DIFFRACTIVE OPTICAL ELEMENT AND METHOD FOR ITS MANUFACTURING

Abstract

Diffractive optical element (10) with one carrier (100), a first diffractive structure (200) arranged on a top side (101) of the support (100) and a second diffractive structure (300) arranged on a bottom side (102) of the support (100), wherein the first diffractive structure (200) comprises microrods grown on the top surface (101) of the support (100).

Description

[0001] The present invention relates to a diffractive optical element and a method for manufacturing a diffractive optical element.

[0002] The use of diffractive optical elements for beam shaping and attenuation of light beams is known from the prior art. For example, diffractive optical elements are used to generate light patterns, such as dot patterns. Diffractive optical elements are also used to ensure the eye safety of laser arrangements. It is known to arrange several diffractive optical elements, designed as individual elements, one above the other to achieve a desired light shaping.

[0003] US 2004 / 0233534A1 describes a diffractive optical element for polarizing light.

[0004] US 5,760,960 A describes cascaded diffraction grating pairs used to produce submicrometer gratings and patterns.

[0005] US 5,258,871 A describes a dual diffraction grating consisting of two light-diffracting surfaces whose grating grooves are inclined to each other.

[0006] One object of the present invention is to provide a diffractive optical element. A further object of the present invention is to provide a method for manufacturing a diffractive optical element. These objects are achieved by a diffractive optical element and by a method for manufacturing a diffractive optical element with the features of the independent claims. Various embodiments are specified in the dependent claims.

[0007] A diffractive optical element comprises a substrate, a first diffractive structure located on the top side of the substrate, and a second diffractive structure located on the bottom side of the substrate. The first diffractive structure comprises microrods grown on the top side of the substrate.

[0008] Advantageously, this diffractive optical element features two monolithically integrated diffractive structures. These two diffractive structures are arranged one behind the other in the light path. The two diffractive structures can have different structures. This allows the diffractive optical element to achieve more precise beam shaping than a diffractive optical element with only one diffractive structure. Due to the monolithic integration of the two diffractive structures, the diffractive optical element can be very robust.

[0009] In one embodiment of the diffractive optical element, the first diffractive structure is covered by a first cover layer. Advantageously, the first cover layer protects the first diffractive structure from damage or impairment of its functionality by external influences. In particular, the first cover layer can prevent the functionality of the first diffractive structure of the diffractive optical element from being reduced by moisture adhering to it.

[0010] In one embodiment of the diffractive optical element, the first cover layer comprises benzocyclobutene (BCB) or SiO2. Advantageously, this allows the cover layer to be arranged simply and cost-effectively over the first diffractive structure and exhibits high resistance to environmental influences.

[0011] In one embodiment of the diffractive optical element, the first cover layer has a refractive index that is lower than that of the first diffractive structure. Advantageously, the first cover layer does not impair the functionality of the first diffractive structure of the diffractive optical element, or only to a minimal extent.

[0012] In one embodiment of the diffractive optical element, the first cover layer has a refractive index that differs from the refractive index of the substrate by no more than 20%, preferably by no more than 10%, and more preferably by no more than 5%. Advantageously, the first cover layer does not impair the functionality of the first diffractive structure of this diffractive optical element, or only to a minimal extent.

[0013] In one embodiment of the diffractive optical element, the first diffractive structure comprises Si3N4, GaN, or TiO2. Advantageously, this results in a high refractive index for the first diffractive structure. Furthermore, this material choice enables simple and cost-effective fabrication of the first diffractive structure using established semiconductor processes.

[0014] In one embodiment of the diffractive optical element, the support comprises glass or sapphire. Advantageously, this results in high transparency of the support in wavelength ranges relevant for the fabrication of diffractive optical elements.

[0015] In one embodiment of the diffractive optical element, the second diffractive structure is covered by a second coating layer. Advantageously, this second coating layer can protect the second diffractive structure of the diffractive optical element from external influences. For example, the second coating layer can protect the second diffractive structure from scratches, condensing moisture, or solvents. This advantageously prevents deterioration of the functionality of the second diffractive structure of the diffractive optical element.

[0016] A method for fabricating a diffractive optical element includes steps for providing a support, forming a first diffractive structure on a top side of the support, and forming a second diffractive structure on a bottom side of the support.

[0017] Advantageously, this method enables the fabrication of a diffractive optical element with two monolithically integrated diffractive structures. The two diffractive structures of the resulting diffractive optical element are arranged serially in the light path of the element and can have different structures. This allows the resulting diffractive optical element to perform better light shaping than a diffractive optical element with only one diffractive structure. Due to the monolithic integration, the resulting diffractive optical element is advantageously robust and insensitive to external influences. A further advantage is the cost-effectiveness of the manufacturing process.

[0018] In one embodiment of the method, this includes a further step for covering the first diffractive structure with a first coating layer. This coating layer can protect the first diffractive structure of the optical element obtainable by the method from impairment of its functionality by external influences. For example, the first coating layer can protect the first diffractive structure from condensing moisture, solvents, or scratches. The coating of the first diffractive structure with the first coating layer can be carried out, for example, by a cathode sputtering process or by spin coating.

[0019] The arrangement of the first diffractive structure involves growing microrods onto the top surface of the support. Advantageously, this method also allows for simple, cost-effective, and highly reproducible fabrication of the first diffractive structure in this variant.

[0020] The properties, features, and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer and more readily understandable in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawings. These drawings are shown in schematic representations. Fig. 1 a cut side view of a beam with a first layer arranged above a top surface; Fig. 2 the carrier with a first diffractive structure formed by structuring the first layer; Fig. 3 the carrier and the first diffractive structure after covering the first diffractive structure with a first covering layer; and Fig. 4 a diffractive optical element formed by arranging a second diffractive structure on a bottom side of the support and covering the second diffractive structure with a second covering layer.

[0021] Fig. Figure 1 shows a schematic cutaway side view of a support 100 intended for the fabrication of a diffractive optical element. The support 100 can also be referred to as a substrate.

[0022] The support 100 is designed as a flat disk with a flat top surface 101 and a flat bottom surface 102, which faces the top surface 101. The support 100 can, for example, have a rectangular shape or a circular disk shape.

[0023] The substrate 100 comprises a material that exhibits high transparency to electromagnetic radiation in at least some wavelength ranges. For example, the material of the substrate 100 can be transparent in the infrared and / or visible spectral range. The substrate 100 can, for example, be sapphire or glass.

[0024] A first layer 210 of a first material 220 has been arranged on the upper surface 101 of the support 100. In the Fig. In the example shown, the first layer 210 is directly adjacent to the top surface 101 of the support 100. However, it is also possible to provide further layers between the top surface 101 of the support 100 and the first layer 210.

[0025] The first layer 210 may, for example, have been applied to the top surface 101 of the carrier 100 by a deposition process. For example, the application of the first layer 210 to the top surface 101 of the carrier 100 may have been carried out by a waxing process, by a sputtering process, by a vapor deposition process, or by another deposition process.

[0026] The first material 220 of the first layer 210 has a refractive index greater than the refractive index of the support 100. For example, the first material 220 of the first layer 210 can have a refractive index of 2.5 or higher in the wavelength range of the electromagnetic spectrum for which the diffractive optical element to be manufactured is intended. The first material 220 of the first layer 210 can, for example, be Si3N4, GaN, or TiO2.

[0027] Fig. Figure 2 shows a schematic cutaway side view of the support 100 and the first layer 210 arranged above the top surface 101 of the support 100 in one of the representations of the Fig. 1 subsequent processing stage.

[0028] The first layer 210 has been structured. Initial openings 230 have been created in the first layer 210, extending through the first layer 210 to the top surface 101 of the support 100. Sections of the first material 220 of the first layer 210 remain between the initial openings 230 created in the first layer 210.

[0029] The creation of the first openings 230 could, for example, have been carried out by an etching process, in particular by a dry chemical etching process. For this purpose, a mask may have been placed over the first layer 210 beforehand, the openings of which defined the positions of the first openings 230 created in the first layer 210. After the creation of the first openings 230, the mask may have been removed again.

[0030] The structured first layer 210 forms a first diffractive structure 200. The first diffractive structure 200 is designed to shape electromagnetic radiation, for example, visible light or light with a wavelength from the infrared spectral range, which travels through the support 100 and through the first diffractive structure 200 in a direction perpendicular to the top surface 101, by diffraction of light. The first diffractive structure 200 can, for example, be designed to generate a light pattern, such as a dot pattern.

[0031] Fig. Figure 3 shows a schematic cutaway side view of the support 100 and the first diffractive structure 200 formed above the top surface 101 of the support 100 in one of the representations of the Fig. 2 subsequent processing stages.

[0032] The first diffractive structure 200 above the top surface 101 of the support 100 has been covered with a first coating layer 400. The first coating layer 400 is intended to protect the first diffractive structure 200 from environmental influences. For example, the first coating layer 400 can prevent condensing moisture from adhering to the first diffractive structure 200 and impairing its functionality. The first coating layer 400 can also protect the first diffractive structure 200 from mechanical damage, such as scratches.

[0033] The first cover layer 400 can, for example, contain benzocyclobutene (BCB) or SiO2.

[0034] The first cover layer 400 has a refractive index that is lower than the refractive index of the first diffractive structure 200. Therefore, the first cover layer 400 does not impair the functionality of the first diffractive structure 200, or only to a small extent.

[0035] It is advantageous if the refractive index of the first cover layer 400 has a similar value to the refractive index of the substrate 100. The refractive index of the first cover layer 400 and the refractive index of the substrate 100 may differ, for example, by no more than 5%, no more than 10%, or no more than 20%.

[0036] The application of the first cover layer 400 can be carried out, for example, by spinning the material of the first cover layer 400 or by a cathode sputtering process.

[0037] The method for forming the first diffractive structure 200 on the top surface 101 of the support 100 involves growing microrods onto the top surface 101 of the support 100. Microrods are micrometer-scale post structures that can be produced by high aspect ratio epitaxial growth. Prior to growing the microrods, a mask can be positioned on the top surface 101 of the support 100, the openings of which define the positions of the microrods to be grown.

[0038] The first diffractive structure 200 formed by the growth of microrods on the upper surface 101 of the support 100 can subsequently also be covered by the first cover layer 400. In this case, the first cover layer 400 can also be formed, for example, by overgrowing the first diffractive structure 200.

[0039] Fig. Figure 4 shows a schematic cutaway side view of the support 100 and the first diffractive structure 200 arranged on the top surface 101 of the support 100 in one of the representations of the Fig. 3 subsequent processing stages.

[0040] A second diffractive structure 300 has been formed on the underside 102 of the support 100, opposite the top surface 101 of the support 100. The formation of the second diffractive structure 300 can be carried out by a process that corresponds to one of the processes described above for forming the first diffractive structure 200. In particular, the second diffractive structure 300 can be formed by the same process as the first diffractive structure 200.

[0041] A second layer 310 of a second material 320 may first be arranged on the underside 102 of the support 100. The second material 320 may, for example, correspond to the first material 220 of the first layer 210. Subsequently, the second layer 310 may be structured to form second openings 330 in the second layer 310, which extend through the second layer 310 to the underside 102 of the support 100. The structuring of the second layer 310 may, for example, have been carried out by an etching process, in particular, for example, by a dry chemical etching process. The structured second layer 310 forms the second diffractive structure 300 on the underside 102 of the support 100.

[0042] Subsequently, the second diffractive structure 300 was also covered by a second cover layer 500. The second cover layer 500 can be designed like the first cover layer 400 and applied using the same method as the first cover layer 400.

[0043] The carrier 100, with the first diffractive structure 200 arranged on the top 101 and the second diffractive structure 300 arranged on the bottom 102, forms a diffractive optical element 10. The diffractive optical element 10 can, for example, be used to shape light, such as visible light or light with a wavelength from the infrared spectral range. For example, the diffractive optical element 10 can be designed to generate a light pattern, such as a dot pattern. The first diffractive structure 200 and the second diffractive structure 300 of the diffractive optical element 10 shape the light passing through the diffractive optical element 10 sequentially.

[0044] In a simplified embodiment of the diffractive optical element 10, the first covering layer 400 covering the first diffractive structure 200 and / or the second covering layer 500 covering the second diffractive structure 300 can be omitted.

[0045] The invention has been illustrated and described in more detail with reference to preferred embodiments. However, the invention is not limited to the disclosed examples.

[0046] Rather, other variations can be derived from this by a person skilled in the art without leaving the scope of protection of the invention. REFERENCE MARK LIST 10 diffractive optical element 100 carriers 101 Top 102 Subpage 200 first diffractive structure 210 first shift 220 first material 230 first opening 300 second diffractive structure 310 second shift 320 second material 330 second opening 400 first cover layer 500 second cover layer

Claims

[1] Diffractive optical element (10) with one carrier (100), a first diffractive structure (200) arranged on a top side (101) of the support (100) and a second diffractive structure (300) arranged on a bottom side (102) of the support (100), wherein the first diffractive structure (200) comprises microrods grown on the top surface (101) of the support (100). [2] Diffractive optical element (10) according to claim 1, wherein the first diffractive structure (200) is covered by a first cover layer (400). [3] Diffractive optical element (10) according to claim 2, wherein the first cover layer (400) comprises benzocyclobutene or SiO2. [4] Diffractive optical element (10) according to one of claims 2 and 3, wherein the first cover layer (400) has a refractive index that is lower than a refractive index of the first diffractive structure (200). [5] Diffractive optical element (10) according to any one of claims 2 to 4, wherein the first cover layer (400) has a refractive index which differs from a refractive index of the support (100) by no more than 20%, preferably by no more than 10%, preferably by no more than 5%. [6] Diffractive optical element (10) according to any one of the preceding claims, wherein the first diffractive structure (200) comprises Si3N4, GaN or TiO2. [7] Diffractive optical element (10) according to one of the preceding claims, wherein the support (100) comprises glass or sapphire. [8] Diffractive optical element (10) according to one of the preceding claims, wherein the second diffractive structure (300) is covered by a second cover layer (500). [9] Method for producing a diffractive optical element (10) by the following steps: - Providing a carrier (100); - Forming a first diffractive structure (200) on a top surface (101) of the support (100), wherein the formation of the first diffractive structure (200) comprises the growth of microrods onto the top surface (101) of the support (100); - Formation of a second diffractive structure (300) on a bottom side (102) of the support (100). [10] Method according to claim 9, wherein the method comprises the following further step: - Covering the first diffractive structure (200) with a first cover layer (400). [11] Method according to one of claims 9 and 10, wherein the method comprises the following further step: - Covering the second diffractive structure (300) with a second covering layer (500).

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