CN117055154A - Heterogeneous integrated three-dimensional waveguide multiplexing any modes and preparation method thereof - Google Patents
Heterogeneous integrated three-dimensional waveguide multiplexing any modes and preparation method thereof Download PDFInfo
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 6
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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
- G02B6/12002—Three-dimensional structures
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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
- G02B6/12004—Combinations of two or more optical elements
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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
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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
- G02B2006/1215—Splitter
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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
- G02B2006/12164—Multiplexing; Demultiplexing
Abstract
The application provides a heterogeneous integrated three-dimensional optical waveguide multiplexing any mode and a preparation method thereof, which relate to the technical field of mode division multiplexing, and adopt two types of few-mode waveguides and single-mode waveguides which are made of different materials, are high and are arranged in position, wherein any mode signal is input into the few-mode waveguides, the single-mode waveguides output basic mode signals, based on the coupling mode theory, when modes in the waveguides meet the phase matching condition, the energy of the modes can be exchanged in the two waveguides, and according to the difference of the phase matching condition between different mode signals in the few-mode waveguides and the basic mode signals in the single-mode waveguides, the multiplexing and the demultiplexing of the modes of the signals in the few-mode waveguides and the modes of the signals in the single-mode waveguides are realized, the design is simple and flexible, the expansion is easy, and the separation and the combination of the optical waveguide modes in a high-integration optical communication system are realized.
Description
Technical Field
The application relates to the technical field of mode division multiplexing, in particular to a heterogeneous integrated three-dimensional optical waveguide multiplexing any mode and a preparation method thereof.
Background
In recent years, emerging technologies such as cloud computing, big data, blockchain and quantum technology are rapidly developed, and the demand for data capacity is also increasing. Based on the relevant predictions, the 2025 annual global data volume will reach 175ZB. The massive data also puts higher and higher requirements on data communication transmission, and optical fiber communication is an important component in a data communication transmission network, and has higher transmission speed and lower transmission loss.
Mode division multiplexing is a multiplexing technique that utilizes the spatial degrees of freedom of light waves to increase the optical communication capacity. The mode division multiplexing technique is not limited to single mode fibers, but there are also studies on higher order modes in few-mode fibers. Since the higher-order mode and the basic mode are not different in information transmission capability, a plurality of information can be simultaneously transmitted on the few-mode optical fiber to expand the information capacity. One of the key technologies in the mode division multiplexing technology is multiplexing and demultiplexing of modes. The directional coupler structure has the advantages of flexible design scheme, strong expansibility and the like, and becomes an important direction of multiplexing and de-multiplexing devices in a research mode of people.
Conventional directional coupler-based mode multiplexers have limited types of modes that can be selected for multiplexing due to manufacturing material and process limitations. However, with the continuous development of optical fiber communication and the need for higher transmission speeds, the requirements for the types of modes that can be multiplexed for the mode multiplexer are also increasing. Therefore, it is very important to design a heterogeneous integrated three-dimensional optical waveguide capable of multiplexing any mode and provide a preparation method thereof, and the development of a mode multiplexing system can bring great promotion effect.
Disclosure of Invention
In order to solve the problem that the multiplexing mode types of the planar waveguide device in the current optical fiber communication are limited, the application provides the heterogeneous integrated three-dimensional optical waveguide multiplexing any mode and the preparation method thereof, which are flexible in design, simple in structure and easy to expand, and the preparation method can well avoid the problem of mutual influence among waveguides with different heights.
In order to solve the problems, the application adopts the following technical scheme:
a heterogeneous integrated three-dimensional optical waveguide multiplexing arbitrary modes, comprising: a few-mode waveguide for inputting an arbitrary mode signal and a single-mode waveguide for outputting a fundamental mode signal; the few-mode waveguide and the single-mode waveguide are positioned on the same plane and are arranged in parallel, the height and the width of the few-mode waveguide are different from those of the single-mode waveguide, and the material of the few-mode waveguide is different from that of the single-mode waveguide; multiplexing and demultiplexing are achieved according to the difference of phase matching conditions between different mode signals in the few-mode waveguide and the fundamental mode signals in the single-mode waveguide, and the mode of the signals in the few-mode waveguide and the mode of the signals in the single-mode waveguide.
According to the technical scheme, the few-mode waveguide and the single-mode waveguide which are arranged in two different materials, heights and positions are adopted, wherein any mode signal is input into the few-mode waveguide, the single-mode waveguide outputs a basic mode signal, based on a coupling mode theory, when the modes in the waveguides meet the phase matching condition, the energy of the modes can be exchanged in the two waveguides, the phase matching condition is changed according to the different phase matching conditions of the modes, multiplexing and demultiplexing of the few-mode waveguide and the single-mode waveguide in any mode can be realized, the design is simple and flexible, the expansion is easy, and the separation and the combination of the optical waveguide modes in the highly integrated optical communication system are realized.
Preferably, the signal of any mode input in the few-mode waveguide includes: [ E 11 ，E 21 ，E 12 ，...，E m,n ]Wherein E is 11 Is a fundamental mode signal, E 21 ，E 12 ，...，E m, Is a specific fundamental mode signal E 11 A high-order mode signal with high order, wherein the fundamental mode signal in the single-mode waveguide is E 11 When the fundamental mode signal E 11 And a higher order mode signal E m,n Phase matching is satisfied when the effective refractive indexes of the few-mode waveguides are equal, and the higher-order mode signals E in the few-mode waveguides m,n Coupled out into the single-mode waveguide and converted into a fundamental mode signal E 11 Whereas the fundamental mode signal E is input in the few-mode waveguide 11 And other order mode signals are not coupled due to phase mismatch and are output in a primary way in the few-mode waveguide.
According to the technical scheme, based on the coupling mode theory, when the modes in the waveguides meet the phase matching condition, the energy of the modes can be exchanged in the two waveguides, and when the phases of the modes are mismatched, the energy of the modes is reserved in the original waveguides, so that the separation and combination control of any mode in the few-mode waveguides is realized.
Preferably, according to the coupled mode theory, the mode amplitude of the few-mode waveguide and the mode amplitude of the single-mode waveguide respectively satisfy:
wherein a is 1 Representing the mode amplitude, a, of a few-mode waveguide 2 And C represents a coupling coefficient for measuring the overlap between core mode fields of different waveguides, z represents an optical power transmission direction, j represents an imaginary unit, and then the power changes of the few-mode waveguide and the single-mode waveguide in the z direction are respectively represented as:
wherein P is 0 For the total power of all mode signals input to the few-mode waveguide, when sin (C) =1, i.e. c= (2m+1) pi/2, m=0, 1,2, higher order mode signal E of the few-mode waveguide is realized m,n 100% of the energy of (a) is transferred to the single-mode waveguide, i.e. coupling occurs, so that mode multiplexing is realized.
Preferably, the higher-order mode signal E of the few-mode waveguide is realized m,n The minimum length of 100% transfer of energy to the single mode waveguide is the coupling length, expressed as:
wherein L is c Representing a higher order mode signal E m,n 100% of the energy transferred to the coupling length of the single mode waveguide.
Preferably, when the coupling region length of the few-mode waveguide and the single-mode waveguide is the coupled higher-order mode signal E m,n Is of the coupling length L c When the energy of the target order mode signal to be coupled in the few-mode waveguide is odd times, the energy of the target order mode signal to be coupled in the few-mode waveguide is completely coupled to the single-mode waveguide, different phase matching is realized, and only the energy of other order mode signals remains in the few-mode waveguide.
The application also provides a preparation method of the heterogeneous integrated three-dimensional waveguide multiplexing any mode, which is used for preparing the heterogeneous integrated three-dimensional waveguide multiplexing any mode and comprises the following steps:
s1, spin-coating a lower cladding layer on the surface of a silicon substrate;
s2: spin coating a layer of first material corresponding to the waveguide on the surface of the lower cladding, carrying out photoresist homogenizing lithography on the first material, spreading photoresist on the surface of the first material at a low rotating speed, volatilizing the photoresist at a high rotating speed, and removing redundant photoresist to achieve ideal thickness;
s3, mask photoetching is carried out;
s4: at room temperature, placing the silicon wafer subjected to mask lithography into a specific developer for development and then fixing to form a sample wafer, and baking the sample wafer on a hot plate to permanently cure the sample wafer;
s5, etching the sample wafer by using a plasma etching machine, setting etching time, etching a waveguide with a set height, and exposing the lower cladding;
s6, preparing waveguides with larger heights in the few-mode waveguide and the single-mode waveguide on the lower cladding, namely uniformly photoetching the second material on the surface of the lower cladding by spin coating a layer of second material corresponding to the waveguides, spreading the photoresist on the surface of the second material at a low rotating speed, volatilizing the photoresist at a high rotating speed, and removing redundant photoresist to reach an ideal thickness;
s7, repeating the steps S3-S5 to obtain waveguides with larger heights in the few-mode waveguides and the single-mode waveguides;
and S8, spin-coating an upper cladding material with a set thickness on the surfaces of the waveguide obtained in the step S2, the waveguide obtained in the step S6 and the lower cladding to obtain the heterogeneous integrated three-dimensional optical waveguide multiplexing any modes.
According to the technical scheme, the photoetching sequence of the two waveguides is controlled, the problem that the upper surface of the waveguide with lower height is concave due to the mutual influence when the waveguides with different heights are subjected to photoetching is avoided, and a better guiding direction is provided for realizing the same type of photoetching.
Preferably, the lower cladding is a polymer EpoClad cladding.
Preferably, in step S3, a sample of the spin-coated photoresist is placed in an equipment compartment of a mask lithography apparatus, and mask lithography is performed on the photoresist according to a pattern file corresponding to a designed waveguide with a smaller height.
Preferably, in step S6, a sample of the spin-coated photoresist is placed in an equipment compartment of a mask lithography apparatus, and mask lithography is performed on the photoresist according to a pattern file corresponding to a designed waveguide with a larger height.
Preferably, the height of the single-mode waveguide is smaller than the height of the few-mode waveguide.
Compared with the prior art, the technical scheme of the application has the beneficial effects that:
the application provides a heterogeneous integrated three-dimensional optical waveguide multiplexing any mode and a preparation method thereof, which adopts a few-mode waveguide and a single-mode waveguide with two different materials, heights and positions, wherein the few-mode waveguide inputs any mode signal, the single-mode waveguide outputs a basic mode signal, based on a coupling mode theory, when the modes in the waveguide meet the phase matching condition, the energy of the modes can be exchanged in the two waveguides, the phase matching condition is changed according to the different phase matching conditions of the modes, the multiplexing and the demultiplexing of the few-mode waveguide and the single-mode waveguide in any mode can be realized, the design is simple and flexible, the expansion is easy, the separation and the combination of the optical waveguide modes in a highly integrated optical communication system are realized, and the preparation method provided by the application can well avoid the problem of the mutual influence between the waveguides with different heights.
Drawings
FIG. 1 shows a schematic structural diagram of a heterogeneous integrated three-dimensional optical waveguide for multiplexing arbitrary modes according to an embodiment of the present application;
FIG. 2 shows a schematic flow chart of a method for preparing a heterogeneous integrated three-dimensional optical waveguide multiplexing any mode according to an embodiment of the present application;
FIG. 3 shows an illustrative view of a heterogeneous integrated three-dimensional optical waveguide fabrication process for multiplexing arbitrary modes as proposed in an embodiment of the present application;
fig. 4 shows an x-y section view of a heterogeneous integrated three-dimensional optical waveguide multiplexing arbitrary modes according to an embodiment of the present application.
Detailed Description
The drawings are for illustrative purposes only and are not to be construed as limiting the present patent;
for better illustration of the present embodiment, some parts of the drawings may be omitted, enlarged or reduced, and do not represent actual dimensions;
it will be appreciated by those skilled in the art that some well known descriptions in the figures may be omitted.
The technical scheme of the application is further described below with reference to the accompanying drawings and the examples;
the positional relationship depicted in the drawings is for illustrative purposes only and is not to be construed as limiting the present patent;
example 1
The embodiment provides a heterogeneous integrated three-dimensional optical waveguide multiplexing any mode, the structure schematic diagram of which is shown in fig. 1, and the heterogeneous integrated three-dimensional optical waveguide multiplexing any mode comprises: a few-mode waveguide 1 for inputting an arbitrary-mode signal and a single-mode waveguide 2 for outputting a fundamental-mode signal; as shown in fig. 1, the few-mode waveguide 1 and the single-mode waveguide 2 are located on the same plane and are arranged in parallel, the height and width of the few-mode waveguide 1 are different from those of the single-mode waveguide 2, and the material of the few-mode waveguide 1 is different from that of the single-mode waveguide 2; multiplexing and demultiplexing are achieved according to the difference of phase matching conditions between different mode signals in the few-mode waveguide 1 and the fundamental mode signals in the single-mode waveguide 2, and the modes of the signals in the few-mode waveguide 1 and the modes of the signals in the single-mode waveguide 2.
In this embodiment, the heterogeneous integrated three-dimensional optical waveguide design of the multiplexing mode is based on a directional coupling structure. The principle of operation of a directional coupler is based on the theory of coupled modes, and ideally, no coupling exists between waveguides, and all waveguides can be considered as independent propagation individuals. In practice, however, if the structure of the waveguide is defective or other waveguides are present around, this may result in energy exchange inside or between the waveguides. When the spacing between parallel waveguides is small, the fields in the waveguides will interact and cause guided modes in the waveguides to couple to each other. The optical power conversion between two parallel waveguides is called directional coupling, and the waveguide coupling characteristics are determined by the waveguide spacing, the coupling length, and the propagation mode.
As shown in fig. 1, the signal of any mode inputted to the few-mode waveguide 1 includes: [ E 11 ，E 21 ，E 12 ，...，E m,n ]Wherein E is 11 Is a fundamental mode signal, E 21 ，E 12 ，...，E m,n Is a specific fundamental mode signal E 11 The fundamental mode signal in the single-mode waveguide 2 is E 11 When the fundamental mode signal E 11 And a higher order mode signal E m,n When the effective refractive indexes of the two are equal, the conversion and the output E can be realized through evanescent coupling after the phase matching is satisfied 11 Mode, higher order mode signal E in few-mode waveguide 1 m,n Coupled out into a single-mode waveguide 2 and converted into a fundamental mode signal E 11 While the fundamental mode signal E is input in the few-mode waveguide 1 11 And other order mode signals are not coupled due to phase mismatch and are output in a primary way in the few-mode waveguide 1.
Example 2
According to the coupled mode theory, the mode amplitude of the few-mode waveguide 1 and the mode amplitude of the single-mode waveguide 2 respectively satisfy:
wherein a is 1 Representing the mode amplitude, a, of the few-mode waveguide 1 2 Representing the mode amplitude of the few-mode waveguide 2, C representing the coupling coefficient for measuring the overlap between the core modes of different waveguides, z representing the optical power transfer direction, j representing the imaginary unit, the power changes of the few-mode waveguide 1 and the single-mode waveguide 2 in the z direction are respectively expressed as:
wherein P is 0 For the total power of all mode signals input to the few-mode waveguide 1, when sin (C) =1, i.e., c= (2m+1) pi/2, m=0, 1,2, higher order mode signal E of the few-mode waveguide 1 is realized m,n 100% of the energy transferred to the single-mode waveguide 2, i.e. coupling takes place, achieving mode multiplexing. High-order mode signal E for realizing few-mode waveguide 1 m,n The minimum length of 100% transfer of energy to the single mode waveguide 2 is the coupling length, expressed as:
wherein L is c Representing a higher order mode signal E m,n 100% of the energy transferred to the coupling length of the single mode waveguide 2.
In an ideal case, when the coupling region length of the few-mode waveguide 1 and the single-mode waveguide 2 is the coupled higher-order mode signal E m,n Is of the coupling length L c The energy of the target order mode signal to be coupled in the few-mode waveguide 1 will be completely coupled to the single-mode waveguide 2, achieving different phase matching,only the energy of the other order mode signals remains in the few-mode waveguide 1.
In the embodiment, the heterogeneous integrated three-dimensional optical waveguide of the multiplexing mode has flexible design, simple structure and strong expansibility. By selecting two waveguide materials, the structure (height, width and interval between waveguides), and changing the phase matching condition, any optical waveguide mode which is wanted to be multiplexed and demultiplexed can be obtained. Meanwhile, the optical waveguide module has the advantages of small volume and stable operation, and can realize the separation and combination of optical waveguide modes in a highly integrated optical communication system.
Example 3
As shown in fig. 2, this embodiment proposes a method for preparing a heterogeneous integrated three-dimensional waveguide of multiplexing arbitrary modes, where the method is used for preparing the heterogeneous integrated three-dimensional waveguide of multiplexing arbitrary modes, referring to fig. 3, and the steps include:
s1, spin-coating a lower cladding layer on the surface of a silicon substrate;
s2: spin coating a layer of first material corresponding to the waveguide on the surface of the lower cladding, carrying out photoresist homogenizing lithography on the first material, spreading photoresist on the surface of the first material at a low rotating speed, volatilizing the photoresist at a high rotating speed, and removing redundant photoresist to achieve ideal thickness;
s3, mask photoetching is carried out;
s4: at room temperature, placing the silicon wafer subjected to mask lithography into a specific developer for development and then fixing to form a sample wafer, and baking the sample wafer on a hot plate to permanently cure the sample wafer;
s5, etching the sample wafer by using a plasma etching machine, setting etching time, etching a waveguide with a set height, and exposing the lower cladding;
s6, preparing waveguides with larger heights in the few-mode waveguide 1 and the single-mode waveguide 2 on the lower cladding, namely uniformly photoetching photoresist on the second material by spin coating a layer of second material corresponding to the waveguides on the surface of the lower cladding, spreading the photoresist on the surface of the second material at a low rotating speed, volatilizing the photoresist at a high rotating speed, and removing redundant photoresist to reach an ideal thickness;
s7, repeating the steps S3-S5 to obtain waveguides with larger heights in the few-mode waveguide 1 and the single-mode waveguide 2;
and S8, spin-coating an upper cladding material with a set thickness on the surfaces of the waveguide obtained in the step S2, the waveguide obtained in the step S6 and the lower cladding to obtain the heterogeneous integrated three-dimensional optical waveguide multiplexing any modes.
The preparation process of the heterogeneous integrated three-dimensional optical waveguide multiplexing any mode based on the steps is shown in fig. 3, and as can be seen from fig. 3, the photoetching sequence control of two waveguides is realized based on the step flow, the problem that the upper surface of the waveguide with lower height is recessed caused by the mutual influence when different height waveguides are photoetched is avoided, a better guiding direction is provided for realizing the same type of photoetching, and as can be seen from fig. 4, the height of the single-mode waveguide 2 is smaller than that of the few-mode waveguide 1. In this embodiment, the lower cladding is a polymer EpoClad cladding. In step S3, the sample with the spin-coated photoresist is placed in an equipment compartment of a mask lithography device, and mask lithography is performed on the photoresist according to the designed pattern file corresponding to the waveguide with the smaller height, and the same is true for the mask lithography in step S6.
For a system of several heterogeneous integrated three-dimensional optical waveguides multiplexing arbitrary modes, see fig. 4, the heights of the few-mode waveguide and the single-mode waveguide are different in each heterogeneous integrated three-dimensional optical waveguide, and the materials are also different in each heterogeneous integrated three-dimensional waveguide, and are shown by four materials in fig. 4. It is to be understood that the above examples of the present application are provided by way of illustration only and are not intended to limit the scope of the application. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. Any modification, equivalent replacement, improvement, etc. which come within the spirit and principles of the application are desired to be protected by the following claims.
Claims (10)
1. A heterogeneous integrated three-dimensional optical waveguide multiplexing arbitrary modes, comprising: a few-mode waveguide (1) for inputting an arbitrary-mode signal and a single-mode waveguide (2) for outputting a fundamental-mode signal; the few-mode waveguide (1) and the single-mode waveguide (2) are positioned on the same plane and are arranged in parallel, the height and the width of the few-mode waveguide (1) are different from those of the single-mode waveguide (2), and the material of the few-mode waveguide (1) is different from that of the single-mode waveguide (2); multiplexing and demultiplexing are achieved according to the difference of phase matching conditions between different mode signals in the few-mode waveguide (1) and the fundamental mode signals in the single-mode waveguide (2), wherein the modes of the signals in the few-mode waveguide (1) and the modes of the signals in the single-mode waveguide (2).
2. The heterogeneous integrated three-dimensional waveguide multiplexing arbitrary modes according to claim 1, characterized in that providing signals of arbitrary modes input in the few-mode waveguide (1) comprises: [ E 11 ，E 21 ，E 12 ，...，E m,n ]Wherein E is 11 Is a fundamental mode signal, E 21 ，E 12 ，...，E m,n Is a specific fundamental mode signal E 11 A high-order mode signal, wherein the fundamental mode signal in the single-mode waveguide (2) is E 11 When the fundamental mode signal E 11 And a higher order mode signal E m,n Is phase matched when the effective refractive indexes of the few-mode waveguides (1) are equal, and the higher-order mode signals E in the few-mode waveguides (1) m,n Coupled out into the single-mode waveguide (2) and converted into a fundamental-mode signal E 11 And the fundamental mode signal E inputted into the few-mode waveguide (1) 11 And other order mode signals are not coupled due to phase mismatch and are output in a primary way in the few-mode waveguide (1).
3. The heterogeneous integrated three-dimensional optical waveguide multiplexing arbitrary modes according to claim 2, characterized in that according to the coupling theory, the mode amplitude of the few-mode waveguide (1) and the mode amplitude of the single-mode waveguide (2) respectively satisfy:
wherein a is 1 Representing the mode amplitude, a, of the few-mode waveguide (1) 2 Representing the mode amplitude of the few-mode waveguide (2), C representing the coupling coefficient for measuring the overlap between the core modes of different waveguides, z representing the optical power transfer direction, j representing the imaginary unit, the power variation of the few-mode waveguide (1) and the single-mode waveguide (2) in the z direction is represented as:
wherein P is 0 For the total power of all mode signals input to the few-mode waveguide (1), when sin (C) =1, i.e. c= (2m+1) pi/2, m=0, 1,2, higher order mode signal E of the few-mode waveguide (1) is realized m,n 100% of the energy of (a) is transferred to the single-mode waveguide (2), namely coupling occurs, and mode multiplexing is realized.
4. A heterogeneous integrated three-dimensional optical waveguide multiplexing arbitrary modes according to claim 3, characterized in that a higher order mode signal E of the few-mode waveguide (1) is realized m,n The minimum length of 100% of the energy transferred to the single mode waveguide (2) is the coupling length, expressed as:
wherein L is c Representing a higher order mode signal E m,n 100% transfer of the energy to the single-mode waveguide (2)Degree.
5. The heterogeneous integrated three-dimensional optical waveguide multiplexing arbitrary modes according to claim 4, characterized in that when the coupling area length of the few-mode waveguide (1) and the single-mode waveguide (2) is the coupled higher-order mode signal E m,n Is of the coupling length L c And the energy of the target order mode signal to be coupled in the few-mode waveguide (1) is completely coupled to the single-mode waveguide (2) to realize different phase matching, and only the energy of the other order mode signals remains in the few-mode waveguide (1).
6. A method for preparing a heterogeneous integrated three-dimensional waveguide for multiplexing an arbitrary mode, wherein the method is used for preparing the heterogeneous integrated three-dimensional waveguide for multiplexing an arbitrary mode according to any one of claims 1 to 5, and comprises the steps of:
s1, spin-coating a lower cladding layer on the surface of a silicon substrate;
s2: spin coating a layer of first material corresponding to the waveguide on the surface of the lower cladding, carrying out photoresist homogenizing photoetching on the first material, spreading photoresist on the surface of the first material at a low rotating speed, volatilizing the photoresist at a high rotating speed, and removing redundant photoresist to achieve ideal thickness;
s3, mask photoetching is carried out;
s4: at room temperature, placing the silicon wafer subjected to mask lithography into a specific developer for development and then fixing to form a sample wafer, and baking the sample wafer on a hot plate to permanently cure the sample wafer;
s5, etching the sample wafer by using a plasma etching machine, setting etching time, etching a waveguide with a set height, and exposing the lower cladding;
s6, preparing waveguides with larger heights in the few-mode waveguide (1) and the single-mode waveguide (2) on the lower cladding, namely spin-coating a layer of second material corresponding to the waveguides on the surface of the lower cladding, uniformly photoetching the second material, spreading photoresist on the surface of the second material at a low rotating speed, volatilizing the photoresist at a high rotating speed, and removing redundant photoresist to achieve ideal thickness;
s7, repeating the steps S3-S5 to obtain waveguides with larger heights in the few-mode waveguide (1) and the single-mode waveguide (2);
and S8, spin-coating an upper cladding material with a set thickness on the surfaces of the waveguide obtained in the step S2, the waveguide obtained in the step S6 and the lower cladding to obtain the heterogeneous integrated three-dimensional optical waveguide multiplexing any modes.
7. The method of fabricating a heterogeneous integrated three-dimensional waveguide according to claim 6, wherein the lower cladding is a polymer EpoClad cladding.
8. The method for preparing a heterogeneous integrated three-dimensional waveguide multiplexing arbitrary modes according to claim 6, wherein in step S3, a sample of spin-coated photoresist is placed into an equipment compartment of a mask lithography apparatus, and mask lithography is performed on the photoresist according to a pattern file corresponding to the designed waveguide with a smaller height.
9. The method for preparing a heterogeneous integrated three-dimensional waveguide multiplexing arbitrary modes according to claim 6, wherein in step S6, a sample of spin-coated photoresist is placed into an equipment compartment of a mask lithography device, and mask lithography is performed on the photoresist according to a pattern file corresponding to the designed waveguide with a larger height.
10. The method of manufacturing a heterogeneous integrated three-dimensional waveguide multiplexing arbitrary modes according to claim 8, characterized in that the height of the single-mode waveguide (2) is smaller than the height of the few-mode waveguide (1).
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