Mode-insensitive 2x2 thermo-optic switch for mode division multiplexing systems

Abstract

A mode insensitive 2x2 thermo-optic switch for mode division multiplexing system belongs to the technical field of planar optical waveguide devices. It is composed of a silicon substrate, a silicon dioxide lower cladding layer, a polymer core layer waveguide and a polymer upper cladding layer. The polymer core layer waveguide is composed of a first input straight waveguide and a second input straight waveguide, a first input S curved waveguide and a second input S curved waveguide, a first coupling arm straight waveguide, a second coupling arm straight waveguide and a third coupling arm straight waveguide, a first output S curved waveguide and a second output curved waveguide, and a first output straight waveguide and a second output straight waveguide. A metal modulation electrode is prepared on the polymer upper cladding layer corresponding to the second coupling arm straight waveguide. The present application realizes the channel switching of LP 01 , LP 11a and LP 11b three modes by adjusting the spacing and coupling length of the coupling arm straight waveguide and whether to apply the modulation electrode, which has important significance in the field of mode division multiplexing applications.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of planar optical waveguide devices, and particularly relates to a mode-insensitive waveguide type 2x2 thermo-optic switch for mode division multiplexing system, which takes silicon as a substrate, takes silicon dioxide as a lower cladding layer of optical waveguide structure, and takes polymer materials with different refractive indexes as a core layer and an upper cladding layer of optical waveguide structure respectively. BACKGROUND

[0002] With the continuous development of the information age, the demand for information capacity of optical communication is rapidly increasing in the sixth generation mobile communication, long-distance network transmission, and super-large network planning technologies. The existing technology of optical communication has gradually reached the limit, and on this basis, it is a very effective way to further improve the capacity of the optical communication system by applying various multiplexing technologies. These multiplexing technologies include time division multiplexing, wavelength division multiplexing, polarization multiplexing, and mode division multiplexing. Among them, the mode division multiplexing technology uses different modes in a single optical fiber to carry different signals, which doubles the efficiency of data transmission. At the same time, the mode division multiplexing technology is not limited to optical fibers, and it has always been one of the research hotspots in the field of photonic integration. Integrated planar optical waveguides are different from optical fibers, and can support multiple mode transmission by adjusting the waveguide size, and the design of the mode division multiplexing system significantly improves the transmission efficiency of the optical fiber transmission system and the chip-level optical interconnection.

[0003] Optical switches are an important part of mode division multiplexing systems and play an important role in the construction, protection, and fault recovery of mode division multiplexing systems. Optical switch devices can realize signal monitoring or signal cross-interconnection functions for optical signals in optical paths or waveguides. Therefore, optical switches with high integration and high performance have always been an important research topic. However, existing optical switches are limited to switching control of the fundamental mode and are sensitive to high-order modes, which cannot simultaneously control the switching of the fundamental mode and high-order modes. In traditional mode division multiplexing systems, in order to realize the switching function, the high-order modes are usually demultiplexed into fundamental modes, and then the routing control of optical signals is performed through a fundamental mode optical switch array. At the output end, a mode multiplexer is used to re-multiplex the fundamental modes into high-order modes, which has a complex structure and increases the system size. Therefore, developing a mode-insensitive multimode optical switch device for mode division multiplexing systems is of great significance for further improving the transmission efficiency of optical networks.

[0004] At present, there are many types of optical switch devices that are widely studied and applied. According to the different modulation principles, the optical switch can be divided into electro-optical switch, thermo-optical switch, acousto-optical switch, magneto-optical switch and the like, wherein the thermo-optical switch is to realize the function of optical switch by using the thermo-optical effect of the material. The refractive index of the solid medium will change under the influence of temperature, and then the phase of the light in the waveguide will change, and the output light intensity will be changed by cooperating with the corresponding waveguide structure. The thermo-optical switch has the advantages of compact structure, low production cost, easy integration and strong scalability, and has great development space in the field of optical integration.

[0005] In addition, in recent years, the optical switch based on polymer material has made certain progress. The polymer material has many advantages, such as large thermo-optical coefficient and low thermal conductivity, so that the device power consumption can be effectively reduced. In addition, the micron-level end face size of the polymer waveguide is convenient for the end face coupling with the optical fiber, and the waveguide-fiber coupling loss can be effectively reduced. The absorption loss of the organic polymer material can be reduced to 0.06 dB / cm and 0.15 dB / cm at 1.31 μm and 1.55 μm respectively by optimizing the synthesis process. Therefore, the polymer material has important application value in the application of integrated optical circuit devices. SUMMARY

[0006] The purpose of the present application is to provide a mode-insensitive 2x2 thermo-optical switch for mode division multiplexing system, which can be used to realize the channel switching of LP 01 , LP 11a , LP 11b three modes.

[0007] The present application adopts silicon as the substrate, silicon dioxide as the lower cladding layer, polymer SU-8 2005 as the polymer core layer waveguide, and polymer PMMA as the upper cladding layer, and fully utilizes the advantages of the organic polymer material, such as adjustable refractive index, low absorption loss and large thermo-optical coefficient. The device preparation process in the present application is simple, compatible with semiconductor process, easy to integrate and suitable for large-scale production.

[0008] The technical scheme adopted by the present application to solve the technical problems is as follows:

[0009] As shown in the accompanying Figure 1 and Figure 2As shown, a mode-insensitive 2x2 thermo-optic switch for a mode division multiplexing system is composed of a silicon substrate 13, a silicon dioxide lower cladding layer 14 prepared on the silicon substrate 13, a polymer core layer waveguide 15 prepared on the silicon dioxide lower cladding layer 14, and a polymer upper cladding layer 16 prepared on the silicon dioxide lower cladding layer 14 and the polymer core layer waveguide 15, the polymer core layer waveguide 15 being buried in the polymer upper cladding layer 16; the polymer core layer waveguide 15 is composed of first and second parallel input straight waveguides 1, 2, first and second input S-bend waveguides 3, 4, first, second and third parallel coupling arm straight waveguides 5, 11, 6, first and second output S-bend waveguides 7, 8, and first and second parallel output straight waveguides 9, 10 in sequence along the light input direction; the first input straight waveguide 1, the first input S-bend waveguide 3, the first coupling arm straight waveguide 5, the first output S-bend waveguide 7 and the first output straight waveguide 9 are connected in sequence, and the second input straight waveguide 2, the second input S-bend waveguide 4, the third coupling arm straight waveguide 6, the second output S-bend waveguide 8 and the second output straight waveguide 10 are connected in sequence; a metal modulation electrode 12 is prepared on the polymer upper cladding layer 16 at a position corresponding to the second coupling arm straight waveguide 11; the refractive index of the polymer core layer waveguide 15 is greater than that of the polymer upper cladding layer 16.

[0010] The structural dimensions of the first input straight waveguide 1, the second input straight waveguide 2, the first output straight waveguide 9 and the second output straight waveguide 10 are the same; the structural dimensions of the first input S-bend waveguide 3, the second input S-bend waveguide 4, the first output S-bend waveguide 7 and the second output S-bend waveguide 8 are the same; the first input S-bend waveguide 3 and the first output S-bend waveguide 7 are symmetrically arranged about the first coupling arm straight waveguide 5, and the second input S-bend waveguide 4 and the second output S-bend waveguide 8 are symmetrically arranged about the third coupling arm straight waveguide 6; the structural dimensions of the first, second and third coupling arm straight waveguides 5, 11, 6 are the same; the length and width of the metal modulation electrode 12 and the second coupling arm straight waveguide 11 are the same; the distance between the first input straight waveguide 1 and the second input straight waveguide 2 is equal to the distance between the first output straight waveguide 9 and the second output straight waveguide 10; the coupling distance between the first coupling arm straight waveguide 5 and the second coupling arm straight waveguide 11 is equal to the coupling distance between the second coupling arm straight waveguide 11 and the third coupling arm straight waveguide 6; the distance between the first input straight waveguide 1 and the second input straight waveguide 2 is greater than the coupling distance between the first coupling arm straight waveguide 5 and the third coupling arm straight waveguide 6.

[0011] Figure 2 (a) is Figure 1A-A' position of the cross section, from bottom to top by the silicon substrate 13, prepared on the silicon substrate 13 of the silica under cladding 14, prepared on the silica under cladding 14 of the two rectangular structure of polymer core layer waveguide 15, prepared on the silica under cladding 14 and polymer core layer waveguide 15 of the polymer upper cladding 16, polymer core layer waveguide 15 buried in the polymer upper cladding 16 (polymer core layer waveguide 15 corresponds to Figure 1 The polymer core layer waveguide structure including the second coupling arm straight waveguide 11); Figure 2 (b) for Figure 1 A-A' position of the cross section, from bottom to top by the silicon substrate 13, prepared on the silicon substrate 13 of the silica under cladding 14, prepared on the silica under cladding 14 of the two rectangular structure of polymer core layer waveguide 15, prepared on the silica under cladding 14 and polymer core layer waveguide 15 of the polymer upper cladding 16, polymer core layer waveguide 15 buried in the polymer upper cladding 16 (polymer core layer waveguide 15 corresponds to Figure 1 The polymer core layer waveguide structure including the second coupling arm straight waveguide 11), the metal modulation electrode 12 is located on the polymer upper cladding 16 directly above the polymer core layer waveguide 15'.

[0012] The working principle of the mode-insensitive waveguide type 2x2 thermo-optic switch is as follows:

[0013] The polymer core layer waveguide can support LP 01 , LP 11a and LP 11b modes by adjusting the waveguide size. When LP 01 / LP 11a / LP 11b mode enters the switch through the first input S-bend waveguide 3, and then is transmitted to the first coupling arm straight waveguide 5. When the metal modulation electrode 12 is not working, because the structure size of the first coupling arm straight waveguide 5 and the second coupling arm straight waveguide 11 is the same, the refractive index of light transmission in the two coupling arm waveguides is the same, the phase matching condition is met, the coupling occurs, the light in the first coupling arm straight waveguide 5 is completely coupled into the second coupling arm straight waveguide 11, and the light continues to transmit in the second coupling arm straight waveguide 11; similarly, the structure size of the second coupling arm straight waveguide 11 and the third coupling arm straight waveguide 6 is the same, the coupling occurs again, the light in the second coupling arm straight waveguide 11 is completely coupled into the third coupling arm straight waveguide 6, and finally LP 01 / LP 11a / LP 11bThe mode is outputted through the second output S-curved waveguide 8 and the second output straight waveguide 10. When the metal modulation electrode 12 works, the refractive index of the second coupling arm straight waveguide 11 changes due to the thermo-optic effect, the refractive index of the first coupling arm straight waveguide 5 and the second coupling arm straight waveguide 11 do not match, the phase matching condition is not met, and the coupling cannot occur, LP 01 / LP 11a / LP 11b The mode continues to be transmitted in the first coupling arm straight waveguide 5 and is finally outputted through the first output S-curved waveguide 7 and the first output straight waveguide 9.

[0014] When LP 01 / LP 11a / LP 11b The working principle is similar when the mode is inputted from the first input straight waveguide 1 of the mode-insensitive waveguide type thermo-optic switch. When the metal modulation electrode 12 does not work, LP 01 / LP 11a / LP 11b The mode is outputted through the first output S-curved waveguide 7 from the first output straight waveguide 9; when the metal modulation electrode 12 works, LP 01 / LP 11a / LP 11b The mode is outputted through the second output S-curved waveguide 8 from the second output straight waveguide 10. The switch can simultaneously switch LP 01 / LP 11a / LP 11b The three modes of output channels, and the three modes of output states are consistent, so as to realize the mode-insensitive switch function.

[0015] Further, taking LP 01 / LP 11a / LP 11b Taking the mode inputted from the first input straight waveguide 1 as an example, the crosstalk, loss and other performances of the mode-insensitive waveguide type 2x2 thermo-optic switch are calculated through the formula IL=-10log 10 (P out / P in ) and CT=-10log 10 (P out / P unexpected )(wherein IL is the insertion loss, CT is the crosstalk, P out is the output power of the expected output port, P in is the input power of the switch, and P unexpected is the power transmitted to the non-expected output port). When LP 01 The mode is inputted from the first input straight waveguide 1, and the metal modulation electrode 12 does not work, LP 01The mode is output from the second output straight waveguide 10, the corresponding insertion loss is 0.032dB, and the crosstalk is 51.377dB, as shown in Figure 6 (a); when the metal modulation electrode 12 works, the LP 01 The mode is output from the first output straight waveguide 9, the corresponding insertion loss is 0.092dB, and the crosstalk is 17.992dB, as shown in Figure 6 (b); when the LP 11a The mode is input from the first input straight waveguide 1, and the metal modulation electrode 12 does not work, the LP 11a The mode is output from the second output straight waveguide 10, the corresponding insertion loss is 0.271dB, and the crosstalk is 21.049dB, as shown in Figure 7 (a); when the metal modulation electrode 12 works, the LP 11a The mode is output from the first output straight waveguide 9, the corresponding insertion loss is 0.208dB, and the crosstalk is 26.892dB, as shown in Figure 7 (b); when the LP 11b The mode is input from the first input straight waveguide 1, and the metal modulation electrode 12 does not work, the LP 11b The mode is output from the second output straight waveguide 10, the corresponding insertion loss is 0.004dB, and the crosstalk is 36.166dB, as shown in Figure 8 (a); when the metal modulation electrode 12 works, the LP 11b The mode is output from the first output straight waveguide 9, the corresponding insertion loss is 0.706dB, and the crosstalk is 17.461dB, as shown in Figure 8 (b).

[0016] Compared with the existing device structure and preparation technology, the beneficial effects of the present application are: the mode-insensitive 2x2 thermo-optic switch structure for a mode division multiplexing system is very simple, the core part is only three adjacent parallel straight waveguide structures, the advantages of a large thermal-optic coefficient of an organic polymer material are fully utilized, the refractive index of the transmission light in the modulation arm is changed by changing the temperature of the modulation arm through the thermo-optic effect, and then whether the coupling between the adjacent coupling arm waveguides occurs is controlled, so that the light transmission path is changed, and the switching function is realized. By adjusting the distance and coupling length of the parallel coupling arm straight waveguide, the output function of the switch being insensitive to three modes is realized, which has important significance in the field of mode division multiplexing application. In addition, the use of polymer material makes the device manufacturing process relatively simple, does not need expensive equipment and process, and has relatively low production cost. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 : the structure diagram of the mode-insensitive 2x2 thermo-optic switch for a mode division multiplexing system according to the present application;

[0018] Figure 2 (a):Figure 1 Cross-sectional view of the device in position A-A';

[0019] Figure 2 (b): Cross-sectional view of the device in position B-B'; Figure 1

[0020] Figure 3 Process flow chart for the fabrication of a mode-insensitive 2x2 thermo-optic switch for a mode division multiplexing system;

[0021] Figure 4 (a): Light field distribution in the input straight waveguide for the LP 01 mode supported in a three-mode waveguide;

[0022] Figure 4 (b): Light field distribution in the input straight waveguide for the LP 11a mode supported in a three-mode waveguide;

[0023] Figure 4 (c): Light field distribution in the input straight waveguide for the LP 11b mode supported in a three-mode waveguide;

[0024] Figure 5 (a): Normalized output power of the LP 01 mode in the two output ports of the mode-insensitive thermo-optic switch as a function of temperature;

[0025] Figure 5 (b): Normalized output power of the LP 11a mode in the two output ports of the mode-insensitive thermo-optic switch as a function of temperature;

[0026] Figure 5 (c): Normalized output power of the LP 11b mode in the two output ports of the mode-insensitive thermo-optic switch as a function of temperature;

[0027] Figure 6 (a): Light field transmission for the LP 01 mode in the off state (T=0 K) of the electrodes;

[0028] Figure 6 (b): Light field transmission for the LP 01 mode in the on state (T=5.2 K) of the electrodes;

[0029] Figure 7 (a): Light field transmission for the LP 11a mode in the off state (T=0 K) of the electrodes;

[0030] Figure 7 ​(b): Electrode in working state (T=5.2K), LP 11a Optical field transmission simulation diagram of mode;

[0031] Figure 8 (a): Electrode in off state (T=0K), LP 11b Optical field transmission simulation diagram of mode;

[0032] Figure 8 (b): Electrode in working state (T=5.2K), LP 11b Optical field transmission simulation diagram of mode;

[0033] Figure 9 : Electrode in off state (T=0K) and working state (T=5.2K), LP 01 Normalized output power of mode transmission as a function of wavelength;

[0034] Figure 10 : Electrode in off state (T=0K) and working state (T=5.2K), LP 11a Normalized output power of mode transmission as a function of wavelength;

[0035] Figure 11 : Electrode in off state (T=0K) and working state (T=5.2K), LP 11b Normalized output power of mode transmission as a function of wavelength;

[0036] As shown in Figure 1 Fig. 1 is a schematic diagram of a mode-insensitive 2x2 thermo-optic switch for a mode division multiplexing system, and the names of the parts are as follows: first input straight waveguide 1 and second input straight waveguide 2, first input S-bent waveguide 3 and second input S-bent waveguide 4, first coupling arm straight waveguide 5, second coupling arm straight waveguide 11 and third coupling arm straight waveguide 6, first output S-bent waveguide 7 and second output S-bent waveguide 8, first output straight waveguide 9 and second output straight waveguide 10, metal modulation electrode 12, silicon substrate 13, and silicon dioxide lower cladding layer 14.

[0037] As shown in Figure 2 Fig. 2 is a schematic diagram of a mode-insensitive 2x2 thermo-optic switch for a mode division multiplexing system, and the names of the parts are as follows: Figure 2 (a) is a schematic diagram of the cross section at position A-A' in Figure 1 Fig. 3, and the names of the parts are as follows: silicon substrate 13, silicon dioxide lower cladding layer 14, polymer core layer waveguide 15 (corresponding to the polymer core layer waveguide structure in Figure 1 Fig. 4, except for the second coupling arm straight waveguide 11), and polymer upper cladding layer 16; (b) is a schematic diagram of the cross section at position B-B' in Figure 1 Fig. 5, and the names of the parts are as follows: silicon substrate 13, silicon dioxide lower cladding layer 14, polymer core layer waveguide 15' (corresponding to the polymer core layer waveguide structure in Figure 1It includes a polymer core waveguide structure containing a second coupling arm straight waveguide 11, a polymer cladding 16, and a metal modulation electrode 12.

[0038] like Figure 3 The diagram shows the fabrication process flow of a mode-insensitive 2×2 thermo-optic switch for a mode-division multiplexing system. Step 31 involves cleaning the silicon substrate. Step 32 involves preparing a silicon dioxide lower cladding layer on the silicon substrate using thermal oxidation. Step 33 involves preparing a polymer core layer film on the silicon dioxide lower cladding layer using spin coating. Step 34 involves preparing a polymer core layer waveguide using photolithography and development. Step 35 involves preparing a polymer upper cladding layer on the silicon dioxide lower cladding layer and the polymer core layer waveguide using spin coating. Step 36 involves preparing a metal film on the polymer upper cladding layer using evaporation. Step 37 involves preparing a photoresist film on the metal film using spin coating. Step 38 involves preparing a metal modulation electrode pattern using photolithography and development. Step 39 involves removing residual photoresist from the metal modulation electrode to obtain the metal modulation electrode.

[0039] like Figure 4 As shown, Figure 4 (a) is the input LP 01 Simulated optical field distribution in a straight waveguide at time input; Figure 4 (b) is the input LP 11a Simulation diagrams of the optical field in the input straight waveguide during mode; Figure 4 (c) is the input LP 11b The simulation diagram shows the optical field distribution in the input straight waveguide during the simulation. During the simulation, the waveguide material and dimensions were the parameters described in Example 1. The simulation results show that the optical field in all three modes is mainly concentrated in the rectangular waveguide, and only the LP waveguide size selected in Example 1 exhibits this characteristic. 01 LP 11a LP 11b This mode ensures the effective transmission of optical signals in the waveguide.

[0040] like Figure 5 The figure shows the normalized output power as a function of electrode temperature for the three transmission modes. Port 1 represents the first output straight waveguide 9, and port 2 represents the second output straight waveguide 10.

[0041] Figure 5 (a) is LP 01 When the mode input is a straight waveguide, the two output ports LP 01The normalized output power of the mode varies with temperature. When the metal modulation electrode 12 is not working, the 1-port output power tends to 0 and the 2-port output power tends to 1; when the metal modulation electrode 12 is working, the modulation temperature T is 5.2 K, the 1-port output light intensity reaches the maximum and tends to 1, and the 2-port output power tends to 0. When the temperature exceeds 5.2 K, the refractive index of the light in the first coupling arm straight waveguide 5 does not match the refractive index of the light in the second coupling arm straight waveguide 11 due to the thermo-optic effect; the higher the temperature, the less the coupling condition is met, resulting in that the light in the first coupling arm straight waveguide 5 cannot be coupled into the second coupling arm straight waveguide 11, thereby realizing the output of light from the 1-port. Considering the realization of the function and the realization of low power consumption, the temperature is selected to be 5.2 K.

[0042] Figure 5 (b) is LP 11a The mode input straight waveguide, the two output ports of LP 11a The normalized output power of the mode varies with temperature. When the metal modulation electrode 12 is not working, the 1-port output power tends to 0 and the 2-port output power tends to 1; when the metal modulation electrode 12 is working, the modulation temperature T is 5.2 K, the 1-port output light intensity reaches the maximum and tends to 1, and the 2-port output power tends to 0; LP 11a The mode characteristics are different from LP 01 The mode and LP 11b The mode, the coupling effect is more likely to occur, and the coupling condition is more difficult to be destroyed, and a very high temperature is required to achieve the effect of LP 01 The mode, and within 10 K temperature, LP 11a The mode is always reciprocally coupled in the first coupling arm straight waveguide 5, the second coupling arm straight waveguide 11 and the third coupling arm straight waveguide 6, and only when the temperature is 5.2 K, the effect is the same as LP 01 The mode and LP 11b The mode effect is consistent, and most of the light is output from the 1-port.

[0043] Figure 5 (c) is LP 11b The mode input straight waveguide, the two output ports of LP 11b The normalized output power of the mode varies with temperature. When the metal modulation electrode 12 is not working, the 1-port output power tends to 0 and the 2-port output power tends to 1; when the metal modulation electrode 12 is working, the modulation temperature T is 5.2 K, the 1-port output light intensity reaches the maximum and tends to 1, and the 2-port output power tends to 0;

[0044] As Figure 6 shown, when the waveguide material and size are the parameters described in Embodiment 1, and the electrode is not working, a mode-insensitive 2x2 thermo-optic switch input LP 01 The light field transmission simulation diagram of the mode.Figure 6 (a) for no external modulation signal, input is LP 01 Mode, the light field is output by port 2 of the switch device; Figure 6 (b) for electrode working (metallic modulation electrode 12 works, T=5.2K) and input is LP 01 Mode, the light field is output by port 1 of the switch device.

[0045] As shown in Figure 7 , for a mode-insensitive 2x2 thermo-optic switch when the waveguide material and size are the parameters described in Embodiment 1, the light field transmission simulation diagram of input LP 11a Mode. Figure 7 (a) for no external modulation signal, input is LP 11a Mode, the light field is output by port 2 of the switch device; Figure 7 (b) for electrode working (metallic modulation electrode 12 works, T=5.2K) and input is LP 11a Mode, the light field is output by port 1 of the switch device.

[0046] As shown in Figure 8 , for a mode-insensitive 2x2 thermo-optic switch when the waveguide material and size are the parameters described in Embodiment 1, the light field transmission simulation diagram of input LP 11b Mode. Figure 8 (a) for no external modulation signal, input is LP 11b Mode, the light field is output by port 2 of the switch device; Figure 8 (b) for electrode working (metallic modulation electrode 12 works, T=5.2K) and input is LP 11b Mode, the light field is output by port 1 of the switch device.

[0047] As shown in Figure 6 , Figure 7 , Figure 8 , it can be seen that input LP 01 , LP 11a , LP 11b Three different modes, when the electrode is not working, the light is output by port 2; when the electrode is working, the light field is output by port 1, which can realize the mode-insensitive switch function.

[0048] As shown in Figure 9 , Figure 10 , Figure 11 , for a mode-insensitive 2x2 thermo-optic switch used in a mode division multiplexing system, the light field transmission simulation diagram of input LP 01 , LP11a LP 11b In mode, the relationship between normalized output power and wavelength.

[0049] Figure 9 For the electrode in the off state and the working state (metal modulation electrode 12 is working, T = 5.2K), LP 01 The curve showing the relationship between the normalized output power of the mode and the wavelength (1.5425μm~1.5625μm). Here, 9 represents the output port of the first output straight waveguide 9 (same as...). Figure 8 The 10 mentioned in the text description represents the output port of the second output straight waveguide 10 (same as port 10). Figure 8 (As described in the text, there are 2 ports). It can be seen that when the electrode is not working, i.e., when the electrode temperature T changes to 0 K, LP... 01 The mode signal light is output from the second output straight waveguide 10 and does not change with wavelength. When the electrode is in operation, i.e., the electrode temperature T changes by 5.2K, LP 01 The mode signal light is output from the first output straight waveguide 9 and does not change with wavelength.

[0050] Figure 10 For the electrode in the off state (T=0K) and the operating state (T=5.2K), LP 11a The curve showing the relationship between the normalized output power of the mode and the wavelength (1.5425μm~1.5625μm). Here, 9 represents the output port of the first output straight waveguide 9 (same as...). Figure 8 The 10 mentioned in the text description represents the output port of the second output straight waveguide 10 (same as port 10). Figure 8 (As described in the text, there are 2 ports). It can be seen that when the electrode is in the off state, i.e., the electrode temperature T changes to 0 K, LP... 11a The mode signal light is output from the second output straight waveguide 10 and is quite sensitive to wavelength changes. When the electrode is in operation, i.e., the electrode temperature T changes to 5.2K, LP 11a The mode signal light is output from the first output straight waveguide 9 and is quite sensitive to wavelength changes.

[0051] Figure 11 For the electrode in the off state (T=0K) and the operating state (T=5.2K), LP 11b The curve showing the relationship between the normalized output power of the mode transmission and the wavelength (1.5425μm~1.5625μm), where 9 represents the output port of the first output straight waveguide 9 (same as...). Figure 8 The 10 mentioned in the text description represents the output port of the second output straight waveguide 10 (same as port 10). Figure 8 The text describes two ports; it can be seen that when the electrode is in the off state, i.e., the electrode temperature T changes to 0K, LP11b The mode is output from the second output straight waveguide 10 and is quite sensitive to wavelength variations. When the electrode is in operation, i.e., the electrode temperature T changes by 5.2K, LP 11b The light in the mode is mainly output from the first output straight waveguide 9 and does not change with wavelength. Detailed Implementation

[0052] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0053] Example 1

[0054] like Figure 1 As shown, the input and output waveguides of the mode-insensitive waveguide-type thermo-optical switch need to support LP. 01 LP 11a and LP 11b Three modes are selected, therefore the width and thickness of the polymer core waveguide are 4μm and 5μm respectively. The length a1 of the first input straight waveguide 1, the second input straight waveguide 2, the first output straight waveguide 9, and the second output straight waveguide 10 is 500μm. The projection lengths a2 and a2' of the first input S-bend waveguide 3, the second input S-bend waveguide 4, the first output S-bend waveguide 7, and the second output S-bend waveguide 8 in the direction parallel to the symmetry line of the first input straight waveguide 1 and the second input straight waveguide 2 are equal and 1000μm, and the projection height h in the direction perpendicular to the symmetry line of the first input straight waveguide 1 and the second input straight waveguide 2 is 15μm. The distance between the first input straight waveguide 1 and the second input straight waveguide 2, and the first output straight waveguide 10 are... The spacings I1 and I1' between waveguide 9 and the second output straight waveguide 10 are equal at 39.1 μm; the lengths a3 of the first coupling arm straight waveguide 5, the second coupling arm straight waveguide 11, and the third coupling arm straight waveguide 6 are 30000 μm; the coupling spacings I2 and I2' between the first coupling arm straight waveguide 5 and the second coupling arm straight waveguide 11, and between the second coupling arm straight waveguide 11 and the third coupling arm straight waveguide 6 are equal at 2.55 μm; the length a4 of the metal modulation electrode 12 fabricated on the polymer cladding corresponding to the position of the second coupling arm straight waveguide 11 is 30000 μm, the width of the metal modulation electrode is 4 μm, and the thickness of the metal modulation electrode is 100 nm; the total length of the device is 34000 μm.

[0055] Example 2

[0056] A mode-insensitive 2×2 thermo-optical switch for a mode division multiplexing system has the following structure: a silicon dioxide lower cladding layer of SO2 with a refractive index of 1.4448; a core layer of polymer material SU-8 with a refractive index of 1.571; and an upper cladding layer of polymer material PMMA with a refractive index of 1.483.

[0057] Example 3: Combination Figure 3The specific preparation process of the present application is as follows:

[0058] Step 31: cleaning the silicon substrate: select a silicon wafer as the base layer, first clean the silicon wafer with acetone organic solvent to remove organic impurities such as oil stains on the surface of the silicon wafer; clean the silicon wafer with anhydrous ethanol solution to remove the residual acetone in the previous step; repeatedly rinse with deionized water to remove the residual ethanol on the surface of the silicon wafer and dry the silicon wafer.

[0059] Step 32: thermal oxidation: a 5μm thick dense silicon dioxide film is grown on the surface of the silicon as the lower cladding layer by chemical reaction of silicon with wet oxygen at high temperature.

[0060] Step 33: spin-coating SU-8 core layer: spin-coat a 5μm thick polymer core layer waveguide material SU-8 2005 on the surface of the silicon dioxide using a spin coater, set the pre-rotation time to 4s (spin coater speed 500rpm) and the post-rotation time to 20s (spin coater speed 2000rpm); during pre-baking, heat to 65℃ for 10min, then heat to 95℃ for 20min, and then naturally cool to room temperature of 25℃.

[0061] Step 34: photoetching and developing: cover the mask plate with a complementary structure to the geometric pattern of the polymer waveguide core layer on the surface of the SU-8 film, and use an ultraviolet photoetching machine to expose the SU-8 to ultraviolet light through the waveguide mask plate, with an exposure time of 4.5s. Since the core layer material SU-8 is a negative photoresist, the area irradiated by ultraviolet light will undergo a photochemical reaction to form a strong acid catalyst, and during post-baking, the molecules in this area will form a stable cross-linked network, thereby forming a waveguide pattern identical to the shape of the mask plate; then remove the mask plate, and use a hot plate instrument to heat the sample to 65℃ for 10min, then heat to 95℃ for 20min, and then cool naturally. Then place the sample in SU-8 developing solution and develop for 5s. At this time, the exposed core layer material will not be eroded and removed by the SU-8 developing solution due to the cross-linking reaction, while the unexposed core layer material is removed; use isopropyl alcohol (liquid) to remove the developing solution remaining on the surface of the sample, and wash with deionized water; place the sample on a hot plate and bake at 120℃ for 30min, and then cool to room temperature;

[0062] Step 35: spin-coating PMMA upper cladding layer: spin-coat 7.5μm (the thickness of the polymer upper cladding layer above the lower cladding layer of silicon dioxide) thick PMMA polymer material as the upper cladding layer of the device on the sample prepared in step

[34] . Set the pre-rotation time to 10s (spin coater speed 300rpm) and the post-rotation time to 30s (spin coater speed 3000rpm). Dry and cure the spin-coated upper cladding layer at 120℃ for 30min.

[0063] Step 36: Evaporating aluminum metal film: A 100 nm thick aluminum film was evaporated on the PMMA by thermal evaporation.

[0064] Step 37: Spin-coating BP212 photoresist: The aluminum film formed in step

[36] was spin-coated with a positive photoresist BP-212 using a spin coater, with a pre-rotation (spin coater rotor speed 500 rpm) for 5 s and a post-rotation (spin coater rotor speed 2500 rpm) for 20 s. The sample was then cured for 20 min at 87°C using a hot plate, and then naturally cooled to room temperature.

[0065] Step 38: Photolithography and development: A photomask plate with the same structure as the geometric pattern of the metal modulated electrode was placed on the surface of the device, and the sample was exposed to light for 2 s using a photolithography machine. The exposed photoresist was then removed by developing the sample in a BP-212 developer solution for 20 s. The sample was then thoroughly rinsed with deionized water and blown dry, and then baked at 87°C for 20 min, and then cooled to room temperature. A 0.5% NaOH solution was used to wet etch the metal modulated electrode, and when a clear and complete aluminum electrode shape appeared, the sample was cleaned with deionized water to remove any residual NaOH solution on the surface.

[0066] Step 39: Removing residual BP212: The surface of the device was cleaned with an ethanol solution to completely remove the BP-212 photoresist attached to the surface of the aluminum electrode. The ethanol solution was then cleaned with deionized water and blown dry, resulting in a mode-insensitive 2x2 thermal optical switch for a mode division multiplexing system.

Claims

1. A mode-insensitive 2x2 thermo-optic switch for use in a mode division multiplexing system, characterized by: From bottom to top, it is composed of a silicon substrate (13), a silicon dioxide undercladding layer (14) prepared on the silicon substrate (13), a polymer core layer waveguide (15) prepared on the silicon dioxide undercladding layer (14), and a polymer overcladding layer (16) prepared on the silicon dioxide undercladding layer (14) and the polymer core layer waveguide (15), and the polymer core layer waveguide (15) is buried in the polymer overcladding layer (16); the polymer core layer waveguide (15) is composed of, in sequence along the light input direction, first and second input straight waveguides (1, 2) parallel to each other, first and second input S-bent waveguides (3, 4), first, second and third coupling arm straight waveguides (5, 11, 6) parallel to each other, first and second output S-bent waveguides (7, 8), and first and second output straight waveguides (9, 10) parallel to each other; the first input straight waveguide (1), the first input S-bent waveguide (3), the first coupling arm straight waveguide (5), the first output S-bent waveguide (7) and the first output straight waveguide (9) are sequentially connected, and the second input straight waveguide (2), the second input S-bent waveguide (4), the third coupling arm straight waveguide (6), the second output S-bent waveguide (8) and the second output straight waveguide (10) are sequentially connected; a metal modulation electrode (12) is prepared on the polymer overcladding layer (16) at a position corresponding to the second coupling arm straight waveguide (11); the first input straight waveguide (1), the second input straight waveguide (2), the first output straight waveguide (9) and the second output straight waveguide (10) have the same structural size; the first input S-bent waveguide (3), the second input S-bent waveguide (4), the first output S-bent waveguide (7) and the second output S-bent waveguide (8) have the same structural size; the first input S-bent waveguide (3) and the first output S-bent waveguide (7) are symmetrically arranged about the first coupling arm straight waveguide (5), and the second input S-bent waveguide (4) and the second output S-bent waveguide (8) are symmetrically arranged about the third coupling arm straight waveguide (6); the first coupling arm straight waveguide (5), the second coupling arm straight waveguide (11) and the third coupling arm straight waveguide (6) have the same structural size; the metal modulation electrode (12) and the second coupling arm straight waveguide (11) have the same length and width; the distance between the first input straight waveguide (1) and the second input straight waveguide (2) is equal to the distance between the first output straight waveguide (9) and the second output straight waveguide (10); the coupling distance between the first coupling arm straight waveguide (5) and the second coupling arm straight waveguide (11) is equal to the coupling distance between the second coupling arm straight waveguide (11) and the third coupling arm straight waveguide (6); the distance between the first input straight waveguide (1) and the second input straight waveguide (2) is greater than the coupling distance between the first coupling arm straight waveguide (5) and the third coupling arm straight waveguide (6); the refractive index of the polymer core layer waveguide (15) is greater than the refractive index of the polymer overcladding layer (16). ​ 2. A mode-insensitive 2x2 thermo-optic switch for use in a mode division multiplexing system as claimed in claim 1, characterized in that: The material of the polymer core waveguide (15) is polymer SU-8, and the material of the polymer upper cladding layer (16) is polymer PMMA.

3. A mode-insensitive 2 x 2 thermo-optic switch for use in a mode division multiplexing system as defined in claim 1, wherein: The length a1 of the first input straight waveguide (1), the second input straight waveguide (2), the first output straight waveguide (9) and the second output straight waveguide (10) is 500 μm; the projection length a2 and a2' of the first input S-curved waveguide (3) and the second input S-curved waveguide (4), the first output S-curved waveguide (7) and the second output S-curved waveguide (8) in the direction parallel to the symmetry line of the first input straight waveguide (1) and the second input straight waveguide (2) are equal to 1000 μm, and the projection height h in the direction perpendicular to the symmetry line of the first input straight waveguide (1) and the second input straight waveguide (2) is 15 μm; the length a3 of the first coupling arm straight waveguide (5), the second coupling arm straight waveguide (11) and the third coupling arm straight waveguide (6) is 30000 μm; The length of the metal modulation electrode (12) is 30000 μm; the spacing I1 and I1' between the first input straight waveguide (1) and the second input straight waveguide (2) and between the first output straight waveguide (9) and the second output straight waveguide (10) are equal to 39.1 μm; the coupling spacing I2 and I2' between the first coupling arm straight waveguide (5) and the second coupling arm straight waveguide (11) and between the second coupling arm straight waveguide (11) and the third coupling arm straight waveguide (6) are equal to 2.55 μm.

4. A mode-insensitive 2×2 thermo-optical switch for a modular multiplexing system as described in claim 1, characterized in that: The thickness of the silicon dioxide lower cladding layer (14) is 5 μm, the thickness of the polymer core waveguide (15) is 5 μm, and the width is 4 μm, the thickness of the polymer upper cladding layer (16) above the silicon dioxide lower cladding layer (14) is 7.5 μm, the thickness of the metal modulation electrode (12) is 100 nm, and the width is 4 μm.

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