A partially doped hollow-core antiresonant active optical fiber and its preparation method

Abstract

This invention discloses a partially doped hollow-core anti-resonant active optical fiber and its fabrication method. The outer cladding (3) of the optical fiber is a circular tube structure. In cross-section, there are circular anti-resonant tubes (1) arranged in a ring inside the outer cladding (3). There is a doped region on the side of the circular anti-resonant tube (1) facing the center of the outer cladding (3). Each circular anti-resonant tube (1) contains an elliptical anti-resonant tube (2). The outer wall of the elliptical anti-resonant tube (2) and the inner wall of the circular anti-resonant tube (1) are in contact at the inner contact point. The hollow-core anti-resonant optical fiber proposed in this patent has gain selectivity, good fundamental mode gain, high amplification efficiency, large fundamental mode field area, and low nonlinearity. The fundamental mode field and the doped region are precisely matched in spatial distribution, which has the advantage of maximizing the efficiency of fundamental mode amplification. This partially doped hollow-core anti-resonant active optical fiber has a simple structure, is easy to realize, and is suitable for mass production.

Description

Technical Field

[0001] This invention relates to the fields of optical fiber communication and optical fiber laser technology, and is particularly applicable to a partially doped hollow-core anti-resonant active optical fiber and its preparation method used in optical fiber amplifiers, lasers or optical fiber light sources. Background Technology

[0002] For ease of understanding, the technical terms involved in this invention are as follows:

[0003] NANF: Nested Antiresonant Nodeless type.

[0004] SMF: Single Mode Fiber.

[0005] C-band: 1530–1565 nm

[0006] L-band: 1565–1625 nm

[0007] O-band: 1260–1360 nm

[0008] Duty cycle: The ratio of the inner diameter to the outer diameter of a hollow circular tube.

[0009] MCVD: Modified chemical vapor deposition.

[0010] Nested Antiresonant Nodeless Type (NANF) fiber has become a research hotspot in the field of optical fiber communication in recent years, with its loss significantly reduced and its development rapid. According to the latest OFC report in 2022, NANF achieved a minimum loss of 0.174 dB / km in the C-band, comparable to or even better than traditional single-mode fiber in the C-band. In the O-band, it achieved a loss of 0.22 dB / km, setting a new record for the lowest loss in the O-band. Regarding nonlinear effects, its performance is far superior to SMF, with NANF exhibiting a loss 3 to 4 orders of magnitude lower than that of SMF. The 2022 publication in *Journal of Lightwave Technology*, titled "Opportunities and Challenges for Long-Distance Transmission in Hollow-core Fibres," theoretically predicted and experimentally verified that NANF (Near-Near-Core Fibre) offers a wider usable bandwidth than SMF (Short-Near-Core Fibre), potentially reaching tens of terahertz, with a propagation speed 50% faster. Compared to the benchmark SMF Raman-amplified C+L system, NANF could potentially achieve a 1.5 to 5 times increase in communication capacity under reasonable system parameter values ​​(including transmit power). This has attracted great interest from scientists and the communications industry, and it is expected to become the next generation of ultra-high-capacity, long-distance communication optical fiber.

[0011] Experiments show that NANF has a transmission speed of 300-400 Tb / s and a transmission distance of 200 to 300 kilometers without repeater amplification. However, there is currently no research on hollow-core anti-resonant active fiber amplifiers for ultra-long-distance transmission. The partially doped hollow-core anti-resonant active fiber involved in this patent can solve the problem of repeater amplification for long-distance hollow-core transmission.

[0012] Chinese patent CN113497404A discloses a rare-earth-doped hollow anti-resonant optical fiber and its preparation method. This structure is doped with rare-earth ions throughout the glass tube ring. The doping range is large and amplifies higher-order modes, which is not conducive to the effective amplification of the fundamental mode and practical application.

[0013] Chinese patent CN110208901A discloses a hollow anti-resonant optical fiber, in which the capillary adopts an alternating structure of high and low refractive index light guiding materials, and the outer cladding adopts high refractive index silicon dioxide. However, this patent provides a passive hollow anti-resonant optical fiber, which cannot achieve amplification and laser transmission.

[0014] US Patent 10859763B2 proposes a hollow antiresonant fiber with nested support rings. However, due to its complex nested structure, it is difficult to manufacture and lacks optical amplification capabilities as it is undoped. It is evident that research in this area by Chinese and US patents is very limited, and the problem of long-distance repeater amplification in hollow antiresonant fibers has not been solved.

[0015] In summary, the currently reported invention patents cannot adequately solve the problem of long-distance transmission using hollow-core anti-resonant optical fibers. This patent proposes a partially doped hollow-core anti-resonant active optical fiber to meet the repeater amplification requirements for next-generation hollow-core optical fiber long-distance transmission. Summary of the Invention

[0016] The purpose of this invention is to solve the problem of fiber technology for repeater amplification in long-distance transmission of hollow-core optical fibers. It adopts an optical fiber structure design that precisely matches the distribution of the fundamental mode field with the distribution of the doped region. Rare earth doping is performed on a specific arc length segment of the anti-resonant cladding tube in the spatial distribution of the fundamental mode in the hollow-core optical fiber, thereby controlling the gain amplification characteristics of the fundamental mode, suppressing the gain of higher-order modes, increasing the loss of higher-order modes, and thus achieving effective amplification of the fundamental mode, solving the technical problem of gain amplification in hollow-core optical fibers.

[0017] To achieve the above objectives, the present invention adopts the following technical solution:

[0018] A partially doped hollow anti-resonant active optical fiber includes an outer cladding layer 3, which is a circular tube structure. In cross-section, there are circular anti-resonant tubes 1 arranged in a ring inside the outer cladding layer 3. There is a doped region on the side of the circular anti-resonant tube 1 facing the center of the outer cladding layer 3. Each circular anti-resonant tube 1 has an elliptical anti-resonant tube 2 inside. The outer wall of the elliptical anti-resonant tube 2 and the inner wall of the circular anti-resonant tube 1 are in contact at the inner contact point.

[0019] The center of each circular anti-resonant tube 1, the center of the inner elliptical anti-resonant tube 2, the inner contact point, and the center of the outer cladding 3 are all on a straight line.

[0020] The outer wall of the circular anti-resonant tube 1 and the inner wall of the outer cladding 3 are in contact with the outer contact point. The center, inner contact point and outer contact point of the circular anti-resonant tube (1) are on the same straight line. Adjacent circular anti-resonant tubes 1 are not in contact and are arranged at equal distances.

[0021] The partially doped hollow anti-resonant active optical fiber according to claim 1 is characterized in that: the arc length of the doped region is 1 / 6-1 / 4 of the circumference, and it is doped with rare earth elements.

[0022] The number of circular anti-resonant tubes 1 is 4-10. The major axis of the elliptical anti-resonant tube 2 is smaller than the diameter of the circular anti-resonant tube 1. The ratio of the major axis to the minor axis, i.e., a / b, is 1.0 to 1.8. When a / b = 1.0, the elliptical anti-resonant tube 2 is a circular tube.

[0023] The central region surrounding the circular anti-resonant tube 1 is a central hollow core. The virtual circumference of the central hollow core is tangent to each of the circular anti-resonant tubes 1. The diameter of the central hollow core is 6μm to 50μm. The space inside the fiber core region and the hollow anti-resonant nested unit is all air.

[0024] The gap g between the circular anti-resonant tubes 1 satisfies the quantitative relationship D. core = (d+2t²+g) / sinπ / n-(d+2t²), where n is the number of circular anti-resonant tubes, and D is the number of circular anti-resonant tubes. core d is the diameter of the fiber core, and d is the diameter of the circular tube.

[0025] The ratio of the diameter of the circular anti-resonant tube 1 to the diameter of the fiber core is d / D. core =0.4 to 0.8, and the duty cycle of the outer cladding layer 3 circular tube is 0.60 to 0.95.

[0026] According to claim 6, for the partially doped hollow anti-resonant active optical fiber, let t2 be the wall thickness of circular anti-resonant tube 1, t1 be the wall thickness of elliptical anti-resonant tube 2, and t2 satisfy the quantitative relationship: Where m is the resonance order, n glass n is the refractive index of the optical fiber glass medium. air t1 is the refractive index of the air layer of the optical fiber, t2 is the wall thickness of the circular tube, λ is the transmission wavelength of the optical fiber, t1 is the wall thickness of the elliptical anti-resonant tube, and t1 / t2 is 0.5 to 2.

[0027] A method for fabricating a partially doped hollow-core anti-resonant active optical fiber, comprising:

[0028] Step 1: Prepare a circular tube. Control the air pressure inside the tube within the range of 0 Pa to +100 Pa relative to atmospheric pressure, and draw the glass tube to obtain the desired circular tube for subsequent fabrication of a preform. The base material of the optical fiber is silicon dioxide, but different materials can be selected depending on the applicable scenario.

[0029] Step 2: Doping is performed on the circular tube. The circular quartz tube is not rotated on the MCVD device, and selective "off-wall doping" deposition is carried out. The temperature is controlled at 1700-2000℃ to obtain a doped circular tube with one-sixth to one-quarter of the surface area.

[0030] Step 3: Draw an elliptical anti-resonant tube. Under the high temperature of an oxyhydrogen flame, control the pressure inside the tube to be a slight negative pressure of -20Pa to -5Pa relative to atmospheric pressure. Rotate the quartz tube to obtain an elliptical anti-resonant tube with a curvature factor ratio of 1 to 1.8 between the major and minor semi-axis.

[0031] Step 4: Combine the elliptical anti-resonant tube and the circular tube drawn in Step 2 and Step 3 with the outer cladding circular tube to form a hollow fiber preform.

[0032] Step 5: Place the assembled preform on the drawing tower, control the drawing temperature to 1900-2300℃ for drawing, and select an appropriate drawing speed to draw it into a hollow anti-resonant optical fiber of a certain size.

[0033] In step 2, a non-rotating MCVD method is used to precisely control the doping process of rare earth elements (Er, Yb, Tm, etc.) within the doping range.

[0034] In step 4, a ring of circular anti-resonant tubes is arranged on the inner wall of the outer cladding tube, with the doped portion of the circular anti-resonant tubes facing inward. An elliptical anti-resonant tube is inserted into each circular anti-resonant tube, and the major axis end of the elliptical anti-resonant tube, the outer end of the circular anti-resonant tube, and the inner wall of the outer cladding tube are in contact with each other at the same position.

[0035] Compared with the prior art, the advantages of the present invention are as follows:

[0036] The hollow-core anti-resonant fiber proposed in this patent has gain selectivity, good fundamental mode gain, high amplification efficiency, large fundamental mode field area, and low fiber nonlinearity.

[0037] The fundamental mode field and the doped region are precisely matched in spatial distribution, which has the limiting advantage of maximizing the efficiency of optical amplification of the fundamental mode. This part-doped hollow anti-resonant active fiber has a simple structure, is easy to implement, and is convenient for mass production.

[0038] This optical fiber is ideally suited for relay amplification in future hollow-core fiber amplification systems, as well as for hollow-core fiber lasers and fiber optic light sources. Attached Figure Description

[0039] Figure 1 This is a flowchart of the method for preparing partially doped hollow anti-resonant active optical fiber provided in this patent example.

[0040] Figure 2 This is a schematic diagram of the structure of the six-tube erbium-doped hollow anti-resonant optical fiber provided in this patent embodiment.

[0041] Figure 3 This is a schematic diagram of the structure of the six-tube ytterbium-doped hollow anti-resonant optical fiber provided in this patent embodiment.

[0042] Figure 4 This is a schematic diagram of the structure of the nine-tube ytterbium-doped hollow anti-resonant optical fiber provided in this patent embodiment.

[0043] Figure 5 This is a schematic diagram of the structure of the five-tube ytterbium-doped hollow anti-resonant optical fiber provided in this patent embodiment.

[0044] Figure 6This is a schematic diagram of the structure of the eight-tube erbium-doped hollow anti-resonant optical fiber provided in this patent embodiment.

[0045] Figure Labels

[0046] 1: Circular anti-resonant diode; 2: Elliptical anti-resonant diode; 3: Outer cladding layer; 4: Doped region

[0047] D core d: Diameter of the fiber core; g: Diameter of the circular tube; d: Gap between the two tubes.

[0048] t1 is the thickness of the elliptical anti-resonant tube; t2 is the thickness of the circular tube; the major semi-axis is a and the minor semi-axis is b;

[0049] The arc length is AB; O1 is the center of the large circular tube; O2 is the center of the circular anti-resonant tube;

[0050] O3 is the center of the elliptical anti-resonant tube; C is the contact point between the anti-resonant nested unit and the outer cladding tube. Detailed Implementation

[0051] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that these embodiments are descriptive and not limiting.

[0052] The following is a detailed description of this patent with reference to the accompanying drawings: The hollow anti-resonant optical fiber consists of an outer cladding 3 circular tube, an anti-resonant nested unit, and a hollow core and doped region; wherein the anti-resonant nested unit consists of several circular anti-resonant tubes 1 and nested elliptical anti-resonant tubes 2; there are no nodes between adjacent circular anti-resonant tubes 1 and the spacing is equal; the arc length of the circular anti-resonant tube 1 directly opposite the central fiber core is doped with the required rare earth elements; the centers of the outer cladding 3 circular tube, the circular anti-resonant tubes 1 and the elliptical anti-resonant tubes 2 are collinear with the outer contact point; the space inside the fiber core region and the hollow anti-resonant nested unit is all air.

[0053] Based on the above scheme, the required rare earth elements are doped into a section of the circular tube of the circular anti-resonant tube 1 that is directly opposite the central fiber core. The arc length of the doped part is 1 / 4 to 1 / 6 of the circumference of the circular tube.

[0054] Based on the above scheme, the centers of the outer cladding tube, the circular anti-resonant tube, and the elliptical anti-resonant tube are collinear with the four points of the outer contact point (O1, O2, O3, and C are collinear). O1 is the center of the outer cladding tube 3, O2 is the center of the circular anti-resonant tube 1, O3 is the center of the elliptical anti-resonant tube 2, and C is the outer contact point between the anti-resonant nested unit and the inner wall of the outer cladding tube 3.

[0055] Based on the above scheme, the diameter D of the air fiber core is... coreThe thickness ranges from 6μm to 50μm, and the space inside the fiber core region and the hollow anti-resonant nested unit is all air.

[0056] Based on the above scheme, the number of anti-resonance nested units composed of the circular anti-resonance tube 1 and the elliptical anti-resonance tube 2 is 5 to 9.

[0057] Based on the above scheme, the wall thickness t2 of the circular tube in the anti-resonance cladding satisfies the quantitative relationship: Where m is the resonance order, n glass n is the refractive index of the optical fiber glass medium. air t1 is the refractive index of the air layer of the optical fiber, t2 is the wall thickness of the circular tube, λ is the transmission wavelength of the optical fiber, t1 is the wall thickness of the elliptical anti-resonant tube, and t1 / t2 is 0.5 to 2.

[0058] Based on the above scheme, the gap g between the circular tubes in the anti-resonance cladding satisfies the quantitative relationship D. core =(d+2t²+g) / sin(π / n)-(d+2t²), where n is the number of circular anti-resonant tubes, and D is the number of circular anti-resonant tubes. core d is the diameter of the fiber core, and d is the diameter of the circular anti-resonant tube 1. d / D core =0.4~0.8.

[0059] Based on the above scheme, the major semi-axis of the elliptical anti-resonant tube (2) should be smaller than the radius of the circular anti-resonant tube 1, and the curvature factor (the ratio of the major semi-axis to the minor semi-axis) a / b should be 1 to 1.8. When a / b = 1, the internal elliptical anti-resonant tube 2 will become a circular tube.

[0060] Based on the above scheme, the process of doping rare earth elements (Er, Yb, Tm, etc.) is carried out in a precise control within the doping range of the (4) round tube using non-rotating MCVD.

[0061] Based on the above scheme, the duty cycle of the outer cladding tube is 0.6 to 0.95.

[0062] Based on the above scheme, the basic material of the optical fiber is silicon dioxide, but different materials can be selected according to the applicable scenario.

[0063] This patent proposes a method for fabricating partially doped hollow-core anti-resonant active optical fibers, such as... Figure 1 The flowchart shows the following:

[0064] Step 1, Prepare a circular tube: Control the gas pressure inside the tube to be within the range of OPa to +100Pa (the difference relative to atmospheric pressure) and draw the glass tube to obtain the desired circular anti-resonant tube, which will be used to make a preform in the future.

[0065] Step 2, doping on the circular anti-resonant tube: The circular quartz tube is not rotated on the MCVD device, and selective "off-wall doping" deposition is performed to obtain a rare earth partially doped circular tube with a circumference of one-sixth to one-quarter.

[0066] Step 3, drawing an elliptical anti-resonant tube: Under the high temperature of an oxyhydrogen flame, the pressure inside the quartz tube is controlled to be a slight negative pressure of -20Pa to -5Pa (the difference relative to atmospheric pressure) to prepare an elliptical anti-resonant tube with a curvature factor (the ratio of the major semi-axis to the minor semi-axis) of 1 to 1.8.

[0067] Step 4: Combine the circular tube and elliptical anti-resonant tube prepared in Steps 2 and 3 with the outer cladding circular tube to form a preform;

[0068] Step 5: Place the assembled preform on the drawing tower for drawing, control the drawing temperature to 1900-2300℃, and select an appropriate drawing speed to draw it into a hollow anti-resonant optical fiber of a certain size.

[0069] The following provides an implementation example based on the manufacturing method described above.

[0070] Implementation Example 1: This patent provides a partially doped hollow anti-resonant erbium-doped active optical fiber.

[0071] Figure 2 The cross-sectional view of the erbium-doped hollow anti-resonant fiber shows that it consists of an outer cladding layer, six nested anti-resonant units, and a doped region. Each nested anti-resonant unit is composed of a circular anti-resonant tube 1 nested within an elliptical anti-resonant tube 2. The nested units are evenly spaced. The interiors of the circular and elliptical anti-resonant tubes 1 and 2, as well as the fiber core, are filled with air. The outer cladding layer 3 has two coating layers. The doped region is an arc AB. Points O1, O2, O3, and C are collinear. O1 is the center of the larger circular tube, O2 is the center of the circular anti-resonant tube, O3 is the center of the elliptical anti-resonant tube, and C is the contact point between the nested anti-resonant unit and the outer cladding tube. The doped portion uses erbium ions to amplify the internal fundamental mode, making it suitable for long-distance transmission repeaters.

[0072] This example demonstrates amplification in the C-band using a hollow-core antiresonant fiber with a center amplification wavelength of λ = 1550 nm and a core diameter of D. core=40μm, the diameter of the circular tube in the anti-resonant cladding is d = 32μm, the number of tubes is 6, the gap between adjacent circular tubes is g = 3.59μm, the wall thickness of the circular tube is t2 = 410nm, the curvature factor of the nested elliptical anti-resonant tube inside the circular tube has a ratio of major axis to minor axis of a / b = 1.8, the major axis of the elliptical anti-resonant tube is 13.68μm, the minor axis is 7.60μm, the ratio of the wall thickness of the elliptical anti-resonant tube to the wall thickness of the circular tube is t1 / t2 = 0.5, the wall thickness of the elliptical anti-resonant tube is t1 = 205nm. Doping region 4 is approximately one-sixth of the area of ​​the circular anti-resonant tube 1 facing the fiber core, doped with erbium ions at a concentration of 1800ppm.

[0073] The outer cladding tube has a wall thickness of 2.76 μm and a duty cycle of 0.95.

[0074] The main parameters of the aforementioned optical fiber are shown in Table 1 below:

[0075] Table 1. Parameters of Partially Doped Hollow-Core Anti-Resonant Active Fibers

[0076] expression parameter Parameter value <![CDATA[D core ]]> Core diameter 40μm <![CDATA[t1]]> Wall thickness of an elliptical anti-resonant tube 205nm <![CDATA[t2]]> Wall thickness of round tube 410nm g The gap between the two round tubes 3.59μm n Number of round tubes 6 d Diameter of the round tube 32μm a semi-major axis of the ellipse 13.68μm b Ellipse semi-minor axis 7.60μm a / b curvature factor 1.8

[0077] The base material of this anti-resonant optical fiber is silicon dioxide. The background loss of this erbium-doped anti-resonant optical fiber in the 1200nm wavelength band is ≤10dB / km. The leakage loss of this optical fiber in the entire C-band communication window is ≤0.01dB / km. It exhibits good bending loss at 1550nm, with a bending loss of <0.05dB / km at a bending radius of 5mm. The absorption coefficient at 980nm wavelength is 3.20dB / m. The gain is greater than 30.0dB in the wavelength range of 1530nm-1565nm, and the noise figure NF is less than 3.92dB.

[0078] Implementation Example 2: This patent provides a partially doped hollow anti-resonant ytterbium-doped active optical fiber;

[0079] Figure 3 A cross-sectional view of a ytterbium-doped hollow anti-resonant optical fiber is shown. This hollow fiber consists of an outer cladding, six nested anti-resonant units, and a doped region. Each nested anti-resonant unit is composed of a circular anti-resonant tube 1 nested within an elliptical circular anti-resonant tube 2. The nested units are evenly spaced. The interiors of the circular and elliptical anti-resonant tubes 1 and 2, as well as the fiber core, are filled with air. The outer cladding tube 3 has two coating layers. The doped region is an arc AB. Points O1, O2, O3, and C are collinear. O1 is the center of the larger circular tube, O2 is the center of the circular anti-resonant tube, O3 is the center of the elliptical anti-resonant tube, and C is the contact point between the nested anti-resonant unit and the outer cladding tube.

[0080] This example demonstrates a hollow-core antiresonant fiber with a central amplification wavelength λ = 1064 nm, doped with ytterbium ions, for laser transmission and amplification. Its core diameter D...core =30μm, the diameter of the circular tube in the anti-resonant cladding is d=26μm, the number of tubes is 6, the gap between adjacent circular tubes is g=1.58μm, the wall thickness of the circular tube is t2=420nm, the curvature factor of the nested elliptical anti-resonant tube inside the circular tube has a ratio of major semi-axis to minor semi-axis of a / b=1.0, the major semi-axis of the elliptical anti-resonant tube is 9.6μm, the minor semi-axis is 9.6μm, the ratio of the wall thickness of the elliptical anti-resonant tube to the wall thickness of the circular tube is t1 / t2=2, the wall thickness of the elliptical anti-resonant tube is t1=840nm. Doping region 4 is doped with ytterbium ions in an area of ​​about one-sixth of the circular anti-resonant tube 1 facing the fiber core, with a concentration of 5600ppm.

[0081] The outer cladding tube has a wall thickness of 27.6 μm and a duty cycle of 0.6.

[0082] The main parameters of the aforementioned optical fibers are shown in Table 2 below:

[0083] Table 2. Parameters of Partially Doped Hollow-Core Anti-Resonant Active Fibers

[0084] expression parameter Parameter value <![CDATA[D core ]]> Core diameter 30μm <![CDATA[t1]]> Wall thickness of an elliptical anti-resonant tube 840nm <![CDATA[t2]]> Wall thickness of round tube 420nm g The gap between the two round tubes 1.58μm n Number of round tubes 6 d Diameter of the round tube 26μm a semi-major axis of the ellipse 9.6μm b Ellipse semi-minor axis 9.6μm a / b curvature factor 1.0

[0085] The base material of this anti-resonant optical fiber is silicon dioxide. The background loss of this anti-resonant ytterbium-doped optical fiber in the 1000-1100nm band is ≤10dB / km, the leakage loss in the 1000-1100nm band is ≤0.05dB / km, the bending loss at 1064nm is good, the bending loss is <0.05dB / km at a bending radius of 10mm, the absorption coefficient at 976nm is 2.40dB / m, and the gain in the 1070nm wavelength range is greater than 25.6dB.

[0086] Implementation Example 3: This patent provides a partially doped hollow anti-resonant ytterbium-doped active optical fiber;

[0087] Figure 4 A cross-sectional view of a ytterbium-doped hollow anti-resonant optical fiber is shown. This hollow fiber consists of an outer cladding, nine nested anti-resonant units, and a doped region. Each nested anti-resonant unit is composed of a circular anti-resonant tube 1 nested within an elliptical circular anti-resonant tube 2. The nested units are evenly spaced. The interiors of the circular and elliptical anti-resonant tubes 1 and 2, as well as the fiber core, are filled with air. The outer cladding tube 3 has two coating layers. The doped region is represented by arc AB. Points O1, O2, O3, and C are collinear. O1 is the center of the larger circular tube, O2 is the center of the circular anti-resonant tube, O3 is the center of the elliptical anti-resonant tube, and C is the contact point between the nested anti-resonant unit and the outer cladding tube. The dashed line represents the largest circle tangent to the nine tubes.

[0088] This example demonstrates a hollow-core antiresonant fiber with a central amplification wavelength λ = 1064 nm, doped with ytterbium ions, for laser transmission and amplification. Its core diameter D... core =33μm, the diameter of the circular tube in the anti-resonant cladding is d =13.2μm, the number of tubes is 9, the gap between adjacent circular tubes is g =2.07μm, the wall thickness of the circular tube is t2 =400nm, the curvature factor of the nested elliptical anti-resonant tube inside the circular tube has a ratio of major axis to minor axis of a / b =1.7, the major axis of the elliptical anti-resonant tube is 5.1μm, the minor axis is 3.0μm, the ratio of the wall thickness of the elliptical anti-resonant tube to the wall thickness of the circular tube is t1 / t2 =424 / 400, and the wall thickness of the elliptical anti-resonant tube is t1 =424nm. Doping region 4 is doped with ytterbium ions in approximately one-quarter of the area of ​​the circular anti-resonant tube 1 facing the fiber core, with a concentration of 7200ppm.

[0089] The outer cladding tube has a wall thickness of 20 μm and a duty cycle of 0.6.

[0090] The main parameters of the aforementioned optical fibers are shown in Table 3 below:

[0091] Table 3. Parameters of Partially Doped Hollow-Core Anti-Resonant Active Fibers

[0092] expression parameter Parameter value <![CDATA[D core ]]> Core diameter 33μm <![CDATA[t1]]> Wall thickness of an elliptical anti-resonant tube 424nm <![CDATA[t2]]> Wall thickness of round tube 400nm g The gap between the two round tubes 2.07μm n Number of round tubes 9 d Diameter of the round tube 13.2μm a semi-major axis of the ellipse 5.1μm b Ellipse semi-minor axis 3.0μm a / b curvature factor 1.7

[0093] The base material of this anti-resonant optical fiber is silicon dioxide. The background loss of this anti-resonant ytterbium-doped optical fiber in the 1000-1100nm band is ≤8dB / km, the leakage loss in the 1000-1100nm band is ≤0.03dB / km, the bending loss at 1064nm is good, the bending loss at a bending radius of 5mm is <0.02dB / km, the absorption coefficient at 976nm is 3.6dB / m, and the gain in the 1080nm wavelength range is greater than 30.0dB.

[0094] Implementation Example 4: This patent provides a partially doped hollow-core anti-resonant ytterbium-doped active optical fiber;

[0095] Figure 5 The image shows a cross-sectional view of a ytterbium-doped hollow anti-resonant fiber. This hollow fiber consists of an outer cladding, five nested anti-resonant units, and a doped region. Each nested anti-resonant unit is composed of a circular anti-resonant tube 1 nested within an elliptical circular anti-resonant tube 2. The nested units are evenly spaced. The interiors of the circular and elliptical anti-resonant tubes 1 and 2, as well as the fiber core, are filled with air. The outer cladding tube 3 has two coating layers. The doped region is represented by arc AB. Points O1, O2, O3, and C are collinear. O1 is the center of the larger circular tube, O2 is the center of the circular anti-resonant tube, O3 is the center of the elliptical anti-resonant tube, and C is the contact point between the nested anti-resonant unit and the outer cladding tube. The dashed line represents the largest circle tangent to the five tubes.

[0096] This example demonstrates a hollow-core antiresonant fiber with a central amplification wavelength λ = 1064 nm, doped with ytterbium ions, for laser transmission and amplification. Its core diameter D... core =6μm, the diameter of the circular tube in the anti-resonant cladding is d = 4.8μm, the number of tubes is 5, the gap between adjacent circular tubes is g = 3.16μm, the wall thickness of the circular tube is t2 = 410nm, the curvature factor of the nested elliptical anti-resonant tube inside the circular tube has a ratio of major semi-axis to minor semi-axis of a / b = 1.7, the major semi-axis of the elliptical anti-resonant tube is 2.04μm, the minor semi-axis is 1.2μm, the ratio of the wall thickness of the elliptical anti-resonant tube to the wall thickness of the circular tube is t1 / t2 = 1, the wall thickness of the elliptical anti-resonant tube is t1 = 410nm. Doping region 4 is doped with ytterbium ions in approximately one-fifth of the area directly opposite the core of the circular anti-resonant tube 1, with a concentration of 8500ppm.

[0097] The outer cladding tube has a wall thickness of 4 μm and a duty cycle of 0.67.

[0098] The main parameters of the aforementioned optical fibers are shown in Table 4 below:

[0099] Table 4. Parameters of Partially Doped Hollow-Core Anti-Resonant Active Fibers

[0100] expression parameter Parameter value <![CDATA[D core ]]> Core diameter 6μm <![CDATA[t1]]> Wall thickness of an elliptical anti-resonant tube 410nm <![CDATA[t2]]> Wall thickness of round tube 410nm g The gap between the two round tubes 3.16μm n Number of round tubes 5 d Diameter of the round tube 4.80μm a semi-major axis of the ellipse 2.04μm b Ellipse semi-minor axis 1.20μm a / b curvature factor 1.7

[0101] The base material of this anti-resonant optical fiber is silicon dioxide. The background loss of this anti-resonant ytterbium-doped optical fiber in the 1000-1100nm band is ≤10dB / km, the leakage loss in the 1000-1100nm band is ≤0.01dB / km, the bending loss at 1064nm is good, the bending loss is <0.03dB / km at a bending radius of 10mm, the absorption coefficient at 976nm is 4.6dB / m, and the gain is 35.0dB in the 1064nm wavelength range.

[0102] Implementation Example 5: This patent provides a partially doped hollow anti-resonant erbium-doped active optical fiber;

[0103] Figure 6 The image shows a cross-sectional view of an erbium-doped hollow anti-resonant fiber. This hollow fiber consists of an outer cladding tube, eight nested anti-resonant units, and a doped region. Each nested anti-resonant unit is composed of a circular anti-resonant tube 1 nested within an elliptical anti-resonant tube 2. The nested units are evenly spaced. The interiors of the circular and elliptical anti-resonant tubes 1 and 2, as well as the fiber core, are filled with air. The outer cladding tube 3 has two coating layers. The doped region is an arc AB. Points O1, O2, O3, and C are collinear. O1 is the center of the large circular tube, O2 is the center of the circular anti-resonant tube, O3 is the center of the elliptical anti-resonant tube, and C is the contact point between the nested anti-resonant unit and the outer cladding tube.

[0104] This example demonstrates amplification in the C-band using a hollow-core antiresonant fiber with a center amplification wavelength of λ = 1550 nm and a core diameter of D. core =50μm, the diameter of the circular tube in the anti-resonant cladding is d=25μm, the number of tubes is 8, the gap between adjacent circular tubes is g=3.20μm, the wall thickness of the circular tube is t2=410nm, the curvature factor of the nested elliptical anti-resonant tube inside the circular tube has a ratio of major axis to minor axis of a / b=1.7, the major axis of the elliptical anti-resonant tube is 11.2μm, the minor axis is 7.0μm, the ratio of the wall thickness of the elliptical anti-resonant tube to the wall thickness of the circular tube is t1 / t2=1, the wall thickness of the elliptical anti-resonant tube is t1=410nm. Doping region 4 is approximately one-quarter of the area of ​​the circular anti-resonant tube 1 facing the fiber core, doped with erbium ions at a concentration of 2500ppm.

[0105] The outer cladding tube has a wall thickness of 15 μm and a duty cycle of 0.77.

[0106] The main parameters of the aforementioned optical fibers are shown in Table 5 below:

[0107] Table 5. Parameters of Partially Doped Hollow-Core Anti-Resonant Active Fibers

[0108] expression parameter Parameter value <![CDATA[D core ]]> Core diameter 50μm <![CDATA[t1]]> Wall thickness of an elliptical anti-resonant tube 410nm <![CDATA[t2]]> Wall thickness of round tube 410nm g The gap between the two round tubes 3.20μm n Number of round tubes 8 d Diameter of the round tube 25μm a semi-major axis of the ellipse 11.2μm b Ellipse semi-minor axis 7.0μm a / b curvature factor 1.7

[0109] The base material of this anti-resonant optical fiber is silicon dioxide. The background loss of this erbium-doped anti-resonant optical fiber in the 1200nm wavelength band is ≤10dB / km. The leakage loss of this optical fiber in the entire C-band communication window is ≤0.01dB / km. It exhibits good bending loss at 1550nm, with a bending loss of <0.01dB / km at a bending radius of 5mm. The absorption coefficient at 980nm is 4.3dB / m. The gain is 34.2dB in the wavelength range of 1530nm-1565nm, and the noise figure NF = 4.16dB.

[0110] The partially doped hollow-core antiresonant active fiber obtained by the above method has the advantages of good fundamental mode gain, strong bending resistance, low transmission loss, large mode field area, low nonlinearity, and the ability to achieve single-mode transmission and amplification with a large fiber core. The partially doped hollow-core antiresonant active fiber provided by this invention is very suitable for repeater amplification in future hollow-core fiber amplification systems, hollow-core fiber lasers, fiber light sources, and repeater amplification in solid fibers.

[0111] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. The present patent has been described in detail with reference to the above embodiments. Those skilled in the art should understand that appropriate modifications, equivalent substitutions, or improvements can be made to the technical solutions described in the foregoing examples, and all such modifications, substitutions, or improvements should be included within the scope of protection of this application.

Claims

1. A partially doped hollow-core anti-resonant active optical fiber, comprising an outer cladding layer (3), characterized in that: The outer cladding (3) is a circular tube structure. In cross-section, there are circular anti-resonant tubes (1) arranged in a ring inside the outer cladding (3). There is a doped region on the side of the circular anti-resonant tube (1) facing the center of the outer cladding (3). The arc length of the doped region is 1 / 6-1 / 4 of the circumference and it is doped with rare earth elements. There is an elliptical anti-resonant tube (2) inside each circular anti-resonant tube (1). The outer wall of the elliptical anti-resonant tube (2) and the inner wall of the circular anti-resonant tube (1) are in contact at the inner contact point.

2. The partially doped hollow-core anti-resonant active optical fiber according to claim 1, characterized in that: The center of each circular anti-resonant tube (1), the center of the inner elliptical anti-resonant tube (2), the inner contact point, and the center of the outer cladding (3) are on a straight line.

3. The partially doped hollow-core anti-resonant active optical fiber according to claim 2, characterized in that: The outer wall of the circular anti-resonant tube (1) and the inner wall of the outer cladding (3) are in contact with the outer contact point. The center of the circular anti-resonant tube (1), the inner contact point and the outer contact point are on the same straight line. Adjacent circular anti-resonant tubes (1) do not contact each other and are arranged at equal distances.

4. The partially doped hollow-core anti-resonant active optical fiber according to any one of claims 1-3, characterized in that: The number of circular anti-resonant tubes (1) is 4-10. The major axis of the elliptical anti-resonant tube (2) is smaller than the diameter of the circular anti-resonant tube (1). The ratio of the major axis to the minor axis, i.e., a / b, is 1.0 to 1.

8. When a / b = 1.0, the elliptical anti-resonant tube (2) is a circular tube.

5. The partially doped hollow-core anti-resonant active optical fiber according to claim 4, characterized in that: The central region surrounding the circular anti-resonant tube (1) is a central hollow core. The circumference of the central hollow core is tangent to each of the circular anti-resonant tubes (1). The diameter of the central hollow core is 6μm to 50μm. The space inside the fiber core region and the hollow anti-resonant nested unit is all air. The gap g between the circular anti-resonant tubes (1) satisfies the quantitative relationship Dcore=(d+2t2+g) / sin(π / n)-(d+2t2), where n is the number of circular anti-resonant tubes (1), Dcore is the diameter of the central hollow core, and d is the diameter of the circular anti-resonant tube (1).

6. The partially doped hollow-core anti-resonant active optical fiber according to claim 5, characterized in that: The ratio of the diameter of the circular anti-resonant tube (1) to the diameter of the central hollow core is d / Dcore = 0.4 to 0.8, and the duty cycle of the outer cladding (3) circular tube is 0.60 to 0.95; let t2 be the wall thickness of the circular anti-resonant tube (1), t2 = 205nm to 840nm.

7. The partially doped hollow-core anti-resonant active optical fiber according to claim 4, characterized in that: Let t2 be the wall thickness of the circular anti-resonant tube (1), t1 be the wall thickness of the elliptical anti-resonant tube (2), where m is the resonance order, nglass is the refractive index of the optical fiber glass medium, nair is the refractive index of the optical fiber air layer, λ is the transmission wavelength of the optical fiber, and t1 / t2 is 0.5~2.

8. A method for fabricating a partially doped hollow-core anti-resonant active optical fiber, characterized in that... include: Step 1: Prepare a circular tube by drawing a glass tube to obtain a circular anti-resonant tube of the required size. Step 2: Dope the circular anti-resonant tube. The circular anti-resonant tube is not rotated on an MCVD device; selective off-wall doping deposition is performed. The arc length of the doped portion of the circular anti-resonant tube is one-sixth to one-quarter of the circumference. Step 3: Prepare an elliptical anti-resonant tube by rotating a quartz tube under a slightly negative pressure at high temperature with an oxyhydrogen flame. Step 4: Combine the circular anti-resonant tube from Step 2 and the elliptical anti-resonant tube from Step 3 with the outer cladding circular tube to form a hollow fiber preform. Step 5: Place the preform on a drawing tower for drawing, controlling the drawing temperature at 1900–2300℃ and selecting an appropriate drawing speed to draw it into a hollow anti-resonant fiber of a certain size.

9. The method for fabricating partially doped hollow anti-resonant active optical fiber according to claim 8, characterized in that: In step 1, the gas pressure range inside the tube is controlled so that the difference between it and atmospheric pressure is 0 Pa to +100 Pa; in step 2, the temperature is controlled at 1700 to 2000 °C, and the rare earth element doping is one or more of Er, Yb, or Tm; in step 3, the micro-negative pressure refers to the difference between the pressure inside the tube and atmospheric pressure of -20 Pa to -5 Pa; in step 4, a ring of circular anti-resonant tubes is arranged on the inner wall of the outer cladding tube, with the doped part of the circular anti-resonant tube facing inward, and an elliptical anti-resonant tube is inserted into each circular anti-resonant tube, with the major axis end of the elliptical anti-resonant tube and the outer end of the circular anti-resonant tube in contact with the inner wall of the outer cladding tube at the same position.

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