A hybrid integrated space division multiplexer based on 3D printing

Abstract

The application relates to the technical field of optical communication devices, in particular to a hybrid integrated space division multiplexer based on 3D printing, which comprises a single-mode array waveguide, a mode multiplexer / demultiplexer, a 3D printed few-mode waveguide and a multicore few-mode optical fiber connected in sequence and used for realizing energy coupling of multiple modes between the single-mode array waveguide and the cores of the multicore few-mode optical fiber; the mode multiplexer / demultiplexer couples the energy of a fundamental mode in the single-mode array waveguide into high-order modes of the 3D printed few-mode waveguide, and the 3D printed few-mode waveguide further couples the energy into each core of the multicore few-mode optical fiber; the single-mode array waveguide, the mode multiplexer / demultiplexer and the 3D printed few-mode waveguide are integrally printed by a 3D two-photon printing technology. The space division multiplexer integrates the functions of a mode multiplexer and a space division fan-in / fan-out device, has the characteristics of high integration, polarization multiplexing and high efficiency, reduces the difficulty of the overall device, and meets the actual needs in the fields of optoelectronic communication and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of optical communication devices, and more particularly to a hybrid integrated space division multiplexer based on 3D printing. Background Art

[0002] With the increasing demand for transmission capacity in optical transmission systems, traditional methods for increasing optical transmission system capacity, such as high-order modulation formats, digital coherent reception, and polarization multiplexing, have already reached their limits in terms of the amplitude, frequency, phase, and polarization of light. Currently, new multiplexing dimensions, utilizing both the mode and the fiber core, are being applied. These new multiplexing dimensions can break through the capacity limits of single-mode fiber and address the capacity issues of current optical transmission systems. With the development of mode-division multiplexing and core-division multiplexing systems, a more dimensional space-division multiplexing system has emerged: the few-mode multi-core transmission system. The transmission medium of this system is primarily few-mode multi-core fiber.

[0003] Through few-mode multi-core multiplexing technology, multi-core multiplexing technology is combined with few-mode multiplexing technology. Few-mode multi-core multiplexing primarily relies on few-mode multi-core fiber as the transmission medium. The cladding of a few-mode multi-core fiber contains multiple few-mode cores, each capable of transmitting multiple LP modes (linear polarization). The advantages of few-mode multi-core fiber are significant, including: 1. Its capacity is equivalent to multiplying the number of cores by the number of modes, and its spectral efficiency far exceeds the transmission capacity of current single-mode fiber. 2. It balances the crosstalk damage and refractive index design difficulties associated with mode multiplexing in few-mode fiber with the fiber setup and manufacturing difficulties associated with multi-core fiber. This reduces the difficulty of further improving mode multiplexing and core multiplexing while ensuring increased transmission capacity. Under the same spatial channel, it can also reduce the requirements for receiver MIMO-DSP (Multiple Input Multiple Output Digital Signal Processing) equalization processing. Combining multiple dimensions, such as mode multiplexing, fiber core multiplexing, wavelength division multiplexing, and polarization multiplexing, will further exceed the capacity of traditional optical transmission systems. Problems with few-mode, multi-core multiplexing systems include: 1. Mode multiplexing components have poor compatibility with 3D-printed few-mode waveguides; 2. Mode multiplexing components and 3D-printed few-mode waveguides increase the complexity of space-division multiplexing components. 3. Due to the high complexity and large size of mode multiplexing components and 3D-printed few-mode waveguides, device integration and compatibility are more difficult. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiency of the existing optical fiber multiplexer that is not compatible with core multiplexing and mode multiplexing, and to provide a hybrid integrated space division multiplexer based on 3D printing that is compatible with both core multiplexing and mode multiplexing.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A 3D-printed hybrid integrated space-division multiplexer is provided, comprising a single-mode array waveguide, a mode multiplexer / demultiplexer, a 3D-printed few-mode waveguide, and a multi-core few-mode optical fiber connected in sequence, for achieving energy coupling of multiple modes between the single-mode array waveguide and the cores of the multi-core few-mode optical fiber; the mode multiplexer / demultiplexer couples the energy of the fundamental mode in the single-mode array waveguide to the higher-order modes of the 3D-printed few-mode waveguide, and the 3D-printed few-mode waveguide then couples the energy to the individual cores of the multi-core few-mode optical fiber; the single-mode array waveguide, the mode multiplexer / demultiplexer, and the 3D-printed few-mode waveguide are integrally printed using 3D two-photon printing technology.

[0007] The present invention discloses a hybrid integrated space division multiplexer based on 3D printing, comprising a single-mode array waveguide, a mode multiplexer / demultiplexer, and a 3D-printed few-mode waveguide connected between the mode multiplexer / demultiplexer and the multi-core few-mode optical fiber, for realizing energy coupling of multiple modes between the core of the multi-core few-mode optical fiber and the single-mode array waveguide. The mode multiplexer / demultiplexer can couple the energy of the fundamental mode into the higher-order mode of the 3D-printed few-mode waveguide, and then use the 3D-printed few-mode waveguide to couple the energy into each core of the multi-core few-mode optical fiber. The single-mode array waveguide, the mode multiplexer / demultiplexer, and the 3D-printed few-mode waveguide are integrally printed and formed by 3D two-photon printing technology, and have a high degree of integration. The space division multiplexer of the present invention integrates the functions of the mode multiplexer and the space division fan-in and fan-out devices, and has the characteristics of high integration, polarization multiplexing, high efficiency, etc., which reduces the difficulty of the overall device and meets the actual needs of optoelectronic communications and other fields.

[0008] Furthermore, the mode multiplexer / demultiplexer includes a tapered coupler or a sub-wavelength grating waveguide.

[0009] Furthermore, the tapered coupler includes a first tapered waveguide and a second tapered waveguide; energy in the first tapered waveguide can be coupled to the second tapered waveguide to perform mode conversion.

[0010] Furthermore, the length of the first tapered waveguide is smaller than the length of the second tapered waveguide; the diameter of the larger end of the first tapered waveguide is smaller than the diameter of the larger end of the second tapered waveguide, and the diameter of the smaller end of the first tapered waveguide is smaller than the diameter of the smaller end of the second tapered waveguide.

[0011] Furthermore, along the direction of energy propagation, the diameter of the first tapered waveguide gradually decreases from 2um to 4um to 1um to 2um; the diameter of the second tapered waveguide gradually increases from 2um to 5um to 3.5um to 6.5um; the interval between the first tapered waveguide and the second tapered waveguide is 0um to 0.6um; the length of the coupling region between the first tapered waveguide and the second tapered waveguide is 0.2um to 2um.

[0012] Furthermore, the sub-wavelength grating waveguide includes a rectangular waveguide and a sub-wavelength grating etched on the rectangular waveguide.

[0013] Furthermore, the refractive index of the rectangular waveguide is 2 to 2.5; the duty cycle of the sub-wavelength grating is 0.4 to 0.6, and the grating period is 0.3um to 0.5um; the width of the sub-wavelength grating waveguide is 0.3um to 2um, and the height is 0.3um to 2um.

[0014] Furthermore, the 3D printed few-mode waveguide is obtained by the following steps:

[0015] Using waveguide mode analysis theory, calculate the number of modes that can be supported in the waveguide and the effective refractive index difference between the modes;

[0016] Determine the core and cladding materials of the optical waveguide, and use the fiber waveguide perturbation theory to adjust the processing materials and structural parameters of the waveguide to reduce the inter-mode coupling coefficient of the waveguide;

[0017] Based on the desired transmission mode, the geometric parameters of the free-form surface reflector are optimized using a wavefront matching inverse design algorithm to obtain the final reflective surface profile of the 3D-printed few-mode waveguide.

[0018] Finally, the preparation of 3D printed few-mode waveguides was realized based on 3D two-photon printing technology.

[0019] Furthermore, the wavefront matching inverse design algorithm is based on the beam diffraction propagation model, and realizes the optimal design of the phase plane by minimizing the wavefront error of the input and output light fields at a fixed position, so that the light field overlap integral is maximized when the input light field passes through the free-form surface reflection surface and the output light field propagates to the same position; after obtaining the corresponding phase plane, the surface fitting phase method is used to obtain the final reflective surface profile, that is, the final structural shape of the 3D printed few-mode waveguide.

[0020] Furthermore, the refractive index of the optical waveguide core is 1.3-1.7, and the refractive index of the cladding material is smaller than the refractive index of the optical waveguide core.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention discloses a hybrid integrated space division multiplexer based on 3D printing, which integrates the functions of a mode multiplexer and a space division fan-in and fan-out device. It has the characteristics of high integration, polarization multiplexing and high efficiency, reduces the difficulty of the overall device, and meets the actual needs of optoelectronic communications and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the structure of a hybrid integrated space division multiplexer based on 3D printing;

[0024] Figure 2 Schematic diagram of the structure of the tapered coupler from a first perspective in Example 1;

[0025] Figure 3 2. It is a schematic structural diagram of the tapered coupler from a second perspective in Example 1;

[0026] Figure 4 This is an image of the light field energy in the first tapered waveguide gradually coupled into the second tapered waveguide through the tapered coupling region in Example 1;

[0027] Figure 5 Schematic diagram of the structure of the subwavelength grating waveguide and 3D printed few-mode waveguide prepared in Example 2;

[0028] Figure 6 This is an image of the light field energy gradually coupled from the subwavelength grating waveguide to the 3D-printed few-mode waveguide in Example 2;

[0029] Figure 7 This is the mode field image output from the 3D-printed few-mode waveguide in Example 2;

[0030] Figure 8 This is an image of the light path reflected by the designed free-form reflection surface in Example 3;

[0031] Figure 9 Schematic diagram of the phase and profile of the reflective surface designed in Example 3;

[0032] Figure 10 Schematic diagram of the design process of 3D printed few-mode waveguide in Example 3.

[0033] In the accompanying drawings: 1. Single-mode array waveguide; 2. Mode multiplexer / demultiplexer; 21. Tapered coupler; 211. First tapered waveguide; 212. Second tapered waveguide; 22. Subwavelength grating waveguide; 3. 3D-printed few-mode waveguide; 4. Multi-core few-mode optical fiber. DETAILED DESCRIPTION

[0034] The present invention is further described below with reference to specific embodiments. The accompanying drawings are for illustrative purposes only and are schematic, not actual, representations. They should not be construed as limiting this patent. To better illustrate the embodiments of the present invention, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted from the drawings.

[0035] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right" and the like indicate directions or positional relationships based on the directions or positional relationships shown in the drawings, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting this patent. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0036] Example 1

[0037] This embodiment is a first embodiment of a hybrid integrated space division multiplexer based on 3D printing. Figure 1 As shown, it includes a single-mode array waveguide 1, a mode multiplexer / demultiplexer 2, a 3D-printed few-mode waveguide 3 and a multi-core few-mode optical fiber 4 connected in sequence, which are used to realize energy coupling of multiple modes between the single-mode array waveguide 1 and the cores of the multi-core few-mode optical fiber 4; the mode multiplexer / demultiplexer 2 couples the energy of the fundamental mode in the single-mode array waveguide 1 to the high-order mode of the 3D-printed few-mode waveguide 3, and the 3D-printed few-mode waveguide 3 then couples the energy to each core of the multi-core few-mode optical fiber 4; the single-mode array waveguide 1, the mode multiplexer / demultiplexer 2 and the 3D-printed few-mode waveguide 3 are integrally printed by 3D two-photon printing technology.

[0038] This embodiment proposes a hybrid integrated space division multiplexer based on 3D printing, which integrates the functions of three parts: a mode multiplexer and a 3D printed few-mode waveguide. The design of the mode multiplexer / demultiplexer 2 is based on the principle of evanescent wave coupling. When a light wave propagates to an interface in a medium, if the incident angle is greater than the critical angle, the light wave cannot completely penetrate the interface, but will form an attenuated electromagnetic wave near the interface. This wave is called an evanescent wave. The intensity of the evanescent wave decreases rapidly with increasing distance from the interface. In a waveguide, when two waveguides are very close, the evanescent wave will couple between the two waveguides. Through proper design, the field of the evanescent wave can be generated in one waveguide and coupled in another waveguide.

[0039] In this embodiment, a structure for a mode multiplexer / demultiplexer 2 is provided. In this embodiment, the waveguide structure of the mode multiplexer / demultiplexer 2 is printed using 3D two-photon printing technology. A nearly adiabatic taper is introduced into one or both waveguides. If the device's cross-section changes slowly enough, power transfer occurs between the waveguides as long as the propagation constants of the modes intersect somewhere along the taper. The advantage of using 3D two-photon printing for waveguide printing lies in its ability to create arbitrary 3D structures by using nonlinear multiphoton polymerization, which uses a pulsed laser to tightly focus a volume of photosensitive resin. By scanning the laser focus in three dimensions, arbitrary 3D structures can be created. This direct and powerful 3D structure fabrication capability enables tasks that are difficult or impossible with traditional photolithography techniques. Compared to laser-etched waveguides on glass platforms, 3D-printed waveguides can be fabricated on a variety of materials and substrates and integrated into photonic circuits, enabling compact and efficient designs for a wide range of optical applications. This wider range of materials allows for the creation of waveguides with a wide refractive index contrast. The photoresist material used has a refractive index between 1.3 and 1.7.

[0040] like Figure 2 and Figure 3 As shown, the mode multiplexer / demultiplexer 2 is a tapered coupler 21, which includes a first tapered waveguide 211 and a second tapered waveguide 212; the energy in the first tapered waveguide 211 can be coupled to the second tapered waveguide 212 for mode conversion.

[0041] The length of the first tapered waveguide 211 is smaller than the length of the second tapered waveguide 212. The diameter of the larger end of the first tapered waveguide 211 is smaller than the diameter of the larger end of the second tapered waveguide 212. The diameter of the smaller end of the first tapered waveguide 211 is smaller than the diameter of the smaller end of the second tapered waveguide 212. The size of the first tapered waveguide 211 is smaller than that of the second tapered waveguide 212. The size of the waveguide gradually changes along the propagation direction, and energy is gradually coupled into the second tapered waveguide 212 along the slowly changing taper. Figure 4 shown.

[0042] In this embodiment, PDMS with a refractive index of 1.379 is used as a cladding material on the outside of the first tapered waveguide 211 and the second tapered waveguide 212; along the energy propagation direction, the diameter of the first tapered waveguide 211 gradually decreases from 2um to 4um to 1um to 2um; the diameter of the second tapered waveguide 212 gradually increases from 2um to 5um to 3.5um to 6.5um; the interval between the first tapered waveguide 211 and the second tapered waveguide 212 is 0um to 0.6um; the length of the coupling region between the first tapered waveguide 211 and the second tapered waveguide 212 is 0.2um to 2um.

[0043] Example 2

[0044] This embodiment is a second embodiment of a hybrid integrated space division multiplexer based on 3D printing. This embodiment is similar to the first embodiment, except that, in this embodiment, the mode multiplexer / demultiplexer 2 is a subwavelength grating waveguide 22. This embodiment utilizes the waveguide structure of the subwavelength grating to regulate the refractive index of the on-chip waveguide. A subwavelength grating is a special photonic structure whose periodic structure is much smaller than the wavelength of the light wave. The design and application of this structure are based on the physical principles of the interaction between light and matter, especially when the wavelength of light is much larger than the grating period. The "subwavelength" feature of a subwavelength grating refers to the fact that the size of its periodic structure (period Λ) is less than a small fraction of the wavelength of the operating light wave (λ). This generally means that the period Λ is much smaller than λ, so that the light wave cannot resolve the periodic structure of the grating, thereby suppressing the diffraction effect. Because the grating period is much smaller than the wavelength of the light wave, the light wave does not see a periodic structure, but rather an effectively homogeneous medium. This medium has an equivalent refractive index that can be adjusted by designing the grating parameters. By controlling the refractive index of the on-chip waveguide using a subwavelength grating structure, the refractive index of the on-chip waveguide can be made close to that of the 3D printed few-mode waveguide 3, thereby coupling the energy transmitted in the on-chip waveguide into the 3D printed few-mode waveguide 3.

[0045] This embodiment uses the As20S80 rectangular waveguide as an example. Its refractive index is about 2.2, while the refractive index of the material of the 3D printed few-mode waveguide 3 is selected as 1.53. Due to the large difference in refractive index between the rectangular waveguide and the photoresist waveguide, this embodiment uses the method of etching a subwavelength grating in the rectangular waveguide to reduce the refractive index of the rectangular waveguide to achieve phase matching conditions between the subwavelength grating waveguide 22 and the 3D printed few-mode waveguide 3. In this embodiment, the refractive index of the rectangular waveguide is 2 to 2.5; the duty cycle of the subwavelength grating is 0.4 to 0.6, and the grating period is 0.3um to 0.5um; the width of the subwavelength grating waveguide 22 is 0.3um to 2um, and the height is 0.3um to 2um. The equivalent refractive index of the waveguide is calculated using the equivalent refractive index formula:

[0046]

[0047] Where n2 is the refractive index of the silica cladding material, which is 1.444 in this embodiment. The equivalent refractive index of the subwavelength grating waveguide 22 is 1.86, which allows the core layer of the subwavelength grating waveguide 22 to be equivalent to a material with a uniform refractive index distribution, and the refractive index of the equivalent material is 1.86. Based on FDTD, a two-dimensional model is established, setting the cladding material to silica and the core material to the subwavelength grating equivalent medium, with a material refractive index of 1.86. The effective refractive index of the TE1 mode of the subwavelength grating waveguide 22 is estimated to be 1.496, which exactly matches the effective refractive index of the TE2 mode in the 3D-printed few-mode waveguide 3, meeting the phase matching condition, and enabling mode coupling from the on-chip subwavelength grating waveguide 22 to the 3D-printed few-mode waveguide 3.

[0048] like Figure 5 As shown in the figure, the light field undergoes the following process in the designed mode multiplexer / demultiplexer 2: A) the light field propagating in the waveguide is modulated by the periodic structure of the subwavelength grating; B) at this time, the subwavelength grating waveguide 22 can be equivalent to a dielectric waveguide with a uniform refractive index distribution. Since the modulated refractive index is close to that of the 3D printed few-mode waveguide 3, the light field energy is gradually coupled into the 3D printed few-mode waveguide 3; C) the coupled light field energy continues to be transmitted in the waveguide of the 3D printed few-mode waveguide 3, realizing mode conversion. Figure 6 and Figure 7 , showing the conversion process of the light field coupled from the subwavelength grating waveguide 22 to the waveguide of the 3D printed few-mode waveguide 3 and the final mode field output by the 3D printed few-mode waveguide 3.

[0049] Example 3

[0050] This embodiment is a third embodiment of a hybrid integrated space division multiplexer based on 3D printing. This embodiment is similar to the first embodiment, except that this embodiment provides a design and preparation method for a multi-core fan-in and fan-out.

[0051] In this embodiment, in the 3D printed few-mode waveguide 3, a free-formed curved reflector is used to realize the connection between the high-order mode from the mode multiplexer / demultiplexer 2 to the multi-core few-mode fiber 4. Figure 10As shown, the propagation direction of the light beam is redirected based on total internal reflection, and the iterative phase surface is precisely fabricated using 3D two-photon printing technology. Based on a beam diffraction propagation model, the phase surface is optimized by minimizing the wavefront error between the input and output light fields at a fixed location. This maximizes the field overlap integral when the input light field propagates back to the same location after passing through the free-form reflective surface, improving coupling efficiency and mode purity. This improves the compactness of the waveguide structure in 3D-printed few-mode waveguides. The smaller size of the waveguide structure reduces light loss during transmission and improves optical signal transmission efficiency. The design of the photoresist material for the waveguide requires comprehensive consideration of the refractive index and optical properties of the waveguide core and cladding materials, as well as the fabrication process. Waveguide mode analysis theory is used to analyze the number of modes supported within the waveguide and the effective refractive index difference between the modes. Fiber waveguide perturbation theory is then used to adjust the waveguide's processing materials and structural parameters to reduce the waveguide's inter-mode coupling coefficient. The wavefront matching inverse algorithm is based on the fundamental idea that when a light field propagates in free space, the forward propagating light field at any point in space should be consistent with the reverse propagating field from the receiving surface to the same position. Therefore, after setting the input and output fields in the system, the goal is to add a reasonable phase modulation plane to the system and modify the light field path so that the input and output fields at each point in the system space are ultimately consistent. The input field is converted into the output field after passing through multiple phase planes. A free-form surface reflector is used to redirect the beam propagation direction and adapt the beam mode field. The geometric parameters of the free-form surface reflector are optimized using the wavefront matching inverse design algorithm. Finally, the 3D printed few-mode waveguide 3 is fabricated using 3D two-photon printing technology.

[0052] Specifically, in terms of the 3D printed few-mode waveguide 3 functions, based on femtosecond laser processing, a connecting waveguide from the on-chip waveguide to the multi-core few-mode optical fiber 4 is prepared. This embodiment comprehensively considers the refractive index and optical properties of the waveguide core and cladding materials, and the preparation process to select the photoresist material for processing the optical waveguide. For example, the refractive index of the waveguide core can be selected to be about 1.53, and the refractive index of the cladding can be selected to be about 1.379. The waveguide mode analysis theory is used to calculate the number of modes that can be supported in the waveguide and the effective refractive index difference between the modules. Based on the mode to be transmitted, the geometric parameters of the free-form surface reflector are optimized by the wavefront matching inverse design algorithm; wherein the wavefront matching algorithm is based on the beam diffraction propagation model, and the phase plane is optimized by minimizing the wavefront error of the input and output light fields at a fixed position, so that the input light field is maximized when it propagates backward to the same position with the output light field after passing through the free-form surface reflection surface. Figure 9 As shown in FIG, after obtaining the corresponding phase plane, the final reflection surface profile can be obtained by using the surface fitting phase method. Preferably, the optimized reflection surface is close to a perfect parabola.

[0053] The final space division multiplexing device is as follows Figure 1 As shown, the light field transmitted in the single-mode array waveguide 1, composed of seven single-mode waveguides, is coupled to the 3D-printed few-mode waveguide 3 using a tapered coupler 21 or a subwavelength grating waveguide 22 to achieve mode conversion. The multi-core few-mode fiber 4 is a seven-core fiber. The mode field energy emitted by the mode multiplexer / demultiplexer 2 is coupled to the seven-core multi-core few-mode fiber 4 through the free-reflection curved waveguide of the 3D-printed few-mode waveguide 3.

[0054] In the specific contents of the above-mentioned specific implementation methods, the various technical features can be combined in any non-contradictory manner. In order to make the description concise, not all possible combinations of the above-mentioned technical features are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0055] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A hybrid integrated space division multiplexer based on 3D printing, characterized in that: The invention comprises a single-mode array waveguide (1), a mode multiplexer / demultiplexer (2), a 3D printed few-mode waveguide (3) and a multi-core few-mode optical fiber (4) connected in sequence, and is used to realize energy coupling of multiple modes between the single-mode array waveguide (1) and the cores of the multi-core few-mode optical fiber (4); the mode multiplexer / demultiplexer (2) couples the energy of the fundamental mode in the single-mode array waveguide (1) to the high-order mode of the 3D printed few-mode waveguide (3), and the 3D printed few-mode waveguide (3) then couples the energy to each core of the multi-core few-mode optical fiber (4); the single-mode array waveguide (1), the mode multiplexer / demultiplexer (2) and the 3D printed few-mode waveguide (3) are integrally printed and formed by 3D two-photon printing technology; wherein: The 3D printed few-mode waveguide (3) is obtained by the following steps: using the waveguide mode analysis theory to calculate the number of modes that can be supported in the waveguide and the effective refractive index difference between the modules; determining the optical waveguide core and cladding materials; based on the mode to be transmitted, optimizing the geometric parameters of the free-form surface reflector by the wavefront matching inverse design algorithm to obtain the final reflection surface profile of the 3D printed few-mode waveguide (3); finally, realizing the preparation of the 3D printed few-mode waveguide (3) based on the 3D two-photon printing technology; The wavefront matching inverse design algorithm is based on the beam diffraction propagation model, and realizes the optimal design of the phase plane by minimizing the wavefront error of the input and output light fields at a fixed position, so that the light field overlap integral is maximized when the input light field propagates to the same position after passing through the free-form surface reflection surface and the output light field; after obtaining the corresponding phase plane, the surface fitting phase method is used to obtain the final reflection surface profile, that is, the final structural shape of the 3D printed few-mode waveguide (3).

2. The hybrid integrated space division multiplexer based on 3D printing according to claim 1, characterized in that: The mode multiplexer / demultiplexer (2) includes a tapered coupler (21) or a sub-wavelength grating waveguide (22).

3. The hybrid integrated space division multiplexer based on 3D printing according to claim 2, characterized in that: The tapered coupler (21) comprises a first tapered waveguide (211) and a second tapered waveguide (212); energy in the first tapered waveguide (211) can be coupled to the second tapered waveguide (212) to perform mode conversion.

4. The hybrid integrated space division multiplexer based on 3D printing according to claim 3, characterized in that: The length of the first tapered waveguide (211) is smaller than the length of the second tapered waveguide (212); the diameter of the larger end of the first tapered waveguide (211) is smaller than the diameter of the larger end of the second tapered waveguide (212); and the diameter of the smaller end of the first tapered waveguide (211) is smaller than the diameter of the smaller end of the second tapered waveguide (212).

5. The hybrid integrated space division multiplexer based on 3D printing according to claim 4, characterized in that: Along the energy propagation direction, the diameter value of the first tapered waveguide (211) gradually decreases from 2um to 4um to 1um to 2um; the diameter value of the second tapered waveguide (212) gradually increases from 2um to 5um to 3.5um to 6.5um; the interval between the first tapered waveguide (211) and the second tapered waveguide (212) is 0um to 0.6um; and the length value of the coupling region between the first tapered waveguide (211) and the second tapered waveguide (212) is 0.2um to 2um.

6. The hybrid integrated space division multiplexer based on 3D printing according to claim 2, characterized in that: The sub-wavelength grating waveguide (22) comprises a rectangular waveguide and a sub-wavelength grating etched on the rectangular waveguide.

7. The hybrid integrated space division multiplexer based on 3D printing according to any one of claims 1 to 6, characterized in that: The refractive index of the rectangular waveguide is 2-2.5; the duty cycle of the sub-wavelength grating is 0.4-0.6, and the grating period is 0.3um-0.5um; the width of the sub-wavelength grating waveguide is 0.3um-2um, and the height is 0.3um-2um.

8. The hybrid integrated space division multiplexer based on 3D printing according to claim 7, characterized in that: The refractive index of the optical waveguide core is 1.3-1.7, and the refractive index of the cladding material is smaller than the refractive index of the optical waveguide core.

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