CN111025473A - SWG waveguide and coupling structure - Google Patents
SWG waveguide and coupling structure Download PDFInfo
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- CN111025473A CN111025473A CN201911157455.3A CN201911157455A CN111025473A CN 111025473 A CN111025473 A CN 111025473A CN 201911157455 A CN201911157455 A CN 201911157455A CN 111025473 A CN111025473 A CN 111025473A
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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
- G02B6/13—Integrated optical circuits characterised by the manufacturing method
- G02B6/136—Integrated optical circuits characterised by the manufacturing method by etching
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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
- G02B6/1225—Basic optical elements, e.g. light-guiding paths comprising photonic band-gap structures or photonic lattices
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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
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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
- G02B2006/12166—Manufacturing methods
- G02B2006/12176—Etching
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Abstract
The invention belongs to the technical field of optical waveguides, and relates to an SWG waveguide and a coupling structure, wherein the SWG waveguide comprises a 220nm thick silicon waveguide core layer and 3 mu m thick SiO2Substrate and SiO 2 μm thick2An upper cladding layer, the coupling structure including a first structure and a second structure, the first structure being an adiabatic taper structure. According to the invention, a mature multilayer etching technology in a CMOS (complementary metal oxide semiconductor) process is utilized, a third dimensional structure change is introduced, so that an SWG waveguide and a coupling structure compatible with the 0.18-micron CMOS process are obtained, and a simulation result shows that 1.55-micron light can be transmitted in the SWG waveguide with low loss, when transition orders of the coupling structure are respectively 10-order and 20-order, the loss is respectively 1.1db and 0.5db, and the result provides a good theoretical basis and technical support for compatible manufacture of the SWG structure by utilizing the CMOS process.
Description
Technical Field
The invention belongs to the technical field of optical waveguides, and relates to an SWG waveguide and a coupling structure.
Background
A sub-wavelength grating (SWG) structure is a metamaterial, meaning a structure composed of periodic or aperiodic masses with characteristic dimensions equal to or smaller than the wavelength of light. The application of the SWG structure in a diffractive optical element has been in history for more than 50 years, each basic building block of the SWG structure is equivalent to the lattice of a photonic crystal, when the size of the block is far smaller than the wavelength of light, diffraction is inhibited, the structure is represented as a material with uniform effective refractive index, and the structure can be used for designing integrated photonic devices with different refractive indexes, mode sizes and dispersion;
in recent years, the SWG structure is widely applied to the field of silicon-based Photonic Integration (PICs), compared with the traditional PIC device, the mode size is greatly increased by reducing the effective refractive index of the SWG structure, the interaction between light and substances is enhanced, and the application of biochemical sensing is facilitated; the SWG structure can accurately control the mode size and has the function of a high-efficiency edge coupler between the optical fiber and the waveguide; they can also be designed to have properties of high thermal stability or specific dispersion, which can be used for thermally stable applications or to realize new optical elements. The SWG structure greatly improves the design flexibility of silicon-based PICs;
SWG structures are typically embedded in conventional PIC networks to serve as isolation devices for special functions, and due to the low effective refractive index of the SWG structures, a coupling structure needs to be established between the SWG structures and the solid waveguide. Coupling between the SWG structure and the solid waveguide is typically achieved by gradually changing the fill factor of the solid waveguide from 1 to that of the SWG structure (where the fill factor is defined as the core volume divided by the total structure volume). Electron beam Exposure (EBL) provides an easy to implement method for the fabrication of such transition structures, since it allows a minimum line width of 10nm, enabling a smooth transition of the fill factor by changing the two-dimensional design of the structure.
Indeed, to the best of the inventors' knowledge, all SWG structures in the prior art to date have been fabricated with EBLs, which limits the application of SWG structures in mass production. Therefore, to achieve a wide range of applications for SWG structures, SWG structure designs compatible with CMOS processes are required. The main challenge facing this work is that the minimum line width of a typical CMOS process is large, which can result in a discontinuous fill factor of the coupled structure if only two-dimensional variations are considered in the design.
Disclosure of Invention
In order to solve the problems proposed in the background art, the invention provides a SWG waveguide and coupling structure compatible with a 0.18 μm CMOS process by introducing a third dimensional structural change using a multi-layer etching technique matured in the CMOS process.
The technical problem solved by the invention is realized by adopting the following technical scheme:
an SWG waveguide and a coupling structure, the SWG waveguide comprises a silicon waveguide core layer, SiO2Substrate and SiO2An upper cladding layer, the coupling structure including a first structure and a second structure, the first structure being an adiabatic taper structure.
The thickness of the silicon waveguide core layer is 220nm and SiO2The thickness of the substrate was 3 μm, SiO2The thickness of the upper cladding was 2 μm.
A suitable wavelength for the SWG waveguide is 1.55 μm.
The width of the SWG waveguide is less than 350 nm.
The width of the SWG was 300 nm.
The SWG waveguide has a fill factor of 50% and a period of 400 nm.
The length of the adiabatic taper structure is 5 μm, the filling factor is 100%, and the width is 450-300 nm.
The second structure has a fill factor of 100-50%, a width of 300nm, and a period of 400 nm.
The invention has the beneficial effects that:
according to the invention, a mature multilayer etching technology in a CMOS (complementary metal oxide semiconductor) process is utilized, and a third-dimension (namely thickness) structural change is introduced, so that an SWG waveguide and a coupling structure compatible with the 0.18-micron CMOS process are obtained, wherein the thickness of the SWG waveguide is 220nm, the width of the SWG waveguide is 300nm, the period of the SWG waveguide is 400nm, and the duty ratio of the SWG waveguide is 50%, and simulation results show that 1.55-micron light can be transmitted in the SWG waveguide with low loss, and when transition orders of the coupling structure are respectively 10 orders and 20 orders, the loss of the coupling structure is respectively 1.1db and 0.5db, so that good theoretical basis and technical support are provided for compatible manufacture of the SWG structure by utilizing the CMOS process.
Drawings
FIG. 1 is a diagram of the electric field distribution of light propagating in various grating waveguides according to the present invention.
FIG. 2 is a graph of a simulated optical field in a SWG waveguide in accordance with the present invention.
Fig. 3 is a diagram of the coupling structure for the 10 and 20 step transitions of the present invention.
FIG. 4 is a diagram of simulation results of the coupling structure of the present invention.
Detailed Description
Example 1
The invention relates to an SWG waveguide and coupling structure, which is characterized in that the inventor utilizes the mature multilayer etching technology in the CMOS process to introduce structural change in the third dimension (namely thickness) to obtain the SWG waveguide and coupling structure compatible with the 0.18 mu m CMOS process;
the invention is carried out based on the SWG waveguide theory, which comprises the following steps: when light is at a refractive index n1And a background material n of refractive index2The electric field can be divided into a vertical direction and a direction parallel to the periodic interface when transmitted in the SWG structure of (1), and the equivalent refractive index is given by:
where a is the width of the SWG structure, Λ is the grating period, and λ is the free-space optical wavelength;
considering a waveguide of W width, the effective refractive index of each mode is:
where m is the modulus, whereby a SWG waveguide of ideal effective refractive index can be obtained.
For a grating having periodicity along the propagation axis, Bragg resonance occurs when the periodicity is equal to the guided half wavelength, when Λ > λ/2neffActing as a derivativeShooting a grating; when lambda is lambda/2 neffBragg reflection occurs; when Λ < λ/2neffLight propagates along the Z-axis with almost no loss, SWG structures can be considered as uniform index waveguides, similar to solid waveguides; FIG. 1 is an electric field distribution of light propagating in various grating waveguides, where in FIG. 1 a) is diffraction, b) is Bragg reflection, c) is light propagating in an SWG waveguide, and d) is light propagating in a solid waveguide;
based on this theory, the inventors first designed a sub-wavelength structure waveguide, which is a 1.55 μm wavelength silicon SWG waveguide comprising a 220nm thick silicon waveguide core layer, a 3 μm thick SiO2Substrate and SiO 2 μm thick2The upper cladding, due to the limitation of the minimum processing line width, Λ is a minimum value of 360nm, and in order to obtain higher manufacturing tolerance, the inventor selects Λ as 400nm and the filling factor is 50%;
according to the SWG waveguide theory, the effective refractive index n of the SWG waveguideeffNeeds to be less than 1.9, and after multiple simulations, the inventor finds that W < 350 can meet the requirement, and in order to obtain higher manufacturing tolerance, W is 300, and the simulated optical field in the SWG waveguide under the above conditions is shown in fig. 2, and by using the structure, a TE0 mode can be obtained, and the waveguide transmission loss is 1.1 × 10-3 db/cm;
the inventors then designed a coupling structure with a solid waveguide width of 450nm, one of the most commonly used waveguide widths in silicon-based PIC designs, requiring a gradual transition from a 450nm wide, 100% fill factor waveguide to a 300nm wide, 50% fill factor waveguide. The transition structure is composed of two parts: the first part is an adiabatic conical structure with a filling factor of 100%, W of 450-300nm and a length of 5 mu m; the second part is a structure with a filling factor of 100-50%, W of 300nm and a period of 400 nm;
the structure design of the second part is calculated by an exhaustive method, a periodic structure which can be prepared by a 0.18 μm CMOS process is listed, in order to ensure the compatibility of the CMOS process, the minimum line width is set to be 180nm, the resolution is set to be 10nm, the etching depth is limited to be 70nm, 150nm and 220nm, the above values are based on MPW service used by processing, and then a structure with the filling factor closest to the requirement is selected from the exhaustive list, for example, in the structure design of the 10-step transition stage, the structure with the filling factor of 50%, 55%, … and 100% is selected, and the detailed content of the coupling structure of the 10-step transition and the 20-step transition which is drawn in the form of GDSII is shown in figure 3.
Example 2
In the embodiment, the optical transmission of the designed SWG waveguide and the loss of the coupling structure at the transition of 10 th order and 20 th order are simulated, and the self-made SWG waveguide and the coupling structure are subjected to optical test;
1) simulation:
the inventors simulated light transmission in the designed SWG waveguide and verified that 1.55 μm light can be transmitted in this structure with low loss, while simulating the loss of the 10-and 20-step transition coupling structures; the specific simulation process is as follows: light sequentially passes through the solid waveguide, the transition structure, the SWG waveguide, the second transition structure and the second solid waveguide to be transmitted, two light field monitors are arranged at the center of each solid waveguide to acquire mode and loss information, the mode is kept as TE0, the coupling structure is in transition of 10 orders and 20 orders, the loss of the transition structure is 1.1db and 0.5db respectively, the specific simulation result is shown in figure 4, and a) in figure 4 is a simulation structure of 10 orders of transition; b) is the light field of the monitor 1; c) is the light field of the monitor 2; d) a simulated structure that is a 20-step transition; e) is the light field of the monitor 3; f) is the light field of the monitor 4;
2) optical testing
The inventor utilizes MPW service provided by the leading center of the institute of microelectronics of Chinese academy of sciences to manufacture the SWG waveguide and the coupling structure with the grating couplers at two ends as shown in FIG. 4, and the specific measurement is carried out on a self-made PIC chip test platform. All measurements were made with the single mode fiber tilted 10 degrees from the normal to the grating coupler surface, for a total of 10 chips, each having three such structures.
The specific test result is as follows: the loss of the 10 th order transition stage is 5.0db, and the loss of the 20 th order transition stage is 2.8db, and the results clearly show that more transition orders can reduce the loss because it can realize smoother transition; whereas the measured loss is greater than the simulation result, which may be due to limited overlay accuracy and process resolution, the narrower CMOS technology can greatly improve coupling efficiency by making the design smoother and better correlation between design and fabrication structures, and nevertheless, the 20-step transition structure provides good coupling efficiency for many low power applications (e.g., biosensing).
The invention designs the SWG waveguide compatible with the 0.18 mu m CMOS process and a coupling structure thereof, wherein the thickness of the SWG waveguide is 220nm, the width of the SWG waveguide is 300nm, the period of the SWG waveguide is 400nm, the duty ratio of the SWG waveguide is 50%, and simulation results show that light of 1.55 mu m can be transmitted in the SWG waveguide with low loss; simulation and experimental tests are carried out on the coupling structure with transition of 10 orders and 20 orders, in order to overcome the limit of minimum line width and realize smooth filling factor conversion, the inventor adopts a multilayer etching process provided by a CMOS process to change the three-dimensional structure of the waveguide, wherein simulation results show that when the transition orders of the coupling structure are respectively 10 orders and 20 orders, the loss of the coupling structure is respectively 1.1db and 0.5 db; the experimental result shows that the loss of the 10-order transition order is 5.0db, the loss of the 20-order transition order is 2.8db, and the self-made structure generates higher loss due to the imperfect preparation process, but the test result still provides good theoretical basis and technical support for manufacturing the SWG structure by utilizing the CMOS compatible technology.
Although the embodiments of the present invention have been described in detail, the description is only a preferred embodiment of the present invention, and should not be considered as limiting the scope of the invention, and all equivalent changes and modifications made within the scope of the present invention should be covered by the claims of the present invention.
Claims (8)
1. An SWG waveguide and coupling structure, characterized by: the SWG waveguide comprises a silicon waveguide core layer, SiO2Substrate and SiO2An upper cladding layer, the coupling structure including a first structure and a second structure, the first structure being an adiabatic taper structure.
2. The method of claim 1The SWG waveguide and coupling structure of (1), characterized in that: the thickness of the silicon waveguide core layer is 220nm and SiO2The thickness of the substrate was 3 μm, SiO2The thickness of the upper cladding was 2 μm.
3. The SWG waveguide and coupling structure of claim 1, wherein: the SWG waveguide is suitable for light with a wavelength of 1.55 μm.
4. The SWG waveguide and coupling structure of claim 1, wherein: the width of the SWG waveguide is less than 350 nm.
5. The SWG waveguide and coupling structure of claim 4, wherein: the width of the SWG waveguide is 300 nm.
6. The SWG waveguide and coupling structure of claim 1, wherein: the SWG waveguide has a fill factor of 50% and a period of 400 nm.
7. The SWG waveguide and coupling structure of claim 1, wherein: the length of the adiabatic taper structure is 5 μm, the filling factor is 100%, and the width is 450-300 nm.
8. The SWG waveguide and coupling structure of claim 1, wherein: the second structure has a fill factor of 100-50%, a width of 300nm, and a period of 400 nm.
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| CN201911157455.3A CN111025473B (en) | 2019-11-22 | 2019-11-22 | Coupling structure for establishing coupling between solid waveguide and SWG waveguide |
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| CN201911157455.3A CN111025473B (en) | 2019-11-22 | 2019-11-22 | Coupling structure for establishing coupling between solid waveguide and SWG waveguide |
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2008257771A (en) * | 2007-04-02 | 2008-10-23 | Ricoh Co Ltd | Optical pickup |
| CN102879849A (en) * | 2012-10-26 | 2013-01-16 | 苏州大学 | Sub-wavelength grating structure polarizer |
| CN103809239A (en) * | 2012-11-09 | 2014-05-21 | 江苏尚飞光电科技有限公司 | Sub-wavelength waveguide and preparation method |
| CN109407229A (en) * | 2018-11-30 | 2019-03-01 | 武汉邮电科学研究院有限公司 | A kind of end coupling device |
-
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- 2019-11-22 CN CN201911157455.3A patent/CN111025473B/en active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2008257771A (en) * | 2007-04-02 | 2008-10-23 | Ricoh Co Ltd | Optical pickup |
| CN102879849A (en) * | 2012-10-26 | 2013-01-16 | 苏州大学 | Sub-wavelength grating structure polarizer |
| CN103809239A (en) * | 2012-11-09 | 2014-05-21 | 江苏尚飞光电科技有限公司 | Sub-wavelength waveguide and preparation method |
| CN109407229A (en) * | 2018-11-30 | 2019-03-01 | 武汉邮电科学研究院有限公司 | A kind of end coupling device |
Non-Patent Citations (2)
| Title |
|---|
| DANIEL BENEDIKOVIC 等: "L-shaped fiber-chip grating couplers with high directionality and low reflectivity fabricated with deep-UV lithography", 《OPTICS LETTERS》 * |
| LAWRENCE R. CHEN等: "Subwavelength Grating Waveguide Devices for Telecommunications Applications", 《IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS》 * |
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Effective date of registration: 20220907 Address after: 100029 Beijing city Chaoyang District Beitucheng West Road No. 3 Patentee after: Institute of Microelectronics, Chinese Academy of Sciences Address before: 300000 a409-4, Tianrun Science Park, No. 110, 6th Street, Binhai New Area Development Zone, Tianjin Patentee before: QIANSE (TIANJIN) NEW MATERIAL TECHNOLOGY Co.,Ltd. |