Edge coupler with metamaterial rib features

Abstract

The present invention relates to an edge coupler having metamaterial rib features, providing a structure of an edge coupler and a method of manufacturing a structure of an edge coupler. A waveguide core includes a waveguide core segment having a first notched sidewall, a second notched sidewall, and an end surface connecting the first notched sidewall and the second notched sidewall. A segment is disposed adjacent the end surface of the waveguide core segment in a spaced apart arrangement, and a plate layer abuts the segment, the first notched sidewall of the waveguide core segment, the second notched sidewall of the waveguide core segment, and the end surface of the waveguide core segment. The segment and the waveguide core segment have a first thickness, and the plate layer has a second thickness that is less than the first thickness.

Description

TECHNICAL FIELD

[0001] The present invention relates to photonic chips, and more particularly to structures of edge couplers and methods of fabricating structures of edge couplers. BACKGROUND

[0002] Photonic chips are used in many applications and systems, including but not limited to data communication systems and data computing systems. Photonic chips integrate optical components (e.g., waveguides, photodetectors, modulators, and optical power splitters) with electronic components (e.g., field effect transistors) on a unified platform. Among other factors, layout area, cost, and operational overhead can be reduced by integrating both types of components on the same chip.

[0003] Edge couplers (also known as spot-size converters) are commonly used to couple light of a given mode from a laser or an optical fiber to an optical component on a photonic chip. The edge coupler can include a waveguide core segment that defines an inverse taper and is disposed adjacent to the laser or the optical fiber. An inverse taper refers to a tapered segment of a waveguide core characterized by a width that gradually increases in the direction of mode propagation. In the edge coupler configuration, the narrow end of the inverse taper provides an end face that is arranged adjacent to the laser or the optical fiber, and the wide end of the inverse taper is connected to another waveguide core segment to route the light to the optical component of the photonic chip.

[0004] As light is transported from the laser or the optical fiber to the photonic chip, the gradually varying cross-sectional area of the inverse taper supports mode conversion and mode size change associated with mode conversion. The narrow end at the top end of the inverse taper does not completely confine the incident mode because the cross-sectional area at the top end of its narrow end is smaller than the mode size. As a result, a significant portion of the electromagnetic field of the incident mode is distributed around the top end of the inverse taper. As the width increases, the inverse taper can support the entire incident mode and eventually confines the electromagnetic field inside the inverse taper.

[0005] Edge couplers can exhibit significant insertion loss, and significant back reflection at the end face. Edge couplers can be characterized by low coupling efficiency due to mismatch of mode shape and mode size with the laser or the optical fiber. Edge couplers can also be susceptible to power-related damage due to poor power handling capability. Edge couplers can also have low fabrication tolerance, and become long and occupy excessive space in the layout area.

[0006] There is a need for improved structures of edge couplers and methods of fabricating structures of edge couplers. SUMMARY

[0007] In one embodiment of the present invention, a structure of an edge coupler is provided. The structure includes a waveguide core having a waveguide core segment. The waveguide core segment has a first notched sidewall, a second notched sidewall, and an end surface connecting the first notched sidewall and the second notched sidewall. The structure also includes a plurality of segments disposed in a spaced apart arrangement proximate the end surface of the waveguide core segment, and a slab layer abutting the plurality of segments, the end surface of the waveguide core segment, the first notched sidewall of the waveguide core segment, and the second notched sidewall of the waveguide core segment. The plurality of segments and the waveguide core segment have a first thickness, and the slab layer has a second thickness less than the first thickness.

[0008] In one embodiment of the present invention, a method of forming a structure of an edge coupler is provided. The method includes forming a waveguide core having a waveguide core segment. The waveguide core segment has a first notched sidewall, a second notched sidewall, and an end surface connecting the first notched sidewall and the second notched sidewall. The method also includes forming a plurality of segments disposed in a spaced apart arrangement proximate the end surface of the waveguide core segment. The method also includes forming a slab layer abutting the plurality of segments, the end surface of the waveguide core segment, the first notched sidewall of the waveguide core segment, and the second notched sidewall of the waveguide core segment. The plurality of segments and the waveguide core segment have a first thickness, and the slab layer has a second thickness less than the first thickness. BRIEF DESCRIPTION OF DRAWINGS

[0009] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various embodiments of the application and, together with the general description of the application given above, and the detailed description of the embodiments given below, serve to explain the embodiments of this application. In these drawings:

[0010] Figure 1 A top view of a structure in an initial fabrication stage of a process method in accordance with an embodiment of the present invention is shown.

[0011] Figure 2 A cross-sectional view of the structure taken generally along line 2-2 in Figure 1

[0012] A cross-sectional view of the structure taken generally along line 2A-2A in Figure 2A Figure 1 A cross-sectional view of the structure taken generally along line 2B-2B in

[0013] Figure 2B Figure 1 A cross-sectional view of the structure taken generally along line 2B-2B in

[0014] Figure 2C A cross-sectional view of the structure taken generally along line 2B-2B in Figure 1 ​​The cross-sectional view of the structure is taken along line 2C-2C.

[0015] Figure 2D Showing the general outline Figure 1 The cross-sectional view of the structure is drawn using the 2D-2D line.

[0016] Figure 3 , Figure 3A , Figure 3B , Figure 3C , Figure 3D Display in Figure 2 , Figure 2A , Figure 2B , Figure 2C , Figure 2D A cross-sectional view of the structure during the manufacturing stage of this process method.

[0017] Figure 4 Display in Figure 3 A cross-sectional view of the structure during the manufacturing stage of this process method.

[0018] Figure 5 A top view showing a structure according to an alternative embodiment of the present invention.

[0019] Figure 6 Showing the general outline Figure 5 The cross-sectional view of the structure is shown in line 6-6.

[0020] Figure 7 A top view showing a structure according to an alternative embodiment of the present invention. Detailed Implementation

[0021] Please refer to Figure 1 , Figure 2 , Figure 2A , Figure 2B , Figure 2C , Figure 2D According to an embodiment of the present invention, the structure 10 of the edge coupler includes a plurality of segments 12 and a waveguide core 28 having waveguide core segments 16 and 18. The segments 12 and waveguide core segments 16, 18 may be arranged longitudinally along the longitudinal axis 20. The waveguide core segment 16 is longitudinally disposed between the segments 12 and the waveguide core segment 18. The structure 10 may have a length ranging from two hundred (200) micrometers to three (3) millimeters.

[0022] Laser can be drawn from source 22 ( Figure 4The laser is laterally guided toward structure 10. The laser may have a given wavelength, intensity, mode shape, and mode size, and structure 10 may provide spot size conversion for the laser. In one embodiment, source 22 may be a semiconductor laser. In one embodiment, source 22 may be an optical fiber. Source 22 is arranged adjacent to structure 10 after subsequent manufacturing stages and during subsequent assembly stages, as described below. The gap or void between source 22 and structure 10 may be filled with air or a refractive index-matching material, or may include one or more lenses.

[0023] Segment 12 is located as a feature in the portion of structure 10 that initially receives the laser from source 22. One of segments of 12 terminates structure 10 to define an end face, and source 22 ( Figure 4 Finally, it is positioned adjacent to this end face. Light propagates within structure 10 in a direction from segment 12 toward waveguide core segments 16, 18. Segments 12 form discrete posts spaced apart along the longitudinal axis 20. Adjacent pairs of segments 12 are separated by gaps. Each segment 12 has opposing sidewalls 80 adjacent to the gap, and opposing sidewalls 82 on its sides. In one embodiment, segment 12 may be centered relative to the longitudinal axis 20.

[0024] Waveguide segment 16 is located within a portion of structure 10 to transmit the laser from segment 12 to waveguide segment 18. Waveguide segment 16 includes notched sidewalls 88 and end surfaces 86 extending between and connecting the notched sidewalls 88. Waveguide segment 16 is a "fishbone" structure, comprising a series of protrusions 14 as features arranged along opposing notched sidewalls 88 of each waveguide segment. Opposing notched sidewalls 88 include notches or grooves to define notches between adjacent pairs of protrusions 14. Segments 12 may be arranged in a row adjacent to end surfaces 86, and end surfaces 86 may terminate waveguide segment 16. Protrusions 14 are arranged at corresponding intervals along longitudinal axis 20 and extend outward in a corresponding direction perpendicular to longitudinal axis 20. In one embodiment, waveguide segment 16 may be centered relative to longitudinal axis 20.

[0025] Fragments 12 can have a width dimension Wl measured between opposing sidewalls 80, and waveguide core segment 16 can have a width dimension W2 measured between opposing notched sidewalls 88 thereof. Fragments 12 can be grouped into a group 44 at the end of structure 10 that includes the end face, and a group 46 disposed between group 44 and waveguide core segment 16. In one embodiment, the width dimension Wl of fragments 12 in group 46 can be greater than the width dimension Wl of fragments 12 in group 44. In one embodiment, the width dimension Wl of fragments 12 can vary in a range from about 0.07 times to about 0.16 times the wavelength of the light received from source 22. In one embodiment, the width dimension W2 of waveguide core segment 16 can vary in a range from about 0.2 times to about 0.28 times the wavelength of the light received from source 22. The wavelength of the light received by structure 10 can be, for example, in a range from 1260 nanometers to 1360 nanometers (O-band).

[0026] In one embodiment, the pitch and duty cycle of fragments 12 can be uniform to define a periodic arrangement. In alternative embodiments, the pitch and / or duty cycle of fragments 12 can be apodized (i.e., non-uniform) to define a non-periodic arrangement. In one embodiment, fragments 12 can have a rectangular patterned shape. In alternative embodiments, fragments 12 can have different patterned shapes, such as an elliptical shape or a trapezoidal shape.

[0027] Waveguide core segment 16 can have a portion 48 adjacent to fragments 12 and a portion 50 adjacent to waveguide core segment 18. The notches between adjacent protrusions 14 extend laterally inward (i.e., perpendicular to longitudinal axis 20) to a greater depth in portion 48 than in portion 50. In one embodiment, the pitch and duty cycle of protrusions 14 can be uniform to define a periodic arrangement. In alternative embodiments, the pitch and / or duty cycle of protrusions 14 can be apodized (i.e., non-uniform) to define a non-periodic arrangement. In one embodiment, the pitch and duty cycle of protrusions 14 can be different than the pitch and duty cycle of fragments 12. In one embodiment, protrusions 14 can have a rectangular patterned shape. In alternative embodiments, protrusions 14 can have different patterned shapes, such as an elliptical shape or a trapezoidal shape.

[0028] The waveguide core segment 18 (continuous and unbroken) can have opposing sidewalls 90 and a width dimension W3 that varies (i.e., is inversely tapered) with position along the longitudinal axis 20 in the direction of light propagation. In one embodiment, the width dimension W3 of the waveguide core segment 18 can increase with increasing distance from the waveguide core segment 16. In one embodiment, the width dimension W3 of the waveguide core segment 18 can vary along its length based on a linear function to provide a trapezoidal shape with a trapezoidal profile viewed in the vertical direction. In an alternative embodiment, the width dimension W3 of the waveguide core segment 18 can vary along its length based on a non-linear function (e.g., quadratic, parabolic, or exponential function).

[0029] The segments 12 and waveguide core 28 can be disposed above a dielectric layer 24. In one embodiment, the dielectric layer 24 can be composed of silicon dioxide. In one embodiment, the dielectric layer 24 can be a buried oxide layer of a silicon-on-insulator substrate, and the silicon-on-insulator substrate can further include an operational substrate 25 composed of a semiconductor material (e.g., monocrystalline silicon).

[0030] The segments 12 and waveguide core 28 can be composed of a semiconductor material, such as monocrystalline silicon. In one embodiment, the segments 12 and waveguide core 28 can be formed simultaneously by patterning a monocrystalline silicon device layer of a silicon-on-insulator substrate using photolithography and etching processes. In one embodiment, the segments 12 and waveguide core 28 can be patterned from the device layer by photolithography and etching processes without etching completely through the device layer, thereby initially forming the slab layer 26, and subsequently, the slab layer 26 can be patterned to shape by a separate set of photolithography and etching processes. When patterning the slab layer 26, the dielectric layer 24 can act as an etch stop layer.

[0031] The slab layer 26 is thinner than the segments 12 and waveguide core segments 16, 18. In one embodiment, the slab layer 26 has a thickness Tl that is significantly less than the thickness T2 of the segments 12 and waveguide core segments 16, 18. The slab layer 26 abuts the lower portions of the segments 12 and waveguide core 28 along a height equal to the thickness Tl. In particular, the slab layer 26 includes a portion 70 that abuts the lower portion of the segment 12 located at the sidewalls 80, 82, a portion 72 that abuts the lower portion of the waveguide core segment 16 located at the notched sidewall 88 and end surface 86, and a portion 74 that abuts the lower portion of the waveguide core segment 18 located at the sidewall 90. The segment 12 is embedded (i.e., surrounded by) the portion 70 of the slab layer 26 along the thickness Tl. The portion 72 of the slab layer 26 is disposed partially within the notch in the notched sidewall 88 of the waveguide core segment 16.

[0032] The slab layer 26 has a side edge 91 and a side edge 92 opposite the side edge 91. The segments 12 and waveguide core segments 16, 18 are disposed laterally between the side edges 91 and 92 and spaced inwardly from the side edges. The slab layer 26 has a width dimension W4 between the side edges 91, 92 that varies between different portions 70, 72, 74 of the slab layer 26. The portion 70 of the slab layer 26 can be tapered so that the width dimension W4 of the portion 70 of the slab layer 26 increases with increasing distance from the end face. In one embodiment, the portion 72 of the slab layer 26 can be non-tapered so that the width dimension W4 of the portion 72 of the slab layer 26 is constant. The portion 74 of the slab layer 26 can be tapered so that the width dimension W4 of the portion 74 of the slab layer 26 increases with increasing distance from the portion 72.

[0033] The segments 12, waveguide core segments 16, 18, and slab layer 26 define a rib waveguide structure. The waveguide core 28 guides the laser light from the structure 10 to other optical components on the photonic chip, such as a modulator or a photodetector.

[0034] The segments 12 and protrusions 14 can be disposed at a small enough spacing along the longitudinal axis 20 so as not to radiate or reflect light at the operating wavelength and act as an effective optical material known as a metamaterial. The segments 12 and protrusions 14 along with the adjoining slab layer 26 define a metamaterial rib feature in the structure 10. The segments 12 effectively provide a subwavelength tapered grating because the dimensions of the features are smaller than the wavelength of light. The protrusions 14 effectively provide another subwavelength grating because the dimensions of the features are smaller than the wavelength of light.

[0035] In alternative embodiments, the segments 12, waveguide core 28 including waveguide core segments 16, 18, and slab layer 26 can be composed of silicon nitride. In alternative embodiments, instead of silicon or silicon nitride, the segments 12, waveguide core 28 including waveguide core segments 16, 18, and slab layer 26 can be composed of silicon oxynitride, aluminum nitride, a III-V compound semiconductor material, silicon germanium, germanium, a polymer, or the like.

[0036] Reference is made to Figure 3 , Figure 3A , Figure 3B , Figure 3C , Figure 3D wherein like reference numerals refer to like parts throughout the several views of the drawings. Figure 2 , Figure 2A , Figure 2B , Figure 2C , Figure 2DSimilar features as in FIG. 1, and in a next fabrication stage, one or more dielectric layers 30 are formed over segments 12 and waveguide core 28. One or more dielectric layers 30 can be composed of silicon dioxide and / or silicon nitride. Over one or more dielectric layers 30, a back-end-of-line stack 32 is formed. Back-end-of-line stack 32 can include interlayer dielectric layers 34 composed of silicon dioxide and intralayer dielectric layers 36 composed of silicon-carbon-nitride (e.g., nitrogen-doped silicon carbide) alternating with interlayer dielectric layers 34 in the layer stack.

[0037] Reference is made to Figure 4 wherein like reference numerals refer to like features throughout Figure 3 Similar features as in FIG. 1, and in a next fabrication stage, portions of back-end-of-line stack 32 can be removed by lithography and etching processes to expose portions of handle substrate 25, and a recess 38 can be formed in the exposed portions of handle substrate 25 by lithography and etching processes. In one embodiment, segments 12 and waveguide core segments 16 can be exposed by the removal of the portions of back-end-of-line stack 32. In one embodiment, segments 12 can terminate at an end face of structure 10 defined at least in part by the formation of recess 38. Source 22 is disposed within recess 38 adjacent the end face.

[0038] Recess 38 can be formed by a multi-step process that ends with a wet chemical etch characterized by an etch rate that depends on the crystalline direction, resulting in a V-shaped or U-shaped recess 38. Recess 38 can extend laterally in handle substrate 25 beneath dielectric layer 24 as an undercut 40 located beneath portions of structure 10. In one embodiment, segments 12 can be located above undercut 40. Undercut 40 can be used to minimize substrate-induced leakage loss of the laser light from source 22. In an alternative embodiment, recess 38 can be formed in handle substrate 25 without forming undercut 40, e.g., if the entrance mode of the laser light from source 22 is small, which can be suitable.

[0039] A dielectric layer 42 can be formed over the portions of structure 10 from which back-end-of-line stack 32 is removed. In one embodiment, dielectric layer 42 can be formed over segments 12 of structure 10. Dielectric layer 42 is composed of a dielectric material, e.g., silicon dioxide, and does not have the stack of various dielectric materials present in back-end-of-line stack 32.

[0040] In any embodiment of structure 10 described herein, structure 10 can be integrated in a photonic chip that includes electronic components and additional optical components. For example, the electronic components can include field effect transistors fabricated by a CMOS process.

[0041] In comparison to conventional edge couplers that include only a waveguide core segment defining an inverted taper, structure 10 can exhibit significant improvements in insertion loss, as well as reduced back reflection at the facet. Structure 10 can achieve high coupling efficiency due to improved matching of the mode shape and mode size with source 22. In comparison to conventional edge couplers that include only a waveguide core segment defining an inverted taper, structure 10 can exhibit higher manufacturing tolerances. In comparison to conventional edge couplers that include only a waveguide core segment defining an inverted taper, structure 10 can be shorter in length, and thus more compact. The shortened length conserves space on a photonic chip. In comparison to conventional edge couplers, structure 10 can exhibit improved power handling, which can reduce its susceptibility to power-related damage. Due to the provision of rib waveguide structure by plate layer 26, waveguide core 28 can interface directly with an optical modulator downstream of waveguide core segment 18.

[0042] Please refer to Figure 5 , Figure 6 According to alternative embodiments of the present invention, structure 10 can be modified to add features in layers above the level that includes segment 12 and waveguide core 28. The additional features can include segments 52, waveguide core segment 56 having protrusions 54, and waveguide core segment 58. Segments 52 and waveguide core segments 56, 58 can be disposed longitudinally along longitudinal axis 60. Waveguide core segment 56 is disposed longitudinally between segment 52 and waveguide core segment 58. In one embodiment, segments 52 and waveguide core segments 56, 58 can be centered with respect to longitudinal axis 60.

[0043] Segment 52 can be disposed above and overlapping segment 12. Waveguide core segment 56 can be disposed above and overlapping waveguide core segment 16, and waveguide core segment 58 can be disposed above and overlapping waveguide core segment 18. Waveguide core segment 56 can have notched side surfaces 57 (notches defining gaps or slots between adjacent pairs of protrusions 54) and end surfaces 59 connecting notched side surfaces 57. Protrusions 64 are disposed spaced apart along longitudinal axis 60 and extend outward transverse to longitudinal axis 60. Segment 52 can be disposed adjacent end surfaces 59, and end surfaces 59 can terminate waveguide core segment 56.

[0044] In one embodiment, segments 52 and waveguide core segments 56, 58 can be composed of a dielectric material, such as silicon nitride, and segment 12 and waveguide core 28, including waveguide core segments 16, 18, can be composed of silicon. The layer of dielectric material can be deposited on one or more of dielectric layers 30 and patterned by photolithography and etching processes to form segments 52 and waveguide core segments 56, 58. The introduction of a material other than silicon, such as silicon nitride, into structure 10 can also reduce power-related losses during the transmission of optical power from source 22 through structure 10 to an optical component on a photonic chip.

[0045] A process is then performed to form the back-end-of-line stack 32, the recess 38, and optionally the undercut 40, and the dielectric layer 42 in place of the removed portion of the back-end-of-line stack 32.

[0046] Referring to Figure 7 According to alternative embodiments of the present application, the structure 10 can be modified so that portions 70 of the plate layer 26 are discontinuous and segmented. Adjacent pairs of segments 12 are separated by gaps 13 that are spaced along the longitudinal axis 20. The plate layer 26 is absent from the gaps 13 between the sidewalls 84 of adjacent pairs of segments 12. The discontinuous portions 70 of the plate layer 26 include segments that are respectively connected to the sidewalls 82 of the segments 12.

[0047] The above-described method is used in the manufacture of integrated circuit chips. The resulting integrated circuits chips can be distributed by the fabricant as raw wafer forms (e.g., as a single wafer having a plurality of unpackaged chips), as bare chips, or in packages. The chips can be integrated with other chips, discrete circuit elements, and / or other signal processing devices as part of the raw wafer forms, as a bare die, or in packages by the fabricant. The final product can be any product that includes integrated circuit chips, such as computer products having central processing units (CPUs) or smart phones.

[0048] As used herein, the term approximately, for example, "about," "substantially," and "essentially," as those terms are typically employed, are not intended to be limiting. Rather, these terms allow for a reasonable amount of variation as would be expected by one of ordinary skill in the art making the measurements at issue, and unless otherwise stated, can indicate + / - 10% of the value stated.

[0049] Terms such as "vertical," "horizontal," and the like are used herein with reference to the example to establish a frame of reference and are not intended to be limiting. As used herein, the term "horizontal" is defined as a plane parallel to the conventional plane of the semiconductor substrate, regardless of its actual three-dimensional spatial orientation. The terms "vertical" and "lateral" refer to directions that are perpendicular to the horizontal as just defined. The term "lateral" refers to a direction in the horizontal plane.

[0050] A feature that is "connected" or "coupled" to another feature can be directly connected or coupled to the other feature or can be indirectly connected or coupled to the other feature through one or more intermediate features. If no intermediate feature is present, then the feature can be "directly connected" or "directly coupled" to the other feature. If at least one intermediate feature is present, then the feature can be "indirectly connected" or "indirectly coupled" to the other feature. If one or more intermediate features are present, then a feature that is "on" or "in contact with" another feature can be directly on or in contact with the other feature. If no intermediate feature is present, then the feature can be "directly on" or "directly in contact with" the other feature. If at least one intermediate feature is present, then the feature can be "not directly on" or "not directly in contact with" the other feature. Different features can be "overlapped" if one feature extends over the other feature and covers a portion thereof, either in direct contact or not in direct contact.

[0051] The description of various embodiments of the application has been made for the purpose of illustration rather than limitation. Many modifications and variations will become apparent to those of ordinary skill in the art, without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application, or technical improvement over technology found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A structure for an edge coupler, characterized in that, The structure includes: A waveguide core includes a first waveguide core segment and a second waveguide core segment adjacent to the first waveguide core segment. The first waveguide core segment has a first notched sidewall, a second notched sidewall, and an end surface connecting the first notched sidewall and the second notched sidewall. The second waveguide core segment, which is continuous and without gaps, has opposing sidewalls and a width dimension that varies along the longitudinal axis in the direction of light propagation. Multiple first segments, adjacent to the end surface of the first waveguide core segment, are arranged in a first spaced configuration; and A plate layer is adjacent to the plurality of first segments, the first notched sidewall of the first waveguide core segment, the second notched sidewall of the first waveguide core segment, and the end surface of the first waveguide core segment. The plate layer has a first side and a second side opposite to the first side. The plurality of first segments, the first waveguide core segment, and the second waveguide core segment are laterally arranged between the first side and the second side. The plate layer has a width dimension between the first side and the second side, and the width dimension varies between different portions of the plate layer. The plurality of first segments and the first waveguide core segment have a first thickness, and the plate layer has a second thickness that is less than the first thickness.

2. The structure as described in claim 1, characterized in that, The segment is embedded in the plate layer at a height equal to the second thickness.

3. The structure as described in claim 1, characterized in that, The second waveguide core segment has the first thickness, the first waveguide core segment is arranged between the second waveguide core segment and the plurality of first segments, and the plate layer is adjacent to the second waveguide core segment.

4. The structure as described in claim 1, characterized in that, The plate has a first portion connected to the plurality of first segments, and the first portion of the plate is tapered, having a first width dimension between the first side and the second side, the first width dimension increasing as the distance from the first waveguide core segment decreases.

5. The structure as described in claim 4, characterized in that, The plate layer has a second portion that is connected to the first waveguide core segment.

6. The structure as described in claim 5, characterized in that, The second portion of the plate is non-tapered and has a second width dimension between the first side and the second side, which is constant.

7. The structure as described in claim 1, characterized in that, The plate has a portion that connects to the first waveguide core segment, and this portion of the plate is non-tapered, having a constant width dimension between the first side and the second side.

8. The structure as described in claim 1, characterized in that, Also includes: The substrate includes a groove adjacent to the plurality of first segments.

9. The structure as described in claim 8, characterized in that, Also includes: dielectric layer, The plurality of first segments and the first waveguide core segment are disposed on the dielectric layer, and the groove extends under the dielectric layer and the plurality of first segments as an undercut.

10. The structure as described in claim 1, characterized in that, The plurality of first segments are distributed in a first group and a second group adjacent to the first waveguide core segment, and the plurality of first segments in the first group have a larger width dimension compared with the plurality of first segments in the second group.

11. The structure as described in claim 1, characterized in that, Also includes: Multiple second segments are arranged at second intervals above the multiple first segments. The plurality of first segments are composed of a first material, and the plurality of second segments are composed of a second material having a composition different from that of the first material.

12. The structure as described in claim 11, characterized in that, Also includes: The third waveguide core segment includes a first recessed sidewall, a second recessed sidewall, and an end surface connecting the first recessed sidewall and the second recessed sidewall. The third waveguide core segment is disposed above the first waveguide core segment and is composed of the second material.

13. The structure as described in claim 12, characterized in that, The first material is silicon, and the second material is silicon nitride.

14. The structure as described in claim 1, characterized in that, The plurality of first segments and the first waveguide core segment are arranged along the longitudinal axis, and the plurality of first segments in adjacent pairs are separated by a gap along the longitudinal axis in the first interval arrangement, and the plate layer is not present in the gap.

15. A method for forming a structure of an edge coupler, characterized in that, The method includes: A waveguide core is formed, comprising a first waveguide core segment and a second waveguide core segment adjacent to the first waveguide core segment. The first waveguide core segment has a first notched sidewall, a second notched sidewall, and an end surface connecting the first notched sidewall and the second notched sidewall. The second waveguide core segment, which is continuous and without gaps, has opposing sidewalls and a width dimension that varies along the longitudinal axis in the direction of light propagation. Forming a plurality of first segments arranged at a first interval on the end surface adjacent to the first waveguide core segment; and A plate layer is formed adjacent to the plurality of first segments, the first notch sidewall of the first waveguide core segment, the second notch sidewall of the first waveguide core segment, and the end surface of the first waveguide core segment. The plate layer has a first side and a second side opposite to the first side. The plurality of first segments, the first waveguide core segment, and the second waveguide core segment are laterally arranged between the first side and the second side. The plate layer has a width dimension between the first side and the second side, and this width dimension varies between different portions of the plate layer. The plurality of first segments and the first waveguide core segment have a first thickness, and the plate layer has a second thickness that is less than the first thickness.

16. The method as described in claim 15, characterized in that, The second waveguide core segment has the first thickness, the plate layer is adjacent to the second waveguide core segment, and the first waveguide core segment is arranged between the second waveguide core segment and the plurality of first segments.

17. The method as described in claim 15, characterized in that, The plate layer is formed by patterning a device layer on a silicon-on-insulator substrate using photolithography and etching processes.

18. The method as described in claim 15, characterized in that, The plate layer has a first portion connected to the plurality of first segments, the plurality of first segments being laterally disposed between the first side and the second side, and the first portion of the plate layer being tapered, having a first width dimension between the first side and the second side, the first width dimension increasing as the distance from the first waveguide core segment decreases.

19. The method as described in claim 15, characterized in that, The plate has a second portion connected to the first waveguide core segment, and the second portion of the plate is non-tapered, having a constant second width dimension between the first side and the second side.

20. The method as described in claim 15, characterized in that, Also includes: Multiple second segments are formed, positioned above the multiple first segments. The plurality of first segments are composed of silicon, and the plurality of second segments are composed of silicon nitride.

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