Mode-insensitive 3*6 optical power divider based on MMI structure and preparation method thereof

Abstract

The invention discloses a mode-insensitive 3 * 6 optical power divider based on an MMI structure and a preparation method thereof, and belongs to the technical field of optical power dividers and preparation thereof. 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 in sequence from bottom to top, the polymer optical waveguide core layer is completely wrapped in the polymer upper cladding, and the refractive index of the polymer optical waveguide core layer is larger than that of the polymer upper cladding and that of the polymer upper cladding; the polymer optical waveguide core layer is based on four cascaded MMI optical waveguide structures, two modes of optical power input from three input ports can be equally divided at six output ports, the mode insensitive function is achieved, and power distribution can be carried out on a fundamental mode and a high-order mode at the same time; a traditional power divider with only one input port is broken through, and the communication capacity is increased again through three input ports. The device can be applied to a mode division multiplexing system, and can realize practical application and large-scale batch production.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical power dividers and their preparation, and specifically relates to a mode-insensitive 3×6 optical power divider based on a multi-mode interference (MMI) structure, which uses a silicon wafer as a substrate, an organic polymer material as an upper cladding and a lower cladding, and an organic polymer material with a refractive index greater than that of the upper and lower claddings as a core layer, and a preparation method thereof. Background Art

[0002] In recent years, with the rapid development of the Internet and electronic information technology, people have an increasing demand for the transmission capacity and speed of communication system information. Traditional communication methods make the signal bandwidth small, easy to attenuate, easy to distort, and have large interference. The emergence and development of optical communication can effectively solve the problems caused by traditional communication. It has the advantages of fast communication speed, large communication capacity, small transmission loss, and long transmission distance.

[0003] In optical communications, in order to further meet the demand for communication capacity, wavelength division multiplexing (WDM), polarization division multiplexing (PDM) and mode division multiplexing (MDM) technologies were born. Among them, mode division multiplexing technology has been widely used and developed as one of the key technologies to improve channel capacity. Mode division multiplexing technology refers to the distribution of data information to multiple mutually orthogonal optical modes. Each mode carries different information as an independent channel, so that it is transmitted simultaneously in a few-mode waveguide, realizing the demand for exponential growth of communication transmission capacity.

[0004] The optical power splitter in the mode division multiplexing system is one of the very important functional devices in the optical communication system, also known as an optical splitter or optical distributor. It has the function of distributing and synthesizing the power of optical signals, that is, distributing one input optical signal to multiple output ports, or distributing multiple input optical signals to one output port, which can reduce the type and quantity of information to be processed, and can also realize the monitoring function of the signal. It has good development prospects and important significance in the optical communication network. The optical power splitter can be divided into optical fiber optical power splitter and planar optical waveguide optical power splitter. In the optical communication system, the traditional optical fiber optical power splitter has a large size, high loss and poor stability, while the planar optical waveguide optical power splitter can effectively solve the above problems and has been widely used. The planar optical waveguide optical power splitter has the advantages of large bandwidth, low loss, compact structure, small size, low cost, good stability, flexible design and high integration.

[0005] The materials of planar waveguide optical power divider include: silicon (Si), silicon dioxide (SiO2), lithium niobate (LiNbO3), polymer, etc. Compared with other materials, polymer materials have low dielectric constant, easy coupling with the end face of optical fiber, adjustable refractive index, and because the refractive index contrast between the core layer and the cladding of polymer materials is small, they are polarization insensitive. The spin coating process is used to prepare polymer films, which has a simple preparation process and low cost. It is a basic material for high-performance photonic devices with great development and application prospects.

[0006] Multimode interference (MMI) is one of the most basic structures in the design of planar optical waveguide devices, and has important application value in optical communication systems and planar optical waveguide mode power dividers. The MMI structure is mainly composed of an input waveguide, a multimode interference waveguide, and an output waveguide. It is easier to realize waveguide interference and realize the function of power distribution through the self-imaging principle. However, the traditional MMI optical power divider can only manipulate the fundamental mode and can only realize power distribution from one input waveguide, which limits its application in mode division multiplexing systems and planar optical waveguide mode power dividers.

[0007] Most of the existing optical power dividers can only realize the power distribution and synthesis of the fundamental mode, and cannot control the transmission of the higher-order mode, which limits the communication capacity in the optical communication system, and requires cascading 3dB power dividers to realize other equal power functions of the mode. Therefore, there is a need for an optical power divider that can simultaneously realize other equal power functions of mode insensitivity and overcome the complex coupling of higher-order modes. Summary of the invention

[0008] In order to overcome the shortcomings of existing optical power dividers, the object of the present invention is to provide a mode-insensitive 3×6 optical power divider based on an MMI structure that can process both fundamental mode and high-order mode and a preparation method thereof.

[0009] The present invention uses a silicon wafer as a substrate, an organic polymer material as an upper cladding and a lower cladding, and an organic polymer material with a refractive index greater than that of the upper and lower claddings as a core layer. The polymer material used in the present invention has a simple preparation process, is easy to couple with optical fibers, is easy to integrate, has a low price, can be mass-produced, and has important practical application value.

[0010] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0011] A mode-insensitive 3×6 optical power divider based on MMI structure can control LP 01 LP 11bThe two modes are composed of, from bottom to top, a silicon wafer substrate 21, a polymer lower cladding layer 22 prepared on the silicon wafer substrate 21, a polymer optical waveguide core layer 23 of a strip structure prepared on the polymer lower cladding layer 22, and a polymer upper cladding layer 24 prepared on the polymer lower cladding layer 22 and the polymer optical waveguide core layer 23. The polymer optical waveguide core layer 23 is completely covered in the polymer upper cladding layer 24. Figure 1 As shown in (a), the polymer optical waveguide core layer 23 is based on four cascaded MMI optical waveguide structures. The two-mode optical powers input from the three input ports can be equally divided into six output ports; from left to right along the propagation direction of light, the polymer optical waveguide core layer 23 is composed of a first input few-mode straight waveguide 11, a second input few-mode straight waveguide 12, a third input few-mode straight waveguide 13, a first input bent waveguide 14, a second input bent waveguide 15, a first input tapered waveguide 16, a second input tapered waveguide 17, and a third input tapered waveguide 18, first multimode interference waveguide 19, first output tapered waveguide 110, second output tapered waveguide 111, third output tapered waveguide 112, first connecting curved waveguide 113, first connecting straight waveguide 114, second connecting curved waveguide 115, third connecting curved waveguide 116, fourth connecting curved waveguide 117, fourth input tapered waveguide 118, second multimode interference waveguide 119, fourth output tapered waveguide 120, fifth output tapered waveguide 121, fifth connecting curved waveguide 122, sixth a connecting curved waveguide 123, a seventh connecting curved waveguide 124, an eighth connecting curved waveguide 125, a second connecting straight waveguide 126, a third connecting straight waveguide 127, a fourth connecting straight waveguide 128, a fifth connecting straight waveguide 129, a fifth input tapered waveguide 130, a sixth input tapered waveguide 131, a seventh input tapered waveguide 132, an eighth input tapered waveguide 133, a third multimode interference waveguide 134, a fourth multimode interference waveguide 135, a sixth output tapered waveguide 136, a seventh output tapered waveguide 137, a An eighth output tapered waveguide 138, a ninth output tapered waveguide 139, a tenth output tapered waveguide 140, an eleventh output tapered waveguide 141, a first output bent waveguide 142, a second output bent waveguide 143, a third output bent waveguide 144, a fourth output bent waveguide 145, a first output few-mode straight waveguide 146, a second output few-mode straight waveguide 147, a third output few-mode straight waveguide 148, a fourth output few-mode straight waveguide 149, a fifth output few-mode straight waveguide 150, and a sixth output few-mode straight waveguide 151 are formed;

[0012] The first multimode interference waveguide 19 has three input ends and three output ends. The first input few-mode straight waveguide 11, the first input curved waveguide 14 and the first input tapered waveguide 16 are connected in sequence as the first input end of the first multimode interference waveguide 1. The second input few-mode straight waveguide 12 and the second input tapered waveguide 17 are connected in sequence as the second input end of the first multimode interference waveguide 1. The third input few-mode straight waveguide 13, the second input curved waveguide 15 and the third input tapered waveguide 18 are connected in sequence as the third input end of the first multimode interference waveguide 1. The first output tapered waveguide 110, the second output tapered waveguide 111 and the third output tapered waveguide 112 are respectively used as the three output ends of the first multimode interference waveguide 19.

[0013] The second multimode interference waveguide 119 has an input end and two output ends. The second output tapered waveguide 111, the first connecting straight waveguide 114 and the fourth input tapered waveguide 118 are sequentially connected to serve as the input end of the second multimode interference waveguide 119. The fourth output tapered waveguide 120 and the fifth output tapered waveguide 121 serve as two output ends of the second multimode interference waveguide 119 respectively.

[0014] The third multimode interference waveguide 134 and the fourth multimode interference waveguide 135 have two input ends and three output ends respectively. The first output tapered waveguide 110, the first connecting curved waveguide 113, the third connecting curved waveguide 116, the second connecting straight waveguide 126 and the fifth input tapered waveguide 130 are sequentially connected as the first input end of the third multimode interference waveguide 134. The fourth output tapered waveguide 120, the fifth connecting curved waveguide 122, the seventh connecting curved waveguide 124, the fourth connecting straight waveguide 128 and the sixth input tapered waveguide 131 are sequentially connected as the second input end of the third multimode interference waveguide 134. The fifth output tapered waveguide 121, the sixth connecting curved waveguide 123, the eighth connecting curved waveguide 125, the fifth connecting straight waveguide 126 and the sixth input tapered waveguide 131 are sequentially connected as the second input end of the third multimode interference waveguide 134. The connecting straight waveguide 129 and the seventh input tapered waveguide 132 are connected in sequence as the first input end of the fourth multimode interference waveguide 135, the third output tapered waveguide 112, the second connecting curved waveguide 115, the fourth connecting curved waveguide 117, the third connecting straight waveguide 127 and the eighth input tapered waveguide 133 are connected in sequence as the second input end of the fourth multimode interference waveguide 135, the sixth output tapered waveguide 136, the seventh output tapered waveguide 137 and the eighth output tapered waveguide 138 are respectively used as the three output ends of the third multimode interference waveguide 134, and the ninth output tapered waveguide 139, the tenth output tapered waveguide 140 and the eleventh output tapered waveguide 141 are respectively used as the three output ends of the fourth multimode interference waveguide 135;

[0015] The sixth output tapered waveguide 136, the first output curved waveguide 142 and the first output few-mode straight waveguide 146 are connected in sequence, the seventh output tapered waveguide 137 and the second output few-mode straight waveguide 147 are connected in sequence, the eighth output tapered waveguide 138, the second output curved waveguide 143 and the third output few-mode straight waveguide 148 are connected in sequence, the ninth output tapered waveguide 139, the third output curved waveguide 144 and the fourth output few-mode straight waveguide 149 are connected in sequence, the tenth output tapered waveguide 140 and the fifth output few-mode straight waveguide 150 are connected in sequence, and the eleventh output tapered waveguide 141, the fourth output curved waveguide 145 and the sixth output few-mode straight waveguide 151 are connected in sequence.

[0016] The polymer optical waveguide core layer 23 is a symmetrical structure about the second input few-mode straight waveguide 12 and its extension line; the first input few-mode straight waveguide 11, the third input few-mode straight waveguide 13, the first output few-mode straight waveguide 146, the third output few-mode straight waveguide 148, the fourth output few-mode straight waveguide 149 and the sixth output few-mode straight waveguide 151 have the same structural dimensions, and their lengths a1 are equal to 500-3000 μm, and their widths w1 are equal to 3-8 μm; the second input few-mode straight waveguide 12, the second output few-mode straight waveguide 147 and the fifth output few-mode straight waveguide 150 have the same structural dimensions, and their lengths a2 are equal to 1000-5500 μm, and their widths w1 are equal to 3-8 μm; the first input curved waveguide 14, the second The input curved waveguide 15, the first connecting curved waveguide 113, the second connecting curved waveguide 115, the third connecting curved waveguide 116 and the fourth connecting curved waveguide 117 have the same structural dimensions, their widths w1 are equal to 3 to 8 μm, the projection lengths a3 along the second input few-mode straight waveguide 12 and its extension line are equal to 1000 to 7000 μm, and the center spacing gap1 between the input end and the output end is equal to 10 to 70 μm; the first input tapered waveguide 16, the third input tapered waveguide 18, the first output tapered waveguide 110 and the third output tapered waveguide 112 have the same structural dimensions, their lengths a4 are equal to 400 to 2000 μm, the outer edges coincide with the outer edges of the first multimode interference waveguide 19, and the outer edges of the first multimode interference waveguide 19 coincide with the outer edges of the first multimode interference waveguide 19. The width w2 of the connection between the first multimode interference waveguide 19 is equal to 8-15 μm, the width w1 of the connection between the first input curved waveguide 14 and the first input tapered waveguide 16, the width w1 of the connection between the second input curved waveguide 15 and the third input tapered waveguide 18, the width w1 of the connection between the first output tapered waveguide 110 and the first connecting curved waveguide 113, and the width w1 of the connection between the third output tapered waveguide 112 and the second connecting curved waveguide 115 are equal to 3-8 μm; the second input tapered waveguide 17 and the second output tapered waveguide 111 have the same structural dimensions, and their lengths a5 are equal to 500-2500 μm, and the width w3 of the connection with the first multimode interference waveguide 19 is equal to 15-25 μm, and the second input tapered waveguide 17 has a length a5 of ... The width w1 of the connection between the fourth input tapered waveguide 118 and the second input few-mode straight waveguide 12 and the width w1 of the connection between the second output tapered waveguide 111 and the first connecting straight waveguide 114 are equal to 3-8 μm; the length a6 of the first multimode interference waveguide 19 is 3000-9000 μm, and the width w4 is 30-90 μm; the length a7 of the first connecting straight waveguide 114 is 500-5000 μm, and the width w1 is 3-8 μm; the length a8 of the fourth input tapered waveguide 118 is 500-3000 μm, and the width w5 of the connection between the fourth input tapered waveguide 118 and the second multimode interference waveguide 119 is 9-25 μm; the length a9 of the second multimode interference waveguide 119 is 500-6000 μm, and the width w6 is 30-80 μm;The fourth output tapered waveguide 120 and the fifth output tapered waveguide 121 have the same structural dimensions, and their lengths a10 are equal to 500-3000 μm, and their widths w7 at the connection with the second multimode interference waveguide 119 are equal to 9-22 μm, and the spacing gap2 between the outer edge and the outer edge of the second multimode interference waveguide 119 is equal to 0-6 μm, and the widths w1 at the connection with the fifth connecting curved waveguide 122 and the sixth connecting curved waveguide 123 are equal to 3-8 μm; the fifth connecting curved waveguide 122, the sixth connecting curved waveguide 123, the seventh connecting curved waveguide 124, and the eighth connecting curved waveguide 125 have the same structural dimensions, and they are connected along the second input few-mode straight waveguide 12 and its extension line. The projection length a11 in the direction is equal to 1000-6000 μm, and the center distance gap3 between the input end and the output end is equal to 10-60 μm; the second connecting straight waveguide 126 and the third connecting straight waveguide 127 have the same structural dimensions, and their length a12 is equal to 2000-12000 μm, and the width w1 is 3-8 μm; the fourth connecting straight waveguide 128 and the fifth connecting straight waveguide 129 have the same structural dimensions, and their length a13 is equal to 50-500 μm, and the width w1 is 3-8 μm; the fifth input tapered waveguide 130, the eighth input tapered waveguide 133, the sixth output tapered waveguide 136, the eighth output tapered waveguide 138, and the ninth output tapered waveguide 139 The sixth input tapered waveguide 131, the seventh input tapered waveguide 132, the seventh output tapered waveguide 137 and the tenth output tapered waveguide 140 have the same structural dimensions, the length a15 thereof is equal to 450 to 2000 μm, the width w8 thereof at the connection between the third multimode interference waveguide 134 and the fourth multimode interference waveguide 135 is equal to 8 to 18 μm, and the outer edges thereof coincide with the outer edges of the third multimode interference waveguide 134 and the fourth multimode interference waveguide 135, respectively; the sixth input tapered waveguide 131, the seventh input tapered waveguide 132, the seventh output tapered waveguide 137 and the tenth output tapered waveguide 140 have the same structural dimensions, the length a15 thereof is equal to 450 to 2000 μm, the width w9 thereof at the connection between the third multimode interference waveguide 134 and the fourth multimode interference waveguide 135 is equal to 9 to 20μm, the center coincides with the center of the third multimode interference waveguide 134 and the fourth multimode interference waveguide 135; the third multimode interference waveguide 134 and the fourth multimode interference waveguide 135 have the same structural dimensions, their length a16 is equal to 3000-10000μm, and their width w10 is equal to 30-100μm; the first output curved waveguide 142, the second output curved waveguide 143, the third output curved waveguide 144 and the fourth output curved waveguide 145 have the same structural dimensions, their projection length a17 along the second input few-mode straight waveguide 12 and its extension line direction is equal to 800-5000μm, and the center distance gap4 between the input end and the output end is equal to 5-50μm. ;

[0017] like Figure 2 Shown Figure 1(a) is a cross-sectional view at the position of the dotted line AA', which consists of, from bottom to top, a silicon wafer substrate 21, 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, and the polymer optical waveguide core layer 23 is embedded in the polymer upper cladding 24; wherein, the thickness of the silicon wafer substrate 21 is 0.5-1 mm, the thickness of the polymer lower cladding 22 is 4-12 μm, the thickness of the polymer optical waveguide core layer 23 is 5-15 μm, and the thickness of the polymer upper cladding on the polymer optical waveguide core layer 23 is 4-12 μm.

[0018] The present invention discloses a method for preparing a mode-insensitive 3×6 optical power divider based on an MMI structure, and the process flow is as follows: Figure 3 As shown, the specific steps are as follows:

[0019] A: Cleaning of silicon wafer substrate

[0020] Wipe the surface of the silicon wafer substrate 21 with a cotton ball with acetone for 2 to 3 times, and then wipe it with a cotton ball with ethanol for 2 to 3 times. After wiping it clean, rinse the surface of the silicon wafer substrate 21 repeatedly with deionized water until it is clean. Finally, blow dry the silicon wafer substrate 21 with nitrogen, put it in a clean culture dish and seal it for storage;

[0021] B: Preparation of polymer lower cladding

[0022] The polymer lower cladding layer is made of an organic polymer material with good transparency (including polycarbonate (PC), polyimide (PI), polyethylene (PE), polyester (PET), polymethyl methacrylate (PMMA), polystyrene (PS), EpoClad and other organic polymer materials with good transparency). The polymer lower cladding material is spin-coated on the cleaned silicon wafer substrate 21 by a spin coating process, the spin coating speed is 1000-5000 rpm, and the material is baked at 95-150° C. for 4-60 minutes. If EpoClad material is used, the whole material needs to be exposed for 5-60 seconds after baking and then baked at 95-150° C. for 4-60 minutes to obtain a polymer lower cladding layer with a thickness of 4-12 μm.

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

[0024] The polymer optical waveguide core layer material includes a series of ultraviolet negative photoresist materials that can be wet-etched, including EpoCore, SU-8 2002, and SU-8 2005, and its refractive index must be higher than the refractive index of the polymer upper and lower cladding materials. The polymer optical waveguide core layer material is spin-coated on the polymer lower cladding 22 by a spin coating process to obtain a polymer optical waveguide core layer film 23', and the spin coating speed is 1000 to 6000 rpm; after the spin coating is completed, pre-baking is performed, that is, the device is baked at 50 to 150°C for 4 to 40 minutes; after naturally cooling to room temperature, it is subjected to plate-alignment photolithography, and the ultraviolet light wavelength of the photolithography machine is 350 to 400nm, and the light-transmitting part of the photolithography mask is the polymer optical waveguide core layer 23 area to be prepared (such as Figure 1 (a) shows), the photolithography mask is closely attached to the silicon wafer substrate 21, and the exposure time is 5 to 50 seconds, so that the area of ​​the polymer optical waveguide core layer 23 to be prepared is exposed to ultraviolet light; after the photolithography is completed, it is baked at a temperature of 50 to 150° C. for 5 to 40 minutes; after cooling naturally to room temperature, it is developed, that is, wet etching in a special developer corresponding to the polymer optical waveguide core layer material for 5 to 90 seconds to remove the unexposed polymer optical waveguide core layer material, and then the residual developer is removed by isopropanol solution, and the isopropanol solution is repeatedly rinsed along the waveguide direction with deionized water to remove the isopropanol solution, and then dried with nitrogen; finally, the film is post-baked, that is, baked at a temperature of 120 to 150° C. for 20 to 60 minutes, so as to prepare a polymer optical waveguide core layer with a thickness of 5 to 15 μm on the polymer lower cladding 22;

[0025] D: Preparation of polymer upper cladding

[0026] The polymer upper cladding material is spin-coated on the polymer optical waveguide core layer 23 and the polymer lower cladding layer 22 by a spin coating process, the spin coating speed is 1000-5000 rpm, and the material is baked at 95-150°C for 4-120 minutes to obtain a polymer upper cladding layer 24 with a thickness of 4-12 μm (the thickness above the polymer optical waveguide core layer 23), thereby completing the preparation of a mode-insensitive 3×6 optical power divider based on an MMI structure.

[0027] Compared with the existing device structure and preparation technology, the beneficial effects of the present invention are:

[0028] The planar optical waveguide type 3×6 optical power divider of the present invention combines the advantages of simple process and low cost of organic polymer materials with large process tolerance and small size of MMI structure; it realizes the mode-insensitive function and can simultaneously distribute power to the fundamental mode and high-order mode; it breaks the traditional power divider that can only input one port, and the three input ports once again realize the increase of communication capacity. The device can be applied to the mode division multiplexing system, with simple manufacturing process, low cost, high efficiency, and can be applied in practice and mass-produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 (a): A schematic diagram of the structure of the mode-insensitive 3×6 optical power divider based on the MMI structure according to the present invention;

[0030] Figure 1 (b): for Figure 1 (a) is an enlarged view of the fourth connecting straight waveguide 128 (fifth connecting straight waveguide 129);

[0031] Figure 2 : Figure 1 (a) Schematic diagram of the cross section at the position of the dotted line AA';

[0032] Figure 3 :Process flow chart of the preparation of mode-insensitive 3×6 optical power divider based on MMI structure;

[0033] Figure 4 (a): LP in the mode-insensitive 3×6 optical power divider based on MMI structure 01 Simulated diagram of the light field distribution of the mode;

[0034] Figure 4 (b): LP in the mode-insensitive 3×6 optical power divider based on MMI structure 11b Simulated diagram of the light field distribution of the mode;

[0035] Figure 5 (a): The mode-insensitive 3×6 optical power divider based on the MMI structure inputs the LP from the first input few-mode straight waveguide 11 01 Simulation diagram of light field transmission of the mode;

[0036] Figure 5 (b) The mode-insensitive 3×6 optical power divider based on the MMI structure inputs the LP from the second input few-mode straight waveguide 12 01 Simulation diagram of light field transmission of the mode;

[0037] Figure 5 (c) The mode-insensitive 3×6 optical power divider based on the MMI structure inputs the LP from the third input few-mode straight waveguide 13 01 Simulation diagram of light field transmission of the mode;

[0038] Figure 5 (d) The mode-insensitive 3×6 optical power divider based on the MMI structure inputs the LP from the first input few-mode straight waveguide 11. 11b Simulation diagram of light field transmission of the mode;

[0039] Figure 5(e) The mode-insensitive 3×6 optical power divider based on the MMI structure inputs the LP from the second input few-mode straight waveguide 12 11b Simulation diagram of light field transmission of the mode;

[0040] Figure 5 (f): The mode-insensitive 3×6 optical power divider based on the MMI structure inputs the LP from the third input few-mode straight waveguide 13 11b Simulation diagram of light field transmission of the mode;

[0041] Figure 6 (a) LP input from the first input few-mode straight waveguide 11 by the mode-insensitive 3×6 optical power divider based on the MMI structure 01 and LP 11b The relationship curve between output power and wavelength in mode;

[0042] Figure 6 (b) LP input from the second input few-mode straight waveguide 12 by the mode-insensitive 3×6 optical power divider based on the MMI structure 01 and LP 11b The relationship between the output power of the mode and the wavelength;

[0043] Figure 6 (c) LP input from the third input few-mode straight waveguide 13 by the mode-insensitive 3×6 optical power divider based on the MMI structure 01 and LP 11b The relationship between the output power of the mode and the wavelength; DETAILED DESCRIPTION

[0044] Example 1

[0045] like Figure 1As shown in (a), the overall device structural parameters are symmetrical about the dotted line aa'; the first input few-mode straight waveguide 11, the third input few-mode straight waveguide 13, the first output few-mode straight waveguide 146, the third output few-mode straight waveguide 148, the fourth output few-mode straight waveguide 149 and the sixth output few-mode straight waveguide 151 have the same structural dimensions, and the length a1 is equal to 1000μm; the width w1 is equal to 5μm; the second input few-mode straight waveguide 12, the second output few-mode straight waveguide 147 and the fifth output few-mode straight waveguide 150 have the same structural dimensions, and the length a2 is equal to 2995μm , the width w1 is equal to 5 μm; the first input curved waveguide 14, the second input curved waveguide 15, the first connecting curved waveguide 113, the second connecting curved waveguide 115, the third connecting curved waveguide 116 and the fourth connecting curved waveguide 117 have the same structural dimensions, the length a3 is equal to 2195 μm, and the center distance gap1 between the input end and the output end of the curved waveguide is equal to 29.25 μm; the first input tapered waveguide 16, the third input tapered waveguide 18, the first output tapered waveguide 110 and the third output tapered waveguide 112 have the same structural dimensions, the length a4 is equal to The outer edge of the first multimode interference waveguide 19 coincides with the outer edge of the first multimode interference waveguide 19, and the width w2 of the connection between the two is equal to 11.5 μm. The width w1 of the connection between the first input tapered waveguide 16 and the third input tapered waveguide 18 and the first input curved waveguide 14 and the second input curved waveguide 15 is equal to 5 μm. The width w1 of the connection between the first output tapered waveguide 110 and the third output tapered waveguide 112 and the first connecting curved waveguide 113 and the second connecting curved waveguide 115 is equal to 5 μm. The second input tapered waveguide 17 and the second output tapered waveguide 11 1 has the same structural dimensions, the length a5 is equal to 1100μm, the width w3 at the connection with the first multimode interference waveguide 19 is equal to 21μm, and the width w1 at the connection with the first connecting straight waveguide 114 is 5μm; the length a6 of the first multimode interference waveguide 19 is 5680μm, and the width w4 is 50μm; the length a7 of the first connecting straight waveguide 114 is 1000μm, and the width w1 is 5μm; the length a8 of the fourth input tapered waveguide 118 is 1500μm, and the width w5 at the connection with the second multimode interference waveguide 119 is 17.5μm; the length a9 of the second multimode interference waveguide 119 is 1400μm, and the width w6 is 50μm; the fourth output tapered waveguide 120 and the fifth output tapered waveguide 121 have the same structural dimensions, and the length a10 is equal to 1500μm, wherein the width w7 at the connection with the second multimode interference waveguide 119 is equal to 17μm, and the gap gap2 between the outer edge and the outer edge of the second multimode interference waveguide 119 is equal to 3μm, and the width w1 at the connection with the fifth connecting curved waveguide 122 and the sixth connecting curved waveguide 123 is equal to 5μm; the fifth connecting curved waveguide 122, the sixth connecting curved waveguide 123, the seventh connecting curved waveguide 124 and The eighth connected curved waveguide 125 has the same structural dimensions, and its projection length a11 along the second input few-mode straight waveguide 12 and its extension line direction is equal to 1600 μm, and the waveguide center spacing gap3 is equal to 21 μm; the second connected straight waveguide 126 and the third connected straight waveguide 127 have the same structural dimensions, the length a12 is equal to 4690 μm, and the width w1 is 5 μm; the fourth connected straight waveguide 128 and the fifth connected straight waveguide 129 have the same structural dimensions, the length a13 is equal to 200 μm, and the width w1 is 5 μm; the fifth input tapered waveguide 130, the eighth input tapered waveguide 133, the sixth output tapered waveguide 136, and the eighth output tapered waveguide 137 are equal to each other. 38. The ninth output tapered waveguide 139 and the eleventh output tapered waveguide 141 have the same structural dimensions, and the length a14 is equal to 840 μm, wherein the width w8 at the connection with the third multimode interference waveguide 134 and the fourth multimode interference waveguide 135 is equal to 15.5 μm, and the outer edge thereof coincides with the outer edge of the third multimode interference waveguide 134 and the fourth multimode interference waveguide 135; the sixth input tapered waveguide 131, the seventh input tapered waveguide 132, the seventh output tapered waveguide 137 and the tenth output tapered waveguide 140 have the same structural dimensions, and the length a15 is equal to 920 μm, wherein the connection with the third multimode interference waveguide 134 and the fourth multimode interference waveguide 135 is equal to 15.5 μm, and the outer edge thereof coincides with the outer edge of the third multimode interference waveguide 134 and the fourth multimode interference waveguide 135. The width w9 is equal to 17μm, and its center coincides with the center position of the third multimode interference waveguide 134 and the fourth multimode interference waveguide 135; the third multimode interference waveguide 134 and the fourth multimode interference waveguide 135 have the same structural dimensions, the length a16 is equal to 5310μm, and the width w10 is equal to 60μm; the first output curved waveguide 142, the second output curved waveguide 143, the third output curved waveguide 144 and the fourth output curved waveguide 145 have the same structural dimensions, and their projection length a17 along the second input few-mode straight waveguide 12 and its extension line direction is equal to 1400μm, and the center distance gap4 between the waveguide input end and the output end is equal to 13μm. .

[0046] like Figure 2As shown, from bottom to top, it is composed of a silicon wafer substrate 21, a polymer lower cladding layer 22 prepared on the silicon wafer substrate 21, a strip-shaped optical waveguide core layer 23 prepared on the polymer lower cladding layer 22, and a polymer upper cladding layer 24 prepared on the optical waveguide core layer 23. The thickness of the silicon wafer substrate 21 is 1 mm, the thickness of the polymer lower cladding layer 22 is 7 μm, the thickness of the polymer optical waveguide core layer 23 is 8 μm, and the thickness of the polymer upper cladding layer is 7 μm (the thickness above the optical waveguide core layer).

[0047] like Figure 4 (a) shows the LP in the mode-insensitive 3×6 optical power divider based on the MMI structure. 01 Simulation diagram of the light field distribution of the mode. In the simulation process, we use the materials and waveguide dimensions used in Example 1. From the figure, we can see that the light field is mainly concentrated in the rectangular waveguide core layer, which can ensure LP 01 The mode optical signal is effectively transmitted in the optical waveguide;

[0048] like Figure 4 (b) shows the LP in the mode-insensitive 3×6 optical power divider based on the MMI structure. 11b Simulation diagram of the light field distribution of the mode. In the simulation process, we use the materials and waveguide dimensions used in Example 1. From the figure, we can see that the light field is mainly concentrated in the rectangular waveguide core layer, which can ensure LP 01 The mode optical signal is effectively transmitted in the optical waveguide;

[0049] like Figure 5 As shown in (a), the mode-insensitive 3×6 optical power divider based on the MMI structure inputs the LP from the first input few-mode straight waveguide 11. 01 The light field transmission simulation diagram of the mode and the light field distribution simulation diagram of the output port. In the simulation process, we use the materials and waveguide dimensions used in Example 1. It can be seen from the simulation diagram that the input LP 01 In mode, the output is 6 LPs with the same power. 01 model;

[0050] like Figure 5 As shown in (b), the mode-insensitive 3×6 optical power divider based on the MMI structure inputs the LP from the second input few-mode straight waveguide 12. 01 The light field transmission simulation diagram of the mode and the light field distribution simulation diagram of the output port. In the simulation process, we use the materials and waveguide dimensions used in Example 1. It can be seen from the simulation diagram that the input LP 01 In mode, the output is 6 LPs with the same power. 01 model;

[0051] like Figure 5As shown in (c), the mode-insensitive 3×6 optical power divider based on the MMI structure inputs the LP from the third input few-mode straight waveguide 13. 01 The light field transmission simulation diagram of the mode and the light field distribution simulation diagram of the output port. In the simulation process, we use the materials and waveguide dimensions used in Example 1. It can be seen from the simulation diagram that the input LP 01 In mode, the output is 6 LPs with the same power. 01 model;

[0052] like Figure 5 As shown in (d), the mode-insensitive 3×6 optical power divider based on the MMI structure inputs the LP from the first input few-mode straight waveguide 11. 11b The light field transmission simulation diagram of the mode and the light field distribution simulation diagram of the output port. In the simulation process, we use the materials and waveguide dimensions used in Example 1. It can be seen from the simulation diagram that the input LP 11b In mode, the output is 6 LPs with the same power. 11b model;

[0053] like Figure 5 As shown in (e), the mode-insensitive 3×6 optical power divider based on the MMI structure inputs the LP from the second input few-mode straight waveguide 12. 11b The light field transmission simulation diagram of the mode and the light field distribution simulation diagram of the output port. In the simulation process, we use the materials and waveguide dimensions used in Example 1. It can be seen from the simulation diagram that the input LP 11b In mode, the output is 6 LPs with the same power. 11b model;

[0054] like Figure 5 As shown in (f), the mode-insensitive 3×6 optical power divider based on the MMI structure inputs the LP from the third input few-mode straight waveguide 13. 11b The light field transmission simulation diagram of the mode and the light field distribution simulation diagram of the output port. In the simulation process, we use the materials and waveguide dimensions used in Example 1. It can be seen from the simulation diagram that the input LP 11b In mode, the output is 6 LPs with the same power. 11b model;

[0055] like Figure 6 As shown in (a), the LP input from the first input few-mode straight waveguide 11 of the mode-insensitive 3×6 optical power divider based on the MMI structure 01 and LP 11b The curve of the relationship between the mode output power and the wavelength shows that between 1500-1600nm, the output power fluctuates slightly with the wavelength, and the device is not sensitive to the wavelength.

[0056] like Figure 6 As shown in (b), the LP input from the second input few-mode straight waveguide 12 by the mode-insensitive 3×6 optical power divider based on the MMI structure 01 and LP 11b The curve of the relationship between the output power of the mode and the wavelength shows that between 1500-1600nm, the output power fluctuates slightly with the wavelength, and the device is not sensitive to the wavelength.

[0057] like Figure 6 As shown in (c), the LP input from the second input few-mode straight waveguide 12 by the mode-insensitive 3×6 optical power divider based on the MMI structure 01 and LP 11b The curve of the relationship between the output power of the mode and the wavelength shows that between 1500-1600nm, the output power fluctuates slightly with the wavelength, and the device is not sensitive to the wavelength.

[0058] Example 2

[0059] like Figure 3 As shown, the preparation method of the 3×6 optical power divider based on the MMI structure of the present invention comprises the following steps:

[0060] (1) Cleaning of silicon wafer substrate: Use cotton balls to absorb acetone solution, and use the cotton balls with acetone to wipe the silicon wafer substrate repeatedly for three times. Then use another cotton ball to absorb ethanol solution, and use the cotton balls with ethanol to wipe the silicon wafer substrate repeatedly for three times. After wiping clean, use deionized water to rinse the silicon wafer substrate repeatedly until it is clean. Finally, use nitrogen to blow dry the silicon wafer substrate, and then put it in a clean culture dish and seal it for storage.

[0061] (2) Preparation of polymer lower cladding: The waveguide lower cladding uses an organic polymer material EpoClad. The lower cladding polymer material is spin-coated on a cleaned silicon wafer substrate at a spin coating speed of 1800 rpm, baked at 120°C for 5 minutes, exposed as a whole for 18 seconds and baked again at 120°C for 5 minutes to obtain a polymer lower cladding with a thickness of 7 μm.

[0062] (3) Preparation of polymer optical waveguide core layer: The optical waveguide polymer core layer material is selected from the ultraviolet negative photoresist material EpoCore that can be etched by wet method. The polymer core layer material is spin-coated on the prepared polymer lower cladding layer by spin coating process. The spin coating speed is 2500 rpm. The thickness of the prepared polymer optical waveguide core layer film 23' is 8 μm. After the spin coating, the prepared polymer optical waveguide core layer film is pre-baked by a step-by-step heating method, that is, the device is first baked at 50°C for 5 minutes, and then baked at 95°C for 5 minutes. After the baking, the temperature is lowered. The prepared polymer optical waveguide core layer film 23' is subjected to plate-to-plate lithography. The ultraviolet light wavelength of the lithography machine is 365 nm. The light-transmitting part of the lithography mask is the polymer optical waveguide core layer 23 area to be prepared (such as Figure 1 (a)), when the photomask is in close contact with the silicon wafer, photolithography is performed, and the exposure time is 16 seconds, so that the polymer optical waveguide core layer 23 area to be prepared is exposed to ultraviolet light; the photolithographic silicon wafer is taken out from the photolithography machine for intermediate baking, that is, first baked at 50°C for 5 minutes, and then baked at 85°C for 15 minutes. After the baking is completed, the temperature is cooled down and the next step is performed after it drops to room temperature; the polymer optical waveguide core layer structure is developed, first wet-etched in Epo developer for 40 seconds to remove the unexposed non-optical waveguide core layer structure, and then the residual developer is removed by isopropanol solution, and the isopropanol solution is repeatedly rinsed along the waveguide direction with deionized water to remove the isopropanol solution, and then dried with nitrogen; finally, the film is post-baked, that is, baked at 125°C for 35 minutes, so that the preparation of the optical waveguide core layer with a strip structure is completed;

[0063] (4) Preparation of polymer upper cladding: The EpoClad polymer material was spin-coated on the silicon wafer with the optical waveguide core structure by spin coating process, the spin coating speed was 1100 rpm, baked at 120°C for 5 minutes, the whole was exposed for 28 seconds, and baked at 120°C for 5 minutes. The thickness of the polymer upper cladding above the waveguide core layer was 7 μm. Thus, a 3×6 optical power divider based on MMI structure that met the requirements was prepared.

[0064] It should be pointed out that the specific implementation methods proposed in the present invention are only representative examples of the present invention. Obviously, the technical solutions of the present invention include but are not limited to the above embodiments, and there may be more forms, such as using waveguide materials such as lithium niobate, silicon, and silicon nitride. And the design can be cascaded and expanded to achieve other power distribution functions. Those skilled in the art who have obtained the invention clearly disclosed or obtained without objection based on the written description of the document belong to the scope of protection of this patent.

Claims

1. A mode-insensitive 3×6 optical power divider based on an MMI structure, characterized in that: The structure is composed of a silicon wafer substrate (21), 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), wherein the polymer optical waveguide core layer (23) is completely covered in the polymer upper cladding (24); the polymer optical waveguide core layer (23) is based on four cascaded MMI optical waveguide structures and is a symmetrical structure with respect to the second input few-mode straight waveguide (12) and its extension line; the two-mode optical power input from the three input ports can be equally divided into power at the six output ports; from left to right along the transmission line of light In the propagation direction, the polymer optical waveguide core layer (23) is composed of a first input few-mode straight waveguide (11), a second input few-mode straight waveguide (12), a third input few-mode straight waveguide (13), a first input bent waveguide (14), a second input bent waveguide (15), a first input tapered waveguide (16), a second input tapered waveguide (17), a third input tapered waveguide (18), a first multimode interference waveguide (19), a first output tapered waveguide (110), a second output tapered waveguide (111), a third output tapered waveguide (112), a first connecting bent waveguide (113), a first connecting straight waveguide (114), a second connecting bent waveguide (115), a third connecting bent waveguide (116), and a fourth connecting bent waveguide. (117), a fourth input tapered waveguide (118), a second multimode interference waveguide (119), a fourth output tapered waveguide (120), a fifth output tapered waveguide (121), a fifth connecting curved waveguide (122), a sixth connecting curved waveguide (123), a seventh connecting curved waveguide (124), an eighth connecting curved waveguide (125), a second connecting straight waveguide (126), a third connecting straight waveguide (127), a fourth connecting straight waveguide (128), a fifth connecting straight waveguide (129), a fifth input tapered waveguide (130), a sixth input tapered waveguide (131), a seventh input tapered waveguide (132), an eighth input tapered waveguide (133), a third multimode interference waveguide (134), a fourth multimode The output cone waveguide (135) is composed of a first output cone waveguide (136), a second output cone waveguide (137), an eighth output cone waveguide (138), a ninth output cone waveguide (139), a tenth output cone waveguide (140), an eleventh output cone waveguide (141), a first output curved waveguide (142), a second output curved waveguide (143), a third output curved waveguide (144), a fourth output curved waveguide (145), a first output few-mode straight waveguide (146), a second output few-mode straight waveguide (147), a third output few-mode straight waveguide (148), a fourth output few-mode straight waveguide (149), a fifth output few-mode straight waveguide (150), and a sixth output few-mode straight waveguide (151); The first multimode interference waveguide (19) has three input ends and three output ends; the first input few-mode straight waveguide (11), the first input curved waveguide (14) and the first input tapered waveguide (16) are connected in sequence to serve as the first input end of the first multimode interference waveguide (1); the second input few-mode straight waveguide (12) and the second input tapered waveguide (17) are connected in sequence to serve as the second input end of the first multimode interference waveguide (1); the third input few-mode straight waveguide (13), the second input curved waveguide (15) and the third input tapered waveguide (18) are connected in sequence to serve as the third input end of the first multimode interference waveguide (1); and the first output tapered waveguide (110), the second output tapered waveguide (111) and the third output tapered waveguide (112) respectively serve as the three output ends of the first multimode interference waveguide (19); The second multimode interference waveguide (119) has an input end and two output ends; the second output tapered waveguide (111), the first connecting straight waveguide (114) and the fourth input tapered waveguide (118) are sequentially connected to serve as the input end of the second multimode interference waveguide (119); the fourth output tapered waveguide (120) and the fifth output tapered waveguide (121) respectively serve as the two output ends of the second multimode interference waveguide (119); The third multimode interference waveguide (134) and the fourth multimode interference waveguide (135) respectively have two input ends and three output ends; the first output tapered waveguide (110), the first connecting curved waveguide (113), the third connecting curved waveguide (116), the second connecting straight waveguide (126) and the fifth input tapered waveguide (130) are sequentially connected to serve as the first input end of the third multimode interference waveguide (134); the fourth output tapered waveguide (120), the fifth connecting curved waveguide (122), the seventh connecting curved waveguide (124), the fourth connecting straight waveguide (128) and the sixth input tapered waveguide (131) are sequentially connected to serve as the second input end of the third multimode interference waveguide (134); the fifth output tapered waveguide (121), the sixth connecting curved waveguide (123), the eighth connecting curved waveguide (125), the The fifth connecting straight waveguide (129) and the seventh input tapered waveguide (132) are connected in sequence to serve as the first input end of the fourth multimode interference waveguide (135); the third output tapered waveguide (112), the second connecting curved waveguide (115), the fourth connecting curved waveguide (117), the third connecting straight waveguide (127) and the eighth input tapered waveguide (133) are connected in sequence to serve as the second input end of the fourth multimode interference waveguide (135); the sixth output tapered waveguide (136), the seventh output tapered waveguide (137) and the eighth output tapered waveguide (138) are respectively used as the three output ends of the third multimode interference waveguide (134); the ninth output tapered waveguide (139), the tenth output tapered waveguide (140) and the eleventh output tapered waveguide (141) are respectively used as the three output ends of the fourth multimode interference waveguide (135); The sixth output tapered waveguide (136), the first output curved waveguide (142) and the first output few-mode straight waveguide (146) are connected in sequence; the seventh output tapered waveguide (137) and the second output few-mode straight waveguide (147) are connected in sequence; the eighth output tapered waveguide (138), the second output curved waveguide (143) and the third output few-mode straight waveguide (148) are connected in sequence; the ninth output tapered waveguide (139), the third output curved waveguide (144) and the fourth output few-mode straight waveguide (149) are connected in sequence; the tenth output tapered waveguide (140) and the fifth output few-mode straight waveguide (150) are connected in sequence; and the eleventh output tapered waveguide (141), the fourth output curved waveguide (145) and the sixth output few-mode straight waveguide (151) are connected in sequence.

2. A mode-insensitive 3×6 optical power divider based on an MMI structure as claimed in claim 1, characterized in that: The first input few-mode straight waveguide (11), the third input few-mode straight waveguide (13), the first output few-mode straight waveguide (146), the third output few-mode straight waveguide (148), the fourth output few-mode straight waveguide (149) and the sixth output few-mode straight waveguide (151) have the same structural dimensions, and their lengths a1 are 500 to 3000 μm and their widths w1 are 3 to 8 μm; the second input few-mode straight waveguide (12), the second output few-mode straight waveguide (147) and the fifth output few-mode straight waveguide (150) have the same structural dimensions, and their lengths a2 are 1000 to 5500 μm and their widths w1 are 3 to 8 μm; the first input curved waveguide (14), the second input curved waveguide (15), the first connecting curved waveguide (151) and the first connecting curved waveguide (152) are connected to the first curved waveguide (153) and the second connecting curved waveguide (154). The waveguide (113), the second connecting curved waveguide (115), the third connecting curved waveguide (116) and the fourth connecting curved waveguide (117) have the same structural dimensions, their width w1 is equal to 3 to 8 μm, their projection length a3 along the second input few-mode straight waveguide (12) and its extension line direction is equal to 1000 to 7000 μm, and the center distance gap1 between the input end and the output end is equal to 10 to 70 μm; the first input tapered waveguide (16), the third input tapered waveguide (18), the first output tapered waveguide (110) and the third output tapered waveguide (112) have the same structural dimensions, their length a4 is equal to 400 to 2000 μm, and their outer edges coincide with the outer edges of the first multimode interference waveguide (19). The width w2 of the connection with the first multimode interference waveguide (19) is equal to 8 to 15 μm, the width w1 of the connection between the first input curved waveguide (14) and the first input tapered waveguide (16), the width w1 of the connection between the second input curved waveguide (15) and the third input tapered waveguide (18), the width w1 of the connection between the first output tapered waveguide (110) and the first connecting curved waveguide (113), and the width w1 of the connection between the third output tapered waveguide (112) and the second connecting curved waveguide (115) are equal to 3 to 8 μm; the second input tapered waveguide (17) and the second output tapered waveguide (111) have the same structural dimensions, and their lengths a5 are equal to 500 to 2500 μm, which is equal to the first multimode interference waveguide (1 9) the width w3 of the connection is equal to 15 to 25 μm, the width w1 of the connection between the second input tapered waveguide (17) and the second input few-mode straight waveguide (12), and the width w1 of the connection between the second output tapered waveguide (111) and the first connecting straight waveguide (114) are equal to 3 to 8 μm; the length a6 of the first multimode interference waveguide (19) is 3000 to 9000 μm, and the width w4 is 30 to 90 μm; the length a7 of the first connecting straight waveguide (114) is 500 to 5000 μm, and the width w1 is 3 to 8 μm; the length a8 of the fourth input tapered waveguide (118) is 500 to 3000 μm, and the width w5 of the connection with the second multimode interference waveguide (119) is 9 to 25 μm;The length a9 of the second multimode interference waveguide (119) is 500-6000 μm, and the width w6 is 30-80 μm; the fourth output tapered waveguide (120) and the fifth output tapered waveguide (121) have the same structural dimensions, and the length a10 thereof is equal to 500-3000 μm, the width w7 at the connection with the second multimode interference waveguide (119) is equal to 9-22 μm, the gap between the outer edge and the outer edge of the second multimode interference waveguide (119) is equal to 0-6 μm, and the width w1 at the connection with the fifth connecting curved waveguide (122) and the sixth connecting curved waveguide (123) is equal to 3-8 μm; the fifth connecting curved waveguide (122) and the sixth connecting curved waveguide (123) are equal to the fifth connecting curved waveguide (122) and the sixth connecting curved waveguide (123) are equal to the fifth connecting curved waveguide (122) and the sixth connecting curved waveguide (123) are equal to the sixth connecting curved waveguide (123) and the fifth connecting curved waveguide (122) are equal to the sixth connecting curved waveguide (123). The connecting curved waveguide (123), the seventh connecting curved waveguide (124) and the eighth connecting curved waveguide (125) have the same structural dimensions, and their projected lengths a11 along the second input few-mode straight waveguide (12) and its extension line are equal to 1000-6000 μm, and the center spacing gap3 between the input end and the output end is equal to 10-60 μm; the second connecting straight waveguide (126) and the third connecting straight waveguide (127) have the same structural dimensions, and their lengths a12 are equal to 2000-12000 μm, and their widths w1 are 3-8 μm; the fourth connecting straight waveguide (128) and the fifth connecting straight waveguide (129) have the same structural dimensions, and their lengths a13 are equal to 5 The fifth input tapered waveguide (130), the eighth input tapered waveguide (133), the sixth output tapered waveguide (136), the eighth output tapered waveguide (138), the ninth output tapered waveguide (139) and the eleventh output tapered waveguide (141) have the same structural dimensions, and their lengths a14 are equal to 400 to 2000 μm, and their widths w8 at the connection points with the third multimode interference waveguide (134) and the fourth multimode interference waveguide (135) are equal to 8 to 18 μm, and their outer edges respectively coincide with the outer edges of the third multimode interference waveguide (134) and the fourth multimode interference waveguide (135); the sixth input tapered waveguide (131 ), the seventh input tapered waveguide (132), the seventh output tapered waveguide (137) and the tenth output tapered waveguide (140) have the same structural dimensions, their length a15 is equal to 450-2000 μm, the width w9 at the connection with the third multimode interference waveguide (134) and the fourth multimode interference waveguide (135) is equal to 9-20 μm, and the center coincides with the center position of the third multimode interference waveguide (134) and the fourth multimode interference waveguide (135); the third multimode interference waveguide (134) and the fourth multimode interference waveguide (135) have the same structural dimensions, their length a16 is equal to 3000-10000 μm, and the width w10 is equal to 30-100 μm;The first output curved waveguide (142), the second output curved waveguide (143), the third output curved waveguide (144) and the fourth output curved waveguide (145) have the same structural dimensions, and their projection lengths a17 along the second input few-mode straight waveguide (12) and its extension line are equal to 800-5000 μm, and the center spacing gap4 between the input end and the output end is equal to 5-50 μm.; 3. The mode-insensitive 3×6 optical power divider based on the MMI structure as claimed in claim 1, characterized in that: The thickness of the silicon wafer substrate (21) is 0.5-1 mm, the thickness of the polymer lower cladding layer (22) is 4-12 μm, the thickness of the polymer optical waveguide core layer (23) is 5-15 μm, and the thickness of the polymer upper cladding layer (24) on the polymer optical waveguide core layer (23) is 4-12 μm.

4. The mode-insensitive 3×6 optical power divider based on the MMI structure as claimed in claim 1, characterized in that: The material of the polymer lower cladding layer (22) and the polymer upper cladding layer (24) is one of polycarbonate, polyimide, polyethylene, polyester, polymethyl methacrylate, polystyrene, and EpoClad; the material of the polymer optical waveguide core layer (23) is one of EpoCore, SU-8 2002, and SU-8 2005.

5. A method for preparing a mode-insensitive 3×6 optical power divider based on an MMI structure according to any one of claims 1 to 4, wherein the steps are as follows: A: Cleaning of silicon wafer substrate The surface of the silicon wafer substrate (21) is repeatedly wiped with a cotton ball containing acetone for 2 to 3 times, and then repeatedly wiped with a cotton ball containing ethanol for 2 to 3 times. After wiping clean, the surface of the silicon wafer substrate (21) is repeatedly rinsed with deionized water until it is clean. Finally, the silicon wafer substrate (21) is blown dry with nitrogen, and placed in a clean culture dish and sealed for storage; B: Preparation of polymer lower cladding The polymer lower cladding layer is made of an organic polymer material with good transparency, and the polymer lower cladding layer material is spin-coated on a cleaned silicon wafer substrate (21) by a spin coating process, the spin coating speed is 1000-5000 rpm, and baked at 95-150° C. for 4-60 minutes; when the EpoClad material is used, the whole material needs to be exposed for 5-60 seconds after baking and then baked at 95-150° C. for 4-60 minutes; the polymer lower cladding layer (22) is obtained; C: Preparation of polymer optical waveguide core layer The polymer optical waveguide core layer material is spin-coated on the polymer lower cladding layer (22) by a spin coating process to obtain a polymer optical waveguide core layer film (23'), and the spin coating speed is 1000-6000 revolutions per minute; after the spin coating is completed, pre-baking is performed, that is, the device is baked at 50-150° C. for 4-40 minutes; after naturally cooling to room temperature, it is subjected to plate-alignment photolithography, the ultraviolet light wavelength of the photolithography machine is 350-400nm, the light-transmitting part of the photolithography mask is the region of the polymer optical waveguide core layer (23) to be prepared, the photolithography mask is closely attached to the silicon wafer substrate (21), and the exposure time is 5-50 seconds, so that the polymer optical waveguide core layer (23) to be prepared is formed. The region of the layer (23) is exposed to ultraviolet light; after the photolithography is completed, a medium bake is performed, that is, baking at a temperature of 50 to 150° C. for 5 to 40 minutes; after natural cooling to room temperature, development is performed, that is, wet etching is performed in a special developer corresponding to the polymer optical waveguide core layer material for 5 to 90 seconds to remove the unexposed polymer optical waveguide core layer material, and then the residual developer is removed by an isopropanol solution, and the isopropanol solution is repeatedly rinsed along the waveguide direction with deionized water to remove the isopropanol solution, and then dried with nitrogen; finally, a post-baking is performed to harden the film, that is, baking at a temperature of 120 to 150° C. for 20 to 60 minutes, thereby preparing a polymer optical waveguide core layer on the polymer lower cladding (22); D: Preparation of polymer upper cladding The polymer upper cladding material is spin-coated on the polymer optical waveguide core layer (23) and the polymer lower cladding (22) by a spin coating process, the spin coating speed is 1000 to 5000 rpm, and the material is baked at 95 to 150° C. for 4 to 120 minutes to obtain a polymer upper cladding (24), thereby completing the preparation of a mode-insensitive 3×6 optical power distributor based on an MMI structure.

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