Fabrication of Low Insertion Loss Spatial Multiplexer / Demultiplexer for Multi-core Optical Fiber

Abstract

This invention relates to a method for fabricating a low insertion loss spatial multiplexer / demultiplexer for multi-core optical fibers, belonging to the field of multi-core optical fiber communication technology. By using single-core fibers of different core diameters at the splice points, this invention effectively improves the fault tolerance of the multiplexer's core arrangement while reducing optical signal leakage at the splice points, thereby reducing insertion loss. This allows for the multiplexing of signals from single-core fibers into multi-core fibers at the input end and the demultiplexing of signals from multi-core fibers into single-core fibers at the output end. The spatial multiplexing / demultiplexer device prepared using this method exhibits lower insertion loss compared to the traditional bundled method, and is simpler and less expensive to operate than polymer waveguide and fused taper methods. The prepared spatial multiplexer / demultiplexer is small, flexible, durable, and suitable for mass production.

Description

Technical Field

[0001] This invention belongs to the field of multi-core optical fiber communication technology, specifically relating to a method for manufacturing a low insertion loss spatial multiplexer / demultiplexer for multi-core optical fibers. Background Technology

[0002] Space division multiplexing (SDM) is a new type of optical fiber communication technology that can significantly increase capacity after wavelength division multiplexing (WDM). It is widely considered by the industry as an effective way to solve the current capacity crisis in optical fiber communication and has become a research hotspot in the field of optical fiber communication in recent years. With the development of technologies such as 5G, IoT, and big data centers, the demand for bandwidth will continue to grow. Multi-core optical fiber communication systems can provide necessary support for the development of these technologies. Multi-core optical fiber is a new type of optical fiber that contains multiple independent optical transmission paths, i.e., multiple fiber cores. Compared with traditional single-core optical fiber, multi-core optical fiber can transmit multiple signals in parallel within the same fiber, thereby significantly improving data transmission capacity and bandwidth. Space division multiplexers / demultiplexers, as key components of multi-core optical fiber communication systems, ensure compatibility between multi-core optical fiber communication systems and existing single-mode optical fiber systems. They are crucial for connecting multi-core optical fibers to standard single-core optical fibers and are of great significance for realizing high-speed, high-capacity, and high-reliability optical fiber communication networks.

[0003] Currently, one method for fabricating multi-core fiber space division multiplexers / demultiplexers is chemical etching. This method typically involves using chemical etchants such as hydrofluoric acid to precisely etch the cladding of a single-core fiber, matching its diameter to the core spacing of the multi-core fiber. This allows the cores of the single-core fiber to align with the individual cores of the multi-core fiber, enabling efficient transmission and distribution of optical signals. The advantages of chemical etching include high precision, small size, simple fabrication method, and low cost. It is suitable for various types of multi-core fibers, including homogeneous and heterogeneous multi-core fibers, and can adapt to complex core arrangements. However, this method also has some drawbacks. For example, the etching process requires precise control; any over- or under-etching can lead to performance degradation. Furthermore, due to core position deviations in the fabricated fiber endface after etching, it may not perfectly match the multi-core fiber, resulting in signal loss during multiplexing / demultiplexing. The largest source of loss is insertion loss at the junction of the device and the multi-core fiber. Therefore, achieving precise arrangement of the multiplexer endface structure or ensuring the fault tolerance of the fabricated structure is a problem that urgently needs to be solved. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies in fabricating space division multiplexers / demultiplexers, which suffer from excessive insertion loss due to inaccurate arrangement of the multiplexer end-face structure, this invention provides a method for fabricating a low-loss multi-core fiber space division multiplexer / demultiplexer. This method enables the signal from a single-core fiber to be multiplexed into a multi-core fiber at the input end, and the signal from the multi-core fiber to be demultiplexed into a single-core fiber at the output end.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for fabricating a low insertion loss space division multiplexer / demultiplexer for multi-core optical fibers includes the following steps:

[0007] (1) Prepare a multi-core optical fiber with N cores, N small-core diameter single-core optical fibers 1, N large-core diameter single-core optical fibers 2, and 2N single-core optical fibers 3; wherein, the core diameter of the small-core diameter single-core optical fiber 1 is 1μm to 2μm smaller than the core diameter of the multi-core optical fiber, the core diameter of the large-core diameter single-core optical fiber 2 is 1μm to 2μm larger than the core diameter of the multi-core optical fiber, and the core diameter of the single-core optical fiber 3 matches that of the multi-core optical fiber; N>1;

[0008] (2) Remove the organic coating layer from one end of single-core optical fiber 1 and single-core optical fiber 2, with the length of the removed organic coating layer being 20mm-30mm; then immerse the portion with the removed organic coating layer in a high-concentration hydrofluoric acid solution to etch the cladding; during etching, cover the surface of the hydrofluoric acid solution with a layer of grease to prevent HF volatilization, until the diameter of the etched cladding layer is greater than the core spacing of the multi-core optical fiber by 1μm-2μm; then immerse the etched portion in a low-concentration hydrofluoric acid solution for further etching until the diameter of the cladding layer in this portion is the same as the core spacing of the multi-core optical fiber, thus producing etched single-core optical fiber 1 and etched single-core optical fiber 2 with etched sections at the front end; the mass concentration of the high-concentration hydrofluoric acid is 35%-45%; the mass concentration of the low-concentration hydrofluoric acid solution is 15%-25%.

[0009] (3) Insert N etched single-core optical fibers 1 and N etched single-core optical fibers 2 into two ceramic heads respectively. The inner diameter of the ceramic head matches the size of the bundled N etched single-core optical fibers. Use adhesive to bond the optical fibers to the inside of the ceramic head. After heating and curing at 100℃~120℃ for 25min~30min, grind and polish the front end of the ceramic head. Use physical contact docking method to dock with both ends of the multi-core optical fiber respectively.

[0010] (4) After removing the coating layer from the uncorroded end of the etched single-core fiber 2, tape it using a tapering machine until the core diameter at the thinnest point of the tapered region of the etched single-core fiber 2 is equal to the core diameter of the single-core fiber 3; after removing the coating layer from the single-core fiber 3, tape it until the core diameter at the thinnest point of the tapered region of the single-core fiber 3 is equal to the core diameter of the single-core fiber 1.

[0011] (5) Use an optical fiber cutter to cut the tapered single-core optical fiber 2 and single-core optical fiber 3 at the thinnest part of the tapered region. Use a fusion splicer to fusion the tapered single-core optical fiber 3 with the uncorroded end of single-core optical fiber 1 and the tapered single-core optical fiber 2 with single-core optical fiber 3 respectively, to make a space-division multiplexer and a space-demultiplexer for multi-core optical fibers.

[0012] In the above methods, the multi-core optical fiber is either a homogeneous multi-core optical fiber or a heterogeneous multi-core optical fiber;

[0013] The diameter of single-core fiber 2 is taken as the large core diameter, and the diameter of single-core fiber 1 is taken as the small core diameter.

[0014] In the above method, the two mating ceramic head parts in the space division multiplexer are N small-core diameter single-core optical fiber etched bundles mating with one N-core optical fiber. That is, when the device is in use, the optical signal is transmitted from the small core diameter to the large core diameter.

[0015] In the above method, during the fabrication of the space division multiplexer, an optical fiber tapering machine is used to tape N single-core optical fibers with the same core diameter as the N-core optical fiber until the core diameter is equal to that of the small core fiber. After cutting, the fibers are then fused with the uncorroded ends of the N small core diameter single-core optical fibers in the space division multiplexer.

[0016] In the above method, the two mating ceramic head parts in the empty demultiplexer are a bundle of N-core optical fibers etched together by N large-core diameter single-core optical fibers, that is, the device uses optical signals to transmit from small core diameter to large core diameter.

[0017] In the methods described above, the N-core optical fibers used in the space division multiplexing / demultiplexing unit are all of the same type, with the same core diameter; where N-core optical fiber refers to a multi-core optical fiber with N cores. When using N single-core optical fibers with different core diameters, the large or small core diameter is relative to the N-core optical fiber.

[0018] In the above method, during the fabrication of the empty demultiplexer, an optical fiber tapering machine is used to taper the uncorroded ends of the N large-diameter single-core optical fibers in the empty demultiplexer until the core diameter is equal to that of the N-core optical fibers. After cutting, the fibers are then fused together with N single-core optical fibers of the same core diameter as the N-core optical fibers.

[0019] In the above method, when tapering, an oxyhydrogen flame is used to tape, and the hydrogen output is controlled at 100-120 SCCM and the oxygen output at 10-20 SCCM. The core diameter at the finest point of the tapered region is controlled by controlling the tapering length.

[0020] In the above method, the tapered cutting and splicing step makes the fiber core diameter of the front end of the fan-in device and the back end of the fan-out device consistent with that of the fiber core in the general optical fiber communication system and splices them together. The resulting space division multiplexer / demultiplexer is suitable for the corresponding optical fiber communication system.

[0021] Insertion loss at the ceramic connector is a crucial indicator for evaluating space division multiplexers / demultiplexers (SDMs). The primary cause of insertion loss is the misalignment between the fiber arrangement on the fabricated SDM / demultiplexer endface and the core position of the multi-core fiber, i.e., core misalignment at the connector. In actual fabrication, errors in fiber etching and ceramic connector fabrication can affect the fiber arrangement on the SDM / demultiplexer endface. Therefore, achieving precise fiber arrangement or improving its fault tolerance is essential for reducing insertion loss. Using traditional etching and bundling methods, fabricating fibers with the same core diameter requires perfect alignment between the manually fabricated multiplexer endface and the multi-core fiber core to achieve low-loss optical signal transmission. However, manually fabricated multiplexers cannot be error-free; structural deviations are unavoidable with traditional methods, leading to signal leakage at the connector and resulting in significant insertion loss. In this invention, single-core optical fibers with different core diameters are selected to fabricate space-division multiplexers / demultiplexers. During use, the optical signal always enters from the smaller core diameter to the larger core diameter. The optical transmission from the smaller core diameter to the larger core diameter results in less loss at the splice point compared to optical transmission with the same core diameter, and the optical signal is less prone to leakage. Furthermore, the internal fiber arrangement of the space-division multiplexer / demultiplexer made of smaller core diameter fiber does not require strict precision. A structural deviation of about 1μm to 2μm can still achieve the transmission of optical signals within the receiving range of the larger core diameter, which improves the fault tolerance of the fabricated end-face structure. This reduces the insertion loss at the splice point of the manually fabricated multiplexer end face, increases the yield, and enhances the transmission performance of the space-division multiplexer / demultiplexer.

[0022] Compared with the prior art, the technical solution proposed in this invention has the following advantages:

[0023] Space division multiplexers / demultiplexers (SDMs) fabricated using small-core to large-core fiber splicing allow for a 1μm–2μm error in fiber arrangement within the ceramic head compared to splicing fibers with the same core diameter. This significantly improves the fault tolerance of the end-face structure for micrometer-scale fibers and multiplexers, reducing insertion loss caused by structural deviations and increasing yield. Simultaneously, the small-core to large-core transmission path reduces optical signal leakage at the splice, further lowering insertion loss. Subsequent tapered fusion splicing makes the fabricated SDM / demultiplexer suitable for general-purpose fiber optic communication systems. For a four-core single-mode SDM, the insertion loss is reduced from the typical 1dB–2dB to 0.69dB, validating the feasibility of the method. This method can also be applied to seven-core, thirteen-core, and other types of SDM / demultiplexers. The fabricated SDM / demultiplexer exhibits even lower insertion loss compared to traditional splicing methods using etched bundles with the same core diameter. Compared to polymer waveguide and clustered tapered methods, it is simpler to operate and lower in cost. The resulting space division multiplexer / demultiplexer is smaller, more flexible, more durable, and can be mass-produced. Attached Figure Description

[0024] Figure 1 A schematic diagram of fan-in device docking in a four-core space-division multiplexer according to an embodiment of the present invention;

[0025] Figure 2 A schematic diagram of the fan-out device docking in a four-core empty demultiplexer according to an embodiment of the present invention;

[0026] Figure 3 Schematic diagram of fiber tapering and cutting according to an embodiment of the present invention;

[0027] Figure 4 Schematic diagram of core package dimensions before and after tapered cutting in the fabrication of a four-core space separation multiplexer according to an embodiment of the present invention;

[0028] Figure 5 Schematic diagram of welding after cutting according to an embodiment of the present invention;

[0029] Figure 6 A schematic diagram of the core package dimensions before and after tapered cutting in the fabrication of a four-core hollow demultiplexer according to an embodiment of the present invention;

[0030] Figure 7 A schematic diagram of a complete four-core space division multiplexer / demultiplexer system according to an embodiment of the present invention;

[0031] Figure 8 Performance of the four-core space division multiplexer fabricated according to embodiments of the present invention;

[0032] Figure 9 A schematic diagram of the fan-in device docking in the seven-core space separation multiplexer of this invention;

[0033] Figure 10 A schematic diagram of the fan-out device connection in the seven-core space separation multiplexer of this invention;

[0034] Figure 11 Schematic diagram of core package dimensions before and after tapered cutting in the fabrication of a seven-core space separation multiplexer according to an embodiment of the present invention;

[0035] Figure 12 A schematic diagram of the core package dimensions before and after tapered cutting in the fabrication of a seven-core hollow demultiplexer according to an embodiment of the present invention;

[0036] Figure 13 A schematic diagram of a complete seven-core space division multiplexer / demultiplexer system according to an embodiment of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0038] In this embodiment of the invention, the adhesive is 353ND glue, which includes two bottles, A and B, and is used in a 10:1 ratio. The curing conditions are heating at 100-120°C for 25-30 minutes.

[0039] In this embodiment of the invention, the etching is carried out in a container equipped with a magnetic stirrer. The stirring vibration is used to ensure uniform distribution and improve the etching uniformity and smoothness of the single-core optical fiber.

[0040] In this embodiment of the invention, the multi-core optical fiber is a homogeneous multi-core optical fiber or a heterogeneous multi-core optical fiber.

[0041] In this embodiment of the invention, when tapering, an oxyhydrogen flame is used. The temperature is controlled by controlling the output of hydrogen and oxygen, and the core diameter at the thinnest part of the tapered region is controlled by controlling the tapering length.

[0042] In this embodiment of the invention, during the corrosion process, a layer of grease is applied to the surface of the hydrofluoric acid solution to prevent HF from evaporating.

[0043] In Embodiment 1 of the present invention, a 4-core optical fiber is used. The cladding diameter of single-core optical fibers 1, 2, and 3 is α, the core diameters are r1, r2, and r3, respectively, and the diameter of the etched optical fiber is β1.

[0044] In Embodiment 2 of the present invention, a 7-core optical fiber is used. The cladding diameter of single-core optical fibers 4, 5, and 3 is α, the core diameters are r4, r5, and r6, respectively, and the diameter of the etched optical fiber is β2.

[0045] Example 1

[0046] Prepare a multi-core optical fiber with 4 cores and a core spacing of 41.5 μm; prepare 4 single-core optical fibers 1 with a cladding diameter α = 125 μm and a core diameter r1 = 8 μm; 4 single-core optical fibers 2 with a cladding diameter α = 125 μm and a core diameter r2 = 10 μm; and 8 single-core optical fibers 3 with a cladding diameter α = 125 μm and a core diameter r3 = 9 μm, wherein the core diameter and mode field diameter of the single-core optical fibers 3 are matched with the core diameter and mode field diameter of the multi-core optical fiber.

[0047] The organic coating layer at one end of single-core optical fibers 1 and 2 is removed, with the length of the removed portion being 2-3 cm. Then, the portion with the removed organic coating layer is immersed in a high-concentration hydrofluoric acid solution to etch the cladding until the etched cladding diameter is greater than the core spacing of the multi-core optical fiber by 2 μm. Next, the etched portion is immersed in a low-concentration hydrofluoric acid solution and etched until the cladding diameter of this portion is the same as the core spacing of the multi-core optical fiber, thus producing an etched single-core optical fiber with an etched section at the front end. The mass concentration of the high-concentration hydrofluoric acid is 40%, and the mass concentration of the low-concentration hydrofluoric acid solution is 20%. The diameter β1 of the etched single-core optical fiber is 41.5 μm.

[0048] Four etched single-core optical fibers 1 and four etched single-core optical fibers 2 were inserted into two ceramic heads with a 100μm aperture, respectively. Low-viscosity adhesive was used to bond the fibers to the ceramic heads. A glue-filled glass tube and heat-shrink tubing were then inserted to reinforce the tail end. After overall heat curing, the front end of the ceramic head was ground and polished. Then, a physical contact splicing method was used to connect the fibers to both ends of the multi-core optical fibers. A schematic diagram of the fan-in device splicing in the four-core space division multiplexer is shown below. Figure 1 As shown in the diagram, the fan-out devices in a four-core demultiplexer are connected in the following way: Figure 2 As shown;

[0049] Remove 2.5cm-3cm of the coating from four single-core optical fibers and clean them with anhydrous ethanol. Taper the fibers using a fiber tapering machine. Control the scanning width and speed of the oxyhydrogen flame, as well as the stretching length and speed, using computer software. The hydrogen flow rate is set to 110 SCCM, the oxygen flow rate to 15 SCCM, and the preset taper length is 1mm in each direction. Cut the fiber at the narrowest point of the taper using a fiber cleaver, following the specific steps as follows. Figure 3 As shown, the parameters before and after tapered cutting are as follows: Figure 4 As shown;

[0050] Remove the coating from the uncorroded end of single-core fiber 1 and fusion splice it with the tapered end of single-core fiber 3. The manufacturing process is as follows: Figure 5 As shown, a space division multiplexer for multi-core optical fibers is fabricated.

[0051] Remove 2.5cm-3cm of the coating from the uncorroded ends of four single-core optical fibers and clean them with anhydrous ethanol. Taper the fibers using a fiber tapering machine. Control the scanning width and speed of the oxyhydrogen flame, as well as the stretching length and speed, via computer software. The hydrogen flow rate is set to 110 SCCM, the oxygen flow rate to 15 SCCM, and the preset taper length is 1mm in each direction. Cut the fiber at the narrowest point of the taper using a fiber cleaver. The parameters before and after tapering are as follows: Figure 6 As shown;

[0052] Remove the coating layer of single-core fiber 3 and fuse it with the tapered end of single-core fiber 2 to make an empty demultiplexer for multi-core optical fibers.

[0053] A schematic diagram of the complete four-core space division multiplexer / demultiplexer system is shown below. Figure 7 As shown. The optical signal is input from four single-core optical fibers, multiplexed through the small-diameter fiber in the fan-in device into the large-diameter four-core optical fiber for transmission, and then demultiplexed out of the four-core optical fiber through the large-diameter fiber in the fan-out device. The performance specifications of the fabricated space division multiplexer are shown in [reference needed]. Figure 8 The performance specifications of the fabricated space separation multiplexer are shown in the figure. Figure 8 The insertion loss of the four-core multiplexer made using this scheme is reduced from the usual 1dB to 2dB to 0.69dB, which greatly improves the transmission performance of the multiplexer.

[0054] Example 2

[0055] Prepare a multi-core optical fiber with 7 cores, a cladding diameter of 125 μm, a core spacing of 42 μm, and a core diameter of 16 μm; prepare 7 single-core optical fibers 4, with a cladding diameter α = 125 μm and a core diameter r4 = 14 μm; 7 single-core optical fibers 5, with a cladding diameter α = 125 μm and a core diameter r5 = 18 μm; and 14 single-core optical fibers 6, with a cladding diameter α = 125 μm and a core diameter r6 = 16 μm, wherein the core diameter and mode field diameter of the single-core optical fibers 6 match the core diameter and mode field diameter of the multi-core optical fiber.

[0056] The organic coating layer at one end of the single-core optical fiber (ends 4 and 5) is removed, with the length of the removed portion being 2-3 cm. This portion is then immersed in a high-concentration hydrofluoric acid solution to etch the cladding until the etched cladding diameter is greater than the core spacing of the multi-core optical fiber (2 μm). The etched portion is then immersed in a low-concentration hydrofluoric acid solution and etched until the cladding diameter of this portion is the same as the core spacing of the multi-core optical fiber, thus creating an etched single-core optical fiber with an etched section at the front end. The high-concentration hydrofluoric acid has a mass concentration of 40%, and the low-concentration hydrofluoric acid solution has a mass concentration of 20%. The diameter β2 of the etched single-core optical fiber is 42 μm.

[0057] Seven etched single-core optical fibers 4 and 7 etched single-core optical fibers 5 were inserted into two ceramic heads with a 125μm aperture, respectively. Low-viscosity adhesive was used to bond the fibers to the ceramic heads. A glue-filled glass tube and heat-shrink tubing were then inserted to reinforce the tail. After overall heat curing, the front end of the ceramic head was ground and polished. Then, a physical contact splicing method was used to connect the fibers to both ends of the multi-core optical fibers. A schematic diagram of the fan-in device splicing in the seven-core space division multiplexer is shown below. Figure 9 As shown in the diagram, the fan-out devices in the seven-core demultiplexer are connected in the following way: Figure 10 As shown;

[0058] Remove 2.5cm-3cm of the coating from 7 single-core optical fibers and clean them with anhydrous ethanol. Taper the fibers using a fiber tapering machine. Control the scanning width and speed of the oxyhydrogen flame, as well as the stretching length and speed, via computer software. The hydrogen flow rate is set to 110 SCCM, and the oxygen flow rate to 15 SCCM. The preset taper length is 1.3mm on each side. Cut the fiber at the narrowest point of the taper using a fiber cleaver. Parameters before and after tapering are as follows. Figure 11 As shown;

[0059] Remove the coating layer from the uncorroded end of single-core fiber 4 and fusion splice it with the tapered end of single-core fiber 6 to make a space division multiplexer for multi-core optical fibers.

[0060] Remove 2.5cm-3cm of the coating from the uncorroded ends of seven single-core optical fibers and clean them with anhydrous ethanol. Taper the fibers using a fiber tapering machine. Control the scanning width and speed of the oxyhydrogen flame, as well as the stretching length and speed, via computer software. The hydrogen flow rate is set to 110 SCCM, the oxygen flow rate to 15 SCCM, and the preset taper length is 1.3mm on each side. Cut the fiber at the narrowest point of the taper using a fiber cleaver. Parameters before and after tapering are as follows: Figure 12 As shown;

[0061] The coating layer of single-core fiber 6 is removed and fused with the tapered end of single-core fiber 5 to make an empty demultiplexer for multi-core optical fibers.

[0062] A schematic diagram of the complete seven-core space division multiplexer / demultiplexer system is shown below. Figure 13 As shown, the optical signal is input from seven single-core optical fibers, multiplexed through the small-diameter fiber in the fan-in device into the seven large-diameter fiber, and then demultiplexed out of the seven fibers through the large-diameter fiber in the fan-out device. Compared with the traditional chemical etching method for clustering and docking, the seven-core multiplexer / demultiplexer fabricated using this method has higher fault tolerance in its end-face structure. The optical signal is transmitted from the small-diameter fiber to the large-diameter fiber, reducing optical signal leakage, thereby reducing loss, increasing yield, and improving the performance of the seven-core space-division multiplexer / demultiplexer.

Claims

1. A method for manufacturing a low insertion loss spatial multiplexer / demultiplexer for multi-core optical fibers, characterized in that, Includes the following steps: (1) Prepare a multi-core optical fiber with N cores, and prepare N small-core single-core optical fibers 1, N large-core single-core optical fibers 2, and 2N single-core optical fibers 3; where N>1; the core diameter of the small-core single-core optical fiber 1 is 1μm~2μm smaller than the core diameter of the multi-core optical fiber, the core diameter of the large-core single-core optical fiber 2 is 1μm~2μm larger than the core diameter of the multi-core optical fiber, and the core diameter of the single-core optical fiber 3 matches that of the multi-core optical fiber; (2) Remove the organic coating layer from one end of single-core optical fiber 1 and single-core optical fiber 2, and then immerse the part with the organic coating layer removed in a high-concentration hydrofluoric acid solution to etch the cladding; wherein, during etching, the surface of the hydrofluoric acid solution is covered with a layer of grease; then immerse the etched part in a low-concentration hydrofluoric acid solution for further etching until the cladding diameter of this part is the same as the fiber core spacing of the multi-core optical fiber, thus producing etched single-core optical fiber 1 and etched single-core optical fiber 2 with etched sections at the front end; wherein, the mass concentration of the high-concentration hydrofluoric acid is 35% to 45%; and the mass concentration of the low-concentration hydrofluoric acid solution is 15% to 25%. (3) Insert N etched single-core optical fibers 1 and N etched single-core optical fibers 2 into two ceramic heads respectively. The inner diameter of the ceramic head matches the size of the bundled N etched single-core optical fibers. After bonding the optical fibers to the inside of the ceramic head with adhesive, heat and cure them. Then grind and polish the front end of the ceramic head and use a physical contact docking method to dock with both ends of the multi-core optical fiber respectively. (4) After removing the coating layer from the uncorroded end of the etched single-core fiber 2, tape it using a tapering machine until the core diameter at the thinnest point of the tapered region of the etched single-core fiber 2 is equal to the core diameter of the single-core fiber 3; after removing the coating layer from the single-core fiber 3, tape it until the core diameter at the thinnest point of the tapered region of the single-core fiber 3 is equal to the core diameter of the single-core fiber 1. (5) Use a fiber optic cutter to cut the tapered single-core fiber 2 and single-core fiber 3 at the thinnest part of the tapered region. Use a fusion splicer to fusion the tapered single-core fiber 3 with the uncorroded end of single-core fiber 1 and the tapered single-core fiber 2 with single-core fiber 3 respectively to make a space-division multiplexer and a space-demultiplexer for multi-core optical fibers. The diameter of the single-core optical fiber 2 is referred to as the large core diameter, and the diameter of the single-core optical fiber 1 is referred to as the small core diameter. A multi-core optical fiber with N cores is called an N-core optical fiber; N-core optical fibers are of the same type and have the same core diameter.

2. The method for manufacturing a low insertion loss spatial multiplexer / demultiplexer for multi-core optical fibers according to claim 1, characterized in that, The multi-core optical fiber is either a homogeneous multi-core optical fiber or a heterogeneous multi-core optical fiber.

3. The method for manufacturing a low insertion loss spatial multiplexer / demultiplexer for multi-core optical fibers according to claim 1, characterized in that, The two mating ceramic head parts in the space division multiplexer are N small-core diameter single-core optical fiber etched bundles mating with one N-core optical fiber. That is, when the device is in use, the optical signal is transmitted from the small core diameter to the large core diameter. Among them, the use of N single-core optical fibers with other core diameters, the large or small core diameter is relative to the N-core optical fiber.

4. The method for manufacturing a low insertion loss spatial multiplexer / demultiplexer for multi-core optical fibers according to claim 1, characterized in that, The two mating ceramic head parts in the empty demultiplexer are a bundle of N-core optical fibers etched together by an N-core single-core optical fiber with a large core diameter. That is, the device uses optical signals to transmit from the small core diameter to the large core diameter.

5. The method for manufacturing a low insertion loss spatial multiplexer / demultiplexer for multi-core optical fibers according to claim 1, characterized in that, In step (2), the length of the portion where the organic coating is removed is 20mm-30mm; The cladding diameter after high-concentration hydrofluoric acid etching is 1μm to 2μm larger than the core spacing of the multi-core optical fiber; the cladding diameter after low-concentration hydrofluoric acid etching is equal to the core spacing of the multi-core optical fiber.

6. The method for manufacturing a low insertion loss spatial multiplexer / demultiplexer for multi-core optical fibers according to claim 1, characterized in that, In step (3), the heating and curing conditions are: heating and curing at 100℃~120℃ for 25min~30min.

7. The method for manufacturing a low insertion loss spatial multiplexer / demultiplexer for multi-core optical fibers according to claim 1, characterized in that, In step (4), during the fabrication of the space division multiplexer, an optical fiber tapering machine is used to tape N single-core optical fibers with the same core diameter as N core optical fibers until the core diameter is equal to that of the small core fiber. After cutting, the fibers are then fused with the uncorroded ends of the N small core diameter single-core optical fibers in the space division multiplexer.

8. The method for manufacturing a low insertion loss spatial multiplexer / demultiplexer for multi-core optical fibers according to claim 1, characterized in that, In step (4), when tapering, an oxyhydrogen flame is used to tape, and the hydrogen output is controlled at 100 SCCM to 120 SCCM and the oxygen output is controlled at 10 SCCM to 20 SCCM. The diameter of the fiber core at the thinnest part of the tapered region is controlled by controlling the tapering length.

9. The method for manufacturing a low insertion loss spatial multiplexer / demultiplexer for multi-core optical fibers according to claim 1, characterized in that, The tapered cutting and fusion splicing process ensures that the front-end fiber of the fan-in device and the rear-end fiber of the fan-out device have the same core diameter as the fiber in the general optical fiber communication system and are fused together. The resulting space division multiplexer / demultiplexer is suitable for the corresponding optical fiber communication system.

10. The method for manufacturing a low insertion loss spatial multiplexer / demultiplexer for multi-core optical fibers according to claim 1, characterized in that, In step (4), during the fabrication of the empty demultiplexer, an optical fiber tapering machine is used to tape the uncorroded ends of the N large-diameter single-core optical fibers in the empty demultiplexer until the core diameter is equal to that of the N-core optical fiber. After cutting, the fibers are then fused with N single-core optical fibers of the same core diameter as the N-core optical fiber.

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