Optical assembly and method for producing same

Abstract

The invention relates to, among others, an optical assembly comprising a substrate (10), a strip waveguide (20) which is positioned on the substrate (10) and which tapers in the direction of a waveguide end (20e) in a waveguide end region (23), and a fiber waveguide (30) on or next to the strip waveguide (20), said fiber waveguide tapering in the direction of a fiber end (30e) in a fiber end region (31), wherein the tapering direction (V1) of the fiber waveguide (30) is opposite the tapering direction (V2) of the strip waveguide (20). Electromagnetic radiation being guided in the fiber waveguide (30) can be coupled from the fiber end region (31) into the waveguide end region (23), and electromagnetic radiation being guided in the strip waveguide (20) can be coupled from the waveguide end region (23) into the fiber end region (31). According to the invention, at least one electrically conductive layer element (40) which influences the coupling behavior between the waveguide end region (23) and the fiber end region (31) is positioned on the substrate (10) next to the waveguide end region (23).

Description

[0001] Description

[0002] Optical arrangement and method for its manufacture

[0003] The invention relates, inter alia, to an optical arrangement having a substrate, a strip waveguide arranged on the substrate, which tapers in a waveguide end region towards a waveguide end, and a fiber waveguide arranged on or next to the strip waveguide, which tapers in a fiber end region towards a fiber end. The taper direction of the fiber waveguide is opposite to the taper direction of the strip waveguide. Electromagnetic radiation guided in the fiber waveguide can couple from the fiber end region into the waveguide end region, and electromagnetic radiation guided in the strip waveguide can couple from the waveguide end region into the fiber end region. Such an arrangement is disclosed in US patent US 11,480,736 B2.In the arrangement described in the US patent, a recess is provided in the substrate to improve the coupling behavior.

[0004] The invention is based on the object of specifying an arrangement with which a particularly high coupling efficiency between the waveguides can be achieved.

[0005] This object is achieved according to the invention by an arrangement having the features of claim 1. Advantageous embodiments of the arrangement according to the invention are specified in the subclaims. 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 radiation from "dipping" into the substrate by acting as a mirror layer due to its electrical conductivity. The layer element thus enables a comparatively free choice of the substrate material: For example, the refractive index of the substrate can be greater than the refractive index of the fiber core or the cladding of the fiber waveguide. The use of the layer element thus 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 can cause in close proximity to optical waveguides.

[0008] The strip waveguide is preferably arranged on a substrate rib of the substrate. An arrangement on a substrate rib advantageously enables a vertical distance between the coupling region and the layer element. It is particularly advantageous if the section of the substrate which is free of 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.

[0009] A portion of the outer contour of the layer element preferably runs parallel to an edge of the tapered waveguide end region of the strip waveguide.

[0010] 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 towards one another.

[0011] 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.

[0012] The electrically conductive layer element is preferably formed by a metal layer, in particular a metal layer containing gold, silver and / or chromium. The invention also relates to a method for producing an optical arrangement, in particular one as described above, in which a strip waveguide which tapers in a waveguide end region towards a waveguide end is produced on a substrate and a fiber waveguide which tapers in a fiber end region towards a fiber end is arranged on or next to the strip waveguide, the tapering direction of the fiber waveguide being aligned opposite to the tapering direction of the strip waveguide.

[0013] According to the invention, with regard to such a method, it is provided that an electrically conductive layer element is applied to the substrate next to the waveguide end region.

[0014] With regard to 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.

[0015] The production of the electrically conductive layer element preferably includes a lift-off process.

[0016] It is particularly advantageous if a waveguide layer with a refractive index that is greater than the refractive index of the substrate is applied to the substrate, a mask is applied to the waveguide layer in the region 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 as part of the lift-off process.

[0017] During the etching, preferably both the unmasked sections of the waveguide layer and the underlying substrate material are etched to form a substrate rib located beneath the strip waveguide.

[0018] It is also advantageous if the application of the electrically conductive layer is carried out by a metal deposition process in which the layer growth rate on surfaces parallel to the surface of the substrate is greater than on surfaces arranged at an angle thereto, in particular perpendicular thereto, that is to say, for example, greater than on the side walls of the substrate rib.

[0019] After applying the electrically conductive layer to the masked strip waveguide and before the lift-off process, an isotropic etching step is preferably performed to free the upper sections of the sidewalls of the substrate rib from the electrically conductive layer. The sidewalls of the substrate rib, free of the electrically conductive layer, separate the layer element from the strip waveguide along a direction perpendicular to the etched surface of the substrate.

[0020] The invention is explained in more detail below using exemplary embodiments, which show, by way of example:

[0021] Figure 1 shows an exemplary embodiment of an arrangement according to the invention in a schematic three-dimensional representation obliquely from the side, Figure 2 shows a strip waveguide and a fiber waveguide of the arrangement according to Figure 1 in a plan view,

[0022] Figure 3 shows an exemplary embodiment of a layer element in a plan view in more detail,

[0023] Figure 4 shows a further exemplary embodiment of a layer element in a plan view in more detail, and

[0024] Fig. 5-9 Process steps for producing the arrangement according to Figure 1 and thus an embodiment of a process according to the invention.

[0025] For the sake of clarity, the same reference symbols are always used in the figures for identical or comparable components.

[0026] Figure 1 shows an exemplary embodiment of an optical arrangement according to the invention. The arrangement comprises, 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 in a waveguide end region 23 toward a tip-shaped waveguide end 20e.

[0027] A fiber waveguide 30 is in turn arranged on the strip waveguide 20, which tapers in a fiber end region 31 in the direction of a tip-shaped fiber end 30e. The taper direction VI 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 has the consequence that electromagnetic radiation guided in the fiber waveguide 30 can couple from the fiber end region 31 into the waveguide end region 23 and electromagnetic radiation guided in the strip waveguide 20 can couple from the waveguide end region 23 into the fiber end region 31.

[0028] In the embodiment according to Figure 1, the refractive index of the substrate 10 is greater than the refractive index of the fiber core and thus also greater than the refractive index of the fiber cladding. In order to nevertheless enable over-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 region of the waveguide 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.

[0029] The layer element 40 is preferably made of an electrically conductive material such as 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.

[0030] In order 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 in plan view, directly onto the strip waveguide 20, without directly touching the strip waveguide 20; a certain minimum distance always remains, specifically in the vertical direction (here meaning the direction perpendicular to the substrate plane of the substrate 10). In other words, at least the side wall sections of the side walls 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.

[0031] In the embodiment according to Figure 1, a portion 41 of the outer contour of the layer element borders the tapered substrate rib 11 and thus lies 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.

[0032] Figure 2 shows the arrangement according to Figure 1 again in a top view.

[0033] Figure 3 shows an exemplary 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, the first and second edges converging in the waveguide end region 23.

[0034] In the plan view, leg sections of the layer element 40 thus clasp the tapered waveguide end region 23 and form a U-shaped clamp for it.

[0035] Figure 4 shows an exemplary embodiment of a layer element 40 which 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, or parallel to the plane of the substrate surface, with increasing distance from the strip waveguide 20. In plan 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.

[0036] Figures 5 to 9 show method steps of an embodiment of a method according to the invention with which the arrangements explained above in connection with Figures 1 to 4 can be produced.

[0037] Figure 5 shows the substrate 10 with a waveguide layer 100, with which the strip waveguide 20 according to Figures 1 to 4 can be produced. For this purpose, a mask 110 is applied to the waveguide layer 100, which mask covers the strip waveguide 20 to be produced. The mask 110 can consist, for example, of photoresist that was appropriately patterned during an exposure step. Alternatively, the mask 110 can be a resist for electron writing; in this case, the structuring is preferably carried out by electron beam writing.

[0038] The following material systems are particularly suitable for the strip waveguide 20 and the substrate 10:

[0039] - AIN, AlGaN, InAlN, InGaN or GaN as waveguide material on a sapphire substrate,

[0040] - InGaAsP as waveguide material on an InP substrate,

[0041] - AlGaAs as waveguide material on a GaAs substrate,

[0042] - Diamond as waveguide material on an AIN, sapphire, SiO2 or Si3N4 substrate,

[0043] - Silicon as waveguide material on a SiO2-Si substrate,

[0044] - LiNbO3 as waveguide material on a sapphire, SiO2 or Si3N4 substrate,

[0045] - TiO2 as waveguide material on a SiO2-Si substrate and

[0046] - Polymer such as SU8, PMMA, BGB as waveguide material on a glass substrate.

[0047] In an etching step, the unmasked region of the waveguide layer 100 is etched away and the strip waveguide 20 is formed, as shown in Figure 6. In this etching step, the substrate rib 11 with its side walls 11a and 11b oriented transversely, preferably perpendicularly or almost perpendicularly (error angle preferably less than 10°) to the substrate surface is also produced. In other words, both the strip waveguide 20 and the substrate rib 11 are preferably produced in one and the same etching step, the positioning of the strip waveguide 20 on the substrate rib 11 being self-adjusting due to the use of only a single mask 110. 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.

[0048] Subsequently, a conductive layer 120, which is to form the later layer element 40 according to Figures 1 to 4, is applied over the entire surface. The conductive layer 120 can be applied, for example, within the scope of a deposition process such as electron beam evaporation, sputtering or the like. The layer thickness of the conductive layer is preferably in a range between 40 and 100 nm. The resulting structure is shown in Figure 7. It is advantageous if the electrically conductive layer 120 is applied by a metal deposition process in which the layer growth rate is greater on surfaces parallel to the surface of the substrate 10 than on surfaces transverse or perpendicular thereto, that is to say, for example, greater than on the vertical side walls 11a and 11b of the strip waveguide 20.

[0049] During the deposition of the conductive layer 120, the side walls 11a and 11b of the substrate rib 11 are generally also coated. In order to free the side walls 11a and 11b from the conductive layer 120 and to obtain lateral access to the mask 110 located beneath the conductive layer 120, a second etching step is carried out, which frees the side walls 11a and 11b from the conductive layer 120. The second etching step is preferably an isotropic etching step, which can be carried out using an etching liquid. Figure 8 shows the exposed side walls 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.

[0050] After the mask 110 has been exposed laterally by the second etching step, it can be dissolved by means of a solvent such as acetone or the like, resulting in a lift-off process in which the electrically conductive layer 120 in the region above the strip waveguide 20 is lifted off and remains only on the substrate surface.

[0051] 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.

[0052] Subsequently, the conductive layer 120 remaining on the substrate surface can be structured by a further etching step in order to form, for example, the shapes shown in Figures 4 and 5 for the layer element 40.

[0053] 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 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.

[0054] Finally, it should be mentioned that the features of all the embodiments described above can be combined with one another in any desired manner in order to form further other embodiments of the invention.

[0055] All features of subclaims can also be combined individually with each of the subordinate claims, either individually or in any combination with one or more other subclaims, in order to obtain further embodiments.

[0056] Reference symbol list

[0057] 10 Substrat

[0058] 11 Substrate rib

[0059] 11a side wall

[0060] 11b Side wall

[0061] 20 strip waveguides

[0062] 20e waveguide end

[0063] 21 edge

[0064] 22 edges

[0065] 23 Waveguide end region

[0066] 24 Middle range

[0067] 30 fiber waveguides

[0068] 30e fiber end

[0069] 31 Fiber end area

[0070] 40 layer element

[0071] Section 41

[0072] Section 42

[0073] 100 waveguide layer

[0074] 110 Mask

[0075] 120 conductive layer

[0076] VI Tapering direction

[0077] V2 taper direction

Claims

Patent 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) in the direction of 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 in that 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 in 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 in that the strip waveguide (20) is arranged on a substrate rib (11) of the substrate (10).

4. Optical arrangement according to claim 3, characterized in that 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 in 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 in 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 in 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 in 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 in 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. A 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 (30) extends in a fiber end region (31) in the direction of a fiber end (30e) tapers, wherein the taper direction (VI) of the fiber waveguide (30) is aligned opposite to the taper direction (V2) of the strip waveguide (20), characterized in that an electrically conductive layer element (40) is applied to the substrate (10) next to the waveguide end region (23).

11. The method according to claim 10, characterized in that the production of the electrically conductive layer element (40) includes a lift-off process.

12. Method according to claim 11, characterized in 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 in 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 in that - after applying 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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