CN117348153A - Multilayer waveguide edge coupler - Google Patents
Multilayer waveguide edge coupler Download PDFInfo
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- CN117348153A CN117348153A CN202311654527.1A CN202311654527A CN117348153A CN 117348153 A CN117348153 A CN 117348153A CN 202311654527 A CN202311654527 A CN 202311654527A CN 117348153 A CN117348153 A CN 117348153A
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- 239000013307 optical fiber Substances 0.000 claims abstract description 23
- 238000005253 cladding Methods 0.000 claims abstract description 17
- 239000000758 substrate Substances 0.000 claims abstract description 13
- 238000011144 upstream manufacturing Methods 0.000 claims description 30
- 230000008878 coupling Effects 0.000 abstract description 22
- 238000010168 coupling process Methods 0.000 abstract description 22
- 238000005859 coupling reaction Methods 0.000 abstract description 22
- 238000004519 manufacturing process Methods 0.000 abstract description 10
- 230000003247 decreasing effect Effects 0.000 abstract description 5
- 239000010410 layer Substances 0.000 description 19
- 239000000835 fiber Substances 0.000 description 17
- 230000003287 optical effect Effects 0.000 description 17
- 239000002356 single layer Substances 0.000 description 14
- 230000006872 improvement Effects 0.000 description 8
- 238000000034 method Methods 0.000 description 7
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 6
- 230000008569 process Effects 0.000 description 6
- 229910052710 silicon Inorganic materials 0.000 description 6
- 239000010703 silicon Substances 0.000 description 6
- 238000010586 diagram Methods 0.000 description 3
- 238000001259 photo etching Methods 0.000 description 3
- 230000005540 biological transmission Effects 0.000 description 2
- 238000004891 communication Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 230000010287 polarization Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 238000001459 lithography Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
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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
- G02B6/10—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
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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
- G02B6/10—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
- G02B6/122—Basic optical elements, e.g. light-guiding paths
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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
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/14—Mode converters
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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
- G02B6/10—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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- 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
- G02B2006/12152—Mode converter
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Abstract
The invention provides a multilayer waveguide edge coupler, which comprises a waveguide cladding, a substrate layer and a mode converter, wherein the waveguide cladding and the substrate layer are arranged up and down, and the mode converter is arranged in the waveguide cladding; two rows of through holes are formed in the waveguide cladding, and the two rows of through holes are positioned on two sides of the mode converter; a cavity is arranged in the substrate layer, and the cavity is positioned below the through hole and is communicated with the through hole; the mode converter comprises N waveguides which are coupled in sequence, wherein the first waveguide is used for being coupled with a single-mode optical fiber, the Nth waveguide is used for being coupled with a single-mode waveguide in a chip, and the thickness from the Nth waveguide to the first waveguide is gradually decreased; and N is an integer greater than 1. The multi-layer waveguide edge coupler provided by the invention realizes low-loss coupling with the optical fiber, and simultaneously reduces the manufacturing precision requirement.
Description
Technical Field
The invention belongs to the technical field of silicon-based photon integration, and particularly relates to a multilayer waveguide edge coupler.
Background
The silicon-based photon chip adopts the silicon waveguide as an optical transmission medium and has the advantages of small size and high performance. However, the mode field size of the traditional single-mode waveguide has large difference from that of the single-mode fiber, the direct coupling loss is high, and a structure matched with the mode field of the single-mode fiber needs to be manufactured on the photonic chip to reduce the coupling loss. There are two modes commonly seen at present, the first mode is to use a grating coupler, and the grating coupler can realize coupling at any position on a chip, but has the defects of polarization sensitivity and small bandwidth. The second way is to use an edge coupler to achieve low loss transmission of optical signals from single mode waveguides to optical fibers by making special structures at the chip edge. The edge coupler is insensitive to polarization, has large optical bandwidth and is suitable for more application scenes.
The typical edge coupler adopts a single-layer adiabatic inverted cone structure to gradually reduce the size of the waveguide along the light emergent direction of the chip, and the size of the waveguide tip at the edge of the chip cannot well limit the light field, so that the mode field of the light field is increased. In order to achieve small coupling loss with single mode fibers, the waveguide tip size at the chip edge needs to be made small, and the shorter the wavelength of light, the higher the waveguide tip size requirement. Taking the common 220nm SOI as an example, the size of the waveguide tip needs to be smaller than 90nm for the communication C-band, and even smaller than 60nm for the communication O-band, which has high requirements for lithography and manufacturing accuracy.
Disclosure of Invention
The invention aims at the defects and provides the multilayer waveguide edge coupler which realizes low-loss coupling with the optical fiber and simultaneously reduces the manufacturing precision requirement.
In order to solve the technical problems, the invention adopts the following technical scheme:
the invention provides a multilayer waveguide edge coupler, which comprises a waveguide cladding, a substrate layer and a mode converter, wherein the waveguide cladding and the substrate layer are arranged up and down, and the mode converter is arranged in the waveguide cladding; two rows of through holes are formed in the waveguide cladding, and the two rows of through holes are positioned on two sides of the mode converter; a cavity is arranged in the substrate layer, and the cavity is positioned below the through hole and is communicated with the through hole; the mode converter comprises N waveguides which are coupled in sequence, wherein the first waveguide is used for being coupled with a single-mode optical fiber, the Nth waveguide is used for being coupled with a single-mode waveguide in a chip, and the thickness from the Nth waveguide to the first waveguide is gradually decreased; and N is an integer greater than 1.
As a further improvement of the present invention, each waveguide includes an light-entering portion and a light-exiting portion connected; two waveguides coupled to each other, wherein the light-emitting portion of the upstream waveguide is coupled to the light-entering portion of the downstream waveguide in a direction from the end of the mode converter coupled to the single-mode optical fiber to the end coupled to the single-mode waveguide; the width of the light-entering portion of each waveguide gradually increases in a direction from the end of the mode converter coupled with the single-mode optical fiber to the end coupled with the single-mode waveguide.
As a further improvement of the invention, two waveguides are coupled, the light outlet of the light outlet part of the upstream waveguide is arranged on the top surface of the light outlet part, and the light inlet of the light inlet part of the downstream waveguide is arranged on the bottom surface of the light inlet part; the light inlet of the downstream waveguide is overlapped on the light outlet of the upstream waveguide, and the light inlet of the downstream waveguide is opposite to the light outlet of the upstream waveguide.
As a further improvement of the present invention, the thickness of the light-entering portion of the first waveguide is equal to the thickness of the light-exiting portion; the thickness of the light-in part of the rest of the waveguides is smaller than that of the light-out part.
As a further improvement of the present invention, two waveguides are coupled, the light outlet of the light outlet part of the upstream waveguide is arranged on the side surface of the light outlet part, and the light inlet of the light inlet part of the downstream waveguide is arranged on the side surface of the light inlet part; the light inlet of the downstream waveguide is arranged at one side of the light outlet of the upstream waveguide, and the light inlet of the downstream waveguide is opposite to the light outlet of the upstream waveguide.
As a further improvement of the present invention, the side surface of the light inlet portion of the downstream waveguide is parallel to the side surface of the light outlet portion of the upstream waveguide.
As a further improvement of the present invention, the thickness of the light-incident portion of the waveguide is equal to the thickness of the light-emitting portion.
As a further improvement of the present invention, the thickness of the light-emitting portion of the nth waveguide is 220nm, and the thickness of the first waveguide is 90nm, 110nm, 130nm or 150nm.
As a further improvement of the present invention, the thickness of the Nth waveguide is 220nm, and the thickness of the first waveguide is 90nm, 110nm, 130nm or 150nm.
As a further development of the invention, the n=2 or n=3.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
(1) The multi-layer waveguide edge coupler provided by the invention adopts at least two waveguides which are sequentially coupled as a mode converter, the first waveguide is coupled with a single-mode optical fiber, the last waveguide is coupled with the single-mode waveguide in the chip, the thickness of the last waveguide from the last waveguide to the first waveguide is gradually decreased, the thickness of the first waveguide coupled with the single-mode optical fiber can be set smaller under the condition that the thickness of the last waveguide is matched with the single-mode waveguide in the chip, and the width of the tip end of the first waveguide is not required to be too small, so that low-loss coupling with the optical fiber can be realized even if the width is larger; when the minimum waveguide tip width of the mode converter is the same as the waveguide tip width of the existing single-layer adiabatic reverse taper structure, the loss of the multi-layer waveguide edge coupler provided by the invention is lower than that of the existing single-layer adiabatic reverse taper structure, and the coupling loss is reduced; when the same low loss is achieved, the minimum waveguide tip width of the mode converter is larger than that of the existing single-layer adiabatic reverse taper structure, and the manufacturing precision requirement is reduced.
(2) The multilayer waveguide edge coupler provided by the invention has the advantages that the thickness of the first waveguide of the mode converter is 90nm, 110nm, 130nm or 150nm and other existing silicon optical process thicknesses, no extra photoetching process is needed, and the manufacturing process is simplified.
Drawings
FIG. 1 is a schematic cross-sectional view of a multilayer waveguide edge coupler of an embodiment of the present invention;
FIG. 2 is a schematic longitudinal cross-sectional view of a multilayer waveguide edge coupler of an embodiment of the present invention;
FIG. 3 is a front view of a first embodiment of a mode converter;
FIG. 4 is a top view of FIG. 3;
FIG. 5 is a schematic diagram of losses corresponding to different minimum tip widths when a multi-layer waveguide edge coupler employing the mode converter of FIG. 3 is coupled to a single mode fiber;
FIG. 6 is a front view of a second embodiment of a mode converter;
FIG. 7 is a top view of FIG. 6;
FIG. 8 is a schematic diagram of losses associated with different minimum tip widths when a multi-layer waveguide edge coupler employing the mode converter of FIG. 6 is coupled to a single mode fiber;
fig. 9 is a schematic diagram of losses corresponding to different wavelengths of light when a multi-layer waveguide edge coupler employing the mode converter of fig. 6 is coupled to a single-mode optical fiber.
The drawings are as follows: the waveguide cladding 1, the through hole 2, the mode converter 3, the light entrance portion 304 of the first waveguide, the light exit portion 303 of the first waveguide, the light entrance portion 302 of the second waveguide, the light exit portion 301 of the second waveguide, the light entrance portion 314 of the third waveguide, the light exit portion 313 of the third waveguide, the light entrance portion 312 of the fourth waveguide, the light exit portion 311 of the fourth waveguide, the on-chip single-mode waveguide 4, and the substrate layer 5.
Detailed Description
The technical scheme of the invention is described in detail below with reference to the accompanying drawings.
The invention provides a multilayer waveguide edge coupler, which comprises a waveguide cladding 1, a substrate layer 5 and a mode converter 3, wherein the waveguide cladding 1 and the substrate layer 5 are arranged up and down, and the mode converter 3 is arranged in the waveguide cladding 1, as shown in fig. 1 and 2. Two rows of through holes 2 are formed in the waveguide cladding 1, and the two rows of through holes are located on two sides of the mode converter 3. A cavity is arranged in the substrate layer 5, and the cavity is positioned below the through hole and communicated with the through hole.
In the multi-layer waveguide edge coupler provided by the invention, the mode converter 3 comprises N waveguides which are coupled in turn, and N is an integer greater than 1. For example, N is 2,3,4,5,6, etc. The first waveguide is used for coupling with a single mode fiber, the nth waveguide is used for coupling with the single mode waveguide 4 in the chip, and the thickness from the nth waveguide to the first waveguide is gradually decreased. For example, when N is 2, the mode converter 3 includes 2 waveguides coupled, the first waveguide is coupled to a single mode fiber, the second waveguide is coupled to an on-chip single mode waveguide, the thickness of the second waveguide is adapted to the thickness of the on-chip single mode waveguide, and the thickness of the first waveguide is smaller than the thickness of the second waveguide. When N is 3, the mode converter 3 includes 3 waveguides coupled in turn, a first waveguide is coupled with a single mode fiber, a third waveguide is coupled with a single mode waveguide in the chip, the thickness of the third waveguide is adapted to the thickness of the single mode waveguide in the chip, the thickness of the second waveguide is smaller than the thickness of the third waveguide, and the thickness of the first waveguide is smaller than the thickness of the second waveguide.
The multi-layer waveguide edge coupler provided by the invention adopts at least two waveguides which are sequentially coupled as the mode converter, the first waveguide is coupled with the single-mode optical fiber, the last waveguide is coupled with the single-mode waveguide in the chip, the thickness of the last waveguide from the last waveguide to the first waveguide is gradually decreased, the thickness of the first waveguide coupled with the single-mode optical fiber can be set smaller under the condition that the thickness of the last waveguide is matched with the single-mode waveguide in the chip, and the width of the tip end of the first waveguide is not required to be too small, so that low-loss coupling with the optical fiber can be realized even if the width is larger.
In the multi-layer waveguide edge coupler provided by the invention, each waveguide comprises a light inlet part and a light outlet part which are connected, along the direction from one end of the mode converter coupled with a single-mode fiber to one end of the single-mode waveguide coupled with the single-mode waveguide, namely, from right to left in fig. 1, wherein the light inlet part is positioned at the upstream of the light outlet part, namely, the light inlet part is positioned at the right end of the light outlet part. The waveguide may be an integral structure, the light-in portion and the light-out portion being two portions thereof; the light-in part and the light-out part are respectively two sub-waveguides, and the two sub-waveguides are connected to form a waveguide. And the two coupled waveguides, the light emergent part of the upstream waveguide is coupled with the light incident part of the downstream waveguide. For example, when N is 2, the mode converter 3 includes 2 waveguides coupled, where the light-entering portion of the first waveguide is coupled to a single-mode optical fiber, the light-exiting portion of the first waveguide is coupled to the light-entering portion of the second waveguide, and the light-exiting portion of the second waveguide is coupled to the on-chip single-mode waveguide. When N is 3, the mode converter 3 includes 3 coupled waveguides, where the light-in portion of the first waveguide is coupled with a single-mode optical fiber, the light-out portion of the first waveguide is coupled with the light-in portion of the second waveguide, the light-out portion of the second waveguide is coupled with the light-in portion of the third waveguide, and the light-out portion of the third waveguide is coupled with the single-mode waveguide in the chip.
Preferably, the widths of the light entrance portions of all the waveguides gradually increase in a direction from the end of the mode converter coupled with the single mode fiber to the end coupled with the single mode waveguide, i.e., gradually increase from right to left. The width of the light-emitting portions of the other waveguides except the nth waveguide is gradually reduced from right to left. The light enters the light-entering portion of the waveguide and then travels leftwards, the width of the light-entering portion gradually increases from right to left so as to be transmitted to the light-exiting portion in a adiabatic manner, and the width of the light-exiting portion gradually decreases from right to left so as to be transmitted from the light-exiting portion to the light-entering portion of the downstream waveguide.
The invention provides two preferable structures of a mode converter, namely, a first structure, two waveguides which are coupled, wherein a light outlet of a light outlet part of an upstream waveguide is arranged on the top surface of the light outlet part, and a light inlet of a light inlet part of a downstream waveguide is arranged on the bottom surface of the light inlet part. The light inlet of the downstream waveguide is overlapped on the light outlet of the upstream waveguide, and the light inlet of the downstream waveguide is opposite to the light outlet of the upstream waveguide. In the structure, the light-in part of the downstream waveguide is overlapped and arranged above the light-out part of the upstream waveguide, N waveguides are sequentially overlapped in the height direction to form N layers of waveguides, two adjacent layers of waveguides are coupled in the height direction, and the thickness of the light-out part of the Nth waveguide is matched with the thickness of the single-mode waveguide in the chip.
Preferably, the thickness of the light-emitting portion of the nth waveguide is 220nm, and the thickness of the first waveguide is 90nm, 110nm, 130nm or 150nm.
The multilayer waveguide edge coupler provided by the invention has the advantages that the thickness of the first waveguide of the mode converter is 90nm, 110nm, 130nm or 150nm and other existing silicon optical process thicknesses, no extra photoetching process is needed, and the manufacturing process is simplified.
Preferably, the thickness of the light-entering portion of the first waveguide is equal to the thickness of the light-exiting portion, and the thickness of the light-exiting portion of the remaining waveguides is the sum of the thickness of the light-entering portion and the thickness of the light-exiting portion of the adjacent downstream waveguide. After the light inlet parts of the adjacent two waveguides and the light outlet part of the downstream waveguide are overlapped on the light outlet part of the upstream waveguide, the overlapped thickness is the thickness of the light outlet part of the downstream waveguide, so that the total thickness of the mode converter is the thickness of the light outlet part of the Nth waveguide, the thickness of the whole mode converter is prevented from being increased after the multilayer waveguides are overlapped, and meanwhile, compared with the case that the upstream waveguide is completely overlapped on the downstream waveguide, the manufacturing difficulty is reduced.
In the second structure, two waveguides are coupled, and the light outlet of the upstream waveguide is arranged on the side surface of the light outlet, and the light inlet of the downstream waveguide is arranged on the side surface of the light inlet. The light inlet of the downstream waveguide is arranged at one side of the light outlet of the upstream waveguide, and the light inlet of the downstream waveguide is opposite to the light outlet of the upstream waveguide. In the structure, the light inlet part of the downstream waveguide is arranged at one side of the light outlet part of the upstream waveguide, N waveguides are sequentially arranged in the horizontal direction, two adjacent waveguides are coupled in the horizontal direction, and the thickness of the light outlet part of the Nth waveguide is matched with the thickness of the single-mode waveguide in the chip. The thickness of the light inlet part of the waveguide is equal to that of the light outlet part, the heights of the N waveguides are sequentially increased, the thickness of the N waveguide is maximum, and the height of the first waveguide is minimum. In the second configuration, adjacent waveguides are laterally disposed and are stacked in height to provide a higher coupling efficiency for TM modes than in the first configuration.
Preferably, the side surface of the light inlet part of the downstream waveguide is parallel to the side surface of the light outlet part of the upstream waveguide, so that adiabatic coupling of the upstream waveguide and the downstream waveguide is realized.
Preferably, the thickness of the nth waveguide is 220nm and the thickness of the first waveguide is 90nm, 110nm, 130nm or 150nm.
The multilayer waveguide edge coupler provided by the invention has the advantages that the thickness of the first waveguide of the mode converter is 90nm, 110nm, 130nm or 150nm and other existing silicon optical process thicknesses, no extra photoetching process is needed, and the manufacturing process is simplified.
Two specific embodiments of the mode converter are provided below, embodiment 1 corresponds to a first configuration of the mode converter, and embodiment 2 corresponds to a second configuration of the mode converter.
Example 1
As shown in fig. 3 and 4, the mode converter includes 2 waveguides, a first waveguide and a second waveguide, respectively. The light incident portion 304 of the first waveguide has a trapezoid shape, and a right end width W2s is smaller than a left end width W1s. The light emitting portion 303 of the first waveguide has a trapezoid shape, the right end width of which is equal to the left end width of the light entering portion 304, and the right end width W1s of which is larger than the left end width W3s. The light incident portion 302 of the second waveguide has a trapezoid shape, and the right end width W2 thereof is smaller than the left end width. The light emitting portion 301 of the second waveguide has a rectangular shape, the right end width of which is equal to the left end width of the light entering portion 302, and the right end width of which is equal to the left end width W1. The length L2 of the light entrance 304 of the first waveguide. The length L1 of the light-emitting portion 303 of the first waveguide is equal to the length L1 of the light-entering portion 302 of the second waveguide. The light outlet of the light outlet portion 303 of the first waveguide is disposed on the top surface of the light outlet portion 303, and the light inlet of the light inlet portion 302 of the second waveguide is disposed on the bottom surface of the light inlet portion 302. The light-in portion 302 of the second waveguide is disposed superimposed on the light-out portion 303 of the first waveguide, and the light-in port of the light-in portion 302 of the second waveguide is opposite to the light-out port of the light-out portion 303 of the first waveguide, so that the light-out portion 303 of the first waveguide and the light-in portion 302 of the second waveguide are coupled. The thickness of the light emitting portion 303 of the first waveguide is equal to the thickness of the light entering portion 304, i.e. the thickness H1 of the first waveguide. The thickness H2 of the light-emitting portion 303 of the second waveguide is greater than the thickness H1 of the first waveguide, and the thickness of the light-emitting portion 303 of the second waveguide is the sum of the thickness of the light-entering portion 302 and the thickness H1 of the first waveguide. In use, the light-in portion 304 of the first waveguide is coupled to a single mode optical fiber and the light-out portion 301 of the second waveguide is coupled to an on-chip single mode waveguide. The optical signal of the single-mode optical fiber is coupled into the optical input part 304 through the right end of the optical input part 304 of the first waveguide, then is transmitted to the left end of the optical input part 304 in an adiabatic manner, then enters the optical input part 302 of the second waveguide from right to left through the optical output part 303 of the first waveguide, and finally enters the single-mode waveguide in the chip through the optical output part 301 of the second waveguide.
The optical chip is based on a 220nm SOI structure. H2 =220nm, h1=130 nm, w2s=w3s=130 nm.
The loss of the edge coupler when the edge coupler was coupled to a single mode fiber at different W2 values was calculated for a wavelength of 1300nm into the edge coupler using the mode converter of example 1 using eigenmode expansion, as shown in fig. 5. When W2< = 100nm, the coupling loss of both TE and TM modes is less than 2dB.
In contrast, using a 220nm single-layer adiabatic reverse taper structure, the waveguide tip widths were 6.2dB, 3.1dB, and 1.5dB for the TM mode coupling loss with a single-mode fiber, respectively, at 100nm, 80nm, and 60 nm. As can be seen from fig. 5, the TM mode coupling loss corresponding to the single mode fiber when the minimum tip width W2 of the waveguide of the mode converter of the embodiment is 100nm, 80nm, and 60nm is 1.8dB, 1.6dB, and 1.3dB, which are far lower than that of the single-layer adiabatic reverse taper structure, respectively.
When the minimum waveguide tip width of the mode converter is the same as the waveguide tip width of the existing single-layer adiabatic reverse taper structure, the loss of the multi-layer waveguide edge coupler provided by the invention is lower than that of the existing single-layer adiabatic reverse taper structure, and the coupling loss is reduced. When the same low loss is achieved, the minimum waveguide tip width of the mode converter is larger than that of the existing single-layer adiabatic reverse taper structure, and the manufacturing precision requirement is reduced.
Example 2
As shown in fig. 6 and 7, the mode converter includes 2 waveguides, a third waveguide and a fourth waveguide, respectively. The light incident portion 314 of the third waveguide has a trapezoid shape, and the right end width W2s is smaller than the left end width W1s. The light emitting portion 313 of the third waveguide has a right trapezoid shape, the right end width of which is equal to the left end width of the light incident portion 314, and the right end width W1s of which is larger than the left end width W3s. The light incident portion 312 of the fourth waveguide has a right trapezoid shape, and the right end width W2 is smaller than the left end width. The light emitting portion 311 of the fourth waveguide has a rectangular shape, the right end width of which is equal to the left end width of the light entering portion 312, and the right end width of which is equal to the left end width W1. The length L2 of the light-entering portion 314 of the third waveguide. The length L1 of the light exit portion 313 of the third waveguide is equal to the length L1 of the light entrance portion 312 of the fourth waveguide. The light outlet of the light outlet portion 313 of the third waveguide is disposed on the side surface of the straight waist of the light outlet portion 313, and the light inlet of the light inlet portion 312 of the fourth waveguide is disposed on the side surface of the straight waist of the light inlet portion 312. The light-in portion 312 of the fourth waveguide is disposed at one side of the light-out portion 313 of the third waveguide, and the light-in port of the light-in portion 312 of the fourth waveguide is opposite to the light-out port of the light-out portion 313 of the third waveguide, so that the light-out portion 313 of the third waveguide and the light-in portion 312 of the fourth waveguide are coupled. The side surface of the light inlet 312 of the fourth waveguide is parallel to the side surface of the light outlet 313 of the third waveguide, and has a Gap. The thickness of the light emitting portion 313 of the third waveguide is equal to the thickness of the light entering portion 314, i.e., the thickness H1 of the third waveguide. The thickness of the light emergent portion 311 of the fourth waveguide is equal to the thickness of the light incident portion 312, i.e., the thickness H2 of the fourth waveguide. The thickness H2 of the fourth waveguide is greater than the thickness H1 of the third waveguide. In use, the light-in portion 314 of the third waveguide is coupled to a single mode optical fiber and the light-out portion 311 of the fourth waveguide is coupled to an on-chip single mode waveguide. The optical signal of the single-mode optical fiber is coupled into the light-in part 314 through the right end of the light-in part 314 of the third waveguide, then is transmitted to the left end of the light-in part 314 in an adiabatic manner, then gradually enters the light-in part 312 of the fourth waveguide from right to left through the light-out part 313 of the third waveguide, finally enters the light-out part 311 of the fourth waveguide, and then enters the single-mode waveguide in the chip.
The optical chip is based on a 220nm SOI structure. H2 =220nm, h1=130 nm, w2s=w3s=130 nm.
The loss of the edge coupler when the edge coupler was coupled to a single mode fiber at different W2 values was calculated for a wavelength of 1300nm into the edge coupler using the mode converter of example 2 using eigenmode expansion, as shown in fig. 8. When W2< = 100nm, the coupling loss of both TE and TM modes is less than 2dB.
In contrast, using a 220nm single-layer adiabatic reverse taper structure, the waveguide tip widths were 6.2dB, 3.1dB, and 1.5dB for the TM mode coupling loss with a single-mode fiber, respectively, at 100nm, 80nm, and 60 nm. As can be seen from fig. 8, the TM mode coupling loss corresponding to the single mode fiber when the minimum tip width W2 of the waveguide of the mode converter of the embodiment is 100nm, 80nm, and 60nm is 1.6dB, 1.9dB, and 0.8dB, which are far lower than that of the single-layer adiabatic reverse taper structure, respectively.
The optical chip is based on a 220nm SOI structure. H2 =220nm, h1=130 nm, w2s=w3s=130 nm, w2=100 nm.
The time domain finite difference method was used to calculate the loss of different wavelengths 1260 nm-1360 nm into the edge coupler of the mode converter of example 2 when coupled to a single mode fiber, as shown in fig. 9. When the wavelength of light is 1260 nm-1360 nm, the coupling loss of TE and TM modes is less than 2dB.
When the minimum waveguide tip width of the mode converter is the same as the waveguide tip width of the existing single-layer adiabatic reverse taper structure, the loss of the multi-layer waveguide edge coupler provided by the invention is lower than that of the existing single-layer adiabatic reverse taper structure, and the coupling loss is reduced. When the same low loss is achieved, the minimum waveguide tip width of the mode converter is larger than that of the existing single-layer adiabatic reverse taper structure, and the manufacturing precision requirement is reduced.
The foregoing has shown and described the basic principles, principal features and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the specific embodiments described above, and that the above specific embodiments and descriptions are provided for further illustration of the principles of the present invention, and that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (10)
1. The multi-layer waveguide edge coupler is characterized by comprising a waveguide cladding (1), a substrate layer (5) and a mode converter (3), wherein the waveguide cladding (1) and the substrate layer (5) are arranged up and down, and the mode converter (3) is arranged in the waveguide cladding (1); two rows of through holes (2) are formed in the waveguide cladding (1), and the two rows of through holes (2) are positioned on two sides of the mode converter (3); a cavity is arranged in the substrate layer (5), and the cavity is positioned below the through hole and communicated with the through hole; the mode converter (3) comprises N waveguides which are sequentially coupled, wherein the first waveguide is used for being coupled with a single-mode optical fiber, the Nth waveguide is used for being coupled with a single-mode waveguide (4) in a chip, and the thickness from the Nth waveguide to the first waveguide is sequentially reduced; and N is an integer greater than 1.
2. The multi-layer waveguide edge coupler of claim 1, wherein each waveguide comprises an input section and an output section connected; two waveguides coupled to each other, wherein the light-emitting portion of the upstream waveguide is coupled to the light-entering portion of the downstream waveguide in a direction from the end of the mode converter coupled to the single-mode optical fiber to the end coupled to the single-mode waveguide; the width of the light-entering portion of each waveguide gradually increases in a direction from the end of the mode converter coupled with the single-mode optical fiber to the end coupled with the single-mode waveguide.
3. The edge coupler of claim 2, wherein the two waveguides are coupled, the light outlet of the upstream waveguide is disposed on the top surface of the light outlet, and the light inlet of the downstream waveguide is disposed on the bottom surface of the light inlet; the light inlet of the downstream waveguide is overlapped on the light outlet of the upstream waveguide, and the light inlet of the downstream waveguide is opposite to the light outlet of the upstream waveguide.
4. The multilayer waveguide edge coupler of claim 2, wherein the thickness of the light-in portion and the thickness of the light-out portion of the first waveguide are equal; the thickness of the light-in part of the rest of the waveguides is smaller than that of the light-out part.
5. The edge coupler of claim 2, wherein the two waveguides are coupled, the light outlet of the upstream waveguide is disposed on the side of the light outlet, and the light inlet of the downstream waveguide is disposed on the side of the light inlet; the light inlet of the downstream waveguide is arranged at one side of the light outlet of the upstream waveguide, and the light inlet of the downstream waveguide is opposite to the light outlet of the upstream waveguide.
6. The edge coupler of claim 5, wherein the side of the light entrance section of the downstream waveguide is parallel to the side of the light exit section of the upstream waveguide.
7. The edge coupler of claim 5, wherein the thickness of the light entrance portion and the thickness of the light exit portion of the waveguide are equal.
8. The edge coupler of claim 4, wherein the thickness of the light exit portion of the nth waveguide is 220nm and the thickness of the first waveguide is 90nm, 110nm, 130nm or 150nm.
9. The multilayer waveguide edge coupler of claim 7, wherein the nth waveguide has a thickness of 220nm and the first waveguide has a thickness of 90nm, 110nm, 130nm or 150nm.
10. The multilayer waveguide edge coupler of claim 3 or 5, wherein N = 2 or N = 3.
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