Few-mode fiber and silicon-based multimode chip coupling structure and preparation method

Abstract

The application discloses a few-mode optical fiber and a silicon-based multi-mode chip coupling structure and a preparation method, and belongs to the technical field of optical elements, systems or instruments. The coupling structure comprises a silicon-based multi-mode chip, a few-mode optical fiber, a few-mode photonic wire bonding waveguide and a fiber base. The silicon-based multi-mode chip comprises a silicon substrate, a buried oxygen layer, a silicon-based waveguide, an upper cladding layer and an inverted cascade tapered waveguide with a subwavelength grating and an alignment mark. The few-mode optical fiber comprises a core and a cladding. The few-mode photonic wire bonding waveguide comprises a square waveguide above the inverted cascade tapered waveguide with a subwavelength grating, a transition waveguide and a curved waveguide. The fiber base is a stepped base used for fixing the positions of the chip and the optical fiber. The silicon-based multi-mode chip is connected with the few-mode optical fiber through the few-mode coupling structure composed of the upper few-mode photonic wire bonding waveguide and the lower inverted cascade tapered waveguide with a subwavelength grating, the mode hybridization effect is enhanced, and the silicon-based rectangular vector mode is matched with the circular linear polarization mode of the few-mode optical fiber.

Description

TECHNICAL FIELD

[0001] The application discloses a few-mode fiber and a silicon-based multi-mode chip coupling structure and a preparation method, relates to integrated optoelectronic device technology, and belongs to the technical field of optical elements, systems or instruments. BACKGROUND

[0002] With the development of optical communication technology, it is very important to improve the capacity of optical communication transmission. In recent years, a very promising technology, mode division multiplexing (MDM) technology, has attracted widespread attention. The orthogonal eigenmodes in the few-mode fiber are used as transmission channels, which opens up a new dimension for multiplexing of optical communication systems and can realize optical transmission of the order of Pb / s, becoming a key technology for building future optical networks. The mode control chip based on silicon-based optoelectronic technology plays an important role in building MDM optical networks.

[0003] The silicon-based optoelectronic integrated chip uses silicon optical technology to integrate a plurality of micro-nano optical devices or optoelectronic devices on a silicon substrate to form a complete new large-scale integrated chip with comprehensive functions, and has the advantages of high performance, low cost and high integration. 2 However, the mode in the few-mode fiber is a circular linear polarization (LP) mode, and the mode field size is greater than 80 mu m 2 . There are differences in mode type and mismatch in mode field size between the two, which makes it difficult to couple the fiber and the silicon-based optoelectronic chip.

[0004] At present, the coupling of the silicon-based multi-mode waveguide and the few-mode fiber mainly includes horizontal coupling and vertical coupling. The horizontal coupling scheme makes the chip waveguide and the fiber in a parallel position, and the alignment tolerance is small, so high-precision alignment between the two is particularly important. Moreover, the chip end face needs to be ground and polished, which increases the process complexity. In addition, the horizontal coupling scheme cannot support vertical modes, greatly limiting the number of coupled modes. The vertical coupling scheme is realized based on a grating coupler, and the fiber can be coupled at any position on the chip surface. However, this scheme has the problems of narrow operating bandwidth, large polarization dependence, phase sensitivity, and limited number of supported modes, which makes it difficult to meet the transmission requirements of MDM.

[0005] The application provides a few-mode fiber and a silicon-based multi-mode chip coupling structure, which can match the silicon-based rectangular vector mode and the LP mode of the few-mode fiber, solve the mode difference and size mismatch between the silicon-based multi-mode waveguide and the few-mode fiber, and have the characteristics of multi-mode, low loss and low temperature sensitivity. SUMMARY

[0006] The application aims at solving the problems of the mismatch of mode and size and temperature sensitivity between the silicon-based multimode chip and the few-mode fiber.

[0007] The application adopts the following technical scheme to achieve the above-mentioned application purposes: a few-mode fiber and silicon-based multimode chip coupling structure, comprising: an upper-layer FM-PWB waveguide and a lower-layer SWG-ICT waveguide prepared on a buried oxygen layer of the silicon-based multimode chip; the upper-layer FM-PWB waveguide is used for connecting the silicon-based multimode chip and the few-mode fiber, and converting a silicon-based rectangular waveguide vector into a circular linear polarization vector mode; the lower-layer SWG-ICT waveguide is coupled with the few modes of the upper-layer FM-PWB waveguide, and the lower-layer subwavelength grating inverted cascaded tapered waveguide is a subwavelength grating formed by at least two tapered waveguide cascades with gradually decreasing widths; the silicon-based waveguide of the silicon-based multimode chip is embedded in the lower-layer subwavelength grating inverted cascaded tapered waveguide through the tapered structure connected to the light-in and light-out ends.

[0008] As a further optimization scheme of the few-mode fiber and silicon-based multimode chip coupling structure, the upper-layer FM-PWB waveguide is composed of a square waveguide, a square-to-circular transition waveguide and a curved waveguide connected to the core of the fiber, the square waveguide is a square structure with equal width and height, the transition waveguide is a square-to-circular prismatic transition structure, the curved waveguide is a circular structure with gradually increasing diameter, the square waveguide is covered above the silicon-based waveguide and the lower-layer SWG-ICT waveguide, one end of the square waveguide is covered above the light-in and light-out ends of the silicon-based waveguide, the other end of the square waveguide is connected to the square port of the transition waveguide, the circular port of the transition waveguide is connected to the small-diameter circular port of the curved waveguide, the large-diameter circular port of the curved waveguide is connected to the few-mode fiber, and the start and end directions of the curved waveguide axis coincide with the waveguide axis of the fiber core.

[0009] As a further optimization scheme of the few-mode fiber and silicon-based multimode chip coupling structure, the few-mode fiber comprises a fiber core and a fiber cladding. One end of the fiber core is connected to the large-diameter circular port of the curved waveguide in the upper-layer FM-PWB waveguide, so as to realize the connection between the small-size square waveguide and the large-size circular fiber.

[0010] As a further optimization scheme of the few-mode fiber and the silicon-based multimode chip coupling structure, the few-mode fiber and the silicon-based multimode chip coupling structure are fixed on a fiber base, and the fiber base is used to fix the positions of the silicon-based multimode chip and the few-mode fiber; the shape of the fiber base can also be designed as a stepped shape to compensate for the height difference between the silicon-based multimode chip and the few-mode fiber, avoid the coupling loss caused by vibration or angle problems, and maximize the efficiency of optical communication.

[0011] As a further optimization scheme of the few-mode fiber and the silicon-based multimode chip coupling structure, the silicon-based multimode chip comprises a silicon substrate, a buried oxygen layer, a silicon-based waveguide, an upper cladding layer, a lower SWG-ICT waveguide, and an alignment mark; the shape of the alignment mark can be a cross mark or a square mark, etc., the position of the alignment mark is symmetrical about the lower SWG-ICT waveguide, and the number of the alignment mark can be two or three, which is determined according to the specific chip size.

[0012] As a further optimization scheme of the few-mode fiber and the silicon-based multimode chip coupling structure, a low refractive index material is covered above the upper FM-PWB waveguide, and the refractive index of the material must be lower than that of the upper FM-PWB waveguide. The square waveguide and the buried oxygen layer have different material refractive indexes, forming an asymmetric structure, which induces an enhanced mode hybridization effect, so that the silicon-based rectangular waveguide vector mode is converted into an upper FM-PWB square vector mode; then, the upper FM-PWB square vector mode is converted into a circular vector mode through a transition waveguide and a curved waveguide, so as to match the LP mode of the optical fiber.

[0013] The preparation method of the few-mode fiber and the silicon-based multimode chip coupling structure comprises the following steps:

[0014] Step 1: a buried oxygen layer is first deposited on a silicon substrate, then a silicon layer is deposited on the buried oxygen layer, the silicon layer is photoetched to form a silicon-based waveguide, a lower SWG-ICT waveguide, and an alignment mark, and finally an upper cladding layer is deposited on the waveguide layer formed by etching the silicon layer;

[0015] Step 2: the cladding layer above the silicon-based waveguide input and output light end, the lower SWG-ICT waveguide, and the alignment mark is windowed;

[0016] Step 3: according to the position of the alignment mark, the upper FM-PWB waveguide is 3D printed by using a two-photon polymerization technology;

[0017] Step 4: the upper FM-PWB waveguide is embedded in a low refractive index cladding material, and the refractive index of the cladding material is lower than that of the upper FM-PWB waveguide.

[0018] As a further optimization scheme of the preparation method of the few-mode fiber and the silicon-based multimode chip coupling structure, the specific method for 3D printing the upper FM-PWB waveguide by using a two-photon polymerization technology in step 3 is as follows:

[0019] Step 3-1, fix the silicon-based multimode chip and the few-mode fiber on the same fiber base;

[0020] Step 3-2, first, clean the silicon-based multimode chip and the fiber core section with alcohol, acetone, etc.; then, deposit photoresist between the silicon-based multimode chip waveguide and the fiber core, detect the actual position of the silicon-based waveguide and the inverted cascade tapered waveguide of the lower subwavelength grating in the photoresist by using 3D machine vision technology; then, design the shape of the upper FM-PWB waveguide according to the position of the silicon-based multimode chip and the few-mode fiber, and use two-photon lithography technology for exposure, etch a square waveguide on the silicon-based waveguide and the lower SWG-ICT waveguide, and etch a transition waveguide and a curved waveguide;

[0021] Step 3-4, finally, remove the unexposed photoresist to obtain the upper FM-PWB waveguide structure.

[0022] As a further optimization scheme of the preparation method of the few-mode fiber and the silicon-based multimode chip coupling structure, the photoresist deposited between the silicon-based multimode chip waveguide and the fiber core uses a two-photon polymerized acrylate polymer material doped with a certain proportion of TiO2 and other high-refractive-index inorganic nanoparticles.

[0023] As a further optimization scheme of the preparation method of the few-mode fiber and the silicon-based multimode chip coupling structure, the buried oxygen layer and the upper cladding are made of silicon-based oxides, such as SiO2 and other materials.

[0024] As a further optimization scheme of the preparation method of the few-mode fiber and the silicon-based multimode chip coupling structure, the silicon-based multimode chip waveguide and the lower SWG-ICT waveguide are made of silicon material.

[0025] As a further optimization scheme of the preparation method of the few-mode fiber and the silicon-based multimode chip coupling structure, the fiber base can be made of materials with high hardness, such as ceramic, copper, iron, steel, etc.

[0026] The present application has the following beneficial effects by adopting the above technical scheme:

[0027] (1) The novel coupling structure of the few-mode fiber and the silicon-based multimode waveguide disclosed by the present application overcomes the problems of mode difference and geometric size mismatch between the silicon-based waveguide and the fiber, and realizes the conversion of the small-size silicon-based waveguide rectangular vector mode to the large-size few-mode fiber LP mode.

[0028] (2) The present application introduces a sub-wavelength grating inverted cascade tapered waveguide as a lower waveguide, spreads the light from the SWG-ICT waveguide to the FM-PWB waveguide through the SWG-ICT waveguide with reduced width, spreads the light field in the SWG-ICT waveguide to the hybrid material FB-PWB waveguide layer, increases the evanescent field and coupling strength, can greatly shorten the required structure length of mode evolution between the upper and lower waveguides, and further reduce the structure transmission loss, and at the same time, the required complex LP mode number of coupling can be realized by controlling the SWG structure parameters.

[0029] (3) The present application introduces FM-PWB technology, connects the silicon-based waveguide with the few-mode fiber through the curved waveguide, does not need to process the end face of the waveguide, and greatly reduces the end face processing and alignment tolerance problems.

[0030] (4) Since TiO2 has a negative thermal optical coefficient, the temperature sensitivity of the lower silicon-based waveguide can be offset, so a certain proportion of high refractive index inorganic nanoparticles is added to the FM-PWB hybrid material, so that the influence of temperature change on the silicon-based waveguide is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is a structural schematic diagram of the silicon-based multimode chip of the present application.

[0032] Figure 2 It is a structural schematic diagram of the silicon-based waveguide and the lower SWG-ICT waveguide connection structure of the present application.

[0033] Figure 3 It is a coupling structure schematic diagram of the upper FM-PWB waveguide and the lower SWG-ICT waveguide of the present application.

[0034] Figure 4 It is a structural schematic diagram of the few-mode fiber of the present application.

[0035] Figure 5 It is a structural schematic diagram of the silicon-based multimode chip waveguide connected with the few-mode fiber through the FM-PWB curved waveguide structure of the present application.

[0036] Figure 6 It is a schematic diagram of the present application in which photoresist is deposited between the chip and the optical fiber in the FM-PWB manufacturing process.

[0037] Figure 7 It is a process schematic diagram of the photoetching of the FM-PWB waveguide of the present application.

[0038] Figure 8 It is a schematic diagram of the FM-PWB waveguide of the present application.

[0039] Figure 9 It is a schematic diagram of the FM-PWB waveguide embedded with low refractive index cladding material of the present application.

[0040] Explanation of reference numerals in the figures: 101, upper cladding layer, 102, buried oxide layer, 103, silicon substrate, 104, silicon-based waveguide, 105, alignment mark, 106, tapered structure, 107, SWG-ICT waveguide, 108, first transition section, 109, second transition section, 201, square waveguide, 202, transition waveguide, 203, curved waveguide, 301, optical fiber core, 302, optical fiber cladding, 401, optical fiber base, 501, photoresist, 502, femtosecond laser, 503, beam expander, 504, laser focal point, 505, low refractive index cladding material. DETAILED DESCRIPTION

[0041] The technical solutions of the application will be described in detail below with reference to the drawings.

[0042] The coupling structure provided by the embodiment realizes the connection of a few-mode optical fiber and a silicon-based multimode chip. The silicon-based chip waveguide is embedded in a subwavelength-grating inverted cascaded-tapered (SWG-ICT) waveguide, and a few-mode photonic wire bonding (FM-PWB) waveguide is etched by photolithography using a photonic wire bonding (PWB) technology above the SWG-ICT waveguide. The coupling structure formed by the upper FM-PWB waveguide and the lower SWG-ICT waveguide utilizes the few-mode coupling mechanism of enhanced mode hybridization, generates a series of enhanced mode hybridization effects in the coupling structure by the difference in refractive index between the upper hybrid material and the buried oxide layer material, converts the silicon-based rectangular waveguide vector mode into an upper FM-PWB square vector mode through the SWG-ICT waveguide, converts the upper FM-PWB square vector mode into a circular vector mode through the FM-PWB waveguide, matches the few-mode optical fiber LP mode, and thus realizes the coupling of the silicon-based multimode chip and the few-mode optical fiber.

[0043] As Figure 1 , Figure 2As shown, the silicon-based multi-mode chip includes: an upper cladding layer 101, a BOX layer 102, a silicon substrate 103, a silicon-based waveguide 104, an alignment mark 105, a taper structure 106, and a SWG-ICT waveguide 107. The out-in end of the silicon-based waveguide 104 is etched to embed into the SWG-ICT waveguide 107 after the taper structure 106. The ideal tip width of the taper structure 106 is zero, but the manufacturing process limits it to be narrow enough. The selected tip width is 60-120 nm, and the center line of the taper structure 106 should be collinear with the center line of the SWG-ICT waveguide 107. The SWG-ICT waveguide 107 is a gradually tapered subwavelength grating, including a first transition section 108 and a second transition section 109 with gradually decreasing widths. Each grating pitch is 0.5 μm, and the slit distance is 0.2 μm. The first transition section 108 is transitioned from 1 μm to 0.7 μm, and the second transition section 109 is transitioned from 0.7 μm to 0.4 μm. After determining the position of the SWG-ICT waveguide 107 in space, four symmetrical alignment marks 105 are placed along the center line of the SWG-ICT waveguide 107, two on one side, and a total of four. The alignment mark can be a cross, a square, or other shapes that are convenient to align. There can be two on one side, or three or four on one side, depending on the specific chip.

[0044] As shown in FIG. 1, the FM-PWB waveguide structure of the embodiment includes a square waveguide 201 on the SWG-ICT waveguide 107, a transition waveguide 202 from square to circular, and a curved waveguide 203. Figure 3 The square waveguide 201 of the front section of the FM-PWB waveguide is about 1 μm wide and high, and the FM-PWB waveguide is symmetrical along the center line of the SWG-ICT waveguide 107.

[0045] As shown in FIG. 1, the FM-PWB waveguide structure of the embodiment includes a square waveguide 201 on the SWG-ICT waveguide 107, a transition waveguide 202 from square to circular, and a curved waveguide 203. Figure 5 The coupling waveguide of the upper FM-PWB waveguide 201 and the SWG-ICT waveguide 107 is connected to the core 301 of the few-mode fiber through the curved waveguide 203. The silicon-based multi-mode chip and the few-mode fiber are placed on the stepped fiber base 401, and the center of the fiber core 301 is aligned with the center of the end face of the curved waveguide 203. The height of the fiber base 401 and the front and back positions of the few-mode fiber can be adjusted in the vertical direction, i.e., the few-mode fiber moves in the y-axis and x-axis. In the x-axis, the center of the fiber is consistent with the center of the light in-out waveguide, and the curved waveguide 203 is only curved in the vertical direction.

[0046] As shown in FIG. 1, the FM-PWB waveguide structure of the embodiment includes a square waveguide 201 on the SWG-ICT waveguide 107, a transition waveguide 202 from square to circular, and a curved waveguide 203. Figure 4As shown, the few-mode fiber comprises a fiber core 301 and a fiber cladding 302, the fiber core 301 is inside and the fiber cladding 302 is outside. The fiber core 301 is generally 50 μm in diameter, much larger than the diameter of a single-mode fiber, and the fiber cladding 302 is about 125 μm in diameter, equal to the diameter of a single-mode fiber.

[0047] Referring to Figures 1 to 9 The preparation method of the coupling structure of the embodiment specifically comprises the following nine steps.

[0048] Step 1, a silicon substrate 103 is provided, which is a 5 μm thick silicon wafer, and the surface is cleaned to remove contaminants such as particles, organic matter and water vapor. A 3 μm SiO2 layer is deposited on the silicon substrate using plasma enhanced chemical vapor deposition (PECVD) technology to form a buried oxide (BOX) layer 102 to provide bottom optical insulation.

[0049] Step 2, a 220 nm Si layer is deposited on the buried oxide layer 102 using PECVD technology to make a waveguide layer; photoresist is applied to the Si layer by dropping the photoresist on the surface of the Si layer and rotating the chip at high speed to apply the photoresist using a spin coating method, which can make the photoresist layer more uniform.

[0050] Step 3, after the photoresist is applied, a light path mask is designed in advance, and an exposure device is used to selectively pass the mask. When the light passes through the mask with the light path pattern, the designed light path pattern can be printed on the Si layer coated with photoresist. The mask and the photoresist pattern have a 1:1 relationship.

[0051] Step 4, after exposure, the photoresist is sprayed with a developing solution to remove the photoresist in the areas not covered by the pattern, so that the printed light path pattern is revealed. The temperature range for developing should be controlled within 21-23℃ with an error of ±0.5°. After developing is completed, it is checked by measuring equipment and an optical microscope to ensure the quality of the light path.

[0052] Step 5, after the photoetching of the light path pattern is completed, an etching process is used to remove the excess Si, leaving only the required silicon-based waveguide 104, SWG-ICT waveguide 107 and alignment mark 105. The etching method uses reactive ion etching, which uses plasma to ionize physical etching and uses the free radicals generated after plasma activation to perform chemical etching, achieving high-precision light path etching.

[0053] Step 6, after etching is completed, 3 μm of SiO2 is deposited on the waveguide layer using PECVD technology as the upper cladding layer 101 of the cladding core layer. The cladding process will form a ridge above all silicon, so a chemical mechanical polishing process is used to make the surface of the chip more flat.

[0054] Step 7, after the fabrication of the silicon-based multimode chip is completed, the silicon-based multimode chip is windowed, and the SiO2 layer above the silicon-based waveguide, the SWG-ICT waveguide and the alignment mark is removed by using a chemical etching method, so as to expose the silicon-based waveguide 104, the SWG-ICT waveguide 107 and the alignment mark 105.

[0055] Step 8, after the windowing is completed, the FM-PWB waveguide is 3D printed by using a two-photon polymerization technology, and the silicon-based multimode waveguide and the few-mode fiber are connected. The specific process of 3D printing the FM-PWB waveguide is as follows: first, the silicon-based multimode chip and the few-mode fiber are placed on the fiber base 401, and the fiber base 401 can be designed in a shape to compensate for the height difference between the silicon-based multimode chip and the few-mode fiber; second, the silicon-based multimode chip is cleaned with acetone, alcohol and the like, and photoresist 501 is deposited between the silicon-based multimode chip and the few-mode fiber that need to be interconnected, and the photoresist 501 uses a TPP acrylate polymer material doped with a certain proportion of TiO2 high-refractive inorganic nanoparticles; then, a femtosecond laser 502 is used as an excitation light source, the wavelength of the femtosecond laser is 532 nm, the repetition frequency is 50 MHz, and the pulse width is 55 fs, the beam of the femtosecond laser 502 is focused into the acrylate polymer hybrid material after passing through an expander 503 by an objective lens, and the laser focus 504 is controlled to scan and engrave a square waveguide 201, a transition waveguide 202 and a curved waveguide 203 in the photoresist 501 according to a designed path by using a three-dimensional moving system, as shown in FIG. 2B, and the three-dimensional moving system is a three-dimensional moving table or a combination of a two-dimensional galvanometer and a one-dimensional moving table; after that, the un-polymerized photoresist 501 is washed away with ethanol and the like, and the FM-PWB waveguide structure shown in FIG. 2C can be obtained. Figure 7 Figure 8

[0056] Step 9, finally, the FM-PWB waveguide is embedded in a 3 μm low-refractive cladding material 505, as shown in FIG. 2D: first, a low-refractive photoresist is deposited, and then it is cured by using an ultraviolet curing process, and finally, the PWB coupling structure is prepared. Figure 9

[0057] Although the present application has been disclosed in the above preferred embodiments, it is not intended to limit the present application. Those skilled in the art without departing from the spirit and scope of the present application can make various modifications and improvements. Therefore, the protection scope of the present application shall be subject to the definition of the claims.​​​

Claims

1. A few-mode fiber and a silicon-based multi-mode chip coupling structure, characterized in that, include: An upper-layer few-mode photon wire-bonded waveguide is used to connect a silicon-based multimode chip and a few-mode optical fiber, and convert the silicon-based rectangular waveguide vector into a circular linear polarization vector mode. The upper-layer few-mode photon wire-bonded waveguide includes: a square waveguide, a transition waveguide, and a curved waveguide. The square waveguide is coated on top of the silicon-based waveguide and the lower-layer subwavelength grating inverted cascade tapered waveguide. The transition waveguide is a prism-shaped transition structure that gradually changes from square to circular. The curved waveguide is a circular structure that changes from thin to thick. One end of the square waveguide covers the optical input and output ends of the silicon-based waveguide, and the other end of the square waveguide is connected to the square port of the transition waveguide. The circular port of the transition waveguide is connected to the small-diameter circular port of the curved waveguide. The large-diameter circular port of the curved waveguide is connected to the few-mode optical fiber. A lower sub-wavelength grating inverted cascaded tapered waveguide is prepared on the buried oxide layer of a silicon-based multi-mode chip. The lower sub-wavelength grating inverted cascaded tapered waveguide is few-mode coupled with the upper few-mode photonic wire-bonded waveguide. The lower sub-wavelength grating inverted cascaded tapered waveguide is a sub-wavelength grating formed by cascading at least two tapered waveguides with gradually decreasing widths. The silicon-based waveguide of the silicon-based multi-mode chip is embedded in the lower sub-wavelength grating inverted cascaded tapered waveguide through a tapered structure connected to its input and output optical ends.

2. The few-mode fiber and silicon-based multi-mode chip coupling structure according to claim 1, characterized in that, The few-mode optical fiber includes: an optical fiber core and an optical fiber cladding covering the outside of the optical fiber core. One end of the optical fiber core is connected to the large-diameter circular port of the curved waveguide, and the starting and ending directions of the curved waveguide axis coincide with the optical fiber core waveguide axis.

3. The few-mode fiber and silicon-based multi-mode chip coupling structure according to claim 1, wherein, The upper layer of the few-mode photon wire bonding waveguide is covered with a layer of material having a lower refractive index than the upper layer of the few-mode photon wire bonding waveguide. The square waveguide and the buried oxide layer of the silicon-based multimode chip form an asymmetric structure.

4. The few-mode fiber and silicon-based multi-mode chip coupling structure according to claim 1, wherein, The coupling structure is integrally fixed on a stepped optical fiber base.

5. The few-mode fiber and silicon-based multi-mode chip coupling structure according to claim 1, wherein, An alignment mark symmetrical with respect to the lower sub-wavelength grating inverted cascaded tapered waveguide is also prepared on the buried oxide layer of the silicon-based multi-mode chip, and the alignment mark is used to align the upper few-mode photon wire bonding waveguide.

6. The method of claim 1 to 5, wherein the method further comprises the steps of: The steps include: ​ Step 1: depositing a buried oxide layer on a silicon substrate, depositing a silicon layer on the buried oxide layer, photolithography the silicon layer to form a silicon-based waveguide, a lower sub-wavelength grating inverted cascaded tapered waveguide, and alignment marks, and depositing an upper cladding layer on the waveguide layer formed by etching the silicon layer; Step 2: Open a window on the upper cladding layer above the silicon-based waveguide input and output optical ends, the lower sub-wavelength grating inverted cascaded tapered waveguide, and the alignment mark to expose the silicon-based waveguide, the lower sub-wavelength grating inverted cascaded tapered waveguide, and the alignment mark; Step 3: Based on the position of the alignment mark, use two-photon polymerization technology to 3D print the upper few-mode photonic wire bonding waveguide; Step 4: embed the upper few-mode photonic wire-bonded waveguide into the low-refractive-index cladding material.

7. The method according to claim 6, wherein the method further comprises the step of: The specific method of using two-photon polymerization technology to 3D print the upper few-mode photonic wire bonding waveguide in step 3 is: ​ Step 3-1, placing the silicon-based multimode chip and the few-mode optical fiber on the optical fiber base; Step 3-2, cleaning the cross section of the silicon-based multimode chip and the optical fiber core, and depositing photoresist between the silicon-based multimode chip waveguide and the optical fiber core; Step 3-3, using femtosecond laser as excitation light source, the beam of femtosecond laser is focused into the acrylate polymer hybrid material by the objective lens after the beam expander, and the laser focus is controlled to scan in the photoresist according to the established path by using the three-dimensional moving system, so as to etch out the square waveguide, transition waveguide and curved waveguide; Step 3-4, washing away the un-polymerized photoresist, to obtain the upper layer of the few-mode photonic wire bonding waveguide structure.

8. The method of claim 6, wherein the method further comprises the steps of: providing a plurality of silicon-based multimode chips; and coupling the plurality of silicon-based multimode chips to the plurality of multimode fibers. The upper cladding layer is a 3 μm thick silicon dioxide layer.

9. The method of claim 7, wherein the method further comprises the steps of: providing a plurality of silicon-based multimode chips; and coupling the plurality of silicon-based multimode chips to the plurality of multimode fibers. The photoresist is a two-photon polymerization acrylate polymer material doped with a certain proportion of TiO2 high-refractive inorganic nanoparticles.

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