Mode-insensitive optical power divider integrated with mode conversion function and preparation method of mode-insensitive optical power divider

Abstract

The invention discloses a mode-insensitive optical power divider integrated with a mode conversion function and a preparation method thereof, and belongs to the technical field of mode converters and optical power dividers. The optical fiber is composed of a silicon wafer substrate, a polymer lower cladding, a polymer optical waveguide core layer and a polymer upper cladding, wherein the polymer optical waveguide core layer is completely wrapped in the polymer upper cladding; the polymer optical waveguide core layer is composed of a first input few-mode straight waveguide, a 3-dB Y-branch beam splitter first branch, a 3-dB Y-branch beam splitter second branch, a first input conical waveguide, a second input conical waveguide, a multi-mode interference waveguide, a first output conical waveguide, a second output conical waveguide, a first output bent waveguide, a second output bent waveguide, a second input conical waveguide, a third input conical waveguide, a fourth input conical waveguide, a fourth input conical waveguide, a fifth input conical waveguide and a sixth input conical waveguide in sequence. A first output few-mode straight waveguide, and a second output few-mode straight waveguide. According to the device, an E11 mode or an E12 mode is input at the input end, and the E11 mode or the E12 mode can be converted into an E21 mode or an E22 mode with the same power at the output end.

Description

Technical Field

[0001] The present invention belongs to the technical field of mode converters and optical power splitters in planar optical waveguide devices, and particularly relates to a mode-insensitive optical power splitter integrating a mode conversion function and a preparation method thereof. Background Art

[0002] With the rapid development of the new generation of communication technologies and the Internet, people's demand for data transmission capacity and data transmission speed is increasing day by day. The emergence and development of optical communication can effectively improve the information transmission speed and expand the communication capacity, and has significant advantages such as fast communication speed, large capacity, and low loss. In an optical communication system, in order to further increase the communication capacity, wavelength division multiplexing (WDM), polarization division multiplexing (PDM), and space division multiplexing (SDM) technologies have been successively proposed. Among them, as an important branch of space division multiplexing technology, mode division multiplexing (MDM) technology can significantly improve the transmission capacity of an optical communication system and is considered a technology with great development and application prospects. The MDM technology can use each mode as an independent transmission channel to carry different information, realizing a multiple increase in the communication transmission capacity and has received extensive attention in recent years.

[0003] In an MDM system, a mode converter is used to achieve the conversion between different modes, which can effectively improve the flexibility and capacity of the MDM system. An optical power splitter is another very important passive device in the MDM system, and its core function is to be able to distribute a single input optical signal to multiple output ports, or vice versa to combine multiple input optical signals into a single output port. This characteristic not only realizes the distribution and synthesis of the optical signal power, but also effectively simplifies the diversity and complexity of information processing and provides a way to monitor the signal. In the current MDM system, the mode converter and the optical power splitter are relatively independent devices and are connected by optical fibers or waveguides to achieve the mode conversion and power distribution functions of the system. This will not only increase the size of the device but also affect the stability of the system. Therefore, there is an urgent need to develop a photonic integration chip that can integrate the mode conversion function and the optical power distribution function.

[0004] Compared with traditional optical fiber technology, the planar optical waveguide structure adopted in the present invention has the advantages of good compatibility with optical fibers, compact structure, small size, low loss, and high integration. The refractive index contrast between the core layer and the cladding of the polymer material used is small, and the device has the characteristic of polarization insensitivity, which increases the stability of the optical communication system. Moreover, the device preparation technology only requires spin coating, photolithography, and wet etching processes, which can significantly reduce the cost of the device and is suitable for large-scale production. Summary of the Invention

[0005] In order to overcome the deficiencies of existing mode converters and optical power splitters, the purpose of the present invention is to provide a mode-insensitive optical power splitter with an integrated mode conversion function based on a symmetric Y-branch and MMI structure and its preparation method.

[0006] The present invention uses a silicon wafer as the substrate, an organic polymer material as the upper cladding and the lower cladding, and an organic polymer material with a refractive index greater than that of the upper and lower claddings as the core layer. The polymer material preparation process adopted in the present invention is simple, easy to couple with optical fibers, easy to integrate, low in price, and can be mass-produced, and has important practical application value.

[0007] The technical solutions adopted by the present invention to solve its technical problems are as follows:

[0008] A mode-insensitive optical power splitter with an integrated mode conversion function, the entire device inputs E 11 or E 12 in two modes at the input end, and based on a symmetric Y-branch, realizes the function of 3dB optical power splitting insensitive to the input mode. An MMI optical waveguide structure can simultaneously realize 3dB power splitting and mode conversion functions insensitive to the optical mode at the two output ports, that is, convert it into two E 21 or E 22 modes with equal power at the output end.

[0009] As Figure 2 shown, a mode-insensitive optical power splitter with an integrated mode conversion function described in the present invention is composed of a silicon wafer substrate 21 from bottom to top, a polymer lower cladding 22 prepared on the silicon wafer substrate 21, a strip-shaped polymer optical waveguide core layer 23 prepared on the polymer lower cladding 22, and a polymer upper cladding 24 prepared on the polymer lower cladding 22 and the polymer optical waveguide core layer 23. The polymer optical waveguide core layer 23 is completely covered by the polymer upper cladding 24; as Figure 1As shown, along the light propagation direction, the polymer optical waveguide core layer 23 is successively composed of a first input few-mode straight waveguide 11, a first branch 12 of a 3-dB Y-branch beam splitter, a second branch 13 of the 3-dB Y-branch beam splitter, a first input tapered waveguide 14, a second input tapered waveguide 15, a multimode interference waveguide 16, a first output tapered waveguide 17, a second output tapered waveguide 18, a first output curved waveguide 19, a second output curved waveguide 110, a first output few-mode straight waveguide 111, and a second output few-mode straight waveguide 112.

[0010] The first input few-mode straight waveguide 11, the first branch 12 of the 3-dB Y-branch beam splitter, and the second branch 13 of the 3-dB Y-branch beam splitter form a 3-dB Y-branch beam splitter; the multimode interference waveguide 16 has two input ends and two output ends. After the first branch 12 of the 3-dB Y-branch beam splitter and the first input tapered waveguide 14 are connected in sequence, they serve as the first input end of the multimode interference waveguide 16. After the second branch 13 of the 3-dB Y-branch beam splitter and the second input tapered waveguide 15 are connected in sequence, they serve as the second input end of the multimode interference waveguide 16. The first output tapered waveguide 17 and the second output tapered waveguide 18 respectively serve as the two output ends of the multimode interference waveguide 16; the first output tapered waveguide 17, the first output curved waveguide 19, and the first output few-mode straight waveguide 111 are connected in sequence, and the second output tapered waveguide 18, the second output curved waveguide 110, and the second output few-mode straight waveguide 112 are connected in sequence.

[0011] The structures and dimensions of the first input few-mode straight waveguide 11, the first output few-mode straight waveguide 111, and the second output few-mode straight waveguide 112 are the same. Their lengths a1, a1’, a1” are equal, ranging from 500 to 5000 μm; their widths w1, w1’, w1” are equal, ranging from 8 to 15 μm. The structures and dimensions of the first branch 12 of the 3-dB Y-branch beam splitter and the second branch 13 of the 3-dB Y-branch beam splitter are the same. The projected lengths a2, a2’ along the extension direction of the first input few-mode straight waveguide 11 are equal, ranging from 500 to 8000 μm. The center distances gap1, gap1’ between the input end and the output end are equal, ranging from 15 to 40 μm. The widths (input end width, middle end width, and output end width) w2, w2’ are equal, ranging from 4 to 7.5 μm. The structures and dimensions of the first input tapered waveguide 14 and the second input tapered waveguide 15 are the same. Their lengths a3, a3’ are equal, ranging from 100 to 4000 μm. The widths w2, w2’ at their connections with the first branch 12 of the 3-dB Y-branch beam splitter and the second branch 13 of the 3-dB Y-branch beam splitter are equal, ranging from 4 to 7.5 μm. The widths w3, w3’ at their connections with the multimode interference waveguide 16 are equal, ranging from 7 to 30 μm. The length a4 of the multimode interference waveguide 16 is from 500 to 10000 μm, and the width w4 is from 40 to 100 μm. The structures and dimensions of the first output tapered waveguide 17 and the second output tapered waveguide 18 are the same. Their lengths a5, a5’ are equal, ranging from 200 to 5000 μm. The widths w5, w5’ at their connections with the multimode interference waveguide 16 are equal, ranging from 19 to 49 μm. The widths w1’, w1” at their connections with the first output curved waveguide 19 and the second output curved waveguide 110 are equal, ranging from 8 to 15 μm. The structures and dimensions of the first output curved waveguide 19 and the second output curved waveguide 110 are the same. The projected lengths a6, a6’ along the extension direction of the first input few-mode straight waveguide 11 are equal, ranging from 500 to 8000 μm. The center distances gap2, gap2’ between the input end and the output end are equal, ranging from 5 to 40 μm. The widths (input end width, middle end width, and output end width) w1’, w1” are equal, ranging from 8 to 15 μm.

[0012] As Figure 2 shown in Figure 1 is the cross-sectional view of the first input few-mode straight waveguide 11 in

[0013] The E in the optical waveguide 11 or E 12The mode is input from the input single-mode straight waveguide 11, and is respectively input into the first input tapered waveguide 14 and the second input tapered waveguide 15 through the first branch 12 of the 3-dB Y-branch beam splitter and the second branch 13 of the 3-dB Y-branch beam splitter. Then, it is transitioned into the multimode interference waveguide 16 through the first input tapered waveguide 14 and the second input tapered waveguide 15. Based on the self-imaging principle of MMI, multiple optical modes are excited and interfere with each other in the multimode interference waveguide 16. Subsequently, it is transitioned and output into the first output curved waveguide 19 and the second output curved waveguide 110 through the first output tapered waveguide 17 and the second output tapered waveguide 18, and finally, two E with equal power are output from the first output single-mode straight waveguide 111 and the second output single-mode straight waveguide 112 21 or E 22 mode.

[0014] A preparation method of a mode-insensitive optical power splitter integrating a mode conversion function according to the present invention is as follows Figure 3 shown, and the steps are as follows:

[0015] A: Cleaning treatment of the silicon wafer substrate

[0016] Use a cotton ball dipped in acetone solution to wipe the silicon wafer substrate 21 repeatedly for 1 to 3 times, and then use another cotton ball dipped in ethanol solution to wipe the silicon wafer substrate 21 that has been wiped with acetone repeatedly for 1 to 3 times. After wiping clean, rinse the silicon wafer substrate 21 with deionized water until it is clean, and finally dry the silicon wafer substrate 21 with nitrogen, and then put it into a clean petri dish and seal it for storage;

[0017] B: Preparation of the polymer waveguide lower cladding

[0018] The polymer waveguide lower cladding selects an organic polymer material with good transparency (including transparent organic polymer materials such as polycarbonate (PC), polyimide (PI), polyethylene (PE), polyester (PET), polymethyl methacrylate (PMMA), polystyrene (PS), EpoClad, etc.). The polymer waveguide lower cladding material is spin-coated on the cleaned silicon wafer substrate 21 through a spin-coating process, and the spin-coating speed is 1000 to 6000 revolutions per minute, and it is baked for 4 to 60 minutes at 90 to 150 °C (if using materials such as EpoClad, it needs to be baked and then integrally exposed to ultraviolet light with a wavelength of 350 to 400 nm for 3 to 50 s, and finally baked for 4 to 60 minutes at 90 to 150 °C), to obtain a polymer lower cladding 22 with a thickness of 4 to 15 μm;

[0019] C: Preparation of the polymer optical waveguide core layer

[0020] The polymer optical waveguide core layer material includes a series of ultraviolet negative photoresist materials that can be wet-etched, such as EpoCore with a negative thermo-optic coefficient, SU-8 2002, and SU-8 2005. The refractive index of the polymer optical waveguide core layer material is higher than that of the polymer upper and lower cladding materials. The polymer optical waveguide core layer material is spin-coated on the polymer lower cladding 22 to form a polymer optical waveguide core layer thin film 23'. The spin-coating speed is 800 - 5500 revolutions per minute, and the thickness of the polymer optical waveguide core layer thin film 23' is 7 - 15 μm. After spin-coating, pre-baking is carried out, that is, by using a stepwise temperature increase method, the device is heated at 50 - 150 °C for 2 - 30 minutes, and then baked at 70 - 135 °C for 3 - 40 minutes. After heating, it is naturally cooled to 20 - 60 °C. Then, photolithography is performed on the polymer optical waveguide core layer thin film 23', that is, by using a mask plate (such as Figure 1 shown) that is complementary to the structure of the polymer optical waveguide core layer 23 to be prepared. The mask plate is closely attached to the surface of the polymer optical waveguide core layer thin film 23', and then exposed to ultraviolet light with a wavelength of 350 - 400 nm for 5 - 40 s, so that the material of the structure of the polymer optical waveguide core layer 23 to be prepared is exposed to ultraviolet light. After photolithography, middle-baking is carried out, that is, heated at 50 - 100 °C for 2 - 30 minutes, and then heated at 75 - 125 °C for 5 - 40 minutes. After heating, it is naturally cooled to room temperature. After cooling, development is carried out, that is, first wet-etched in the corresponding developer of the polymer optical waveguide core layer material for 5 - 80 s to remove the polymer optical waveguide core layer thin film of the non-polymer optical waveguide core layer 23 structure that is not exposed, leaving only the polymer waveguide core layer structure corresponding to the mask plate structure. Then, it is placed in an isopropyl alcohol solution to wash away the unexposed polymer optical waveguide core layer material and the developer remaining on the surface of the device, and then rinsed with deionized water (when rinsing, it is necessary to rinse along the waveguide direction to prevent damage to the waveguide) to remove the isopropyl alcohol solution on the surface of the device, and dried with nitrogen. Finally, post-baking and hardening are carried out, that is, heated at 120 - 160 °C for 20 - 60 minutes, thereby obtaining a strip-shaped polymer optical waveguide core layer 23 on the polymer lower cladding 22;

[0021] D: Preparation of the polymer waveguide upper cladding

[0022] The upper cladding of the polymer waveguide is made of the same organic polymer material with good transparency as the lower cladding of the polymer waveguide. The polymer upper cladding material is spin-coated on the prepared polymer optical waveguide core layer 23 and the polymer lower cladding 22 through a spin-coating process. The spin-coating speed is 1000 - 6000 revolutions per minute, and it is baked for 4 - 60 minutes at 90 - 150 °C (if EpoClad material is used, etc., it needs to be exposed as a whole under ultraviolet light with a wavelength of 350 - 400 nm for 3 - 50 s after spin-coating, and then baked for 4 - 60 minutes at 90 - 150 °C), to obtain a polymer upper cladding 24 with a thickness of 4 - 15 μm (the thickness of the polymer upper cladding above the polymer optical waveguide core layer), thus completing the preparation of the mode-insensitive optical power splitter with the integrated mode conversion function described in the present invention. Compared with the existing device structure and preparation technology, the beneficial effects of the present invention are:

[0023] The mode-insensitive optical power splitter with the integrated mode conversion function described in the present invention combines the advantages of simple process and low cost of organic polymer materials, simple Y-branch structure and uniform output, large process tolerance and small size of the MMI structure, etc., realizes the mode-insensitive function, can simultaneously realize mode conversion and power distribution, breaks the traditional cascading method, the device can be applied to the mode division multiplexing system, the manufacturing process is simple, the cost is low, the efficiency is high, and practical application can be realized for large-scale mass production. Description of the Drawings

[0024] Figure 1 : Schematic structural diagram of a mode-insensitive optical power splitter with the integrated mode conversion function described in the present invention;

[0025] Figure 2 : Figure 1 Cross-sectional schematic diagram of the structure of the first input few-mode straight waveguide 11 in ;

[0026] Figure 3 : Process flow chart for the preparation of a mode-insensitive optical power splitter with the integrated mode conversion function;

[0027] Figure 4 (a): Simulation diagram of the optical field distribution of the E 11 mode in the mode-insensitive optical power splitter with the integrated mode conversion function;

[0028] Figure 4 (b): Simulation diagram of the optical field distribution of the E 21 mode in the mode-insensitive optical power splitter with the integrated mode conversion function;

[0029] Figure 4 (c): Simulation diagram of the optical field distribution of the E 12 mode in the mode-insensitive optical power splitter with the integrated mode conversion function;

[0030] Figure 4 (d): E in the mode-insensitive optical power splitter integrating mode conversion function 22 Simulation diagram of the optical field distribution in the mode

[0031] Figure 5 (a): Optical field transmission simulation diagram of E mode input to the mode-insensitive optical power splitter integrating mode conversion function 11 ;

[0032] Figure 5 (b): Optical field transmission simulation diagram of E mode input to the mode-insensitive optical power splitter integrating mode conversion function 12 ;

[0033] Figure 6 (a): Curve of the output power of E mode versus wavelength at the two output ports of the mode-insensitive optical power splitter integrating mode conversion function 21 ;

[0034] Figure 6 (b): Curve of the output power of E mode versus wavelength at the two output ports of the mode-insensitive optical power splitter integrating mode conversion function 22 ;

[0035] As Figure 1 shown, the schematic plan view of the mode-insensitive optical power splitter integrating mode conversion function, and the names of each component are: the first input single-mode straight waveguide 11, the first branch 12 of the 3-dB Y-branch splitter, the second branch 13 of the 3-dB Y-branch splitter, the first input tapered waveguide 14, the second input tapered waveguide 15, the multimode interference waveguide 16, the first output tapered waveguide 17, the second output tapered waveguide 18, the first output curved waveguide 19, the second output curved waveguide 110, the first output single-mode straight waveguide 111, and the second output single-mode straight waveguide 112.

[0036] As Figure 2 shown, it is Figure 1 the schematic cross-sectional view of the structure of the first input single-mode straight waveguide 11 in the mode-insensitive optical power splitter integrating mode conversion function, and the names of each component are: silicon wafer substrate 21, polymer lower cladding 22, polymer optical waveguide core layer 23, and polymer upper cladding 24.

[0037] As Figure 3 shown, 21 in the figure is the silicon substrate, 22 is the polymer lower cladding prepared by the spin coating process, 23 is the polymer optical waveguide core layer prepared by the spin coating, photolithography, and wet etching processes, and 24 is the polymer upper cladding prepared by the spin coating process.

[0038] AsFigure 4 As shown in (a), the simulated optical field distribution of the E mode in the mode-insensitive optical power splitter integrated with the mode conversion function. During the simulation, we selected the materials and waveguide dimensions used in Example 1. As can be seen from the figure, the optical field is mainly concentrated in the first input few-mode straight waveguide 11, ensuring the effective transmission of the E mode optical signal in the optical waveguide; 11 As shown in (a), the simulated optical field distribution of the E mode in the mode-insensitive optical power splitter integrated with the mode conversion function. During the simulation, we selected the materials and waveguide dimensions used in Example 1. As can be seen from the figure, the optical field is mainly concentrated in the first input few-mode straight waveguide 11, ensuring the effective transmission of the E mode optical signal in the optical waveguide; 11 mode optical signal in the optical waveguide;

[0039] As Figure 4 As shown in (b), the simulated optical field distribution of the E mode in the mode-insensitive optical power splitter integrated with the mode conversion function. During the simulation, we selected the materials and waveguide dimensions used in Example 1. As can be seen from the figure, the optical field is mainly concentrated in the first input few-mode straight waveguide 11, ensuring the effective transmission of the E 21 As shown in (b), the simulated optical field distribution of the E mode in the mode-insensitive optical power splitter integrated with the mode conversion function. During the simulation, we selected the materials and waveguide dimensions used in Example 1. As can be seen from the figure, the optical field is mainly concentrated in the first input few-mode straight waveguide 11, ensuring the effective transmission of the E 21 mode optical signal in the optical waveguide;

[0040] As Figure 4 As shown in (c), the simulated optical field distribution of the E mode in the mode-insensitive optical power splitter integrated with the mode conversion function. During the simulation, we selected the materials and waveguide dimensions used in Example 1. As can be seen from the figure, the optical field is mainly concentrated in the first input few-mode straight waveguide 11, ensuring the effective transmission of the E 12 As shown in (c), the simulated optical field distribution of the E mode in the mode-insensitive optical power splitter integrated with the mode conversion function. During the simulation, we selected the materials and waveguide dimensions used in Example 1. As can be seen from the figure, the optical field is mainly concentrated in the first input few-mode straight waveguide 11, ensuring the effective transmission of the E 12 mode optical signal in the optical waveguide;

[0041] As Figure 4 As shown in (d), the simulated optical field distribution of the E mode in the mode-insensitive optical power splitter integrated with the mode conversion function. During the simulation, we selected the materials and waveguide dimensions used in Example 1. As can be seen from the figure, the optical field is mainly concentrated in the first input few-mode straight waveguide 11, ensuring the effective transmission of the E 22 As shown in (d), the simulated optical field distribution of the E mode in the mode-insensitive optical power splitter integrated with the mode conversion function. During the simulation, we selected the materials and waveguide dimensions used in Example 1. As can be seen from the figure, the optical field is mainly concentrated in the first input few-mode straight waveguide 11, ensuring the effective transmission of the E 22 mode optical signal in the optical waveguide;

[0042] As Figure 5 As shown in (a), the simulated optical field transmission diagram of the E mode output with two equal powers and the simulated optical field distribution diagram at the output port when the mode-insensitive optical power splitter integrated with the mode conversion function inputs the E 11 mode. During the simulation, we selected the materials and waveguide dimensions used in Example 1. As can be seen from the figure, when inputting the E 21 As shown in (a), the simulated optical field transmission diagram of the E mode output with two equal powers and the simulated optical field distribution diagram at the output port when the mode-insensitive optical power splitter integrated with the mode conversion function inputs the E 11 mode, the output is 2 E 21 modes with the same power;

[0043] As Figure 5 As shown in (b), the mode-insensitive optical power splitter integrated with the mode conversion function inputs the E 12The mode output is two Es with equal power 22 The simulation diagram of the optical field transmission of the mode and the simulation diagram of the optical field distribution at the output port. During the simulation, we selected the materials and waveguide dimensions used in Example 1. As can be seen from the figure, when inputting E 12 mode, the output is 2 Es with the same power 22 mode;

[0044] As Figure 6 (a) shows the relationship curve of the output power of E 21 mode at the two output ports of the mode-insensitive optical power splitter integrated with the mode conversion function. It can be seen that in the range of 1400 - 1700 nm, the output power fluctuates less with the change of wavelength, and the device is insensitive to wavelength.

[0045] As Figure 6 (b) shows the relationship curve of the output power of E 22 mode at the two output ports of the mode-insensitive optical power splitter integrated with the mode conversion function. It can be seen that in the range of 1400 - 1700 nm, the output power fluctuates less with the change of wavelength, and the device is insensitive to wavelength. Specific implementation manner

[0046] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0047] Example 1

[0048] As Figure 1As shown in the figure, the structures and dimensions of the first input few-mode straight waveguide 11, the first output few-mode straight waveguide 111, and the second output few-mode straight waveguide 112 are the same. The lengths a1, a1', and a1" are equal, which is 2000 μm; the widths w1, w1', and w1" are equal, which is 11 μm. The structures and dimensions of the first branch 12 of the 3-dB Y-branch splitter and the second branch 13 of the 3-dB Y-branch splitter are the same. The projected lengths a2 and a2' along the extension direction of the first input few-mode straight waveguide 11 are equal, which is 2000 μm, and the center distances gap1 and gap1' between the input end and the output end are equal, which is 17.25 μm. The widths (input end width, middle end width, and output end width) w2 and w2' are equal, which is 5.5 μm. The structures and dimensions of the first input tapered waveguide 14 and the second input tapered waveguide 15 are the same. The lengths a3 and a3' are equal, which is 1114 μm. The widths w2 and w2' at the connection with the first branch 12 of the 3-dB Y-branch splitter and the second branch 13 of the 3-dB Y-branch splitter are equal, which is 5.5 μm, and the widths w3 and w3' at the connection with the multimode interference waveguide 16 are equal, which is 10 μm. The length a4 of the multimode interference waveguide 16 is 1430 μm, and the width w4 is 50 μm. The structures and dimensions of the first output tapered waveguide 17 and the second output tapered waveguide 18 are the same. The lengths a5 and a5' are equal, which is 1611 μm. The widths w5 and w5' at the connection with the multimode interference waveguide 16 are equal, which is 23 μm. The structures and dimensions of the first output curved waveguide 19 and the second output curved waveguide 110 are the same. The projected lengths a6 and a6' along the extension direction of the first input few-mode straight waveguide 11 are equal, which is 2000 μm, and the center distances gap2 and gap2' between the input end and the output end are equal, which is 10 μm. The widths (input end width, middle end width, and output end width) w1' and w1" are equal, which is 11 μm.

[0049] As Figure 2 shown in Figure 1 the cross-sectional view of the first input few-mode straight waveguide 11 in the figure, the thickness of the silicon wafer substrate 21 is 1 mm, the thickness of the polymer waveguide lower cladding 22 is 10 μm, the thickness of the polymer optical waveguide core layer 23 is 10 μm, and the thickness of the polymer waveguide upper cladding above the polymer optical waveguide core layer 23 is 10 μm (the upper cladding thickness above the polymer optical waveguide core layer).

[0050] The preparation method of the mode-insensitive optical power splitter integrating the mode conversion function described in the present invention is shown in the attached Figure 3 , and is specifically described as follows:

[0051] A: Cleaning treatment of the silicon wafer substrate

[0052] Use a cotton ball dipped in acetone solution to wipe the silicon wafer substrate 21 repeatedly for 2 times, and then use another cotton ball dipped in ethanol solution to wipe the silicon wafer substrate 21 that has been wiped with acetone repeatedly for 2 times. After wiping clean, rinse the silicon wafer substrate 21 with deionized water until it is clean. Finally, blow-dry the silicon wafer substrate 21 with nitrogen, and then put it into a clean petri dish and seal it for storage;

[0053] B: Preparation of Polymer Waveguide Lower Cladding

[0054] The polymer waveguide lower cladding selects the organic polymer material EpoClad with good transparency. The polymer waveguide lower cladding material is spin-coated on the cleaned silicon wafer substrate 21 through a spin-coating process. The spin-coating speed is 3000 revolutions per minute, baked at 120 °C for 10 minutes, then exposed as a whole under ultraviolet light with a wavelength of 365 nm for 15 s, and finally baked at 120 °C for 15 minutes to obtain a polymer lower cladding 22 with a thickness of 10 μm;

[0055] C: Preparation of Polymer Optical Waveguide Core Layer

[0056] The polymer optical waveguide core layer material is a negative photoresist material of EpoCore with a negative thermo-optic coefficient. The polymer optical waveguide core layer material is spin-coated on the polymer lower cladding 22 to form a polymer optical waveguide core layer thin film 23. The spin-coating speed is 2500 revolutions per minute, and the thickness of the polymer optical waveguide core layer thin film 23 is 10 μm; After spin-coating, pre-baking is carried out, that is, using a stepwise heating method, the device is heated at 60 °C for 5 minutes, and then baked at 90 °C for 15 minutes. After heating, it is naturally cooled to 25 °C; Then, photolithography is performed on the polymer optical waveguide core layer thin film 23, that is, using a mask plate complementary to the structure of the polymer optical waveguide core layer 23 to be prepared (such as Figure 1As shown in the figure, the mask plate is closely attached to the surface of the polymer optical waveguide core layer thin film 23, and then exposed to ultraviolet light with a wavelength of 365 nm for 15 s, so that the material of the polymer optical waveguide core layer 23 structure to be prepared is exposed to ultraviolet light; after lithography, a medium baking operation is carried out, that is, heating at 55 °C for 5 minutes, and then heating at 85 °C for 20 minutes, and then naturally cooling to room temperature after heating; after the temperature reduction is completed, development is carried out, that is, first wet etching for 30 s in the developer corresponding to the polymer optical waveguide core layer material to remove the polymer optical waveguide core layer thin film of the non-polymer optical waveguide core layer 23 structure that has not been exposed, leaving only the polymer waveguide core layer structure corresponding to the mask plate structure, and then putting it into an isopropyl alcohol solution to wash away the unexposed polymer optical waveguide core layer material and developer remaining on the surface of the device, and then rinsing with deionized water (rinsing along the waveguide direction to prevent damage to the waveguide) to remove the isopropyl alcohol solution on the surface of the device, and drying with nitrogen; finally, post-baking and film hardening are carried out, that is, heating at 130 °C for 30 minutes, so as to obtain a strip-shaped polymer optical waveguide core layer 23 on the polymer lower cladding 22;

[0057] D: Preparation of the polymer waveguide upper cladding

[0058] The polymer waveguide upper cladding selects the organic polymer material EpoClad with good transparency, which is the same as that of the polymer waveguide lower cladding. The polymer upper cladding material EpoClad is spin-coated on the prepared polymer optical waveguide core layer 23 and polymer lower cladding 22 through a spin-coating process. The spin-coating speed is 2500 revolutions per minute, baked at 120 °C for 10 minutes, then exposed to ultraviolet light with a wavelength of 365 nm as a whole for 18 s, and finally baked at 120 °C for 15 minutes to obtain a polymer upper cladding 24 with a thickness of 10 μm (the thickness of the polymer upper cladding above the polymer optical waveguide core layer), thus completing the preparation of the mode-insensitive optical power splitter with the integrated mode conversion function described in the present invention.

[0059] It should be noted that the specific implementation manners proposed in the present invention are only representative examples of the present invention, and should not be construed as limiting the scope of any disclosed technology or the content that may be claimed, but should be construed as a description of the features of specific embodiments that may be specific to the disclosed technology. Obviously, the technical solutions of the present invention include but are not limited to the above embodiments, and there can be more forms, such as using waveguide materials such as lithium niobate, silicon, and silicon nitride. Those skilled in the art, which are clearly disclosed in the present invention or obtained without any objection according to the written description of the document, all fall within the scope protected by this patent.

Claims

1. A mode-insensitive optical power splitter integrated with a mode conversion function, characterized in that: It is composed of a silicon wafer substrate (21) from bottom to top, a polymer lower cladding (22) prepared on the silicon wafer substrate (21), a polymer optical waveguide core layer (23) with a strip structure prepared on the polymer lower cladding (22), and a polymer upper cladding (24) prepared on the polymer lower cladding (22) and the polymer optical waveguide core layer (23). The polymer optical waveguide core layer (23) is completely covered by the polymer upper cladding (24); along the light propagation direction, the polymer optical waveguide core layer (23) is successively composed of a first input few-mode straight waveguide (11), a first branch (12) of a 3-dB Y-branch splitter, a second branch (13) of a 3-dB Y-branch splitter, a first input tapered waveguide (14), a second input tapered waveguide (15), a multimode interference waveguide (16), a first output tapered waveguide (17), a second output tapered waveguide (18), a first output bent waveguide (19), a second output bent waveguide (110), a first output few-mode straight waveguide (111), and a second output few-mode straight waveguide (112); the first input few-mode straight waveguide (11), the first branch (12) of the 3-dB Y-branch splitter, and the second branch (13) of the 3-dB Y-branch splitter form a 3-dB Y-branch splitter; the multimode interference waveguide (16) has two input ends and two output ends. The first branch (12) of the 3-dB Y-branch splitter and the first input tapered waveguide (14) are sequentially connected and used as the first input end of the multimode interference waveguide (16). The second branch (13) of the 3-dB Y-branch splitter and the second input tapered waveguide (15) are sequentially connected and used as the second input end of the multimode interference waveguide (16). The first output tapered waveguide (17) and the second output tapered waveguide 18 are respectively used as the two output ends of the multimode interference waveguide (16); the first output tapered waveguide (17), the first output bent waveguide (19), and the first output few-mode straight waveguide (111) are sequentially connected, and the second output tapered waveguide (18), the second output bent waveguide (110), and the second output few-mode straight waveguide (112) are sequentially connected.

2. The mode-insensitive optical power splitter with an integrated mode conversion function according to claim 1, wherein: The structures and dimensions of the first output few-mode straight waveguide (111) and the second output few-mode straight waveguide (112) are the same. The lengths a1, a1', and a1'' are equal, ranging from 500 to 5000 μm; the widths w1, w1', and w1'' are equal, ranging from 8 to 15 μm. The structures and dimensions of the first branch (12) of the 3-dB Y-branch splitter and the second branch (13) of the 3-dB Y-branch splitter are the same. The projected lengths a2 and a2' along the extension direction of the first input few-mode straight waveguide (11) are equal, ranging from 500 to 8000 μm. The center distances gap1 and gap1' between the input end and the output end are equal, ranging from 15 to 40 μm. The widths w2 and w2' are equal, ranging from 4 to 7.5 μm. The structures and dimensions of the first input tapered waveguide (14) and the second input tapered waveguide (15) are the same. The lengths a3 and a3' are equal, ranging from 100 to 4000 μm. The widths w2 and w2' at the connection with the first branch (12) of the 3-dB Y-branch splitter and the second branch (13) of the 3-dB Y-branch splitter are equal, ranging from 4 to 7.5 μm. The widths w3 and w3' at the connection with the multimode interference waveguide (16) are equal, ranging from 7 to 30 μm. The length a4 of the multimode interference waveguide (16) is from 500 to 10000 μm, and the width w4 is from 40 to 100 μm. The structures and dimensions of the first output tapered waveguide (17) and the second output tapered waveguide (18) are the same. The lengths a5 and a5' are equal, ranging from 200 to 5000 μm. The widths w5 and w5' at the connection with the multimode interference waveguide (16) are equal, ranging from 19 to 49 μm. The widths w1' and w1'' at the connection with the first output curved waveguide (19) and the second output curved waveguide (110) are equal, ranging from 8 to 15 μm. The structures and dimensions of the first output curved waveguide (19) and the second output curved waveguide (110) are the same. The projected lengths a6 and a6' along the extension direction of the first input few-mode straight waveguide (11) are equal, ranging from 500 to 8000 μm. The center distances gap2 and gap2' between the input end and the output end are equal, ranging from 5 to 40 μm. The widths w1' and w1'' are equal, ranging from 8 to 15 μm.

3. The mode-insensitive optical power splitter integrated with a mode conversion function according to claim 1, wherein: The thickness of the silicon wafer substrate (21) is 0.5 to 1 mm, the thickness of the polymer waveguide lower cladding (22) is 4 to 15 µm, the thickness of the polymer optical waveguide core layer (23) is 7 to 15 µm, and the thickness of the polymer waveguide upper cladding (24) above the polymer optical waveguide core layer (23) is 4 to 15 µm.

4. The mode-insensitive optical power splitter integrated with a mode conversion function according to claim 1, wherein: The material of the polymer waveguide lower cladding (22) is polycarbonate, polyimide, polyethylene, polyester, polymethyl methacrylate, polystyrene, or EpoClad; the material of the polymer optical waveguide core layer (23) is EpoCore, SU-8 2002, or SU-8 2005; the material of the polymer waveguide upper cladding (24) is polycarbonate, polyimide, polyethylene, polyester, polymethyl methacrylate, polystyrene, or EpoClad; and the refractive index of the polymer optical waveguide core layer material is higher than that of the polymer upper and lower cladding materials.

5. The preparation method of a mode-insensitive optical power splitter integrating a mode conversion function according to any one of claims 1 to 4 is as follows: A: Cleaning treatment of the silicon wafer substrate Wipe the silicon wafer substrate (21) 1 to 3 times repeatedly with a cotton ball dipped in acetone solution, and then wipe the silicon wafer substrate (21) that has been wiped with acetone 1 to 3 times repeatedly with another cotton ball dipped in ethanol solution. After wiping clean, rinse the silicon wafer substrate (21) with deionized water until it is clean. Finally, dry the silicon wafer substrate (21) with nitrogen, and then put it into a clean petri dish and seal it for storage; B: Preparation of the polymer waveguide lower cladding Spin-coat the polymer waveguide lower cladding material on the cleaned silicon wafer substrate (21) through the spin-coating process. The spin-coating speed is 1000 to 6000 revolutions per minute, and bake it for 4 to 60 minutes at 90 to 150 °C; when using EpoClad material, it needs to be baked and then exposed as a whole under ultraviolet light with a wavelength of 350 to 400 nm for 3 to 50 s, and finally baked for 4 to 60 minutes at 90 to 150 °C; finally, the polymer lower cladding (22) is obtained; C: Preparation of the polymer optical waveguide core layer Adopt the spin-coating process to spin-coat the polymer optical waveguide core layer material on the polymer lower cladding (22) to form a polymer optical waveguide core layer thin film (23). The spin-coating speed is 800 to 5500 revolutions per minute; after spin-coating, perform pre-baking, that is, adopt a stepwise heating method to heat the device at 50 to 150 °C for 2 to 30 minutes, and then bake it at 70 to 135 °C for 3 to 40 minutes. After heating, let it cool naturally to 20 to 60 °C; then perform photolithography on the polymer optical waveguide core layer thin film (23), that is, use a mask plate complementary to the structure of the polymer optical waveguide core layer (23) to be prepared, press the mask plate tightly against the surface of the polymer optical waveguide core layer thin film (23), and then expose it under ultraviolet light with a wavelength of 350 to 400 nm for 5 to 40 s, so that the material of the polymer optical waveguide core layer (23) structure to be prepared is exposed by ultraviolet light; after photolithography, perform mid-baking operation, that is, heat it at 50 to 100 °C for 2 to 30 minutes, and then heat it at 75 to 125 °C for 5 to 40 minutes. After heating, let it cool naturally to room temperature; after cooling, perform development, that is, first wet-etch in the developer corresponding to the polymer optical waveguide core layer material for 5 to 80 s to remove the polymer optical waveguide core layer thin film of the non-polymer optical waveguide core layer (23) structure that has not been exposed, leaving only the polymer waveguide core layer structure corresponding to the mask plate structure, and then put it into an isopropanol solution to wash away the unexposed polymer optical waveguide core layer material and developer remaining on the surface of the device, and then rinse it with deionized water to remove the isopropanol solution on the surface of the device, and dry it with nitrogen; finally, perform post-baking and hardening, that is, heat it at 120 to 160 °C for 20 to 60 minutes, thereby obtaining a strip-shaped polymer optical waveguide core layer (23) on the polymer lower cladding 22; D: Preparation of the polymer waveguide upper cladding The polymer upper cladding material is spin-coated on the prepared polymer optical waveguide core layer (23) and polymer lower cladding (22) by a spin-coating process at a spin-coating speed of 1000 - 6000 revolutions per minute and baked for 4 - 60 minutes at 90 - 150 °C; when using materials such as EpoClad, after spin-coating, it is necessary to first perform overall exposure under ultraviolet light with a wavelength of 350 - 400 nm for 3 - 50 s, and then bake for 4 - 60 minutes at 90 - 150 °C; finally, the polymer upper cladding (24) is obtained, thus completing the preparation of the mode-insensitive optical power splitter with the integrated mode conversion function.

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