Edge coupler

Abstract

The present utility model provides an edge coupler, comprising: a silicon substrate, a silicon oxide buried layer, and an optical waveguide layer which are sequentially stacked. In the thickness direction of the silicon substrate, the optical waveguide layer is provided with a first surface on the side facing away from the silicon substrate, a first groove and a second groove are formed in the first surface, and one or more waveguides are embedded in the optical waveguide layer between the first groove and the second groove. No suspended structure or cantilever beam structure is provided directly below the optical waveguide layer located between the first groove and the second groove, so that the mechanical performance of the edge coupler is high. Moreover, in the thickness direction of the silicon substrate, the first groove and the second groove extend into the silicon substrate from the first surface so as to limit the lateral optical field, thereby reducing the leakage of the optical field of the edge coupler into the silicon substrate, and facilitating improvement of the optical coupling efficiency of the edge coupler.

Description

Edge Coupler

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on June 14, 2023, with application number 202321512302.8 and invention name “Edge Coupler”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The utility model relates to the technical field of photon equipment, in particular to a side coupler. Background Art

[0003] In recent years, photonic integrated circuit chips have effectively reduced the cost and power consumption of optical communication modules and are a key technology for achieving optical interconnection. The mode field diameter of a typical single-mode silicon optical waveguide is on the order of hundreds of nanometers, while the mode field diameter (MFD) of ordinary single-mode optical fibers required for coupling and alignment with photonic integrated circuit chips (such as silicon photonic chips) is 9-10μm. This significant mode field mismatch between the two makes direct coupling with a narrow alignment tolerance and results in significant optical coupling losses.

[0004] Commonly used silicon waveguide couplers include two main types: grating couplers and edge couplers. Grating couplers offer advantages such as wide alignment tolerance, ease of packaging, and on-chip testing. However, they suffer from low coupling efficiency and a narrow operating bandwidth. Edge couplers, on the other hand, offer advantages such as high coupling efficiency and a wide operating bandwidth. Utility Model Content

[0005] The purpose of the utility model is to provide a side coupler, which is used to take both the optical coupling efficiency and mechanical performance of the side coupler into consideration.

[0006] The purpose of this utility model is achieved by the following technical solutions:

[0007] According to one aspect of the present invention, there is provided an edge coupler, comprising: a silicon substrate, a silicon oxide buried layer, and an optical waveguide layer stacked in sequence;

[0008] The optical waveguide layer has a first surface facing away from the silicon substrate in a thickness direction of the silicon substrate, a first groove and a second groove are provided on the first surface, and one or more waveguides are embedded in the optical waveguide layer between the first groove and the second groove;

[0009] Along a thickness direction perpendicular to the silicon substrate, the edge coupler has an outer end surface coupled to the outside world, the waveguide extends from the interior of the edge coupler to the outer end surface, and the waveguide is configured to have a first mode size on a side away from the outer end surface of the edge coupler and a second mode size on a side close to the outer end surface of the edge coupler, wherein the first mode size is larger than the second mode size;

[0010] Wherein, along the thickness direction perpendicular to the silicon substrate, the first groove and the second groove both penetrate the edge coupler, and along the thickness direction of the silicon substrate, the first groove and the second groove both penetrate into the silicon substrate from the first surface.

[0011] Furthermore, the first groove and the second groove extend into the silicon substrate to a thickness of 10-40 μm.

[0012] Furthermore, the depth of the first groove is defined as d1, the width of the first groove is defined as w1, wherein 2≤d1 / w1≤5; the depth of the second groove is defined as d2, the width of the second groove is defined as w2, wherein 2≤d2 / w2≤5.

[0013] In some embodiments, the ratio of the depth to the width of the first groove and the second groove is equal.

[0014] In some embodiments, the first groove and the second groove are filled with epoxy resin.

[0015] Optionally, each of the waveguides is any one of a silicon waveguide, a silicon nitride waveguide, a silicon oxynitride waveguide, and a lithium niobate waveguide.

[0016] Optionally, in a direction pointing from the inside of the edge coupler to the outer end surface, at least a portion of each of the waveguides includes an inverted wedge structure.

[0017] In some embodiments, the entirety of each of the waveguides is in an inverted wedge-shaped structure.

[0018] In some embodiments, a plurality of waveguides are embedded side by side on a side of the optical waveguide layer close to the silicon oxide buried layer.

[0019] In some embodiments, the plurality of waveguides are configured to be flush at ends proximate the outer end surface of the edge coupler.

[0020] In some embodiments, the optical waveguide layer is silicon dioxide.

[0021] In some embodiments, the side coupler further includes a protective layer, where the protective layer covers the optical waveguide layer of the side coupler; wherein the material of the protective layer is silicon nitride.

[0022] This utility model provides a solution for balancing the optical coupling efficiency and mechanical performance of an edge coupler. The edge coupler comprises a first groove and a second groove on the first surface of its optical waveguide layer, facing away from the silicon substrate. One or more waveguides are embedded within the optical waveguide layer between the first and second grooves. Because there are no suspended structures or cantilever beam structures directly below the optical waveguide layer between the first and second grooves, the edge coupler exhibits superior mechanical performance. Furthermore, along the thickness direction of the silicon substrate, both the first and second grooves extend deep into the silicon substrate from the first surface to confine the lateral light field, reducing leakage of the light field from the edge coupler into the silicon substrate and facilitating improved optical coupling efficiency.

[0023] Furthermore, a layer of silicon nitride may be covered on the optical waveguide layer of the edge coupler and in the first groove and the second groove as a protective layer, thereby improving the water vapor resistance of the edge coupler and extending the normal working life of the edge coupler. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other implementation methods can be obtained based on these drawings without paying any creative work.

[0025] FIG1 shows a schematic structural diagram of an edge coupler in a conventional technology;

[0026] FIG2 shows a second example of a schematic structural diagram of a side coupler in a conventional technology;

[0027] FIG3 shows a third example of a schematic structural diagram of a side coupler in a conventional technology;

[0028] FIG4 shows a schematic structural diagram of an edge coupler provided in the first embodiment of the present application;

[0029] FIG5A shows a schematic cross-sectional structural diagram of an edge coupler provided in FIG4 along the AA' direction;

[0030] FIG5B shows a schematic top view of a waveguide in an edge coupler provided in FIG4 ;

[0031] FIG6 shows a schematic structural diagram of an edge coupler provided in a second embodiment of the present application;

[0032] FIG7 shows a schematic cross-sectional structural diagram of an edge coupler provided in FIG6 along the BB' direction;

[0033] FIG8 shows a schematic structural diagram of an edge coupler provided in a third embodiment of the present application;

[0034] FIG9 shows a schematic cross-sectional structural diagram of the edge coupler provided in FIG8 along the CC′ direction. DETAILED DESCRIPTION

[0035] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In addition, in order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the following preferred embodiments are specifically cited and described in detail with reference to the accompanying drawings.

[0036] In the description of the present invention, it should be noted that, unless otherwise expressly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be directly connected, or indirectly connected through an intermediate medium, or it can be internal communication between two elements or an interaction relationship between two elements. The meaning of chip in this article may include bare chips. When it comes to method steps, the sequence illustrated in this article represents an exemplary scheme, but does not represent a limitation on the sequence. For ordinary technicians in this field, the specific meanings of the above terms in this utility model can be understood according to specific circumstances.

[0037] As used herein, the term "substrate" can refer to the substrate of a diced wafer or the substrate of an undiced wafer. It should be understood that the term "film" encompasses layers and, unless otherwise specified, should not be interpreted as indicating vertical or horizontal thickness. It should be noted that the thicknesses of the various material layers of the edge coupler structure shown in the figures are merely illustrative and do not represent actual thicknesses.

[0038] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] FIG1 shows a first example of a schematic structural diagram of a side coupler in a commonly used technique; FIG2 shows a second example of a schematic structural diagram of a side coupler in a commonly used technique; and FIG3 shows a third example of a schematic structural diagram of a side coupler in a commonly used technique.

[0040] As shown in Figure 1, in Example 1, the edge coupler structure is a typical one. This edge coupler has a cantilever beam structure, and uses deep trench etching and isotropic etching to etch the silicon substrate of the SOI (Silicon On Insulator) structure to prevent leakage of the optical field into the substrate. However, the etching processes involved in deep trench etching and isotropic etching are relatively complex, which can reduce the yield rate during optical chip production. Furthermore, because the waveguide is suspended below, supported only by support arms on the sides, if the support arms are too wide, the structural losses will increase, while if the support arms are too narrow, the structure may collapse. Furthermore, the edge coupler is prone to breakage during the subsequent optical chip packaging process. During flip-chip soldering and bumping processes, various adhesives and dirt may be adsorbed on the edge coupler surface through the grooves, causing performance degradation. Over long-term use, moisture can enter the surface silicon dioxide layer, affecting the performance of the edge coupler.

[0041] As shown in Figure 2, in Example 2, the silica on both sides of the waveguide on the edge coupler is etched to form shallow grooves on both sides of the waveguide. The light field is slowly transferred from the waveguide on the edge coupler to the silica waveguide. The shallow grooves on both sides are partially etched, but not etched into the SOI substrate. The light field mode spot is still small, suitable for coupling with small mode spot fibers. When coupled with SMF-28 fibers, the optical loss is large. In addition, during long-term use, water vapor can easily enter the surface silica layer, thereby affecting the performance of the edge coupler.

[0042] As shown in FIG3 , in Example 3, the side coupler is still a cantilever beam structure, and it also has the same technical problems as in Example 1, so they will not be described here in detail.

[0043] In view of this, embodiments of the present invention provide a solution for balancing the optical coupling efficiency and mechanical performance of the edge coupler.

[0044] At least one embodiment of the present application provides an edge coupler, the edge coupler comprising: a silicon substrate, a silicon oxide buried layer, and an optical waveguide layer stacked in sequence;

[0045] The optical waveguide layer has a first surface facing away from the silicon substrate along the thickness direction of the silicon substrate, a first groove and a second groove are provided on the first surface, and one or more waveguides are embedded in the optical waveguide layer between the first groove and the second groove;

[0046] Along a thickness direction perpendicular to the silicon substrate, the edge coupler has an outer end surface coupled to the outside world, the waveguide extends from the interior of the edge coupler to the outer end surface, and the waveguide is configured to have a first mode size on a side away from the outer end surface of the edge coupler and a second mode size on a side close to the outer end surface of the edge coupler, wherein the first mode size is larger than the second mode size;

[0047] In which, along the thickness direction perpendicular to the silicon substrate, the first groove and the second groove both penetrate the edge coupler, and in the thickness direction of the silicon substrate, the first groove and the second groove both penetrate the optical waveguide layer, the silicon oxide buried layer and a portion of the silicon substrate.

[0048] As can be seen above, the edge coupler comprises a first groove and a second groove on the first surface of its optical waveguide layer, facing away from the silicon substrate. One or more waveguides are embedded within the optical waveguide layer between the first and second grooves. Because there are no overhanging structures or cantilever beam structures directly below the optical waveguide layer between the first and second grooves, the edge coupler exhibits superior mechanical performance. Furthermore, along the thickness direction of the silicon substrate, both the first and second grooves extend deep into the silicon substrate from the first surface, confining the lateral light field and reducing leakage of the light field from the edge coupler into the silicon substrate, thereby improving the optical coupling efficiency of the edge coupler. Example

[0049] FIG4 shows a schematic structural diagram of a side coupler provided in the first embodiment of the present application; FIG5A shows a schematic cross-sectional structural diagram of the side coupler provided in FIG4 along the AA′ direction.

[0050] As shown in FIG. 4 and FIG. 5A , the edge coupler provided in the first embodiment of the present application includes: a silicon substrate 110 , a silicon oxide buried layer 120 , and an optical waveguide layer 130 , which are stacked in sequence.

[0051] In the thickness direction of the silicon substrate, the optical waveguide layer 130 has a first surface 100 a facing away from the silicon substrate 110 . A first groove 210 and a second groove 220 are provided on the first surface 100 a . One or more waveguides 300 are embedded in the optical waveguide layer 130 between the first groove 210 and the second groove 220 .

[0052] Along the thickness direction perpendicular to the silicon substrate 110, the edge coupler has an outer end face 100d coupled to the outside world, and the waveguide 300 extends from the inside of the edge coupler to the outer end face 100d. Each of the waveguides 300 is configured to have a first mode size on a side away from the outer end face of the edge coupler (i.e., corresponding to 100c in the figure), and a second mode size on the outer end face 100d close to the edge coupler, wherein the first mode size is larger than the second mode size, so as to expand the mode spot size of light leaving the silicon photonic chip (not shown) and then enter the external optical fiber (not shown), and conversely, perform mode spot conversion on the light input from the external optical fiber (shrinking the mode spot size of the light), and couple the light after mode spot conversion to the optical device (such as a detector, modulator, etc.) in the silicon photonic chip.

[0053] In the thickness direction perpendicular to the silicon substrate 110 , both the first groove 210 and the second groove 220 penetrate the edge coupler, and in the thickness direction of the silicon substrate 110 , both the first groove 210 and the second groove 220 penetrate the optical waveguide layer 130 , the silicon oxide buried layer 120 , and a portion of the silicon substrate 110 .

[0054] In this embodiment, the edge coupler includes only one waveguide 300 .

[0055] Exemplarily, the optical waveguide layer 130 is silicon dioxide, and the waveguide 300 is any one of a silicon waveguide, a silicon nitride waveguide, a silicon oxynitride waveguide, and a lithium niobate waveguide.

[0056] Furthermore, as shown in FIG5B , at least a portion of the waveguide 300, directed from the interior of the edge coupler toward the outer end face 100d, includes an inverted wedge-shaped structure. This allows the light coupled from the silicon photonic chip to gradually expand after undergoing spot conversion in the waveguide 300 within the edge coupler. As the light approaches the outer end face 100d of the edge coupler, it forms a hybrid waveguide with the surrounding optical waveguide layer 130 (e.g., silica), matching the spot diameter of the external optical fiber.

[0057] In some embodiments, the entire waveguide 300 has an inverted wedge-shaped structure.

[0058] Furthermore, the first groove 210 and the second groove 220 extend into the silicon substrate 110 to a thickness of 10 to 40 μm. A normal silicon substrate is approximately 690 μm thick, and if thinned, the thickness is approximately 250 μm. That is, in this embodiment, although the first groove 210 and the second groove 220 are relatively deep trenches, they do not affect the stability of the overall structure of the edge coupler and do not pose a risk of breakage. Therefore, they can both laterally confine the light field and reduce absorption of the light field by the silicon substrate 110.

[0059] Furthermore, the depth of the first groove 210 is defined as d1, and the width of the first groove 210 is defined as w1, wherein 2≤d1 / w1≤5; the depth of the second groove 220 is defined as d2, and the width of the second groove 220 is defined as w2, wherein 2≤d2 / w2≤5.

[0060] In some embodiments, the ratio of the depth to the width of the first groove 210 and the second groove 220 is equal to facilitate manufacturing with uniform specifications.

[0061] In some other embodiments, the ratio of the depth to the width of the first groove 210 and the second groove 220 may also be different.

[0062] In some embodiments, the first groove 210 and the second groove 220 are filled with epoxy resin (not shown) to form a protective film on the sidewalls of the first groove 210 and the second groove 220 to prevent moisture from entering through the optical waveguide layer 130 exposed by the sidewalls of the first groove 210 and the second groove 220, thereby affecting the normal working performance of the edge coupler. Example

[0063] FIG6 shows a schematic structural diagram of a side coupler provided in the second embodiment of the present application; FIG7 shows a schematic cross-sectional structural diagram of the side coupler provided in FIG6 along the BB′ direction.

[0064] Referring to Figures 6 and 7 , the difference from the first embodiment is that in this embodiment, the side coupler includes two waveguides 300 embedded in the optical waveguide layer 130. In some alternative embodiments, the side coupler includes more than two waveguides 300 embedded in the optical waveguide layer 130, for example, three, four, or five waveguides. This embodiment is not limited here. Each waveguide 300 can be any one of a silicon waveguide, a silicon nitride waveguide, a silicon oxynitride waveguide, and a lithium niobate waveguide.

[0065] By arranging two or more waveguides to jointly participate in the adjustment of the light field mode spot size, the sensitivity of the shape or size of a single waveguide itself to the mode field diameter of the single waveguide is reduced while ensuring the coupling efficiency.

[0066] In some embodiments, a plurality of waveguides 300 are embedded side by side on a side of the optical waveguide layer 130 close to the silicon oxide buried layer 120 .

[0067] In some embodiments, the plurality of waveguides 300 are configured to be flush at their ends near the outer end surface 100d of the edge coupler, so as to form a hybrid waveguide of any one of a silicon waveguide, a silicon nitride waveguide, a silicon oxynitride waveguide, and a lithium niobate waveguide and silicon oxide near the outer end surface 100d of the edge coupler, so as to jointly confine the light field. Example

[0068] FIG8 shows a schematic structural diagram of a side coupler provided in the third embodiment of the present application; FIG9 shows a schematic cross-sectional structural diagram of the side coupler provided in FIG8 along the CC' direction.

[0069] 8 and 9 , the difference from the first embodiment is that in this embodiment, to prevent moisture from easily entering the silicon oxide on the upper side of the side coupler during long-term use, thereby causing a degradation in the normal working performance of the side coupler, the side coupler further includes a protective layer 140. The protective layer 140 covers the optical waveguide layer 130 of the side coupler and can also cover the first groove 210 and the second groove 220 (i.e., the groove bottom and sidewalls). The protective layer 140 is made of silicon nitride, which has good film adhesion and can provide good protection on the surface of the side coupler.

[0070] Furthermore, the protective layer 140 is also beneficial for improving the scratch resistance of the surface of the edge coupler.

[0071] Embodiments of the present invention provide a solution for balancing the optical coupling efficiency and mechanical performance of an edge coupler. The edge coupler comprises: a silicon substrate, a buried silicon oxide layer, and an optical waveguide layer stacked in sequence. The edge coupler comprises a first groove and a second groove disposed on a first surface of the optical waveguide layer facing away from the silicon substrate; one or more waveguides are embedded within the optical waveguide layer between the first and second grooves. Because there are no overhanging structures or cantilever beam structures directly below the optical waveguide layer between the first and second grooves, the edge coupler exhibits enhanced mechanical performance. Furthermore, along the thickness direction of the silicon substrate, the first and second grooves extend deep into the silicon substrate from the first surface to confine lateral light fields, reducing leakage of the optical field from the edge coupler into the silicon substrate and thereby improving the optical coupling efficiency of the edge coupler.

[0072] Furthermore, a layer of silicon nitride may be covered on the optical waveguide layer of the edge coupler and in the first groove and the second groove as a protective layer, thereby improving the water vapor resistance of the edge coupler and extending the normal working life of the edge coupler.

[0073] The above is only a preferred embodiment of the present invention and is not intended to limit the scope of implementation of the present invention. All equivalent changes and modifications based on the shape, structure, characteristics and spirit described in the claims of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A side coupler, It is characterized in that include: A silicon substrate, a silicon oxide buried layer and an optical waveguide layer are sequentially stacked; In the thickness direction of the silicon substrate, the optical waveguide layer has a first surface facing away from the silicon substrate, a first groove and a second groove are provided on the first surface, and one or more waveguides are embedded in the optical waveguide layer between the first groove and the second groove; Along a thickness direction perpendicular to the silicon substrate, the edge coupler has an outer end surface coupled to the outside, the waveguide extends from the inside of the edge coupler to the outer end surface, and the waveguide is configured to have a first mode size on a side away from the outer end surface of the edge coupler and a second mode size on a side close to the outer end surface of the edge coupler, wherein the first mode size is larger than the second mode size; Wherein, along the thickness direction perpendicular to the silicon substrate, both the first groove and the second groove penetrate the edge coupler, and along the thickness direction of the silicon substrate, both the first groove and the second groove extend from the first surface into the silicon substrate.

2. The edge coupler according to claim 1, It is characterized in that The first groove and the second groove extend into the silicon substrate to a thickness of 10-40 μm.

3. The edge coupler according to claim 2, It is characterized in that The depth of the first groove is defined as d1, and the width of the first groove is defined as w1, wherein 2≤d1 / w1≤5; The depth of the second groove is defined as d2, and the width of the second groove is defined as w2, wherein 2≤d2 / w2≤5.

4. The edge coupler as claimed in claim 3, It is characterized in that The ratio of the depth to the width of the first groove and the second groove is equal.

5. The side coupler according to any one of claims 1 to 4, It is characterized in that The first groove and the second groove are filled with epoxy resin.

6. The edge coupler according to claim 1, It is characterized in that Each of the waveguides is any one of a silicon waveguide, a silicon nitride waveguide, a silicon oxynitride waveguide, and a lithium niobate waveguide.

7. The edge coupler according to claim 6, It is characterized in that At least a portion of each of the waveguides includes an inverted wedge-shaped structure pointing from the interior of the edge coupler toward the outer end surface.

8. The edge coupler according to claim 7, It is characterized in that Each of the waveguides is in an inverted wedge-shaped structure.

9. The side coupler according to claim 7 or 8, It is characterized in that A plurality of waveguides are embedded side by side on one side of the optical waveguide layer close to the silicon oxide buried layer.

10. The edge coupler according to claim 9, It is characterized in that A plurality of waveguides are configured to be flush at ends proximate to the outer end surface of the edge coupler.

11. The edge coupler according to claim 1, It is characterized in that The optical waveguide layer is silicon dioxide.

12. The side coupler of claim 11, It is characterized in that Also includes: a protective layer, the protective layer covering the optical waveguide layer of the edge coupler; Wherein, the material of the protective layer is silicon nitride.

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