A nested antiresonant hollow-core optical fiber and its preparation method

Abstract

The present invention belongs to the field of optical fiber communication technology, specifically a nested antiresonant hollow-core optical fiber and a preparation method thereof. The nested antiresonant hollow-core optical fiber of the present invention comprises: an optical fiber outer cladding, a nested antiresonant ring and a core region. The preparation method comprises: first assembling and fitting the embedded components, fixed tubular shapes and sleeves of each tube of the optical fiber preform, and then fusing and blowing to form a stable and reliable optical fiber preform structure; then, during drawing the optical fiber preform, the shape of each component is controlled by adjusting the inflation pressure to achieve a nested antiresonant ring with negative curvature, and a nested antiresonant hollow-core optical fiber is drawn. The present invention adopts an antiresonant hollow-core optical fiber preform, and the internal structure is greatly simplified, so that high-precision positioning of antiresonant structural elements can be achieved, and the antiresonant ring can be pulled thinner, so that the antiresonant hollow-core optical fiber maintains a low transmission loss, avoiding the limitations and complexity of traditional manufacturing methods.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber communication, and in particular relates to a hollow-core optical fiber, an optical fiber and a preparation method thereof. Background Art

[0002] Traditional solid-core optical fibers, such as step-index optical fibers, use a material with a higher refractive index for the core and a material with a lower refractive index for the cladding, allowing light to be guided by total internal reflection. New hollow-core optical fibers are no longer limited to the traditional total internal reflection light-guiding principle. The refractive index of the core of the optical fiber can be lower than that of the cladding, and optical fibers with a low-refractive-index core can also transmit light. Based on the different light-guiding mechanisms, hollow-core optical fibers are roughly divided into three categories: hollow-core Bragg-clad optical fibers, hollow-core photonic bandgap optical fibers, and hollow-core antiresonant optical fibers. Unlike earlier hollow-core photonic bandgap optical fibers, the light-guiding mechanism of hollow-core antiresonant optical fibers does not rely on the photonic bandgap effect, so the requirements for the cladding refractive index arrangement are not strict. They have unique advantages such as simple structure, high transmission bandwidth, large core size, and low overlap of mode field energy with the cladding material.

[0003] Hollow-core optical fiber has its unique advantages. Compared with solid-core optical fiber, the Kerr nonlinearity of air is three orders of magnitude lower than that of silica material, which greatly reduces the nonlinear coefficient of hollow-core optical fiber. In addition, this type of optical fiber has smaller dispersion and 30% lower latency, making it particularly suitable for optical communication transmission. It has become a frontier and hot topic in the field of optical fiber technology research.

[0004] Despite the significant advantages offered by hollow-core fibers in their applications, their transmission loss remains higher than that of traditional solid-core fibers. Recent discoveries have shown that hollow-core fibers based on the antiresonance principle, with appropriate structural design, can effectively reduce these transmission losses. In particular, fibers with nested structural elements have the potential to be used as ultra-long-haul communication fibers. In antiresonant fibers, light in the air is confined to the core by surrounding multiple quartz rings. Transmission loss is primarily determined by leakage loss and surface scattering loss. Furthermore, the presence of nodes at the junctions between the quartz rings, particularly those with varying thicknesses, introduces spurious and spectrally dense resonant loss peaks within the antiresonance region, resulting in additional losses.

[0005] Further reducing loss is a key issue in hollow-core fiber manufacturing. However, due to the complex internal shape of hollow-core fibers, particularly those with nested structural elements, even slight geometric deviations on the order of the operating wavelength of the transmitted light can lead to changes in antiresonance conditions in order to maintain them, making accurate and repeatable fabrication difficult. Deviations from the target geometry can be caused by the configuration of the fiber preform and disproportionate deformation during the drawing of the intermediate.

[0006] Document WO2018169487A1 discloses a method for manufacturing an antiresonant hollow-core optical fiber preform, wherein the first cladding region includes a plurality of rods, and the second cladding region includes a plurality of tubes surrounded by an outer cladding tube. The rods, tubes, and cladding tubes are combined together to form a preform by a "stack-drawing" technique. Before the preform is stretched, the ends of the preform are sealed by applying a sealant. For example, a UV adhesive is used as a sealant. The complex internal geometry of this method makes it difficult to prepare accurately and repeatably. A slight deviation in the geometry will cause the antiresonance condition to be destroyed, affecting the low attenuation and wide transmission spectrum performance.

[0007] Document CN115521059A proposes an optical fiber preform assembled from a polygonal inner-bore sleeve and a polygonal capillary tube, then controlling the pressure increase in the polygonal capillary during the drawing process to create an optical fiber with a negative curvature antiresonant ring structure. However, the polygonal capillary tube in this method is extremely difficult to manufacture, and the connection plate structure during the drawing process is also unstable, resulting in poor optical performance repeatability of the drawn optical fiber.

[0008] Document CN115745391A proposes a method for preparing an integrated hollow-core optical fiber preform and optical fiber. The initial preform is obtained by drilling. During drawing, the axial hole is filled with air at a pressure higher than that at the center of the casing. The axial hole bulges toward the casing's center hole, forming an antiresonant ring with negative curvature. However, during actual inflation, the quartz wall thickness between the axial hole and the casing's center hole is arc-shaped and uneven, resulting in significant fluctuations in the wall thickness of the antiresonant ring, affecting the antiresonance effect. Furthermore, the roughness of the inner walls of the axial hole and the center hole after drilling can dramatically increase the surface scattering loss of the hollow-core optical fiber, making it impossible to achieve low-loss performance.

[0009] In the known "stack-and-draw" technique for hollow-core fibers, numerous components must be precisely joined together. The fabrication of an antiresonant hollow-core fiber requires the connection and fixing of several nodeless antiresonant tubes to the inner surface of a cladding tube. This is particularly challenging for nested antiresonant hollow-core fibers, where the antiresonant tubes consist of an outer tube and an inner tube. The multi-layer antiresonant structure is particularly challenging to fabricate, and ensuring uniformity is difficult. However, achieving low loss and a wide transmission spectrum requires both uniform wall thickness and azimuthal uniformity, which are not easily achieved using the "stack-and-draw" technique. Summary of the Invention

[0010] In view of the problems existing in the prior art, the object of the present invention is to provide a high-precision, low-difficulty, high-performance anti-resonant hollow-core optical fiber and a preparation method thereof.

[0011] The present invention first provides an antiresonant hollow-core optical fiber preform for preparing antiresonant hollow-core optical fiber. By fitting and fixing the various tubes within the optical fiber preform, and then fusing and blowing to form a stable structure, the positioning of the various components within the optical fiber preform is made more secure and precise, preventing the position of the antiresonant ring within the optical fiber preform from shifting and twisting during the subsequent drawing process. Compared with the traditional stacking method, the internal structure is greatly simplified, but the high-precision positioning of the antiresonant structural elements can be achieved in a sufficiently stable and repeatable manner. During the subsequent drawing process to prepare the antiresonant hollow-core optical fiber, the various components within the optical fiber preform are firmly bonded throughout, which can make the antiresonant ring thinner, maintain low transmission loss for the antiresonant hollow-core optical fiber, and avoid the limitations and complexity of traditional manufacturing methods.

[0012] The anti-resonant hollow-core optical fiber preform provided by the present invention comprises: a sleeve, an embedded element and a tubular element; wherein:

[0013] The sleeve is a quartz tube with a circular outer cross section and a polygonal inner cross section; the embedded element and the tubular element are wrapped inside the sleeve.

[0014] The embedded element is a quartz tube structure; the embedded element is originally a circular tube, which is inside the sleeve and its outer edge is tangent to the polygonal inner cavity wall inside the sleeve (see Figure 1 After heating and introducing a suitable amount of pressure gas into the embedded component to expand the embedded component, the contact range between the embedded component and the polygon inside the sleeve changes from the tangent point to the partial surface fit (see Figure 2 ), forming an embedded component.

[0015] The tubular element, specifically a quartz capillary, is fixedly arranged at the angle formed by the adjacent inner walls of the polygonal inner cavity of the sleeve, and is in contact with the two inner walls of the sleeve. The area surrounded by the capillaries constitutes the center hole of the preform rod. The number of tubular elements is the same as the number of sides of the polygonal inner cavity of the sleeve, see Figure 3 .

[0016] The method for preparing an antiresonant hollow-core optical fiber provided by the present invention comprises the following specific steps:

[0017] (1) Preparing an antiresonant hollow-core optical fiber preform, the specific steps are:

[0018] (1) Prepare a quartz rod, grind its outer surface and drill a polygonal hole inside it to make a sleeve; the cross section of the sleeve is circular on the outside and polygonal on the inside;

[0019] A circular quartz tube is prepared and processed so that its outer diameter is equal to the inscribed circle diameter of the polygon inside the sleeve and its wall thickness reaches the designed target value, thereby producing an embedded component;

[0020] (2) Insert the circular quartz assembly into the sleeve, heat the combined sleeve and embedded component by various methods such as hydrogen-oxygen flame, heating furnace or laser welding, and introduce gas of appropriate pressure into the embedded component to expand the embedded component so that the contact range between the embedded component and the polygon in the sleeve changes from the tangent point to the partial surface fit, thereby forming the embedded component;

[0021] (3) Place the tubular element at the angle formed by the adjacent walls of the polygonal inner cavity of the sleeve, so that it fits the two inner walls of the sleeve; and fix it to each corner of the polygon inside the sleeve using various heating methods such as oxyhydrogen flame, heating furnace, or laser welding. The number of tubular elements is the same as the number of sides of the polygonal inner cavity of the sleeve. In this way, an antiresonant hollow-core optical fiber preform is obtained.

[0022] (2) Preparation of antiresonant hollow core optical fiber, the specific steps are as follows:

[0023] (1) Drawing the prepared antiresonant hollow core optical fiber preform into an intermediate, during which nitrogen gas at a pressure of 0.5 to 4 kPa is introduced into the tubular element, and nitrogen gas at a pressure of 0.1 to 1 kPa is introduced between the embedded element and the tubular element to expand the embedded element and the tubular element, while maintaining the embedded element and the tubular element in a non-contact state; Figure 4 As shown;

[0024] (2) Insert the prepared hollow core optical fiber intermediate into the quartz outer tube, see Figure 4 As shown. It is assembled with the inflation mold, and inflation microtubes of different sizes are inserted into the embedded element, the tubular element, and between the embedded element and the tubular element for independent gas supply. Vacuum is drawn between the hollow-core optical fiber intermediate and the quartz outer sleeve.

[0025] (3) The size and shape of the embedded element and the tubular element are controlled by adjusting different pressure values. The pressure of the gas in the embedded element, the tubular element, and the space between the embedded element and the tubular element is 0.1-2.0 kPa, 10-20 kPa, and 2-10 kPa, respectively, thereby controlling the size and shape of the embedded element and the tubular element. Due to the internal and external pressure difference and the surface tension, the drawing forms a nested anti-resonant inner ring and a nested anti-resonant outer ring with negative curvature, forming a nested anti-resonant ring (the number of which is the number of tubular elements), and adjacent anti-resonant rings do not contact each other. All anti-resonant rings together form a ring-shaped anti-resonant layer, and the area surrounded by the anti-resonant layer constitutes the core of the hollow-core optical fiber. The anti-resonant layer and the sleeve and outer sleeve after drawing together constitute the cladding for protecting the core. Thus, a nested anti-resonant hollow-core optical fiber is obtained, whose structure includes: an outer cladding layer of optical fiber (i.e., a quartz outer sleeve), a nested anti-resonant ring layer, and a core region. The core region is defined by an inscribed circle of the area surrounded by multiple evenly arranged anti-resonant rings.

[0026] Furthermore, in step (1):

[0027] The interior of the sleeve is a regular polygon with the number of sides being greater than or equal to 4.

[0028] The embedded element and the tubular element are both circular.

[0029] The outer diameter of the sleeve is 20-80 mm, and the ratio of the diameter of the circumscribed circle of the regular polygon inside the sleeve to the outer diameter of the sleeve is 0.2-0.8.

[0030] The wall thickness of the embedded component ranges from 1 to 8 mm.

[0031] The outer diameter of the tubular element is 1 to 5 mm, and the wall thickness ranges from 0.2 to 2 mm.

[0032] The gas introduced into the embedded component is any one or more of compressed air, nitrogen, helium and argon.

[0033] The embedded element partially fits within the polygonal portion of the sleeve, specifically meaning that the embedded element fits within any side of the sleeve polygon for a length of not less than 40% of the side length of the sleeve polygon, and the distance between the side of the embedded element and the tubular element is not less than 10% of the outer diameter of the tubular element. The difference in length between each side of the sleeve polygon and the embedded element for the partial fit does not exceed 5%.

[0034] Furthermore, in step (2):

[0035] The outer diameter of the quartz outer sleeve is determined by the core diameter and cladding diameter of the target nested antiresonant hollow core optical fiber.

[0036] The gas introduced into each component in the sleeve is any one or more of compressed air, nitrogen, helium and argon.

[0037] Adjacent antiresonant rings formed after wire drawing do not contact each other (ie, there is a gap between them).

[0038] The core diameter is 8 to 55 μm, and the cladding diameter is 80 to 330 μm.

[0039] The wall thickness t of the fiber nested antiresonant ring ranges from 0.1 to 2 μm and also meets the antiresonant reflection condition:

[0040]

[0041] where λ m is the resonant wavelength, m is the order of the antiresonant layer, and n is the refractive index of the nested antiresonant ring.

[0042] The prepared nested antiresonant hollow-core optical fiber has low transmission loss, with the lowest transmission loss at 1550nm being ≤1dB / km, and even better being ≤0.2dB / km.

[0043] Compared with the prior art, the present invention has the following beneficial effects.

[0044] (1) The anti-resonant hollow-core optical fiber preform proposed in the present invention is fixed by fitting the various tubes therein, and then fused and blown to form a stable structure, so that the positioning between the various components in the optical fiber preform is more secure and precise, and the position of the anti-resonant ring in the optical fiber preform is prevented from being offset and twisted during the subsequent drawing process.

[0045] (2) In the preparation method of the present invention, a nested antiresonant ring with negative curvature is achieved by fusing a tubular element to the corners of a regular polygon inside a sleeve. Using only circular and tubular quartz pieces, an antiresonant hollow-core fiber preform can be prepared, significantly simplifying the internal structure and making the preparation process simple, easy to implement, and highly stable, significantly improving the transmission performance of the optical fiber.

[0046] (3) The present invention prepares a nested antiresonant hollow-core optical fiber by drawing the above-mentioned antiresonant hollow-core optical fiber preform, which can achieve high-precision positioning of antiresonant structural elements in a sufficiently stable and repeatable manner. During the drawing process, the components in the optical fiber preform are tightly adhered throughout the entire process, which can make the antiresonant ring thinner, improve the consistency of each antiresonant ring, and maintain a low transmission loss of the antiresonant hollow-core optical fiber, avoiding the limitations and complexity of traditional manufacturing methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a schematic diagram of assembling an antiresonant hollow-core optical fiber preform provided in Example 1 of the present invention.

[0048] Figure 2 It is a schematic diagram of preparing an antiresonant hollow-core optical fiber preform provided in Example 1 of the present invention.

[0049] Figure 3 It is a structural schematic diagram of an antiresonant hollow-core optical fiber preform provided in Example 1 of the present invention.

[0050] Figure 4 It is a structural schematic diagram of an antiresonant hollow-core optical fiber intermediate and a quartz outer sleeve provided in Example 1 of the present invention.

[0051] Figure 5 It is a schematic structural diagram of the nested antiresonant hollow-core optical fiber provided in Example 1 of the present invention.

[0052] Figure 6 This is a transmission loss curve diagram of a nested antiresonant hollow-core optical fiber provided in Example 1 of the present invention.

[0053] Figure 7 This is a mode field diagram of a nested antiresonant hollow-core optical fiber provided in Example 1 of the present invention.

[0054] Figure 8This is a distribution diagram of transmission loss test data at 1550nm of a nested antiresonant hollow-core optical fiber prepared by the method of the present invention in Example 2 of the present invention.

[0055] Figure 9 This is a distribution diagram of transmission loss test data at 1550nm for preparing nested antiresonant hollow-core optical fibers using the "stacking method / positioning method" in Example 2 of the present invention.

[0056] Figure 10 This is a distribution diagram of transmission loss test data at 1550nm of a nested antiresonant hollow-core optical fiber prepared by the "punching method" in Example 2 of the present invention.

[0057] Numbers in the figure: 1-sleeve, 2-quartz tube, 3-embedded element, 4-tubular element, 5-antiresonant hollow-core fiber preform, 6-intermediate, 7-nested antiresonant inner ring, 8-nested antiresonant outer ring, 9-nested antiresonant hollow-core fiber, 10-quartz outer sleeve. DETAILED DESCRIPTION

[0058] The present invention is further described below through embodiments in conjunction with the accompanying drawings.

[0059] The anti-resonant hollow-core optical fiber preform provided by the present invention comprises: a sleeve, an embedded element and a tubular element; wherein:

[0060] The sleeve is a quartz tube with a circular outer cross section and a polygonal inner cross section, and the embedded element and the tubular element are wrapped inside.

[0061] The embedded element, a quartz tube structure, is located inside the sleeve, with its outer edge tangent to the polygon inside the sleeve. The combined sleeve and embedded element are heated, and gas at an appropriate pressure is introduced into the embedded element to expand the embedded element, causing its contact area with the polygon inside the sleeve to change from a tangent point to a partial fit.

[0062] The tubular element, a quartz tube structure, is fixedly positioned at the angle formed by adjacent inner walls of the sleeve, conforming to both inner walls. The area enclosed by the capillaries forms the preform's central hole. The number of tubular elements is equal to the number of sides of the polygon within the sleeve.

[0063] The method for preparing the antiresonant hollow-core optical fiber preform comprises the following specific steps:

[0064] (1) Prepare a quartz rod, grind its outer diameter and drill its inner polygon to make a sleeve. Prepare a quartz tube, process its outer diameter to be equal to the inscribed circle diameter of the inner polygon of the sleeve, and make its wall thickness reach the design target value to make an embedded component.

[0065] (2) The embedded component is assembled and inserted into the sleeve, and the combined sleeve and embedded component are heated by various methods such as hydrogen-oxygen flame, heating furnace or laser welding, and a gas of appropriate pressure is introduced into the embedded component to expand the embedded component so that the contact range between the embedded component and the polygon in the sleeve changes from the tangent point to partial fit.

[0066] (3) Place the tubular element at the angle formed by adjacent inner walls of the sleeve, fitting it to the two inner walls of the sleeve. Use various heating methods, such as an oxyhydrogen flame, a heating furnace, or laser welding, to secure it to each corner of the regular polygon inside the sleeve. This produces an antiresonant hollow-core fiber preform.

[0067] The method for preparing a nested antiresonant hollow-core optical fiber using the above-mentioned antiresonant hollow-core optical fiber preform comprises the following specific steps:

[0068] (1) The prepared antiresonant hollow-core optical fiber preform is drawn into an intermediate. During the drawing process, gas of appropriate pressure is introduced into the tubular element and between the embedded element and the tubular element to expand the embedded element and the tubular element, while keeping the embedded element and the tubular element in a non-contact state.

[0069] (2) The prepared hollow-core optical fiber intermediate is inserted into a quartz outer sleeve and assembled with an inflation mold. Inflatable microtubes of different sizes are inserted into the embedded element, the tubular element, and between the embedded element and the tubular element for independent gas supply. A vacuum is drawn between the hollow-core optical fiber intermediate and the quartz outer sleeve.

[0070] (3) By adjusting different pressure values ​​to control the size and shape of the embedded elements and tubular elements, due to the internal and external pressure difference and the effect of surface tension, the drawing process forms nested antiresonant rings with negative curvature. All antiresonant rings together form a ring-shaped antiresonant layer. The area surrounded by the antiresonant layer constitutes the core of the hollow-core fiber. The antiresonant layer, the drawn sleeve, and the outer sleeve together form the cladding that protects the core. In this way, a nested antiresonant hollow-core fiber is produced.

[0071] Example 1,

[0072] (1) Preparation of antiresonant hollow-core fiber preform:

[0073] Prepare a quartz rod, grind its outer diameter and drill its inner polygon until its diameter is 60mm and its inner part is processed into a regular pentagon with a diameter of 45mm. Then prepare a quartz tube 2 with an outer diameter of 36.3mm and a wall thickness of 1.3mm. Insert the quartz tube 2 into the inner part of the sleeve 1 and make it tangent to the polygon inside the sleeve 1. Figure 1The combined sleeve and embedded component are heated using an oxyhydrogen flame, and nitrogen gas with a pressure of 0.1 MPa is introduced into the quartz tube 2 to expand the quartz tube 2 so that the contact range between the quartz tube 2 and the polygon inside the sleeve 1 changes from the tangent point to a partial fit, thereby obtaining the embedded component 3, as shown in FIG. Figure 2 As shown. The quartz tube 2 is bonded to one side of the polygon inside the sleeve 1 for a length of 23.5 mm, thereby obtaining an embedded component 3. Five quartz tubular components 4 are prepared, with an outer diameter of 6.5 mm and a wall thickness of 1.1 mm. They are fixed at the angle formed by the adjacent inner walls of the sleeve, and bonded to the two inner walls of the sleeve. The tubular components 4 are fused and fixed to each corner of the regular polygon inside the sleeve using an oxyhydrogen flame, thereby obtaining an antiresonant hollow-core optical fiber preform 5, as shown. Figure 3 shown.

[0074] (2) Preparation of nested antiresonant hollow-core fiber:

[0075] like Figure 4 As shown, the prepared antiresonant hollow-core optical fiber preform 5 is drawn into an intermediate 6 in a graphite heating furnace. During the drawing, nitrogen gas with a pressure of 1.5 KPa is introduced into the tubular element, and nitrogen gas with a pressure of 0.5 KPa is introduced between the embedded element and the tubular element to expand the embedded element and the tubular element, and to keep the embedded element and the tubular element in a non-contact state. The prepared hollow-core optical fiber intermediate 6 is inserted into a quartz outer sleeve and assembled with an inflation mold. Inflatable microtubes of different sizes are inserted into the embedded element, the tubular element, and between the embedded element and the tubular element for independent gas supply, and a vacuum is drawn between the hollow-core optical fiber intermediate and the quartz outer sleeve. The inflation pressures in the embedded element, the tubular element, and between the embedded element and the tubular element are 1.1 KPa, 14.2 KPa, and 5.2 KPa, respectively, thereby controlling the size and shape of the embedded element and the tubular element. As shown Figure 5 As shown, due to the internal and external pressure difference and the effect of surface tension, drawing forms a nested antiresonant inner ring 7 and a nested antiresonant outer ring 8 with negative curvature. The adjacent antiresonant rings formed after drawing do not contact each other, and all the antiresonant rings together constitute a ring-shaped antiresonant layer. The area surrounded by the antiresonant layer constitutes the core of the hollow-core optical fiber. The antiresonant layer and the sleeve and outer sleeve after drawing together constitute the cladding that protects the core. Thus, a nested antiresonant hollow-core optical fiber 9 is obtained. The outer diameter of the cladding of the nested antiresonant hollow-core optical fiber 9 is 250μm, the core diameter is 40μm, the inner diameter of the nested antiresonant inner ring 7 is 24μm, the minimum wall thickness is 1.15μm, and the inner diameter of the nested antiresonant outer ring 8 is 43.7μm, and the minimum wall thickness is 1.15μm. As shown Figure 6 As shown, the transmission loss of this fiber at 1550nm is 0.2dB / km, and the mode field diagram of this nested antiresonant hollow core fiber is as follows Figure 7 shown.

[0076] Example 2

[0077] The nested antiresonant hollow-core optical fiber preforms were repeatedly prepared and drawn according to the above-mentioned Example 1 of the present invention, and only optical fibers with a single reel length of not less than 500m were retained. The transmission loss of the nested antiresonant hollow-core optical fibers prepared with a total length of 50km was tested at 1550nm using the truncation method. The data distribution is as follows: Figure 8 As shown. Then, the "stacking method / positioning method" (reference patent CN113905991A) and the "punching method" (reference patent CN115745391A) were used to prepare nested antiresonant hollow-core optical fibers. The relevant parameters of the optical fibers were consistent with the cladding outer diameter, core diameter, and minimum wall thickness of the nested antiresonant inner ring and outer ring of the nested antiresonant hollow-core optical fiber in Example 1. The transmission loss test at 1550nm was conducted on the prepared 50km nested antiresonant hollow-core optical fibers using the truncation method. The data distribution is shown as follows: Figure 9 and Figure 10 shown.

[0078] A comparison shows that the median transmission loss data of the nested antiresonant hollow-core optical fiber prepared by the present invention is smaller, and the data distribution is the most convergent. The median transmission loss data of the nested antiresonant hollow-core optical fiber prepared by the "stacking method / positioning method" is slightly higher than the experimental data of the present invention, but the data distribution is very discrete, indicating that the repeatability of the prepared optical fiber is poor. The overall distribution of the transmission loss data of the nested antiresonant hollow-core optical fiber prepared by the "punching method" is more convergent, but the median transmission loss is relatively large. The reason is that the punching method causes microcracks and poor roughness on the surface of the quartz component, causing the surface scattering loss to worsen.

[0079] After considering the specification and practicing the invention disclosed herein, those skilled in the art will readily understand that the foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. The above specific implementations may be partially adjusted, replaced with equivalents, improved, etc. in various ways by those skilled in the art without departing from the principles and purpose of the present invention. The scope of protection of the present invention shall be based on the claims and shall not be limited by the above specific implementations, and all implementations thereof shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing an antiresonant hollow-core optical fiber, characterized in that: The specific steps are as follows: (1) Preparation of an antiresonant hollow-core optical fiber preform, the specific steps are as follows: (1) Prepare a quartz rod, grind its outer surface and drill its inner polygonal hole to make a sleeve; its cross section is circular on the outside and polygonal on the inside; A quartz tube is prepared and processed so that its outer diameter is equal to the inscribed circle diameter of the polygon inside the sleeve and its wall thickness reaches the design target value, thereby manufacturing an embedded component; (2) Assemble the embedded component and insert it into the sleeve, heat the assembled sleeve and embedded component, and introduce a suitable amount of pressure gas into the embedded component to expand the embedded component so that the contact range between the embedded component and the polygon in the sleeve changes from the tangent point to the partial surface fit; (3) placing the tubular element at the angle formed by the adjacent walls of the polygonal inner cavity of the sleeve, so as to fit the two inner walls of the sleeve; fixing it on each corner of the polygon inside the sleeve by heating; the number of the tubular elements is the same as the number of sides of the polygonal inner cavity of the sleeve; thereby, an antiresonant hollow core optical fiber preform is obtained; (2) Preparation of antiresonant hollow-core optical fiber, the specific steps are as follows: (1) Drawing the prepared antiresonant hollow-core optical fiber preform into an intermediate, during which nitrogen gas with a pressure of 0.5 to 4 kPa is introduced into the tubular element, and nitrogen gas with a pressure of 0.1 to 1 kPa is introduced between the embedded element and the tubular element to expand the embedded element and the tubular element, while maintaining the embedded element and the tubular element in a non-contact state; (2) inserting the prepared hollow-core optical fiber intermediate into a quartz outer tube and assembling it with an inflation mold, inserting inflation microtubes of different sizes into the embedded element, the tubular element, and between the embedded element and the tubular element for independent gas supply, and evacuating the space between the hollow-core optical fiber intermediate and the quartz outer tube; (3) The size and shape of the embedded element and the tubular element are controlled by adjusting different pressure values. Specifically, the pressure of the gas inside the embedded element, inside the tubular element, and between the embedded element and the tubular element is 0.1~2.0 KPa, 10~20 KPa, and 2~10 KPa, respectively, thereby controlling the size and shape of the embedded element and the tubular element. Due to the internal and external pressure difference and the effect of surface tension, the wire drawing forms a nested anti-resonant inner ring and a nested anti-resonant outer ring with negative curvature, forming a nested anti-resonant ring. The number of nested anti-resonant rings is the same as the number of tubular elements, and adjacent anti-resonant rings do not touch each other. All antiresonance rings together form a ring-shaped antiresonance layer. The area surrounded by the antiresonance layer constitutes the core of the hollow-core optical fiber. The antiresonance layer, the drawn sleeve, and the outer sleeve together form the cladding that protects the core. Thus, a nested antiresonant hollow-core optical fiber is obtained, the structure of which includes an optical fiber outer cladding layer, a nested antiresonant ring layer and a core region, wherein the core region is defined by an inscribed circle of a region surrounded by a plurality of evenly arranged antiresonant rings.

2. The preparation method according to claim 1, characterized in that In step (1): The interior of the sleeve is a regular polygon with the number of sides being greater than or equal to 4; The embedded element and the tubular element are both circular; The outer diameter of the sleeve is 20-80 mm, and the ratio of the diameter of the circumscribed circle of the regular polygon inside the sleeve to the outer diameter of the sleeve is 0.2-0.8; The wall thickness of the embedded component is 1 to 8 mm; The outer diameter of the tubular element is 1-5 mm and the wall thickness is 0.2-2 mm; The gas introduced into the embedded component is any one or more of compressed air, nitrogen, helium and argon; The partial fit between the embedded component and the inner polygon of the sleeve specifically means that the fitting length between the embedded component and any side of the inner polygon of the sleeve is not less than 40% of the side length of the inner polygon, and the distance between the side of the embedded component and the tubular component is not less than 10% of the outer diameter of the tubular component; the difference in the length of the partial fit between each side of the inner polygon of the sleeve and the embedded component does not exceed 5%.

3. The preparation method according to claim 2, characterized in that In step (2): The outer diameter of the quartz outer sleeve is determined by the core diameter and cladding diameter of the target nested antiresonant hollow-core optical fiber; The gas introduced into each component in the sleeve is any one or more of compressed air, nitrogen, helium and argon; There is a gap between adjacent anti-resonance rings formed after wire drawing; The core diameter is 8-55 μm, and the cladding diameter is 80-330 μm.

4. The preparation method according to claim 3, characterized in that The wall thickness t of the nested antiresonant ring ranges from 0.1 to 2 μm and also satisfies the antiresonant reflection condition: ，m=1, 2, 3, ...； in λ m is the resonant wavelength, m is the order of the antiresonant layer, and n is the refractive index of the nested antiresonant ring.

5. An antiresonant hollow-core optical fiber obtained by the preparation method according to any one of claims 1 to 4.

6. An antiresonant hollow-core optical fiber preform for preparing the antiresonant hollow-core optical fiber according to claim 5, characterized in that: It includes a sleeve, an embedded element and a tubular element; wherein: The sleeve is a quartz tube with a circular outer cross section and a polygonal inner cross section; the embedded element and the tubular element are wrapped inside the sleeve; The embedded element is a quartz tube structure, which is inside the sleeve and its outer edge is tangent to the polygonal inner cavity wall of the sleeve. When heated and a gas of appropriate pressure is introduced into the embedded element to expand the embedded element, the contact range between the embedded element and the polygon inside the sleeve changes from a tangent point to a partial linear fit. The tubular element is a quartz capillary tube, which is fixedly arranged at the angle formed by adjacent inner wall surfaces of the polygonal inner cavity in the sleeve, and fits in with the two inner wall surfaces of the sleeve. The area surrounded by several capillaries constitutes the center hole of the preform rod; the number of tubular elements is the same as the number of sides of the polygonal inner cavity inside the sleeve.

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