A mode-selectable modulated four-mode waveguide optical switch and its manufacturing method

Abstract

A mode-selectable modulated four-mode waveguide optical switch and its manufacturing method belong to the technical field of planar optical waveguide devices. It consists of a silicon wafer substrate, a polymer lower cladding, a strip-shaped polymer optical waveguide core layer, a polymer upper cladding, and a heating electrode. The optical switch of the present invention utilizes the advantages of an asymmetric Y-branch structure and a simple MMI optical waveguide structure, as well as the large thermo-optic coefficient of organic polymer materials, to achieve switching of four optical modes by heating the MMI structure; by heating different heating electrodes, switching functions can be realized for two of the four modes, or for all four modes simultaneously; in addition, the use of polymer materials makes the device manufacturing process simpler, only requiring conventional processes such as spin coating, photolithography, and wet etching, effectively reducing production costs, improving the production efficiency of the device, and facilitating large-scale mass production, enabling this mode optical switch to be applied in practice.

Description

Technical Field

[0001] The present invention belongs to the technical field of planar optical waveguide devices, and particularly relates to a mode-selectable modulated four-mode waveguide optical switch with a silicon wafer as a substrate and an organic polymer material with a high thermo-optic coefficient as an optical waveguide core layer and a cladding layer, and a preparation method thereof. Background Art

[0002] With the rapid development of Internet technology, 5G communication technology, and big data, the amount of data that needs to be transmitted and processed in life has increased greatly. The traditional communication method is mainly based on electrical interconnection, and it is currently difficult to meet the demand for the rapidly growing data transmission volume. Therefore, optical interconnection has become the key to solving this problem. Compared with traditional electrical interconnection, optical interconnection uses optical signals as the medium for information data transmission. Since light has a faster transmission speed, optical interconnection effectively increases the information transmission speed and communication capacity. However, due to the influence of the nonlinear effect of optical fibers and the Shannon limit, it is difficult to further improve the communication capacity of traditional single-mode optical communication. In order to further improve the communication capacity, researchers have proposed various multiplexing technologies such as wavelength division multiplexing, polarization division multiplexing, and mode division multiplexing. Mode division multiplexing technology uses signal light of different modes as the carrier for information transmission. The signal lights of different modes are orthogonal to each other and can be transmitted simultaneously in a multimode optical fiber without affecting each other. The signal light of each mode can be used as an independent channel to transmit information, which doubles the communication capacity of the channel.

[0003] The mode optical switch is one of the most important devices in the mode division multiplexing system and is widely used in optical communication systems. In the traditional mode division multiplexing system, if it is necessary to modulate an optical signal, usually, different optical modes are first demultiplexed into different single-mode waveguides through a mode demultiplexer and converted into the fundamental mode, and then each fundamental mode is modulated through a separate optical switch, which usually requires a large device size and high power consumption. In order to overcome this limitation, it is necessary to develop a new type of flexible and adjustable mode optical switch that can not only implement the switch function for multiple optical modes simultaneously but also select to implement the switch function for a certain or certain modes.

[0004] Compared with the mode optical switch based on optical fibers, the mode optical switch based on the planar optical waveguide structure can not only be well compatible with optical fibers but also has the advantages of a compact structure, small insertion loss, small mode-dependent loss, high integration, and flexible design. And because it is prepared by using traditional photolithography, etching and other processes, it is easy to mass-produce. In order to make the device more flexible, the phase of the signal light can be modulated through the electro-optic effect, thermo-optic effect, etc. to realize the switch function.

[0005] According to different material systems, waveguide-type mode optical switches can be divided into many types. Among them, optical waveguide devices based on the silica / silicon material system have a large refractive index difference between the core layer and the cladding layer, which is beneficial to the miniaturization and integration of devices. However, their processes are complex and expensive. Nevertheless, optical waveguide devices based on polymer materials not only have simple preparation processes, but also can be compatible with semiconductor processes, have low costs, and can be doped with functions. In addition, polymer materials have a large thermo-optic coefficient and low thermal conductivity. Therefore, optical waveguide devices based on polymer materials can be modulated through the thermo-optic effect, and the power consumption required is low. The mode optical switch prepared using these properties has the advantages of flexible structure and low power consumption.

[0006] However, most traditional mode optical switches can only achieve selectable modulation of one mode or simultaneous modulation of all modes, and cannot flexibly select the modulation mode of the device, thereby restricting the application range of mode optical switches. Summary of the Invention

[0007] In order to overcome the deficiencies of traditional mode optical switches, the purpose of the present invention is to provide a four-mode waveguide optical switch with selectable modulation and its preparation method.

[0008] The present invention cascades a traditional asymmetric Y-branch optical waveguide structure and a Multimode interference (MMI) optical waveguide structure. In the structural design of planar optical waveguide devices, both the asymmetric Y-branch optical waveguide structure and the MMI optical waveguide structure are the most basic device structures and the most easily implemented waveguide solutions, and have important application values in the field of optical communication and the field of planar optical waveguide mode optical switches. It is mainly composed of input / output straight waveguides, an asymmetric Y-branch structure, and an MMI structure. Its modulation principle is to couple different optical modes into different branches through the asymmetric Y-branch structure and convert them into the E 11 mode or the E 12 mode, and then through the design of the MMI structure, enable it to realize the switching function for the E 11 mode and the E 12 mode, so as to achieve a modulation function that is insensitive to all optical modes.

[0009] The present invention uses a silicon wafer as a substrate, and polymers with different refractive indices are used as the optical waveguide cladding layer and core layer materials respectively. The refractive index of the polymer material used to make the optical waveguide core layer is greater than that of the cladding material and has a thermo-optic effect. The present invention makes full use of the advantages of polymer materials such as large thermo-optic coefficient, variety, and strong processability. The preparation process of the present invention is simple and compatible with semiconductor processes, and can realize large-scale integration and production, so it has important practical application value.

[0010] The technical solutions adopted by the present invention to solve its technical problems are as follows:

[0011] As shown in the Figure 1 accompanying Figure 2 drawing (which is a sectional view taken along the A-A' position in

[0012] the Figure 2 drawing), a selectable mode modulation four-mode waveguide optical switch according to the present invention is composed of, from bottom to top, a silicon substrate 31, a polymer lower cladding 32 prepared on the silicon substrate 31 by spin coating, a polymer optical waveguide core layer 33 with a strip structure prepared on the polymer lower cladding 32 by spin coating, photolithography, and wet etching, and a polymer upper cladding 34 prepared on the polymer lower cladding 32 and the polymer optical waveguide core layer 33 by spin coating. 11 21 12 22 As shown in the

[0013] drawing, the polymer optical waveguide core layer 33 is formed by cascading an asymmetric Y-branch structure and an MMI optical waveguide structure. Along the light propagation direction from left to right, it successively consists of an input few-mode straight waveguide 1 (capable of transmitting E 11 21 12 22 mode), a first input bending waveguide 2, a second input bending waveguide 3, a first input tapered waveguide 4, a second input tapered waveguide 5, a first bending waveguide 6, a second bending waveguide 7, a first tapered waveguide 8, a second tapered waveguide 9, a first multimode waveguide 10, a second multimode waveguide 11, a third tapered waveguide 12, a fourth tapered waveguide 13, a third bending waveguide 14, a fourth bending waveguide 15, a first output tapered waveguide 16, a second output tapered waveguide 17, a first output bending waveguide 18, a second output bending waveguide 19, and an output few-mode straight waveguide 20; on the polymer upper cladding 34 above the first multimode waveguide 10 and the second multimode waveguide 11, a first heating electrode 21, a second heating electrode 22, and a third heating electrode 23 (the electrode material is Al, Au, or Cr) are prepared. The first heating electrode 21, the second heating electrode 22, and the third heating electrode 23 are collectively referred to as the heating electrode 35; the first heating electrode (21) is prepared at a position between the first multimode waveguide (10) and the second multimode waveguide (11), the second heating electrode (22) is prepared at an outer position of the first multimode waveguide (10), and the third heating electrode (23) is prepared at an outer position of the second multimode waveguide (11).The input few-mode straight waveguide 1, the first input bent waveguide 2, and the second input bent waveguide 3 together form an input asymmetric Y-branch structure; the first output bent waveguide 18, the second output bent waveguide 19, and the output few-mode straight waveguide 20 together form an output asymmetric Y-branch structure; the first tapered waveguide 8, the first multimode waveguide 10, and the third tapered waveguide 12 together form a first MMI optical waveguide structure; the second tapered waveguide 9, the second multimode waveguide 11, and the fourth tapered waveguide 13 together form a second MMI optical waveguide structure; the first input tapered waveguide 4 and the first bent waveguide 6 are used to connect the input asymmetric Y-branch structure and the first MMI optical waveguide structure, the second input tapered waveguide 5 and the second bent waveguide 7 are used to connect the input asymmetric Y-branch structure and the second MMI optical waveguide structure, the third bent waveguide 14 and the first output tapered waveguide 16 are used to connect the first MMI optical waveguide structure and the output asymmetric Y-branch structure, and the fourth bent waveguide 15 and the second output tapered waveguide 17 are used to connect the second MMI optical waveguide structure and the output asymmetric Y-branch structure.

[0014] The input few-mode straight waveguide 1 and the output few-mode straight waveguide 20 have the same shape and their lengths are equal to L 1 , which is 200 to 2000 μm; the lengths of the first input bent waveguide 2, the second input bent waveguide 3, the first output bent waveguide 18, and the second output bent waveguide 19 are equal to L 2 , which is 500 to 3000 μm; the lengths of the first input tapered waveguide 4, the second input tapered waveguide 5, the first output tapered waveguide 16, and the second output tapered waveguide 17 are equal to L 3 , which is 50 to 300 μm; the first bent waveguide 6, the second bent waveguide 7, the third bent waveguide 14, and the fourth bent waveguide 15 have the same shape and their lengths are equal to L 4 , which is 500 to 2000 μm; the first tapered waveguide 8, the second tapered waveguide 9, the third tapered waveguide 12, and the fourth tapered waveguide 13 have the same shape and their lengths are equal to L 5 , which is 200 to 800 μm; the first multimode waveguide 10 and the second multimode waveguide 11 have the same shape and their lengths are equal to L 6 , which is 400 to 2000 μm; the first heating electrode 21, the second heating electrode 22, and the third heating electrode 23 have the same shape and their lengths are equal to L 7 , which is 400 to 2000 μm.

[0015] The input few-mode straight waveguide 1 and the output few-mode straight waveguide 20 have equal widths of W 1 , which is 6 to 21 μm; the first input bent waveguide 2 and the first output bent waveguide 18 have equal widths of W 2, ranging from 4 to 14 μm; the starting width of the first input tapered waveguide 4 is equal to the ending width of the first output tapered waveguide 16, both being W 2 , ranging from 4 to 14 μm; the widths of the second input curved waveguide 3 and the second output curved waveguide 19 are equal, both being W 1 -W 2 , ranging from 2 to 7 μm; the ending widths of the second input tapered waveguide 5 and the second output tapered waveguide 17 are equal, both being W 1 -W 2 , ranging from 2 to 7 μm; the widths of the first curved waveguide 6, the second curved waveguide 7, the third curved waveguide 14, and the fourth curved waveguide 15 are equal, both being W 3 , ranging from 3 to 12 μm; the ending width of the first input tapered waveguide 4, the starting width of the first tapered waveguide 8, the ending width of the second input tapered waveguide 5, the starting width of the second tapered waveguide 9, the starting width of the first output tapered waveguide 16, the ending width of the third tapered waveguide 12, the starting width of the second output tapered waveguide 17, and the ending width of the fourth tapered waveguide 13 are equal, both being W 3 , ranging from 3 to 12 μm; the ending widths of the first tapered waveguide 8, the second tapered waveguide 9, the starting width of the third tapered waveguide 12, and the starting width of the fourth tapered waveguide 13 are equal, both being W 4 , ranging from 4 to 20 μm; the widths of the first multimode waveguide 10 and the second multimode waveguide 11 are equal, both being W 5 , ranging from 15 to 50 μm; the widths of the first heating electrode 21, the second heating electrode 22, and the third heating electrode 23 are equal, both being W 6 , ranging from 5 to 20 μm; the distances between the first heating electrode 21 and the first multimode waveguide 10, the first heating electrode 21 and the second multimode waveguide 11, the second heating electrode 22 and the first multimode waveguide 10, and the third heating electrode 23 and the second multimode waveguide 11 are equal, both being W 7 , ranging from 1 to 10 μm; the first multimode waveguide 10, the second multimode waveguide 11, the first heating electrode 21, the second heating electrode 22, and the third heating electrode 23 are parallel to each other.

[0016] Light is input from the input single-mode straight waveguide 1. After passing through the input asymmetric Y-branch structure, different optical modes enter different branches: when the input is the E 11 mode, the signal light is coupled into the first input curved waveguide 2 through the input asymmetric Y-branch structure, and the coupled mode is the E 11 mode; when the input is the E 21 mode, the signal light is coupled into the second input curved waveguide 3 through the input asymmetric Y-branch structure, and the coupled mode is the E 11 mode; when the input is the E 12In the [specific mode], the signal light is coupled into the first input curved waveguide 2 through the input asymmetric Y-branch structure, and the coupled mode is E 12 mode; when the input is E 22 mode, the signal light is coupled into the second input curved waveguide 3 through the input asymmetric Y-branch structure, and the coupled mode is E 12 mode; the signal light coupled into the first input curved waveguide 2 is input into the first MMI optical waveguide structure through the first input tapered waveguide 4 and the first curved waveguide 6. By designing the length of the first MMI optical waveguide, the output end of the first MMI optical waveguide is the self-image position of E 11 mode and E 12 mode. Therefore, when there is no modulation, the signal light is output from the first MMI optical waveguide structure, and the mode of the output signal light is the same as that of the signal light input into the first MMI optical waveguide structure. Then it is output through the third curved waveguide 14 and the first output tapered waveguide 16, enters the output asymmetric Y-branch structure, and is then coupled into the output few-mode straight waveguide 20 through the first output curved waveguide 18. The mode of the signal light coupled into the output few-mode straight waveguide 20 is the same as the mode of the signal light input into the input few-mode straight waveguide 1; when modulating the first heating electrode 21 (the second heating electrode 22 and the third heating electrode 23 are used for mode selection modulation. The second heating electrode 22 is located outside the first MMI optical waveguide structure and is far from the second MMI optical waveguide structure. Therefore, when heating the second heating electrode 22, only the first MMI optical waveguide structure is modulated, and the second MMI optical waveguide structure is not affected because it is far away; the third heating electrode 23 is located outside the second MMI optical waveguide structure and is far from the first MMI optical waveguide structure. Therefore, when heating the third heating electrode 23, only the second MMI optical waveguide structure is modulated, and the first MMI optical waveguide structure is not affected because it is far away; the functions of the three heating electrodes are different. When modulating four modes simultaneously, select to heat the first heating electrode 21. When only modulating E 11 and E 12 mode without modulating E 21 and E 22 mode, heat the second heating electrode 22. When only modulating E 21 and E 22 mode without modulating E 11 and E 12 mode, heat the third heating electrode 23), the effective refractive index of the MMI waveguide changes, and the multimode interference effect inside the waveguide also changes. The output end of the first MMI optical waveguide structure is no longer the self-image position of E 11 mode and E 12 mode, but a mixed light of multiple modes. Since the output end of the first MMI optical waveguide only supports E 11 mode and E 12mode, so almost no signal light is output from the first MMI optical waveguide structure, and at this time almost no signal light is output from the output few-mode straight waveguide 20; the signal light coupled into the second input curved waveguide 3 is input into the second MMI optical waveguide structure through the second input tapered waveguide 5 and the second curved waveguide 7. By designing the length of the second MMI optical waveguide, the output end of the MMI optical waveguide structure is the self-imaging position of the E 11 mode and E 12 mode. Therefore, when there is no modulation, the signal light is output from the second MMI optical waveguide structure, and the mode of the output signal light is the same as that of the signal light input into the second MMI optical waveguide structure. Then it is output through the fourth curved waveguide 15 and the second output tapered waveguide 17, enters the output asymmetric Y-branch structure, and is then coupled into the output few-mode straight waveguide 20 through the second output curved waveguide 19. The mode of the signal light coupled into the output few-mode straight waveguide 20 is the same as the mode of the signal light input into the input few-mode straight waveguide 1; when modulating the first heating electrode 21, the effective refractive index of the second MMI optical waveguide structure changes, and the multimode interference effect inside the waveguide also changes. The output end of the second MMI optical waveguide structure is no longer the self-imaging position of the E 11 mode and E 12 mode, but a mixed light of multiple modes. Since the output end of the second MMI optical waveguide only supports the E 11 mode and E 12 mode, so almost no signal light is output from the second MMI optical waveguide structure, and at this time almost no signal light is output from the output few-mode straight waveguide 20.

[0017] The thickness of the silicon wafer substrate 31 is 0.5 - 3 mm, the thickness of the polymer undercladding 32 is 3 - 15 μm, the thickness of the polymer optical waveguide core layer 33 is 3 - 15 μm, the thickness of the polymer overcladding 34 (the thickness of the polymer overcladding above the polymer optical waveguide core layer) is 3 - 17 μm, and the thickness of the heating electrode 35 is 50 - 400 nm.

[0018] The preparation method of a mode-selectable modulation four-mode waveguide optical switch according to the present invention is shown in the appendix Figure 3 , and is specifically described as follows:

[0019] A: Cleaning treatment of the silicon wafer substrate

[0020] Gently wipe the silicon wafer substrate with cotton balls dipped in acetone and ethanol respectively, rinse with deionized water and dry with nitrogen, then put it into a clean petri dish and seal it for storage;

[0021] B: Preparation of the polymer undercladding

[0022] The polymer undercladding material (a series of organic polymer materials with good transparency including polycarbonate (PC), polyimide (PI), polystyrene (PS), polyethylene (PE), polyester (PET), EpoClad, etc.) is spin-coated on the cleaned silicon wafer substrate by a spin-coating process to form a polymer undercladding film at a rotational speed of 1000 - 5000 revolutions per minute; then the spin-coated polymer undercladding film is heated at 90 °C - 140 °C for 5 - 20 minutes, and then exposed as a whole under ultraviolet light with a wavelength of 350 - 400 nm for 3 - 30 seconds, and after exposure, it is heated again at 90 °C - 140 °C for 20 - 60 minutes, thereby obtaining a polymer undercladding 32 with a thickness of 3 - 15 μm on the silicon wafer substrate;

[0023] C: Preparation of the polymer optical waveguide core layer

[0024] The polymer optical waveguide core layer material with a negative thermo-optic coefficient (the optical waveguide core layer material is a series of wet-etchable ultraviolet negative photoresist materials including EpoCore, SU-8 2002, SU-8 2005, and the refractive index of the polymer optical waveguide core layer material is higher than that of the polymer cladding material) is spin-coated on the polymer undercladding 32 by a spin-coating process to form a polymer core layer film at a rotational speed of 700 - 5000 revolutions per minute, and the thickness of the polymer core layer film is 3 - 15 μm; the spin-coated polymer core layer film is pre-baked by a stepwise temperature increase method, that is, heated at 50 °C - 100 °C for 3 - 20 minutes, and then heated at 80 °C - 120 °C for 3 - 20 minutes, and after heating, the temperature is lowered to 50 °C - 80 °C; then the polymer core layer film is lithographed, that is, a mask plate complementary to the polymer core layer structure to be prepared (such as Figure 2 as shown) is used to expose under ultraviolet light with a wavelength of 350 - 400 nm for 5 - 30 seconds, so that the material of the polymer core layer structure to be prepared is exposed to ultraviolet light; after lithography, it is heated at 50 °C - 100 °C for 3 - 20 minutes, and then heated at 80 °C - 120 °C for 5 - 30 minutes for medium baking, and after heating, the temperature is lowered to 20 °C - 30 °C; after the temperature is lowered, development is carried out, that is, first wet-etched in the developer corresponding to the optical waveguide core layer material for 5 - 60 seconds to remove the non-optical waveguide core layer structure that is not exposed, then put into isopropyl alcohol to wash away the unexposed optical waveguide core layer material and developer remaining on the device surface, and then rinsed with deionized water (rinsing should be carried out along the waveguide direction to prevent damage to the waveguide) to remove the isopropyl alcohol on the device surface, and dried with nitrogen; finally, post-baking and film hardening are carried out, that is, heated at 120 °C - 160 °C for 30 - 60 minutes, thereby obtaining a strip-shaped polymer optical waveguide core layer 33 on the polymer undercladding 32;

[0025] D: Preparation of the polymer overcladding

[0026] The polymer upper cladding material (a series of organic polymer materials with good transparency including polycarbonate (PC), polyimide (PI), polystyrene (PS), polyethylene (PE), polyester (PET), EpoClad, etc.) is spin-coated on the polymer lower cladding 32 and the polymer optical waveguide core layer 33 by a spin-coating process to form a polymer upper cladding film, and the spin-coating speed is 700 - 5000 revolutions per minute; then the spin-coated polymer upper cladding film is heated, that is, heated at 90 °C - 140 °C for 5 - 20 minutes; then the polymer upper cladding film is integrally exposed, that is, exposed under ultraviolet light with a wavelength of 350 - 400 nm for 3 - 30 seconds; after exposure, it is heated again, that is, heated at 90 - 140 °C for 20 - 60 minutes, thereby obtaining a polymer upper cladding with a thickness of 3 - 17 μm (the thickness of the polymer upper cladding above the polymer optical waveguide core layer).

[0027] E: Preparation of the heating electrode

[0028] A heating electrode film with a thickness of 50 - 400 nm is deposited on the polymer upper cladding 34 by a vacuum evaporation process, and then a positive photoresist BP 212 with a thickness of 1 - 3 µm is spin-coated on the heating electrode film, and the spin-coating speed is 1000 - 3000 revolutions per minute; the device spin-coated with the photoresist BP 212 is heated, that is, heated at a temperature of 70 °C - 100 °C for 10 - 30 minutes, and after heating, it is cooled to 20 °C - 30 °C; then alignment lithography is carried out, and the mask has the same structure as the heating electrode to be prepared (as Figure 2 shown), that is, exposed under ultraviolet light with a wavelength of 350 - 400 nm, and the exposure time is 1 - 5 seconds, so that the photoresist BP 212 film in the area other than the heating electrode is exposed; after exposure, the device is placed in a NaOH solution with a mass concentration of 2 - 5 ‰ for 10 - 60 seconds to remove the exposed photoresist BP 212 film, and then rinsed with deionized water and dried with nitrogen; the device is heated again, that is, heated at 80 °C - 120 °C for 10 - 30 minutes, and after heating, it is cooled to 20 °C - 30 °C; then the heating electrode is developed, that is, the device is placed in a NaOH solution with a mass concentration of 2 - 5 ‰ for 1 - 15 minutes to remove the electrode film part in the area other than the heating electrode, rinsed repeatedly with deionized water and dried with nitrogen, and finally the device is placed in ethanol for 3 - 10 seconds to remove the unexposed photoresist BP 212 on the heating electrode, rinsed with deionized water again, and dried with nitrogen, thereby obtaining the mode-selectable modulation four-mode waveguide optical switch of the present invention.

[0029] Compared with the existing device structures and fabrication technologies, the beneficial effects of the present invention are as follows: The waveguide-type mode-selectable modulation four-mode waveguide optical switch of the present invention utilizes the advantages of the simple asymmetric Y-branch structure and MMI optical waveguide structure and the large thermo-optic coefficient of organic polymer materials, and realizes the switching of four optical modes by heating the MMI structure; by heating different heating electrodes, the switching function can be realized for two of the four modes, or the switching function can be realized for all four modes simultaneously; in addition, the use of polymer materials makes the device fabrication process simpler, only requiring conventional processes such as spin coating, photolithography, and wet etching, effectively reducing the production cost, improving the production efficiency of the device and facilitating large-scale mass production, enabling this mode of optical switch to be applied in practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 : Cross-sectional schematic diagram of the mode-selectable modulation four-mode waveguide optical switch of the present invention;

[0031] Figure 2 : Schematic diagram of the structure of the mode-selectable modulation four-mode waveguide optical switch of the present invention;

[0032] Figure 3 : Process flow chart for fabricating the mode-selectable modulation four-mode waveguide optical switch;

[0033] Figure 4 (a): Optical field transmission simulation diagram of the mode-selectable modulation four-mode waveguide optical switch when inputting E 11 mode at ΔT1 = 0 K;

[0034] Figure 4 (b): Output end optical field distribution simulation diagram of the mode-selectable modulation four-mode waveguide optical switch when inputting E 11 mode at ΔT1 = 0 K;

[0035] Figure 4 (c): Optical field transmission simulation diagram of the mode-selectable modulation four-mode waveguide optical switch when inputting E 11 mode at ΔT1 = 32 K;

[0036] Figure 4 (d): Output end optical field distribution simulation diagram of the mode-selectable modulation four-mode waveguide optical switch when inputting E 11 mode at ΔT1 = 32 K;

[0037] Figure 5 (a): Optical field transmission simulation diagram of the mode-selectable modulation four-mode waveguide optical switch when inputting E 21 mode at ΔT1 = 0 K;

[0038] Figure 5(b): Simulated optical field distribution at the output end of the mode-selectable modulated four-mode waveguide optical switch when inputting mode E at ΔT1 = 0 K 21 Simulated diagram of the optical field distribution

[0039] Figure 5 (c): Simulated optical field transmission of the mode-selectable modulated four-mode waveguide optical switch when inputting mode E at ΔT1 = 32 K 21 Simulated diagram of the optical field transmission

[0040] Figure 5 (d): Simulated optical field distribution at the output end of the mode-selectable modulated four-mode waveguide optical switch when inputting mode E at ΔT1 = 32 K 21 Simulated diagram of the optical field distribution

[0041] Figure 6 (a): Simulated optical field transmission of the mode-selectable modulated four-mode waveguide optical switch when inputting mode E at ΔT1 = 0 K 12 Simulated diagram of the optical field transmission

[0042] Figure 6 (b): Simulated optical field distribution at the output end of the mode-selectable modulated four-mode waveguide optical switch when inputting mode E at ΔT1 = 0 K 12 Simulated diagram of the optical field distribution

[0043] Figure 6 (c): Simulated optical field transmission of the mode-selectable modulated four-mode waveguide optical switch when inputting mode E at ΔT1 = 32 K 12 Simulated diagram of the optical field transmission

[0044] Figure 6 (d): Simulated optical field distribution at the output end of the mode-selectable modulated four-mode waveguide optical switch when inputting mode E at ΔT1 = 32 K 12 Simulated diagram of the optical field distribution

[0045] Figure 7 (a): Simulated optical field transmission of the mode-selectable modulated four-mode waveguide optical switch when inputting mode E at ΔT1 = 0 K 22 Simulated diagram of the optical field transmission

[0046] Figure 7 (b): Simulated optical field distribution at the output end of the mode-selectable modulated four-mode waveguide optical switch when inputting mode E at ΔT1 = 0 K 22 Simulated diagram of the optical field distribution

[0047] Figure 7 (c): Simulated optical field transmission of the mode-selectable modulated four-mode waveguide optical switch when inputting mode E at ΔT1 = 32 K 22 Simulated diagram of the optical field transmission

[0048] Figure 7 (d): Simulated optical field distribution at the output end of the mode-selectable modulated four-mode waveguide optical switch when inputting mode E at ΔT1 = 32 K22 Simulation diagram of the optical field distribution at the output end of the mode;

[0049] Figure 8 : The four-mode waveguide optical switch with mode-selectable modulation inputs E 11 、E 21 、E 12 and E 22 The curve of the output varying with the heating temperature ΔT1 of the first heating electrode 21 when in the mode;

[0050] Figure 9 : The four-mode waveguide optical switch with mode-selectable modulation inputs E 11 、E 21 、E 12 and E 22 The curve of the output varying with the heating temperature ΔT2 of the second heating electrode 22 when in the mode;

[0051] Figure 10 : The four-mode waveguide optical switch with mode-selectable modulation inputs E 11 、E 21 、E 12 and E 22 The curve of the output varying with the heating temperature ΔT3 of the third heating electrode 23 when in the mode;

[0052] Figure 11 : When ΔT1 = 0 K and ΔT1 = 32 K, the four-mode waveguide optical switch with mode-selectable modulation inputs E 11 、E 21 、E 12 and E 22 The curve of the output of the optical signal varying with the wavelength when in the mode;

[0053] Such as Figure 1 shown, it is Figure 2 The cross-sectional schematic diagram at the A-A' position in, and the names of each component are: silicon wafer substrate 31, polymer lower cladding 32, polymer optical waveguide core layer 33, polymer upper cladding 34, heating electrode 35.

[0054] Such as Figure 2As shown in the figure, it is a schematic plan view of a mode-selectable modulated four-mode waveguide optical switch. The names of each component are: input few-mode straight waveguide 1, first input bent waveguide 2, second input bent waveguide 3, first input tapered waveguide 4, second input tapered waveguide 5, first bent waveguide 6, second bent waveguide 7, first tapered waveguide 8, second tapered waveguide 9, first multimode waveguide 10, second multimode waveguide 11, third tapered waveguide 12, fourth tapered waveguide 13, third bent waveguide 14, fourth bent waveguide 15, first output tapered waveguide 16, second output tapered waveguide 17, first output bent waveguide 18, second output bent waveguide 19, output few-mode straight waveguide 20, first heating electrode 21, second heating electrode 22, and third heating electrode 23.

[0055] As Figure 3 shown, in the figure, 31 is a silicon substrate, 32 is a polymer undercladding prepared by a spin-coating process, 33 is a polymer optical waveguide core layer prepared by spin-coating, photolithography, and wet etching processes, 34 is a polymer overcladding prepared by a spin-coating process, and 35 is a heating electrode.

[0056] As Figure 4 shown in (a), the simulated optical field transmission diagram of the input E 11 mode when ΔT1 = 0 K. During the simulation process, we selected the materials and waveguide dimensions used in Example 1. It can be seen that in the case of ΔT1 = 0 K, the switch is in the on state;

[0057] As Figure 4 shown in (b), the simulated output-end optical field distribution diagram of the input E 11 mode when ΔT1 = 0 K. During the simulation process, we selected the materials and waveguide dimensions used in Example 1. It can be seen that in the case of ΔT1 = 0 K, the switch is in the on state and the output is the E 11 mode;

[0058] As Figure 4 shown in (c), the simulated optical field transmission diagram of the input E 11 mode when ΔT1 = 32 K. During the simulation process, we selected the materials and waveguide dimensions used in Example 1. It can be seen that in the case of ΔT1 = 32 K, the switch is in the off state;

[0059] As Figure 4 shown in (d), the simulated output-end optical field distribution diagram of the input E 11 mode when ΔT1 = 32 K. During the simulation process, we selected the materials and waveguide dimensions used in Example 1. It can be seen that in the case of ΔT1 = 32 K, there is almost no signal light output at the output end;

[0060] As Figure 5As shown in (a), when ΔT1 = 0 K, input E 21 Simulation diagram of optical field transmission in the 21 mode. During the simulation, we selected the materials and waveguide dimensions used in Example 1. It can be seen that when ΔT1 = 0 K, the switch is in the on state;

[0061] As Figure 5 shown in (b), when ΔT1 = 0 K, input E 21 Simulation diagram of the optical field distribution at the output end in the 21 mode. During the simulation, we selected the materials and waveguide dimensions used in Example 1. It can be seen that when ΔT1 = 0 K, the switch is in the on state and the output is the 21 mode; 21 mode;

[0062] As Figure 5 shown in (c), when ΔT1 = 32 K, input E 21 Simulation diagram of optical field transmission in the 21 mode. During the simulation, we selected the materials and waveguide dimensions used in Example 1. It can be seen that when ΔT1 = 32 K, the switch is in the off state;

[0063] As Figure 5 shown in (d), when ΔT1 = 32 K, input E 21 Simulation diagram of the optical field distribution at the output end in the 21 mode. During the simulation, we selected the materials and waveguide dimensions used in Example 1. It can be seen that when ΔT1 = 32 K, there is almost no signal light output at the output end;

[0064] As Figure 6 shown in (a), when ΔT1 = 0 K, input E 12 Simulation diagram of optical field transmission in the 12 mode. During the simulation, we selected the materials and waveguide dimensions used in Example 1. It can be seen that when ΔT1 = 0 K, the switch is in the on state;

[0065] As Figure 6 shown in (b), when ΔT1 = 0 K, input E 12 Simulation diagram of the optical field distribution at the output end in the 12 mode. During the simulation, we selected the materials and waveguide dimensions used in Example 1. It can be seen that when ΔT1 = 0 K, the switch is in the on state and the output is the 12 mode; 12 mode;

[0066] As Figure 6 shown in (c), when ΔT1 = 32 K, input E 12 Simulation diagram of optical field transmission in the 12 mode. During the simulation, we selected the materials and waveguide dimensions used in Example 1. It can be seen that when ΔT1 = 32 K, the switch is in the off state;

[0067] As Figure 6As shown in (d), when ΔT1 = 32 K, input E 12 Simulation diagram of the optical field distribution at the output end of the mode. During the simulation, we selected the materials and waveguide dimensions used in Example 1. It can be seen that when ΔT1 = 32 K, there is almost no signal light output at the output end;

[0068] As Figure 7 shown in (a), when ΔT1 = 0 K, input E 22 Simulation diagram of the optical field transmission of the mode. During the simulation, we selected the materials and waveguide dimensions used in Example 1. It can be seen that when ΔT1 = 0 K, the switch is in the on state;

[0069] As Figure 7 shown in (b), when ΔT1 = 0 K, input E 22 Simulation diagram of the optical field distribution at the output end of the mode. During the simulation, we selected the materials and waveguide dimensions used in Example 1. It can be seen that when ΔT1 = 0 K, the switch is in the on state and the output is the E 22 mode;

[0070] As Figure 7 shown in (c), when ΔT1 = 32 K, input E 22 Simulation diagram of the optical field transmission of the mode. During the simulation, we selected the materials and waveguide dimensions used in Example 1. It can be seen that when ΔT1 = 32 K, the switch is in the off state;

[0071] As Figure 7 shown in (d), when ΔT1 = 32 K, input E 22 Simulation diagram of the optical field distribution at the output end of the mode. During the simulation, we selected the materials and waveguide dimensions used in Example 1. It can be seen that when ΔT1 = 32 K, there is almost no signal light output at the output end;

[0072] Figure 8 : The output curves of the four-mode waveguide optical switch with selectable modulation of the mode when inputting E 11 , E 21 , E 12 and E 22 mode change with the heating temperature ΔT1 of the first heating electrode 21. When the first heating electrode 21 is heated, the signal light of the four modes can all realize the switching function;

[0073] Figure 9 : The output curves of the four-mode waveguide optical switch with selectable modulation of the mode when inputting E 11 , E 21 , E 12 and E 22The curve of the output versus the heating temperature ΔT2 of the second heating electrode 22 in the [mode]. When the second heating electrode 22 is heated, only the E 11 mode and the E 12 mode can achieve the switching function, and the E 21 mode and the E 22 mode do not change with the heating of the second heating electrode 22;

[0074] Figure 10 : The four-mode waveguide optical switch with selectable modulation of the [mode] inputs E 11 、E 21 、E 12 and E 22 The curve of the output versus the heating temperature ΔT3 of the third heating electrode 23 in the [mode]. When the third heating electrode 23 is heated, only the E 21 mode and the E 22 mode can achieve the switching function, and the E 11 mode and the E 12 mode do not change with the heating of the third heating electrode 23;

[0075] Figure 11 : The four-mode waveguide optical switch with selectable modulation of the [mode] at ΔT1 = 0 K and ΔT1 = 32 K, the output curves of the optical signals of the inputs E 11 、E 21 、E 12 and E 22 versus wavelength can be seen that the switch is not sensitive to wavelength changes; Detailed implementation manners

[0076] Example 1

[0077] The present invention will be further described below with reference to the accompanying drawings and examples.

[0078] As shown in the attached Figure 1 figure (for Figure 2(Cross-sectional view at position A-A’), from bottom to top, it consists of a silicon wafer substrate 31, a polymer lower cladding 32 prepared by spin coating on the silicon wafer substrate 31, a polymer optical waveguide core layer 33 with a strip structure prepared by spin coating, photolithography, and wet etching on the polymer lower cladding 32, a polymer upper cladding 34 prepared by spin coating on the polymer optical waveguide core layer 33, a first heating electrode 21, a second heating electrode 22, and a third heating electrode 23 prepared by vacuum evaporation, photolithography, and wet etching on the polymer upper cladding 34. The electrode material is Al, and the first heating electrode 21, the second heating electrode 22, and the third heating electrode 23 are collectively referred to as the Al heating electrode 35. The thickness of the silicon wafer substrate 31 is 1 mm, the thickness of the polymer lower cladding 32 is 7 μm, the thickness of the polymer optical waveguide core layer 33 is 9 μm, the thickness of the polymer upper cladding 34 (the thickness above the polymer optical waveguide core layer 33) is 7 μm, and the thickness of the Al heating electrode 35 is 200 nm.

[0079] As Figure 2 shown, the input few-mode straight waveguide 1 and the output few-mode straight waveguide 20 have the same shape and their lengths are equal to L 1 , which is 1000 μm; the lengths of the first input bent waveguide 2, the second input bent waveguide 3, the first output bent waveguide 18, and the second output bent waveguide 19 are equal to L 2 , which is 1600 μm; the lengths of the first input tapered waveguide 4, the second input tapered waveguide 5, the first output tapered waveguide 16, and the second output tapered waveguide 17 are equal to L 3 , which is 120 μm; the first bent waveguide 6, the second bent waveguide 7, the third bent waveguide 14, and the fourth bent waveguide 15 have the same shape and their lengths are equal to L 4 , which is 1000 μm; the first tapered waveguide 8, the second tapered waveguide 9, the third tapered waveguide 12, and the fourth tapered waveguide 13 have the same shape and their lengths are equal to L 5 , which is 450 μm; the first multimode waveguide 10 and the second multimode waveguide 11 have the same shape and their lengths are equal to L 6 , which is 790 μm; the first heating electrode 21, the second heating electrode 22, and the third heating electrode 23 have the same shape and their lengths are equal to L 7 , which is 790 μm.

[0080] The widths of the input few-mode straight waveguide 1 and the output few-mode straight waveguide 20 are equal to W 1 , which is 10 μm; the widths of the first input bent waveguide 2 and the first output bent waveguide 18 are equal to W 2 , which is 20 / 3 μm; the starting width of the first input tapered waveguide 4 and the terminating width of the first output tapered waveguide 16 are equal to W 2, it is 20 / 3 μm; the widths of the second input curved waveguide 3 and the second output curved waveguide 19 are equal, being W 1 -W 2 , it is 10 / 3 μm; the termination widths of the second input tapered waveguide 5 and the second output tapered waveguide 17 are equal, being W 1 -W 2 , it is 10 / 3 μm; the widths of the first curved waveguide 6, the second curved waveguide 7, the third curved waveguide 14, and the fourth curved waveguide 15 are equal, being W 3 , it is 5 μm; the termination width of the first input tapered waveguide 4, the starting width of the first tapered waveguide 8, the termination width of the second input tapered waveguide 5, the starting width of the second tapered waveguide 9, the starting width of the first output tapered waveguide 16, the termination width of the third tapered waveguide 12, the starting width of the second output tapered waveguide 17, and the termination width of the fourth tapered waveguide 13 are equal, being W 3 , it is 5 μm; the termination widths of the first tapered waveguide 8, the second tapered waveguide 9, the starting width of the third tapered waveguide 12, and the starting width of the fourth tapered waveguide 13 are equal, being W 4 , it is 10 μm; the widths of the first multimode waveguide 10 and the second multimode waveguide 11 are equal, being W 5 , it is 25 μm; the widths of the first heating electrode 21, the second heating electrode 22, and the third heating electrode 23 are equal, being W 6 , it is 10 μm; the distances between the first heating electrode 21 and the first multimode waveguide 10, the distances between the first heating electrode 21 and the second multimode waveguide 11, the distances between the second heating electrode 22 and the first multimode waveguide 10, and the distances between the third heating electrode 23 and the second multimode waveguide 11 are equal, being W 7 , it is 2 μm; the first multimode waveguide 10, the second multimode waveguide 11, the first heating electrode 21, the second heating electrode 22, and the third heating electrode 23 are parallel to each other.

[0081] Light is input from the input single-mode straight waveguide 1. After passing through the input asymmetric Y-branch structure, different optical modes enter different branches: when the input is the E 11 mode, the signal light is coupled into the first input curved waveguide 2 through the input asymmetric Y-branch structure, and the coupled mode is the E 11 mode; when the input is the E 21 mode, the signal light is coupled into the second input curved waveguide 3 through the input asymmetric Y-branch structure, and the coupled mode is the E 11 mode; when the input is the E 12 mode, the signal light is coupled into the first input curved waveguide 2 through the input asymmetric Y-branch structure, and the coupled mode is the E 12 mode; when the input is the E 22In the [mode], the signal light is coupled into the second input curved waveguide 3 through the input asymmetric Y-branch structure, and the coupled mode is E 12 mode; the signal light coupled into the first input curved waveguide 2 passes through the first input tapered waveguide 4 and the first curved waveguide 6. By designing the length of the first MMI optical waveguide structure, the output end of the first MMI optical waveguide structure is the self-imaging position of the E 11 mode and E 12 mode. Therefore, when there is no modulation, the signal light is output from the first MMI optical waveguide structure, and the mode of the output signal light is the same as that of the signal light input to the first MMI optical waveguide structure. Then it is output through the third curved waveguide 14 and the first output tapered waveguide 16, enters the output asymmetric Y-branch structure, and is coupled into the output few-mode straight waveguide 20 through the first output curved waveguide 18. The mode coupled into the output few-mode straight waveguide 20 is the same as the mode input to the input few-mode straight waveguide 1; when the first heating electrode 21 is modulated, the effective refractive index of the MMI waveguide changes, and the multimode interference effect inside the waveguide also changes. The output end of the first MMI optical waveguide is no longer the self-imaging position of the E 11 mode and E 12 mode, but a mixed light of multiple modes; since the output end of the first MMI waveguide only supports E 11 mode and E 12 mode, almost no signal light is output from the first MMI optical waveguide structure, and at this time almost no signal light is output from the output few-mode straight waveguide 20; the signal light coupled into the second input curved waveguide 3 passes through the second input tapered waveguide 5 and the second curved waveguide 7. By designing the length of the second MMI optical waveguide structure, the output end of the second MMI optical waveguide structure is the self-imaging position of the E 11 mode and E 12 mode. Therefore, when there is no modulation, the signal light is output from the second MMI optical waveguide structure, and the mode of the output signal light is the same as that of the signal light input to the second MMI optical waveguide structure. Then it is output through the fourth curved waveguide 15 and the second output tapered waveguide 17, enters the output asymmetric Y-branch structure, and is coupled into the output few-mode straight waveguide 20 through the second output curved waveguide 19. The mode coupled into the output few-mode straight waveguide 20 is the same as the mode input to the input few-mode straight waveguide 1; when the first heating electrode 21 is modulated, the effective refractive index of the MMI waveguide changes, and the multimode interference effect inside the waveguide also changes. The output end of the second MMI optical waveguide is no longer the self-imaging position of the E 11 mode and E 12 mode, but a mixed light of multiple modes; since the output end of the second MMI waveguide only supports E 11 mode and E 12In this mode, almost no signal light is output from the second MMI optical waveguide structure, and at this time, almost no signal light is output from the output few-mode straight waveguide 20 either.

[0082] As Figure 4 (a) shows, when the input is the E 11 mode, at ΔT1 = 0 K (ΔT represents the temperature change value of the heating electrode before and after applying voltage to the heating electrode), the signal light of the E 11 mode is input from the input few-mode straight waveguide 1, and after passing through the input asymmetric Y-branch structure, it is coupled into the first input curved waveguide 2. The coupled mode is E 11 mode. It is input into the first MMI optical waveguide structure through the first input tapered waveguide 4 and the first curved waveguide 6. The output mode from the first MMI optical waveguide structure does not change, and then it is output through the third curved waveguide 14 and the first output tapered waveguide 16, enters the output asymmetric Y-branch structure, and is coupled into the output few-mode straight waveguide 20 through the first output curved waveguide 18. The coupled mode is E 11 mode. The switch is in the on state, and the intensity of the output optical signal is the same as that of the input optical signal.

[0083] As Figure 4 (b) shows, when the input is the E 11 mode, at ΔT1 = 0 K, the signal light of the E 11 mode is input from the input few-mode straight waveguide 1, and after passing through the input asymmetric Y-branch structure, it is coupled into the first input curved waveguide 2. The coupled mode is E 11 mode. It is input into the first MMI optical waveguide structure through the first input tapered waveguide 4 and the first curved waveguide 6. The output mode from the first MMI optical waveguide structure does not change, and then it is output through the third curved waveguide 14 and the first output tapered waveguide 16, enters the output asymmetric Y-branch structure, and is coupled into the output few-mode straight waveguide 20 through the first output curved waveguide 18. The coupled mode is E 11 mode. The switch is in the on state, and the mode of the output optical signal is the same as that of the input optical signal.

[0084] As Figure 4 (c) shows, when the input is the E 11 mode, at ΔT1 = 32 K, the signal light of the E 11 mode is input from the input few-mode straight waveguide 1, and after passing through the input asymmetric Y-branch structure, it is coupled into the first input curved waveguide 2. The coupled mode is E 11In the OFF state, the signal light is input into the first MMI optical waveguide structure through the first input tapered waveguide 4 and the first bent waveguide 6. Since a voltage is applied to the first heating electrode 21 to heat-modulate the first MMI optical waveguide structure, no signal light is output from the first MMI optical waveguide structure. Therefore, no signal light is output from the output single-mode straight waveguide 20.

[0085] As Figure 4 shown in (d), when the input is the E 11 mode, at ΔT1 = 32 K, the signal light of the E 11 mode is input from the input single-mode straight waveguide 1, coupled into the first input bent waveguide 2 after passing through the input asymmetric Y-branch structure, and the coupled mode is the E 11 mode. It is input into the first MMI optical waveguide structure through the first input tapered waveguide 4 and the first bent waveguide 6. Since a voltage is applied to the first heating electrode 21 to heat-modulate the first MMI optical waveguide structure, no signal light is output from the first MMI optical waveguide structure. Therefore, no signal light is output from the output single-mode straight waveguide 20. At this time, it is in the OFF state and no optical signal is output.

[0086] As Figure 5 shown in (a), when the input is the E 21 mode, at ΔT1 = 0 K, the signal light of the E 21 mode is input from the input single-mode straight waveguide 1, coupled into the second input bent waveguide 3 after passing through the input asymmetric Y-branch structure, and the coupled mode is the E 11 mode. It is input into the second MMI optical waveguide structure through the second input tapered waveguide 5 and the second bent waveguide 7. The output mode from the second MMI optical waveguide structure remains unchanged, then it is output through the fourth bent waveguide 15 and the second output tapered waveguide 17, enters the output asymmetric Y-branch structure, and is coupled into the output single-mode straight waveguide 20 through the second output bent waveguide 19. The coupled mode is the E 21 mode. The switch is in the ON state, and the intensity of the output optical signal is the same as that of the input optical signal.

[0087] As Figure 5 shown in (b), when the input is the E 21 mode, at ΔT1 = 0 K, the signal light of the E 21 mode is input from the input single-mode straight waveguide 1, coupled into the second input bent waveguide 3 after passing through the input asymmetric Y-branch structure, and the coupled mode is the E 11The mode is input into the second MMI optical waveguide structure via the second input tapered waveguide 5 and the second curved waveguide 7. The mode remains unchanged when output from the second MMI optical waveguide structure, and then is output via the fourth curved waveguide 15 and the second output tapered waveguide 17, enters the output asymmetric Y-branch structure, and is coupled to the output few-mode straight waveguide 20 via the second output curved waveguide 19. The coupled mode is E 21 mode, the switch is in the on state, and the mode of the output optical signal is the same as that of the input optical signal;

[0088] As Figure 5 (c) shows that when the input is E 21 mode, at ΔT1 = 32 K, the signal light of the E 21 mode is input from the input few-mode straight waveguide 1, and after passing through the input asymmetric Y-branch structure, it is coupled into the second input curved waveguide 3. The coupled mode is E 11 mode. It is input into the second MMI optical waveguide structure via the second input tapered waveguide 5 and the second curved waveguide 7. Since a voltage is applied to the first heating electrode 21 to heat-modulate the second MMI optical waveguide structure, no signal light is output from the second MMI optical waveguide structure. Therefore, no signal light is output from the output few-mode straight waveguide 20, and it is in the off state at this time;

[0089] As Figure 5 (d) shows that when the input is E 21 mode, at ΔT1 = 32 K, the signal light of the E 21 mode is input from the input few-mode straight waveguide 1, and after passing through the input asymmetric Y-branch structure, it is coupled into the second input curved waveguide 3. The coupled mode is E 11 mode. It is input into the second MMI optical waveguide structure via the second input tapered waveguide 5 and the second curved waveguide 7. Since a voltage is applied to the first heating electrode 21 to heat-modulate the second MMI optical waveguide structure, no signal light is output from the second MMI optical waveguide structure. Therefore, no signal light is output from the output few-mode straight waveguide 20, and it is in the off state at this time, and no optical signal is output;

[0090] As Figure 6 (a) shows that when the input is E 12 mode, at ΔT1 = 0 K, the signal light of the E 12 mode is input from the input few-mode straight waveguide 1, and after passing through the input asymmetric Y-branch structure, it is coupled into the first input curved waveguide 2. The coupled mode is E 12The mode is input into the first MMI optical waveguide structure through the first input tapered waveguide 4 and the first bent waveguide 6. The mode remains unchanged when output from the first MMI optical waveguide structure, and then is output through the third bent waveguide 14 and the first output tapered waveguide 16, enters the output asymmetric Y-branch structure, and is coupled to the output few-mode straight waveguide 20 through the first output bent waveguide 18. The coupled mode is E 12 mode. The switch is in the on state, and the intensity of the output optical signal is the same as that of the input optical signal;

[0091] As Figure 6 (b) shows that when the input is E 12 mode, at ΔT1 = 0 K, the signal light of the E 12 mode is input from the input few-mode straight waveguide 1, is coupled into the first input bent waveguide 2 after passing through the input asymmetric Y-branch structure, and the coupled mode is E 12 mode. The mode is input into the first MMI optical waveguide structure through the first input tapered waveguide 4 and the first bent waveguide 6. The mode remains unchanged when output from the first MMI optical waveguide structure, and then is output through the third bent waveguide 14 and the first output tapered waveguide 16, enters the output asymmetric Y-branch structure, and is coupled to the output few-mode straight waveguide 20 through the first output bent waveguide 18. The coupled mode is E 12 mode. The switch is in the on state, and the mode of the output optical signal is the same as that of the input optical signal;

[0092] As Figure 6 (c) shows that when the input is E 12 mode, at ΔT1 = 32 K, the signal light of the E 12 mode is input from the input few-mode straight waveguide 1, is coupled into the first input bent waveguide 2 after passing through the input asymmetric Y-branch structure, and the coupled mode is E 12 mode. The mode is input into the first MMI optical waveguide structure through the first input tapered waveguide 4 and the first bent waveguide 6. Since a voltage is applied to the first heating electrode 21 to heat-modulate the first MMI optical waveguide structure, no signal light is output from the first MMI optical waveguide structure, so no signal light is output from the output few-mode straight waveguide 20, and it is in the off state at this time;

[0093] As Figure 6 (d) shows that when the input is E 12 mode, at ΔT1 = 32 K, the signal light of the E 12 mode is input from the input few-mode straight waveguide 1, is coupled into the first input bent waveguide 2 after passing through the input asymmetric Y-branch structure, and the coupled mode is E 12In the off state, the signal light is input into the first MMI optical waveguide structure through the first input tapered waveguide 4 and the first bent waveguide 6. Since a voltage is applied to the first heating electrode 21 to heat-modulate the first MMI optical waveguide structure, no signal light is output from the first MMI optical waveguide structure. Therefore, no signal light is output from the output single-mode straight waveguide 20, and there is no optical signal output at this time.

[0094] As Figure 7 (a) shows, when the input is the E 22 mode, at ΔT1 = 0 K, the signal light of the E 22 mode is input from the input single-mode straight waveguide 1, coupled into the second input bent waveguide 3 after passing through the input asymmetric Y-branch structure, and the coupled mode is E 12 mode. It is input into the second MMI optical waveguide structure through the second input tapered waveguide 5 and the second bent waveguide 7. The mode output from the second MMI optical waveguide structure remains unchanged, and then it is output through the fourth bent waveguide 15 and the second output tapered waveguide 17, enters the output asymmetric Y-branch structure, and is coupled into the output single-mode straight waveguide 20 through the second output bent waveguide 19. The coupled mode is E 22 mode. The switch is in the on state, and the intensity of the output optical signal is the same as that of the input optical signal.

[0095] As Figure 7 (b) shows, when the input is the E 22 mode, at ΔT1 = 0 K, the signal light of the E 22 mode is input from the input single-mode straight waveguide 1, coupled into the second input bent waveguide 3 after passing through the input asymmetric Y-branch structure, and the coupled mode is E 12 mode. It is input into the second MMI optical waveguide structure through the second input tapered waveguide 5 and the second bent waveguide 7. The mode output from the second MMI optical waveguide structure remains unchanged, and then it is output through the fourth bent waveguide 15 and the second output tapered waveguide 17, enters the output asymmetric Y-branch structure, and is coupled into the output single-mode straight waveguide 20 through the second output bent waveguide 19. The coupled mode is E 22 mode. The switch is in the on state, and the mode of the output optical signal is the same as that of the input optical signal.

[0096] As Figure 7 (c) shows, when the input is the E 22 mode, at ΔT1 = 32 K, the signal light of the E 22 mode is input from the input single-mode straight waveguide 1, coupled into the second input bent waveguide 3 after passing through the input asymmetric Y-branch structure, and the coupled mode is E 12In the off state, the signal light is input into the second MMI optical waveguide structure through the second input tapered waveguide 5 and the second curved waveguide 7. Since a voltage is applied to the first heating electrode 21 to heat-modulate the second MMI optical waveguide structure, no signal light is output from the second MMI optical waveguide structure. Therefore, no signal light is output from the output single-mode straight waveguide 20.

[0097] As Figure 7 shown in (d), when the input is the E 22 mode, at ΔT1 = 32 K, the signal light of the E 22 mode is input from the input single-mode straight waveguide 1, coupled into the second input curved waveguide 3 after passing through the input asymmetric Y-branch structure, and the coupled mode is the E 12 mode. It is then input into the second MMI optical waveguide structure through the second input tapered waveguide 5 and the second curved waveguide 7. Since a voltage is applied to the first heating electrode 21 to heat-modulate the second MMI optical waveguide structure, no signal light is output from the second MMI optical waveguide structure. Therefore, no signal light is output from the output single-mode straight waveguide 20, and in this case, it is in the off state with no optical signal output.

[0098] As Figure 8 shown, at ΔT1 = 0 K, the outputs for the input E 11 , E 21 , E 12 and E 22 modes are almost 0 dB; at ΔT1 = 32 K, the outputs for the input E 11 , E 21 , E 12 and E 22 modes are less than -20 dB. It can be seen that when the heating electrode 21 is heated, the signal light of the four modes can all achieve the switching function, and when the heating temperature is 32 K, the extinction ratios of the four modes are all greater than 20 dB.

[0099] As Figure 9 shown, at ΔT2 = 0 K, the outputs for the input E 11 , E 21 , E 12 and E 22 modes are almost 0 dB; at ΔT2 = 32 K, the outputs for the input E 11 mode and E 12 mode are less than -25 dB, while the outputs for the E 21 mode and E 22 mode hardly change with ΔT2. It can be seen that when the heating electrode 22 is heated, the E 11 mode and E 12 mode can achieve the switching function with an extinction ratio greater than 25 dB, while the E 21 mode and E22 The mode does not change;

[0100] As Figure 10 shown, at ΔT3 = 0 K, the outputs for input E 11 , E 21 , E 12 and E 22 modes are almost 0 dB; at ΔT3 = 32 K, the outputs for input E 21 mode and E 22 mode are less than -25 dB, while the outputs for E 11 mode and E 12 mode hardly change with ΔT3. It can be seen that when heating the heating electrode 23, a switching function can be achieved for E 21 mode and E 22 mode, with an extinction ratio greater than 25 dB, while the E 11 mode and E 12 mode do not change;

[0101] The first heating electrode 21 is located between the first MMI optical waveguide structure and the second MMI optical waveguide structure. When heating the first heating electrode 21, the first MMI optical waveguide structure and the second MMI optical waveguide structure can be modulated simultaneously; the second heating electrode 22 is located outside the first MMI optical waveguide structure and is far from the second MMI optical waveguide structure. Therefore, when heating the second heating electrode 22, only the first MMI optical waveguide structure is modulated, and the second MMI optical waveguide structure is not affected as it is far away; the third heating electrode 23 is located outside the second MMI optical waveguide structure and is far from the first MMI optical waveguide structure. Therefore, when heating the third heating electrode 23, only the second MMI optical waveguide structure is modulated, and the first MMI optical waveguide structure is not affected as it is far away; the functions of the three heating electrodes are different. When modulating four modes simultaneously, the first heating electrode 21 is selected for heating. When only modulating E 11 and E 12 modes without modulating E 21 and E 22 modes, the second heating electrode 22 is heated. When only modulating E 21 and E 22 modes without modulating E 11 and E 12 modes, the third heating electrode 23 is heated.

[0102] As Figure 11 shown, when respectively inputting E 11 , E 21 , E 12 and E 22Mode. When ΔT1 = 0 K and ΔT1 = 32 K, the output wavelength-dependent curve is shown. It can be seen that when ΔT1 = 0 K, the output is almost 0 dB and hardly changes with wavelength. When ΔT1 = 32 K, the output is less than -18 dB in the wavelength range of 1520 nm - 1620 nm, and the output is not sensitive to wavelength changes.

[0103] Example 2

[0104] Cleaning treatment of the silicon wafer substrate 31: Gently wipe the silicon wafer substrate with cotton balls dipped in acetone and ethanol respectively, rinse with deionized water and dry with nitrogen, then place it in a clean petri dish and seal it for storage;

[0105] Preparation of the polymer lower cladding 32 by spin coating: Spin coat the polymer lower cladding material EpoClad on the already cleaned silicon wafer substrate by spin coating at a speed of 3500 revolutions per minute; then heat the spin-coated polymer film, heat it at 120 °C for 10 minutes; expose the polymer film as a whole, expose it under ultraviolet light with a wavelength of 365 nm for 15 seconds; heat it again after exposure, heat it at 140 °C for 30 minutes, so that the polymer lower cladding 32 is prepared on the silicon wafer substrate, and the thickness of the prepared polymer lower cladding 32 is 7 μm;

[0106] Preparation of the polymer optical waveguide core layer 33 including the input / output region, asymmetric Y-branch region, MMI waveguide structure region, tapered waveguide region, and curved waveguide region by spin coating, photolithography, and wet etching processes: Spin coat the polymer optical waveguide core layer material EpoCore with a negative thermo-optic coefficient on the device prepared with the polymer lower cladding to form a film at a speed of 1400 revolutions per minute, and the thickness of the polymer film is 9 μm; then pre-bake the spin-coated polymer film, using a stepwise heating method, heat it at 60 °C for 5 minutes, and then heat it at 95 °C for 10 minutes, and cool it to 60 °C after heating; perform photolithography on the polymer core layer film, and the waveguide mask is complementary to the structure of the polymer core layer to be prepared (such as Figure 2As shown, exposure is carried out under ultraviolet light with a wavelength of 365 nm for 18 seconds, so that the optical waveguide core layer materials in the input / output area, asymmetric Y-branch area, MMI waveguide structure area, curved waveguide area, and tapered waveguide area of the device to be fabricated are exposed to ultraviolet light; after photolithography, medium baking is carried out, heating at 60 °C for 5 minutes, and then heating at 85 °C for 10 minutes, and after heating is completed, the temperature is lowered to 25 °C; then development is carried out. First, wet etching is carried out in the developer corresponding to the optical waveguide core layer material for 50 seconds to remove the unexposed non-optical waveguide core layer structure, and then it is placed in isopropyl alcohol to wash away the residual unexposed optical waveguide core layer material and developer on the surface of the device, and then rinsed with deionized water (rinsing should be carried out along the waveguide direction to prevent damage to the waveguide) to remove the isopropyl alcohol on the surface of the device, and then dried with nitrogen; finally, post-baking and film hardening are carried out, heating at 140 °C for 30 minutes, so that a strip-shaped polymer optical waveguide core layer 33 is fabricated on the polymer lower cladding 32;

[0107] The polymer upper cladding 34 is fabricated by spin coating: The polymer upper cladding material EpoClad is spin coated on the device on which the polymer optical waveguide core layer has been fabricated by spin coating, the spin coating speed is 1000 revolutions per minute, and the thickness of the polymer thin film is 7 μm; then the spin-coated polymer thin film is heated, heating at 120 °C for 10 minutes; the polymer thin film is exposed as a whole, exposure is carried out under ultraviolet light with a wavelength of 365 nm for 20 seconds; after exposure, heating is carried out again, heating at 140 °C for 30 minutes, so that the polymer upper cladding 34 is fabricated on the device;

[0108] The Al heating electrode 35 is fabricated by vacuum evaporation, spin coating, photolithography, and wet etching processes: A 200-nm-thick Al heating electrode thin film is deposited on the polymer upper cladding by vacuum evaporation, and then positive photoresist BP 212 is spin coated on the Al heating electrode thin film at a speed of 2500 revolutions per minute, and the thickness of the fabricated BP 212 thin film is 2 µm; the device spin coated with photoresist BP 212 is heated, heating at 87 °C for 20 minutes, and after heating is completed, the temperature is lowered to 25 °C; alignment photolithography is carried out, and the mask plate has the same structure as the heating electrode to be fabricated (such as Figure 2As shown, exposure is carried out under ultraviolet light with a wavelength of 365 nm for 2 seconds, so that the photoresist BP 212 film in the area other than the heating electrode is exposed; the device is placed in a NaOH solution with a mass concentration of 5‰ for 20 seconds to remove the exposed photoresist BP 212, then rinsed with deionized water and dried with nitrogen; the device is heated again, heated at 95 °C for 10 minutes, and cooled to 25 °C after heating; development of the Al heating electrode is carried out, the device is placed in a NaOH solution with a mass concentration of 5‰ for 5 minutes, and the Al heating electrode film in the area other than the heating electrode is partially removed, rinsed repeatedly with deionized water and dried with nitrogen; the device is placed in ethanol for 5 seconds to remove the unexposed photoresist BP 212 on the Al heating electrode, then rinsed with deionized water, and finally dried with nitrogen, thus obtaining the mode-selectable modulation four-mode waveguide optical switch of the present invention.

[0109] In this way, a mode-selectable modulation four-mode waveguide optical switch that meets the requirements is prepared. It should be noted that although this patent document contains descriptions of many details, it should not be construed as a limitation on the scope of any disclosed technology or what may be claimed, but rather as a description of the features of specific embodiments that may be specific to the disclosed technology. The present invention can also have many variations, such as using waveguide materials such as lithium niobate, silicon, and silicon nitride. Those skilled in the art, based on what is clearly disclosed in the present invention or obtained without any objection according to the written description of the document, fall within the scope of protection of this patent.

Claims

1. A four-mode waveguide optical switch with selectable modulation modes, characterized in that: it is composed of a silicon wafer substrate from bottom to top, a polymer lower cladding prepared on the silicon wafer substrate, a strip-shaped polymer optical waveguide core layer prepared on the polymer lower cladding, and a polymer upper cladding prepared on the polymer lower cladding and the polymer optical waveguide core layer; the polymer optical waveguide core layer is formed by cascading an asymmetric Y-branch structure and an MMI optical waveguide structure, and is successively composed of an input few-mode straight waveguide, a first input bending waveguide, a second input bending waveguide, a first input tapered waveguide, a second input tapered waveguide, a first bending waveguide, a second bending waveguide, a first tapered waveguide, a second tapered waveguide, a first multimode waveguide, a second multimode waveguide, a third tapered waveguide, a fourth tapered waveguide, a third bending waveguide, a fourth bending waveguide, a first output tapered waveguide, a second output tapered waveguide, a first output bending waveguide, a second output bending waveguide and an output few-mode straight waveguide along the light propagation direction; on the polymer upper cladding above the first multimode waveguide and the second multimode waveguide, a first heating electrode, a second heating electrode and a third heating electrode are prepared, the first heating electrode is prepared at a position between the first multimode waveguide and the second multimode waveguide, the second heating electrode is prepared at an outer position of the first multimode waveguide, and the third heating electrode is prepared at an outer position of the second multimode waveguide; the input few-mode straight waveguide, the first input bending waveguide and the second input bending waveguide together constitute an input asymmetric Y-branch structure; the first output bending waveguide, the second output bending waveguide and the output few-mode straight waveguide together constitute an output asymmetric Y-branch structure; the first tapered waveguide, the first multimode waveguide and the third tapered waveguide together constitute a first MMI optical waveguide structure; the second tapered waveguide, the second multimode waveguide and the fourth tapered waveguide together constitute a second MMI optical waveguide structure; the first input tapered waveguide and the first bending waveguide are used to connect the input asymmetric Y-branch structure and the first MMI optical waveguide structure, the second input tapered waveguide and the second bending waveguide are used to connect the input asymmetric Y-branch structure and the second MMI optical waveguide structure, the third bending waveguide and the first output tapered waveguide are used to connect the first MMI optical waveguide structure and the output asymmetric Y-branch structure, and the fourth bending waveguide and the second output tapered waveguide are used to connect the second MMI optical waveguide structure and the output asymmetric Y-branch structure; Light is input from the input few-mode straight waveguide. After passing through the input asymmetric Y-branch structure, different optical modes enter different branches; the input few-mode straight waveguide can transmit E 11 , E 21 , E 12 , E 22 modes; the widths of the input few-mode straight waveguide and the output few-mode straight waveguide are equal, which is W 1 , the widths of the first input curved waveguide and the first output curved waveguide are equal, which is W 2 , the widths of the second input curved waveguide and the second output curved waveguide are equal, which is W 1 -W 2 , and W 2 ≠W 1 -W 2 ; by designing the lengths of the first MMI optical waveguide structure and the second MMI optical waveguide structure respectively, the self-imaging positions of the E 11 mode and the E 12 mode are obtained at the output ends of the first MMI optical waveguide structure and the second MMI optical waveguide structure.

2. The four-mode waveguide optical switch with selectable modulation modes according to claim 1, characterized in that: The input few-mode straight waveguide and the output few-mode straight waveguide have the same shape, and their length L 1 is equal, ranging from 200 to 2000 μm; the lengths L of the first input curved waveguide, the second input curved waveguide, the first output curved waveguide, and the second output curved waveguide 2 are equal, ranging from 500 to 3000 μm; the lengths L of the first input tapered waveguide, the second input tapered waveguide, the first output tapered waveguide, and the second output tapered waveguide 3 are equal, ranging from 50 to 300 μm; the first curved waveguide, the second curved waveguide, the third curved waveguide, and the fourth curved waveguide have the same shape, and their length L 4 is equal, ranging from 500 to 2000 μm; the first tapered waveguide, the second tapered waveguide, the third tapered waveguide, and the fourth tapered waveguide have the same shape, and their length L 5 is equal, ranging from 200 to 800 μm; the first multimode waveguide and the second multimode waveguide have the same shape, and their length L 6 is equal, ranging from 400 to 2000 μm; the first heating electrode, the second heating electrode, and the third heating electrode have the same shape, and their length L 7 is equal, ranging from 400 to 2000 μm.

3. The four-mode waveguide optical switch with selectable modulation modes according to claim 1, characterized in that: The width W of the input few-mode straight waveguide and the output few-mode straight waveguide 1 The width W of the first input curved waveguide and the first output curved waveguide is equal to 6~21 μm; 2 The starting width of the first input tapered waveguide and the ending width of the first output tapered waveguide are equal to 4~14 μm; 2 The width W of the second input curved waveguide and the second output curved waveguide is equal to 4~14 μm; 1 -W 2 The termination width W of the second input tapered waveguide and the second output tapered waveguide is equal to 2~7 μm. 1 -W 2 The widths W of the first curved waveguide, the second curved waveguide, the third curved waveguide, and the fourth curved waveguide are equal to 2~7 μm; 3 The terminal width of the first input tapered waveguide, the starting width of the first tapered waveguide, the terminal width of the second input tapered waveguide, the starting width of the second tapered waveguide, the starting width of the first output tapered waveguide, the terminal width of the third tapered waveguide, the starting width of the second output tapered waveguide, and the terminal width W of the fourth tapered waveguide are equal to 3~12 μm; the terminal width of the first input tapered waveguide, the starting width of the first tapered waveguide, the starting width of the second output tapered waveguide, and the terminal width W of the fourth tapered waveguide 3 are equal to 3~12 μm; the end width of the first tapered waveguide, the end width of the second tapered waveguide, the starting width of the third tapered waveguide, and the starting width W of the fourth tapered waveguide 4 The widths W of the first multimode waveguide and the second multimode waveguide are equal to 4~20 μm; 5 The widths W of the first heating electrode, the second heating electrode, and the third heating electrode are equal to 15~50 μm; 6 are equal to 5~20 μm; the spacing between the first heating electrode and the first multimode waveguide, the spacing between the first heating electrode and the second multimode waveguide, the spacing between the second heating electrode and the first multimode waveguide, and the spacing between the third heating electrode and the second multimode waveguide W 7 are equal to 1~10 μm; the first multimode waveguide, the second multimode waveguide, the first heating electrode, the second heating electrode, and the third heating electrode are parallel to each other.

4. The four-mode waveguide optical switch with selectable modulation modes according to claim 1, characterized in that: the thickness of the silicon wafer substrate is 0.5 - 3 mm, the thickness of the polymer lower cladding is 3 - 15 μm, the thickness of the polymer optical waveguide core layer is 3 - 15 μm, the thickness of the polymer upper cladding above the polymer optical waveguide core layer is 3 - 17 μm, and the thicknesses of the first heating electrode, the second heating electrode and the third heating electrode are the same, which is 50 - 400 nm.

5. The four-mode waveguide optical switch with selectable modulation modes according to claim 1, It is characterized in that: The polymer lower cladding material and the polymer upper cladding material are polycarbonate, polyimide, polystyrene, polyethylene, polyester or EpoClad; the polymer optical waveguide core layer material is EpoCore, SU-8 2002 or SU-8 2005, and the refractive index of the polymer optical waveguide core layer material is higher than that of the polymer upper and lower cladding materials; the heating electrode material is Al, Au or Cr.

6. The preparation method of a mode-selectable modulation four-mode waveguide optical switch according to any one of claims 1 to 5, the steps are as follows: A: Cleaning treatment of the silicon wafer substrate Gently wipe the silicon wafer substrate with cotton balls dipped in acetone and ethanol respectively, rinse with deionized water and dry with nitrogen, then put it into a clean petri dish and seal it for storage; B: Preparation of the polymer lower cladding The polymer lower cladding material is spin-coated on the cleaned silicon wafer substrate by spin coating to form a polymer lower cladding film, and the rotation speed is 1000 - 5000 revolutions per minute ； Then the spin-coated polymer lower cladding film is heated at 90 °C - 140 °C for 5 - 20 minutes, and then integrally exposed under ultraviolet light with a wavelength of 350 - 400 nm for 3 - 30 seconds. After exposure, it is heated again at 90 °C - 140 °C for 20 - 60 minutes, so as to obtain a polymer lower cladding on the silicon wafer substrate; C: Preparation of the polymer optical waveguide core layer The polymer optical waveguide core layer material with a negative thermo-optic coefficient is spin-coated on the polymer lower cladding by spin coating to form a polymer core layer film, and the rotation speed is 700 - 5000 revolutions per minute; the spin-coated polymer core layer film is pre-baked by a stepwise heating method, that is, heated at 50 °C - 100 °C for 3 - 20 minutes, and then heated at 80 °C - 120 °C for 3 - 20 minutes. After heating, it is cooled to 50 °C - 80 °C; then the polymer core layer film is lithographed, that is, a mask complementary to the polymer core layer structure to be prepared is used, and it is exposed under ultraviolet light with a wavelength of 350 - 400 nm for 5 - 30 seconds, so that the material of the polymer core layer structure to be prepared is exposed to ultraviolet light; after lithography, it is heated at 50 °C - 100 °C for 3 - 20 minutes, and then heated at 80 °C - 120 °C for 5 - 30 minutes for medium baking. After heating, it is cooled to 20 °C - 30 °C; after cooling, development is carried out, that is, first wet etched in the developer corresponding to the optical waveguide core layer material for 5 - 60 seconds to remove the non-optical waveguide core layer structure that is not exposed, then put into isopropanol to wash away the unexposed optical waveguide core layer material and developer residues on the device surface, then rinsed with deionized water to remove the isopropanol on the device surface, and dried with nitrogen; finally, post-baking and film hardening are carried out, that is, heated at 120 °C - 160 °C for 30 - 60 minutes, so as to obtain a strip-shaped polymer optical waveguide core layer on the polymer lower cladding; D: Preparation of the polymer upper cladding The polymer upper cladding material is spin-coated on the polymer lower cladding and the polymer optical waveguide core layer by spin coating to form a polymer upper cladding film, and the spin coating speed is 700 to 5000 revolutions per minute; then the spin-coated polymer upper cladding film is heated, that is, heated at 90 °C to 140 °C for 5 to 20 minutes; then the polymer upper cladding film is integrally exposed, that is, exposed under ultraviolet light with a wavelength of 350 to 400 nm for 3 to 30 seconds; after exposure, it is heated again, that is, heated at 90 to 140 °C for 20 to 60 minutes, thereby obtaining the polymer upper cladding; E: Preparation of heating electrode The heating electrode film is deposited on the polymer upper cladding by vacuum evaporation process, and then a positive photoresist BP 212 with a thickness of 1 to 3 µm is spin-coated on the heating electrode film, and the rotation speed is 1000 to 3000 revolutions per minute; the device spin-coated with photoresist BP 212 is heated, that is, heated at a temperature of 70 °C to 100 °C for 10 to 30 minutes, and after heating, it is cooled to 20 °C to 30 °C; then alignment lithography is carried out, and the mask plate has the same structure as the heating electrode to be prepared, that is, exposed under ultraviolet light with a wavelength of 350 to 400 nm, and the exposure time is 1 to 5 seconds, so that the photoresist BP 212 film in the area other than the heating electrode is exposed; After exposure, the device is placed in a NaOH solution with a mass concentration of 2 to 5 ‰ for 10 to 60 seconds to remove the exposed photoresist BP212 film, and then rinsed with deionized water and dried with nitrogen; The device is heated again, that is, heated at 80 °C to 120 °C for 10 to 30 minutes, and after heating, it is cooled to 20 °C to 30 °C; then the heating electrode is developed, that is, the device is placed in a NaOH solution with a mass concentration of 2 to 5 ‰ for 1 to 15 minutes to remove part of the electrode film in the area other than the heating electrode, rinsed repeatedly with deionized water and dried with nitrogen, and finally the device is placed in ethanol for 3 to 10 seconds to remove the unexposed photoresist BP 212 on the heating electrode, then rinsed with deionized water and dried with nitrogen, thereby obtaining a mode-selectable modulated four-mode waveguide optical switch.

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