Optical arrangement and methods for its manufacture

Abstract

The invention relates, among other things, to an optical arrangement with a substrate (10), a strip waveguide (20) arranged on the substrate (10) which tapers in a waveguide end region (23) towards a waveguide end (20e), and a fiber waveguide (30) arranged on or next to the strip waveguide (20) which tapers in a fiber end region (31) towards a fiber end (30e), wherein the taper direction (V1) of the fiber waveguide (30) is opposite to the taper direction (V2) of the strip waveguide (20) and can couple electromagnetic radiation guided in the fiber waveguide (30) from the fiber end region (31) to the waveguide end region (23) and electromagnetic radiation guided in the strip waveguide (20) from the waveguide end region (23) to the fiber end region (31). According to the invention, at least one electrically conductive layer element (40) influencing the coupling behavior between the waveguide end region (23) and the fiber end region (31) is arranged on the substrate (10) next to the waveguide end region (23).

Description

[0001] The invention relates, among other things, to an optical arrangement comprising a substrate, a strip waveguide arranged on the substrate which tapers towards a waveguide end in a waveguide end region, and a fiber waveguide arranged on or adjacent to the strip waveguide which tapers towards a fiber end in a fiber end region. The direction of taper of the fiber waveguide is opposite to the direction of taper of the strip waveguide. Electromagnetic radiation guided in the fiber waveguide can couple from the fiber end region to the waveguide end region, and electromagnetic radiation guided in the strip waveguide can couple from the waveguide end region to the fiber end region. Such an arrangement is disclosed in U.S. Patent 11,480,736 B2. In the arrangement described in the U.S. patent, a recess in the substrate is provided to improve the coupling behavior.

[0002] Further arrangements with tapered strip waveguides for coupling with fiber waveguides are known from publications US 2016 / 0103279 A1 and DE 10 2018 110 001 A1.

[0003] The invention is based on the objective of providing an arrangement with which a particularly high coupling efficiency between the waveguides can be achieved.

[0004] This problem is solved according to the invention by an arrangement with the features according to claim 1. Advantageous embodiments of the arrangement according to the invention are specified in the dependent claims.

[0005] According to the invention, at least one electrically conductive layer element influencing the coupling behavior between the waveguide end region and the fiber end region is arranged on the substrate next to the waveguide end region.

[0006] A significant advantage of the arrangement according to the invention is that the layer element provided according to the invention can prevent or at least reduce the "diving in" of radiation into the substrate by acting as a reflective layer due to its electrical conductivity. The layer element thus allows for a comparatively free choice of substrate material: for example, the refractive index of the substrate can be higher than the refractive index of the fiber core or the cladding of the fiber waveguide. The use of the layer element therefore makes it possible, for example, to use a semiconductor material as the substrate material and a glass or polymer fiber as the fiber waveguide, and to provide the described coupling of the fiber waveguide to a strip waveguide integrated in a photonic chip.

[0007] It is advantageous if the layer element is separated from the strip waveguide by a section of the substrate that is free of the electrically conductive layer element. A certain distance reduces the optical losses that electrically conductive materials in close proximity to optical waveguides can cause.

[0008] The strip waveguide is preferably arranged on a substrate rib of the substrate. An arrangement on a substrate rib advantageously allows for a vertical distance between the coupling area and the layer element.

[0009] It is particularly advantageous if the section of the substrate that is free from the electrically conductive layer element and separates the layer element from the strip waveguide comprises sidewall sections of the sidewalls of the substrate rib or is formed solely by sidewall sections of the sidewalls.

[0010] A section of the outer contour of the layer element preferably runs parallel to an edge of the tapered waveguide end region of the strip waveguide.

[0011] It is particularly advantageous if a section of the outer contour of the at least one layer element runs parallel to a first edge of the tapered waveguide end region of the strip waveguide and another section of the outer contour of the at least one layer element or a section of the outer contour of another layer element runs parallel to a second edge of the tapered waveguide end region of the strip waveguide, wherein the first and second edges of the tapered waveguide end region converge.

[0012] It is also advantageous if the layer element is U- or V-shaped in plan view, with leg sections of the layer element clasping the tapered waveguide end region.

[0013] The electrically conductive layer element is preferably formed by a metal layer, in particular a metal layer containing gold, silver and / or chromium.

[0014] The invention further relates to a method for manufacturing an optical arrangement, in particular one as described above, in which a strip waveguide, which tapers towards a waveguide end in a waveguide end region, is manufactured on a substrate and a fiber waveguide, which tapers towards a fiber end in a fiber end region, is arranged on or next to the strip waveguide, wherein the taper direction of the fiber waveguide is oriented opposite to the taper direction of the strip waveguide.

[0015] According to the invention, with regard to such a method, it is provided that an electrically conductive layer element is applied to the substrate in addition to the waveguide end region.

[0016] Regarding the advantages of the method according to the invention and advantageous embodiments of the method according to the invention, reference is made to the above statements in connection with the arrangement according to the invention and its advantageous embodiment.

[0017] The production of the electrically conductive layer element preferably includes a lift-off process.

[0018] It is particularly advantageous if a waveguide layer with a refractive index greater than that of the substrate is applied to the substrate, a mask is applied to the waveguide layer in the area of ​​the strip waveguide to be produced, the unmasked sections of the waveguide layer are removed by etching to form the strip waveguide, an electrically conductive layer is applied to the masked strip waveguide and to the substrate, and the electrically conductive layer above the strip waveguide is removed during the lift-off process.

[0019] During the etching process, preferably both the unmasked sections of the waveguide layer and the underlying substrate material are etched, forming a substrate rib located below the strip waveguide.

[0020] It is also advantageous if the electrically conductive layer is applied by a metal deposition process in which the layer growth rate is greater on surfaces parallel to the surface of the substrate than on surfaces arranged at an angle to it, in particular perpendicularly, i.e., for example, greater than on the side walls of the substrate rib.

[0021] After the electrically conductive layer is applied to the masked strip waveguide and prior to the lift-off process, an isotropic etching step is preferably performed to remove the electrically conductive layer from the upper sections of the substrate rib's sidewalls. The electrically conductive layer-free sidewalls of the substrate rib separate the layer element from the strip waveguide along a direction perpendicular to the etched substrate surface.

[0022] The invention is explained in more detail below using exemplary embodiments, which show, for example: Fig. 1 An embodiment of an arrangement according to the invention in a schematic three-dimensional representation taken obliquely from the side, Fig. 2 a strip waveguide and a fiber waveguide of the arrangement according to Fig. 1 in a top view, Fig. 3. An embodiment of a layer element in a top view, shown in more detail. Fig. 4. A further embodiment of a layer element is shown in more detail in a top view, and Fig. 5-9 Procedure steps for manufacturing the arrangement according to Fig. 1 and thus an embodiment of a method according to the invention.

[0023] For the sake of clarity, the same reference symbols are always used in the figures for identical or comparable components.

[0024] The Fig. Figure 1 shows an embodiment of an optical arrangement according to the invention. The arrangement includes, among other things, a substrate 10 on which a strip waveguide 20 is arranged. The edges 21 and 22 of the strip waveguide 20 converge towards a pointed waveguide end 20e in a waveguide end region 23.

[0025] A fiber waveguide 30 is arranged on the strip waveguide 20, tapering in a fiber end region 31 towards a pointed fiber end 30e. The taper direction V1 of the fiber waveguide 30 is opposite to the taper direction V2 of the strip waveguide 20. The taper of the fiber waveguide 30 and the strip waveguide 20 results in electromagnetic radiation guided in the fiber waveguide 30 being able to couple from the fiber end region 31 to the waveguide end region 23, and electromagnetic radiation guided in the strip waveguide 20 being able to couple from the waveguide end region 23 to the fiber end region 31.

[0026] In the embodiment according to Fig. The refractive index of the substrate 10 is greater than the refractive index of the fiber core and therefore also greater than the refractive index of the fiber cladding. To nevertheless allow coupling of radiation into the fiber waveguide 30, or to minimize coupling of radiation into the substrate 10 and thus achieve a high degree of coupling between the fiber waveguide 30 and the strip waveguide 20, at least one electrically conductive layer element 40 is arranged on the substrate 10 next to the waveguide end region 23 of the strip waveguide 20. The layer element 40 is located in the waveguide region of the strip waveguide 20 and the fiber waveguide 30 and thus influences the coupling behavior between the waveguide end region 23 and the fiber end region 31 by acting as a mirror that prevents or at least reduces the penetration of electromagnetic radiation into the substrate 10.

[0027] The layer element 40 preferably consists of an electrically conductive material such as a metal or a metal alloy, for example gold, silver, or chromium, or a mixture of these metals. However, other electrically conductive materials such as ITO can also be used.

[0028] To ensure a certain spatial distance between the strip waveguide 20 and the layer element 40 in a particularly simple manner, the strip waveguide 20 is arranged on a substrate rib 11. The arrangement on the substrate rib 11 has the advantage that the layer element 40 can project directly onto the substrate rib 11 and thus, viewed from above, directly onto the strip waveguide 20 without directly touching it; a certain minimum distance always remains, specifically in the vertical direction (meaning the direction perpendicular to the substrate plane of the substrate 10). In other words, at least the side wall sections 11a and 11b of the substrate rib 11 that are free of the layer element 40 separate the strip waveguide 20 from the layer element 40.

[0029] In the embodiment according to Fig. 1 A section 41 of the outer contour of the layer element borders the tapered substrate rib 11 and is thus parallel to the tapered waveguide end region 23 of the strip waveguide 20; such a parallel course reduces optical losses and increases the coupling efficiency between the fiber waveguide 30 and the strip waveguide 20.

[0030] The Fig. 2 shows the arrangement according to Fig. 1. Again in a top view.

[0031] The Fig. Figure 3 shows an embodiment of a large-area layer element 40, which projects directly onto the substrate rib 11 both in the waveguide end region 23 and in the untapered central region 24. Due to the vertical distance between the strip waveguide 20 and the adjacent substrate surface, a section 41 of the outer contour of the layer element 40 always runs parallel to a first edge 21 of the strip waveguide 20 at a distance corresponding to the rib height minus the thickness of the layer element 40, and another section 42 of the outer contour of the layer element 40 runs parallel to a second edge 22 of the strip waveguide 20 at the same distance, with the first and second edges converging in the waveguide end region 23.

[0032] In the top view, leg sections of the layer element 40 thus clasp the tapered waveguide end region 23 and form a U-shaped clamp for it.

[0033] The Fig. Figure 4 shows an embodiment of a layer element 40 that projects directly onto the substrate rib 11 only in the waveguide end region 23; in the untapered central region 24, the distance between the strip waveguide 20 and the layer element 40 increases linearly in the horizontal direction, i.e., parallel to the plane of the substrate surface, with increasing distance from the strip waveguide 20. In a top view, the leg sections of the layer element 40 thus only clasp the tapered waveguide end region 23 and form a V-shaped clamp for it.

[0034] The Fig. Figures 5 to 9 show process steps of an exemplary embodiment of a method according to the invention, with which the above-mentioned phenomena in connection with the Fig. Have the arrangements described in points 1 to 4 produced.

[0035] The Fig. Figure 5 shows the substrate 10 with a waveguide layer 100, with which the strip waveguide 20 is connected according to the Fig. 1 to 4 can be produced. For this purpose, a mask 110 is applied to the waveguide layer 100, covering the strip waveguide 20 to be produced. The mask 110 can, for example, consist of photoresist that has been structured accordingly in an exposure step. Alternatively, the mask 110 can be a resist for electron beam writing; in this case, the structuring is preferably carried out by electron beam writing.

[0036] The following material systems are particularly suitable for the strip waveguide 20 and the substrate 10: - AlN, AlGaN, InAlN, InGaN or GaN as waveguide material on a sapphire substrate, - InGaAsP as a waveguide material on an InP substrate, - AlGaAs as a waveguide material on a GaAs substrate, - Diamond as waveguide material on an AlN, sapphire, SiO2 or Si3N4 substrate, - Silicon as a waveguide material on a SiO2-Si substrate, - LiNbO3 as a waveguide material on a sapphire, SiO2 or Si3N4 substrate, - TiO2 as a waveguide material on a SiO2-Si substrate and - Polymers such as SU8, PMMA, BCB as waveguide material on a glass substrate.

[0037] In one etching step, the unmasked area of ​​the waveguide layer 100 is etched away and the striped waveguide 20 is formed, as shown in the Fig. Figure 6 shows that in this etching step, the substrate rib 11 is also produced simultaneously, with its side walls 11a and 11b oriented transversely, preferably perpendicularly or almost perpendicularly (angle of error preferably less than 10°) to the substrate surface. In other words, both the strip waveguide 20 and the substrate rib 11 are preferably produced in one and the same etching step, wherein the positioning of the strip waveguide 20 on the substrate rib 11 is self-adjusting due to the use of only a single mask 110.

[0038] In order to obtain side walls 11a and 11b that are as vertical as possible, it is advantageous if the etching step is an anisotropic etching step, for example a dry etching step.

[0039] Subsequently, a conductive layer 120 is applied across the entire surface, which forms the basis for the later layer element 40 according to the Fig. The conductive layer 120 is to be applied to form 1 to 4. The application of the conductive layer 120 can be carried out, for example, using a deposition process such as electron beam evaporation, sputtering, or the like. The thickness of the conductive layer is preferably in the range between 40 and 100 nm. The resulting structure is in the Fig. 7 shown. It is advantageous if the electrically conductive layer 120 is applied by a metal deposition process in which the layer growth rate on surfaces parallel to the surface of the substrate 10 is greater than on surfaces perpendicular or perpendicular to it, i.e., for example, greater than on the perpendicular side walls 11a and 11b of the strip waveguide 20.

[0040] During the deposition of the conductive layer 120, the side walls 11a and 11b of the substrate rib 11 are typically also coated. To remove the conductive layer 120 from the side walls 11a and 11b and to provide lateral access to the mask 110 located beneath the conductive layer 120, a second etching step is performed, which removes the conductive layer 120 from the side walls 11a and 11b. The second etching step is preferably an isotropic etching step, which can be carried out using an etching liquid. Fig. Figure 8 shows the exposed sidewalls 11a and 11b of the substrate rib 11 after the second etching step. The thickness of the remaining electrically conductive layer 120 is preferably in a range between 10 and 30 nm.

[0041] After the second etching step has exposed the mask 110 laterally, it can be dissolved using a solvent such as acetone or the like, resulting in a lift-off process in which the electrically conductive layer 120 in the area above the strip waveguide 20 is lifted off and remains only on the substrate surface.

[0042] The Fig. Figure 9 shows the strip waveguide 20 freed from the conductive layer 120. It can be seen that the upper, uncoated side walls 11a and 11b of the substrate rib 11 separate the strip waveguide 20 from the layer element 40.

[0043] Subsequently, the conductive layer 120 remaining on the substrate surface can be structured by a further etching step, for example to achieve the desired effect in the Fig. 4 and Fig. to develop the 5 shown shapes for the layer element 40.

[0044] After completion of the layer element 40, the tapered fiber end 30e of the fiber waveguide 30 can be placed onto the tapered waveguide end region 23 of the strip waveguide 20 to connect the Fig. To complete the arrangement shown in Figure 1. Alternatively, the fiber waveguide 30 can also be placed next to the strip waveguide on the substrate 10 or the layer element 40.

[0045] Finally, it should be mentioned that the features of all embodiments described above can be combined with each other in any way to form further other embodiments of the invention.

[0046] Furthermore, all features of dependent claims can each be combined with each of the subordinate claims, either individually or in any combination with one or more other dependent claims, to obtain further embodiments. List of reference symbols 10 substrate 11 Substrate rib 11a Side wall 11b Side wall 20 strip waveguides 20e Waveguide end 21 Rand 22 Rand 23 Waveguide end region 24 Middle range 30 fiber optic waveguides 30e Fiber end 31 Fiber end area 40 layer element Section 41 Section 42 100 waveguide layer 110 mask 120 conductive layer V1 tapering direction V2 tapering direction

Claims

[1] Optical arrangement with - a substrate (10), - a strip waveguide (20) arranged on the substrate (10), which tapers in a waveguide end region (23) towards a waveguide end (20e), and - a fiber waveguide (30) arranged on or next to the strip waveguide (20), which tapers in a fiber end region (31) towards a fiber end (30e), wherein the taper direction (V1) of the fiber waveguide (30) is opposite to the taper direction (V2) of the strip waveguide (20) and can couple electromagnetic radiation guided in the fiber waveguide (30) from the fiber end region (31) into the waveguide end region (23) and electromagnetic radiation guided in the strip waveguide (20) from the waveguide end region (23) into the fiber end region (31), characterized bythat on the substrate (10) next to the waveguide end region (23) at least one electrically conductive layer element (40) influencing the coupling behavior between the waveguide end region (23) and the fiber end region (31) is arranged. [2] Optical arrangement according to claim 1, characterized by that the layer element (40) is separated from the strip waveguide (20) by a portion (41, 42) of the substrate (10) which is free of the electrically conductive layer element (40). [3] Optical arrangement according to one of the preceding claims, characterized by that the strip waveguide (20) is arranged on a substrate rib (11) of the substrate (10). [4] Optical arrangement according to claim 3, characterized bythat the section (41, 42) of the substrate (10) which is free of the electrically conductive layer element (40) and separates the layer element (40) from the strip waveguide (20) comprises side wall sections of the side walls (11a, 11b) of the substrate rib (11) or is formed solely by side wall sections of the side walls (11a, 11b). [5] Optical arrangement according to one of the preceding claims, characterized by that the refractive index of the substrate (10) is greater than the refractive index of the fiber core or the cladding of the fiber waveguide (30). [6] Optical arrangement according to one of the preceding claims, characterized by that a section (41, 42) of the outer contour of the layer element (40) runs parallel to an edge of the tapered waveguide end region (23) of the strip waveguide (20). [7] Optical arrangement according to one of the preceding claims, characterized by , that - a section (41, 42) of the outer contour of the at least one layer element (40) runs parallel to a first edge (21, 22) of the tapered waveguide end region (23) of the strip waveguide (20) and - another section (41, 42) of the outer contour of the at least one layer element (40) or a section (41, 42) of the outer contour of another layer element (40) runs parallel to a second edge (21, 22) of the tapered waveguide end region (23) of the strip waveguide (20), wherein the first and second edges (21, 22) of the tapered waveguide end region (23) converge towards one another. [8] Optical arrangement according to one of the preceding claims, characterized by that the layer element (40) is U-shaped or V-shaped in plan view, with leg sections of the layer element (40) clasping the tapered waveguide end region (23). [9] Optical arrangement according to one of the preceding claims, characterized by that the electrically conductive layer element (40) is formed by a metal layer, in particular a metal layer containing gold, silver and / or chromium. [10] Method for producing an optical arrangement, in particular an arrangement according to one of the preceding claims, in which - a strip waveguide (20) is produced on a substrate (10), which strip waveguide tapers in a waveguide end region (23) towards a waveguide end (20e), and - a fiber waveguide (30) is arranged on or next to the strip waveguide (20), which fiber waveguide tapers in a fiber end region (31) towards a fiber end (30e), wherein the taper direction (V1) of the fiber waveguide (30) is oriented opposite to the taper direction (V2) of the strip waveguide (20), characterized bythat an electrically conductive layer element (40) is applied to the substrate (10) next to the waveguide end region (23). [11] Method according to claim 10, characterized by that the production of the electrically conductive layer element (40) includes a lift-off process. [12] Method according to claim 11, characterized by , that - a waveguide layer (100) having a refractive index greater than the refractive index of the substrate (10) is applied to the substrate (10), - a mask (110) is applied to the waveguide layer (100) in the region of the strip waveguide (20) to be produced, - the unmasked sections of the waveguide layer (100) are removed by etching to form the strip waveguide (20), - an electrically conductive layer (120) is applied to the masked strip waveguide (20) and to the substrate (10), and - as part of the lift-off process, the electrically conductive layer (120) above the strip waveguide (20) is removed. [13] Method according to claim 12, characterized by that during the etching, both the unmasked sections of the waveguide layer (100) and the substrate material located thereunder are etched to form a substrate rib (11) located below the strip waveguide (20). [14] Method according to claim 13, characterized by , that - after the application of the electrically conductive layer (120) on the masked strip waveguide (20) and before the lift-off process, an isotropic etching step is carried out, with which upper sections of the side walls (11a, 11b) of the substrate rib (11) are freed from the electrically conductive material (120), - whereby the portions of the side walls (11a, 11b) of the substrate rib (11) free of the electrically conductive material (120) separate the layer element (40) from the strip waveguide (20) along a direction perpendicular to the etched surface of the substrate (10).

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