CN114089482B - Grating coupler - Google Patents

Grating coupler Download PDF

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CN114089482B
CN114089482B CN202111460079.2A CN202111460079A CN114089482B CN 114089482 B CN114089482 B CN 114089482B CN 202111460079 A CN202111460079 A CN 202111460079A CN 114089482 B CN114089482 B CN 114089482B
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arc section
arc
grating coupler
layer
grating
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CN114089482A (en
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张小平
张梦雨
王逸松
李铭晖
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Tsinghua University
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/34—Optical coupling means utilising prism or grating
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12083—Constructional arrangements
    • G02B2006/12107—Grating
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12133—Functions
    • G02B2006/12147—Coupler

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  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
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  • Optical Integrated Circuits (AREA)

Abstract

The invention discloses a grating coupler. The grating coupler includes: a substrate layer, an oxide layer, a waveguide layer and a covering layer which are sequentially laminated together from bottom to top. The waveguide layer is made of semiconductor materials. The waveguide layer is etched with a nano/micron-sized arc section array structure grating, the arc section array structure grating comprises a plurality of concentric arc sections, etching grooves are formed between every two adjacent arc sections, the proximal arc section is used as an optical signal input end, the distal arc section is used as an optical signal output end, the proximal arc section is the arc section closest to the circle center, the distal arc section is the arc section farthest from the circle center, and the circle center is the circle center of each arc section. The width of the circular arc segment is determined by the wavelength of the optical signal entering the grating coupler. And the lengths of all the arc sections are sequentially increased from the proximal arc section to the distal arc section. The grating coupler provided by the application improves the coupling efficiency of optical signals.

Description

Grating coupler
Technical Field
The invention relates to the field of optical devices, in particular to a grating coupler.
Background
At present, optical communication faces the problem of coupling efficiency between an optical waveguide chip and an optical fiber, the width of a fiber core of the optical fiber is ten micrometers, the width of a common waveguide on the optical chip is in the range of hundreds of nanometers, and the width of the whole structure of a branching and routing device designed on the chip is in the micrometer level. The loss of optical signals in the waveguide during input and transmission is very large, the coupling control of the optical signals between optical fibers and between the optical fibers and optical devices is kept, the coupling efficiency is improved, and the method is an important precondition for the optical chip to be integrated and applied on a large scale.
The existing coupling structure mainly comprises a silicon (Si) waveguide coated with a polymer to form an inverted cone structure, a cantilever beam type coupler, a sub-wavelength grating type, a double-layer cone structure, a multilayer SiN structure and the like. However, the coupling efficiency problem is not fully considered in the above coupling structure, which results in low coupling efficiency.
Disclosure of Invention
The invention aims to provide a grating coupler with high coupling efficiency.
In order to achieve the purpose, the invention provides the following scheme:
a grating coupler comprising: a substrate layer, an oxide layer, a waveguide layer and a covering layer which are sequentially laminated together from bottom to top;
the waveguide layer is made of a semiconductor material;
the waveguide layer is etched with a nano/micron arc section array structure grating, the arc section array structure grating comprises a plurality of concentric arc sections, and etching grooves are formed between adjacent arc sections, wherein a proximal arc section is used as an optical signal input end, a distal arc section is used as an optical signal output end, the proximal arc section is the arc section closest to the circle center, the distal arc section is the arc section farthest from the circle center, and the circle center is the circle center of each arc section;
the width of the arc segment is determined by the wavelength of the optical signal entering the grating coupler;
and the lengths of all the arc sections are sequentially increased from the proximal arc section to the distal arc section.
Optionally, the widths of the circular arc segments are equal, and the width t of each circular arc segment is calculated according to the following formula:
Figure BDA0003388010370000021
wherein n is 1 Representing the refractive index of the material of the waveguide layer, n 2 Representing the refractive index of the material of the cover layer, n 3 Denotes the refractive index, λ, of the material of the oxide layer 0 Represents the wavelength of the optical signal entering the grating coupler, and m represents the beam waist radius of the optical signal entering the grating coupler.
Optionally, the grating coupler further includes: the optical fiber and the waveguide are respectively connected with the telecentric arc section and the proximal arc section of the arc section array structure grating.
Optionally, at least a partial region of the waveguide coincides with the proximal circular arc segment.
Optionally, the material of the waveguide layer is silicon.
Optionally, the material of the oxide layer and/or the cover layer is a semiconductor compound material.
Optionally, the material of the oxide layer and/or the cover layer is silicon dioxide.
Optionally, the substrate layer is made of a semiconductor material and a compound thereof.
Optionally, the substrate layer is made of silicon, silicon nitride, aluminum oxide, or gallium arsenide.
Optionally, the depth of the etching groove is 100nm.
According to the specific embodiment provided by the invention, the following technical effects are disclosed: the grating coupler provided by the application comprises a substrate layer, an oxidation layer, a waveguide layer and a covering layer which are sequentially laminated together from bottom to top. The waveguide layer is made of a semiconductor material; the waveguide layer is etched with a nano/micron arc section array structure grating, the nano/micron arc section array structure grating comprises a plurality of concentric arc sections, etching grooves are formed between every two adjacent arc sections, wherein the proximal arc section is used for being connected with the waveguide, the distal arc section is used for being connected with the optical fiber, the proximal arc section is the arc section closest to the center of a circle, the distal arc section is the arc section farthest from the center of a circle, and the center of the circle is the center of the circle of each arc section. The width of the arc segment is determined by the wavelength of the optical signal entering the grating coupler; the lengths of the arc sections are sequentially increased from the proximal arc section to the distal arc section. Based on the arc section array structure grating, the light signal which is upwards diffracted from the etching groove and the light signal which is upwards diffracted from the arc section are interfered to expand, and the two beams of light signals which are downwards diffracted are interfered to cancel, so that the upwards diffraction efficiency of the grating coupler is improved, and the coupling efficiency of the grating coupler is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a schematic diagram of a grating coupler according to an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of an arc segment array structure grating according to an embodiment of the present invention;
FIG. 3 is a plan view showing the symmetrical structure of the input arc segment array structure grating and the output arc segment array structure grating in the embodiment of the present invention;
FIG. 4 is a schematic diagram of another grating coupler according to an embodiment of the present invention;
FIG. 5 is a diagram illustrating transmission of an optical signal in a grating coupler according to an embodiment of the present invention;
fig. 6 is a front view of a grating coupler in an embodiment of the present invention.
Detailed Description
It is noted that, in the present application, words such as "exemplary" or "for example" are used to mean exemplary, illustrative, or descriptive. Any embodiment or design described herein as "exemplary" or "such as" is not necessarily to be construed as preferred or advantageous over other embodiments or designs. Rather, use of the word "exemplary" or "such as" is intended to present concepts related in a concrete fashion.
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The present application provides a grating coupler, see fig. 1, comprising: a substrate layer 1, an oxide layer 2, a waveguide layer 3 and a covering layer 4 sequentially laminated together from bottom to top.
The material of the waveguide layer 3 is, for example, a semiconductor material such as Si.
The material of the above-mentioned oxide layer 2 and the above-mentioned cap layer 4 is exemplified by a semiconductor compound material such as SiO 2 。
The material of the above-mentioned substrate layer 1 is exemplified by semiconductor materials and compounds thereof, such as silicon (Si), silicon nitride (SiN), aluminum oxide (AlO), gallium arsenide (GaAs), and the like.
The waveguide layer 3 is disposed on the substrate layer 1 subjected to the front side polishing process, and the waveguide layer 3 is etched with a nano/micron-sized arc-segment array structure grating, as shown in fig. 2, the arc-segment array structure grating includes a plurality of concentric arc segments, an etching groove is formed between adjacent arc segments, wherein the depth of the etching groove is 100nm as an example.
The proximal arc segment is used as an optical signal input end, the distal arc segment is used as an optical signal output end, the proximal arc segment is the arc segment closest to the circle center, the distal arc segment is the arc segment farthest from the circle center, and the circle center is the circle center of each arc segment.
The lengths of the arc sections are sequentially increased from the proximal arc section to the distal arc section.
The width of the arc segment is determined by the wavelength of the optical signal entering the grating coupler.
Specifically, the width t of each arc segment can be calculated according to the following formula:
Figure BDA0003388010370000041
wherein n is 1 Representing the refractive index of the material of the waveguide layer, n 2 Denotes the refractive index of the cover material, n 3 Denotes the refractive index, λ, of the material of the oxide layer 0 Represents the wavelength of the optical signal entering the grating coupler, and m represents the beam waist radius of the optical signal entering the grating coupler.
Referring to fig. 3, the left half part in fig. 3 is an arc segment array structure grating between the optical fiber and the waveguide when an optical signal is transmitted from the optical fiber to the waveguide, the optical fiber is connected to the left side of the arc segment array structure grating, and the waveguide is connected to the right side of the arc segment array structure grating. The right half of fig. 3 is an arc-segment array structure grating between the waveguide and the optical fiber when the optical signal is transmitted from the waveguide to the optical fiber, the waveguide is connected to the left side of the arc-segment array structure grating, and the optical fiber is connected to the right side of the arc-segment array structure grating.
In some embodiments, referring to fig. 4 and 5, the grating coupler provided by the present application further comprises: optical fibers and waveguides. The waveguide is exemplarily a tapered waveguide, the optical fiber and the tapered waveguide are respectively disposed at two sides of the arc array structure grating and respectively connected to a telecentric arc segment and a proximitial arc segment of the arc array structure grating, that is, when the waveguide and the arc array structure grating form a passage, the waveguide is connected to a minimum arc segment of the arc array structure grating, and the optical fiber is located at a maximum arc segment of the arc array structure grating.
The arrangement direction of the arc sections in the arc section array structure grating is the same as the transmission direction of the signals.
In some embodiments, at least a portion of the waveguide overlaps with its corresponding arc segment (i.e., the proximal arc segment) to reduce the problem of reduced coupling efficiency caused by relative displacement between the waveguide and the grating.
The grating coupler is described in detail below with reference to fig. 6:
referring to fig. 6, the grating coupler is typically formed by a Silicon-On-Insulator (SOI) substrate. The bottom layer material of SOI is Si with thickness t 1 . The upper layer of the substrate is an oxide layer 2 made of SiO 2 Thickness t 2 . Over the oxide layer 2 is a waveguide layer 3 of Si, of thickness t 3 Wherein t is 1 ＝t 3 . A covering layer 4 is arranged above the waveguide layer 3 and made of SiO 2 Thickness t 4 。
The arc section array structure grating is arranged in the waveguide layer 3, the left end (i.e. taper region) of the waveguide layer 3 is connected with at least one partial region of the input port of the input optical fiber, and the length is L t The right end of the taper region is close to the maximum arc section of the grating with the arc section array structure.
In the waveguide layer 3, the length of the tail region of the waveguide layer 3 is L 0 。
The depth of an etching groove between adjacent circular arc sections in the arc section array structure grating is h, the width of the circular arc section is d, the equal line spacing of the two circular arc sections is p, the width of the etching groove is (p-d), and the length of a waveguide area is L g ＝N*p，N＝{1,2,3，…}。
The center of a circle is taken at the left end area of the waveguide layer 3, and the central angle theta, r = L t ，r inner ，r outer . Taking concentric circles, wherein the central angle theta of the concentric circles is r and r respectively inner 、r outer Etching the end face of the waveguide layer 3 for radius; radius r and radius r inner The depth of the etching groove is h =100nm, and the etching groove is a No. 1 etching groove; radius r inner And radius r outer The area without etching between the two is No. 1 circular arc section.
Further, in the waveguide layer 3, concentric circles are taken, the central angles θ of which are [ r + (N-1) × p [ ]]、[r inner +(N-1)*p]The radius is etched on the end face of the waveguide layer 3, the etching depth is h, and the etching grooves between the two radii after etching are N number etching grooves in sequence, wherein N = {1,2,3, \ 8230 }. [ r ] of inner +(N-1)*p]、[r outer +(N-1)*p]The unetched areas between the radii are N number circular arc segments in sequence, N = {1,2,3, \8230; }.
Based on the optical field pattern matching theory, the optical signal diffracted upwards from the etching groove and the optical signal diffracted upwards from the arc section are interfered to expand, and the two beams of optical signals diffracted downwards are interfered to be cancelled, so that the upward diffraction efficiency of the grating coupler is improved, high-efficiency coupling is realized, and the problem of the coupling efficiency between an optical waveguide chip and an optical fiber is solved.
In the present specification, the embodiments are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims (9)

1. A grating coupler, comprising: a substrate layer, an oxide layer, a waveguide layer and a covering layer which are sequentially laminated together from bottom to top;
the waveguide layer is made of a semiconductor material;
the waveguide layer is etched with a nano/micron arc section array structure grating, the arc section array structure grating comprises a plurality of concentric arc sections, and etching grooves are formed between adjacent arc sections, wherein a proximal arc section is used as an optical signal input end, a distal arc section is used as an optical signal output end, the proximal arc section is the arc section closest to the circle center, the distal arc section is the arc section farthest from the circle center, and the circle center is the circle center of each arc section;
the width of the arc segment is determined by the wavelength of the optical signal entering the grating coupler;
the widths of the circular arc segments are equal, and the width t of each circular arc segment is calculated according to the following formula:
Figure FDA0003738799070000011
wherein n is 1 Representing the refractive index of the material of the waveguide layer, n 2 Denotes the refractive index of the cover material, n 3 Denotes the refractive index, λ, of the material of the oxide layer 0 Represents a wavelength of an optical signal entering the grating coupler, and m represents a beam waist radius of the optical signal entering the grating coupler;
and the lengths of all the arc sections are sequentially increased from the proximal arc section to the distal arc section.
2. The grating coupler of claim 1, further comprising: the optical fiber and the waveguide are respectively connected with the telecentric arc section and the proximal arc section of the arc section array structure grating.
3. The grating coupler of claim 2, wherein at least a portion of the waveguide coincides with the proximal arc segment.
4. The grating coupler of claim 1 wherein the material of the waveguide layer is silicon.
5. The grating coupler of claim 1, wherein the material of the oxide layer and/or the cap layer is a semiconductor compound material.
6. The grating coupler of claim 5, wherein the material of the oxide layer and/or the cap layer is silicon dioxide.
7. The grating coupler of claim 1, wherein the substrate layer is a semiconductor material and compounds thereof.
8. The grating coupler of claim 7, wherein the substrate layer is silicon, silicon nitride, aluminum oxide, or gallium arsenide.
9. The grating coupler of claim 1, wherein the etched grooves have a depth of 100nm.
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CN115842241B (en) * 2022-12-23 2024-04-02 上海铭锟半导体有限公司 Waveguide grating antenna based on evanescent wave regulation and control and manufacturing method

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CN101915965B (en) * 2010-08-23 2013-11-06 清华大学 Grating coupler and package structure thereof
WO2014021815A1 (en) * 2012-07-30 2014-02-06 Hewlett-Packard Development, Company L.P. Optical coupling system and method for fabricating the same
CN106461865A (en) * 2014-03-18 2017-02-22 华为技术有限公司 Grating coupler and manufacturing method therefor
WO2016197376A1 (en) * 2015-06-11 2016-12-15 华为技术有限公司 Grating coupler and preparation method therefor
US10992104B2 (en) * 2015-12-17 2021-04-27 Ii-Vi Delaware, Inc. Dual layer grating coupler
CN109031522A (en) * 2018-07-16 2018-12-18 浙江工业大学 A kind of grating coupler of low back-reflection
CN111175896A (en) * 2020-02-21 2020-05-19 电子科技大学 High-efficiency grating coupler with large bandwidth

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