beam combiner (2) by forming a nanostructured surface (5) in the surface layer (11) . 15. Method according to any of the claims 10 to 14, wherein an optical element (1) according to any of claims 1 to 9 is produced .