Alkali-doped optical fiber with reduced attenuation

Abstract

The method for manufacturing an optical fiber includes steps of drawing a first optical fiber preform with a first drawing tension to manufacture a first alkali-doped optical fiber, and drawing the first optical fiber preform with a second drawing tension to manufacture a second alkali-doped optical fiber, and measuring the attenuation of the first alkali-doped optical fiber and the attenuation of the second alkali-doped optical fiber, where the attenuation of the second alkali-doped optical fiber is smaller. In addition to this, the method also includes a step of setting the drawing tension to the second drawing tension, and a step of drawing a second optical fiber preform with the second drawing tension to manufacture a third alkali-doped optical fiber. The third alkali-doped optical fiber has an attenuation of about 1.50 dB / km or less at 850 nm and an attenuation of about 0.155 dB / km or less at 1550 nm.

Description

Priority

[0001] This application claims the benefit of priority under 35 U.S.C. § 120 to U.S. Provisional Patent Application No. 63 / 395,507, filed on August 5, 2022, and all disclosures of this provisional application are relied upon and incorporated herein by reference.

Technical Field

[0002] The present disclosure relates to optical fibers. More particularly, the present disclosure relates to alkali-doped optical fibers with reduced attenuation.

Background Art

[0003] In the field of communications, the importance of the role played by optical fibers is increasing. Optical fibers operate by propagating light beams. Typically, an optical fiber includes a core and a cladding. The core is for propagating light, and the cladding is for confining light within the core by reflection.

[0004] To perform long-distance transmission of signals in a short time, optical fibers need to operate within a very specific range of waveguide parameters such as a small attenuation loss value. Attenuation is the loss of a signal in an optical fiber. Thus, the attenuation of an optical fiber is measured as the amount of light loss between the light input into the optical fiber and the light output from the optical fiber. The attenuation of an optical fiber results from the absorption characteristics, scattering characteristics, and bending losses of the fiber, all of which are affected by the material of the fiber and the fiber structure itself.

Summary of the Invention

[0005] According to aspects of the present disclosure, an optical fiber with reduced attenuation is provided. For example, as detailed in the following description, aspects of the present disclosure include doping the optical fiber with an alkali, adjusting the temperature of the optical fiber downstream of the drawing furnace, optimizing the drawing tension when drawing the optical fiber, or any combination thereof. All of these features contribute to reducing the attenuation of the final optical fiber obtained by drawing. More specifically, all of these features contribute to reducing the attenuation at wavelengths of 850 nm and 1550 nm in the final optical fiber obtained by drawing.

[0006] In an embodiment, the step of optimizing the drawing tension to reduce attenuation may include the step of reducing the drawing tension. However, in order to keep the drawing tension relatively low, it is usually necessary to draw the fiber at a high temperature, which may increase the hydrogen sensitivity of the optical fiber. More specifically, increasing the temperature in this way may increase the number of oxygen-rich non-bridging oxygen defects in the fiber. Such oxygen-rich non-bridging oxygen defects are known to react with hydrogen to form hydroxyl groups. Since hydroxyl groups absorb wavelengths within the communication window and increase the attenuation of optical signals, the formation of hydroxyl groups is not desirable. The concentration of oxygen-rich non-bridging oxygen defects is reflected in the attenuation measured at 850 nm.

[0007] Therefore, aspects of the present disclosure further include the step of adding a reducing agent to the optical fiber in order to suppress the hydrogen sensitivity of the optical fiber.

[0008] Embodiments of the present disclosure relate to a method for manufacturing an optical fiber. The method includes forming an alkali-doped silica-containing glass tube, collapsing the glass tube to form a first glass rod, depositing a silica soot on the first glass rod to form a first glass body, depositing an additional silica soot on the first glass body, exposing the silica soot on the first glass body to a halide dopant, exposing the silica soot on the first glass body to a reducing agent, consolidating the silica soot on the first glass body to form a first parent preform, and forming a first optical fiber preform from the first parent preform. The method further includes drawing the first optical fiber preform at a first drawing tension to produce a first alkali-doped optical fiber, drawing the first optical fiber preform at a second drawing tension to produce a second alkali-doped optical fiber, measuring the attenuation of the first alkali-doped optical fiber to obtain a first attenuation measurement value for the first alkali-doped optical fiber, measuring the attenuation of the second alkali-doped optical fiber to obtain a second attenuation measurement value for the second alkali-doped optical fiber, and determining that the second attenuation measurement value is less than the first attenuation measurement value. Additionally, the method includes setting the drawing tension to the second drawing tension and drawing a second optical fiber preform made in a process similar to that of the first optical fiber preform at the second drawing tension to produce a third alkali-doped optical fiber. The third alkali-doped optical fiber has an attenuation of about 1.50 dB / km or less at 850 nm and an attenuation of about 0.155 dB / km or less at 1550 nm. In some embodiments, the first glass rod is doped with an alkali selected from the group consisting of sodium, potassium, rubidium, or combinations thereof.

[0009] Embodiments of the present disclosure relate to a method for manufacturing an optical fiber. The method includes forming an alkali-doped silica-containing glass tube, collapsing the glass tube to form a first glass rod, depositing a silica soot on the first glass rod to form a first glass body, depositing an additional silica soot on the first glass body, exposing the silica soot on the first glass body to a halide dopant, exposing the silica soot on the first glass body to a reducing agent, consolidating the silica soot on the first glass body to form a first parent preform, and forming a first optical fiber preform from the first parent preform. Further, the method includes drawing the first optical fiber preform at a first drawing tension to produce a first alkali-doped optical fiber, drawing the first optical fiber preform at a second drawing tension to produce a second alkali-doped optical fiber, measuring the attenuation of the first alkali-doped optical fiber to obtain a first attenuation measurement value for the first alkali-doped optical fiber, measuring the attenuation of the second alkali-doped optical fiber to obtain a second attenuation measurement value for the second alkali-doped optical fiber, and the step that the second attenuation measurement value is less than the first attenuation measurement value. Additionally, the method includes setting the drawing tension to the second drawing tension and drawing a second optical fiber preform at the second drawing tension to produce a third alkali-doped optical fiber. The third alkali-doped optical fiber has an attenuation of about 1.50 dB / km or less at 850 nm and an attenuation of about 0.155 dB / km or less at 1550 nm. In some embodiments, the first glass rod is doped with an alkali containing at least one of sodium, potassium, rubidium, cesium, lithium, or combinations thereof.

[0010] Embodiments of the present disclosure relate to a method for manufacturing an optical fiber. The method includes forming an alkali-doped silica-containing glass tube, collapsing the glass tube to form a glass rod, depositing a silica soot on the glass rod to form a glass body, depositing an additional silica soot on the glass body, exposing the silica soot on the glass body to a halide dopant, exposing the silica soot on the glass body to a reducing agent, consolidating the silica soot on the glass body to form a preform precursor, forming an optical fiber preform from the preform precursor, and drawing the optical fiber preform at a drawing tension of about 60 grams to about 90 grams to form an alkali-doped optical fiber. The method further includes exposing the alkali-doped optical fiber to a cooling device provided downstream of the drawing furnace and operating within a range of about 900°C to about 1300°C for a time of about 0.05 seconds or more. The alkali-doped optical fiber has an attenuation of about 1.50 dB / km or less at 850 nm and an attenuation of about 0.155 dB / km or less at 1550 nm.

[0011] Embodiments of the present disclosure relate to a method for manufacturing an optical fiber. The method includes forming an alkali-doped silica-containing glass tube, collapsing the glass tube to form a glass rod, depositing a silica coat on the glass rod to form a glass body, depositing an additional silica coat on the glass body, exposing the silica coat on the glass body to a halide dopant, exposing the silica coat on the glass body to a reducing agent, consolidating the silica coat on the glass body to form a parent preform, forming an optical fiber preform from the parent preform, drawing a first portion of the optical fiber preform with a first drawing tension to form a first alkali-doped optical fiber, and drawing a second portion of the optical fiber preform with a second drawing tension lower than the first drawing tension to form a second alkali-doped optical fiber. The second alkali-doped optical fiber has an attenuation of about 1.50 dB / km or less at 850 nm and an attenuation of about 0.155 dB / km or less at 1550 nm. In some embodiments, the second portion occupies more than 60% of the parent material. In some embodiments, the first drawing tension is 100 g to 200 g and the second drawing tension is 40 g to 50 g.

[0012] In the following detailed description, further features and advantages will be described. The following further features and advantages will be readily understood by those skilled in the art to some extent from the description, or may be understood by practicing the embodiments, claims, and accompanying drawings described herein.

[0013] It should be understood that both the foregoing general description and the following detailed description are exemplary only and are intended to provide an overview or framework for understanding the nature and characteristics described in the claims.

[0014] The accompanying drawings are attached to enhance understanding and are incorporated herein and form a part thereof. The drawings illustratively show selected embodiments of the present disclosure and, in conjunction with the following detailed description, are for explaining the principles and operations of the methods, products, and compositions included in the present disclosure.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0016] This disclosure provides teachings that enable the implementation of the present disclosure, and by referring to the following description, drawings, examples, and claims, the present disclosure can be more easily understood. For this purpose, those skilled in the art will recognize and understand that there can be many modifications to various aspects of the embodiments described herein that still yield beneficial results. It will also be apparent that some of the desirable advantages of the present embodiments can be obtained even when some features are selected from the features of the present embodiments and other features are not utilized. Therefore, those skilled in the art will recognize that many modifications and applications are possible, that they can be desirable in certain situations, and that they are part of the present disclosure. Accordingly, it should be understood that the present disclosure is not limited to the specific compositions, articles, devices, and methods disclosed, unless otherwise specified. It should also be understood that the terms used herein are for the purpose of describing specific embodiments only and are not intended to be limiting.

[0017] In this specification and the appended claims, many terms are used, and they are defined as having the following meanings.

[0018] "Optical fiber" refers to a waveguide having a glass portion, and this glass portion includes at least a core portion.

[0019] The "mode field diameter" ("MFD") of an optical fiber is defined as follows.

[0020]

Number

[0021] In the formula, f(r) is the electric field distribution component in the cross-sectional direction of the guided optical signal, and r is the radial position in the fiber. As is well known in the art, f(r) is calculated from the refractive index profile of the fiber. The "mode field diameter" ("MFD") varies depending on the wavelength of the optical signal. In this specification, the mode field diameters for wavelengths of 1310 nm and 1550 nm are reported. For specific wavelengths, they are indicated when referring to the mode field diameter. Unless otherwise specified, the mode field diameter refers to the mode field diameter of the LP 01 mode at the specified wavelength.

[0022] The "effective area" of an optical fiber is defined as follows.

[0023]

Equation

[0024] In the formula, f(r) is the electric field component in the cross-sectional direction of the guided optical signal, and r is the radial position in the fiber. The "effective area" ("A eff ") varies depending on the wavelength of the optical signal. In this specification, it should be understood that it refers to the effective area for a wavelength of 1550 nm.

[0025] In this specification, the term "attenuation" means the loss of optical intensity that occurs when a signal propagates along an optical fiber. The measurement of attenuation is performed in accordance with the standard of IEC 60793-1-40 "Attenuation measurement methods".

[0026] As used herein, "cable cutoff wavelength" ("cable cutoff") refers to a cutoff test performed on a 22 m long cable in accordance with the provisions of IEC 60793-1-44, "Measurement methods and test procedures - Cut-off wavelength".

[0027] The optical fiber disclosed herein may include a core region, and in addition thereto, may further include a cladding region surrounding the core region and a coating surrounding the cladding region. Both the core region and the cladding region are formed of glass. The cladding region may include a plurality of concentric regions. In some embodiments, these plurality of concentric regions include one or more trench regions that constitute a depressed-index cladding region. The coating may include at least a primary coating and a secondary coating. Further, the optical fiber disclosed herein may be a single-mode optical fiber or a multi-mode optical fiber. As will be described in detail in the following description, the optical fiber disclosed herein is formed from an optical fiber preform using a drawing process.

[0028] FIG. 1 shows a cross section of an exemplary optical fiber 10. As shown in FIG. 1, the fiber 10 includes a core 12, an inner cladding 14, and an outer cladding 16. In some embodiments, the fiber 10 further includes a trench region (low refractive index cladding region) between the inner cladding 14 and the outer cladding 16. The core 12 can be, for example, a glass body formed of silica glass (any of un-doped silica glass, up-doped silica glass, down-doped silica glass). As the up-doped silica glass, for example, silica glass doped with germanium (e.g., GeO2), phosphorus (e.g., P2O5), aluminum (e.g., Al2O3), chlorine (Cl), an alkali metal, or any combination thereof can be mentioned as will be detailed in the following description.

[0029] The inner cladding 14 is continuously provided between the core 12 and the outer cladding 16 so as to surround the core 12. The core 12 can have a higher relative refractive index than the inner cladding 14 and the outer cladding 16. Thus, the refractive index of the core 12 (D 1,max %), the refractive index of the inner cladding 14 (D2%), and the refractive index of the outer cladding 16 (D3%) follow the relationship of D 1,max % > D2%, D 1,max % > D3%. Further, in some embodiments, D 1,max % > D3% > D2%. In some embodiments, the inner cladding 14 has a distinct core-cladding boundary with the core 12. However, configurations in which the inner cladding 14 does not have a distinct boundary with the core 12 are also contemplated. Similarly, the inner cladding 14 may have a distinct cladding boundary with the outer cladding 16, or may be configured not to have a distinct boundary with the outer cladding 16.

[0030] One or more coating layers can be further provided on the outer cladding 16 such that the outermost layer of the coating layer becomes the outermost layer of the fiber 10. Each coating layer can be a polymer material.

[0031] The core 12 can contain one or more alkali metal dopants, and the average concentration of the alkali metal dopants in the core 12 can be from about 50 ppm to about 500 ppm, or from about 100 ppm to about 450 ppm, or from about 150 ppm to about 400 ppm. The average alkali concentration in the light transmission region can be defined as follows.

[0032] [Number]

[0033] wherein C alkali (r) is the alkali concentration as a function of the radial position, and the MFD is the mode field diameter of the optical fiber at 1550 nm. In some embodiments, the concentration of the alkali metal dopant decreases along the radius of the core. Therefore, the concentration of the dopant is highest at the center line of the fiber 10. The alkali metal dopant can be, for example, one or more of sodium, potassium, lithium, cesium, rubidium. In addition to or instead of this, as the alkali metal source, bromide, iodide, fluoride, or a combination thereof can also be included. The alkali metal dopant can be a metal oxide of these alkali metals, for example, Na2O, K2O, Li2O, Cs2O, Rb2O, or a mixture thereof. In some embodiments, the alkali metal is KBr, KI, KNO3, or a mixture thereof. By adding an alkali metal dopant to the core 12, the attenuation of the fiber 10 is reduced. Specifically, the alkali metal dopant reduces the viscosity of the core 12 and promotes the relaxation of the glass in the glass transition region during the fiber drawing of the optical fiber. When the glass relaxation of the core 12 is promoted during fiber drawing, the fictive temperature of the glass decreases, so Rayleigh scattering and attenuation are reduced.

[0034] In addition to the alkali metal dopant, core 12 can further include additional dopants. For example, core 12 can include chlorine, fluorine, or both as dopants. Further, inner cladding 14, outer cladding 16, or both can be doped with one or more dopants such as halide dopants. In some embodiments, this halide is fluorine.

[0035] As shown in FIG. 2, optical fiber 10 can be manufactured by fiber manufacturing system 100. System 100 generally includes a drawing furnace 102, and drawing furnace 102 includes a heating element 106 and a muffle 104. As shown in FIG. 2, when glass preform 120 is vertically disposed within muffle 104, heating element 106 supplies heat to at least the bottom of preform 120. Then, from the heated preform 120, optical fiber 10 is drawn (in the form of an uncoated bare optical fiber).

[0036] When drawing the fiber 10, the root portion 122 of the base material 120 is pulled by the traction machine 140 and wound up by the spoon (reel) 150. The traction machine 140 enables the drawing of the optical fiber 10 with various drawing tensions. Further, the system 100 can further include a tension control device 127. In some embodiments, the tension control device 127 can set the drawing tension to a desired tension by adjusting the temperature of the heating element 106. Usually, when the temperature of the furnace 102 is increased, the tension of the fiber being drawn decreases, and when the temperature of the furnace 102 is decreased, the tension of the fiber being drawn increases. In addition to or instead of this, the drawing tension can also be changed by adjusting the drawing speed of the fiber by the traction machine 140, and this speed can also be controlled by the control device 127. In some embodiments, the control device 127 can operate according to the tension set value selected by the user. Therefore, in such embodiments, the control device 127 can adjust the heating element 106, the traction machine 140, or both so that the drawing tension of the base material 120 corresponds to the tension set value selected by the user. As will be described in detail below, the drawing tension of the base material 120 can be selected to reduce the attenuation of the fiber obtained by drawing.

[0037] Further, the system 100 can also include additional components (for example, the monitor 124) for monitoring and adjusting the diameter of the fiber 10. In some embodiments, the monitor 124 is used to adjust the speed of the traction machine 140 so as to keep the diameter of the fiber 10 constant. The tension measurement device 126 can measure the tension of the fiber 10 so that the desired drawing tension is maintained. Further, the system 100 can further include a cooling device 128 and a coating device 130. The fiber 10 is an uncoated bare fiber until it reaches the coating device 130, and a polymer-based coating can be applied to the outer surface of this bare optical fiber by the coating device 130. Then, the coated fiber can be wound up by the reel 150 after passing through a coating curing device (not shown).

[0038] The tractor 140 is configured to perform wire drawing of the fiber 10 with various wire drawing tensions. The inventors of the present disclosure have discovered that by optimizing the wire drawing tension of the optical fiber, the attenuation of the optical fiber can be reduced. For example, when the wire drawing tension decreases, the attenuation of the optical fiber obtained by wire drawing is generally reduced to a certain extent. Embodiments of the present disclosure include a method for efficiently and quickly identifying the wire drawing tension that is optimal for attenuation reduction. The inventors of the present disclosure conducted tests on wire drawing 23 fibers with different wire drawing tensions (i.e., wire drawing tensions of 40 grams, 60 grams, 80 grams, 100 grams, and 140 grams), and identified the minimum attenuation value in this test. In FIG. 3, each fiber is shown as a data point. It should also be noted that all 23 fibers obtained in this test were manufactured from the same base material using the same standard process. As shown in FIG. 3, among the fibers obtained in the test, the attenuation of the fiber wire-drawn with a tension of 60 grams and the fiber wire-drawn with a tension of 80 grams was the smallest. It should be noted that neither the wire drawing tension of 60 grams nor the wire drawing tension of 80 grams is the minimum wire drawing tension in the test shown in FIG. 3. Nevertheless, it was found that the attenuation was minimized among the fibers obtained in the test when the wire drawing tension was set to 60 grams and 80 grams.

[0039] When the drawing tension is reduced, the relaxation of the glass in the glass transition region of the fiber is promoted, and the attenuation of the fiber obtained by drawing can be reduced. Further, when the drawing tension is reduced, the stress in the fiber is reduced, and as a result, the perturbation at the core-clad interface of the fiber obtained by drawing is suppressed. If such perturbation is suppressed, the small-angle scattering in the optical fiber obtained by drawing is reduced, and the attenuation is suppressed. However, if the drawing temperature is increased accordingly to reduce the drawing tension, the number of glass defect centers in the optical fiber obtained by drawing will increase. Some of such defect centers are the direct cause of attenuation at 1550 nm. Further, if there are oxygen-rich non-bridging oxygen defects in the optical fiber, the hydrogen sensitivity of the optical fiber will increase. Therefore, there exists an optimum point where reducing the drawing tension up to this point is optimal for reducing attenuation.

[0040] Embodiments of the present disclosure include a step of optimizing the drawing tension during the fiber manufacturing process to produce a fiber with reduced attenuation. In the embodiments disclosed herein, the drawing tension for manufacturing the fiber 10 with reduced attenuation can be from about 50 grams to about 100 grams, or from about 50 grams to about 90 grams, or from about 50 grams to about 80 grams, or from about 50 grams to about 70 grams, or from about 60 grams to about 90 grams, or from about 60 grams to about 100 grams, or from about 60 grams to about 90 grams, or from about 60 grams to about 80 grams, or from about 60 grams to about 70 grams, or from about 65 grams to about 95 grams, or from about 65 grams to about 85 grams, or from about 65 grams to about 75 grams, or from about 55 grams to about 95 grams, or from about 55 grams to about 85 grams, or from about 55 grams to about 75 grams, or from about 55 grams to about 65 grams, or from about 55 grams to about 60 grams. Also, in other embodiments, the drawing tension for manufacturing the fiber 10 with reduced attenuation can be up to about 200 grams, or up to about 175 grams, or up to about 150 grams, or up to about 125 grams, or up to about 100 grams, or from about 50 grams to about 200 grams, or from about 100 grams to about 200 grams, or from about 150 grams to about 200 grams, or from about 175 grams to about 200 grams.

[0041] Note that, as described in this specification, although attenuation may be suppressed by optimizing the drawing tension, it may also result in an increase in the number of oxygen-rich non-bridging oxygen defects that contribute to an increase in the hydrogen sensitivity of the fiber. More specifically, as described above, in order to keep the drawing tension relatively small, it is usually necessary to set the temperature during the drawing process to a relatively high temperature. This is because a relatively high temperature is required to obtain the viscosity necessary to reduce the tension of the optical fiber. However, if the temperature during the fiber drawing process is set to such a high temperature, the bond breakage of the fiber may increase. More specifically, when the drawing temperature increases, the Si-O bonds in the silica matrix of the fiber are broken, and non-bridging oxygen defects are formed. Non-bridging oxygen defects refer to dangling bonds of oxygen. The formation of non-bridging oxygen defects can be schematically represented as follows.

[0042]

Number

[0043] In the formula, "≡" represents three coordination sites of silicon (usually occupied by oxygen), "." represents a radical, ".Si≡" represents a dangling bond of silicon (often called an E' defect), and "Si-O." represents a non-bridging oxygen defect (dangling bond of oxygen). And in the presence of hydrogen, a hydroxyl group can be formed from the non-bridging oxygen group by the following reaction.

[0044]

Number

[0045] The hydroxyl group (SiOH in the above reaction) is known to absorb the wavelength of the communication window, increasing the attenuation of the optical fiber. Therefore, although the attenuation of the optical fiber obtained by drawing can be reduced by optimizing the drawing tension during the fiber drawing process, if the drawing tension is thus lowered, non-bridging oxygen defect centers may be formed, increasing the hydrogen sensitivity of the fiber. And, for example, during the fiber drawing process, if non-bridging oxygen groups come into contact with hydrogen and hydroxyl groups are formed, the attenuation of the fiber may increase again. Furthermore, other defect centers formed during the drawing process may also cause an increase in attenuation at wavelengths in the communication window including 1550 nm. Thus, in the embodiments disclosed herein, the attenuation of the optical fiber is minimized by the influence of stress on the relaxation of the glass during the drawing process, the tension-related perturbation at the core-clad interface causing small-angle scattering, and the attenuation and optimized drawing tension resulting from the formation of defect centers within the optical fiber.

[0046] As will be described in detail in the following explanation, in order to suppress the hydrogen sensitivity of the fiber, a reducing agent can be added to the inner cladding 14, the outer cladding 16, or both during the manufacture of the optical fiber. The reducing agent can include at least one of carbon monoxide (CO), silicon tetrachloride (SiCl4), chloromethane (CH3Cl), dichloromethane (CH2Cl2), chloroform (CHCl3), or a mixture thereof. As will be described in detail in the following explanation, the reducing agent can be added in the halide densification step.

[0047] FIG. 4 shows an exemplary process 200 for manufacturing an optical fiber preform according to an embodiment disclosed in this specification using the outside vapor deposition (OVD) method. As shown, in step 210, a silica-containing glass tube is formed. By flowing alkali metal vapor through this glass tube and heating it from the outside of the tube with a traversing burner, the alkali metal can be deposited on the inside of the tube. The glass tube is heated from the outside to the inside by the traversing burner to promote the diffusion of the alkali metal into the glass tube. To promote the rapid diffusion of the alkali metal and prevent devitrification, the glass tube needs to be heated to a sufficient temperature. In some embodiments, the glass tube is heated to a temperature of at least about 1500 °C, or at least about 1700 °C, or at least about 2000 °C.

[0048] The alkali metal can be diffused into the soot deposition layer to a depth of about 100 micrometers, or at least about 300 micrometers, or at least about 500 micrometers, or from about 100 micrometers to about 500 micrometers from the inner surface of the tube. The diffusion depth of the alkali metal oxide before collapsing the glass tube is from about 100 micrometers to about 500 micrometers from the inner surface which is the diffusion surface of the tube. In some embodiments, the concentration of the diffused alkali metal oxide dopant in the glass tube varies radially within the tube. For example, the glass tube can be doped such that the concentration of the alkali metal oxide in the inner half of the radial direction of the tube is relatively high and the concentration of the alkali metal oxide in the outer half of the radial direction of the tube is relatively low. The boundary point between the inner half and the outer half is defined as half of the radial thickness of the tube and can be set at that position. And for example, it is preferable to diffuse the alkali metal oxide such that the peak concentration in the outer half of the radial direction is less than 50% of the peak concentration in the inner half of the radial direction.

[0049] Furthermore, the resulting silica glass tube and the additional glass deposited on this glass tube are "essentially free of water". In this case, "water" refers to the hydroxyl group OH. Water can cause an absorption peak to occur at 1383 nm or near it, which can be included within the communication operating wavelength range of the optical fiber. This absorption peak may have an adverse effect on the attenuation of the fiber. Therefore, it is desirable to minimize the OH content of the glass tube as much as possible and reduce this absorption peak (sometimes called the water peak). The OH content of the glass tube is preferably less than about 100 mass ppb, and more preferably less than about 20 mass ppb. In order to make the glass tube substantially free of water before diffusing the alkali metal oxide dopant, conventional chlorine drying techniques can be used during the manufacture of the glass tube.

[0050] And, as further shown in process 200, after diffusing the alkali metal into the soot deposition layer, a heating step (step 220) can be performed to collapse the glass tube partway to densify the glass tube. By partially collapsing the glass tube, the surface area of the inner part of the glass tube is reduced. Although the alkali metal may move out of the optical fiber through the inner part of this fiber, by reducing the surface area of the inner part, the alkali metal can be suppressed from going out of the fiber. Therefore, by collapsing the glass tube partway, the loss of the alkali metal can be suppressed.

[0051] Then, in step 230, the glass tube is etched with an etchant suitable for removing silica glass. The etching of the glass tube can be carried out to a depth sufficient to remove unwanted impurities. In some embodiments, an HF solution or a fluoride gas can be used as the etchant. Then, in step 240 after this etching step, the glass tube is collapsed by further heating the glass tube with a heat source to form an alkali-doped silica glass rod. Step 240 can further include a step of depositing an additional silica coat layer on the glass rod to form a glass body. The alkali-doped silica glass body produced at the end of this step 240 becomes the precursor of the core 12 of the optical fiber obtained by drawing.

[0052] Next, a clad layer can be formed by depositing an additional dopant-added silica glass layer on the glass body (step 250). For example, the additional silica glass layer can be doped with a halide such as fluorine. By depositing such an additional silica coat layer, an inner clad 14 and an outer clad 16 can be formed on the core portion of the base material. In an embodiment, the formation of the additional silica coat layer can be performed by a method known in the art such as sleeving on a silica glass tube (either a glass tube or a sleeve tube), deposition of a silica glass sleeve by chemical vapor deposition, or both sleeving and chemical vapor deposition. When laminating an additional silica coat layer to form the inner clad 14 and the outer clad 16, it may be necessary to perform the additional deposition step several times until the desired thickness is obtained. In that case, following each deposition step, drying of the silica coat, doping with a halide, and consolidation are performed (step 260). The inner clad 14 and the outer clad 16 can also be doped with a halide such as fluorine. The halide dopant can be supplied to the silica glass as a halide-containing gas. When the final consolidation step of step 260 is completed, a precursor of the base material is formed.

[0053] Process 200 further includes an additional step 270 of adding a reducing agent. As described above, a reducing agent is added to the base material precursor to suppress the hydrogen sensitivity of the fibers drawn from the base material precursor. At step 260 of process 200, the reducing agent can be added to the silica soot simultaneously. In some embodiments, the reducing agent is added to the silica soot that forms the inner cladding 14, the outer cladding 16, or both of the optical fiber obtained by drawing. At the step of doping the halide in step 260, the reducing agent can be added to the silica soot. In some embodiments, the halide is fluorine, and at the step of doping with fluorine, the reducing agent is added to the silica soot. In an exemplary embodiment, at the step of doping the silica soot with the halide, the reducing agent is added to the silica soot that forms the inner cladding 14.

[0054] As described above, the silica soot of the base material precursor can be exposed to the reducing agent simultaneously with the exposure to the dopant-containing gas. For example, the silica soot that forms the inner cladding 14 can be exposed to the reducing agent simultaneously with the exposure to the dopant-containing gas. In a plurality of embodiments, the reducing agent is a gas and is mixed with a carrier gas. The carrier gas can be an inert gas such as helium. The mixing of the reducing agent with the carrier gas can be performed such that the reducing agent contained in the mixed gas is at least about 1000 ppm, or at least about 1500 ppm, or at least about 2000 ppm, or at least about 2500 ppm, or at least about 3000 ppm, or at least about 3500 ppm, or at least about 4000 ppm, or at least about 4500 ppm, or at least about 5000 ppm, or at least about 5500 ppm. In addition to or instead of this, the mixed gas can contain a reducing agent of up to about 20000 ppm, or up to about 15000 ppm, or up to about 10000 ppm, or up to about 5000 ppm. In some embodiments, the mixed gas contains a reducing agent of about 2000 ppm to about 5500 ppm, or about 2500 ppm to about 5000 ppm, or about 3000 ppm to about 4500 ppm. The remaining gas can be the carrier gas.

[0055] In some embodiments, as described above, the silica soot forming the cladding of the optical fiber 10 (i.e., the inner cladding 14, the outer cladding 16, or both) is exposed to a reducing agent (when mixing the reducing agent with the carrier gas). The silica soot forming the cladding can be exposed to the reducing agent at a temperature of about 800°C to about 1500°C, or about 1100°C to about 1500°C, or about 1300°C to about 1500°C for a processing time of about 30 minutes to about 10 hours.

[0056] In some embodiments, in the consolidation step of step 260, the silica soot forming the inner cladding 14, the outer cladding 16, or both is exposed to a reducing agent. For example (when mixing the reducing agent with the carrier gas), the reducing agent can be present in the processing chamber over the execution time of the consolidation step. Note that the exposure of the reducing agent in this consolidation step can be performed instead of or in addition to the exposure of the reducing agent in the step of doping with the halide in step 260.

[0057] The concentration of the reducing agent in the carrier gas, the temperature at which the silica soot is treated with the reducing agent, and the length of time the silica soot is treated with the reducing agent are selected such that the oxidation state of the cladding of the drawn optical fiber is reduced to a set level.

[0058] After adding the reducing agent to the silica soot and then consolidating the silica soot, the base material precursor is consolidated in step 280 to form the final optical fiber base material. At this stage, the completed optical fiber base material is in a state where it can be drawn into an alkali-doped and reducing-agent-doped optical fiber (using the above-described system 100). Other methods for forming alkali-doped silica optical fibers are disclosed in U.S. Patent No. 7,524,780, U.S. Patent No. 7,469,559, and U.S. Patent Application Publication No. 2007 / 0297735, and the entire contents of each of these specifications are hereby incorporated by reference into this specification.

[0059] As described above, by adding a reducing agent to the optical fiber, the hydrogen sensitivity of the optical fiber obtained by drawing can be reduced. More specifically, the hydrogen sensitivity decreases due to the decrease in the concentration of non-bridging oxygen defect centers by the reducing agent. Such hydrogen sensitivity is considered to be derived from raising the drawing temperature as the drawing tension is lowered. As described above, while lowering the drawing tension increases the hydrogen sensitivity, it also has the effect of reducing the attenuation of the fiber obtained by drawing. The smaller the attenuation of the optical fiber, the higher the signal transmission efficiency of the fiber.

[0060] Also, performing temperature adjustment of the optical fiber 10 downstream of the drawing furnace (for example, drawing furnace 102) is also useful for suppressing attenuation of the fiber obtained by drawing. More specifically, by performing temperature adjustment of the optical fiber 10 downstream of the drawing furnace, glass defects of the type that cause attenuation and other types of defects that cause an increase in hydrogen sensitivity can be thermally annealed. Referring again to FIG. 2, in some embodiments, the cooling device 128 adjusts the temperature of the fiber to further suppress the attenuation of the fiber obtained by drawing. The cooling device 128 can heat or cool the optical fiber 10 when the fiber 10 passes through the cooling device 128. In some embodiments, the cooling device 128 operates at a temperature of about 900°C to about 1300°C, or about 900°C to about 1200°C, or about 1000°C to about 1150°C, or about 1050°C to about 1125°C. The temperature of the optical fiber 10 when entering the cooling device 128 can be about 1050°C to about 1300°C, or about 1100°C to about 1250°C, or about 1150°C to about 1200°C. The cooling / heating rate of the optical fiber 10 in the cooling device 128 is about 1000°C / second and about 5000°C / second, or about 1500°C / second to about 3500°C / second, or about 2000°C / second to about 3000°C / second. The time for which the optical fiber 10 is exposed to the heating / cooling treatment of the cooling device 128 can be about 0.05 seconds or more, or about 0.08 seconds or more, or about 0.10 seconds or more, or about 0.20 seconds or more, or about 0.30 seconds or more, or about 0.50 seconds or more. Also, in addition to or instead of this, the time for which the optical fiber 10 is exposed to the heating / cooling treatment of the cooling device 128 can also be about 4 seconds or less, or about 3 seconds or less, or about 2 seconds or less, or about 1 second or less, or about 0.90 seconds or less. In some embodiments, such exposure time is about 0.05 seconds to about 2 seconds, or about 0.08 seconds to about 1 second, or about 0.10 seconds to about 0.80 seconds, or about 0.40 seconds to about 0.60 seconds.

[0061] In addition, an embodiment of the present disclosure also includes a process 300 for manufacturing an optical fiber 10 with reduced attenuation as shown in FIG. 5. Step 310 of process 300 includes the step of manufacturing an optical fiber preform containing a reducing agent. Therefore, step 310 can be executed according to each step of process 200. As described above, a reducing agent can be added in the step of doping the halide of process 200, the step of consolidation, or both of these steps. Therefore, for example, in some embodiments, the reducing agent is added to the cladding (e.g., inner cladding 14) of the optical fiber preform simultaneously with the halide-containing gas in a gaseous state. In some embodiments, this halide is fluorine. Furthermore, the preform can comprise an alkali-doped core.

[0062] In step 320 of process 300, an optical fiber is drawn from this optical fiber preform using system 100. The drawing of the optical fiber can be performed by a tractor 140 operating at a drawing tension in the range of about 50 grams to about 100 grams (or any of the drawing tensions described above) as described above. Further, in step 330 of process 300, the temperature of the drawn fiber is adjusted by a cooling device 128 downstream of the drawing furnace 102. As described above, the cooling device 128 can operate in the range of about 900 °C to about 1300 °C (or any of the temperatures described above). By step 330, an optical fiber 10 with reduced attenuation can be manufactured while keeping the number of oxygen-rich non-bridging oxygen defects low.

[0063] FIG. 6 shows another process 400 for manufacturing an optical fiber with reduced attenuation. In step 410 of process 400, a first optical fiber preform is manufactured. The first optical fiber preform can be manufactured according to each step of process 200 disclosed in the above description. Thus, as described above, the first optical fiber preform includes an alkali-doped core and a reducing agent-doped cladding. Then, in step 420, a plurality of optical fibers are drawn from the first optical fiber preform with a plurality of drawing tensions. For example, in step 420, (i) a first drawing tension (e.g., 100 grams) can be used to draw a first optical fiber from the first optical fiber preform, (ii) a second drawing tension (e.g., 90 grams) can be used to draw a second optical fiber from the first optical fiber preform, (iii) a third drawing tension (e.g., 80 grams) can be used to draw a third optical fiber from the first optical fiber preform, and (iv) a fourth drawing tension (e.g., 70 grams) can be used to draw a fourth optical fiber from the first optical fiber preform. In some embodiments, the plurality of drawing tensions are different from each other. Thus, for example, the first drawing tension, the second drawing tension, the third drawing tension, and the fourth drawing tension are clearly distinguishable drawing tensions that are different from each other. Step 420 can be performed using system 100 including cooling device 128.

[0064] Next, at step 430, the attenuation of each drawn optical fiber is measured. For example, the attenuation of the first optical fiber, the second optical fiber, the third optical fiber, and the fourth optical fiber is measured respectively. Then, at step 440, the smallest attenuation measurement value is identified. For example, it can be determined that among these optical fibers, the fourth optical fiber has the smallest attenuation measurement value. And at step 450, the drawing tension of system 100 is set to the reference drawing tension. This reference drawing tension corresponds to the drawing tension of the optical fiber with the smallest attenuation. Therefore, in the above example, since the fourth optical fiber has the smallest attenuation and it was drawn with a tension of 70 grams, the reference drawing tension is set to a tension of 70 grams. Thus, in this example, system 100 is set to a reference drawing tension of 70 grams.

[0065] Then, at step 460 of process 400, the second optical fiber base material is drawn by system 100 with the reference drawing tension. The second optical fiber base material is manufactured by the same process as the first optical fiber base material. In the case of the above example, the second optical fiber base material will be drawn with a reference drawing tension of 70 grams.

[0066] The reference drawing tension is the drawing tension optimized to minimize attenuation. Therefore, in an embodiment of process 400, first, the reference drawing tension is identified using the first optical fiber base material. Next, by drawing the second optical fiber base material with this reference drawing tension, drawing can be performed on the second optical fiber base material to have excellent attenuation characteristics. Process 400 provides a system that efficiently identifies the optimal drawing tension for drawing an optical fiber with excellent attenuation characteristics.

[0067] Embodiments of the present disclosure also include a step of changing the drawing tension during the drawing of the optical fiber preform so that the optical fiber obtained by drawing has reduced attenuation. More specifically, as shown in FIG. 7, process 500 includes a step of manufacturing an optical fiber preform (step 510). The optical fiber preform can be manufactured according to each step of process 200 disclosed in the above description. Thus, as described above, the optical fiber preform includes an alkali-doped core and a reducing agent-doped cladding. And in step 520, a first optical fiber is drawn from a first portion of the optical fiber preform with a first drawing tension. In step 530, a second optical fiber is drawn from a second portion of the optical fiber preform with a second drawing tension. Thus, process 500 includes a step of changing the drawing tension from the first drawing tension to the second drawing tension (during the drawing of the optical fiber preform). The second drawing tension can be a tension lower than the first drawing tension. Thus, two tensions, namely the first drawing tension and the second drawing tension, are applied to one optical fiber preform.

[0068] In some embodiments, the second drawing tension is a tension lower than the first drawing tension. Further, in some embodiments, the first drawing tension and the second drawing tension are each a tension range. The first drawing tension and the second drawing tension can be any of the ranges disclosed in the above description. In some embodiments, the first drawing tension ranges from about 100 grams to about 200 grams, or from about 100 grams to about 150 grams. In addition to or instead of this, in some embodiments, the second drawing tension ranges from about 40 grams to about 90 grams, or from about 60 grams to about 80 grams. The first drawing tension is greater than the second drawing tension, and the difference can be about 10 grams or more, or about 10 grams or more, or about 15 grams or more, or about 20 grams or more, or about 25 grams or more, or about 30 grams or more.

[0069] In some embodiments of process 500, about 50% or less of the length of the optical fiber preform is drawn with a first drawing tension. In other embodiments, about 40% or less, or about 30% or less, or about 20% or less, or about 15% or less, or about 10% or less, or about 5% or less, or about 2.5% or less, or about 2% or less, or about 1% or less of the length of the optical fiber preform is drawn with the first drawing tension. Accordingly, about 50% or more of the length of the optical fiber preform is drawn with a second drawing tension. In other embodiments, about 60% or more, or about 70% or more, or about 75% or more, or about 80% or more, or about 85% or more, or about 90% or more, or about 95% or more, or about 97.5% or more, or about 98% or more, or about 99% or more of the length of the optical fiber preform is drawn with the second drawing tension.

[0070] The attenuation of the optical fiber manufactured according to the method disclosed herein at 850 nm is about 1.50 dB / km or less, or about 1.45 dB / km or less, or about 1.40 dB / km or less, or about 1.38 dB / km or less, or about 1.37 dB / km or less, or about 1.36 dB / km or less, or about 1.35 dB / km or less, or about 1.34 dB / km or less, or about 1.32 dB / km or less, or about 1.31 dB / km or less, or about 1.30 dB / km or less. In some embodiments, the attenuation of the optical fiber manufactured according to the description herein at 850 nm is from about 1.50 dB / km to about 1.30 dB / km, or from about 1.45 dB / km to about 1.31 dB / km, or from about 1.40 dB / km to about 1.32 dB / km. In some embodiments, the attenuation of the optical fiber manufactured according to the description herein at 850 nm is 1.387 dB / km or 1.389 dB / km.

[0071] Furthermore, the attenuation of the optical fiber manufactured according to the method disclosed herein at 1550 nm is about 0.155 dB / km or less, or about 0.150 dB / km or less, or about 0.145 dB / km or less, or about 0.140 dB / km or less, or about 0.138 dB / km, or about 0.135 dB / km, or about 0.130 dB / km. In some embodiments, the attenuation of the optical fiber manufactured according to the description herein at 1550 nm is from about 0.155 dB / km to about 0.130 dB / km, or from about 0.150 dB / km to about 0.135 dB / km, or from about 0.145 dB / km to about 0.138 dB / km.

[0072] Therefore, the optical fiber manufactured according to the method disclosed herein exhibits low attenuation as disclosed in the above description, whether at a wavelength of 850 nm or 1550 nm. Since many commercial systems operate at a wavelength of 850 nm, low attenuation at 850 nm is advantageous for commercial applications. Furthermore, since the absorption wavelength of many hydrogen defects is 1550 nm, low attenuation at 1550 nm is advantageous for identifying the hydrogen sensitivity of the fiber.

[0073] Furthermore, the effective area of the optical fiber manufactured according to the method disclosed herein at 1550 nm is about 160 μm 2 or less. In some embodiments, the effective area at 1550 nm is about 150 μm 2 or less, or about 140 μm 2 or less, or about 130 μm 2 or less, or about 120 μm 2 or less, or about 110 μm 2 or less, or about 100 μm 2 or less, or about 90 μm 2 or less, or about 80 μm 2 or less. In some further embodiments, the effective area at 1550 nm is from about 70 μm 2 to about 160 μm 2 In some embodiments, the effective area at 1550 nm is from about 75 μm 2 to about 155 μm 2 or from about 80 μm 2~about 150 μm 2 or about 85 μm 2 ~about 150 μm 2 or about 90 μm 2 ~about 145 μm 2 or about 95 μm 2 ~about 140 μm 2 or about 100 μm 2 ~about 135 μm 2 or about 105 μm 2 ~about 130 μm 2 or about 110 μm 2 ~about 125 μm 2 or about 115 μm 2 ~about 120 μm 2 or a combination of ranges having any of these values as endpoints.

[0074] Furthermore, the mode field diameter of the optical fiber disclosed herein at a wavelength of 1550 nm is in the range of about 10.0 micrometers to about 15.0 micrometers, or about 11.0 micrometers to about 14.0 micrometers, or about 11.0 micrometers to about 13.0 micrometers. In some embodiments, the mode field diameter at a wavelength of 1550 nm is about 11.5 micrometers, or about 13.0 micrometers.

[0075] The cable cutoff of the optical fiber disclosed herein is about 1530 nm or less, or about 1500 nm or less, or about 1450 nm or less, or about 1400 nm or less.

[0076] According to one aspect of the present disclosure, the dispersion of the optical fiber at 1550 nm is less than 22 ps / nm / km, and the dispersion slope at 1550 nm is less than 0.1 picosecond / nm 2 / km. For example, the dispersion at 1550 nm can be about 15 picoseconds / nm / km to about 22 picoseconds / nm / km, about 16 picoseconds / nm / km to about 22 picoseconds / nm / km, about 16 picoseconds / nm / km to about 21 picoseconds / nm / km, about 17 picoseconds / nm / km to about 21 picoseconds / nm / km, about 17 picoseconds / nm / km to about 20 picoseconds / nm / km.

[0077] Unless otherwise expressly stated, it is not at all intended that any method described in this specification be construed as requiring that each step (process) be performed in a specific order. Therefore, unless the order of the steps is actually described in the method claims, or unless other descriptions indicating that each step is limited to a specific order are clearly made in the claims or the detailed description of the invention, the specific order of each step being inferred, regardless of what order it may be, is not intended.

[0078] It will be apparent to those skilled in the art that various modifications and changes can be made without departing from the spirit and scope of the present invention. Since those skilled in the art can conceive of modifications, combinations, partial combinations, and changes of the embodiments of the present disclosure while incorporating the intent and spirit of the present invention, the present invention should be construed as including all within the scope of the appended claims and their equivalents.

[0079] Hereinafter, preferred embodiments of the present invention will be described item by item.

[0080] Embodiment 1 A method for manufacturing an optical fiber, the method comprising: forming an alkali-doped silica-containing glass tube; collapsing the glass tube to form a first glass rod; depositing a silica soot on the first glass rod to form a first glass body; depositing additional silica soot on the first glass body; exposing the silica soot on the first glass body to a halide dopant; exposing the silica soot on the first glass body to a reducing agent; consolidating the silica soot on the first glass body to form a first base material precursor; forming a first optical fiber base material from the first base material precursor; Drawing the first optical fiber preform with a first drawing tension to produce a first alkali-doped optical fiber, and drawing the first optical fiber preform with a second drawing tension to produce a second alkali-doped optical fiber; Measuring the attenuation of the first alkali-doped optical fiber to obtain a first attenuation measurement value for the first alkali-doped optical fiber, measuring the attenuation of the second alkali-doped optical fiber to obtain a second attenuation measurement value for the second alkali-doped optical fiber, and the second attenuation measurement value being smaller than the first attenuation measurement value; Setting the drawing tension to the second drawing tension; Drawing a second optical fiber preform with the second drawing tension to produce a third alkali-doped optical fiber; including; The method wherein the third alkali-doped optical fiber has an attenuation of about 1.50 dB / km or less at 850 nm and an attenuation of about 0.155 dB / km or less at 1550 nm.

[0081] Embodiment 2 The method according to Embodiment 1, wherein the first optical fiber preform and the second optical fiber preform are made by the same process.

[0082] Embodiment 3 The method according to Embodiment 1 or 2, further including exposing the silica soot of the second optical fiber preform to the halide dopant and the reducing agent.

[0083] Embodiment 4 The method according to any one of Embodiments 1 to 3, wherein the first glass rod is doped with an alkali containing at least one of sodium, potassium, and rubidium.

[0084] Embodiment 5 The method according to any one of Embodiments 1 to 4, wherein the reducing agent is carbon monoxide (CO), silicon tetrachloride (SiCl4), chloromethane (CH3Cl), dichloromethane (CH2Cl2), chloroform (CHCl3), or a mixture thereof.

[0085] Embodiment 6 The method according to any one of Embodiments 1 to 5, further comprising the step of wire-drawing the second optical fiber preform with a wire-drawing tension of about 60 grams to about 90 grams.

[0086] Embodiment 7 The method according to any one of Embodiments 1 to 6, wherein the attenuation at 850 nm is about 1.45 dB / km or less.

[0087] Embodiment 8 The method according to Embodiment 7, wherein the attenuation at 850 nm is about 1.40 dB / km or less.

[0088] Embodiment 9 The method according to any one of Embodiments 1 to 8, wherein the attenuation at 1550 nm is about 0.150 dB / km or less.

[0089] Embodiment 10 The method according to Embodiment 9, wherein the attenuation at 1550 nm is about 0.145 dB / km or less.

[0090] Embodiment 11 A method for manufacturing an optical fiber, the method comprising: forming an alkali-doped silica-containing glass tube; collapsing the glass tube to form a glass rod; depositing a silica coat on the glass rod to form a glass body; depositing an additional silica coat on the glass body; exposing the silica coat on the glass body to a halide dopant; exposing the silica coat on the glass body to a reducing agent; Consolidating the silica coat on the glass body to form a base material precursor; Forming an optical fiber preform from the base material precursor; Drawing the optical fiber preform with a drawing tension of about 60 grams to about 90 grams to form an alkali-doped optical fiber; Exposing the alkali-doped optical fiber to a cooling device provided downstream of the drawing furnace and operating within a range of about 900 °C to about 1300 °C for a time of about 0.05 seconds or more; comprising; wherein the attenuation of the alkali-doped optical fiber at 850 nm is about 1.50 dB / km or less and the attenuation at 1550 nm is about 0.155 dB / km or less.

[0091] Embodiment 12 The method according to embodiment 11, wherein the glass rod is doped with an alkali containing at least one of sodium, potassium, and rubidium.

[0092] Embodiment 13 The method according to embodiment 11 or 12, wherein the reducing agent is carbon monoxide (CO), silicon tetrachloride (SiCl4), chloromethane (CH3Cl), dichloromethane (CH2Cl2), chloroform (CHCl3), or a mixture thereof.

[0093] Embodiment 14 The method according to embodiment 13, wherein the reducing agent is carbon monoxide (CO) or silicon tetrachloride (SiCl4).

[0094] Embodiment 15 The method according to any one of embodiments 11 to 14, wherein the alkali-doped optical fiber is exposed to the cooling device for a time of about 0.05 seconds to about 2 seconds.

[0095] Embodiment 16 The method according to any one of Embodiments 11 to 15, wherein the silica coat on the glass body is simultaneously exposed to the halide dopant and the reducing agent.

[0096] Embodiment 17 The method according to Embodiment 16, wherein the reducing agent is added to a carrier gas to form a mixed gas containing the reducing agent at about 500 ppm to about 20,000 ppm.

[0097] Embodiment 18 The method according to Embodiment 17, wherein the mixed gas contains the reducing agent at about 2000 ppm to about 5500 ppm.

[0098] Embodiment 19 The method according to Embodiment 16, wherein the halide is fluorine.

[0099] Embodiment 20 The method according to any one of Embodiments 11 to 19, wherein the attenuation at 850 nm is about 1.45 dB / km or less.

[0100] Embodiment 21 The method according to Embodiment 20, wherein the attenuation at 850 nm is about 1.40 dB / km or less.

[0101] Embodiment 22 The method according to any one of Embodiments 11 to 21, wherein the attenuation at 1550 nm is about 0.150 dB / km or less.

[0102] Embodiment 23 The method according to Embodiment 22, wherein the attenuation at 1550 nm is about 0.145 dB / km or less.

[0103] Embodiment 24 The method according to any one of Embodiments 11 to 19, wherein the attenuation at 850 nm is about 1.40 dB / km or less and the attenuation at 1550 nm is about 0.145 dB / km or less.

[0104] Embodiment 25 The method according to any one of Embodiments 11 to 24, wherein the wire tension is about 60 grams to about 80 grams.

[0105] Embodiment 26 The method according to any one of Embodiments 11 to 25, wherein the cooling device heats, cools, or both heats and cools the fiber at a rate of 1000 ° C / second and about 5000 ° C / second.

[0106] Embodiment 27 The method according to any one of Embodiments 11 to 26, wherein the alkali concentration in the core of the alkali-doped optical fiber is about 50 ppm to about 500 ppm.

[0107] Embodiment 28 The method according to Embodiment 27, wherein the alkali contains sodium, potassium, lithium, cesium, rubidium, bromide, iodide, fluoride, or a combination thereof.

[0108] Embodiment 29 The effective area of the alkali-doped optical fiber at 1550 nm is about 70 μm 2 ~ about 160 μm 2 The method according to any one of Embodiments 11 to 28.

[0109] Embodiment 30 The effective area of the alkali-doped optical fiber at 1550 nm is about 100 μm 2 ~ about 135 μm 2 The method according to Embodiment 29.

[0110] Embodiment 31 A method for manufacturing an optical fiber, the method comprising: Forming an alkali-doped silica-containing glass tube; Collapsing the glass tube to form a glass rod; Depositing a silica coat on the glass rod to form a glass body; Depositing an additional silica coat on the glass body; Exposing the silica coat on the glass body to a halide dopant; Exposing the silica coat on the glass body to a reducing agent; Consolidating the silica coat on the glass body to form a base material precursor; Forming an optical fiber preform from the base material precursor; Drawing a first portion of the optical fiber preform with a first wire drawing tension to form a first alkali-doped optical fiber; Drawing a second portion of the optical fiber preform with a second wire drawing tension to form a second alkali-doped optical fiber; comprising, wherein the first wire drawing tension is higher than the second wire drawing tension, wherein the second alkali-doped optical fiber has an attenuation of about 1.50 dB / km or less at 850 nm and an attenuation of about 0.155 dB / km or less at 1550 nm.

[0111] Embodiment 32 The method according to embodiment 31, wherein the first glass rod is doped with an alkali containing at least one of sodium, potassium, and rubidium.

[0112] Embodiment 33 The method according to embodiment 31 or 32, wherein the first wire drawing tension ranges from about 100 grams to about 200 grams.

[0113] Embodiment 34 The method according to any one of embodiments 31 to 33, wherein the second wire drawing tension ranges from about 40 grams to about 90 grams.

[0114] Embodiment 35 The method according to any one of embodiments 31 to 34, wherein about 60% or more of the length of the optical fiber preform is drawn with the second wire drawing tension.

[0115] Embodiment 36 The method according to any one of Embodiments 31 to 35, wherein about 70% or more of the length of the optical fiber preform is wire-drawn with the second wire-drawing tension.

[0116] Embodiment 37 The method according to any one of Embodiments 31 to 36, wherein the reducing agent is carbon monoxide (CO), silicon tetrachloride (SiCl4), chloromethane (CH3Cl), dichloromethane (CH2Cl2), chloroform (CHCl3), or a mixture thereof.

[0117] Embodiment 38 The method according to any one of Embodiments 31 to 37, wherein the attenuation at 850 nm is about 1.45 dB / km or less.

[0118] Embodiment 39 The method according to Embodiment 38, wherein the attenuation at 850 nm is about 1.40 dB / km or less.

[0119] Embodiment 40 The method according to any one of Embodiments 31 to 39, wherein the attenuation at 1550 nm is about 0.150 dB / km or less.

[0120] Embodiment 41 The method according to Embodiment 40, wherein the attenuation at 1550 nm is about 0.145 dB / km or less.

Description of Reference Numerals

[0121] 10 Optical fiber 12 Core 14 Inner cladding 16 Outer cladding 100 Fiber manufacturing system 102 Wire-drawing furnace 104 Muffle 106 Heating element 120 Preform 122 Root portion 124 Monitor 126 Tension measurement device 127 Tension control device 128 Cooling device 130 Coating device 140 Tractor 150 Reel

Claims

Claim 1 A method for manufacturing an optical fiber, the method comprising: forming an alkali-doped silica-containing glass tube; collapsing the glass tube to form a first glass rod; depositing a silica soot on the first glass rod to form a first glass body; depositing additional silica soot on the first glass body; exposing the silica soot on the first glass body to a halide dopant; exposing the silica soot on the first glass body to a reducing agent; consolidating the silica soot on the first glass body to form a first preform precursor; forming a first optical fiber preform from the first preform precursor; drawing the first optical fiber preform at a first drawing tension to produce a first alkali-doped optical fiber and drawing the first optical fiber preform at a second drawing tension to produce a second alkali-doped optical fiber; measuring the attenuation of the first alkali-doped optical fiber to obtain a first attenuation measurement value for the first alkali-doped optical fiber and measuring the attenuation of the second alkali-doped optical fiber to obtain a second attenuation measurement value for the second alkali-doped optical fiber, wherein the second attenuation measurement value is less than the first attenuation measurement value; setting the drawing tension to the second drawing tension; drawing a second optical fiber preform at the second drawing tension to produce a third alkali-doped optical fiber; comprising: wherein the third alkali-doped optical fiber has an attenuation of about 1.50 dB / km or less at 850 nm and an attenuation of about 0.155 dB / km or less at 1550 nm. Claim 2 The method of claim 1, wherein the first optical fiber preform and the second optical fiber preform are made by the same process. Claim 3 The method of claim 1, further comprising exposing the silica soot of the second optical fiber preform to the halide dopant and the reducing agent. Claim 4 The method of claim 1, wherein the first glass rod is doped with an alkali containing at least one of sodium, potassium, and rubidium. Claim 5 The reducing agent is carbon monoxide (CO), silicon tetrachloride (SiCl ４ ), chloromethane (CH ３ Cl), dichloromethane (CH ２ Cl ２ ), chloroform (CHCl ３ ), or a mixture thereof. The method according to any one of claims 1 to 4. Claim 6 The method according to any one of claims 1 to 4, further comprising the step of wire-drawing the second optical fiber preform with a wire-drawing tension of about 60 grams to about 90 grams.

7. The method according to any one of claims 1 to 4, wherein the attenuation at 850 nm is about 1.45 dB / km or less.

8. The method according to claim 7, wherein the attenuation at 850 nm is about 1.40 dB / km or less.

9. The method according to any one of claims 1 to 4, wherein the attenuation at 1550 nm is about 0.150 dB / km or less.

10. A method for manufacturing an optical fiber, the method comprising: forming an alkali-doped silica-containing glass tube; collapsing the glass tube to form a glass rod; depositing a silica soot on the glass rod to form a glass body; depositing an additional silica soot on the glass body; exposing the silica soot on the glass body to a halide dopant; exposing the silica soot on the glass body to a reducing agent; consolidating the silica soot on the glass body to form a preform precursor; forming an optical fiber preform from the preform precursor; wire-drawing the optical fiber preform with a wire-drawing tension of about 60 grams to about 90 grams to obtain an alkali-doped optical fiber; exposing the alkali-doped optical fiber to a cooling device provided downstream of the wire-drawing furnace and operating within a range of about 900 °C to about 1300 °C for a time of about 0.05 seconds or more; comprising The alkali-doped optical fiber has an attenuation at 850 nm of about 1.50 dB / km or less and an attenuation at 1550 nm of about 0.155 dB / km or less.

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