Multi-pass cavity for an optical device for spatially manipulating optical radiation

Abstract

The present invention relates to a multi-pass cavity (1) comprising first and second optical elements (3, 3'), each having a main surface with a respective reflecting surface (3b, 3b'), at least one of the reflecting surfaces (3b, 3b') being microstructured. The main surfaces (3a, 3a') are arranged opposite each other such that the reflecting surfaces (3b, 3b') are arranged according to a predetermined geometry of the multi-pass cavity (1). The multi-pass cavity (1) comprises two spacers (2, 2') for assembling the first and second optical elements (3, 3'), the spacers (2, 2') being firmly fixed to the main surfaces of the first and second optical elements in order to maintain a predetermined geometry between the two reflecting surfaces (3b, 3b').

Description

Detailed Description of the Invention

[0001] (Technical Field) The present invention relates to an optical device for manipulating light emission. More specifically, the present invention relates to an optical device comprising a multi-pass cavity configured to modify the lateral phase profile of light emission. (Background Art)

[0002] International Publication No. WO 2019 / 129954 (A1) discloses an optical device designated by the acronym MPLC (Multi Plane Light Conversion) that enables any integral spatial transformation of light emission. Such a device was first proposed in the document "Programmable unitary spatial mode manipulation" by Morizur et al., J. Opt. Soc. Am. A / Vol. 27, No. 11 / November 2010, and the documents U.S. Patent No. US9250454, International Publication No. WO 2019 / 129949, and U.S. Patent Application Publication No. US2017 / 010463 propose further specific embodiments.

[0003] In the embodiment proposed by International Publication No. WO 2019 / 129954 (A1), referring to FIGS. 1a and 1b of the present application, the optical device comprises a multi-pass cavity 1 composed of an assembly of a planar support 7 having a receiving surface 7a, an alignment part 4, and two reflective optical elements 3, 3' arranged opposite to each other. The first optical element 3 has a microstructured main surface 3a facing the inside of the cavity 1. This microstructure is configured to modify the phase of the incident light emission that is reflected multiple times during propagation in the cavity 1 along the general direction P of propagation in the cavity. More specifically, the main surface 3a of the first optical element 3 includes a plurality of microstructured zones 6, and each microstructured zone 6 is arranged on the main surface 3a to accurately receive the incident light emission and apply a primary phase conversion thereto. The alignment part 4 ensures good parallelism between the two reflective optical elements 3, 3' and enables the positioning and orientation of the second optical element 3'.

[0004] In order to fully understand how the iterative application of these primary conversions enables a selected conversion of the incident light radiation and how the optical element 3 can be designed to perform such a conversion, reference may be made to the various cited state-of-the-art documents. These documents are also referred to in order to obtain an example of a method for the digital design of the microstructure arranged on the main surface 3a of the optical element 3. These digital models of the microstructure can be used, for example, for manufacturing the first optical element 3 by lithography, machining, shaping, and / or engraving of the optical component.

[0005] In this assembly, in order to accurately perform a spatial conversion on the incident light radiation, it is important to maintain a very good parallelism of the order of a few micro-radians between the two reflective optical elements 3, 3'. This becomes increasingly true the longer the cavity and / or the greater the number of reflections.

[0006] Regardless of the method used to manufacture an optical element having a microstructured reflective surface, it may be desirable for this element to be composed of a plurality of materials. Thus, this optical element can be formed from a solid part, for example formed from glass, with a layer, for example a layer formed from a reflective metal, formed thereon. The metal layer has a microstructure, and its exposed surface forms the main surface 3a of the first optical element 3 facing the inside of the cavity 1. By providing a functional layer having a microstructure on the first optical element in the form of a solid part, the function performed by this element can be separated. Thus, the nature of the functional layer can be selected with regard to its microstructuring and light reflection properties. The nature of the solid part can be selected to ensure the rigidity of the assembly and, for example, to dissipate the heat generated in the microstructured zone 6 by reflection of the light radiation.

[0007] Regardless of the composition of the first reflective optical element, the first reflective optical element is prone to deformation due to temperature. Since this element is firmly fixed to the support, this deformation can tend to bend the element and deflect the reflective surface obliquely from its nominal position under ambient temperature. This is even more true if the first optical element is composed of materials with different coefficients of expansion. The same applies to the second optical element. Such deformation affects the parallelism of the two reflective optical elements that define the cavity, thereby affecting the quality of the optical conversion performed on the incident light radiation. This conversion is particularly sensitive to angular deviations of the reflective surface and is much more sensitive than the fixed deviations of the relative arrangement of the optical elements that do not affect this parallelism.

[0008] The parallelism of the two reflective optical elements of a prior art MPLC optical device can also be affected for other reasons. This is especially the case when the optical elements 3, 3', the planar support 2, and the alignment part 4 are not made of the same material. In this case too, temperature variations with respect to the temperature at which these elements were assembled can lead to variations in the exact positioning of the parts relative to each other. The positioning can also change by applying mechanical forces such as vibrations or shocks or direct pressure to one of the parts.

[0009] (Object of the Invention) The present invention aims to improve all or some of the aforementioned drawbacks. More specifically, the object of the present invention is to propose a multi-pass cavity for an MPLC device that is more robust to mechanical stress than those known in the prior art. In particular, the multi-pass cavity according to the present invention can accurately perform a spatial conversion on incident light radiation over a wide temperature range. The present invention is particularly applicable to providing a multi-pass cavity formed of optical components made of materials having coefficients of expansion that are not all the same, or to including optical components made of materials having different coefficients of expansion. (Summary of the Invention)

[0010] To achieve this object, the object of the present invention is to propose a multi-passage cavity provided with first and second optical elements each having a main surface with a reflecting surface, at least one of the reflecting surfaces being microstructured. The main surfaces are arranged opposite to each other such that the reflecting surfaces are arranged according to a predetermined geometry.

[0011] According to the present invention, the multi-passage cavity comprises two spacers for assembling the first and second optical elements, the spacers being firmly fixed to the main surfaces of the first and second optical elements in order to maintain a predetermined geometry between the two reflecting surfaces.

[0012] According to other advantageous non-limiting features of the present invention, alone or according to any technically feasible combination, the following applies. - The microstructured reflecting surface has a plurality of microstructured zones defining a general propagation direction of the radiation in the cavity, and the two assembly spacers extend between the first and second optical elements along the general propagation direction. - The microstructured zones are arranged on the reflecting surface between the two assembly spacers. - The two assembly spacers are arranged symmetrically on both sides of the reflecting surface. - The assembly spacers consist of separate wedges. - The two assembly spacers form the two arms of a U-shaped wedge. - The two assembly spacers form the two arms of an O-shaped wedge. - The two assembly spacers are monolithically integrated on the main surface side of the first or second optical element, and then the main surface of the first optical element is assembled directly to the main surface of the second optical element. - One dimension of the two assembly spacers is adjustable. - The optical element having the microstructured reflecting surface is formed from a solid part provided with a functional layer, the functional layer forming the reflecting surface, and the solid part and the functional layer having different coefficients of thermal expansion. - The two reflecting surfaces are planar and arranged parallel to each other. - The first optical element and the second optical element have different coefficients of thermal expansion.

[0013] According to another aspect, the present invention provides a multi-passage cavity comprising first and second optical elements each having a main surface with a reflective surface, wherein the reflective surface of the first optical element is microstructured and the main surfaces are arranged opposite to each other such that the reflective surfaces are arranged according to a predetermined geometry.

[0014] According to the present invention, the multi-passage cavity · A wedge having two assembly parts, the wedge being firmly fixed to the main surface of the first optical element, · A support having a receiving surface, the wedge and the second optical element being firmly fixed to the receiving surface.

[0015] According to an advantageous feature, the wedge can be U-shaped or O-shaped.

[0016] According to yet another aspect, the present invention provides an MPLC optical device comprising a multi-passage cavity (1) according to one of the previously disclosed embodiments and an input stage and / or an output stage assembled to the multi-passage cavity. (Brief Description of the Drawings)

[0017] Other features and advantages of the present invention will become apparent from the following detailed description of the invention with reference to the accompanying drawings.

[0018] Figure 1a shows the multi-passage cavity of a prior art MPLC device. Figure 1b shows the multi-passage cavity of a prior art MPLC device. Figure 2a shows respectively an assembled view and an exploded view of the multi-passage cavity according to the present invention. Figure 2b shows respectively an assembled view and an exploded view of the multi-passage cavity according to the present invention. Figure 2c is a front view of the main surfaces of the first optical element and the second optical element. Figure 3a shows another embodiment of the multi-passage cavity according to the present invention. Figure 3b shows another embodiment of the multi-channel cavity according to the present invention. Figure 3c shows another embodiment of the multi-channel cavity according to the present invention. Figure 4 shows another embodiment of the multi-channel cavity according to the present invention. Figure 5 shows another embodiment of the multi-channel cavity according to the present invention. (Mode for Carrying Out the Invention)

[0019] Very generally speaking, this specification relates to an MPLC optical device for manipulating incident light radiation to form converted light radiation. Advantageously, the shapes of the incident light radiation and the converted light radiation are different from each other. The manipulation of the incident light radiation includes a controlled modification of the lateral phase profile of this radiation during a plurality of primary conversions that are combined to contribute to the execution of a predetermined optical function. This may include spatial multiplexing or demultiplexing of the incident radiation, or any other mode conversion in the spatial domain, for example, a controlled change in the shape of the light beams constituting the incident light radiation. For example, it may include four or more primary conversions, such as, for example, 8, 10, 12, 14, or 20 or more basic conversions.

[0020] The MPLC optical device comprises a multi-channel cavity 1 for converting incident light radiation into converted light radiation. The optical device may optionally comprise other elements, such as an input stage and / or an output stage, to guide the introduction of the incident light radiation and the extraction of the converted light radiation from the cavity 1, respectively, if this radiation is not simply introduced into and / or extracted from the device 1 by simple free-space propagation.

[0021] The multi-channel cavity 1 according to various embodiments is, referring to the figures, composed of an arrangement of two optical elements 3, 3' each having main faces 3a, 3a', and each of these main faces has a reflecting face 3b, 3b'. The main faces 3a, 3a' of the two optical elements 3, 3' are arranged opposite to each other such that the reflecting faces define a specific geometry of the multi-channel cavity 1.

[0022] In the illustrated embodiment, the two reflecting surfaces 3b, 3b' are planar and arranged parallel to each other. In this normal case, the predetermined geometry corresponds to a fixed scalar spacing value between the two reflecting surfaces 3b, 3b'.

[0023] However, this configuration of planar and parallel surfaces is not essential. More generally, the predetermined geometry may correspond to a predetermined spacing profile separating the reflecting surfaces 3b, 3b' of the two optical elements 3, 3'.

[0024] However, in both cases, it is important that the defined geometry of the cavity, whether defined as a scalar quantity or as a profile, does not change over time, especially under the influence of temperature or external forces, so that the MPLC optical device continues to function fully. In other words, it is important that the geometry of the cavity does not deviate from or deviate excessively from the predetermined geometry over time.

[0025] At least one of the reflecting surfaces 3b, 3b' of the optical elements 3, 3' is microstructured. For the sake of simplicity of expression, the microstructured reflecting surface and the optical element having this surface are referred to as "3b" and "3", respectively, in the remainder of the present disclosure. However, generally speaking, the reflecting surfaces 3b, 3b' of the first and / or second optical elements 3, 3' can be microstructured. Otherwise, if only one of the optical elements 3 has a microstructured reflecting surface 3b, the other optical element 3' has a simple reflecting surface 3b' such as a mirror.

[0026] This microstructure is configured to modify the spatial phase of the incident light radiation, which is reflected multiple times as it propagates through the cavity 1 in the general propagation direction P of the radiation within the cavity. For this purpose, the microstructured reflecting surface can be composed of a plurality of distinct microstructured zones 6 extending along the propagation direction P. Each microstructured zone 6 is precisely arranged on the main surface 3b of the optical element so as to receive the incident light radiation, reflect it, and apply a primary phase conversion thereto.

[0027] However, the microstructured zones 6 do not necessarily have to be separate from each other, and any other microstructured configuration may be suitable as long as it allows for a specific conversion of the incident radiation applied during multiple reflections.

[0028] The "microstructured surface" is understood, by way of example, to mean that the plane or surface can have "pixels" with dimensions in the range from less than a few microns to more than several hundred microns. Each pixel has a height of up to a few microns or up to several hundred microns with respect to the average plane defining the plane or surface in question. Thus, the microstructured surface can have a resolution (in its average plane) and a height ("from peak to valley") ranging from a fraction of the central wavelength of the radiation whose spatial phase is modified to several hundred times or several thousand times this wavelength.

[0029] The optical elements 3, 3' can have any suitable shape. As already mentioned, these optical elements are selected such that their reflecting surfaces 3b, 3b' are completely planar (except for the microstructure), but this is not essential. Generally speaking, the microstructure of the reflecting surface 3b (or multiple reflecting surfaces) is determined during its digital design according to the shape and relative positioning of the reflecting surfaces 3b, 3b', and thus according to the geometry of the cavity. Thus, it is important that this geometry remains stable in order to enable an accurate conversion of the incident light radiation, especially when the cavity 1 is subjected to forces that would deform it, such as those occurring during large temperature offsets.

[0030] There may be a discrepancy between the ideal cavity geometry used to design the microstructure and the measured distance between the reflecting surfaces 3b, 3b', which should be noted may be due to the manufacturing tolerances of the optical components forming the cavity and the assembly tolerances of these components. This deviation is stable over time and, if moderate, does not affect the correct operation of the device or can be compensated by adjusting the position and angle of the incident light radiation with respect to the cavity.

[0031] Therefore, the predetermined geometry substantially corresponds to this profile when the spacing profile between the two reflecting surfaces 3b, 3b' is measured at room temperature and no mechanical stress is applied to the cavity.

[0032] The first optical element 3, the second optical element 3', and all other components forming the cavity can be selected from any suitable material. The material may be quartz, glass, fused silica, metal or silicon, or a plastic material. Within the scope of the present invention, the components forming the cavity do not have to be made of materials having the same coefficient of thermal expansion.

[0033] The optical elements 3, 3' or some of them may be formed from a plurality of materials having different coefficients of thermal expansion. This is particularly applicable to the optical element 3 having the microstructured reflecting surface 3b. As can be seen in FIG. 2a, it may thus be formed from a solid part 4 having a functional layer 5, the functional layer forming the microstructured reflecting surface 3b, and the solid part 4 and the functional layer 5 having different coefficients of thermal expansion. The advantages of such a configuration were explained in the introduction section of this application.

[0034] Thus, the solid part 4 may be made of quartz, glass, fused silica, metal or silicon, or a plastic material. The functional layer 5 may consist of or contain, for example, a metal (gold, silver, nickel), a dielectric, or an insulating resin (for example, a resin sold under the trade name ORMOCOMP®), or the like. The functional layer 5 may be formed on the solid part by any suitable technique such as assembly, deposition, plating, or the like. The first approach

[0035] To enable a robust assembly of the first optical element 3 and the second optical element 3', the multi-pass cavity 1 according to the first approach also comprises two spacers 2, 2' that enable the first and second optical elements 3, 3' to be assembled directly with each other. These two so-called "assembly" spacers are firmly fixed to the main surfaces 3a, 3a' of the first and second optical elements 3, 3'. Each spacer 2, 2' is firmly fixed to the main surface of the first optical element 3 and the main surface of the second optical element 3.

[0036] "Firmly fixed" is understood to mean that each assembly spacer 2, 2' is held by the two optical elements 3, 3' without any degree of freedom.

[0037] They are accurately dimensioned to maintain a predetermined geometry between the reflecting surfaces 3b, 3b' supported by the main surfaces 3a, 3a' of the two optical elements 3, 3' even when a significant force is applied to the cavity 1. In other words, the large force applied to the cavity 1 may deform some of the parts that make up the cavity 1, but these deformations do not preferentially affect the reflecting surfaces 3b, 3b', so that the predetermined geometry can be maintained. Thus, even in the presence of deflections that may be caused by mechanical forces due to heat, for example, the two reflecting surfaces 3b, 3b' exhibit a stable average angle, and these angles have a significant impact on the conversion provided by the cavity. To promote this stabilization, the two spacers 2, 2' can be arranged symmetrically on both sides of the reflecting surfaces 3b, 3b'.

[0038] Advantageously, as can be seen from the figure, the two assembly spacers 2, 2' extend between the first optical element 3' and the second optical element 3' along the general propagation direction P of the radiation in the cavity. When the multi-pass cavity 1 is formed, the microstructured zone 6 is arranged on the reflecting surface 3b arranged between the two assembly spacers 2, 2'.

[0039] In this configuration, a force applied to the cavity or a deformation of one of the cavity parts has little or no effect on the spacing of the reflecting surfaces 3b, 3b', and thus on the internal geometry of the cavity, and its parameters are firmly fixed by the presence of the two assembly spacers 2, 2'.

[0040] When the spacers 2, 2' are assembled on both sides of the reflecting surface along the propagation direction P, the cavity has two lateral openings for introducing the incident light radiation therein and collecting the converted light radiation.

[0041] The assembly spacers 2, 2' can take the form of at least one additional part hereinafter referred to as a "wedge" in the remainder of this specification. This or these wedges (plural) can be assembled on the main surfaces 3a, 3a' of the optical elements 3, 3' by means of an adhesive material (which can be UV or temperature curable), by mechanical clamping, by laser melting, or by molecular adhesion.

[0042] In the embodiments shown in FIGS. 2a and 2b, the two assembly spacers 2, 2' consist of two separate wedges.

[0043] In the embodiment shown in [FIG. 3a], the two assembly spacers 2, 2' form the two arms of a single U-shaped wedge. In this configuration, one of the lateral openings of the cavity is closed by the U-shaped base.

[0044] In the embodiments shown in FIGS. 3b and 3c, the two spacers form the two arms of a single O-shaped wedge, and the two lateral openings of the cavity are closed by the wedge.

[0045] Nevertheless, in order to enable the light radiation to propagate through the lateral openings, the wedge material can be selected to be transparent to the incident or converted light radiation, thus enabling the optical device to function properly.

[0046] More generally, the spacers 2, 2' are configured to provide side or face openings that allow the propagation of optical radiation into and out of the cavity 1 and can be assembled with the optical elements 3, 3'. These openings may be essentially mechanical or optical through the transparency of the material forming the spacer. Alternatively, passages may be provided in one and / or the other of the first and second optical elements 3, 3' that allow optical radiation to propagate into and out of the cavity 1.

[0047] In the embodiment shown in FIG. 3c, two face openings, referred to as E and S, are provided respectively to allow incident radiation to be introduced into the cavity and the converted radiation to be emitted from the cavity. These openings are of a mechanical nature and are arranged between the second optical component 3' and the wedge. The second optical component 3' has a dimension smaller than that of the wedge in the general propagation direction P, thus freeing up passages on both sides of the second optical component 3' that form the openings.

[0048] In the embodiment shown in FIG. 3b, the first face opening E is similar to that shown in FIG. 3c and is arranged between the second optical component 3' and the wedge. The second face opening S is arranged between the wedge and the first optical component 3. Thus, each of the first and second optical components 3, 3' has a dimension smaller than that of the wedge in the general propagation direction. Thus, this frees up two passages that form the face openings E, S of the cavity.

[0049] Note that the cavity with face openings is compatible not only with the O-shaped wedges as shown in FIGS. 3b and 3c, but also with all the embodiments shown.

[0050] Rather than being provided in the form of at least one wedge, the two assembly spacers can be integrally and monolithically formed on the main surface side of the first or second optical element. These embodiments are shown in FIGS. 4 and 5. These spacers then form a protrusion of the optical element that carries them (with respect to the reflective surface). In this case, the main surface 3a of the first optical element is directly assembled to the main surface 3a' of the second optical element via the protrusion forming the spacer, and the cavity 1 does not include the other parts necessary for its configuration.

[0051] Generally speaking, in this first approach, the first and second optical elements, and optionally parts other than the wedge(s), are not required to form the multi-passage cavity 1. In particular, there is no need to provide a support.

[0052] In an embodiment corresponding to this first approach, at least one of the spacers can be configured such that the dimension of the spacer extending from one reflective surface to the other reflective surface is adjustable. For example, a heating element such as a resistor may be attached to at least one of the spacers, or the spacer may be formed from a piezoelectric material provided with control electrodes. By controlling the voltage applied to the resistor or the electrodes, it is possible to finely adjust the size of the spacer separating the two optical elements and bring them closer to a predetermined geometry. Second approach

[0053] For the purpose of proposing a robust multi-passage cavity 1, in a second approach, some of whose embodiments are shown in FIGS. 6 and 7, a support 7 having a receiving surface on which the second optical element 3' is firmly fixed (i.e., assembled without degrees of freedom) is provided. This assembly can be carried out directly or via the cube 4, and as shown in FIG. 6, the second optical element 3' can be oriented towards the support 7.

[0054] The wedge 8, which includes two assembly parts, is also firmly held on the main surface 3a of the first optical element 3. This can be a U-shaped or O-shaped wedge, as already presented in an embodiment corresponding to the first approach. The first optical element 3 has a microstructured reflective surface. The assembly parts of the wedge 8 are preferably assembled symmetrically on both sides of the microstructured reflective surface 3b of the first optical element 3. They can extend along the general propagation direction P. They tend to reinforce the first optical element 3 on the side of the reflective surface 3b, thereby preventing deformation of this surface when a force is applied.

[0055] The wedge 8 that supports the first optical element 3 is also firmly fixed to the receiving surface of the support 7 in an arrangement that defines a predetermined geometry between the two reflective surfaces.

[0056] Similar to the first approach, the large force applied to the cavity 1 according to the second approach may deform a part of the components constituting the cavity 1, particularly the first optical element 3. However, since these deformations do not occur preferentially at the reflective surface, a predetermined geometry can be maintained.

[0057] As can be seen in FIG. 7, the support 7 does not need to contact the entire range on one side of the wedge 8 and one side of the second optical element 3'. It can be an element that forms a bridge between these two parts and contacts only a part of their sides.

[0058] Of course, the present invention is not limited to the two approaches and the described embodiments, and alternative embodiments can be added without departing from the scope of the present invention defined by the claims.

[0059] Accordingly, the optical device can optionally comprise an input stage and / or an output stage assembled in a cavity, which respectively guide the introduction of the incident light radiation and the extraction of the converted radiation. These stages may correspond to an optical fiber or an optical fiber network (this or these fibers may or may not be provided with lenses), or may comprise a laser source, optical elements such as dichroics, lenses, concave mirrors, polarization controllers, MEMS, chip / tilt control mirrors, SLM matrices, diffraction gratings, diaphragms, glass plates with surface treatment. In particular, these stages can be attached to at least one of the edges of the optical element or to at least one of the spacers.

Brief Description of the Drawings

[0060]

Figure 1a

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Claims

1. A multi-pass cavity (1) comprising a first optical element and a second optical element (3, 3'), each having a main surface with a reflecting surface (3b, 3b'), wherein at least one of the reflecting surfaces (3b, 3b') is microstructured, and the main surfaces (3a, 3'a) are arranged opposite to each other such that the reflecting surfaces (3b, 3b') are arranged according to a predetermined geometry of the multi-pass cavity (1). The multi-pass cavity (1) comprises two spacers (2, 2') for assembling the first optical element and the second optical element (3, 3'), and each of the spacers (2, 2') is firmly fixed to the main surface of the first optical element (3) and the main surface of the second optical element (3) to maintain a predetermined geometry between the two reflecting surfaces (3b, 3b').

2. The microstructured reflecting surface (3b) has a plurality of microstructured zones defining a general propagation direction (P) of radiation within the cavity, and the two assembly spacers (2, 2') extend between the first optical element and the second optical element (3, 3') along the general propagation direction (P). The multi-pass cavity (1) according to Claim 1

3. The microstructured zone (6) is arranged on the reflecting surface (3b) between the two assembly spacers (2, 2'). The multi-pass cavity (1) according to Claim 2

4. The two assembly spacers (2, 2') are symmetrically arranged on both sides of the reflecting surfaces (3, 3'). The multi-pass cavity (1) according to any one of Claims 1 to 3

5. The assembly spacer (2, 2') consists of a separate wedge. The multi-pass cavity (1) according to any one of Claims 1 to 4

6. The two assembly spacers (2, 2') form two arms of a U-shaped wedge. The multi-pass cavity (1) according to any one of Claims 1 to 4

7. The two assembly spacers (2, 2') form two arms of an O-shaped wedge. The multi-pass cavity (1) according to any one of Claims 1 to 3

8. The two assembly spacers (2, 2') are monolithically integrated with the first optical element or the second optical element (3, 3') on the main surface side, and then the main surface of the first optical element (3) is directly assembled to the main surface of the second optical element (3'). The multi-channel cavity (1) according to any one of claims 1 to 4.

9. The dimensions of the two assembly spacers (2, 2') are adjustable. The multi-channel cavity (1) according to any one of claims 1 to 8.

10. The optical element (3) having the microstructured reflective surface (3b) is formed from a solid portion (4) provided with a functional layer (5). The functional layer (5) forms the reflective surface (3b). The solid portion (4) and the functional layer (5) have different coefficients of thermal expansion. The multi-channel cavity (1) according to any one of claims 1 to 9.

11. The two reflective surfaces (3b, 3b') are planar and arranged parallel to each other. The multi-channel cavity (1) according to any one of claims 1 to 10.

12. The first optical element (3) and the second optical element (3') have different coefficients of thermal expansion. The multi-channel cavity (1) according to any one of claims 1 to 11.

13. A multi-channel cavity (1) comprising a first optical element and a second optical element (3, 3') each having a main surface with a reflective surface (3b, 3b'), wherein the reflective surface (3b) of the first optical element (3) is microstructured, and the main surfaces (3a, 3a') are arranged opposite to each other such that the reflective surfaces (3b, 3b') are arranged according to a predetermined geometry. The multi-channel cavity (1) - A wedge (8) comprising two assembly parts, which is firmly fixed to the main surface (3a) of the first optical element (3), and the two assembly parts are assembled on both sides of the microstructured reflective surface (3b) of the first optical element (3) to reinforce the microstructured reflective surface. The wedge (8) and - A support (7) having a receiving surface, wherein the wedge (8) and the second optical element (3') are firmly fixed to the receiving surface. The multi-channel cavity (1) comprising the support (7).

14. The wedge is U-shaped or O-shaped. The multi-channel cavity (1) according to claim 13.

15. An MPLC optical device comprising the multi-channel cavity (1) according to any one of claims 1 to 14, and an input stage and / or an output stage assembled to the multi-channel cavity (1).

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