CN115576054A - Mode spot converter based on integration of graded index waveguide and two-dimensional inverted cone waveguide - Google Patents
Mode spot converter based on integration of graded index waveguide and two-dimensional inverted cone waveguide Download PDFInfo
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- CN115576054A CN115576054A CN202211405474.5A CN202211405474A CN115576054A CN 115576054 A CN115576054 A CN 115576054A CN 202211405474 A CN202211405474 A CN 202211405474A CN 115576054 A CN115576054 A CN 115576054A
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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
- 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
- G02B6/12—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
- G02B6/1228—Tapered waveguides, e.g. integrated spot-size transformers
Abstract
The invention discloses a mode spot converter based on integration of a graded index waveguide and a two-dimensional inverted-cone-shaped waveguide, which comprises a silicon substrate, the graded index waveguide, a silica substrate, the two-dimensional inverted-cone-shaped waveguide and a cladding, wherein the silica substrate, the two-dimensional inverted-cone-shaped waveguide and the cladding are sequentially positioned on one side above the silica substrate, and the graded index waveguide is positioned on the other side above the silicon substrate and is attached to the two-dimensional inverted-cone-shaped waveguide; a first input port and a first output port are respectively arranged on opposite surfaces of the graded-index waveguide, a second input port and a second output port are arranged at two ends of a long shaft of the two-dimensional inverted-cone waveguide, and the first output port is attached to the second input port; incident light is incident from the first input port, is output from the first output port after being converged by the graded index waveguide, is incident into the two-dimensional inverted-cone waveguide through the second input port for adiabatic transmission, and is finally output from the second output port to be coupled with the integrated silicon waveguide.
Description
Technical Field
The invention belongs to the technical field of integrated optics, and particularly relates to a mode spot converter based on integration of a graded index waveguide and a two-dimensional inverted cone waveguide.
Background
The silicon photon platform can realize the integration of a high-speed optical active device and an optical passive device, and meanwhile, the preparation process of the silicon photon platform is compatible with a CMOS (complementary metal oxide semiconductor) process, can be integrated with an integrated circuit, and is a research hotspot in the field of optical communication. However, in the coupling process of the integrated silicon waveguide and the optical fiber, larger coupling loss exists, and the wide application of the silicon photonic platform is restricted. Spot SizeConverter (SSC) is a photonic device proposed for low loss coupling of optical fibers to integrated optical waveguides. Compared with a vertical grating coupler, the spot size converter has the characteristics of low coupling loss, low polarization correlation and the like, and the core structure of a typical spot size converter design is a section of inverted-cone-shaped waveguide. Through the inverted conical silicon waveguide, the size of an optical mode field can be changed constantly, and under the condition that the length of the conical waveguide is long enough, the optical mode field can be expanded from submicron-level mode spots to micron-level mode spots with extremely low loss, so that low-loss coupling with an optical fiber is realized.
The silicon optical mode spot mode converter comprises a silicon dioxide cantilever, a transition waveguide, a main waveguide, a silicon substrate, a first cladding, a second cladding and a third cladding, wherein the first cladding is arranged above the silicon substrate, the main waveguide is arranged above the first cladding, the second cladding is arranged between the main waveguide and the transition waveguide, and the third cladding is arranged on the transition waveguide; the silica cantilever is connected to the outer side of the transition waveguide, and the center of the optical path of the silica cantilever and the center of the optical path of the transition waveguide are on the same longitudinal section; the width and thickness of the silicon dioxide cantilever are gradually reduced along the direction of an input optical path. Can solve the problem of low coupling efficiency caused by mismatching of optical mode spots of a silicon-based photoelectronic chip and an optical fiber or a laser, but cannot be compatible with the existing commercial silicon-based photonics chip processing platform
The width of the cone tip of the existing inverted cone-shaped waveguide is usually below 200nm, however, the width of the existing commercial silicon-based photonic chip processing platform for the waveguide is limited to be above 200nm, and obviously, the inverted cone-shaped waveguide cannot be compatible with the existing commercial silicon-based photonic chip processing platform. Therefore, how to keep the coupling with low loss while the width of the tapered tip of the reverse tapered waveguide reaches 200nm is a key issue.
In addition, the size of the spot obtained by the spot-size converter expansion is usually about 3 μm, and in order to match the spot size, the existing coupling system usually uses a high NA fiber or a tapered fiber in terms of fiber selection, which requires processing of a standard single-mode fiber, which obviously increases the cost of the coupling system. It is therefore also a concern to achieve low loss coupling to integrated optical waveguides for the mode spot size (about 8-10 μm) of standard single mode optical fibers.
Disclosure of Invention
In order to solve the above problems, the present invention aims to provide a spot size converter based on the integration of a graded index waveguide and a two-dimensional inverted tapered waveguide,
in order to achieve the purpose, the invention adopts the following technical scheme: the mode spot converter based on integration of the graded index waveguide and the two-dimensional inverted cone waveguide comprises a silicon substrate, the graded index waveguide, a silicon dioxide substrate, the two-dimensional inverted cone waveguide and a cladding, wherein the silicon dioxide substrate, the two-dimensional inverted cone waveguide and the cladding are sequentially positioned on one side above the silicon dioxide substrate, and the graded index waveguide is positioned on the other side above the silicon substrate and is attached to the two-dimensional inverted cone waveguide;
a first input port and a first output port are respectively arranged on opposite surfaces of the graded-index waveguide, a second input port and a second output port are arranged at two ends of a long shaft of the two-dimensional inverted-cone waveguide, and the first output port is attached to the second input port;
incident light is incident from the first input port, is output from the first output port after being converged by the graded index waveguide, is incident into the two-dimensional inverted-cone waveguide through the second input port for adiabatic transmission, and is finally output from the second output port to be coupled with the integrated silicon waveguide.
The cladding is made of silicon dioxide and is formed by combining an outer cladding and an inner cladding.
The inner cladding has a refractive index higher than that of the outer cladding, and has a width and thickness smaller than those of the outer cladding.
The medium of the graded index waveguide is silicon dioxide, and the refractive index distribution in the silicon dioxide is accurately controlled through an ion implantation process, so that the graded index distribution is realized.
The graded refractive index is distributed in depth, from top to bottom, the refractive index distribution is increased according to parabolic distribution, and after the highest refractive index is reached, the refractive index distribution is decreased according to Gaussian distribution; in the transverse direction, the refractive index distribution is gaussian, and the highest refractive index is located at the center.
The incident light is a standard single-mode fiber with the mode spot size of 8-10 mu m, and the mode spot size of the standard single-mode fiber is compressed to 3-4 mu m after passing through the graded index waveguide.
The material of two-dimentional back taper waveguide is silicon, and for the back taper, second input port is the awl point, and the thickness and the width of two-dimentional back taper waveguide begin to follow light propagation direction linear increase from the awl point, end up in second output port department.
The length design of the two-dimensional inverted cone waveguide follows the adiabatic transmission principle, the width of the cone tip is higher than 200nm, incident light is coupled at the first output port and the second input port, and the coupling loss is within 0.5 dB.
The silicon dioxide substrate is a silicon wafer inherent structure, and the thickness of the silicon dioxide substrate is consistent with that of the silicon substrate.
The operating wavelength of the spot size converter is 1550nm.
Compared with the prior art, the invention has the following advantages:
1. the light beam with the mode field diameter of 8-10 microns in the standard single-mode fiber is compressed to the mode field diameter of 3-4 microns through the graded index waveguide, compression is carried out without loss, meanwhile, the design of the two-dimensional inverted cone waveguide follows the principle of adiabatic transmission, the transmission loss is extremely low, and the transmission loss of the two-section waveguide structure is optimized, so that the total coupling loss of the spot size converter is optimized.
2. The invention has the possibility of manufacturing by a commercial silicon-based photonic chip processing platform, and the width of the cone tip of the two-dimensional inverted cone-shaped waveguide is 200nm, so that the invention is compatible with the current commercial silicon-based photonic chip processing platform and has wide application range.
Drawings
In order to more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings described below are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without inventive efforts.
FIG. 1 is a schematic diagram of a spot size converter according to the present invention;
FIG. 2 is a front view of the construction of the spot converter of the present invention;
FIG. 3 is a left side view of the construction of the spot converter of the present invention;
FIG. 4 is a top view of the construction of the spot converter of the present invention;
FIG. 5 is a depth-wise refractive index profile of a graded index waveguide in accordance with the present invention;
FIG. 6 is a refractive index profile in the lateral direction of a graded index waveguide in accordance with the present invention;
FIG. 7 is a simulation diagram of the light source of the present invention set to 8 μm in diameter, 1.55 μm in wavelength, and TE mode;
in the figure, 1-silicon substrate; 2-graded index waveguide; 21-a first input port; 22 a first output port; 3-a silicon dioxide substrate; 4-two-dimensional inverted cone waveguide; 41-a second input port; 42-second output port 5-cladding; 50-an inner cladding; 60-outer cladding.
Detailed Description
The present invention will be further described with reference to the accompanying drawings and specific embodiments, but it should not be understood that the scope of the subject matter of the present invention is limited to the following embodiments, and various modifications, substitutions and alterations made based on the common technical knowledge and conventional means in the art without departing from the technical idea of the present invention are included in the scope of the present invention.
Referring to fig. 1-4, the mode spot converter based on the integration of the graded-index waveguide and the two-dimensional inverted-cone-shaped waveguide comprises a silicon substrate 1, a graded-index waveguide 2, a silica substrate 3, a two-dimensional inverted-cone-shaped waveguide 4 and a cladding 5, wherein the silica substrate 3, the two-dimensional inverted-cone-shaped waveguide 4 and the cladding 5 are sequentially located on one side above the silica substrate 3, and the graded-index waveguide 2 is located on the other side above the silicon substrate 1 and is attached to the two-dimensional inverted-cone-shaped waveguide 4;
a first input port 21 and a first output port 22 are respectively arranged on opposite surfaces of the graded-index waveguide 2, a second input port 41 and a second output port 42 are arranged at two ends of a long shaft of the two-dimensional inverted-cone-shaped waveguide 4, and the first output port 22 is attached to the second input port 41;
since light has the characteristic of propagating from the low-refractive-index medium to the high-refractive-index medium, the thickness of the silicon dioxide substrate 3 is consistent with that of the silicon substrate, and an optical mode field of the silicon waveguide layer can be well prevented from leaking into the silicon substrate 1.
Examples of the following; referring to fig. 7, a standard single mode fiber with a diameter of 8 μm and a wavelength of 1.55 μm is used as incident light to enter the graded-index waveguide 2 from the first input port 21, a medium of the graded-index waveguide 2 is silica, and refractive index distribution inside the silica is accurately controlled by an ion implantation process, so as to realize the distribution of the graded index. Referring to fig. 5 or 6, the graded index profile is distributed in depth, and from top to bottom, the index profile increases according to a parabolic profile, and after reaching the highest index, it decreases according to a gaussian profile; in the transverse direction, the refractive index distribution is gaussian, with the highest refractive index at the central location. After the standard single mode fiber passes through the graded index waveguide 2, the size of a mode spot is compressed to 3 mu m;
a standard single mode fiber with a spot size compressed to 3 μm is coupled at the first output port 22 to the third input port 41 and then enters the two-dimensional inverted tapered waveguide 4 through the second input port 41. The two-dimensional inverted-cone-shaped waveguide 4 is made of silicon and is in an inverted cone shape, the second input port 41 is a cone tip, the width of the cone tip is 200nm, and the thickness and the width of the two-dimensional inverted-cone-shaped waveguide 4 linearly increase from the cone tip along the light propagation direction until the second output port 42 is cut off. The length design of the dimensional inverted cone-shaped waveguide 4 follows the adiabatic transmission principle, the transmission process keeps the transmission of a fundamental mode, and a high-order mode in the waveguide is not excited;
incident light is adiabatically transmitted in the two-dimensional inverted cone waveguide 4, and is finally transmitted into the two-dimensional inverted cone waveguide 4 from the cladding 5, the cladding 5 is made of silicon dioxide, and the cladding 5 is formed by combining an outer cladding 60 and an inner cladding 50. The widths and thicknesses of the inner cladding (50) and the outer cladding (60) can be reasonably designed to reduce coupling loss, the refractive index difference between the inner cladding and the outer cladding can be realized by controlling parameters in the process of preparing silicon dioxide by PECVD, the refractive index of the inner cladding 50 of the embodiment is higher than that of the outer cladding 60, and the width and thickness of the inner cladding 50 are both smaller than those of the outer cladding 60.
With the transmission of light, the boundary condition of the cross section of the two-dimensional inverted cone waveguide 4 is changed continuously, the light is subjected to mode matching continuously in the transmission process, the micron-sized mode spot is matched to the submicron-sized mode spot gradually, and finally the light is completely limited in the eigenmode of the silicon waveguide, the working wavelength of the mode spot converter is 1550nm, and finally the coupling loss is within 0.5 dB.
The mode spot converter based on the integration of the graded-index waveguide and the two-dimensional inverted-cone waveguide is provided by the invention. The detailed description is given to the structure and the working principle of the present invention by using specific examples, and the above description of the embodiments is only used to help understanding the method and the core idea of the present invention. It should be noted that, for those skilled in the art, without departing from the principle of the present invention, it is possible to make various improvements and modifications to the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
Claims (10)
1. Speckle converter based on gradual change refractive index waveguide and two-dimentional back taper waveguide are integrated, its characterized in that: the silicon substrate (3), the two-dimensional inverted-cone-shaped waveguide (4) and the cladding (5) are arranged on one side above the silicon substrate (3) from bottom to top, and the graded-index waveguide (2) is located on the other side above the silicon substrate (1) and is attached to the two-dimensional inverted-cone-shaped waveguide (4);
a first input port (21) and a first output port (22) are respectively arranged on opposite surfaces of the graded-index waveguide (2), a second input port (41) and a second output port (42) are arranged at two ends of a long shaft of the two-dimensional inverted-cone-shaped waveguide (4), and the first output port (22) is attached to the second input port (41);
incident light enters from the first input port (21), is converged by the graded index waveguide (2) and then is output from the first output port (22), then enters the two-dimensional inverted-cone-shaped waveguide (4) through the second input port (41) for adiabatic transmission, and finally is output through the second output port (41) to be coupled with the integrated silicon waveguide.
2. The integrated graded-index-waveguide-and-two-dimensional inverted-tapered-waveguide-based spot size converter according to claim 1, wherein: the cladding (5) is made of silicon dioxide, and the cladding (5) is formed by combining an outer cladding (60) and an inner cladding (50).
3. The integrated spot size converter based on a graded-index waveguide and a two-dimensional inverted-cone waveguide of claim 2, wherein: the refractive index of the inner cladding (50) is higher than that of the outer cladding (60), and the width and thickness of the inner cladding (50) are both smaller than those of the outer cladding (60).
4. The integrated graded-index-waveguide-and-two-dimensional inverted-tapered-waveguide-based spot size converter according to claim 1, wherein: the medium of the graded index waveguide (2) is silicon dioxide, and the refractive index distribution in the silicon dioxide is accurately controlled through an ion implantation process, so that the graded index distribution is realized.
5. The integrated graded-index-waveguide-and-two-dimensional inverted-tapered-waveguide-based spot size converter according to claim 4, wherein: the graded refractive index is distributed in depth, from top to bottom, the refractive index distribution is increased according to parabolic distribution, and after the highest refractive index is reached, the refractive index distribution is decreased according to Gaussian distribution; in the transverse direction, the refractive index distribution is gaussian, with the highest refractive index at the central location.
6. The integrated spot-size converter based on graded-index waveguide and two-dimensional inverted-cone waveguide according to claim 1 or 4, wherein: the incident light is standard single-mode fiber with the mode spot size of 8-10 mu m, and the mode spot size of the standard single-mode fiber is compressed to 3-4 mu m after the standard single-mode fiber passes through the graded index waveguide (2).
7. The integrated graded-index-waveguide-and-two-dimensional inverted-tapered-waveguide-based spot size converter according to claim 1, wherein: the two-dimensional inverted-cone-shaped waveguide (4) is made of silicon and is inverted-cone-shaped, the second input port (41) is a cone tip, and the thickness and the width of the two-dimensional inverted-cone-shaped waveguide (4) are linearly increased from the cone tip along the light propagation direction until the second output port (42) is cut off.
8. The integrated spot-size converter based on a graded-index waveguide and a two-dimensional inverted-cone waveguide according to claim 1 or 7, wherein: the length design of the two-dimensional inverted cone waveguide (4) follows the adiabatic transmission principle, the width of a cone tip is higher than 200nm, incident light is coupled at the first output port (22) and the second input port (41), and the coupling loss is within 0.5 dB.
9. The integrated spot size converter based on a graded-index waveguide and a two-dimensional inverted-cone waveguide according to claim 1, wherein: the silicon dioxide substrate (3) is of a silicon wafer inherent structure, and the thickness of the silicon dioxide substrate is consistent with that of the silicon substrate (1).
10. The integrated spot size converter based on a graded-index waveguide and a two-dimensional inverted-cone waveguide according to claim 1, wherein: the operating wavelength of the spot size converter is 1550nm.
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| CN202211405474.5A CN115576054A (en) | 2022-11-10 | 2022-11-10 | Mode spot converter based on integration of graded index waveguide and two-dimensional inverted cone waveguide |
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| CN202211405474.5A CN115576054A (en) | 2022-11-10 | 2022-11-10 | Mode spot converter based on integration of graded index waveguide and two-dimensional inverted cone waveguide |
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