Cleaning step for removing metal or metal oxide from porous glass body

Abstract

A manufacturing method comprising: (a) a first vapor phase growth step comprising vapor phase growth of a first porous glass body of a glass-forming material and a doping component on a substrate; (b) a cleaning step after the first vapor phase growth step, the cleaning step comprising exposing the first porous glass body to a cleaning gas at a cleaning temperature for a cleaning period, wherein the cleaning gas (i) removes metal or metal oxide from the first porous glass body, (ii) changes the oxidation state of metal or metal oxide in the first porous glass body, or (iii) a combination of (i) and (ii); and (c) a second vapor phase growth step after the cleaning step, the second vapor phase growth step comprising vapor phase growth of a second porous glass body of a glass-forming material on the first porous glass body to yield a porous preform for optical fibers.

Description

Technical Field

[0001] This application claims the benefit of priority under 35 U.S.C. § 120 to U.S. Provisional Application No. 63 / 462,704, filed Apr. 28, 2023, the content of which is relied upon herein and incorporated herein by reference in its entirety.

[0002] Technical Field The present disclosure relates to the manufacture of optical fibers, and more particularly to the manufacture of optical fibers including a cleaning step of removing metal or metal oxide, or both, from a porous glass body from which the optical fiber is ultimately formed.

Background Art

[0003] Optical fibers may be used as a medium for transmitting light, and often have data embedded therein. Optical fibers may include a core and a cladding surrounding the core. The core may have a higher refractive index than the cladding. In such cases, light is transmitted through the core without substantially escaping from the core to the cladding due to total internal reflection within the core. After being transmitted through the optical fiber, the light is converted into an electrical signal with data embedded therein.

[0004] In the manufacture of optical fibers, an initial step may be the production of a preform. To fabricate the preform, an outside vapor deposition (OVD) process may be utilized. In OVD, the innermost part of the core is formed by growing a silica soot doped with a dopant (to increase the refractive index) on a rotating bait rod. A burner vaporizes the silica and dopant raw materials and then grows them layer by layer on the bait rod. Then, undoped silica can be added over the doped silica. After adding the core and cladding and removing the bait rod, the preform may be subjected to a heat treatment called consolidation or sintering. Then, the preform can be heated and drawn into an optical fiber.

[0005] However, there is a problem in that optical fibers stretched from preforms fabricated using OVD can exhibit suboptimal attenuation. Attenuation refers to the loss of signal strength as light travels through the optical fiber. [Overview of the Initiative]

[0006] This disclosure addresses a problem relating to a cleaning step performed after a first vapor phase growth step for growing porous doped silica glass. The cleaning step utilizes a cleaning gas, such as a halogen gas, a hydrogen halide gas, or carbon monoxide, or a combination thereof. The cleaning gas removes metal or metal oxide from the porous doped silica glass or alters the oxidation state of the metal or metal oxide within the porous doped silica glass. Porous doped silica glass with a low metal or metal oxide content, or with a metal or metal oxide content in a different oxidation state, is further processed into an optical fiber. The optical fiber exhibits less attenuation than the optical fiber would have exhibited without the cleaning step.

[0007] According to a first aspect of the present disclosure, a manufacturing method includes: (a) a first vapor phase growth step comprising vapor phase growth of a first porous glass body of a glass-forming material and a doping component on a substrate; (b) a cleaning step following the first vapor phase growth step, the cleaning step comprising exposing the first porous glass body to a cleaning gas at a cleaning temperature for a cleaning period, wherein the cleaning gas (i) removes metal or metal oxide from the first porous glass body, (ii) changes the oxidation state of metal or metal oxide in the first porous glass body, or (iii) a combination of (i) and (ii); and (c) a second vapor phase growth step following the cleaning step, the second vapor phase growth step comprising vapor phase growth of a second porous glass body of a glass-forming material on the first porous glass body to yield a porous preform for optical fibers.

[0008] A second aspect of this disclosure provides a method according to the first aspect, wherein the substrate comprises Al2O3.

[0009] A third aspect of this disclosure provides a method according to the first or second aspect, wherein the glass-forming material comprises SiO2.

[0010] A fourth aspect of the present disclosure presents a method according to any one of the first to third aspects, wherein a first vapor phase growth step utilizes a burner to react a first raw material for a glass-forming material and a first raw material for a doping component to form a layer of a first porous glass body on a substrate.

[0011] According to a fifth aspect of this disclosure, a method according to the fourth aspect is presented, wherein the first raw material for the glass-forming material comprises SiCl4.

[0012] According to a sixth aspect of this disclosure, a method of the fourth or fifth aspect is presented, wherein the first raw material for the doping component comprises GeCl4.

[0013] A seventh aspect of the present disclosure provides a method according to any one of the first to sixth aspects, wherein the first porous glass body grown in vapor phase on a substrate comprises GeO2-doped SiO2.

[0014] According to the eighth aspect of the present disclosure, the method according to any one of the first to seventh aspects further includes a substrate removal step, which includes removing the substrate from the first porous glass body before the cleaning step.

[0015] According to a ninth aspect of the present disclosure, a method is presented according to any one of the first to eighth aspects, wherein the first porous glass body contains a larger amount of metal or metal oxide before the cleaning step than after the cleaning step.

[0016] According to a tenth aspect of the present disclosure, a method is presented according to any one of the first to ninth aspects, wherein (i) the cleaning gas comprises a halogen gas, a hydrogen halide gas, or carbon monoxide, (ii) the cleaning temperature is 800°C or higher, and (iii) the cleaning period is 30 minutes or longer.

[0017] According to an eleventh aspect of this disclosure, a method of the tenth aspect is presented, wherein the cleaning gas includes Cl2.

[0018] A twelfth aspect of the present disclosure presents a method according to the tenth aspect, wherein (i) the cleaning gas comprises a halogen gas or a hydrogen halogen gas, (ii) the hydrogen gas or hydrogen halogen gas of the cleaning gas comprises a partial pressure of 7 Torre or more, (iii) the cleaning temperature is in the range of 1000°C to 1200°C, and (iv) the cleaning period is in the range of 1.0 hour to 8.0 hours.

[0019] A thirteenth aspect of the present disclosure provides a method according to the tenth aspect, wherein (i) the cleaning gas comprises carbon monoxide, and (ii) the carbon monoxide in the cleaning gas comprises a partial pressure in the range of 1 Torre to 10 Torre.

[0020] According to a fourteenth aspect of the present disclosure, a method is presented according to any one of the tenth to thirteenth aspects, wherein the cleaning gas further comprises O2 for at least a portion of the cleaning period.

[0021] According to a 15th aspect of this disclosure, a method is presented which is one of the first to 14th aspects, wherein the cleaning period is approximately 2 to 4 hours.

[0022] According to a sixteenth aspect of the present disclosure, a method is presented which is one of the first to fifteenth aspects, wherein the second vapor phase growth step utilizes a burner to react a second raw material for a glass-forming material to form a layer of the second porous glass body on the first porous glass body.

[0023] According to a seventeenth aspect of the present disclosure, a method according to the sixteenth aspect is presented, in which a second raw material for a glass-forming material contains SiCl4.

[0024] According to an eighteenth aspect of the present disclosure, a method according to the sixteenth aspect is presented, in which a second raw material for a glass-forming material contains octamethylcyclotetrasiloxane.

[0025] According to a nineteenth aspect of the present disclosure, a method according to any one of the first to eighteenth aspects is presented, in which a second porous glass body grown by vapor deposition on a first porous glass body contains SiO2.

[0026] According to a twentieth aspect of the present disclosure, a method according to any one of the first to twentieth aspects is presented, in which the first vapor deposition step, the cleaning step, and the second vapor deposition step are each performed in a different furnace.

[0027] According to a twenty-first aspect of the present disclosure, the method according to any one of the first to twentieth aspects further includes a second cleaning step in which, after the second vapor deposition step, the porous preform is exposed to a cleaning gas at a cleaning temperature for a cleaning period, and the cleaning gas (i) removes a metal or metal oxide from the porous preform, (ii) changes the oxidation state of a metal or metal oxide in the porous preform, or (iii) is a combination of (i) and (ii).

[0028] According to a twenty-second aspect of the present disclosure, a method according to any one of the first to twenty-first aspects is presented, in which the first porous glass body contains a higher weight percentage of a doping component than the second porous glass body.

[0029] According to a twenty-third aspect of the present disclosure, the method according to any one of the first to twenty-second aspects further includes a core sintering step in which the porous preform is sintered to form a sintered preform.

[0030] According to a 24th aspect of the present disclosure, the method according to the 23rd aspect further includes a re-drawing step including re-drawing a sintered preform into a core cane.

[0031] According to a 25th aspect of the present disclosure, the method according to the 24th aspect further includes an outer cladding step including (i) forming a porous outer cladding layer on the core cane, and a sintering step including (ii) sintering the porous outer cladding layer to provide an optical fiber preform.

[0032] According to a 26th aspect of the present disclosure, the method according to any one of the 1st to 25th aspects further includes an optical fiber drawing step including drawing an optical fiber from an optical fiber preform made from a porous preform.

[0033] According to a 27th aspect of the present disclosure, there is provided a method according to any one of the 1st to 26th aspects, wherein (i) the optical fiber exhibits attenuation of electromagnetic radiation having a wavelength of 1310 nm of 0.324 dB / km or less when measured by an optical time domain reflectometer, and (ii) the optical fiber exhibits attenuation of electromagnetic radiation having a wavelength of 1550 nm of 0.185 dB / km or less when measured by an optical time domain reflectometer.

Brief Description of Drawings

[0034] [Figure 1] It is a schematic flowchart of a manufacturing method according to the present disclosure, including a vapor phase growth step and a cleaning step. [Figure 2] It is a conceptual diagram of the vapor phase growth step of the method of FIG. 1, illustrating the vapor phase growth of a porous glass body on a substrate. [Figure 3] It is a conceptual diagram of the cleaning step of the method of FIG. 1, illustrating the porous glass body of FIG. 2, which is disposed in a furnace and subjected to a cleaning temperature in the presence of a cleaning gas to remove one or more metals from the porous glass body and / or change the oxidation state(s) of one or more metals or metal oxides in the porous glass body. [Figure 4]Figure 1 shows a front cross-sectional view of a porous preform fabricated according to the method shown, illustrating the first porous glass body and the second porous glass body placed thereon, as well as the conversion of the porous preform to a sintered preform for carrying out the core sintering step of the method shown in Figure 1. [Figure 5] This is a conceptual diagram of the re-drawing step of the method in Figure 1, illustrating with multiple core canes drawn from the sintered preform in Figure 4. [Figure 6] Figure 5 illustrates the vapor phase growth of the porous outer cladding layer onto the core cane, and is a conceptual diagram of the outer cladding step in the method shown in Figure 1. [Figure 7] Figure 6 shows a front cross-section of the optical fiber preform after another sintering step of the method in Figure 1, illustrating the sintering of a porous outer cladding layer added via the outer cladding step in Figure 6, with the outer cladding layer on the second core portion above the first core portion. [Figure 8] Figure 7 is a schematic diagram of an optical fiber extending from an optical fiber preform. [Figure 9] The graph plots the relative refractive index of the optical fiber in the core portion as a function of the distance from the centerline of the optical fiber, illustrating how the relative refractive index gradually changes in order to control the flow rate of the doping component raw material (here, GeCl4) during the first vapor phase growth step, relating to Example 1 and Comparative Example 2. [Figure 10] Regarding Example 1 and Comparative Example 2, the graph plots the attenuation at 1550 nm as a function of the attenuation at 1310 nm, illustrating that the optical fiber fabricated according to the method in Figure 1, which includes the cleaning step in Figure 3, exhibits lower attenuation than the optical fiber fabricated according to the method without the cleaning step. [Figure 11] Regarding Example 3, the graph plots the attenuation at 1550 nm as a function of the attenuation at 1310 nm, illustrating that the optical fiber subjected to the cleaning step in Figure 3 for approximately 2 to 4 hours exhibits lower attenuation than the optical fiber subjected to the cleaning step for 8 hours. [Modes for carrying out the invention]

[0035] Referring to Figures 1 and 2, a manufacturing method 10 that addresses the aforementioned decay problem is described herein. In a first vapor phase growth step 12, method 10 includes vapor phase growth of a first porous glass body 14 and doping components of the glass-forming material onto a substrate 16. Vapor phase growth is the growth of a thin film of material (in this specification, the first porous glass body 14 and doping components of the glass-forming material) onto a substrate (in this specification, the substrate 16) via a vapor phase. Generally, the raw materials for the grown material are vaporized, for example, through the application of heat. The vaporized raw materials react to form reaction products, which are directed onto the substrate 16 and formed thereon as a thin film of the material.

[0036] A variety of vapor phase growth processes can be used for the first vapor phase growth step 12. For example, an improved version of chemical vapor deposition (CVD) can be used. In this improved version of CVD, a substrate 16 having a centerline 18 is inserted through a hollow glass handle 20 and mounted on a lathe (not shown). The lathe rotates and translates the substrate 16 near a burner 22. The burner 22 generates a flame that heats the substrate 16. A gas mixture of a first raw material for the glass-forming material and a first raw material for the doping component is introduced into the flame. The flame reacts the gas mixture of the first raw materials. The reaction growth product or multiple products 24 are on the substrate 16 as a layer of the first porous glass body 14. The layer accumulates until the desired size of the first porous glass body 14 is achieved. This improved version of CVD is sometimes referred to as outside vapor deposition (OVD). The reaction product or multiple products 24 are sometimes referred to as "soot". The substrate 16 may be referred to as a "bait substrate" or "bait rod." The reaction of the precursor gas mixture in the flame is a flame hydrolysis or oxidation reaction.

[0037] In some embodiments, the substrate 16 (e.g., bait rod) is a metal, a metal alloy, or a ceramic. In some embodiments, the substrate 16 contains aluminum oxide (e.g., Al2O3). In other embodiments, the substrate 16 contains high-purity silica glass. High-purity silica glass can be porous.

[0038] In some embodiments, the first raw material for the glass-forming material is silicon tetrachloride (SiCl4) or comprises silicon tetrachloride (SiCl4). In other embodiments, the first raw material for the glass-forming material is tetraethyl orthosilicate (TEOS), silane (SiH4), or octamethylcyclotetrasiloxane ([CH3)2SiO]4, also known as D4), or comprises them. Other first raw materials for the glass-forming material are possible, and this list is not intended to be exclusive.

[0039] In some embodiments, the first raw material for the doping component is germanium tetrachloride (GeCl4) or contains it. In other embodiments, the first raw material for the doping component is germane (GeH4), diborane (B2H6), phosphine (PH3), titanium tetrachloride (TiCl4), titanium tetraisopropoxide (Ti(OCH(CH3)2)4), hydrogen fluoride (HF), tetrafluoromethane (CF4), silicon tetrafluoride (SiF4), aluminum chloride (AlCl3), aluminum nitrate (Al(NO3)3), erbium chloride (ErCl3), or erbium nitrate (Er(NO3)3), or contains them. Other first raw materials for the doping component are possible, and this list is not intended to be exclusive.

[0040] In some cases, the gas mixture for the first vapor phase growth step 12 includes oxygen gas (O2).

[0041] As a result of the first vapor phase growth step 12, the first porous glass body 14 grown on the substrate 16 contains SiO2 as glass. In embodiments, the doping component is GeO2. Other doping components may also be used. For example, the dopant may be or may contain P2O5, SiF4, B2O3, Al2O3, Er2O3, or TiO2, depending on the first raw material for the doping component used in the first vapor phase growth step 12. This list is not exclusive, and other doping components are also possible. If, during the first vapor phase growth step 12, the reaction products condense to form the first porous glass body 14, the atoms of the doping component (e.g., Ge atoms) or the oxide of the doping component (e.g., GeO2) will substitute for silicon atoms or silica (SiO2) in the silica network of the first porous glass body 14. The incorporation of the doping component modifies one or more properties of the optical fiber portion formed from the first porous glass body 14, such as the refractive index.

[0042] In embodiments, method 10 further includes a substrate removal step 26. The substrate removal step 26 is performed after the first vapor phase growth step 12. The substrate removal step 26 includes removing the substrate 16 from the first porous glass body 14. In embodiments, a coating of a release agent is applied to the substrate 16 before the first vapor phase growth step 12. An exemplary release agent is a carbonaceous material such as carbon soot. The carbon soot forms a sacrificial layer that prevents the first porous glass body 14 from adhering to the substrate 16. During the formation of the first porous glass body 14, the sacrificial carbon layer is gradually oxidized and vaporized, creating a narrow gap between the substrate 16 and the first porous glass body 14. The narrow gap facilitates the removal of the substrate 16 from the first porous glass body 14. Other release agents may also be used.

[0043] Referring to Figure 3, Method 10 further includes a cleaning step 28. The cleaning step 28 is performed after the first vapor phase growth step 12, and if performed, a substrate removal step 26 is carried out. The cleaning step 28 includes exposing the first porous glass body 14 to a cleaning gas 29 at a high temperature over a cleaning period. The cleaning gas 29 either (i) removes metal or metal oxide from the first porous glass body 14, (ii) changes the oxidation state of the metal or metal oxide in the first porous glass body 14, or (iii) a combination of both (i) and (ii). In short, the first porous glass body 14 contains a greater amount of metal or metal oxide before the cleaning step 28 than after the cleaning step 28.

[0044] Without being constrained by theory, the first vapor phase growth step 12 is thought to cause the formation of one or more metals or metal oxides within the first porous glass body 14, in addition to the formation of the glass-forming material and doping components. One or more metals or metal oxides may arise from impurities in the first raw materials or doping components, or as contaminants from the equipment used for vapor phase growth. Theoretically, one or more metals or metal oxides are undesirable because they increase the attenuation exhibited by the resulting optical fiber. The one or more metals or metal oxides theorized to be present within the first porous glass body 14 are difficult to quantify because they may be present in the range of parts per billion. In the washing step 28, the removal of one or more metals or metal oxides, or the alteration of the oxidation state of one or more metals or metal oxides, reduces the attenuation of the optical fiber produced from the first porous glass body 14.

[0045] To carry out the cleaning step 28, the first porous glass body 14 is placed in a furnace 31, the temperature inside the furnace 31 is raised to the cleaning temperature, and the cleaning gas 29 is introduced into the furnace 31 in which the first porous glass body 14 is placed. In embodiments, the cleaning gas 29 used in cleaning step 28 includes one or more of halogen gases, hydrogen halides, and carbon monoxide (CO). Examples of halogen gases and hydrogen halides include chlorine gas (Cl2) and hydrogen chloride gas (HCl), respectively. In embodiments, the hydrogen gas or hydrogen halide gas in the cleaning gas 29 has a partial pressure of 7 Torre (about 933 Pa) or more. In other embodiments, the carbon monoxide in the cleaning gas 29 has a partial pressure in the range of 1 Torre (about 133 Pa) to 10 Torre (about 1333 Pa).

[0046] Without being constrained by theory, halogen gases and hydrogen halides are thought to react with metals and metal oxides to form gaseous metal halides that diffuse from the first porous glass body. Similarly, carbon monoxide is thought to react with metal oxides to form metals and carbon dioxide. For example, chlorine gas (Cl2) and hydrogen chloride gas (HCl) react with metals and metal oxides to form gaseous metal chlorides. When the metal and metal oxide are iron (Fe) and iron oxide (Fe2O3), respectively, the following reactions can occur: [ka] The reaction between iron oxide (Fe2O3) and carbon monoxide (CO) produces iron (Fe), making the reaction to produce iron chloride (FeCl2) and iron chloride (FeCl3) more efficient. As described above, iron chloride (FeCl2) and iron chloride (FeCl3) readily diffuse from the first porous glass body 14. Different halogen gases and hydrogen halides react with other metals and metal oxides in a similar manner to produce readily diffusible gaseous metal halides.

[0047] In the embodiments, the cleaning temperature is 800°C or higher. In the embodiments, the cleaning temperature is in the range of 800°C to 1200°C. In the embodiments, the cleaning temperature is in the range of 1000°C to 1200°C. In the embodiments, the cleaning temperature is 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, or 1200°C, or any range defined by any two of these values ​​(e.g., 1050°C to 1150°C, 900°C to 1100°C, etc.). The cleaning temperature is below the temperature at which the sintering and densification of the first porous glass body 14 (further discussed below) begins. The porosity of the first porous glass body 14 facilitates the removal of one or more metals or metal oxides and / or changes in the oxidation state of one or more metals or metal oxides. If the cleaning temperature is below 800°C, the removal of one or more metals or metal oxides, and / or changes in the oxidation state of one or more metals or metal oxides, is unlikely to occur to a sufficient extent. If the cleaning temperature is above 1200°C, metal halides may be formed, and sintering and densification may occur to an undesirable extent before they diffuse from the first porous glass body 14.

[0048] In the embodiment, the cleaning period of cleaning step 28 is 30 minutes or longer. In the embodiment, the cleaning period is in the range of 1.0 hour to 8.0 hours. In the embodiment, the cleaning period is 30 minutes, 1.0 hour, 1.5 hours, about 2 hours, 2.0 hours, 2.5 hours, 3.0 hours, 3.5 hours, about 4 hours, 4.0 hours, 4.5 hours, 5.0 hours, 5.5 hours, 6.0 hours, 6.5 hours, 7.0 hours, 7.5 hours, or 8.0 hours, or any range defined by any two of these values ​​(e.g., 1.0 hour to 2.5 hours, 2.0 hours to 5.5 hours, about 2 hours to about 4 hours, etc.). If the cleaning period is less than 30 minutes, cleaning step 28 is unlikely to have removed a sufficient amount of one or more metals or metal oxides from the first porous glass body 14, or to have altered the oxidation state of one or more metals or metal oxides. If the washing period exceeds 8.0 hours, the washing step 28 is likely to remove an undesirable amount of dopant (e.g., Ge or GeO2) from the first porous glass body 14 and may excessively oxidize the SiO2 of the first porous glass body 14.

[0049] In the embodiment, the cleaning gas 29 further contains oxygen gas (O2) for at least a portion of the cleaning period. For example, the portion of the cleaning period in which the cleaning gas 29 contains oxygen gas is about 30 minutes. The oxygen gas is thought to further improve the attenuation of the optical fiber ultimately produced from the first porous glass body 14, although the exact reason for this improvement is not known.

[0050] Method 10 further includes a second vapor phase growth step 30. The second vapor phase growth step 30 includes growing a second porous glass body 32 of the glass-forming material on the first porous glass body 14. Referring also to Figure 4, the result of the second vapor phase growth step 30 is a porous preform 34 for optical fibers. The second vapor phase growth step 30 is performed after the cleaning step 28. As mentioned above, the glass-forming material of the second porous glass body 32 can be silicon dioxide (SiO2).

[0051] Similar to the first vapor phase growth step 12, in this embodiment, the second vapor phase growth step 30 is an OVD process utilizing a burner 22 that generates a flame. A second raw material for the glass-forming material is introduced into the flame, and the second raw material reacts. The product of the reaction grows as a layer of the second porous glass body 32 on the first porous glass body 14. The first vapor phase growth step 12 and the second vapor phase growth step 30 can be collectively referred to as a “soot-on-soot” growth process. In this embodiment, after the second vapor phase growth step 30, porous silicon dioxide (SiO2) is laid on porous silicon dioxide doped with germanium dioxide (GeO2).

[0052] In some embodiments, the second raw material for the glass-forming material is silicon tetrachloride (SiCl4) or contains silicon tetrachloride (SiCl4). In other embodiments, the second raw material for the glass material is tetraethyl orthosilicate (TEOS), silane (SiH4), or octamethylcyclotetrasiloxane ([CH3)2SiO]4, also known as D4), or contains them. Other second raw materials for the glass material are possible, and this list is not intended to be exclusive. In some embodiments, doping components are not used in the second vapor phase growth step 30. In some embodiments, the second porous glass body 32 consists essentially of silicon dioxide (SiO2).

[0053] In particular, the use of silicon tetrachloride (SiCl4) can further remove (or change the oxidation state of) one or more metals or metal oxides still present in the first porous glass body 14. In addition to SiO2, burning SiCl4 in the presence of oxygen gas (O2) produces chlorine gas (Cl2). Furthermore, the combustion of methane gas (CH4) present in the burner 22, which generates a flame, produces water (H2O) in addition to carbon monoxide (CO) and oxygen gas (O2). Next, chlorine gas (Cl2) and water (H2O) react to produce hydrogen chloride gas (HCl) and oxygen (O2). As described above, chlorine gas (Cl2) and hydrogen chloride gas (HCl) react with metals and metal oxides to form gaseous metal chlorides that diffuse from the first porous glass body 14.

[0054] In the embodiment, the first vapor phase growth step 12, the cleaning step 28, and the second vapor phase growth step 30 are each performed in different furnaces. For example, only the cleaning step 28 is performed in furnace 31, while the first vapor phase growth step 12 and the second vapor phase growth step 30 are performed in different furnaces. One advantage of performing these steps in different furnaces is that each of steps 12, 28, and 30 can be performed simultaneously. Doing so speeds up the process of producing the final optical fiber and allows for the use of different raw materials for the glass-forming material of the first porous glass body 14 and the second porous glass body 32 in different furnaces. In one embodiment, SiCl4 is used as the raw material for the first porous glass body 14 in the first furnace, and octamethyltetrasiloxane is used as the raw material for the second porous glass body 32 in the second furnace. However, it is not necessary for the first vapor phase growth step 12, the cleaning step 28, and the second vapor phase growth step 30 to all be performed in different furnaces.

[0055] In embodiments, method 10 further includes a second cleaning step 36. The second cleaning step 36 is performed after the second vapor phase growth step 30. The second cleaning step 36 includes exposing the porous preform 34 to a cleaning gas 29 at a cleaning temperature for a cleaning period, such as in a furnace 31. The cleaning gas 29 either (i) removes metal or metal oxide from the porous preform 34, (ii) changes the oxidation state of the metal or metal oxide in the porous preform 34, or (iii) a combination of (i) and (ii). The considerations for cleaning step 28 do not need to be repeated in this specification and apply similarly to the second cleaning step 36.

[0056] Referring to Figure 4, after the second vapor phase growth step 30, the porous preform 34 thus formed includes a second porous glass body 32 radially arranged around the first porous glass body 14. Due to the removal of the substrate 16 in the substrate removal step 26, the porous preform 34 further includes internal cavities 38 corresponding to the space previously occupied by the substrate 16. The first porous glass body 14 contains a larger weight percentage of doping components (e.g., dopants) than the second porous glass body 32. In this embodiment, the first porous glass body 14 contains a larger weight percentage of germanium dioxide (GeO2) than the second porous glass body 32.

[0057] In embodiments, method 10 further includes a core sintering step 40. The core sintering step 40 includes sintering the porous preform 34 to form a sintered preform 42. The core sintering step 40 collapses the pores in the porous preform 34. In embodiments, the core sintering step 40 is performed at a temperature above about 1300°C and causes compression of the porous preform 34 through the collapse of the pore structure to provide a fully densified glass body (sintered preform 42) having a first core portion 52 and a second core portion 54 surrounding the first core portion 52.

[0058] Referring further to Figure 5, the method further includes a re-stretching step 41. For the re-stretching step 41, the sintered preform 42 is heated in a re-stretching furnace 43 and stretched into core canes 45 having a diameter 47 smaller than the original diameter of the sintered preform 42. More specifically, a glass handle 49 is attached to the sintered preform 42, and the sintered preform 42 is attached to a moving downfeed support 51 above the re-stretching furnace 43. A sacrificial glass rod 53, which may be attached to the bottom of the sintered preform 42, is pulled by a motor-driven tractor 57, thereby stretching the core canes 45 at a suitable speed. The diameter 47 of the core canes 45 resulting from the re-stretching step 41 is preferably in the range of 15 mm to 35 mm, such as 24 mm to 26 mm. During the re-stretching step 41, a number of core canes 45 are formed from the sintered preform 42, and the internal cavities 38 collapse due to the reduction in diameter 47. In other words, the internal cavities 38 present in the sintered preform 42 do not exist in the core cane 45.

[0059] Referring further to Figure 6, in the embodiment, method 10 further includes an external cladding step 44. The external cladding step 44 includes forming a porous external cladding layer 50 on top of the core cane 45. The core cane 45 can be used as a bait substrate, and the porous external cladding layer 50 is grown as an overcladding using a chemical vapor deposition method such as the method using a burner 22, as described above. The glass handle 42 is attached to the core cane 54, and a reaction product 24 (e.g., SiO2) made from combustion raw materials is formed on top of the core cane 45. The raw materials can be, among other things, octamethylcyclotetrasiloxane.

[0060] Referring further to Figure 7, in this embodiment, method 10 further includes another sintering step 46 for sintering the porous outer cladding layer 50. The sintering of the porous outer cladding layer 50 is carried out at a temperature above approximately 1300°C and induces compression of the porous outer cladding layer 50 through the collapse of its pore structure, thereby providing a fully densified glass body, which is now referred to as the optical fiber preform 48. Thus, the optical fiber preform 48 includes an outer cladding layer 55 from the outer porous cladding layer 50, a first core portion 52 from the core cane 54 (via the first porous glass body 14), and a second core portion 54 from the core cane 54 (via the second porous glass body 32). The first core portion 52 and the second core portion 54 may be referred to as the primary core portion and the secondary core portion, respectively. The outer cladding layer 55 is disposed on top of the second core portion 54, which is disposed on top of the first core portion 52.

[0061] Referring further to Figure 8, in this embodiment, method 10 further includes an optical fiber stretching step 56. The optical fiber stretching step 56 includes stretching an optical fiber 60 from a preform (e.g., optical fiber preform 48) made from a porous preform 34. It should be noted that there are methods for making a preform from which an optical fiber 60 can be stretched, which do not include the external cladding step 44 and the sintering step 46. For example, the first porous glass body 14 can itself be the cladding layer in the cane-in-suit process. In any case, stretching an optical fiber 60 from an optical fiber preform 50 can be achieved by placing the optical fiber preform 50 in a stretching tower, heating the optical fiber preform 48 with a heating element 62 to soften the glass network, pulling thin strands of glass from the softened optical fiber preform 50 as an optical fiber 60, coating the optical fiber 60 with a coater 64, and then spooling the optical fiber 60 onto a spool 66.

[0062] In the embodiments, the optical fiber exhibits an acceptable level of attenuation, largely due to the cleaning step 28. In the embodiments, the optical fiber exhibits attenuation of electromagnetic radiation with a wavelength of 1310 nm at 0.32 dB / km or less. In the embodiments, the optical fiber exhibits attenuation of electromagnetic radiation with a wavelength of 1550 nm at 0.18 dB / km or less. In the embodiments, the optical fiber exhibits attenuation of electromagnetic radiation with a wavelength of 1310 nm at 0.324 dB / km or less. In the embodiments, the optical fiber exhibits attenuation of electromagnetic radiation with a wavelength of 1550 nm at 0.185 dB / km or less. The attenuation values ​​are measured with an optical time-domain reflectometer according to the International Electrotechnical Commission (IEC) international standard: IEC60793-1-40 Method C. [Examples]

[0063] Example 1 - In Example 1, a first vapor phase growth step was performed to grow a first porous glass body on a substrate with SiO2 as the glass-forming material and GeO2 as the doping component. The first raw material for the glass-forming material was SiCl4. The first raw material for GeO2 was GeCl4. The flow rate of GeCl4 was controlled during the first vapor phase growth step to generate a graded core profile within the optical fiber, and the α profile had an α value in the range of, for example, 2 to greater than 6, exhibiting a relative refractive index (Δ) of 0% to 0.5% (relative to SiO2). The relative refractive index changes as a function of position from the centerline due to the controlled flow rate of GeCl4 during the first vapor phase growth step, as illustrated in Figure 9. The wavelength of the relative refractive index values ​​in Figure 9 is 1550 nm.

[0064] Next, the first porous glass body was subjected to a cleaning step. For the cleaning step, the first porous glass body was placed in a furnace and exposed to a cleaning gas of Cl2 at a cleaning temperature of approximately 1125°C for a cleaning period of 2 hours. 5-6% O2 was also added for the first 30 minutes. The Cl2 flow rate was 5 slpm (standard liters / min). The cleaned first porous glass body was then subjected to a second vapor phase growth step to grow a second porous glass body of glass-forming material on the first porous glass body. The second raw material for the glass-forming material for the second vapor phase growth step was oxymethylcyclotetrasiloxane. The first vapor phase growth step, the cleaning step, and the second vapor phase growth step were all carried out in different furnaces. As a result, a porous preform for optical fibers was obtained. The porous preform was then subjected to a core sintering step and a re-stretching step to form a core cane. One of the corecanes was subjected to an external cladding step to apply a porous external cladding layer of SiO2 from octamethylcyclotetrasiloxane raw materials, and then subjected to another sintering step to form an optical fiber preform. The optical fiber preform was then subjected to an optical fiber stretching step to obtain a number of optical fiber samples for testing.

[0065] The attenuation of optical fiber samples was measured. The attenuation values ​​for each sample were recorded. A graphical plot of the attenuation measurements for Example 1 is reproduced in Figure 10. As the graph illustrates, most of the attenuation values ​​for electromagnetic radiation with a wavelength of 1310 nm were less than 0.324 dB / km. Similarly, most of the attenuation values ​​for electromagnetic radiation with a wavelength of 1550 nm were less than 0.185 dB / km.

[0066] Comparative Example 2 - In Comparative Example 2, numerous optical fiber samples were prepared in the same manner as the samples in Example 1, except that the cleaning step was not performed. The attenuation measurement values ​​for each sample were recorded. The graphical plot of the attenuation measurement values ​​for Comparative Example 2A is also reproduced in Figure 10. As the graph illustrates, all attenuation measurement values ​​for electromagnetic radiation with a wavelength of 1310 nm were greater than 0.324 dB / km. Similarly, all attenuation measurement values ​​for electromagnetic radiation with a wavelength of 1550 nm were greater than 0.185 dB / km. Thus, it is demonstrated that the cleaning step of the first porous glass body reduces the attenuation exhibited by the resulting optical fibers.

[0067] Example 3 - In Example 3, a number of optical fibers were fabricated in the same manner as the optical fibers of Example 1, including a cleaning step. The exception was that the cleaning period was varied. Four sets of sample optical fibers were produced, each having one of four different cleaning periods: 2 hours, 3 hours, 4 hours, and 8 hours. The attenuation measurements for each sample were recorded. A graphical plot of the attenuation measurements for Example 3 is also reproduced in Figure 11. As the graph illustrates, samples with cleaning periods of 2 hours and 3 hours exhibited the lowest attenuation values ​​for electromagnetic radiation with wavelengths of 1310 nm and 1550 nm. Many of the optical fibers in this group of samples (2 hours and 3 hours) exhibited attenuation of less than 0.324 dB / km at 1310 nm and less than 0.185 dB / km at 1550 nm. Samples obtained after a 4-hour cleaning period generally showed attenuation of less than 0.324 dB / km at 1310 nm, but generally showed attenuation of more than 0.185 dB / km at 1550 nm. Samples obtained after an 8-hour cleaning period showed attenuation of more than 0.324 dB / km at 1310 nm and more than 0.185 dB / km at 1550 nm. Based on the current data, the optimal cleaning period is approximately 2 to 4 hours. As mentioned above, it is theorized that longer cleaning periods (e.g., approximately 3 hours in Example 3) resulted in optical fibers exhibiting greater attenuation due to excessive oxidation of SiO2 in the core.

Claims

1. A manufacturing method, A first vapor phase growth step includes vapor-growth of a first porous glass body of glass forming material and doping components onto a substrate, A cleaning step following the first vapor phase growth step, wherein the cleaning step includes exposing the first porous glass body to a cleaning gas at a cleaning temperature for a cleaning period, wherein the cleaning gas (i) removes metal or metal oxide from the first porous glass body, (ii) changes the oxidation state of metal or metal oxide within the first porous glass body, or (iii) a combination of (i) and (ii), A manufacturing method comprising: a second vapor phase growth step following the cleaning step, wherein the second vapor phase growth step includes vapor-growing a second porous glass body of the glass-forming material on the first porous glass body to obtain a porous preform for optical fibers.

2. The aforementioned substrate is Al ２ O ３ The method according to claim 1, including the method described in claim 1.

3. The glass forming material is SiO ２ The method according to claim 1 or 2, including the method according to claim 1 or 2.

4. The method according to any one of claims 1 to 3, wherein the first vapor phase growth step utilizes a burner to react the first raw material for the glass-forming material and the first raw material for the doping component to form a layer of the first porous glass body on the substrate.

5. The first raw material for the glass forming material is SiCl ４ The method according to claim 4, including the method described in claim 4.

6. The first raw material for the doping component is GeCl ４ The method according to claim 4 or 5, including the method described in claim 4 or 5.

7. The first porous glass body, which is vapor-grown on the substrate, is GeO ２ SiO doped ２ The method according to any one of claims 1 to 6, including the method described in any one of claims 1 to 6.

8. The method according to any one of claims 1 to 7, further comprising a substrate removal step, which includes removing the substrate from the first porous glass body before the cleaning step.

9. The method according to any one of claims 1 to 8, wherein the first porous glass body contains a larger amount of the metal or metal oxide before the cleaning step than after the cleaning step.

10. The cleaning gas includes a halogen gas, a hydrogen halide gas, or carbon monoxide. The washing temperature is 800°C or higher. The method according to any one of claims 1 to 9, wherein the cleaning period is 30 minutes or more.

11. The aforementioned cleaning gas, Cl ２ The method according to claim 10, including the method described in claim 10.

12. The cleaning gas includes the halogen gas or the hydrogen halogen gas, The hydrogen gas or hydrogen halogen gas in the cleaning gas contains a partial pressure of 7 Torre or more. The washing temperature is within the range of 1000°C to 1200°C. The method according to claim 10, wherein the cleaning period is within the range of 1.0 hour to 8.0 hours.

13. The cleaning gas contains carbon monoxide, The method according to claim 10, wherein the carbon monoxide in the cleaning gas has a partial pressure in the range of 1 Torr to 10 Torr.

14. The cleaning gas contains O during at least a part of the cleaning period. ２ The method according to any one of claims 10 to 13, further comprising.

15. The method according to any one of claims 1 to 14, wherein the cleaning period is within the range of about 2 hours to about 4 hours.

16. The method according to any one of claims 1 to 15, wherein the second vapor phase growth step utilizes a burner to react a second raw material for the glass-forming material to form a layer of the second porous glass body on the first porous glass body.

17. The second raw material for the glass forming material is SiCl ４ The method according to claim 16, including the method described in claim 16.

18. The method according to claim 16, wherein the second raw material for the glass-forming material comprises octamethylcyclotetrasiloxane.

19. The second porous glass body, which is vapor-grown on the first porous glass body, is composed of SiO ２ The method according to any one of claims 1 to 18, including the method described in any one of claims 1 to 18.

20. The method according to any one of claims 1 to 19, wherein the first vapor phase growth step, the cleaning step, and the second vapor phase growth step are each performed in different furnaces.

21. The method according to any one of claims 1 to 20, further comprising a second cleaning step, after the second vapor phase growth step, the porous preform being exposed to a cleaning gas at a cleaning temperature for a cleaning period, wherein the cleaning gas is (i) removes metal or metal oxide from the porous preform, (ii) alters the oxidation state of metal or metal oxide in the porous preform, or (iii) a combination of (i) and (ii).

22. The method according to any one of claims 1 to 21, wherein the first porous glass body contains the doping component in a larger weight percentage than the second porous glass body.

23. The method according to any one of claims 1 to 22, further comprising a core sintering step of sintering the porous preform to form a sintered preform.

24. The method according to claim 23, further comprising a re-stretching step of re-stretching the sintered preform into a core cane.

25. An external cladding step, which includes forming a porous external cladding layer on the core cane, The method according to claim 24, further comprising a sintering step, which includes sintering the porous outer cladding layer to obtain an optical fiber preform.

26. The method according to any one of claims 1 to 25, further comprising the step of stretching an optical fiber from an optical fiber preform made from the porous preform.

27. When measured with an optical time-domain reflectometer, the optical fiber exhibits attenuation of electromagnetic radiation having a wavelength of 1310 nm or less at 0.324 dB / km. The method according to any one of claims 1 to 26, wherein the optical fiber exhibits attenuation of electromagnetic radiation having a wavelength of 1550 nm or less of 0.185 dB / km when measured with an optical time-domain reflectometer.

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