Three-dimensional mode multiplexer / demultiplexer and preparation method thereof

Abstract

The invention discloses a three-dimensional mode multiplexer / demultiplexer and a preparation method thereof, and belongs to the technical field of mode multiplexers / demultiplexers and preparation thereof. The optical fiber comprises a silicon substrate, a lower cladding, a lower core layer, a middle cladding, an upper core layer and an upper cladding from bottom to top, the lower core layer is composed of a lower-layer input few-mode straight waveguide, a lower-layer asymmetric Y-branch beam splitter first branch, a lower-layer asymmetric Y-branch beam splitter second branch, a lower-layer connection conical waveguide, a lower-layer first heat insulation conical waveguide, a lower-layer second heat insulation conical waveguide, a lower-layer first output few-mode straight waveguide and a lower-layer second output few-mode straight waveguide. The upper core layer is composed of an upper-layer first heat insulation conical waveguide, an upper-layer second heat insulation conical waveguide, an upper-layer first output bent waveguide, an upper-layer second output bent waveguide, an upper-layer first output few-mode straight waveguide and an upper-layer second output few-mode straight waveguide. The device is prepared from a polymer material, the process is simple and compatible with a semiconductor process, and the device has important practical application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of mode multiplexers / demultiplexers and their preparation, and particularly relates to a three-dimensional mode multiplexer / demultiplexer using silicon as a substrate and using organic polymer materials as the lower cladding, lower core layer, intermediate cladding, upper core layer and upper cladding, and a preparation method thereof. Background Art

[0002] In recent years, optical fiber communication has gradually become the most important means of digital communication, with many advantages such as long transmission distance, large bandwidth, low transmission loss, and large transmission capacity. However, driven by the explosive growth of the demand for high-capacity communication, communication systems based on single-mode optical fibers have been difficult to meet the increasing demand for communication capacity. To solve this problem, a variety of multiplexing technologies have been proposed one after another. Among them, the mode division multiplexing (MDM) technology in the space division multiplexing (SDM) technology can significantly improve the transmission capacity of optical communication systems, can provide a multiplexing function for more data in a limited space, can use each mode as an independent transmission channel to carry different information, and realizes a multiple-fold increase in the communication transmission capacity. It is considered a promising technical direction to solve the transmission capacity demand of traditional single-mode optical fibers.

[0003] The mode multiplexer / demultiplexer in a mode division multiplexing (MDM) system is an important component and also an essential key component in a high-capacity optical communication system, and can be used to realize the conversion and multiplexing from the fundamental mode to higher-order modes and the conversion and demultiplexing from higher-order modes to the fundamental mode. There are many structures that can realize mode multiplexing and demultiplexing. Among them, the directional coupling (DC) structure has outstanding advantages because of its simple structure and strong scalability, and can realize the multiplexing / demultiplexing of multiple modes through a cascaded manner. However, the traditional directional coupling structure composed of waveguides with two parallel planar arms of equal height can only realize the coupling between modes with the same symmetry and cannot realize the multiplexing and demultiplexing of arbitrary modes; in addition, the traditional DC structure has a limited bandwidth and is difficult to cover the C+L band. Therefore, it is of great significance to develop a mode multiplexer / demultiplexer that can manipulate arbitrary waveguide modes and has a large bandwidth. Summary of the Invention

[0004] The purpose of the present invention is to provide a three-dimensional mode multiplexer / demultiplexer for realizing bandwidth improvement and manipulating arbitrary modes and a preparation method thereof. To overcome the deficiencies of existing mode multiplexers / demultiplexers, the present invention uses a silicon wafer as a substrate, uses organic polymer materials as the lower cladding, intermediate cladding and upper cladding of the waveguide, and uses organic polymer materials with a relatively large refractive index as the lower core layer and upper core layer of the waveguide.

[0005] A three-dimensional mode multiplexer / demultiplexer according to the present invention is shown in the attached Figure 1 figure (a cross-sectional view taken at the position A-A' in Figure 2 ), and from bottom to top, it is composed of a silicon substrate 31, a polymer optical waveguide lower cladding 32 prepared on the silicon substrate 31, a strip-shaped polymer optical waveguide lower core layer 33 prepared on the polymer optical waveguide lower cladding 32, a polymer optical waveguide intermediate cladding 34 prepared on the polymer optical waveguide lower cladding 32 and the strip-shaped polymer optical waveguide lower core layer 33, a strip-shaped polymer optical waveguide upper core layer 35 prepared on the polymer optical waveguide intermediate cladding 34, and a polymer optical waveguide upper cladding 36 prepared on the polymer optical waveguide intermediate cladding 34 and the strip-shaped polymer optical waveguide upper core layer 35. The strip-shaped polymer optical waveguide lower core layer 33 is covered in the polymer optical waveguide intermediate cladding 34, and the strip-shaped polymer optical waveguide upper core layer 35 is covered in the polymer optical waveguide upper cladding 36.

[0006] As shown in 2(a), along the light propagation direction, the strip-shaped polymer optical waveguide lower core layer 33 is composed of a lower-layer input few-mode straight waveguide 21, a first branch 22 of a lower-layer asymmetric Y-branch beam splitter, a second branch 23 of the lower-layer asymmetric Y-branch beam splitter, a lower-layer connecting tapered waveguide 24, a first adiabatic tapered waveguide 25 in the lower layer, a second adiabatic tapered waveguide 26 in the lower layer, a first output few-mode straight waveguide 27 in the lower layer, and a second output few-mode straight waveguide 28 in the lower layer; the strip-shaped polymer optical waveguide upper core layer 35 is composed of a first adiabatic tapered waveguide 29 in the upper layer, a second adiabatic tapered waveguide 210 in the upper layer, a first output bent waveguide 211 in the upper layer, a second output bent waveguide 212 in the upper layer, a first output few-mode straight waveguide 213 in the upper layer, and a second output few-mode straight waveguide 214 in the upper layer;

[0007] Among them, the lower-layer input few-mode straight waveguide 21, the first branch 22 of the lower-layer asymmetric Y-branch beam splitter, and the second branch 23 of the lower-layer asymmetric Y-branch beam splitter form an asymmetric Y-branch beam splitter. The symmetry axes of the first adiabatic tapered waveguide 29 in the upper layer and the first adiabatic tapered waveguide 25 in the lower layer are horizontally offset by a certain distance and are arranged in parallel. The symmetry axes of the second adiabatic tapered waveguide 210 in the upper layer and the second adiabatic tapered waveguide 26 in the lower layer are horizontally offset by a certain distance and are arranged in parallel. The first branch 22 of the lower-layer asymmetric Y-branch beam splitter, the lower-layer connecting tapered waveguide 24, the first adiabatic tapered waveguide 25 in the lower layer, and the first output few-mode straight waveguide 27 in the lower layer are sequentially connected. The second branch 23 of the lower-layer asymmetric Y-branch beam splitter, the second adiabatic tapered waveguide 26 in the lower layer, and the second output few-mode straight waveguide 28 in the lower layer are sequentially connected. The first adiabatic tapered waveguide 29 in the upper layer, the first output bent waveguide 211 in the upper layer, and the first output few-mode straight waveguide 213 in the upper layer are sequentially connected. The second adiabatic tapered waveguide 210 in the upper layer, the second output bent waveguide 212 in the upper layer, and the second output few-mode straight waveguide 214 in the upper layer are sequentially connected.

[0008] By reasonably designing the size changes of the upper first adiabatic tapered waveguide 29, the lower first adiabatic tapered waveguide 25, the upper second adiabatic tapered waveguide 210, and the lower second adiabatic tapered waveguide 26, the width of the waveguide is slowly and continuously changed, enabling the optical signal to smoothly adapt to these changes during transmission, avoiding mode coupling and energy loss, thereby realizing the adiabatic functions of the upper first adiabatic tapered waveguide 29, the lower first adiabatic tapered waveguide 25, the upper second adiabatic tapered waveguide 210, and the lower second adiabatic tapered waveguide 26.

[0009] Such as Figure 2(a), (b), and (c) show that the length a1 of the lower-layer input few-mode straight waveguide 21 is 200 to 5000 μm, and the width w1 is 8 to 15 μm; the first branch 22 of the lower-layer asymmetric Y-branch beam splitter and the second branch 23 of the lower-layer asymmetric Y-branch beam splitter have the same structural dimensions except for the width. The projection lengths a2 and a2' along the extension direction of the lower-layer input few-mode straight waveguide 21 are equal, being 500 to 8000 μm, and the center distances gap1 and gap1' between the input and output ends of the two are equal, being 5 to 50 μm; the width w2 of the first branch 22 of the lower-layer asymmetric Y-branch beam splitter is 1.9 to 19 μm, and the width w3 of the second branch 23 of the lower-layer asymmetric Y-branch beam splitter is 3.1 to 31 μm; the length a3 of the lower-layer connecting tapered waveguide 24 is 100 to 2000 μm, the width w2' at its connection with the first branch 22 of the lower-layer asymmetric Y-branch beam splitter is 1.9 to 19 μm, and the width gradually increases to the width w4 of 2.8 to 7.8 μm at its connection with the first adiabatic tapered waveguide 25 of the lower layer; the length a4 of the first adiabatic tapered waveguide 25 of the lower layer is 300 to 5300 μm, the width w4 at its connection with the lower-layer connecting tapered waveguide 24 is 2.8 to 7.8 μm, and the width gradually increases to the width w5 of 3.6 to 8.6 μm at its connection with the first output few-mode straight waveguide 27 of the lower layer; the length a5 of the second adiabatic tapered waveguide 26 of the lower layer is 350 to 6350 μm, the width w3' at its connection with the second branch 23 of the lower-layer asymmetric Y-branch beam splitter is 3.1 to 31 μm, and the width gradually increases to the width w6 of 3.5 to 10.5 μm at its connection with the second output few-mode straight waveguide 28 of the lower layer; the length a6 of the first output few-mode straight waveguide 27 of the lower layer is 400 to 10000 μm, and the width w5' is 3.6 to 8.6 μm; the length a7 of the second output few-mode straight waveguide 28 of the lower layer is 400 to 10000 μm, and the width w6' is 3.5 to 10.5 μm; the length a4 of the first adiabatic tapered waveguide 29 of the upper layer is 500 to 5300 μm, the center distance gap2 in the horizontal direction between it and the first adiabatic tapered waveguide 25 of the lower layer is 1 to 6 μm, the distance G1 in the vertical direction is 1 to 10 μm, and its width gradually decreases from w7 of 1.8 to 6.8 μm to the width w8 of 1.5 to 6.5 μm at its connection with the first output bending waveguide 211 of the upper layer; the length a5 of the second adiabatic tapered waveguide 210 of the upper layer is 800 to 6300 μm, the center distance gap3 in the horizontal direction between it and the second adiabatic tapered waveguide 26 of the lower layer is 1.5 to 6.5 μm, the distance G1' in the vertical direction is 1 to 10 μm, and its width gradually decreases from w9 of 2.6 to 8.6 μm to the width w10 of 1.8 to 6.8μm; the projection length a8 of the upper first output curved waveguide 211 along the extension line direction of the lower input few-mode straight waveguide 21 is 300 to 5000μm, and the center distance gap4 between the input end and the output end is 3 to 35μm; the projection length a9 of the upper second output curved waveguide 212 along the extension line direction of the lower input few-mode straight waveguide 21 is 300 to 5000μm, and the center distance gap5 between the input end and the output end is 3 to 35μm; the upper first output few-mode The length a10 of the straight waveguide 213 is 100 to 5000 μm, and the width w8' is 1.5 to 6.5 μm. The length a11 of the upper second output few-mode straight waveguide 214 is 100 to 5000 μm, and the width w10' is 1.8 to 6.8 μm. Among them, w2'=w2, w3'=w3, w5'=w5, w6'=w6, w8'=w8, w10'=w10, a2'=a2, gap1'=gap1, and G1'=G1.

[0010] Figure 1 The thickness of the silicon substrate 31 is 0.5 to 2 mm, the thickness of the polymer optical waveguide lower cladding 32 is 4 to 20 μm, the thickness of the strip-structured polymer optical waveguide lower core layer 33 is 7 to 15 μm, the thickness of the polymer optical waveguide intermediate cladding 34 above the strip-structured polymer optical waveguide lower core layer 33 is 1 to 10 μm, the thickness of the strip-structured polymer optical waveguide upper core layer 35 is 2 to 10 μm, and the thickness of the polymer optical waveguide upper cladding 36 above the strip-structured polymer optical waveguide upper core layer 35 is 4 to 20 μm.

[0011] Working process of mode demultiplexer: The mode demultiplexer inputs the E in the optical waveguide from the lower layer input few-mode straight waveguide 21 11 mode, coupled to the second branch 23 of the lower asymmetric Y-branch beam splitter (the design of the asymmetric Y-branch is based on the effective refractive index matching principle of the waveguide mode. By selecting a suitable arm width, the E 11 、E 12 (E 21 、E 22 ) mode and the effective refractive index of E 11 、E 12 (E 11 、E 12 ) mode in the wide (narrow) arm, thereby achieving efficient mode separation), and outputs E from the second output few-mode straight waveguide 28 of the lower layer through the second adiabatic tapered waveguide 26 of the lower layer. 11 Mode; E in the optical waveguide input from the lower layer input few-mode straight waveguide 21 21 Mode, with E 11The mode is coupled to the first branch 22 of the lower-layer asymmetric Y-branch beam splitter in a form, passes through the lower-layer connecting tapered waveguide 24 and outputs to the lower-layer first adiabatic tapered waveguide 25, and finally outputs E from the lower-layer first output few-mode straight waveguide 27 11 mode; E in the optical waveguide is input from the lower-layer input few-mode straight waveguide 21 12 mode, coupled to the second branch 23 of the lower-layer asymmetric Y-branch beam splitter. When passing through the lower-layer second adiabatic tapered waveguide 26 (the modes in the two waveguides in the coupling region, due to their equal effective refractive indices, the coupling coefficient between the two is not zero, meeting the phase matching condition, and optical energy exchange occurs), the signal light is in the form of E 11 mode and is coupled into the upper-layer second adiabatic tapered waveguide 210 for transmission to achieve mode field matching, and finally outputs E through the upper-layer second output bending waveguide 212 and the upper-layer second output few-mode straight waveguide 214 11 mode; E in the optical waveguide is input from the lower-layer input few-mode straight waveguide 21 22 mode, and is coupled to the first branch 22 of the lower-layer asymmetric Y-branch beam splitter in a form of E 12 mode. When passing through the lower-layer connecting tapered waveguide 24 and outputting to the lower-layer first adiabatic tapered waveguide 25, the signal light is in the form of E 11 mode and is coupled into the upper-layer first adiabatic tapered waveguide 29 for transmission to achieve mode field matching, and finally outputs E through the upper-layer first output bending waveguide 211 and the upper-layer first output few-mode straight waveguide 213 11 mode. The mode multiplexer is the reverse input and output of the above optical path.

[0012] A preparation method of a three-dimensional mode multiplexer / demultiplexer according to the present invention has a preparation process flow as Figure 3 shown, and its steps are as follows:

[0013] A: Cleaning treatment of the silicon substrate 31

[0014] Wipe the silicon substrate 31 repeatedly 1 to 3 times with a cotton ball dipped in acetone solution, then wipe the silicon substrate 31 repeatedly 1 to 3 times with another cotton ball dipped in ethanol solution, then rinse it clean with deionized water, and finally dry the silicon substrate 31 with nitrogen

[0015] B: Preparation of the polymer optical waveguide lower cladding 32

[0016] The lower cladding of the polymer optical waveguide is made of an organic polymer material with good transparency (including polyethylene (PE), polyester (PET), polycarbonate (PC), polyimide (PI), polymethyl methacrylate (PMMA), polystyrene (PS), EpoClad, etc.). The polymer waveguide lower cladding material is spin-coated on the cleaned silicon substrate 31 through a spin-coating process. The spin-coating speed is 1000 - 6000 revolutions per minute, and it is baked at 100 - 150 °C for 2 - 40 minutes (if using materials such as EpoClad, it needs to be baked and then integrally exposed to ultraviolet light with a wavelength of 350 - 400 nm for 2 - 40 s, and finally baked at 100 - 150 °C for 10 - 60 minutes) to obtain a polymer optical waveguide lower cladding 32 with a thickness of 4 - 20 μm;

[0017] C: Preparation of the lower core layer 33 of the polymer optical waveguide in strip structure

[0018] The material of the lower core layer of the polymer optical waveguide is selected as an ultraviolet negative photoresist material with a negative thermo-optic coefficient and can be wet-etched (including EpoCore, SU-8 2002, SU-8 2005, etc.). The refractive index of the material of the lower core layer of the polymer optical waveguide is higher than that of the material of the lower cladding of the polymer optical waveguide, the intermediate cladding of the polymer optical waveguide, and the upper cladding of the polymer optical waveguide. The material of the lower core layer of the polymer optical waveguide is spin-coated on the lower cladding 32 of the polymer optical waveguide to form a lower core layer film 33' of the polymer optical waveguide. The spin-coating speed is 600 - 5500 revolutions per minute, and the thickness of the lower core layer film 33' of the polymer optical waveguide is 7 - 15 μm; after spin-coating, pre-baking is carried out, that is, by using a method of stepwise heating, the device is heated at 40 - 120 °C for 2 - 30 minutes, and then baked at 70 - 130 °C for 2 - 40 minutes. After heating, it is naturally cooled to room temperature; then, alignment lithography is performed on the lower core layer film 33' of the polymer optical waveguide, that is, using the same structure as the lower core layer of the polymer optical waveguide to be prepared (such as Figure 2(as shown in (a)) a complementary mask plate is closely attached to the surface of the polymer optical waveguide lower core layer thin film 33'. Then, it is exposed under ultraviolet light with a wavelength of 350 - 400 nm for 3 - 30 s, so that the polymer optical waveguide lower core layer materials in the areas of the lower input few-mode straight waveguide 21, the first branch 22 of the lower asymmetric Y-branch beam splitter, the second branch 23 of the lower asymmetric Y-branch beam splitter, the lower connecting tapered waveguide 24, the first adiabatic tapered waveguide 25 of the lower layer, the second adiabatic tapered waveguide 26 of the lower layer, the first output few-mode straight waveguide 27 of the lower layer, and the second output few-mode straight waveguide 28 of the lower layer of the device to be fabricated are exposed to ultraviolet light. After lithography, a medium baking operation is carried out, that is, it is heated at 40 - 90 °C for 2 - 30 minutes, and then heated at 75 - 120 °C for 2 - 40 minutes. After heating, it is naturally cooled to room temperature. After cooling, development is carried out. First, it is wet-etched in the developer corresponding to the polymer optical waveguide lower core layer material for 5 - 80 s to remove the polymer optical waveguide lower core layer thin film of the non-polymer optical waveguide lower core layer 33 structure that has not been exposed, leaving only the polymer waveguide lower core layer structure corresponding to the mask plate structure. Then, it is placed in an isopropyl alcohol solution to wash away the unexposed polymer optical waveguide lower core layer material and the developer remaining on the surface of the device, and then rinsed with deionized water (when rinsing, it is necessary to rinse along the waveguide direction to prevent damage to the waveguide) to remove the isopropyl alcohol solution on the surface of the device, and then dried with nitrogen. Finally, post-baking and hardening are carried out, that is, it is heated at 110 - 160 °C for 20 - 60 minutes, thereby fabricating a strip-shaped polymer optical waveguide lower core layer 33 on the polymer optical waveguide lower cladding 32;

[0019] D: Preparation of the polymer optical waveguide intermediate cladding 34

[0020] The polymer optical waveguide intermediate cladding material (in the same device, using the same polymer optical waveguide lower cladding material, polymer optical waveguide intermediate cladding material, and polymer optical waveguide upper cladding material has the best effect) is spin-coated on the prepared polymer optical waveguide lower cladding 32 and polymer optical waveguide lower core layer 33 by spin-coating process. The spin-coating speed is 800 - 6000 revolutions per minute, and it is baked at 100 - 150 °C for 2 - 40 minutes (if using materials such as EpoClad, etc., it is necessary to first expose the whole under ultraviolet light with a wavelength of 350 - 400 nm for 2 - 40 s after spin-coating, and then heat at 100 - 150 °C for 10 - 60 minutes), to fabricate a polymer optical waveguide intermediate cladding 34 with a thickness of 1 - 10 μm (the thickness of the polymer optical waveguide intermediate cladding above the polymer optical waveguide lower core layer);

[0021] E: Preparation of the strip-shaped polymer optical waveguide upper core layer 35

[0022] The upper core layer material of the polymer optical waveguide is selected from ultraviolet negative photoresist materials with negative thermo-optic coefficients and suitable for wet etching (including EpoCore, SU-8 2002, SU-8 2005, etc.). The refractive index of the upper core layer material of the polymer optical waveguide is higher than that of the lower cladding material, the intermediate cladding material, and the upper cladding material of the polymer optical waveguide. In the same device, it is optimal to select the same upper core layer and lower core layer materials of the polymer optical waveguide. The upper core layer material of the polymer optical waveguide is spin-coated on the intermediate cladding 34 of the polymer optical waveguide to form the upper core layer thin film 35'. The spin-coating speed is 600 - 6000 revolutions per minute, and the thickness of the upper core layer thin film 35' is 2 - 10 μm. After spin-coating, pre-baking is carried out. Using a stepwise temperature increase method, the device is heated at 40 - 100 °C for 2 - 30 minutes, and then baked at 70 - 130 °C for 2 - 40 minutes. After heating, it is naturally cooled to room temperature. Then, alignment lithography is performed on the upper core layer thin film 35' of the polymer optical waveguide, that is, using a mask plate complementary to the structure of the upper core layer of the polymer optical waveguide to be prepared (such as Figure 2 (shown in (a)), the mask plate is closely attached to the surface of the upper core layer thin film 35' of the polymer optical waveguide, and then exposed to ultraviolet light with a wavelength of 350 - 400 nm for 3 - 30 s, so that the lower core layer material of the polymer optical waveguide in the areas of the upper first adiabatic tapered waveguide 29, the upper second adiabatic tapered waveguide 210, the upper first output bending waveguide 211, the upper second output bending waveguide 212, the upper first output few-mode straight waveguide 213, and the upper second output few-mode straight waveguide 214 of the device to be prepared is exposed to ultraviolet light. After lithography, it is taken off the lithography machine for post-baking operation, that is, heated at 40 - 90 °C for 2 - 30 minutes, and then heated at 75 - 120 °C for 2 - 40 minutes. After heating, it is naturally cooled to room temperature. After cooling, development is carried out. First, wet etching is performed in the developer corresponding to the upper core layer material of the polymer optical waveguide for 5 - 80 s to remove the upper core layer thin film of the polymer optical waveguide that is not part of the upper core layer 35 structure of the polymer optical waveguide that has not been exposed, leaving only the upper core layer structure of the polymer waveguide corresponding to the mask plate structure. Then, it is placed in an isopropyl alcohol solution to wash away the unexposed upper core layer material of the polymer optical waveguide and the developer remaining on the surface of the device, and then rinsed with deionized water (when rinsing, it is necessary to rinse along the waveguide direction to prevent damage to the waveguide) to remove the isopropyl alcohol solution on the surface of the device, and then dried with nitrogen. Finally, post-baking and hardening are carried out, that is, heated at 110 - 160 °C for 20 - 60 minutes, thereby obtaining the strip-shaped upper core layer 35 of the polymer optical waveguide on the lower cladding 34 of the polymer optical waveguide;

[0023] F: Preparation of the upper cladding 36 of the polymer optical waveguide

[0024] The polymer upper cladding material (in the same device, it is best to use the same polymer optical waveguide lower cladding material, polymer optical waveguide intermediate cladding material, and polymer optical waveguide upper cladding material) is spin-coated on the prepared polymer optical waveguide intermediate cladding 34 and the polymer optical waveguide upper core layer 35 of the strip structure. The spin-coating speed is 1000 - 6000 revolutions per minute, and it is baked for 2 - 40 minutes at 100 - 150 °C (if using materials such as EpoClad, etc., after spin-coating, it needs to be integrally exposed to ultraviolet light with a wavelength of 350 - 400 nm for 2 - 40 s first, and then heated at 100 - 150 °C for 10 - 60 minutes), to obtain a polymer optical waveguide upper cladding 36 with a thickness of 4 - 20 μm (the thickness of the polymer optical waveguide upper cladding above the polymer optical waveguide upper core layer), thereby obtaining the three-dimensional mode multiplexer / demultiplexer of the present invention.

[0025] Compared with the existing device structure and preparation technology, the beneficial effects of the present invention are:

[0026] The three-dimensional mode multiplexer / demultiplexer of the present invention uses upper and lower two-layer waveguides to form a vertical DC structure, realizes the coupling between different symmetry modes, and can manipulate any waveguide mode; introduces an adiabatic tapered waveguide structure to solve the bandwidth problem of traditional DC; adopts an asymmetric Y-branch structure to improve the bandwidth of the device while reducing the device size, and the device can be applied to a mode division multiplexing system. The polymer material used in the device has a low cost, and the refractive index contrast between the core layer and the cladding of the polymer material is small, making the device have the characteristic of polarization insensitivity and increasing the stability of the optical communication system. In addition, using polymer materials to prepare the device has a simple process and is compatible with semiconductor processes, which is conducive to the functional integration and large-scale production of the device, and has important practical application value. Description of the Drawings

[0027] Figure 1 : Cross-sectional schematic diagram of the three-dimensional mode multiplexer / demultiplexer of the present invention;

[0028] Figure 2 (a): Schematic diagram of the structure of the polymer optical waveguide core layer of the three-dimensional mode multiplexer / demultiplexer of the present invention;

[0029] Figure 2 (b): Figure 2 Top view of the structure of the upper first adiabatic tapered waveguide 29 and the lower first adiabatic tapered waveguide 25 in (a);

[0030] Figure 2 (c): Figure 2 Top view of the structure of the upper second adiabatic tapered waveguide 210 and the lower second adiabatic tapered waveguide 26 in (a);

[0031] Figure 3 : Process flow chart for fabricating the three-dimensional mode multiplexer / demultiplexer according to the present invention;

[0032] Figure 4 (a): Simulated optical field distribution diagram of the E mode in the three-dimensional mode multiplexer / demultiplexer according to the present invention; 11 in the three-dimensional mode multiplexer / demultiplexer according to the present invention;

[0033] Figure 4 (b): Simulated optical field distribution diagram of the E mode in the three-dimensional mode multiplexer / demultiplexer according to the present invention; 21 in the three-dimensional mode multiplexer / demultiplexer according to the present invention;

[0034] Figure 4 (c): Simulated optical field distribution diagram of the E mode in the three-dimensional mode multiplexer / demultiplexer according to the present invention; 12 in the three-dimensional mode multiplexer / demultiplexer according to the present invention;

[0035] Figure 4 (d): Simulated optical field distribution diagram of the E mode in the three-dimensional mode multiplexer / demultiplexer according to the present invention; 22 in the three-dimensional mode multiplexer / demultiplexer according to the present invention;

[0036] Figure 5 (a): Simulated optical field transmission diagram of the output E mode of the three-dimensional mode multiplexer according to the present invention; 11 in the three-dimensional mode multiplexer according to the present invention;

[0037] Figure 5 (b): Simulated optical field transmission diagram of the output E mode of the three-dimensional mode multiplexer according to the present invention; 21 in the three-dimensional mode multiplexer according to the present invention;

[0038] Figure 5 (c): Simulated optical field transmission diagram of the output E mode of the three-dimensional mode multiplexer according to the present invention; 12 in the three-dimensional mode multiplexer according to the present invention;

[0039] Figure 5 (d): Simulated optical field transmission diagram of the output E mode of the three-dimensional mode multiplexer according to the present invention; 22 in the three-dimensional mode multiplexer according to the present invention;

[0040] Figure 6 : Curve of the coupling efficiency of the four modes of the three-dimensional mode multiplexer according to the present invention varying with wavelength;

[0041] As Figure 1 shown, cross-sectional schematic diagram of the three-dimensional mode multiplexer / demultiplexer (at the A-A' position in (a)), and the names of each component are: silicon substrate 31, polymer optical waveguide lower cladding 32, strip-shaped polymer optical waveguide lower core layer 33, polymer optical waveguide intermediate cladding 34, strip-shaped polymer optical waveguide upper core layer 35, polymer optical waveguide upper cladding 36; Figure 2 (a) in the three-dimensional mode multiplexer / demultiplexer according to the present invention;

[0042] As shown Figure 2 in Fig. (a), it is a schematic plan view of a three-dimensional mode multiplexer / demultiplexer based on an asymmetric Y-branch and a double-layer adiabatic tapered waveguide structure. The names of each component are: lower-layer input few-mode straight waveguide 21, first branch 22 of the lower-layer asymmetric Y-branch beam splitter, second branch 23 of the lower-layer asymmetric Y-branch beam splitter, lower-layer connecting tapered waveguide 24, first lower-layer adiabatic tapered waveguide 25, second lower-layer adiabatic tapered waveguide 26, first lower-layer output few-mode straight waveguide 27, second lower-layer output few-mode straight waveguide 28, first upper-layer adiabatic tapered waveguide 29, second upper-layer adiabatic tapered waveguide 210, first upper-layer output bent waveguide 211, second upper-layer output bent waveguide 212, first upper-layer output few-mode straight waveguide 213, and second upper-layer output few-mode straight waveguide 214; Figure 2 (b) is Figure 2 a schematic structural view of the first lower-layer adiabatic tapered waveguide 25 and the first upper-layer adiabatic tapered waveguide 29 in (a); Figure 2 (c) is Figure 2 a schematic structural view of the second lower-layer adiabatic tapered waveguide 26 and the second upper-layer adiabatic tapered waveguide 210 in (a);

[0043] As shown Figure 3 in the figure, 31 is a silicon substrate, 32 is a polymer lower cladding prepared on the silicon substrate 31 by a spin coating process, 33 is a strip-shaped polymer optical waveguide lower core layer prepared on the polymer optical waveguide lower cladding 32 by a spin coating, photolithography, and wet etching process, 34 is a polymer optical waveguide intermediate cladding prepared on the polymer optical waveguide lower cladding 32 and the strip-shaped polymer optical waveguide lower core layer 33 by a spin coating process, 35 is a strip-shaped polymer optical waveguide upper core layer prepared on the polymer optical waveguide intermediate cladding 34 by a spin coating, photolithography, and wet etching process, and 36 is a polymer optical waveguide upper cladding prepared on the polymer optical waveguide intermediate cladding 34 and the strip-shaped polymer optical waveguide upper core layer 35 by a spin coating process;

[0044] As shown Figure 4 in Fig. (a), it is a simulated light field distribution diagram of the E 11 mode in a three-dimensional mode multiplexer / demultiplexer based on an asymmetric Y-branch and a double-layer adiabatic tapered waveguide structure. During the simulation process, we selected the materials and waveguide dimensions used in Example 1. As can be seen from the figure, the light field is mainly concentrated in the rectangular waveguide core layer ( Figure 2 the lower-layer input few-mode straight waveguide 21 in (a)), ensuring the effective transmission of the E 11 mode optical signal in the optical waveguide; if used as a multiplexer, the E 11 mode signal light is input from the second lower-layer output few-mode straight waveguide 28; if used as a demultiplexer, the E 11The mode signal light is input from the lower-layer few-mode straight waveguide 21;

[0045] As Figure 4 (b) shows the simulated optical field distribution of the E mode in the three-dimensional mode multiplexer / demultiplexer based on the asymmetric Y-branch and double-layer adiabatic tapered waveguide structure. During the simulation, we selected the materials and waveguide dimensions used in Example 1. As can be seen from the figure, the optical field is mainly concentrated in the rectangular waveguide core layer ( 21 the lower-layer few-mode straight waveguide 21 in (a)), ensuring the effective transmission of the E mode optical signal in the optical waveguide; If used as a multiplexer, the E mode signal light is input from the lower-layer first output few-mode straight waveguide 27; If used as a demultiplexer, the E mode signal light is input from the lower-layer few-mode straight waveguide 21; Figure 2 (a) the lower-layer few-mode straight waveguide 21), ensuring the effective transmission of the E mode optical signal in the optical waveguide; If used as a multiplexer, the E mode signal light is input from the lower-layer first output few-mode straight waveguide 27; If used as a demultiplexer, the E mode signal light is input from the lower-layer few-mode straight waveguide 21; 21 mode optical signal in the optical waveguide; If used as a multiplexer, the E mode signal light is input from the lower-layer first output few-mode straight waveguide 27; If used as a demultiplexer, the E mode signal light is input from the lower-layer few-mode straight waveguide 21; 21 mode signal light is input from the lower-layer first output few-mode straight waveguide 27; If used as a demultiplexer, the E mode signal light is input from the lower-layer few-mode straight waveguide 21; 21 mode signal light is input from the lower-layer few-mode straight waveguide 21;

[0046] As Figure 4 (c) shows the simulated optical field distribution of the E mode in the three-dimensional mode multiplexer / demultiplexer based on the asymmetric Y-branch and double-layer adiabatic tapered waveguide structure. During the simulation, we selected the materials and waveguide dimensions used in Example 1. As can be seen from the figure, the optical field is mainly concentrated in the rectangular waveguide core layer ( 12 the lower-layer few-mode straight waveguide 21 in (a)), ensuring the effective transmission of the E mode optical signal in the optical waveguide; If used as a multiplexer, the E mode signal light is input from the upper-layer second output few-mode straight waveguide 214; If used as a demultiplexer, the E mode signal light is input from the lower-layer few-mode straight waveguide 21; Figure 2 (a) the lower-layer few-mode straight waveguide 21), ensuring the effective transmission of the E mode optical signal in the optical waveguide; If used as a multiplexer, the E mode signal light is input from the upper-layer second output few-mode straight waveguide 214; If used as a demultiplexer, the E mode signal light is input from the lower-layer few-mode straight waveguide 21; 12 mode optical signal in the optical waveguide; If used as a multiplexer, the E mode signal light is input from the upper-layer second output few-mode straight waveguide 214; If used as a demultiplexer, the E mode signal light is input from the lower-layer few-mode straight waveguide 21; 12 mode signal light is input from the upper-layer second output few-mode straight waveguide 214; If used as a demultiplexer, the E mode signal light is input from the lower-layer few-mode straight waveguide 21; 12 mode signal light is input from the lower-layer few-mode straight waveguide 21;

[0047] As Figure 4 (d) shows the simulated optical field distribution of the E mode in the three-dimensional mode multiplexer / demultiplexer based on the asymmetric Y-branch and double-layer adiabatic tapered waveguide structure. During the simulation, we selected the materials and waveguide dimensions used in Example 1. As can be seen from the figure, the optical field is mainly concentrated in the rectangular waveguide core layer ( 22 the lower-layer few-mode straight waveguide 21 in (a)), ensuring the effective transmission of the E mode optical signal in the optical waveguide; If used as a multiplexer, the E mode signal light is input from the upper-layer first output few-mode straight waveguide 213; If used as a demultiplexer, the E mode signal light is input from the lower-layer few-mode straight waveguide 21; Figure 2 (a) the lower-layer few-mode straight waveguide 21), ensuring the effective transmission of the E mode optical signal in the optical waveguide; If used as a multiplexer, the E mode signal light is input from the upper-layer first output few-mode straight waveguide 213; If used as a demultiplexer, the E mode signal light is input from the lower-layer few-mode straight waveguide 21; 22 mode optical signal in the optical waveguide; If used as a multiplexer, the E mode signal light is input from the upper-layer first output few-mode straight waveguide 213; If used as a demultiplexer, the E mode signal light is input from the lower-layer few-mode straight waveguide 21; 22 mode signal light is input from the upper-layer first output few-mode straight waveguide 213; If used as a demultiplexer, the E mode signal light is input from the lower-layer few-mode straight waveguide 21; 22 mode signal light is input from the lower-layer few-mode straight waveguide 21;

[0048] As Figure 5As shown in (a), for the three-dimensional mode multiplexer based on the asymmetric Y-branch and double-layer adiabatic tapered waveguide structure, when inputting mode E from the second lower output few-mode straight waveguide 28, the light field transmission simulation diagram of mode E and the light field distribution simulation diagram of the output port in the lower input few-mode straight waveguide 21 are as follows. During the simulation process, we select the materials and waveguide dimensions used in Embodiment 1. As can be seen from the figure, when inputting mode E, the output is mode E; 11 When inputting mode E, the output is mode E in the lower input few-mode straight waveguide 21; 11 The light field transmission simulation diagram of mode E and the light field distribution simulation diagram of the output port. During the simulation process, we select the materials and waveguide dimensions used in Embodiment 1. As can be seen from the figure, when inputting mode E, the output is mode E; 11 When inputting mode E, the output is mode E; 11 mode;

[0049] As Figure 5 As shown in (b), for the three-dimensional mode multiplexer based on the asymmetric Y-branch and double-layer adiabatic tapered waveguide structure, when inputting mode E from the first lower output few-mode straight waveguide 27, the light field transmission simulation diagram of mode E and the light field distribution simulation diagram of the output port in the lower input few-mode straight waveguide 21 are as follows. During the simulation process, we select the materials and waveguide dimensions used in Embodiment 1. As can be seen from the figure, when inputting mode E, the output is mode E; 11 When inputting mode E, the output is mode E in the lower input few-mode straight waveguide 21; 21 The light field transmission simulation diagram of mode E and the light field distribution simulation diagram of the output port. During the simulation process, we select the materials and waveguide dimensions used in Embodiment 1. As can be seen from the figure, when inputting mode E, the output is mode E; 11 When inputting mode E, the output is mode E; 21 mode;

[0050] As Figure 5 As shown in (c), for the three-dimensional mode multiplexer based on the asymmetric Y-branch and double-layer adiabatic tapered waveguide structure, when inputting mode E from the second upper output few-mode straight waveguide 214, the light field transmission simulation diagram of mode E and the light field distribution simulation diagram of the output port in the lower input few-mode straight waveguide 21 are as follows. During the simulation process, we select the materials and waveguide dimensions used in Embodiment 1. As can be seen from the figure, when inputting mode E, the output is mode E; 11 When inputting mode E, the output is mode E in the lower input few-mode straight waveguide 21; 12 The light field transmission simulation diagram of mode E and the light field distribution simulation diagram of the output port. During the simulation process, we select the materials and waveguide dimensions used in Embodiment 1. As can be seen from the figure, when inputting mode E, the output is mode E; 11 When inputting mode E, the output is mode E; 12 mode;

[0051] As Figure 5 As shown in (d), for the three-dimensional mode multiplexer based on the asymmetric Y-branch and double-layer adiabatic tapered waveguide structure, when inputting mode E from the first upper output few-mode straight waveguide 213, the light field transmission simulation diagram of mode E and the light field distribution simulation diagram of the output port in the lower input few-mode straight waveguide 21 are as follows. During the simulation process, we select the materials and waveguide dimensions used in Embodiment 1. As can be seen from the figure, when inputting mode E, the output is mode E; 11 When inputting mode E, the output is mode E in the lower input few-mode straight waveguide 21; 22 The light field transmission simulation diagram of mode E and the light field distribution simulation diagram of the output port. During the simulation process, we select the materials and waveguide dimensions used in Embodiment 1. As can be seen from the figure, when inputting mode E, the output is mode E; 11 When inputting mode E, the output is mode E; 22 mode;

[0052] As Figure 6As shown, the curves of the coupling efficiency of four modes of the three-dimensional mode multiplexer based on the asymmetric Y-branch and double-layer adiabatic tapered waveguide structure with respect to wavelength are presented. It can be seen that this mode multiplexer can achieve the multiplexing function of four modes well, and the output is not sensitive to wavelength changes. CR in the figure 11 、CR 12 、CR 13 、CR 14 represent the coupling efficiency, corresponding to the E 11 、E 12 、E 21 、E 22 modes respectively. Specific Embodiments

[0053] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0054] Embodiment 1

[0055] As shown in the attached Figure 1 figure (which is the cross-sectional view at the A-A' position in Figure 2 ), the three-dimensional mode multiplexer / demultiplexer consists of a silicon substrate 31 from bottom to top, a polymer optical waveguide lower cladding 32 prepared on the silicon substrate 31, a strip-shaped polymer optical waveguide lower core layer 33 prepared on the polymer optical waveguide lower cladding 32, a polymer optical waveguide intermediate cladding 34 prepared on the polymer optical waveguide lower cladding 32 and the strip-shaped polymer optical waveguide lower core layer 33, a strip-shaped polymer optical waveguide upper core layer 35 prepared on the polymer optical waveguide intermediate cladding 34, and a polymer optical waveguide upper cladding 36 prepared on the polymer optical waveguide intermediate cladding 34 and the strip-shaped polymer optical waveguide upper core layer 35. Moreover, the strip-shaped polymer optical waveguide lower core layer 33 is coated in the polymer optical waveguide intermediate cladding 34, and the strip-shaped polymer optical waveguide upper core layer 35 is coated in the polymer optical waveguide upper cladding 36.

[0056] As shown in the attached Figure 2(a), (b), and (c) show that the length a1 of the lower-layer input few-mode straight waveguide 21 is 1000 μm, and the width w1 is 10 μm; the lower-layer asymmetric Y-branch beam splitter first branch 22 and the lower-layer asymmetric Y-branch beam splitter second branch 23 have the same structural dimensions except for the width. The projection lengths a2 and a2' along the extension direction of the lower-layer input few-mode straight waveguide 21 are equal to 3000 μm, and the center distances gap1 and gap1' between the input and output ends of the two are equal to 10 μm. The width w2 of the lower-layer asymmetric Y-branch beam splitter first branch 22 is 3.8 μm, and the width w3 of the lower-layer asymmetric Y-branch beam splitter second branch 23 is 6.2 μm; the length a3 of the lower-layer connecting tapered waveguide 24 is 1000 μm, the width w2' at its connection with the lower-layer asymmetric Y-branch beam splitter first branch 22 is 3.8 μm, and the width w4 at its connection with the lower-layer first adiabatic tapered waveguide 25 is 4.8 μm; the length a4 of the lower-layer first adiabatic tapered waveguide 25 is 2300 μm, the width w4 at its connection with the lower-layer connecting tapered waveguide 24 is 4.8 μm, and the width gradually increases to the width w5 of 5.6 μm at its connection with the lower-layer first output few-mode straight waveguide 27; the length a5 of the lower-layer second adiabatic tapered waveguide 26 is 3350 μm, the width w3' at its connection with the lower-layer asymmetric Y-branch beam splitter second branch 23 is 6.2 μm, and the width gradually increases to the width w6 of 7 μm at its connection with the lower-layer second output few-mode straight waveguide 28; the length a6 of the lower-layer first output few-mode straight waveguide 27 is 4000 μm, and the width w5' is 5.6 μm; the length a7 of the lower-layer second output few-mode straight waveguide 28 is 3950 μm, and the width w6' is 7 μm; the length a4 of the upper-layer first adiabatic tapered waveguide 29 is 2300 μm, the center distance gap2 in the horizontal direction from the lower-layer first adiabatic tapered waveguide 25 is 3 μm, and the distance G1 in the vertical direction is 4 μm. From the direction of the width of the lower-layer input few-mode straight waveguide 21 input, the width w7 is 3.8 μm and gradually changes to the width w8 of 3 μm at its connection with the upper-layer first output bent waveguide 211; the length a5 of the upper-layer second adiabatic tapered waveguide 210 is 3350 μm, the center distance gap3 in the horizontal direction from the lower-layer second adiabatic tapered waveguide 26 is 3 μm, and the distance G1' in the vertical direction is 4 μm. From the direction of the width of the lower-layer input few-mode straight waveguide 21 input, the width w9 is 4.6 μm and gradually changes to the width w10 of 3.8 μm; the projection length a8 of the upper-layer first output bent waveguide 211 along the extension direction of the lower-layer input few-mode straight waveguide 21 is 3000 μm, and the center-to-center spacing gap4 between its input end and output end is 12 μm; the projection length a9 of the upper-layer second output bent waveguide 212 along the extension direction of the lower-layer input few-mode straight waveguide 21 is 1900 μm, and the center-to-center spacing gap5 between its input end and output end is 15 μm; the length a10 of the upper-layer first output few-mode straight waveguide 213 is 1000 μm, and the width w8' is 3 μm; the length a11 of the upper-layer second output few-mode straight waveguide 214 is 2050 μm, and the width w10' is 3.8 μm.

[0057] The thickness of the silicon substrate 31 is 1 mm, the thickness of the polymer optical waveguide lower cladding 32 is 10 μm, the thickness of the strip-shaped polymer optical waveguide lower core layer 33 is 9 μm, the thickness of the polymer optical waveguide intermediate cladding 34 above the strip-shaped polymer optical waveguide lower core layer 33 is 4 μm, the thickness of the strip-shaped polymer optical waveguide upper core layer 35 is 4 μm, and the thickness of the polymer optical waveguide upper cladding 36 above the strip-shaped polymer optical waveguide upper core layer 35 is 10 μm.

[0058] The mode demultiplexer inputs the E 11 mode in the optical waveguide from the lower-layer input few-mode straight waveguide 21, couples it to the second branch 23 of the lower-layer asymmetric Y-branch beam splitter, and passes through the lower-layer second adiabatic tapered waveguide 26 to output the E 11 mode from the lower-layer second output few-mode straight waveguide 28; inputs the E 21 mode in the optical waveguide from the lower-layer input few-mode straight waveguide 21, couples it to the first branch 22 of the lower-layer asymmetric Y-branch beam splitter in the form of the E 11 mode, outputs it to the lower-layer first adiabatic tapered waveguide 25 through the lower-layer connecting tapered waveguide 24, and finally outputs the E 11 mode from the lower-layer first output few-mode straight waveguide 27; inputs the E 12 mode in the optical waveguide from the lower-layer input few-mode straight waveguide 21, couples it to the second branch 23 of the lower-layer asymmetric Y-branch beam splitter. When passing through the lower-layer second adiabatic tapered waveguide 26 (in the modes of the two waveguides in the coupling region, since their effective refractive indices are equal, the coupling coefficient between the two is not zero, meeting the phase matching condition, and optical energy exchange occurs), the signal light couples into the upper-layer second adiabatic tapered waveguide 210 for transmission in the E 11 mode to achieve mode field matching, and finally outputs the E 11 mode through the upper-layer second output bent waveguide 212 and the upper-layer second output few-mode straight waveguide 214; inputs the E 22 mode in the optical waveguide from the lower-layer input few-mode straight waveguide 21, in the E 12The optical mode is coupled to the first branch 22 of the lower-layer asymmetric Y-branch splitter in a form, passes through the lower-layer connecting tapered waveguide 24, and when output to the lower-layer first adiabatic tapered waveguide 25, the signal light is in the E 11 mode and is coupled into the upper-layer first adiabatic tapered waveguide 29 for transmission to achieve mode field matching, and finally is output in the E 11 mode through the upper-layer first output bending waveguide 211 and the upper-layer first output few-mode straight waveguide 213. The mode multiplexer is the reverse input and output of the above optical path.

[0059] Embodiment 2

[0060] A: Cleaning treatment of the silicon substrate 31

[0061] Wipe the silicon substrate 31 repeatedly 2 times with a cotton ball dipped in acetone solution, then wipe it repeatedly 2 times with another cotton ball dipped in ethanol solution, then rinse it clean with deionized water, and finally blow-dry the silicon substrate 31 with nitrogen, put it into a clean petri dish and seal it;

[0062] B: Preparation of the polymer optical waveguide lower cladding 32

[0063] Spin-coat the polymer optical waveguide lower cladding material EpoClad on the cleaned silicon substrate 31 by spin-coating process at a spin-coating speed of 2000 revolutions per minute, bake it at 120 °C for 10 minutes, then expose it integrally under ultraviolet light with a wavelength of 365 nm for 12 s, and finally bake it at 120 °C for 20 minutes to obtain the polymer optical waveguide lower cladding 32 with a thickness of 10 μm;

[0064] C: Preparation of the strip-shaped polymer optical waveguide lower core layer 33

[0065] Spin-coat the polymer optical waveguide core layer material EpoCore on the polymer optical waveguide lower cladding 32 by spin-coating process to form the polymer optical waveguide lower core layer thin film 33', the spin-coating speed is 2800 revolutions per minute, and the thickness of the polymer optical waveguide lower core layer thin film 33' is 9 μm; after spin-coating, perform pre-baking, that is, use a stepwise heating method to heat the device at 55 °C for 3 minutes, then bake it at 90 °C for 20 minutes, and after heating, let it cool naturally to room temperature; then perform alignment lithography on the polymer optical waveguide lower core layer thin film 33', that is, use the same Figure 2(As shown in (a)), a complementary mask plate is tightly attached to the surface of the polymer optical waveguide lower core layer thin film 33'. Then, it is exposed under ultraviolet light with a wavelength of 365 nm for 10 s, so that the polymer optical waveguide lower core layer materials in the areas of the lower-layer input few-mode straight waveguide 21, the first branch 22 of the lower-layer asymmetric Y-branch beam splitter, the second branch 23 of the lower-layer asymmetric Y-branch beam splitter, the lower-layer connecting tapered waveguide 24, the first adiabatic tapered waveguide 25 of the lower layer, the second adiabatic tapered waveguide 26 of the lower layer, the first output few-mode straight waveguide 27 of the lower layer, and the second output few-mode straight waveguide 28 of the lower layer of the device to be fabricated are exposed to ultraviolet light. After lithography, a medium baking operation is carried out, that is, it is heated at 55 °C for 5 minutes, and then heated at 85 °C for 20 minutes. After heating, it is naturally cooled to room temperature. After the temperature drops, development is carried out. First, it is wet-etched in the developer corresponding to the polymer optical waveguide lower core layer material for 20 s to remove the polymer optical waveguide lower core layer thin film of the non-polymer optical waveguide lower core layer 33 structure that has not been exposed, leaving only the polymer waveguide lower core layer structure corresponding to the mask plate structure. Then, it is placed in an isopropyl alcohol solution to wash away the unexposed polymer optical waveguide lower core layer material and the developer remaining on the surface of the device, and then rinsed with deionized water (when rinsing, it is necessary to rinse along the waveguide direction to prevent the waveguide from being damaged) to remove the isopropyl alcohol solution on the surface of the device, and then dried with nitrogen. Finally, post-baking and hardening are carried out, that is, it is heated at 125 °C for 40 minutes, thereby obtaining a strip-shaped polymer optical waveguide lower core layer 33 on the polymer optical waveguide lower cladding 32;

[0066] D: Preparation of the polymer optical waveguide intermediate cladding 34

[0067] The polymer optical waveguide lower cladding material EpoClad is spin-coated on the prepared polymer optical waveguide lower cladding 32 and polymer optical waveguide lower core layer 33 through a spin-coating process. The spin-coating speed is 1500 revolutions per minute. It is baked at 120 °C for 10 minutes, and then exposed as a whole under ultraviolet light with a wavelength of 365 nm for 12 s, and then heated at 120 °C for 20 minutes to obtain a polymer optical waveguide intermediate cladding 34 with a thickness of 4 μm (the thickness of the polymer optical waveguide intermediate cladding above the polymer optical waveguide lower core layer);

[0068] E: Preparation of the strip-shaped polymer optical waveguide upper core layer 35

[0069] The polymer optical waveguide core layer material EpoCore was spin-coated on the polymer optical waveguide intermediate cladding 34 by spin-coating process to form the polymer optical waveguide upper core layer thin film 35'. The spin-coating speed was 3500 revolutions per minute, and the thickness of the polymer optical waveguide upper core layer thin film 35' was 4 μm. After spin-coating, pre-baking was carried out. By using the method of stepwise temperature increase, the device was heated at 55 °C for 3 minutes, and then baked at 90 °C for 20 minutes. After heating, it was naturally cooled to room temperature. Then, alignment lithography was performed on the polymer optical waveguide upper core layer thin film 35', that is, a mask plate complementary to the structure of the polymer optical waveguide upper core layer to be prepared (such as Figure 2 (as shown in (a)) was used. The mask plate was closely attached to the surface of the polymer optical waveguide upper core layer thin film 35', and then exposed to ultraviolet light with a wavelength of 365 nm for 10 s, so that the polymer optical waveguide lower core layer material in the areas of the upper first adiabatic tapered waveguide 29, upper second adiabatic tapered waveguide 210, upper first output bent waveguide 211, upper second output bent waveguide 212, upper first output few-mode straight waveguide 213, and upper second output few-mode straight waveguide 214 of the device to be prepared was exposed to ultraviolet light. After lithography, it was taken off the lithography machine for medium baking operation, that is, heated at 55 °C for 5 minutes, and then heated at 85 °C for 20 minutes. After heating, it was naturally cooled to room temperature. After cooling, development was carried out. First, it was wet-etched in the developer corresponding to the polymer optical waveguide upper core layer material for 20 s to remove the polymer optical waveguide upper core layer thin film of the non-polymer optical waveguide upper core layer 35 structure that was not exposed, leaving only the polymer optical waveguide upper core layer structure corresponding to the mask plate structure. Then, it was put into an isopropyl alcohol solution to wash away the unexposed polymer optical waveguide upper core layer material and developer remaining on the surface of the device, and then rinsed with deionized water (when rinsing, it was necessary to rinse along the waveguide direction to prevent the waveguide from being damaged) to remove the isopropyl alcohol solution on the surface of the device, and then dried with nitrogen. Finally, post-baking and hardening were carried out, that is, heated at 125 °C for 40 minutes, so as to obtain the strip-shaped polymer optical waveguide upper core layer 35 on the polymer optical waveguide lower cladding 34;

[0070] F: Preparation of the polymer optical waveguide upper cladding 36

[0071] The polymer optical waveguide lower cladding material EpoClad was spin-coated on the prepared polymer optical waveguide intermediate cladding 34 and the strip-shaped polymer optical waveguide upper core layer 35 by spin-coating process. The spin-coating speed was 1800 revolutions per minute, baked at 120 °C for 10 minutes, and then exposed to ultraviolet light with a wavelength of 365 nm as a whole for 12 s, and then heated at 120 °C for 20 minutes), to obtain the polymer optical waveguide upper cladding 36 with a thickness of 10 μm (the thickness of the polymer optical waveguide upper cladding above the polymer optical waveguide upper core layer), thus completing the preparation of the three-dimensional mode multiplexer / demultiplexer described in the present invention.

[0072] It should be noted that the specific embodiments mentioned in this patent are only representative examples of the present invention, and should not be construed as limiting the scope of any disclosed technology or what may be claimed. Instead, they should be construed as descriptions of the features of specific embodiments that may be specific to the disclosed technology. Obviously, the present invention is not limited to the details of the above exemplary embodiments, and there can be more forms and design materials, such as using waveguide materials like lithium niobate, silicon, silicon nitride, etc. Any reference signs in the claims should not be regarded as limiting the claimed claims. Those skilled in the art, which are clearly disclosed in the present invention or obtained without any objection according to the written description of the document, fall within the scope protected by this patent.

Claims

1. A three-dimensional mode multiplexer / demultiplexer, characterized in that: From bottom to top, it is composed of a silicon substrate (31), a polymer optical waveguide lower cladding (32) prepared on the silicon substrate (31), a strip-shaped polymer optical waveguide lower core layer (33) prepared on the polymer optical waveguide lower cladding (32), a polymer optical waveguide intermediate cladding (34) prepared on the polymer optical waveguide lower cladding (32) and the strip-shaped polymer optical waveguide lower core layer (33), a strip-shaped polymer optical waveguide upper core layer (35) prepared on the polymer optical waveguide intermediate cladding (34), and a polymer optical waveguide upper cladding (36) prepared on the polymer optical waveguide intermediate cladding (34) and the strip-shaped polymer optical waveguide upper core layer (35). The strip-shaped polymer optical waveguide lower core layer (33) is covered in the polymer optical waveguide intermediate cladding (34), and the strip-shaped polymer optical waveguide upper core layer (35) is covered in the polymer optical waveguide upper cladding (36). Along the light propagation direction, the strip-shaped polymer optical waveguide lower core layer (33) is composed of a lower input few-mode straight waveguide (21), a first branch (22) of a lower asymmetric Y-branch beam splitter, a second branch (23) of the lower asymmetric Y-branch beam splitter, a lower connecting tapered waveguide (24), a first adiabatic tapered waveguide (25) at the lower layer, a second adiabatic tapered waveguide (26) at the lower layer, a first output few-mode straight waveguide (27) at the lower layer, and a second output few-mode straight waveguide (28) at the lower layer. The strip-shaped polymer optical waveguide upper core layer (35) is composed of a first adiabatic tapered waveguide (29) at the upper layer, a second adiabatic tapered waveguide (210) at the upper layer, a first output curved waveguide (211) at the upper layer, a second output curved waveguide (212) at the upper layer, a first output few-mode straight waveguide (213) at the upper layer, and a second output few-mode straight waveguide (214) at the upper layer. The lower input few-mode straight waveguide (21), the first branch (22) of the lower asymmetric Y-branch beam splitter, and the second branch (23) of the lower asymmetric Y-branch beam splitter form an asymmetric Y-branch beam splitter. The symmetry axis of the first adiabatic tapered waveguide (29) at the upper layer is horizontally offset by a certain distance and is parallel to the symmetry axis of the first adiabatic tapered waveguide (25) at the lower layer. The symmetry axis of the second adiabatic tapered waveguide (210) at the upper layer is horizontally offset by a certain distance and is parallel to the symmetry axis of the second adiabatic tapered waveguide (26) at the lower layer. The first branch (22) of the lower asymmetric Y-branch beam splitter, the lower connecting tapered waveguide (24), the first adiabatic tapered waveguide (25) at the lower layer, and the first output few-mode straight waveguide (27) at the lower layer are sequentially connected. The second branch (23) of the lower asymmetric Y-branch beam splitter, the second adiabatic tapered waveguide (26) at the lower layer, and the second output few-mode straight waveguide (28) at the lower layer are sequentially connected. The first adiabatic tapered waveguide (29) at the upper layer, the first output curved waveguide (211) at the upper layer, and the first output few-mode straight waveguide (213) at the upper layer are sequentially connected. The second adiabatic tapered waveguide (210) at the upper layer, the second output curved waveguide (212) at the upper layer, and the second output few-mode straight waveguide (214) at the upper layer are sequentially connected.The refractive index of the material of the lower core layer (33) of the polymer optical waveguide with a strip structure and the upper core layer (35) of the polymer optical waveguide with a strip structure is higher than that of the materials of the lower cladding layer (32), the intermediate cladding layer (34), and the upper cladding layer (36) of the polymer optical waveguide.

2. The three-dimensional mode multiplexer / demultiplexer according to claim 1, characterized in that: The length a1 of the lower-layer input few-mode straight waveguide (21) is 200 - 5000 μm, and the width w1 is 8 - 15 μm; the first branch (22) of the lower-layer asymmetric Y-branch beam splitter and the second branch (23) of the lower-layer asymmetric Y-branch beam splitter have the same structural dimensions except for the width. Their projected lengths a2 and a2' along the extension direction of the lower-layer input few-mode straight waveguide (21) are equal, being 500 - 8000 μm, and the center distances gap1 and gap1' between their input and output ends are equal, being 5 - 50 μm; the width w2 of the first branch (22) of the lower-layer asymmetric Y-branch beam splitter is 1.9 - 19 μm, and the width w3 of the second branch (23) of the lower-layer asymmetric Y-branch beam splitter is 3.1 - 31 μm; the length a3 of the lower-layer connecting tapered waveguide (24) is 100 - 2000 μm, the width w2' at its connection with the first branch (22) of the lower-layer asymmetric Y-branch beam splitter is 1.9 - 19 μm, and the width gradually increases to the width w4 of 2.8 - 7.8 μm at its connection with the lower-layer first adiabatic tapered waveguide (25); the length a4 of the lower-layer first adiabatic tapered waveguide (25) is 300 - 5300 μm, the width w4 at its connection with the lower-layer connecting tapered waveguide (24) is 2.8 - 7.8 μm, and the width gradually increases to the width w5 of 3.6 - 8.6 μm at its connection with the lower-layer first output few-mode straight waveguide (27); the length a5 of the lower-layer second adiabatic tapered waveguide (26) is 350 - 6350 μm, the width w3' at its connection with the second branch (23) of the lower-layer asymmetric Y-branch beam splitter is 3.1 - 31 μm, and the width gradually increases to the width w6 of 3.5 - 10.5 μm at its connection with the lower-layer second output few-mode straight waveguide (28); the length a6 of the lower-layer first output few-mode straight waveguide (27) is 400 - 10000 μm, and the width w5' is 3.6 - 8.6 μm; the length a7 of the lower-layer second output few-mode straight waveguide (28) is 400 - 10000 μm, and the width w6' is 3.5 - 10.5 μm; the length a4 of the upper-layer first adiabatic tapered waveguide (29) is 500 - 5300 μm, the center distance gap2 in the horizontal direction between it and the lower-layer first adiabatic tapered waveguide (25) is 1 - 6 μm, the distance G1 in the vertical direction is 1 - 10 μm, and its width gradually decreases from w7 of 1.8 - 6.8 μm to the width w8 of 1.5 - 6.5 μm at its connection with the upper-layer first output bent waveguide (211); the length a5 of the upper-layer second adiabatic tapered waveguide (210) is 800 - 6300 μm, the center distance gap3 in the horizontal direction between it and the lower-layer second adiabatic tapered waveguide (26) is 1.5 - 6.5 μm, the distance G1' in the vertical direction is 1 - 10 μm, and its width gradually decreases from w9 of 2.6 - 8.6 μm to the width w10 of 1.8 - 6...8 μm; the projection length a8 of the upper-layer first output bending waveguide (211) along the extension direction of the lower-layer input few-mode straight waveguide (21) is 300 to 5000 μm, and the center distance gap4 between its input end and output end is 3 to 35 μm; the projection length a9 of the upper-layer second output bending waveguide (212) along the extension direction of the lower-layer input few-mode straight waveguide (21) is 300 to 5000 μm, and the center distance gap5 between its input end and output end is 3 to 35 μm; the length a10 of the upper-layer first output few-mode straight waveguide (213) is 100 to 5000 μm, and the width w8' is 1.5 to 6.5 μm; the length a11 of the upper-layer second output few-mode straight waveguide (214) is 100 to 5000 μm, and the width w10' is 1.8 to 6.8 μm;. where w2’ = w2, w3’ = w3, w5’ = w5, w6’ = w6, w8’ = w8, w10’ = w10, a2’ = a2, gap1’ = gap1, G1’ = G1.

3. The three-dimensional mode multiplexer / demultiplexer according to claim 1, wherein: The thickness of the silicon substrate (31) is 0.5 - 2 mm, the thickness of the polymer optical waveguide lower cladding (32) is 4 - 20 μm, the thickness of the strip-shaped polymer optical waveguide lower core layer (33) is 7 - 15 μm, the thickness of the polymer optical waveguide intermediate cladding (34) above the strip-shaped polymer optical waveguide lower core layer (33) is 1 - 10 μm, the thickness of the strip-shaped polymer optical waveguide upper core layer (35) is 2 - 10 μm, and the thickness of the polymer optical waveguide upper cladding (36) above the strip-shaped polymer optical waveguide upper core layer (35) is 4 - 20 μm.

4. The three-dimensional mode multiplexer / demultiplexer according to claim 1, wherein: The materials of the polymer optical waveguide lower cladding (32), the polymer optical waveguide intermediate cladding (34) and the polymer optical waveguide upper cladding (36) are one of polyethylene, polyester, polycarbonate, polyimide, polymethyl methacrylate, polystyrene, EpoClad, and the materials of the strip-shaped polymer optical waveguide lower core layer (33) and the strip-shaped polymer optical waveguide upper core layer (35) are one of EpoCore, SU-8 2002, SU-8 2005.

5. A method for preparing a three-dimensional mode multiplexer / demultiplexer according to any one of claims 1 to 4, comprising the following steps: A: Cleaning treatment of the silicon substrate (31) Wipe the silicon substrate (31) repeatedly 1 - 3 times with a cotton ball dipped in acetone solution, then wipe the silicon substrate (31) repeatedly 1 - 3 times with another cotton ball dipped in ethanol solution, then rinse it thoroughly with deionized water, and finally dry the silicon substrate (31) with nitrogen. B: Preparation of the polymer optical waveguide lower cladding (32) Spin-coat the polymer waveguide lower cladding material on the cleaned silicon substrate (31) by spin-coating process, with a spin-coating speed of 1000 - 6000 revolutions per minute, and bake it for 2 - 40 minutes at 100 - 150 °C; when using EpoClad material, it needs to be baked and then exposed as a whole to ultraviolet light with a wavelength of 350 - 400 nm for 2 - 40 s, and finally baked at 100 - 150 °C for 10 - 60 minutes to obtain the polymer optical waveguide lower cladding (32). C: Preparation of the strip-shaped polymer optical waveguide lower core layer 33 The polymer optical waveguide lower core layer material is spin-coated on the polymer optical waveguide lower cladding (32) by spin coating to form a polymer optical waveguide lower core layer thin film (33'), and the spin coating speed is 600 to 5500 revolutions per minute; after spin coating, pre-baking is carried out, that is, by the method of stepwise heating, the device is heated at 40 to 120 °C for 2 to 30 minutes, and then baked at 70 to 130 °C for 2 to 40 minutes, and after heating, it is naturally cooled to room temperature; then alignment lithography is carried out on the polymer optical waveguide lower core layer thin film (33'), that is, using a mask plate complementary to the polymer optical waveguide lower core layer structure to be prepared, the mask plate is closely attached to the surface of the polymer optical waveguide lower core layer thin film (33'), and then exposed to ultraviolet light with a wavelength of 350 to 400 nm for 3 to 30 s, so that the polymer optical waveguide lower core layer materials in the areas of the lower-layer input few-mode straight waveguide (21), the first branch of the lower-layer asymmetric Y-branch beam splitter (22), the second branch of the lower-layer asymmetric Y-branch beam splitter (23), the lower-layer connecting tapered waveguide (24), the first adiabatic tapered waveguide of the lower layer (25), the second adiabatic tapered waveguide of the lower layer (26), the first output few-mode straight waveguide of the lower layer (27), and the second output few-mode straight waveguide of the lower layer (28) of the device to be prepared are exposed to ultraviolet light; after lithography, mid-baking operation is carried out, that is, heating at 40 to 90 °C for 2 to 30 minutes, and then heating at 75 to 120 °C for 2 to 40 minutes, and after heating, it is naturally cooled to room temperature; after cooling, development is carried out; first, wet etching is carried out in the developer corresponding to the polymer optical waveguide lower core layer material for 5 to 80 s to remove the polymer optical waveguide lower core layer thin film of the non-polymer optical waveguide lower core layer (33) structure that is not exposed, leaving only the polymer waveguide lower core layer structure corresponding to the mask plate structure, then it is placed in an isopropyl alcohol solution to wash away the unexposed polymer optical waveguide lower core layer material and developer remaining on the surface of the device, then rinsed with deionized water to remove the isopropyl alcohol solution on the surface of the device, and then blown dry with nitrogen; finally, post-baking and hardening are carried out, that is, heating at 110 to 160 °C for 20 to 60 minutes, so as to obtain a strip-shaped polymer optical waveguide lower core layer (33) on the polymer optical waveguide lower cladding (32); D: Preparation of the polymer optical waveguide intermediate cladding (34) The polymer optical waveguide intermediate cladding material is spin-coated on the prepared polymer optical waveguide lower cladding (32) and polymer optical waveguide lower core layer (33) by spin coating, the spin coating speed is 800 to 6000 revolutions per minute, baked at 100 to 150 °C for 2 to 40 minutes, and when using EpoClad material, it is necessary to first expose the whole body to ultraviolet light with a wavelength of 350 to 400 nm for 2 to 40 s after spin coating, and then heat at 100 to 150 °C for 10 to 60 minutes to obtain the polymer optical waveguide intermediate cladding (34); E: Preparation of the strip-shaped polymer optical waveguide upper core layer (35) The polymer optical waveguide upper core layer material is spin-coated on the polymer optical waveguide intermediate cladding (34) by a spin-coating process to form a polymer optical waveguide upper core layer thin film (35’), and the spin-coating speed is 600 - 6000 revolutions per minute; after spin-coating, pre-baking is carried out. By using a stepwise temperature increase method, the device is heated at 40 - 100 °C for 2 - 30 minutes, and then baked at 70 - 130 °C for 2 - 40 minutes. After heating, it is naturally cooled to room temperature; then, alignment lithography is performed on the polymer optical waveguide upper core layer thin film (35’), that is, a mask plate complementary to the polymer optical waveguide upper core layer structure to be prepared is used. The mask plate is closely attached to the surface of the polymer optical waveguide upper core layer thin film (35’), and then exposed to ultraviolet light with a wavelength of 350 - 400 nm for 3 - 30 s, so that the polymer optical waveguide lower core layer materials in the areas of the upper first adiabatic tapered waveguide (29), upper second adiabatic tapered waveguide (210), upper first output bending waveguide (211), upper second output bending waveguide (212), upper first output few-mode straight waveguide (213), and upper second output few-mode straight waveguide (214) of the device to be prepared are exposed to ultraviolet light; after lithography, it is taken off the lithography machine for medium baking operation, that is, heated at 40 - 90 °C for 2 - 30 minutes, and then heated at 75 - 120 °C for 2 - 40 minutes. After heating, it is naturally cooled to room temperature; after cooling, development is carried out; first, wet etching is carried out in the developer corresponding to the polymer optical waveguide upper core layer material for 5 - 80 s to remove the polymer optical waveguide upper core layer thin film of the non-polymer optical waveguide upper core layer (35) structure that is not exposed, leaving only the polymer waveguide upper core layer structure corresponding to the mask plate structure, then it is put into an isopropanol solution to wash away the unexposed polymer optical waveguide upper core layer material and developer residues on the device surface, and then rinsed with deionized water to remove the isopropanol solution on the device surface, and then dried with nitrogen; finally, post-baking and hardening are carried out, that is, heated at 110 - 160 °C for 20 - 60 minutes, thereby obtaining a strip-shaped polymer optical waveguide upper core layer (35) on the polymer optical waveguide lower cladding (34); F: Preparation of the polymer optical waveguide upper cladding (36) The polymer upper cladding material is spin-coated on the prepared polymer optical waveguide intermediate cladding (34) and the strip-shaped polymer optical waveguide upper core layer (35) by a spin-coating process. The spin-coating speed is 1000 - 6000 revolutions per minute, and it is baked at 100 - 150 °C for 2 - 40 minutes. When using EpoClad material, it needs to be exposed to ultraviolet light with a wavelength of 350 - 400 nm for 2 - 40 s as a whole after spin-coating, and then heated at 100 - 150 °C for 10 - 60 minutes to obtain the polymer optical waveguide upper cladding (36), thereby obtaining the three-dimensional mode multiplexer / demultiplexer described above.

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