A method for manufacturing a high numerical aperture device polarization maintaining optical fiber and a product

Abstract

This invention discloses a method and product for fabricating polarization-maintaining optical fibers for high numerical aperture devices. The method includes the following steps: (1) depositing a core layer for forming a core rod using an in-tube deposition method; (2) etching according to a preset etching area to remove the core layer and form a low-stress short region; (3) obtaining a solid segmented preform after sintering and shrinking; (4) machining the processing section to obtain a perforated sleeve; (5) inserting a stress rod to form a polarization-maintaining optical fiber preform for drawing. The method for fabricating polarization-maintaining optical fibers for high numerical aperture devices of this invention uses an in-tube deposition method to achieve high numerical aperture doping of the core rod, and then uses a "segmented etching" method to create a low-stress processing section, thereby preparing a core rod structure with a high-stress doped core and a low-stress processing section. Subsequent cutting and drilling and other machining processes are then performed, which improves the yield, improves the concentricity and curvature of the preform, and ultimately improves the performance of the optical fiber.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber technology, and more specifically, relates to a method and product for fabricating polarization-maintaining optical fibers for high numerical aperture devices. Background Technology

[0002] With the explosive growth of mobile internet, data traffic in communication networks has increased rapidly, placing higher demands on fiber optic backbone networks. Current exploration of EDFA and WDM technologies is limited, and existing communication solutions cannot meet the demands of transmission rates increasing to 1.6TG / 3.2T or even higher. Optical communication manufacturers urgently need to find new technological breakthroughs to improve transmission capabilities, meet user needs, and alleviate pressure. With the maturity of technologies such as digital signal processing (DSP) and optical device manufacturing, coherent optical communication based on these technologies is well-suited to breaking through the technical bottlenecks of long-distance, high-bandwidth fiber optic communication.

[0003] In coherent optical communication, when coupling the front-end silicon photonic chip, it is necessary to use a small mode field polarization-maintaining fiber for direct coupling. At the same time, the splicing performance between it and a 9μm polarization-maintaining fiber with a larger mode field must also be considered. Therefore, the core-cladding concentricity index will affect the splicing performance.

[0004] High numerical aperture (NPA) polarization-maintaining fibers have high doping levels, making them difficult to manufacture using conventional processes. Current challenges in producing this type of fiber include: due to the high NPA, the core region has a large doping concentration, leading to significant differences in the coefficients of thermal expansion and viscosity between the core and cladding, resulting in substantial stress within the core. This stress makes the fiber preform prone to cracking during machining. In the fabrication of conventional NPA single-mode fibers, machining occurs at the ends of the preform, such as during cleaving, tapering, and tail splicing, resulting in short cracks at these ends that do not affect the normal production of the middle section. However, in the fabrication of polarization-maintaining NPA fibers, drilling holes near both sides of the core can cause through-cracks throughout the entire core, making subsequent production impossible.

[0005] Japanese Patent Publication No. JP11-199260 discloses this type of small-mode-field coupled optical fiber with a relatively high numerical aperture. It involves axially splicing a short core rod and a pure quartz connector multiple times, forming the cladding using an external spraying method, and processing the pure quartz connector portion. This method suffers from cumbersome fabrication requiring multiple splicing operations. Furthermore, the core ends of the core rod are easily deformed due to compression during the splicing process. Multiple splicing operations deteriorate the overall curvature and concentricity of the original rod, still posing a risk of rod breakage. Summary of the Invention

[0006] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a method and product for fabricating polarization-maintaining fibers with high numerical aperture devices. The purpose is to perform regional etching during the fabrication of the core layer of high numerical aperture polarization-maintaining fibers using in-tube deposition to form low-stress, short regions for subsequent machining processes. This reduces the risk of fiber breakage while improving the concentricity and curvature of the preform, thereby improving the fiber's geometric parameters and performance. This solves the technical problems of low yield or performance deficiencies in existing high numerical aperture polarization-maintaining fibers.

[0007] To achieve the above objectives, according to one aspect of the present invention, a method for fabricating a polarization-maintaining fiber for high numerical aperture devices is provided, comprising the following steps:

[0008] (1) A core layer for forming a mandrel is deposited using an in-tube deposition method to obtain a prefabricated liner; the doping amount of Ge in the core layer is greater than or equal to 1.8% of the relative refractive index difference Δ of the core layer.

[0009] (2) In the prefabricated liner obtained in step (1), etching is performed according to the preset etching area to remove the core layer and form a low-stress short region, thereby obtaining a segmented liner with a core layer and a low-stress short region distributed axially.

[0010] (3) The segmented liner obtained in step (2) is sintered and shrunk to obtain a solid segmented preform. The solid segmented preform has a core bar formed by sintering and shrunk core layer and a processing section formed by sintering and shrunk low stress short area in the central region of the solid segmented preform.

[0011] (4) Position the processing section on the solid segmented preform obtained in step (3), perform machining on the processing section, and obtain a perforated sleeve with holes for fitting stress rods.

[0012] (5) Insert stress rods into the holes of the perforated sleeve obtained in step (3) to form polarization-maintaining fiber preforms and draw them to obtain the polarization-maintaining fiber of the high numerical aperture device.

[0013] Preferably, in the method for fabricating the polarization-maintaining fiber for high numerical aperture devices, the relative refractive index difference Δ of the core layer is ≤3.8%, wherein the contribution rate of fluorine doping in the core layer is -0.033% to -0.9%, and preferably the core layer diameter is controlled to be 0.8 to 1.0 mm.

[0014] Preferably, the fabrication method of the high numerical aperture device polarization-maintaining fiber includes step (2) as follows:

[0015] A vaporized fluorine-containing etchant is introduced into a prefabricated liner tube, and the core layer is etched by heating in a preset etching area; the fluorine-containing etchant in the prefabricated liner tube is controlled to react sufficiently with the core layer, and the dosage of the fluorine-containing etchant is controlled according to the core layer diameter d.

[0016] Preferably, the method for fabricating the high numerical aperture device polarization-maintaining fiber involves etching on a reflow lathe, wherein the fluorinated etchant is Freon or hexafluoroethane; the ratio of the furnace travel speed in the etched area to the non-etched area is 1:5 to 10, and the furnace travel speed in the etched area is between 35 and 45 mm / min; preferably,

[0017] Heating temperature: 1580–1680℃; Freon flow rate: 40–60 sccm in the etched area, 0 sccm in the non-etched area; Etching pass number adjusted according to core diameter d, controlled within [|π*d] 2 |,|π*d 2 |+1] passes, where || is the floor function and d is the core diameter in millimeters.

[0018] Preferably, in the method for fabricating the polarization-maintaining fiber for high numerical aperture devices, the length of the low-stress short region is between 80±30 mm.

[0019] Preferably, the method for preparing the polarization-maintaining fiber for high numerical aperture devices includes, in step (4), machining processes including cutting, tapering, tailing, and / or drilling.

[0020] Preferably, the fabrication method of the high numerical aperture device polarization-maintaining fiber includes the following machining steps in step (4):

[0021] The preform is cut in the processing section to obtain a slit preform; the middle part of the slit preform has a core-encased structure, with the core layer being a core rod formed by sintering and shrinking in the center and a pure quartz cladding on the outside; the two ends of the preform have low-stress end faces formed by the processing section.

[0022] Drill holes from the low-stress end face of the slit preform to form axially penetrating holes in the pure quartz cladding portion on both sides of the mandrel for inserting stress rods.

[0023] Preferably, in the method for fabricating the polarization-maintaining fiber of the high numerical aperture device, step (4) involves positioning by recording the etched area and / or by scanning with a polarizing microscope.

[0024] According to another aspect of the present invention, a polarization-maintaining fiber preform for a high numerical aperture device provided by the present invention is provided, comprising a perforated sleeve and a stress bar.

[0025] The perforated sleeve has a core-encased structure in the middle, with a core rod formed by the core layer being sintered and shrunk at the center and a pure quartz cladding on the outside; the prefabricated mother rod has low-stress end faces formed by cutting processing sections at both ends; the pure quartz cladding portions on both sides of the core rod have axially penetrating holes; the stress rod is inserted into the holes.

[0026] Preferably, the high numerical aperture device polarization-maintaining fiber preform has a core layer refractive index difference Δ of 1.8 to 3.8%; its curvature is ≤1mm / 1000mm, and its core-cladding concentricity is ≤0.3mm.

[0027] According to another aspect of the present invention, a polarization-maintaining fiber for high numerical aperture devices is provided, which is prepared by drawing a preform for the high numerical aperture device polarization-maintaining fiber provided by the present invention.

[0028] Preferably, the high numerical aperture device polarization-maintaining fiber has a typical difference in self-fusion loss of 0.01 dB, compared to a typical fusion splicing loss of 0.22 dB compared to a conventional 9 μm polarization-maintaining fiber.

[0029] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0030] The present invention discloses a method for fabricating polarization-maintaining optical fibers with high numerical aperture devices. After achieving high numerical aperture doping of the core rod using in-tube deposition, a low-stress processing segment is fabricated using a "segmented etching" method. This results in a core rod structure with high-stress doped core and low-stress processing segment intervals. Subsequent mechanical processing such as cutting and drilling is then performed. This method avoids the problem of core rod through-cracks caused by cutting or drilling during subsequent use, improves the yield, and enhances the concentricity and curvature of the preform, ultimately improving the performance of the optical fiber.

[0031] The high numerical aperture device polarization-maintaining fiber preform provided by this invention exhibits good concentricity and bowing. The resulting high numerical aperture device polarization-maintaining fiber has low self-fusion loss. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the etching process for removing the core layer in the etched area of ​​the present invention.

[0033] Figure 2 Schematic diagram of solid segmented preforms prepared by melt shrinkage;

[0034] Figure 3 This is a schematic diagram of the slit preform structure;

[0035] Figure 4 Schematic diagram of drilling holes for slitting precast bars;

[0036] Figure 5 A schematic diagram of polarization-maintaining fiber preform assembly, showing the assembly of perforated sleeves and stress bars;

[0037] Figure 6 Schematic diagram of fiber preform drawing for polarization-maintaining optical fiber;

[0038] Figure 7 A schematic diagram of the polarization-maintaining fiber end face structure of the high resin aperture device provided by the present invention.

[0039] Figure 8 Schematic diagram of segmented etching of the liner tube according to an embodiment of the present invention

[0040] Figure 9 Schematic diagram of a 400mm long solid segmented precast bar according to an embodiment of the present invention.

[0041] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1 is a liner, 2 is a fluorine-containing etchant, and 3 is a heating furnace. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0043] In this invention, the refractive index difference Δ is calculated as follows:

[0044]

[0045] Where, n core n is the refractive index of the fiber core. Si The refractive index is that of pure quartz.

[0046] The method for fabricating polarization-maintaining optical fibers for high numerical aperture devices provided by this invention includes the following steps:

[0047] (1) A core layer for forming a mandrel is deposited using an in-tube deposition method to obtain a prefabricated liner; the doping amount of Ge in the core layer is ≥1.8% of the relative refractive index difference Δ of the core layer.

[0048] Preferably, the core layer diameter is controlled to be 0.8–1.0 mm, the relative refractive index difference Δ between the core layer and the core rod is 1.8–3.8%, and the contribution rate of fluorine doping in the core layer is -0.033% to -0.9%.

[0049] (2) In the prefabricated liner obtained in step (1), etching is performed according to the preset etching area to remove the core layer and form a low-stress short region, resulting in a segmented liner with the core layer and the low-stress short region distributed axially at intervals; the low-stress section region is the remaining part after removing the core layer, and is designed according to the refractive index profile of the optical fiber, mostly made of pure quartz or fluorine-doped quartz; specifically, such as Figure 1 As shown:

[0050] A vaporized fluorinated etchant is introduced into a prefabricated liner, and the core layer is etched by heating in a predetermined etching area. The reaction between the fluorinated etchant and the core layer is controlled to be sufficient. Since the etched area is connected to the non-etched area, excessive fluorinated etchant can cause a deviation between the core layer deposition thickness and the designed thickness in the etched and non-etched areas. Specifically, the dosage of the fluorinated etchant is controlled according to the core layer diameter d.

[0051] Preferred solution: Etching is performed on a melting lathe, and the fluorinated etchant is Freon or hexafluoroethane; the ratio of the furnace travel speed of the etched area to that of the non-etched area is 1:5 to 10, and the furnace travel speed of the etched area is between 35 and 45 mm / min, so as to ensure that the etched area reaches the etching reaction temperature while the temperature of the non-etched area is below the etching reaction temperature, thereby improving the etching accuracy.

[0052] Heating temperature: 1580–1680℃; Freon flow rate: 40–60 sccm in the etched area, 0 sccm in the non-etched area; Etching pass number adjusted according to core diameter d, controlled within [|π*d] 2 |,|π*d 2 |+1] passes, where || is the floor function, and d is the core diameter in millimeters; based on experience, the etching end face area is controlled to be within 0.25mm per pass. 2 The etching precision is sufficient to meet the requirements.

[0053] The length of the low-stress short region is 80±30mm.

[0054] (3) The segmented liner obtained in step (2) is sintered and shrunk to obtain a solid segmented preform. The central region of the solid segmented preform has a core bar formed by the sintering and shrunking of the core layer and a processing section formed by the sintering and shrunking of a low-stress short region, such as... Figure 2 As shown;

[0055] The preferred solution adopts low-speed, low-power, micro-positive pressure melting and shrinking, with the melting and shrinking speed controlled between 10 and 20 mm / min, the melting and shrinking power controlled between 5 and 10 kW, and the pressure inside the tube controlled between 5 and 10 mbar higher than atmospheric pressure.

[0056] Solid segmented preforms consist of a single-piece core and processed segments, resulting in excellent collimation and core-cladding concentricity. This ensures that each part of the finished optical fiber has an ideal geometric structure, leading to good transmission performance, polarization retention, and low splice loss. The core undergoes a heat-forming and shrinking process, eliminating some stress and significantly reducing the risk of core breakage during subsequent machining steps.

[0057] (4) Position the processing section on the solid segmented precast bar obtained in step (3), perform machining on the processing section to obtain a perforated sleeve with holes for fitting stress bars; the machining includes cutting, tapering, connecting the tail bar, and / or drilling;

[0058] The machining section can be located by recording the etched area or by scanning with a polarizing microscope. The polarizing microscope can accurately locate the machining section by utilizing the refractive index difference between the high-refractive-index mandrel and the machining section.

[0059] After the low-stress short-area burn-in and shrinkage, the highly doped core layer is completely encapsulated. During machining, especially drilling, the probability of cracking or breaking of the rod is greatly reduced because the highly doped core layer is firmly fixed.

[0060] Typical machining steps are as follows:

[0061] The preforms are cut into smaller pieces in the processing section, such as... Figure 3 As shown; the middle part of the slit preform has a core-encased structure, with the core layer formed by sintering and shrinking in the center and a pure quartz cladding on the outside; the two ends of the preform have low-stress end faces formed by cutting the processing section;

[0062] Drill holes from the low-stress end face of the precast bar to create axially penetrating holes in the pure quartz cladding portions on both sides of the core bar for inserting the stress bar. Figure 4 As shown.

[0063] (5) Insert a stress rod into the hole position of the punched sleeve obtained in step (4), such as Figure 5 As shown, the polarization-maintaining fiber preform is drawn into fibers, as follows: Figure 6 As shown, the polarization-maintaining fiber of the high numerical aperture device was fabricated.

[0064] The present invention provides a polarization-maintaining fiber preform for high numerical aperture devices, comprising a perforated sleeve and a stress bar.

[0065] The perforated sleeve has a core-cladding structure in the middle, with a core rod formed by the solidification and shrinkage of the core layer at the center and a pure quartz cladding on the outside. The prefabricated master rod has low-stress end faces formed by cutting processing sections at both ends. The pure quartz cladding portions on both sides of the master rod have axially penetrating holes. The stress rod is inserted into these holes. The refractive index difference Δ between the core rod and the core layer is 1.8–3.8%, with a fluorine doping contribution rate of -0.033% to -0.9%. The diameter of the pure quartz cladding is controlled at 40±0.5 mm, with a curvature ≤1 mm / 1000 mm and a concentricity ≤0.3 mm.

[0066] The high numerical aperture device polarization-maintaining fiber provided by this invention, such as... Figure 7As shown, the preform for polarization-maintaining fiber of the above-mentioned high numerical aperture device is drawn into fibers. Its typical self-fusion loss difference is 0.01 dB, which is a significant improvement compared to the typical fusion splicing loss of 0.22 dB for ordinary 9 μm polarization-maintaining fiber. Commonly used geometric parameters are satisfied: cladding diameter 125 ± 1 μm, cladding roundness ≤ 2%, core-cladding concentricity ≤ 1 μm, coating diameter 245 ± 5 μm. Commonly used optical parameters are satisfied: mode field diameter @1310 3.5 ± 0.5 μm, mode field diameter @1550 4.0 ± 0.5 μm, cutoff wavelength 1100~1290 nm, beat length @1550 ≤ 3 mm, crosstalk @1550 ≤ -30 dB / 100 m, 10 mm 10-turn macrobend loss ≤ 0.01 dB, 10 mm 5-turn macrobend crosstalk ≤ -30 dB.

[0067] The following is an example:

[0068] Example 1

[0069] The method for fabricating high numerical aperture device polarization-maintaining fiber in step 1 provided by this invention includes the following steps:

[0070] (1) The in-tube deposition method is used to deposit the core layer used to form the mandrel to obtain the prefabricated liner.

[0071] The mandrel was prepared using the PCVD process, first depositing a pure quartz cladding, then depositing a highly Ge-doped core layer. Due to the high Ge doping content in the core layer, to ensure axial uniformity of the doping and reduce the volatilization of deposited germanium dioxide at high temperatures during core layer deposition, the furnace temperature needed to be controlled below 1100℃, the deposition rate 0.5–1.0 g / min, and the tube pressure controlled at 10–15 mbar to improve conversion efficiency and avoid problems such as bubbles. The core layer diameter was controlled at 0.8–1.0 mm, the core layer Δ was controlled at 2.4% ± 0.2%, and the pure quartz cladding diameter was 40 ± 0.5 mm.

[0072] (2) In the prefabricated liner obtained in step (1), etching is performed according to the preset etching area to remove the core layer and form a low-stress short region, thereby obtaining a segmented liner with the core layer and the low-stress short region distributed axially at intervals; specifically:

[0073] Segmented etching of the liner (e.g.) Figure 8 As shown, the filled area is the etched area. Specific etching parameters are as follows:

[0074]

[0075]

[0076] After multiple tests, using these parameters, 3-4 etching passes are sufficient to completely etch the core layer in the etched area without causing bending or deformation of the liner. π*d 2=3.14, where d is 1 mm, and the number of etching passes is 3 to 4.

[0077] (3) The segmented liner obtained in step (2) is sintered and shrunk to obtain a solid segmented preform. The central region of the solid segmented preform has a core rod formed by the sintering and shrunking of the core layer and a processing segment formed by the sintering and shrunking of a low-stress short region distributed axially at intervals. Specifically:

[0078] The etched liner is then melted and shrunk. Due to the high doping content in the core layer and the significant viscosity difference between the core glass and the cladding glass, this invention employs low-speed, low-power, and slightly positive-pressure melting and shrunking. The melting and shrunking speed is controlled at 10–20 mm / min, the melting and shrunking power at 5–10 kW, and the internal pressure at 5–10 mbar above atmospheric pressure. This produces a solid preform with a core roundness ≤2%, rod roundness ≤0.3%, core-cladding concentricity ≤0.3 mm, and curvature ≤1 mm / 1000 mm. The etched area forms a pure quartz portion, facilitating subsequent cutting and drilling.

[0079] The specific parameters are shown in the table below:

[0080] Core roundness 1.6 0.7 0.5 1.3 0.9 Rod roundness 0.3 0.2 0.1 0.3 0.2 Core-packet concentricity 0.2 0.3 0.2 0.2 0.1 Bow curvature 0.9 0.4 0.5 0.8 0.7

[0081] (4) Position the processing section on the solid segmented preform obtained in step (3), perform machining on the processing section, and obtain a perforated sleeve with holes for fitting stress rods.

[0082] The shrunk solid preform was observed under a polarizing microscope, clearly distinguishing the pure quartz portion and the core layer. A 50mm length was measured from the boundaries of the core layer towards the pure quartz portion and marked. The marked sections were then cut to obtain three 400mm long solid segmented preforms, as shown below. Figure 9 As shown, slit preforms are obtained.

[0083] The slit preforms are punched with a hole coordinate of ±8.5mm and a hole diameter of 13mm to obtain a punched sleeve.

[0084] Stress bars were prepared using PCVD technology, with the diameter of the boron region controlled at 11–12 mm and the doping concentration controlled at 18 ± 2% mol.

[0085] (5) Insert stress rods into the holes of the perforated sleeve obtained in step (4) to form a polarization-maintaining fiber preform, and then draw it to obtain the polarization-maintaining fiber of the high numerical aperture device. Specifically:

[0086] All glass raw materials (including 1 perforated sleeve and 2 stress rods) are cleaned (alkali washing, acid washing, water washing) and thoroughly dried before being assembled into polarization-maintaining RIT, i.e. polarization-maintaining fiber preform.

[0087] The assembled polarization-maintaining RIT is placed in a drawing furnace for drawing. High NA polarization-maintaining fiber is obtained. Its parameters meet the following requirements: 1) Geometric parameters: cladding diameter 125±1um, cladding roundness ≤1%, core-cladding concentricity ≤0.5um, coating diameter 245±5um; 2) Optical parameters: cutoff wavelength 1100~1290nm, mode field diameter @1310 3.5±0.5um, mode field diameter @1550 4.0±0.5um, beat length @1550≤3mm, crosstalk @1550≤-30dB / 100m, and has good end-face polishing performance.

[0088] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for fabricating polarization-maintaining optical fibers for high numerical aperture devices, characterized in that, Includes the following steps: (1) A core layer for forming a mandrel is deposited using an in-tube deposition method to obtain a pre-fabricated liner; the doping amount of Ge in the core layer makes the relative refractive index difference Δ of the core layer ≥ 1.8%; (2) In the prefabricated liner obtained in step (1), segmented etching is performed according to the preset etching area to remove the core layer and form a low-stress short region, thereby obtaining a segmented liner with a core layer and a low-stress short region distributed axially. (3) The segmented liner obtained in step (2) is sintered and shrunk to obtain a solid segmented preform. The solid segmented preform has a core bar formed by sintering and shrunk core layer and a processing section formed by sintering and shrunk low stress short area in the central region of the solid segmented preform. (4) Position the processing section on the solid segmented preform obtained in step (3), perform machining on the processing section, and obtain a perforated sleeve with holes for fitting stress rods. (5) Insert stress rods into the holes of the perforated sleeve obtained in step (3) to form polarization-maintaining fiber preforms and draw them to obtain the polarization-maintaining fiber of the high numerical aperture device.

2. The method for fabricating polarization-maintaining optical fiber for high numerical aperture devices as described in claim 1, characterized in that, The relative refractive index difference Δ of the core layer is ≤3.8%, wherein the contribution rate of fluorine doping in the core layer is -0.033% to -0.9%; the diameter of the core layer is controlled to be 0.8 to 1.0 mm.

3. The method for fabricating polarization-maintaining optical fiber for high numerical aperture devices as described in claim 1, characterized in that, Step (2) is as follows: A vaporized fluorine-containing etchant is introduced into a prefabricated liner tube, and the core layer is etched by heating in a preset etching area; the fluorine-containing etchant in the prefabricated liner tube is controlled to react sufficiently with the core layer, and the dosage of the fluorine-containing etchant is controlled according to the core layer diameter d.

4. The method for fabricating polarization-maintaining optical fiber for high numerical aperture devices as described in claim 3, characterized in that, Etching is performed on a melting lathe, and the fluorinated etchant is Freon or hexafluoroethane; the ratio of the furnace travel speed of the etched area to the non-etched area is 1:5~10, and the furnace travel speed of the etched area is between 35~45mm / min. The heating temperature is 1580-1680℃, the freon flow rate of the etching area is 40-60sccm, the freon flow rate of the non-etching area is 0; the etching times are adjusted according to the core layer diameter d, and the etching times are controlled in the range of |π*d 2 | or |π*d 2 |+1 times, wherein | | is the floor operation, and d is the core layer diameter in millimeter.

5. The method for fabricating polarization-maintaining optical fiber for high numerical aperture devices as described in claim 1, characterized in that, The length of the low-stress short region is between 80±30 mm.

6. The method for fabricating polarization-maintaining optical fiber for high numerical aperture devices as described in claim 1, characterized in that, The machining process described in step (4) includes cutting, tapering, tailing, and / or drilling.

7. The method for fabricating polarization-maintaining optical fiber for high numerical aperture devices as described in claim 6, characterized in that, Step (4) The machining steps are as follows: The preform is cut in the processing section to obtain a slit preform; the middle part of the slit preform has a core-encased structure, with the core layer being a core rod formed by sintering and shrinking in the center and a pure quartz cladding on the outside; the two ends of the preform have low-stress end faces formed by the cutting in the processing section. Drill holes from the low-stress end face of the slit preform to form axially penetrating holes in the pure quartz cladding portion on both sides of the mandrel for inserting stress rods.

8. The method for fabricating polarization-maintaining optical fiber for high numerical aperture devices as described in claim 1, characterized in that, Step (4) Positioning is performed by recording the etched area and / or by scanning with a polarizing microscope.

9. A polarization-maintaining fiber preform for high numerical aperture devices, characterized in that, Prepared according to the preparation method described in any one of claims 1 to 8.

10. The polarization-maintaining fiber preform for high numerical aperture devices as described in claim 9, characterized in that, Includes perforated sleeves and stress bars; The perforated sleeve has a core-encased structure in the middle, with a core rod formed by the core layer being sintered and shrunk at the center and a pure quartz cladding on the outside; the prefabricated mother rod has low-stress end faces formed by cutting processing sections at both ends; the pure quartz cladding portions on both sides of the core rod have axially penetrating holes; the stress rod is inserted into the holes.

11. The polarization-maintaining fiber preform for high numerical aperture devices as described in claim 10, characterized in that, The refractive index difference Δ of the core rod is 1.8~3.8%; its curvature is ≤1mm / 1000mm, and its core-pack concentricity is ≤0.3mm.

12. A polarization-maintaining fiber for high numerical aperture devices, characterized in that, The high numerical aperture device polarization-maintaining fiber preform is prepared by drawing as described in any one of claims 9 to 11.

13. The polarization-maintaining fiber for high numerical aperture devices as described in claim 12, characterized in that, The typical difference in self-fusion loss is 0.01 dB.

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