CN113296189B - Silicon-based optical waveguide mode filter based on directional coupling structure and preparation method thereof - Google Patents
Silicon-based optical waveguide mode filter based on directional coupling structure and preparation method thereof Download PDFInfo
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- CN113296189B CN113296189B CN202110549167.3A CN202110549167A CN113296189B CN 113296189 B CN113296189 B CN 113296189B CN 202110549167 A CN202110549167 A CN 202110549167A CN 113296189 B CN113296189 B CN 113296189B
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- 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
- G02B6/13—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
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Abstract
Orientation-based methodA silicon-based optical waveguide mode filter with a coupling structure and a preparation method thereof belong to the technical field of integrated optoelectronics. The silicon Core waveguide Core consists of a silicon substrate, an upper silicon dioxide cladding layer, a lower silicon dioxide cladding layer, an input waveguide Core1 and an output waveguide Core2, wherein the two silicon Core layers are positioned between the upper silicon dioxide cladding layer and the lower silicon dioxide cladding layer and have the same structural parameters; the input waveguide Core1 and the output waveguide Core2 are few-mode waveguides and can simultaneously transmit E11、E21、E31Three modes; the input waveguide Core1 and the output waveguide Core2 are both straight waveguide structures with rectangular sections; the filtering function of a specific mode can be realized by designing the sizes of the input waveguide Core1 and the output waveguide Core2, the waveguide spacing between the two waveguides and the coupling length of the silicon Core layer. The preparation method is simple, does not need complex and expensive process equipment and high-difficulty preparation technology, is compatible with the traditional semiconductor process, is easy to integrate, is suitable for large-scale production, plays an important role in a mode division multiplexing transmission system, and has very wide application prospect.
Description
Technical Field
The invention belongs to the technical field of integrated optoelectronics, and particularly relates to a silicon-based optical waveguide mode filter based on a directional coupling structure and a preparation method thereof.
Background
With the rapid development of communication technology and the continuous progress of technology, especially with the rapid development of services such as 5G, multimedia, artificial intelligence, etc., various intelligent devices are gradually popularized and applied, a "big data era" based on data storage, transmission and processing puts higher demands on the transmission of a communication network and a single chip multiprocessor, and how to realize on-chip interconnection communication among hundreds of thousands of processor cores is a key for determining the performance of the single chip multiprocessor in the future. The traditional metal electrical interconnection network is restricted by physical characteristics, and the speed, delay, noise and power consumption levels cannot meet the high-speed and large-capacity requirements of future on-chip integrated communication. The optical interconnection has the advantages of extremely high bandwidth, ultra-fast transmission rate, high anti-interference performance and the like as a new interconnection mode. The combination of micro-electronics and photoelectrons, and the formation of a photoelectric hybrid integrated chip by using an optical interconnection network to replace an electric interconnection network among integrated circuit chips or even inside the chips is one of the important technical development directions of super-large-scale integrated circuits in the post-molar age.
Silicon-based optoelectronic technology, as an important solution for carrying a large amount of data transmission, can realize mass production, low cost, high integration and is compatible with CMOS process, wherein the most important is to reduce power consumption and increase transmission rate. In the process of rapid development of silicon-based optoelectronic technology, more and more research institutions are actively researching silicon-based optoelectronic technology. In the silicon-based optoelectronic technology, a silicon-based integrated mode multiplexing/demultiplexing device is one of the key optical interconnection devices on a super-high speed chip, and in a mode division multiplexing/demultiplexing system, light in different modes is required to be separated or filtered sometimes, so that mode selection multiplexing or filtering is realized. The invention provides the silicon-based optical waveguide mode filter based on the directional coupling structure, which has a simple structure and a compact size.
Disclosure of Invention
The invention aims to provide a mode filtering device which can filter or separate a basic mode and enable the high-order mode to be continuously transmitted when the high-order mode and the basic mode are transmitted in a few-mode waveguide. The invention is a passive device and has higher process tolerance.
Compared with the traditional filter, the silicon-based optical waveguide mode filter based on the directional coupling structure is more suitable for a mode division multiplexing/demultiplexing system. Due to the limitation of nonlinear shannon capacity, the transmission capacity of the single-mode waveguide system gradually reaches the upper limit, and the mode division multiplexing technology plays a key role in solving the problem. In the mode division multiplexing technology, a mode division multiplexing/demultiplexing device based on a planar optical waveguide structure has important application, and transmission and selection between a high-order mode and a fundamental mode transmitted in an optical waveguide are very important links. The present invention provides a device capable of separating high-order mode signal light from signal light in which a plurality of mode signals are mixed, while fundamental mode signal light is separated or filtered. Meanwhile, the preparation method provided by the invention is simple, only needs some common semiconductor equipment and conventional manufacturing processes, does not need complex and expensive process equipment and high-difficulty preparation technology, is compatible with the traditional semiconductor process, is easy to integrate, is suitable for large-scale production, and has important application prospect.
The technical scheme adopted by the invention for solving the technical problems is as follows:
the invention relates to a silicon-based optical waveguide mode filter based on a directional coupling structure, which is characterized in that: the silicon Core waveguide Core consists of a silicon substrate, an upper silicon dioxide cladding layer, a lower silicon dioxide cladding layer, an input waveguide Core1 and an output waveguide Core2, wherein the silicon Core layer is located between the upper silicon dioxide cladding layer and the lower silicon dioxide cladding layer, the structure parameters of the input waveguide Core1 and the structure parameters of the output waveguide Core2 are the same, the refractive indexes of the upper silicon dioxide cladding layer and the lower silicon dioxide cladding layer are 1.445, and the refractive index of the silicon Core layer is 3.455. The input waveguide Core1 and the output waveguide Core2 are few-mode waveguides and can simultaneously transmit E11、E21、E31Three modes. Inputting signal light of three modes into an input waveguide CoreIn fig. 1, signal light of three modes is gradually coupled into the output waveguide Core2 due to the coupling principle, but due to the difference of effective refractive indexes of the signal light of three modes, energy is desired to be completely coupled into the output waveguide Core2, and the coupling length corresponding to each mode is different. The invention can realize the filtering function of a specific mode by designing the sizes of the input waveguide Core1 and the output waveguide Core2 of the silicon Core layer, the waveguide distance between the two waveguides and the coupling length (the straight waveguide length of the two waveguides).
The input waveguide Core1 and the output waveguide Core2 are each a straight waveguide structure that is rectangular in cross-section and has S-shaped bends at their respective input and output ends, and the Core1 is narrowed at the trailing end. The purpose of the S-bend design is to separate the two cores 1 and 2 at the input and output ends, and the tail end narrowing design is to reduce the effect of the filtered signal light on the output waveguide Core 2. The influence of S-shaped bending and tail end narrowing on the extinction ratio and crosstalk can be ignored, and the filtering function is not influenced.
The working process of the device of the invention is as follows: input E from Input port of Input waveguide Core111、E21、E31Three modes of signal light, three signal lights are transmitted in the input waveguide Core1, enter the straight waveguide coupling region, and pass through the directional coupler composed of the input waveguide Core1 and the output waveguide Core2, E21、E31The signal light of the mode is coupled into the Output waveguide Core2 in the straight waveguide coupling region, and is Output from the Output port Output, and E11The majority of the energy of the mode is left in the input waveguide Core1 and is filtered out through the S-bend; or to Input E from Input port Input11、E21、E31Mode, Output E from Output port21Mode, filter out E11And E31Mode(s).
In order to obtain the optimal coupling length, parameters influencing the coupling length, such as the structural size of the waveguide and the spacing between the waveguides, need to be simulated and calculated. In the standard CMOS process adopted by the invention, the height of the silicon core layer waveguide is 220 nm. For input waveguide Core1 using Lumerical MODE softwareThe width and the mode effective refractive index are simulated and scanned, and when the width of the waveguide is 1.42 mu m, the input and output waveguides have stable E11、E21、E31Three modes, so the width of the silicon core layer waveguide is selected to be 1.42 μm. The directional coupling region adopts a symmetrical waveguide structure, so that the height of the output waveguide Core2 is 220nm, and the width is 1.42 μm.
The influence of the waveguide pitch on the coupling length is significant, and in order to obtain a suitable coupling length, the relationship of the waveguide pitch between the input waveguide Core1 and the output waveguide Core2 on the coupling length and the coupling efficiency was calculated by scanning with the use of the statistical MODE software. Three different modes E under different waveguide spacing are obtained11、E21、E31Coupling efficiency versus coupling length. The appropriate waveguide spacing and coupling length is determined by the performance requirements of the device. At each different waveguide spacing, at E ensuring output port11Normalized power of signal light of mode is less than 7%, E21、E31And selecting a proper coupling length under the condition that the normalized power of the signal light of the mode is more than 92 percent. In order to meet the requirement of miniaturization of the device and considering the preparation process, the invention finally selects the waveguide spacing d to be 180nm and 170 nm. And further parameter simulation is carried out on the devices at the two waveguide pitches.
Through calculating the relation between the coupling length and the normalized transmissivity of different modes of light, the device can be found out that the function of the device can be expanded by changing the coupling length, and the E can be further filtered11And E31Mode, only E21The mode is passed, and at the same time, the device of the function is further optimized by simulation.
The silicon-based optical waveguide mode filter based on the directional coupling structure can be manufactured on an SOI (silicon-on-insulator, substrate Si-SiO)2Top Si structure) as shown in fig. 3.
The invention relates to a preparation method of a silicon-based optical waveguide mode filter based on a directional coupling structure, which comprises the following steps:
1) cleaning the SOI wafer: cleaning an SOI (silicon on insulator) sheet with the top Si thickness of 220nm by using propanol for 10-20 minutes, then respectively ultrasonically cleaning by using methanol, isopropanol and deionized water for 8-15 minutes, drying water vapor on the surface of the SOI sheet at 130-180 ℃ after drying by using nitrogen;
2) glue homogenizing: spin-coating PMMA electron beam photoresist (PMMA: polymethyl methacrylate), the rotating speed of the spin coating is 2000-3000 rpm, and the spin coating time is 50-70 seconds;
3) pre-baking: pre-baking the SOI wafer spin-coated with the PMMA photoresist in the step 2), wherein the pre-baking temperature is 170-190 ℃, and the pre-baking time is 8-15 minutes;
4) electron Beam Lithography (EBL, E-Beam Lithography): carrying out electron beam lithography on the SOI sheet subjected to pre-baking in the step 3), wherein the acceleration voltage of processed electron beams is 10-30 kV, and the beam current is 100-200 pA, so that a photoresist pattern with the structure consistent with that of the input waveguide Core1 and the output waveguide Core2 is obtained on the PMMA photoresist, and taking out the SOI sheet after the lithography is finished;
5) and (3) developing: and (3) placing the SOI sheet after photoetching in the step 4) into a mixed solution of methyl isobutyl ketone (MIBK) and Isopropanol (IPA) at room temperature for development for 30-40 seconds, wherein the molar ratio of the MIBK to the IPA is 1:3, fixing in IPA solution for 40-60 seconds, removing PMMA photoresist which is not subjected to electron beam lithography, and then baking for 3-6 minutes at 50-70 ℃ and 8-15 minutes at 85-95 ℃;
6) etching: etching the SOI sheet after the heat baking in the step 5) by using an ICP (inductively Coupled plasma) etching machine, wherein the silicon chip layer except the structures of the input waveguide Core1 and the output waveguide Core2 is etched due to the masking effect of the photoresist pattern which is consistent with the structures of the input waveguide Core1 and the output waveguide Core2, the etching time is controlled to ensure that the etching depth is 220nm, and the etching gas is SF6And C4F8(ii) a The source power of the ICP etcher is 30-100W, the bias power is 1-10W, the etching time is about 1 minute and 40 seconds, and the etching gas is SF6And C4F8The flow rates of the etching gas are respectively 5-15 sccm and 10-20 sccm;
7) washing residual glue: respectively carrying out ultrasonic cleaning on the SOI sheet subjected to ICP etching in the step 6) for 8-15 minutes by using acetone, methanol, isopropanol and deionized water, so as to remove PMMA photoresist remaining on the surface of the waveguide;
8) growing silicon dioxide: and (3) regrowing a silicon dioxide upper cladding layer with the total thickness (including the thickness of the upper cladding layer on the upper surface of the waveguide and the thickness of the cladding layer on the side surface of the waveguide core layer) of 0.5-1.5 mu m on the SOI sheet subjected to the PMMA photoetching removal in the step 7) by using a Plasma Enhanced Chemical Vapor Deposition (PECVD) technology, wherein the total flow of used oxygen and silane is 30-70 sccm, the ratio of the oxygen to the silane is 0.5-10, the argon flow is 50-200 sccm, the radio frequency power is 40-100W, the substrate temperature is 200-500 ℃, and the working pressure is 1000-2000 mTorr, so that the silicon-based optical waveguide mode filter based on the directional coupling structure is obtained.
Compared with the prior art, the invention has the beneficial effects that:
the invention designs a silicon-based optical waveguide mode filter based on a directional coupling structure. The invention selects proper coupling length to realize input E by calculating the effective refractive index of the mode11、E21、E31Mode, output E21And E31Mode, filter out E11Modes (waveguide spacing 180nm and 170nm, coupling length 102 μm and 94 μm, respectively), or to achieve input E11、E21、E31Mode, output E21Mode, filter out E11And E31Modes (waveguide spacing 180nm and 170nm, coupling length 126 μm and 116 μm, respectively). The device plays an important role in a mode division multiplexing transmission system and has very wide application prospect. And the manufacturing process is simple, the size of the device is small, and the photoelectric hybrid integration is facilitated.
Drawings
FIG. 1: the invention relates to a three-dimensional structure schematic diagram of a silicon-based optical waveguide mode filter based on a directional coupling structure.
FIG. 2: the cross-sectional structures of the input waveguide Core1 and the output waveguide Core2 at the dashed lines in fig. 1 are schematically shown, and the Core1 and the Core2 constitute a horizontally symmetric directional coupler.
FIG. 3: the invention relates to a preparation process flow chart of a silicon-based optical waveguide mode filter based on a directional coupling structure.
FIG. 4: normalized output power versus coupling length curves for 3 modes at different waveguide spacings: (a) - (f) waveguide pitches 220nm, 210nm, 200nm, 190nm, 180nm and 170nm, respectively.
FIG. 5: implementing the function as passing through E21、E31Mode, filter out E11Mode and waveguide spacing of 180nm, E11、E21、E31The variation relation curve (a) of normalized output power of the three modes along with the wavelength (1500 nm-1600 nm); implementing the function as passing through E21、E31Mode, filter out E11Mode and waveguide spacing of 170nm, E11、E21、E31The variation curve (b) of normalized output power of the three modes along with the wavelength (1500 nm-1600 nm).
FIG. 6: implementing the function as passing through E21Mode, filter out E11、E31Mode and waveguide spacing of 180nm, E11、E21、E31The variation relation curve (a) of normalized output power of the three modes along with the wavelength (1500 nm-1600 nm); implementing the function as passing through E21Mode, filter out E11、E31Mode and waveguide spacing of 170nm, E11、E21、E31The variation curve (b) of normalized output power of the three modes along with the wavelength (1500 nm-1600 nm).
Detailed Description
Example 1:
1. cleaning the SOI wafer: and (3) putting the standard SOI wafer with the top layer silicon thickness of 220nm into an ultrasonic cleaning machine, cleaning for 15 minutes by using a propanol solution, and cleaning for 10 minutes by using methanol, isopropanol and deionized water in the ultrasonic cleaning machine. Drying the cleaned SOI wafer by a nitrogen gun, and drying the SOI wafer on a hot plate at 150 ℃ for 5 minutes to dry the surface water vapor of the sample wafer;
2. glue homogenizing: putting the dried SOI wafer into a spin coater, and spin-coating PMMA photoresist at the spin speed of 2500rpm for 60 seconds;
3. pre-baking: placing the sample wafer after glue homogenizing on a hot plate for pre-drying at 180 ℃ for 10 minutes;
4. electron Beam Lithography (EBL, E-Beam Lithography): putting a photoresist sample wafer which is subjected to spin coating into an EBL equipment cabin, moving the sample wafer to a preset scanning position, scanning a specific position on the photoresist sample wafer by using a waveguide pattern file which is designed in advance to form a waveguide pattern on the wafer, automatically scanning the waveguide pattern according to the specified waveguide pattern after aligning the focus of an electron gun, setting the acceleration voltage of a processed electron beam to be 20kV, setting the beam current to be 120pA, and taking the wafer out of the EBL equipment cabin after directly writing the structure;
5. and (3) developing: putting the photoetching finished SOI piece into a mixed solution of methyl isobutyl ketone (MIBK) and IPA at room temperature, wherein the molar ratio is MIBK: developing for 35 seconds with IPA (1: 3), fixing for 50 seconds in IPA solution, developing to obtain a waveguide pattern photoetched by electron beam lithography, baking at 60 deg.C for 5 min, and baking at 90 deg.C for 10 min;
6. etching: etching the developed SOI wafer by using an ICP (inductively Coupled plasma) etching machine, wherein the source power of the ICP etching machine is 80W, the bias power is 5W, the etching time is about 1 minute and 40 seconds, and the etching gas is SF6And C4F8The gas flow is respectively 10sccm and 15sccm, and the etching depth is 220 nm;
7. washing residual glue: and (3) leaving some electron beam exposure PMMA on the waveguide after the etching is finished, respectively carrying out ultrasonic cleaning for 10 minutes by using acetone, methanol, isopropanol and deionized water, and drying the SOI sample wafer by using a nitrogen gun after the cleaning is finished.
8. Growing silicon dioxide: a silicon dioxide layer with the total thickness of 1 mu m is grown on the dried SOI sheet by using a PECVD technology to serve as an upper cladding layer for protecting a device, the total flow of oxygen and silane is 60sccm, the ratio of the oxygen to the silane is 2, the flow of argon is 90sccm, the radio frequency power is 40W, the temperature of a substrate is 350 ℃, and the working pressure is 1500 mTorr. Thereby obtaining the silicon-based optical waveguide mode filter based on the directional coupling structure.
Example 2:
as shown in fig. 1, in order to realize that a plurality of modes are input into an input waveguide and a high-order mode is output from an output waveguide, the invention separates a fundamental mode from a device and realizes a mode filtering function. The adopted structure is a directional coupling structure, and the principle is that the effective refractive indexes of light in different modes transmitted in a few-mode waveguide are different, so that ideal coupling, namely energy is completely coupled from one optical waveguide to another optical waveguide, and the required coupling lengths are different. E is realized by adjusting the size parameters of the waveguides and the waveguide spacing between the waveguides and setting the proper coupling length21、E31Mode light achieving ideal coupling in the coupling region, E11The mode light is left in the input waveguide and is guided out by the S-shaped waveguide, and the function of filtering the mode is realized.
As shown in fig. 2, wherein the components are: a silicon substrate 1, a silica lower cladding layer 2, an output waveguide Core23 and an input waveguide Core 14, a silica upper cladding layer 5. The input few-mode waveguide Core1 has a width of 1.42 μm and a height of 220 nm. The output waveguide Core2 is symmetrical to the input waveguide and has the same structural dimensional parameters. Because the thickness of the silicon core layer of the selected standard SOI is 220nm, the height of the waveguide core layer selected by the waveguide structure is 220 nm. E can be present at a waveguide width of 1.4211、E21、E31Three modes. E when the waveguide width was 1.42 μm by using Lumerical MODE software11、E21、E31The effective refractive indices of the three modes were calculated. Wherein E11The effective refractive index of the mode is 2.775505, E21The effective refractive index of the mode is 2.623981, E31The effective index of the mode is 2.357665.
As shown in fig. 3, (a) is the cleaned SOI wafer; (b) an SOI sheet with PMMA photoresist coated on the surface in a spinning mode; (c) an SOI sheet with an input waveguide Core1 and output waveguide Core2 photoresist mask pattern; (d) an SOI sheet having a structure of an input waveguide Core1 and an output waveguide Core2 after mask lithography; (e) an SOI sheet having a structure of an input waveguide Core1 and an output waveguide Core2 for removing residual glue; (f) the SOI sheet with the structure of the input waveguide Core1 and the output waveguide Core2 is a spin-on silicon dioxide upper cladding layer, namely the silicon-based optical waveguide mode filter based on the directional coupling structure.
As shown in fig. 4: the coupling length at 1550nm wavelength for E was calculated using a Lumerical MODE at waveguide pitches of 220nm, 210nm, 200nm, 190nm, 180nm and 170nm, respectively11、E21、E31The coupling efficiency of the three modes affects. For E11Mode light, normalized power of output waveguide less than 0.1, E21、E31The normalized power of the mode light output waveguide is greater than 0.95. When the above conditions are satisfied, the coupling length intervals corresponding to different waveguide pitches are listed as follows: the coupling length interval of the waveguide spacing of 220nm is 140 μm to 143 μm, and the coupling length interval of the waveguide spacing of 210nm is 138 μm; the coupling length interval of the waveguide spacing of 200nm is 125-126 μm; the coupling length interval of the waveguide spacing of 190nm is 112-116 μm; the coupling length interval with the waveguide spacing of 180nm is 99-105 μm; the coupling length interval of the waveguide spacing 170nm is 90 μm to 97 μm. Under the condition that the coupling efficiency parameters are not different, the invention selects the structural parameters with relatively smaller device size. Under the condition that the waveguide spacing is 180nm and 170nm, the waveguide spacing is 180nm and the coupling length is 102 μm finally selected in view of the manufacturing process, and the process tolerance can reach +/-3 μm. At this time, E11、E21、E31The normalized power of the three modes at the output port is 0.07464, 0.96646 and 0.98442 respectively, and further transmission E can be realized21、E31Mode, filter out E11And (5) completing a mold filtering function.
As shown in fig. 5, the transmittance of the mode filter was calculated as a function of wavelength over the wavelength range from 1500nm to 1600 nm. The change in the transmission of the output waveguide output port of the device was calculated for waveguide pitches of 180nm and 170nm, respectively, and coupling lengths of 102 μm and 94 μm, respectively. It can be seen that E is the same for the case where the waveguide pitch is 180nm11Transmittance of mode is maintained below 0.1, E21The transmittance of the mode at the output port of the output waveguide does not substantially vary with wavelength, E31Mode is in transmissionThe transmittance of the output port of the waveguide can be more than 90% in the wavelength range of 1542nm to 1582 nm. E at a waveguide spacing of 170nm11The transmissivity of the output waveguide output ports of the modes is less than 0.82, E21The transmission of the modes at the output port of the output waveguide is greater than 82.4%, E31The transmission of the modes at the output ports of the output waveguides is greater than 90% over the wavelength range of 1546nm to 1589 nm.
Meanwhile, the mode filter can further realize function expansion, as shown in FIG. 4, under the condition that the waveguide spacing is 180nm and 170nm, when the coupling length is respectively selected to be 126 μm and 116 μm, the input E can be realized11、E21、E31Signal light of three modes, passing only E21Mode, filter out E11、E31Mode(s). On the basis, the change of the transmissivity of the output port of the output waveguide is further calculated, and the calculation result is shown in figure 6, and the filter mode function can be realized in the wavelength range of 1500nm to 1600 nm.
In a word, the silicon-based optical waveguide mode filter based on the directional coupling structure provided by the invention realizes the functions of inputting signal light in three different modes, finally outputting a high-order mode, filtering a fundamental mode and filtering the mode. And different mode filtering functions can be realized by changing the length of the coupling region. The device structure has very important application in optical communication systems and on-chip optical interconnection technology.
It should be noted that the specific embodiments are only representative examples of the present invention, and it is obvious that the technical solution of the present invention is not limited to the above-mentioned examples, and many variations are possible, and different waveguide materials, such as polymers, silicon nitride, lithium niobate, other organic and inorganic materials, etc. may be used. Those skilled in the art, having the benefit of this disclosure, and being able to ascertain without limitation the invention so disclosed or obvious from the written description, are to be protected by the present patent.
Claims (2)
1. A silicon-based optical waveguide mode filter based on a directional coupling structure is characterized in that: the silicon Core waveguide Core consists of a silicon substrate, an upper silicon dioxide cladding layer, a lower silicon dioxide cladding layer, an input waveguide Core1 and an output waveguide Core2, wherein the two silicon Core layers are positioned between the upper silicon dioxide cladding layer and the lower silicon dioxide cladding layer and have the same structural parameters; the input waveguide Core1 and the output waveguide Core2 are few-mode waveguides and can simultaneously transmit E11、E21、E31Three modes; the input waveguide Core1 and the output waveguide Core2 are both straight waveguide structures with rectangular sections; the input waveguide Core1 and the output waveguide Core2 have S-shaped bends at their respective input and output ends, and the Core1 is narrowed at the tail end; the input waveguide Core1 and the output waveguide Core2 are both 220nm in height and 1.42 μm in width; input E is achieved when the waveguide spacing is 180nm and 170nm, and the coupling lengths are 102 μm and 94 μm, respectively11、E21、E31Mode, output E21And E31Mode, filter out E11A mode; input E is achieved when the waveguide spacing is 180nm and 170nm, and the coupling lengths are 126 μm and 116 μm, respectively11、E21、E31Mode, output E21Mode, filter out E11And E31A mode; the refractive index of the silica upper and lower cladding layers was 1.445, and the refractive index of the silicon core layer was 3.455.
2. The method for preparing a silicon-based optical waveguide mode filter based on a directional coupling structure as claimed in claim 1, comprising the steps of:
1) cleaning the SOI wafer: cleaning an SOI (silicon on insulator) sheet with the top Si thickness of 220nm by using propanol for 10-20 minutes, then respectively ultrasonically cleaning by using methanol, isopropanol and deionized water for 8-15 minutes, drying water vapor on the surface of the SOI sheet at 130-180 ℃ after drying by using nitrogen;
2) glue homogenizing: spin-coating PMMA photoresist on the surface of the dried SOI sheet in the step 1), wherein the spin-coating speed is 2000-3000 rpm, and the spin-coating time is 50-70 seconds;
3) pre-baking: pre-baking the SOI wafer spin-coated with the PMMA photoresist in the step 2), wherein the pre-baking temperature is 170-190 ℃, and the pre-baking time is 8-15 minutes;
4) electron beam lithography: carrying out electron beam lithography on the SOI sheet subjected to pre-baking in the step 3), thereby obtaining a photoresist pattern with the structure consistent with that of the input waveguide Core1 and the output waveguide Core2 on the PMMA photoresist, and taking out the SOI sheet after the lithography is finished;
5) and (3) developing: and (3) placing the SOI sheet after photoetching in the step 4) into a mixed solution of MIBK and IPA at room temperature for development for 30-40 seconds, wherein the molar ratio of the MIBK to the IPA is 1:3, fixing in IPA solution for 40-60 seconds, removing PMMA photoresist which is not subjected to electron beam lithography, and then baking for 3-6 minutes at 50-70 ℃ and 8-15 minutes at 85-95 ℃;
6) etching: etching the SOI sheet after the heat baking in the step 5) by using an ICP etching machine, etching the silicon chip layer except the input waveguide Core1 and the output waveguide Core2 under the mask action of a photoresist pattern which is consistent with the structures of the input waveguide Core1 and the output waveguide Core2, controlling the etching time to ensure that the etching depth is 220nm, and etching gas is SF6And C4F8；
7) Washing residual glue: respectively carrying out ultrasonic cleaning on the SOI sheet subjected to ICP etching in the step 6) for 8-15 minutes by using acetone, methanol, isopropanol and deionized water, so as to remove PMMA photoresist remaining on the surface of the waveguide;
8) growing silicon dioxide: growing a silicon dioxide upper cladding with the thickness of 0.5-1.5 mu m on the SOI sheet subjected to the PMMA photoetching removal in the step 7) by using a plasma enhanced chemical vapor deposition technology, thereby obtaining the silicon-based optical waveguide mode filter based on the directional coupling structure.
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| US4911513A (en) * | 1988-01-14 | 1990-03-27 | Commissariat A L'energie Atomique | Integrated optical device allowing for the separation of polarized components of a guided electromagnetic field and the method of making the device |
| CN107765366A (en) * | 2017-11-02 | 2018-03-06 | 中山大学 | A kind of silicon nitride polarization beam apparatus of asymmetrical shape and preparation method thereof |
| CN110161626A (en) * | 2019-05-17 | 2019-08-23 | 南京邮电大学 | A kind of three-dimensional silica base mode selection switch and preparation method thereof |
| CN110780381A (en) * | 2019-12-02 | 2020-02-11 | 中国科学院半导体研究所 | Polarization beam splitter with asymmetric three-waveguide structure and preparation method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US4911513A (en) * | 1988-01-14 | 1990-03-27 | Commissariat A L'energie Atomique | Integrated optical device allowing for the separation of polarized components of a guided electromagnetic field and the method of making the device |
| CN107765366A (en) * | 2017-11-02 | 2018-03-06 | 中山大学 | A kind of silicon nitride polarization beam apparatus of asymmetrical shape and preparation method thereof |
| CN110161626A (en) * | 2019-05-17 | 2019-08-23 | 南京邮电大学 | A kind of three-dimensional silica base mode selection switch and preparation method thereof |
| CN110780381A (en) * | 2019-12-02 | 2020-02-11 | 中国科学院半导体研究所 | Polarization beam splitter with asymmetric three-waveguide structure and preparation method thereof |
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