Grating couplers and optical chips

Abstract

The present application relates to the technical field of grating couplers, and in particular to a grating coupler and an optical chip. The grating coupler includes: a substrate; a reflective grating structure located on one side of the substrate, the reflective grating structure including a plurality of first grating units spaced apart; a transmission grating structure located on the side of the reflective grating structure away from the substrate, the transmission grating structure including a plurality of second grating units spaced apart, at least some of the first grating units being arranged correspondingly to the second grating units. The present application sets at least some of the first grating units to correspond to the second grating units, so that when the transmission grating structure is formed, there is no residue between adjacent second grating units, so that the second grating units are etched more cleanly, thereby improving the directionality and coupling efficiency of the grating coupler. Specifically, in the present application, the orthographic projection of at least some of the first grating units on the substrate can be set within the orthographic projection of the second grating units on the substrate.

Description

Technical Field

[0001] The present application relates to the technical field of grating couplers, and in particular to a grating coupler and an optical chip. Background Art

[0002] Optical fiber, the primary medium for optical signal transmission, is typically designed to support low-loss propagation of optical signals within its core. Optical waveguides are used to guide, couple, modulate, and detect optical signals. In related technologies, due to the significant mismatch between the optical fiber's mode field and that of the waveguide, a coupler is required to couple light from the optical fiber into the waveguide. However, the coupling efficiency of these couplers is low.

[0003] Therefore, how to optimize the structure of the coupler to make it more efficient has become an urgent problem to be solved. Summary of the Invention

[0004] Based on this, it is necessary to provide a grating coupler and an optical chip to address the problem of low efficiency of couplers in the prior art.

[0005] In order to achieve the above object, a grating coupler is provided, comprising:

[0006] substrate;

[0007] a reflective grating structure, located on one side of the substrate, the reflective grating structure comprising a plurality of first grating units arranged at intervals;

[0008] A transmission grating structure is located on a side of the reflection grating structure away from the substrate, wherein the transmission grating structure includes a plurality of second grating units arranged at intervals, and at least some of the orthographic projections of the second grating units on the substrate are located within the orthographic projections of the first grating units on the substrate.

[0009] In one embodiment, the first grating units are arranged in a first period, the second grating units are arranged in a second period, and the first period is equal to the second period.

[0010] In one embodiment, the material of the transmission grating structure includes silicon nitride, and the material of the reflection grating structure includes silicon.

[0011] In one embodiment, the grating coupler further comprises:

[0012] The waveguide structure is arranged in the same layer as the transmission grating structure. The transmission grating structure has a light incident end and a light exit end that are arranged opposite to each other. The waveguide structure is located at the light exit end of the transmission grating structure.

[0013] In one embodiment, the reflective grating structure extends below the waveguide structure.

[0014] In one embodiment, the reflective grating structure includes a first connecting structure, the first connecting structure is used to connect adjacent first grating units, and the height of the first connecting structure is lower than the height of the first grating units;

[0015] and / or,

[0016] The transmission grating structure includes a second connecting structure, where the second connecting structure is used to connect adjacent second grating units, and a height of the second connecting structure is lower than a height of the second grating units.

[0017] In one embodiment, the grating coupler comprises:

[0018] a first upper cladding layer, covering the reflective grating structure and filling between adjacent first grating units;

[0019] The second upper cladding layer covers the transmission grating structure and fills the space between adjacent second grating units.

[0020] In one embodiment, the material of the first upper cladding layer and the second upper cladding layer includes silicon dioxide.

[0021] In one embodiment, the grating coupler comprises:

[0022] The lower cladding layer is located between the reflective grating structure and the substrate.

[0023] On the other hand, an optical chip is further provided, comprising the grating coupler provided in any of the aforementioned embodiments.

[0024] The grating coupler and optical chip of the present application have the following beneficial effects: First, by arranging at least part of the first grating unit to correspond to the second grating unit, when forming the transmission grating structure, there is no residue between the adjacent second grating units, so that the second grating unit is etched more cleanly, thereby improving the directionality and coupling efficiency of the grating coupler. Specifically, in the present application, the orthographic projection of at least part of the first grating unit on the substrate can be arranged to be located within the orthographic projection of the second grating unit on the substrate, so that the second grating unit is etched more cleanly. Secondly, in the present application, by stacking the reflective grating structure and the transmission grating structure, the reflective grating structure reflects light to the transmission grating structure, thereby increasing the utilization rate of light and further improving the coupling efficiency of the grating coupler. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the conventional technology, the following briefly introduces the drawings required for use in the embodiments or the conventional technology descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 is a schematic diagram of a grating coupler provided in one embodiment;

[0027] Figure 2 is a schematic diagram of a first connection structure provided in one embodiment;

[0028] Figure 3 is a schematic diagram of a second connection structure provided in one embodiment;

[0029] Figure 4 is a schematic diagram of a first connection structure and a second connection structure provided in one embodiment;

[0030] Figure 5 A schematic diagram of a grating coupler test provided in one embodiment;

[0031] Figure 6 is a flow chart of a method for preparing a grating coupler provided in one embodiment;

[0032] Figure 7 FIG. 1 is a schematic diagram of a grating coupler provided in another embodiment.

[0033] Explanation of the reference numerals: grating coupler-100; substrate-110; reflective grating structure-120; first connecting structure-121; transmission grating structure-130; second connecting structure-131; waveguide structure-140; first upper cladding-151; second upper cladding-152; lower cladding-153.

[0034] In order to better describe and illustrate the embodiments and / or examples of the inventions disclosed herein, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the accompanying drawings should not be considered to limit the scope of the disclosed inventions, the presently described embodiments and / or examples, and any of the best modes currently understood for these inventions. DETAILED DESCRIPTION

[0035] To facilitate understanding of the present application, a more comprehensive description of the present application will be provided below with reference to the accompanying drawings. The drawings illustrate preferred embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present disclosure.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0037] In each embodiment, unless otherwise specified or limited, the terms "installed," "connected," "connected," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediate medium; internal communication between two elements, or interaction between two elements, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in each embodiment based on the specific circumstances.

[0038] It should be understood that when an element or layer is referred to as being "on, adjacent to, connected to, or coupled to" another element or layer, it may be directly on, adjacent to, connected to, or coupled to the other element or layer, or there may be intervening elements or layers. In contrast, when an element is referred to as being "directly on, directly adjacent to, directly connected to, or directly coupled to" another element or layer, there may be no intervening elements or layers. It should be understood that although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers, doping types, and / or portions, these elements, components, regions, layers, doping types, and / or portions should not be limited by these terms. These terms are merely used to distinguish one element, component, region, layer, doping type, or portion from another element, component, region, layer, doping type, or portion. Therefore, without departing from the teachings of the present embodiment, the first element, component, region, layer, doping type, or portion discussed below may be represented as a second element, component, region, layer, or portion.

[0039] Spatially relative terms such as "below," "beneath," "beneath," "above," "above," etc., may be used herein to describe the relationship of an element or feature shown in the figures to other elements or features. It should be understood that in addition to the orientations shown in the figures, spatially relative terms also include different orientations of the device in use and operation. For example, if the device in the drawings is turned over, an element or feature described as "below" or "beneath" or "beneath" the other elements will be oriented "above" the other elements or features. Thus, the exemplary terms "below" and "below" can include both the above and below orientations. In addition, the device can also include alternative orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptors used herein are to be interpreted accordingly.

[0040] As used herein, the singular forms "a," "an," and "the" may also include the plural forms, unless the context clearly indicates otherwise. It should also be understood that when the terms "comprising" and / or "including" are used in this specification, they may specify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. At the same time, when used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0041] Embodiments of the present application are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the present application. Variations from the illustrated shapes due to, for example, manufacturing techniques and / or tolerances are to be expected. Thus, embodiments of the present application should not be limited to the specific shapes of regions illustrated herein but are intended to include deviations in shapes due to, for example, manufacturing techniques. The regions shown in the figures are schematic in nature, and their shapes do not represent the actual shapes of regions of a device and do not limit the scope of the embodiments of the present application.

[0042] As mentioned in the background art, the grating coupler changes the transmission direction of the light field through Bragg diffraction and couples the light into the waveguide. The inventors have found that when etching to form a grating coupler, the etching is often not clean, thereby forming residues in the grating coupler. The residue may cause irregular oscillations in the coupling efficiency curve of the grating coupler, making it difficult to de-embed the coupling loss of the grating coupler. Specifically, when preparing a grating coupler, a reflective grating structure is first prepared (the reflective grating structure includes a plurality of first grating units spaced apart), and then a material layer of a transmission grating structure is formed on the entire surface above the reflective grating structure. Thereafter, the material layer is etched to form a transmission grating structure. At this time, the inventors found that when etching the material layer above adjacent first grating units, the material layer is difficult to etch cleanly, thereby forming residues, which affects the coupling efficiency of the grating coupler.

[0043] Based on this, in one embodiment, see Figures 1 to 4 , a grating coupler 100 is provided. The grating coupler 100 may include a substrate 110, a reflective grating structure 120, and a transmission grating structure 130.

[0044] The substrate 110 may be made of a semiconductor material. For example, the substrate 110 may include silicon, silicon germanium, silicon germanium carbon, silicon carbide, etc. Alternatively, for example, the substrate 110 may be a layered substrate 110 including silicon on insulator (SOI) or silicon germanium on insulator.

[0045] The reflective grating structure 120 may be located on one side of the substrate 110. The reflective grating structure 120 may be configured to reflect light away from the substrate 110. For example, the reflective grating structure 120 may extend along a first direction. The reflective grating structure 120 may be made of silicon, for example. The reflective grating structure 120 may include a plurality of first grating units spaced apart from each other. This embodiment does not limit the specific size of the first grating units, nor does it limit the distance between adjacent first grating units.

[0046] The transmission grating structure 130 can be located on a side of the reflective grating structure 120 away from the substrate 110. The transmission grating structure 130 can be used to transmit light. For example, the reflective grating structure 120 can extend along a first direction. Materials for the transmission grating structure include silicon nitride, etc. The transmission grating structure 130 can include a plurality of second grating units spaced apart from each other.

[0047] Specifically, at least some of the first grating units are arranged correspondingly to the second grating units. As an example, the first grating units and the second grating units can be arranged in a one-to-one correspondence.

[0048] Furthermore, at least a portion of the orthographic projections of the first grating elements on substrate 110 are located within the orthographic projections of the second grating elements on substrate 110. In one possible example, the cross-sectional area of the first grating elements can be less than or equal to the cross-sectional area of the second grating elements. In another possible example, no first grating elements are exposed between adjacent second grating elements. Furthermore, the first grating elements are arranged in a first period, and the second grating elements are arranged in a second period, with the first period being equal to the second period. This embodiment does not limit the first and second periods, nor does it limit parameters such as the duty cycle of the first and second grating elements.

[0049] In this embodiment, first, by arranging at least some of the first grating units to correspond to the second grating units, no residue remains between adjacent second grating units when forming the transmission grating structure 130, allowing for cleaner etching of the second grating units, thereby improving the directivity and coupling efficiency of the grating coupler 100. Furthermore, in this embodiment, the orthographic projections of at least some of the first grating units on the substrate 110 can be arranged within the orthographic projections of the second grating units on the substrate 110, thereby further improving the etching of the second grating units. Secondly, in this embodiment, by stacking the reflective grating structure 120 and the transmission grating structure 130, the reflective grating structure 120 reflects light toward the transmission grating structure 130, thereby increasing light utilization and further improving the coupling efficiency of the grating coupler 100.

[0050] Also, in a possible example, see Figure 2 、 Figure 3 and Figure 4The reflective grating structure 120 includes a first connecting structure 121, which is used to connect adjacent first grating units. The height of the first connecting structure 121 is lower than the height of the first grating units. In another possible example, the transmission grating structure 130 includes a second connecting structure 131, which is used to connect adjacent second grating units. The height of the second connecting structure 131 is lower than the height of the second grating units.

[0051] Understandable, see Figure 2 、 Figure 3 and Figure 4 The reflective grating structure 120 and the transmission grating structure 130 can be arranged continuously. In the above two examples, there is no limitation on the specific application scenarios of the first connecting structure 121 and the second connecting structure 131, nor on the specific dimensions of the first connecting structure 121 and the second connecting structure 131. In other words, the first connecting structure 121 and the second connecting structure 131 can be arranged according to needs.

[0052] See also Figure 5 Testing of the grating coupler in this embodiment shows that, for the O-band, the grating coupler's peak coupling efficiency is -1.25 dB (75%), 37% higher than that of a single-layer silicon nitride grating coupler. Its 1 dB bandwidth is 40 nm, and its 3 dB bandwidth is close to 100 nm. This shows that the grating coupler 100 in this embodiment is adaptable to the O-band. Furthermore, this embodiment does not limit the scope of application of the grating coupler 100.

[0053] In one embodiment, see Figure 1 , the grating coupler 100 further includes a waveguide structure 140 .

[0054] The waveguide structure 140 can be disposed in the same layer as the transmission grating structure 130. The waveguide structure 140 can be used to guide light emitted from the transmission grating structure 130. For example, the transmission grating structure 130 has a light input end and a light output end oppositely disposed, and the waveguide structure 140 can be located at the light output end of the transmission grating structure 130. Specifically, the waveguide structure 140 can be spaced apart from the last second grating unit at the light output end. The material of the waveguide structure 140 can be the same as that of the transmission grating structure 130. For example, the material of the waveguide structure 140 can include silicon nitride, etc.

[0055] The reflective grating structure 120 may extend to below the waveguide structure 140. As an example, at least one first grating unit in the reflective grating structure 120 may be located below the waveguide structure 140.

[0056] In this embodiment, the waveguide structure 140 is disposed in the same layer as the transmission grating structure 130, so that the waveguide structure 140 can directionally guide the light emitted from the transmission grating structure 130, thereby improving the coupling efficiency of the grating coupler 100. Furthermore, in this embodiment, the reflective grating structure 120 can extend below the waveguide structure 140, so that the reflective grating structure 120 can reflect more light, thereby allowing the waveguide structure 140 to directionally guide more light.

[0057] In one embodiment, see Figure 1 The grating coupler 100 includes a first upper cladding layer 151 , a second upper cladding layer 152 , and a lower cladding layer 153 .

[0058] The first upper cladding layer 151 may cover the reflective grating structure 120 and fill the space between adjacent first grating units. As an example, the material of the first upper cladding layer 151 may include silicon dioxide, etc. Furthermore, the side of the first upper cladding layer 151 facing away from the substrate 110 may have a flat surface.

[0059] The second upper cladding layer 152 may cover the transmission grating structure 130 and fill the gaps between adjacent second grating units. As an example, the material of the second upper cladding layer 152 may include silicon dioxide or the like.

[0060] The lower cladding layer 153 may be located between the reflective grating structure 120 and the substrate 110. As an example, the material of the lower cladding layer 153 may include silicon dioxide or the like.

[0061] This embodiment does not limit the specific thicknesses of the first upper cladding layer 151, the second upper cladding layer 152, and the lower cladding layer 153. In addition, the grating coupler 100 may also have other film layers.

[0062] In this embodiment, by providing film layers such as the first upper cladding layer 151, the second upper cladding layer 152, and the lower cladding layer 153, structures such as the reflective grating structure 120 and the transmission grating structure 130 are protected, and the external environment is prevented from affecting the reflective grating structure 120 and the transmission grating structure 130, thereby improving the transmission efficiency of light.

[0063] Based on the same inventive concept, please refer to Figure 6 In one embodiment, a method for preparing a grating coupler 100 is provided. The method for preparing the grating coupler 100 mainly includes the following steps:

[0064] Step S2: providing a substrate 110 .

[0065] Step S4: forming a reflective grating structure 120 on the substrate 110. The reflective grating structure 120 extends along a first direction. The reflective grating structure 120 includes a plurality of first grating units arranged at intervals.

[0066] Step S6 : forming a transmission grating structure 130 on the reflection grating structure 120 . The transmission grating structure 130 extends along the first direction and includes a plurality of second grating units arranged at intervals. At least some of the first grating units are arranged corresponding to the second grating units.

[0067] In step S2, see Figure 1 As an example, substrate 110 may be made of a semiconductor material. As an example, substrate 110 may include silicon, silicon germanium, silicon germanium carbon, silicon carbide, etc. Alternatively, as another example, substrate 110 may be a layered substrate 110 including silicon on insulator (SOI) or silicon germanium on insulator.

[0068] In step S4, a silicon layer may be formed on the substrate 110 using a deposition process, and then the silicon layer may be etched to form the reflective grating structure 120. For example, the deposition process may include, but is not limited to, one or more of chemical vapor deposition, atomic layer deposition, high-density plasma deposition, plasma-enhanced chemical vapor deposition (PECVD), and spin-on dielectric layer processing. For example, the etching process may include at least one of reactive ion etching, inductively coupled plasma etching, or high-density plasma etching.

[0069] Afterwards, a silicon dioxide layer with a fixed thickness may be grown by PECVD or thermal oxidation to serve as the first upper cladding layer 151 of the reflective grating structure 120 , and the first upper cladding layer 151 may be planarized by chemical mechanical polishing (CMP).

[0070] In step S6, a silicon nitride layer of a fixed thickness is deposited on the polished first upper cladding layer 151 using PECVD or low-pressure chemical vapor deposition (LPCVD). The transmission grating structure 130 is then fabricated on the silicon nitride layer through photolithography and etching processes. Furthermore, the waveguide structure 140 may be formed simultaneously.

[0071] Afterwards, a silicon dioxide layer may be deposited by PECVD as the second upper cladding layer 152 , and the second upper cladding layer 152 may be planarized by CMP.

[0072] See also Figure 1, at least some of the first grating units are arranged corresponding to the second grating units. In one possible example, at this time, the cross-sectional area of the first grating units can be less than or equal to the cross-sectional area of the second grating units. In another possible example, at this time, no first grating units are exposed between adjacent second grating units. Furthermore, the first grating units are arranged in a first period, and the second grating units are arranged in a second period, and the first period is equal to the second period. This embodiment does not limit the first period and the second period, nor does it limit parameters such as the duty cycle of the first grating units and the second grating units.

[0073] It should be understood that although Figure 6 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. In addition, Figure 6 At least part of the steps may include multiple steps or multiple stages. These steps or stages are not necessarily performed at the same time, but can be performed at different times. The order of execution of these steps or stages is not necessarily one by one, but can be performed in turn or alternately with other steps or at least part of the steps or stages in other steps.

[0074] Based on the same inventive concept, in one embodiment, an optical chip is provided, which includes a grating coupler 100 formed by combining any one or several embodiments in the present application.

[0075] As an example, a structure such as an optical fiber may be provided at the light incident end of the transmission grating structure 130 of the grating coupler 100 .

[0076] Also, see Figure 7 In other cases, the etching process can be improved to eliminate residues between adjacent second grating units. In this case, the orthographic projection of the second grating unit on substrate 110 can overlap with the orthographic projection of the first grating unit on substrate 110. Furthermore, the first grating unit and the second grating unit can have the same period but be staggered.

[0077] In the description of this application, the reference terms "some embodiments", "other embodiments", "ideal embodiments", etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this application, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. In addition, these specific features, structures or characteristics can be combined in one or more embodiments in any suitable manner. It should be understood that "this embodiment" or "one embodiment" mentioned throughout the specification means that the specific features, structures or characteristics related to the embodiment are included in at least one embodiment of the present application. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment.

[0078] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features of the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of the present application.

[0079] The embodiments described above only express several implementation methods of the present application, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all fall within the scope of protection of the present application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims. The above description is only the preferred implementation method of the present application, and does not limit the scope of the patent in this application. All equivalent structural transformations made by using the contents of the description and drawings of this application under the inventive concept of this application, or direct / indirect application in other related technical fields are included in the scope of protection of the patent in this application.

Claims

1. A grating coupler, characterized in that: include: substrate; a reflective grating structure, located on one side of the substrate, the reflective grating structure comprising a plurality of first grating units arranged at intervals; a transmission grating structure located on a side of the reflective grating structure away from the substrate, the transmission grating structure comprising a plurality of second grating units arranged at intervals, at least some of the first grating units being arranged corresponding to the second grating units, and at least some of the first grating units having a smaller cross-sectional area than the second grating units; A first upper cladding layer covers the reflective grating structure and fills between adjacent first grating units so that the reflective grating structure is spaced apart from the transmission grating structure. The first grating units are arranged in a first period, and the second grating units are arranged in a second period, and the first period is equal to the second period.

2. The grating coupler according to claim 1, wherein The material of the transmission grating structure includes silicon nitride, and the material of the reflection grating structure includes silicon.

3. The grating coupler according to claim 1, wherein The grating coupler further comprises: The waveguide structure is arranged in the same layer as the transmission grating structure. The transmission grating structure has a light incident end and a light exit end that are arranged opposite to each other. The waveguide structure is located at the light exit end of the transmission grating structure.

4. The grating coupler according to claim 3, wherein The reflective grating structure extends below the waveguide structure.

5. The grating coupler according to claim 4, characterized in that The waveguide structure is spaced apart from the last second grating unit at the light emitting end.

6. The grating coupler according to claim 1, wherein The reflective grating structure includes a first connecting structure, wherein the first connecting structure is used to connect adjacent first grating units, and a height of the first connecting structure is lower than a height of the first grating units; and / or, The transmission grating structure includes a second connecting structure, where the second connecting structure is used to connect adjacent second grating units, and a height of the second connecting structure is lower than a height of the second grating units.

7. The grating coupler according to claim 1, wherein The grating coupler comprises: The second upper cladding layer covers the transmission grating structure and fills the space between adjacent second grating units.

8. The grating coupler according to claim 1, wherein The grating coupler comprises: The lower cladding layer is located between the reflective grating structure and the substrate.

9. An optical chip, characterized in that: The optical chip comprises the grating coupler according to any one of claims 1 to 8.

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