Patent Application
20230168428
The present disclosure relates to optical fibers. More specifically, the present disclosure relates to a method of manufacturing low loss optical fibers with low water peak and low attenuation for C-band and L-band transmission.
Optical fibers are utilized in a variety of telecommunication applications. Manufacturing processes for producing optical fibers typically include drawing an optical fiber from a heated glass preform in a draw furnace, cooling the drawn optical fiber, and coating the optical fiber.
According to one aspect of the present disclosure, a method of manufacturing a preform of an optical fiber where the optical fiber has a core region and a cladding region includes forming a porous cladding soot blank by depositing silica soot on a core cane. The core cane includes a core portion having a composition corresponding to at least a portion of the core region of the optical fiber and a concentration of an alkali metal oxide in a core portion of the core cane is between 0.1 wt. % and 1.5 wt. %. The method includes exposing the porous cladding soot blank to a fluorine-doping precursor in the presence of SiCl4, the fluorine-doping precursor doping the porous cladding soot blank with fluorine to form a fluorine-doped porous cladding soot blank. The exposing comprises providing a flow of the fluorine-doping precursor to the porous cladding soot blank. The method includes consolidating the fluorine-doped porous cladding soot blank in presence or absence of a fluorine-doping precursor to form a consolidated fluorine-doped cladding cane, the consolidating comprising exposing the fluorine-doped porous cladding soot blank to SiCl4. The composition of the core portion of the core cane comprises silica doped with an alkali metal oxide.
According to another aspect of the present disclosure, a method of manufacturing an optical fiber where the optical fiber has a core region and a cladding region includes forming an alkali-doped core cane. The alkali-doped core cane includes a portion having a composition corresponding to at least a portion of the core region of the optical fiber. The method includes forming a porous cladding soot blank by depositing silica soot on the alkali-doped core cane and exposing the porous cladding soot blank to a fluorine-doping precursor. The fluorine-doping precursor dopes the silica soot with fluorine to form a fluorine-doped porous cladding soot blank. The step of exposing comprises providing a flow of the fluorine-doping precursor to the porous cladding soot blank. The method includes consolidating the fluorine-doped porous cladding soot blank in the absence or presence of the flow of the fluorine-doping precursor to form a fluorine-doped cladding cane, the fluorine-doped cladding cane having a portion with a composition corresponding to the cladding region of the optical fiber. The step of exposing comprises exposing the porous cladding soot blank to the fluorine-doping precursor in the presence of SiCl4 or the step of consolidating comprises exposing the fluorine-doped porous cladding soot blank to SiCl4.
According to another aspect of the present disclosure, an optical fiber includes a core region, the core region comprising silica glass doped with an alkali metal oxide. A cladding region surrounds and is directly adjacent to the core region. The cladding region comprises a depressed-index cladding region surrounding the core region. The depressed-index cladding region comprises silica glass doped with a first concentration of fluorine. The depressed-index cladding region has a relative refractive index Δ3 with a minimum relative refractive index Δ3min in a range from −0.80% to −0.30%. The cladding region includes an outer cladding region surrounding and directly adjacent to the depressed-index cladding region. The outer cladding region comprises silica glass doped with a second concentration of fluorine less than the first concentration of fluorine. The outer cladding region has a relative refractive index Δ4 such that Δ4−Δ3min>0.05%. The optical fiber has a time-to-peak (TTP) hydrogen aging value at 23° C. of less than 100 hours upon exposure of the optical fiber to a gas atmosphere having a total pressure of 1 atm and containing a partial pressure of 0.01 atm H2 and a partial pressure of 0.99 atm N2. The optical fiber exhibits an attenuation <0.16 dB/km at 1583 nm and the attenuation monotonically increases between about 1570 nm and about 1600 nm.
The following is a description of the figures in the accompanying drawings. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.
In the drawings:
Additional features and advantages will be set forth in the detailed description that follows and will be apparent to those skilled in the art from the description, or recognized by practicing the embodiments as described in the following description, together with the claims and appended drawings.
As used herein, the term “and/or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.
In this document, relational terms, such as first and second, top and bottom, and the like, are used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions.
Modifications of the disclosure will occur to those skilled in the art and to those who make or use the disclosure. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and not intended to limit the scope of the disclosure, which is defined by the following claims, as interpreted according to the principles of patent law, including the doctrine of equivalents.
For purposes of this disclosure, the term “coupled” (in all of its forms: couple, coupling, coupled, etc.) generally means the joining of two components directly or indirectly to one another. Such joining may be stationary in nature or movable in nature. Such joining may be achieved with the two components and any additional intermediate members being integrally formed as a single unitary body with one another or with the two components. Such joining may be permanent in nature, or may be removable or releasable in nature, unless otherwise stated.
As used herein, the term “about” means that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. When the term “about” is used in describing a value or an end-point of a range, the disclosure should be understood to include the specific value or end-point referred to. Whether or not a numerical value or end-point of a range in the specification recites “about,” the numerical value or end-point of a range is intended to include two embodiments: one modified by “about,” and one not modified by “about.” It will be further understood that the end-points of each of the ranges are significant both in relation to the other end-point, and independently of the other end-point.
The terms “substantial,” “substantially,” and variations thereof as used herein are intended to note that a described feature is equal or approximately equal to a value or description. For example, a “substantially planar” surface is intended to denote a surface that is planar or approximately planar. Moreover, “substantially” is intended to denote that two values are equal or approximately equal. In some embodiments, “substantially” may denote values within about 10% of each other, such as within about 5% of each other, or within about 2% of each other.
As used herein the terms “the,” “a,” or “an,” mean “at least one,” and should not be limited to “only one” unless explicitly indicated to the contrary. Thus, for example, reference to “a component” includes embodiments having two or more such components unless the context clearly indicates otherwise.
Directional terms as used herein—for example up, down, right, left, front, back, top, bottom—are made only with reference to the figures as drawn and are not intended to imply absolute orientation.
“Radial position,” “radial distance,” or the radial coordinate “r” refers to radial position relative to the centerline (r=0) of the core in the optical fiber. The length dimension “micron” may be referred to herein as micron or μm.
The “refractive index profile” is the relationship between refractive index, or relative refractive index, and the radial distance r from the centerline of the core. For relative refractive index profiles depicted herein as having step boundaries between adjacent cladding regions, normal variations in processing conditions may preclude obtaining sharp step boundaries at the interface of adjacent regions. It is to be understood that although boundaries of refractive index profiles may be depicted herein as step changes in the refractive index, the boundaries in practice may be rounded, or otherwise deviate from perfect step function characteristics. It is further understood that the value of the relative refractive index may vary with radial position within the core region and/or any of the cladding regions.
When relative refractive index varies with radial position in a particular region of the fiber (core region and/or any of the cladding regions), it may be expressed in terms of its actual or approximate functional dependence or in terms of an average value applicable to the region. Unless otherwise specified, if the relative refractive index of a region (core region and/or any of the cladding regions) is expressed as a single value, it is understood that the relative refractive index in the region is constant, or approximately constant, and corresponds to the single value or that the single value represents an average value of a non-constant relative refractive index dependence with radial position in the region. Whether by design or a consequence of normal manufacturing variability, the dependence of relative refractive index on radial position may be sloped, curved, or otherwise non-constant.
The “relative refractive index” or “relative refractive index percent” as used herein with respect to optical fibers and fiber cores of optical fibers is defined as:
where n(r) is the refractive index at the radial distance r from the centerline of the core at a wavelength of 1550 nm, unless otherwise specified, and nc is about 1.444, which is the refractive index of undoped silica glass at a wavelength of 1550 nm. As used herein, the relative refractive index is represented by Δ (or “delta”) or Δ % (or “delta %) and its values are given in units of “%” unless otherwise specified. Relative refractive index may also be expressed as Δ(r) or Δ(r) %. When the refractive index of a region is less than the reference index nc, the relative refractive index is negative and can be referred to as a depressed-index region, a trench, or a moat. When the refractive index of a region is greater than the reference index nc, the relative refractive index is positive and the region can be said to be raised or to have a positive index.
Moreover, the term “α-profile,” also referred to as an “alpha profile”, refers to a relative refractive index profile Δ(r) that has the following functional form:
where ro is the point at which Δ(r) is maximum, r1 is the point at which Δ(r) is zero, and r is in the range ri≤r≤rf, where ri is the initial point of the α-profile, rf is the point of the α-profile, and α is a real number. In some embodiments, examples shown herein can have a core alpha of 1≤α≤100. In practice, even when the target profile is an alpha profile, some level of deviation from the ideal configuration can occur. Therefore, the alpha parameter for an optical fiber may be obtained from the best fit of the measured index profile, as is known in the art.
The disclosure herein related to an optical fiber preform (also referred to herein as a “preform”) or elements used in fabrication thereof such as, for example, a cane, rod, soot blank, or deposition tube. A core cane or core rod is a consolidated glass body having a composition corresponding to at least a portion of the core or core region of an optical fiber drawn from the preform. An optical fiber preform is a consolidated glass article suitable for drawing into an optical fiber. An optical fiber preform includes a central core region surrounded by one or more cladding regions, where the refractive indices of the core region and cladding region(s) are configured such that an optical fiber drawn from the complete optical fiber preform acts as a waveguide for light having a wavelength of 1550 nm. Additionally, as used herein, a “cane,” a “core region” or “core,” a “cladding region” or “cladding”, and other similar terms mean consolidated glass. In some embodiments, the consolidated glass is prepared by depositing soot (e.g., soot particles comprising silica or doped silica) to form a porous body (e.g., core soot to form porous core soot blank or cladding soot to form porous cladding soot blank) and consolidating the soot. In some embodiments, a porous body is formed on consolidated glass (e.g., cladding soot deposited on a core cane to form a porous cladding soot blank).
As used herein, “ppm,” unless otherwise specifically noted otherwise, refers to parts per million by weight, or “ppm by weight,” or “ppm by Wt,” and a measurement in weight percent (wt %) can be converted to ppm by multiplying by a factor of 10,000.
Referring to
Dopants may be utilized to increase or decrease the relative refractive index of the core 12 and the cladding 14. An up-dopant is used to refer to a dopant that increases the relative refractive index relative to pure undoped silica. Non-limiting up-dopants include, for example, chlorine. Down-dopants are used to refer to a dopant that decreases the relative refractive index relative to undoped, pure silica. Non-limiting examples of down-dopants include, for example, fluorine and boron.
Referring to
In the illustrated example, the core 12 comprises a central core 16 region extending to about 1 micron located along a centerline 18 of the core 12. The central core region 16 contains a lower average concentration of chlorine than is contained in an outer core region 20, which extends around the central core region 16 from about 1 micron to about 4 microns of the core 12. The average concentration of chlorine present in the central core region 16 may be less than about 100 ppm or less than about 50 ppm. The average concentration of chlorine in the outer core region 20 may be greater than about 500 ppm, greater than about 750 ppm, greater than about 1000 ppm, or greater than about 1500 ppm. The peak concentration of chlorine in the core 12 is generally greater than about 500 ppm, greater than about 1000 ppm, or greater than about 1500 ppm.
The average concentration of fluorine present in the central core region 16 is generally greater than about 500 ppm, greater than about 750 ppm, or greater than about 1000 ppm. The average concentration of fluorine in the outer core region 20 is likewise greater than about 500 ppm, greater than about 750 ppm, or greater than about 1000 ppm. The average concentration of fluorine across the entire core 12 is generally greater than about 500 ppm and less than about 4000 ppm. The concentration of fluorine in the core 12 is generally between is between about 0.15 wt. % and about 0.25 wt. %. There is a low level of fluorine in the core 12, and the core 12 has a slightly positive delta due to potassium in the core 12.
The optical fiber 10 also includes the alkali metal oxide. The alkali metal oxide is generally an oxide of at least one of K, Na, Li, Cs, Rb, or combinations thereof. The alkali metal oxide may include at least one of K2O, Na2O, LiO2, Rb2O, Cs2O, or combinations thereof. Generally, the concentration of the alkali metal oxide in the core region 12 is between 0.1 wt. % and 1.5 wt. %. In certain aspects, the alkali metal oxide may be formed from KI and O2.
An exemplary concentration profile for a dopant is illustrated in
In various examples, the optical fiber 10 formed by the disclosed process contains no or little germanium in the core 12. In such examples, the silica glass core 12 and the cladding 14 of the optical fiber 10 includes sufficient concentrations of up-dopant and/or down-dopants to form the relative refractive index profile within the scope of the present disclosure. The relative refractive index of the cladding 14 is less than the core 12. As discussed herein, the index-decreasing dopant (down-dopant) for use in the cladding 14 is generally fluorine.
The optical fiber 10 with the relative refractive index profile 22, as illustrated in
An exemplary relative refractive index profile 22 is illustrated in
The negative relative refractive indices may be formed using the down-dopants, such as fluorine. In various examples, the moat 26 is silica glass that is doped with a first concentration of fluorine, and the outer cladding region 28 is silica glass doped with a second concentration of fluorine. The second concentration of fluorine is less than the first concentration of fluorine, resulting in the lower relative refractive index in the moat 26. Generally, about 1 wt. % Cl doping increases A by about 0.1%, and about 1 wt. % F decreases by about 0.3%. When Cl and F are both present, the effect of each Cl and F on Δ is independent and that the concentrations balance to lead to the A disclosed herein.
The relative concentration of chlorine may also be different between the moat 26 and the outer cladding region 28. In various examples, the moat 26 has a first concentration of chlorine, and the outer cladding region 28 has a second concentration of chlorine. The second concentration of chlorine may be less than the first concentration of chlorine.
With reference to
In
With reference to
Referring to
As described herein, various locations in the optical fiber 10 are described as “regions.” For example, the inner core region 16, the outer core region 20, and the cladding region 14 (including the inner cladding region 24, the moat region 26, and the outer cladding region 28). The corresponding location in the preform 50 may be described as a “portion.” For example, an inner core portion corresponding to the inner core region 16, an outer core portion corresponding with the outer core region 24, and a cladding portion 14 corresponding with the cladding region 14. Further, an inner cladding portion corresponds with the inner cladding region 24, a moat portion or a depressed-index cladding portion corresponds with the moat region 26, and an outer cladding region corresponds with the outer cladding region 28.
To form the preform 50, an initial or core silica soot tube 110 is formed via a soot burner 112 depositing multiple layers of silica soot onto a mandrel 114 (step 60). The soot tube 110 defines a central channel 116 that extends along a longitudinal extent of the soot tube 110. The resulting soot tube 110 is dried using chlorine drying techniques (e.g., exposure to Cl2) (step 62). The soot tube 110 is then treated with fluorine (step 64) by exposing the porous soot tube 110 to a fluorine-containing atmosphere (e.g., fluorine sweeping with a fluorine-doping precursor, such as SiF4), for a time and at a temperature sufficient to remove a majority or all of the chlorine remaining from the drying step (e.g., step 62). The intent of the fluorine treatment of the soot tube 110 is to remove the chlorine, such that interaction with chlorine does not contribute to the devitrification of the glass. The exposure to the fluorine-containing atmosphere may be accomplished at a temperature less than 1100° C. to avoid doping the soot tube 110 with high levels of fluorine. The fluorine treatment, however, may introduce low levels of fluorine into the soot tube 110. Small levels of fluorine may also help with lowering the fictive temperature of the glass, without negatively impacting the concentration fluctuation contribution to Rayleigh scattering.
The fluorine-doped soot tube 110 is then sintered and consolidated into a consolidated tube 118 (step 66). In various examples, the soot tube 110 includes between about 0.1 wt. % and about 0.4 wt. % of fluorine after consolidation. In certain aspects, the consolidated tube 118 may be drawn into a series of smaller consolidated tubes 118. The consolidated tube 118 or the resulting smaller tubes 118 are each assembled with a handle 120 and transferred from the mandrel 114 to the spinning lathe positioned proximate to a heat source 122. The spinning lathe may be a glass-working lathe or a modified chemical vapor deposition (MCVD) glass-forming lathe. The handle 120 may be a glass handle 120 that becomes an integral part of the preform 50. The handle 120 provides a support structure for later processing steps. The handle 120 is coupled to the lathe, where the handle 120, and consequently, the consolidated tube 118 are rotated and translated with respect to the soot burner 112.
The consolidated tube 118 defines an annular reservoir 130 for receiving an alkali metal doping material 132. The material is formed of oxygen (02) and an alkali salt, which is introduced in the annular reservoir 130. An alkali metal source compound 132 includes at least one of K, Na, Li, Cs, Rb, Br, I, and F. The alkali metal source compound 132 may be at least one of KBr, KI, and KNO3. The alkali metal oxide diffused into the consolidated tube 118 may be K2O, Na2O, LiO2, Rb2O, and Cs2O. The annular reservoir 130 is formed proximate to one end of the consolidated tube 118 by forging two annular neck-like deformations in the wall of the consolidated tube 118 by flame working or otherwise welding the annular reservoir 130 to the consolidated tube 118. The consolidated tube 118 has the central channel 116 for allowing the diffusion along a length of the soot tube 110.
The alkali metal source compound 132 is introduced into the central channel 116 of the consolidated tube 118 at the reservoir 130 and heated by the heat source 122 to form a vapor as the consolidated tube 118 is rotated in the lathe (step 68). The alkali halide precursor is evaporated and flows through the consolidated tube 118 (e.g., a substrate tube). A carrier gas, such as oxygen (02), is flowed into an inlet 134 of the consolidated tube 118 through a rotating seal 136. In
In certain aspects, the dopant may be K2O. The O2 may flow over KI and a gas phase K2O may form, which is carried downstream for doping the consolidated tube 118. More preferably, K is the dopant, and K is deposited and diffused into the consolidated tube 118. This process may be quicker than depositing K2O and may therefore be the preferable method for doping the consolidated tube 118 with a select alkali weight percent. The downstream portion 138 of the consolidated tube 118 should be heated to a sufficient temperature to promote rapid diffusion of the alkali metal oxide or alkali metal into the interior surface 140 and to prevent devitrification of the consolidated tube 118. For example, the downstream portion 138 of the consolidated tube 118 may be heated to a temperature between about 1500° C. and about 2000° C.
The heat source 122 is traversed along a length of the consolidated tube 118 to form a moving hot spot to diffuse the alkali metal oxide into the consolidated tube 118. The alkali metal oxide may be diffused to a depth between about 100 microns and 500 microns from the interior surface 140, forming an alkali-doped consolidated tube 150. The concentration of the diffused alkali metal oxide dopant generally varies radially, with a higher concentration (in wt. %) on an inner half 152 and a lower concentration in an outer half 154. A vacuum is drawn on the alkali-doped consolidated tube 150 and the heat is increased to relax or partially collapse the alkali-doped tube 150. The alkali-doped consolidated tube 150 may be cut into base material ingots 156 for further processing.
To prevent crystallization of the alkali metal or an alkali halide (e.g., KCl), it may be advantageous that the alkali-doped consolidated tube 150, and any additional soot deposited thereon, be substantially chlorine free. Substantially chlorine free generally means exhibiting a chlorine content sufficiently low that optical losses due to alkali chlorine are generally avoided.
For example, the chlorine content in the alkali-doped consolidated tube 150 may be less than about 500 ppm by weight, less than about 100 ppm, or less than about 50 ppm. The crystalline phase may be cristabolite, which is a silica phase, with the alkali metal helping the crystalline formation via lowering viscosity. However, other crystallization may form without departing from the teachings herein.
It may be advantageous for the alkali-doped consolidated tube 150, and any additional soot deposited thereon, to be substantially free of “water.” As described herein, “water” refers to the hydroxyl group, OH. Water is generally responsible for a water peak (i.e., an absorption peak due to hydroxyl groups) centered at or about 1383 nm. This absorption peak may extend into an operating wavelength region of the optical fiber 10 (e.g., 1310 nm or 1550 nm), and therefore may have a negative effect on the attenuation of the optical fiber 10. It is generally advantageous to reduce the water peak by reducing the OH content of the glass. For example, the alkali-doped consolidated tube 150 may contain less than about 100 ppm by weight of OH. To remove the “water” from the consolidated tube 150, chlorine drying techniques may be utilized.
The alkali-doped consolidated tube 150 may be etched with an etchant, such as an aqueous HF solution (step 70). The etchant may remove a depth of silica from the interior surface of the alkali-doped consolidated tube 150 to remove or reduce impurities that may have diffused through the interior surface of the consolidated tube 150 during alkali doping and/or consolidation. It is also contemplated that a fluorine gas, such as CF4, SF4, NF3, C2F6, or a combination thereof may be used as the etchant. The depth for the silica removal may depend on the processing conditions during the diffusion and collapsing processes. Removal to a depth of about 5% of the total diffusion depth of the alkali metal oxide may be advantageous.
Once the etching process is complete, the alkali-doped consolidated tube 150 is further heated to fully collapse the alkali-doped consolidated tube 150 downstream of the alkali metal source compound 132 to close the central channel 116 to form a cylinder of glass, referred to herein as a core rod 160 (step 72). The core rod 160 is a solid alkali-doped glass body, which is separated from the portion of the alkali-doped consolidated tube 150 that includes the annular reservoir 130. The core rod 160 at least partially forms the central core portion of the preform 50, which corresponds with the central core region 16 in the resulting optical fiber 10 obtained after drawing the preform 50. The core rod 160 may be sized by redraw. Additionally, the core rod 106 may be etched to remove some or all of hydrated glass or hydroxyl groups that may have been formed by a heat source (e.g., a torch) during the collapsing process. However, additional etching may not be necessary when a dry heat source, such as an induction or resistance heater, a plasma torch, or a dry heat source using non-hydrogen containing fuel (e.g., CO), is used for the collapsing process. The dry heat source may minimize re-wetting (e.g., reabsorption and/or diffusion of OH into) the consolidated tube 150 to reduce attenuation without supplying or producing H2, OH, or H2O.
The core rod 160 is generally the end product of the first stage 42 of the manufacturing method 40. The core rod 160 is then utilized as the initial product for the second stage 44 of forming the outer core portion 50 of the preform 50, corresponding with the outer core region 20. The soot burner 112 is used to deposit multiple layers of porous silica soot onto the core rod 160 to form a porous core soot blank 162 (step 74). The soot may be deposited on the core rod 160 using an outside vapor deposition (OVD) method. Generally, a flame is emitted from the soot burner 112. A silica precursor gas-vapor mixture is oxidized or combusted within the flame to form a silica-containing soot stream directed toward the core rod 160.
The porous core soot blank 162 is formed by translating the core rod 160 multiple times relative to the soot burner 112 to cause a build-up of layers of silica soot-containing layers to form a soot coating. The translational motion is generally achieved by moving the soot burner 112 relative to the core rod 160; however, the core rod 160 may be moved relative to the soot burner 112 without departing from the teachings herein. Alternatively, both the soot burner 112 and the core rod 160 may be moved. The soot coating forms at least a portion of the core 12 (e.g., an outer radial portion of the inner core region 16 or the outer core region 20) and may also include a portion of the cladding 14 (e.g., inner cladding region 24) of an optical fiber 10 drawn from the preform 50 and may be formed substantially of pure silica.
The porous core soot blank 162 is dried using chlorine drying techniques and heat (step 76). The porous core soot blank 162 is then treated with fluorine (step 78) by exposing the porous core soot blank 162 to the fluorine-containing atmosphere for a time and at a temperature sufficient to remove a majority or all of the chlorine remaining from the drying step (e.g., step 76). The fluorine-containing atmosphere may include a fluorine-doping precursor, such as SiF4 or CF4 and may introduce low levels of fluorine as a dopant into the porous regions of the porous core soot blank 162.
The fluorine-treated soot blank 162 is then sintered and consolidated by heating to form a core cane 164 (step 80). This process generally forms the core portion of the preform 50 that forms the core 12 having both the central core region 16 and the outer core region 20 of the optical fiber 10 drawn from the preform 50. The core cane 164 is redrawn (heated and sized to a smaller diameter) and cut as needed to form a core cane 166 (step 82) for processing in the third stage 46. Additional core layers may be added to produce a core cane 164/166 with three or more core regions of a core cane 164/166 that includes at least one core region and at least one cladding region without departing from the teachings herein.
The third stage 46 of the method 40 forms the moat portion of the preform 50 that forms the trench or moat 26 of the cladding region 14, and may also optionally produce inner cladding region 24 of the cladding region 14 of the optical fiber drawn from the preform 50. The core cane 166 produced in the second stage 44 of the method 40 is utilized as the initial product of the third stage 46 of the method 40. The core cane 166 is further processed to add additional glass layers, which ultimately form the depressed-index cladding region or moat 26 (step 84). The soot burner 112 is utilized to deposit multiple layers of soot on the core cane 166 to form a subsequent porous cladding soot blank 170. The resulting porous cladding soot blank 170 is dried using chlorine drying techniques (step 86). The porous cladding soot blank 170 is doped with a down-dopant for moat depression, preferably in a cladding-doping atmosphere containing a fluorine-doping precursor such as SiF4 or CF4 (step 88). In various examples, the porous cladding soot blank 170 is exposed to the fluorine-doping precursor for between about 60 minutes and 120 minutes at about 1225° C. In certain aspects, the cladding-doping atmosphere may also include SiCl4, which may be advantageous for decreasing attenuation of the resulting optical fiber 10 as discussed further herein.
The fluorine-doped porous cladding soot blank 170 is then sintered and consolidated (step 90) by down driving through a hot zone of about 1450° C. to about 1500° C. at about 7-10 mm/min to form a cladding cane 172. The consolidating may be conducted in the presence of a non-carbon reducing agent, such as SiCl4. In various examples, the reducing agent SiCl4 is present during the entire consolidating process when the preform 50 goes to full-porosity. Alternatively, the SiCl4 may be present up to a minimum density for the consolidated state (e.g., up to a density of 1.6 g/cm3, 1.7 g/cm3, 1.8 g/cm3, or 1.9 g/cm3), after which the presence of SiCl4 may be optional. The consolidation of the cladding cane 172 is generally conducted in the absence or with minimal levels of the fluorine-doping precursor used to form the moat 26 in the cladding region 14.
In certain aspects the fluorine-doping precursor may be actively evacuated from the environment. Alternatively, the supply of the fluorine-doping precursor may be deactivated. The fluorine-doping precursor is reduced to minimal or trace levels during the consolidation of the cladding cane 172.
The reducing agent may be utilized in one or two steps during the manufacturing process, including when the porous cladding soot blank 170 is exposed to the fluorine-doping precursor (step 88), when the porous cladding soot blank 170 is consolidated into the cladding cane 172 (step 90), or during both steps. The porous cladding soot blank 170 and/or the cladding cane 172 are exposed to the non-carbon reducing agent (e.g., SiCl4) to control an oxidation state. The SiCl4 is included in a reducing gas environment that has a predefined concentration of the non-carbon reducing agent. In various examples, the concentration of the non-carbon reducing agent is in a range from about 0.1 vol. % to about 15 vol. % of the overall reducing gas environment during these processes. In additional examples, the concentration of the non-carbon reducing agent is in a range from about 0.5 vol. % to about 10 vol. % of the gas environment. The SiCl4 may be introduced into the gas environment during the fluorine-doping process (step 88), the sintering process (step 90), or during both the fluorine-doping and sintering processes (steps 88, 90). In certain aspects, the treatment with SiCl4 may be more effective during the sintering process 90 when the preform 50 goes to full-porosity. The cladding cane 172 is preferably redrawn to a pre-determined diameter into a cladding cane 174 (step 92) for over cladding and use in the fourth stage 48 of the manufacturing method 40, as discussed further herein.
The use of the reducing agent SiCl4 in the third stage 46 assists in controlling the oxidation state of the glass forming the moat 26. However, the use of SiCl4 during moat formation can be counterproductive to the down-doping with fluorine because when incorporated as a dopant, Cl acts as an up-dopant and counteracts the index-decreasing effect of F. The conditions at which SiCl4 is used in third stage 46 are controlled so that the SiCl4 controls oxidation state (by acting as a reducing agent), while not substantially introducing Cl as a dopant and thus not affecting the relative refractive index profile of the resulting optical fiber 10. In certain aspects, the concentration of SiCl4 in the gas environment during a sintering process (step 90) is from about 0.25 mol. % to about 6 mol. %. In additional examples, the concentration of SiCl4 in the gas environment during a sintering process (step 90) is from about 0.25 mol. % to about 4 mol. %. In further examples, the concentration of SiCl4 in the gas environment during a sintering process (step 90) is from about 1 mol. % to about 3 mol. %.
Referring still to
A common constituent known to be present in the deployment environment of optical fibers is hydrogen. Optical fibers 10 with alkali-doped cores are utilized in terrestrial and submarine networks due to their intrinsically low attenuation of optical signals. However, during use in the field over time, such optical fibers 10 can be prone to hydrogen aging if oxygen-rich hydrogen aging defects are formed during the fiber processing. Hydrogen aging occurs when hydrogen interacts with oxygen-rich hydrogen aging defects to form defects (e.g., hydroxyl groups) that cause light of specific wavelengths to be absorbed, thus increasing the attenuation of the optical fiber 10 at those wavelengths. Typically, known oxygen-rich hydrogen aging defects have a characteristic of hydro-I response, i.e. the concentration of the oxygen-rich hydrogen aging defect continues to scale with time with a scaling factor of log(time). It is advantageous to change an oxidation state of the optical fiber 10 to significantly lower the concentration of the oxygen-rich hydrogen aging defects in the optical fiber 10, thereby reducing the prevalence of oxygen-rich hydrogen aging defects and hydrogen aging sensitivity of the optical fiber 10 or creating hydrogen aging insensitivity of the optical fiber 10.
Optical fibers 10 are routinely tested for hydrogen aging. In the hydrogen aging testing used herein, the optical fibers 10 are exposed to a gas atmosphere containing H2 at 23° C. for a predefined period of time. The gas atmosphere includes H2 in the presence of an inert gas. For purposes of testing hydrogen aging in the present disclosure, the H2-containing gas atmosphere is at a total pressure of 1.0 atm and includes a partial pressure of 0.01 atm of hydrogen (H2) gas and a partial pressure of 0.99 atm of nitrogen (N2) gas. During the hydrogen aging test, various wavelengths of light are introduced to the optical fiber 10 and monitored for changes in attenuation as a function of exposure time to the H2-containing gas atmosphere relative to an initial attenuation of the optical fiber 10 before exposure to the H2-containing atmosphere.
For example, one wavelength of interest for telecommunications applications is 1383 nm. In the hydrogen aging tests disclosed herein, this wavelength is monitored. The elapsed time from when the optical fiber 10 is exposed to the H2-containing gas to the time that the onset of an increase in absorption at 1383 nm occurs is referred to herein as the 1383 nm “time-to-peak” (or “Time-to-Peak”) value (which may be abbreviated herein as TTP). The importance of this measurement is that when exposed to H2 for an extended time, such as one week, as described herein, reactive oxygen centers in oxygen-rich hydrogen aging defects in the optical fiber 10 react with the hydrogen to form —OH species (e.g., silanol groups) that absorb light at common telecommunications wavelengths with the absorbance being the greatest at about 1383 nm. The formation of absorbing —OH species upon exposure of the fiber to hydrogen gas over time is a process referred to herein as hydrogen aging.
In one tested example, four single-mode optical fibers having diameters of 125 μm were manufactured by forming and drawing each fiber from a different preform to test hydrogen aging. Each preform was formed by forming a core cane, forming cladding soot on the core cane, and consolidating the cladding soot. The consolidation of cladding soot included: a first phase, which was an isothermal phase in which the cladding soot was exposed to a first processing gas containing Cl2 for about 240 minutes at a temperature of about 1150° C. to dry the cladding soot; and a second phase, in which the cladding soot was exposed to a second processing gas for about 6 hours at a temperature of between about 1150° C. and about 1500° C. The four preforms from which the four fibers were drawn were manufactured in substantially the same manner except that the processing gases for the first and second phases of each of the four preforms contained different concentrations of Cl2 and CO (with the remaining gas including helium) as indicated in Table 1 below. Each of the fibers from Table 1 include a Germania doped core, silica inner cladding, a fluorine doped trench, and chlorine doped outer cladding. In comparison, each layer of the optical fiber 10 of the present disclosure is doped with fluorine with the exception of an inner approximately 30% of the core 12 and the fiber 10 is alkali doped. The fibers from Table 1 are similar in structure but differ from the present fiber 10 by composition.
Each of the four fibers was exposed to a gas atmosphere at 1 atm total pressure that included a partial pressure of H2 of 0.01 atm and a partial pressure of N2 of 0.99 atm at 23° C. The time for the hydrogen to diffuse through the fiber cladding to the fiber core under these conditions was measured in terms of the TTP for each fiber. TTP was measured on the basis of the time dependence of the attenuation of an optical signal having a wavelength of 1383 nm and corresponded to the time following exposure of the fiber to the H2-containing gas at which a steep increase in attenuation was observed. At exposure times less than TTP, essentially no change in attenuation was observed at 1383 nm. At an exposure time equal to TTP, an onset in an increase in attenuation at 1383 nm was observed. At exposure times greater than TTP, a pronounced increase in attenuation at 1383 nm was observed. The fiber drawn from Preform #1 had an average TTP at 1383 nm of approximately 105 hours. The fiber drawn from Preform #2 had an average TTP at 1383 nm of about 76 hours. The fiber drawn from Preform #3 had an average TTP at 1383 nm of about 58 hours. The fiber drawn from Preform #4 had an average TTP at 1383 nm of about 40 hours. This testing method may be used to determine the TTP of fibers, including the fibers 10 disclosed herein using non-carbon reducing agents, such as SiCl4.
Low values of TTP (short TTP times) signify a low concentration of oxygen-rich hydrogen aging defects in the cladding region(s) of the optical fiber. Hydrogen from the gas atmosphere contacts the optical fiber at an exterior surface and diffuses in a radially inward direction through the cladding to the core. If the hydrogen encounters an oxygen-rich defect in the cladding as it diffuses, it reacts with it to form a hydroxyl group and diffusion terminates. Oxygen-rich hydrogen aging defects closest to the exterior surface of the optical fiber are converted to hydroxyl groups at early exposure times. Upon formation of a hydroxyl group, the oxygen-rich hydrogen aging defect is neutralized and subsequent exposure of the optical fiber to the H2-containing gas atmosphere allows for diffusion of hydrogen to oxygen-rich hydrogen aging defects located further from the surface and closer to the core. As exposure time increases, hydroxyl groups form closer and closer to the core. At short exposure times, the hydroxyl groups are too far removed from the core to interact with the optical signal and no increase in attenuation is observed. At sufficiently long exposure times, OH groups form sufficiently close to the core region (e.g., in the core region itself or in portions of the cladding region sufficiently close to the core region) to interact with the optical signal (e.g., through absorption) to cause attenuation of the optical signal. TTP marks the exposure time at which the OH groups that form begin to become sufficiently close to the core to interact with the optical signal. A low TTP implies a short time for OH groups to form sufficiently close to the core to interact with the optical signal, which is consistent with a low concentration of oxygen-rich defects in the core region.
In order to prevent such aging and absorbance, which results in reduced transmission signal strength, optical fibers may be treated with a reducing agent to reduce the aging and absorption. One conventional approach is for optical fibers to be treated with deuterium gas to form —OD species from reactive oxygen centers, such as oxygen-rich hydrogen aging defects, present in the fiber. Unlike —OH, —OD does not absorb at 1383 nm. When using deuterium gas, oxygen leakage is also tightly controlled during a draw process of the resulting fiber. The D2 treatment occurs on the fiber after the conclusion of the draw process and not performed during the draw itself. Deuterium gas, however, is expensive and it is desirable to identify other methods to remedy hydrogen aging.
A second conventional method for reducing oxygen-rich hydrogen aging defects include exposing the preform of the optical fiber to carbon monoxide (CO) as a reducing agent during consolidation (or doping), as illustrated in the above example associated with Table 1. However, carbon monoxide results in an absorption peak in the L-band portion of the telecommunications spectrum, generally at a wavelength at or about 1583 nm and, to a lesser extent, an absorption peak in the C-band portion of the telecommunications spectrum, generally at a wavelength at or about 1547 nm. Absorption wavelengths in the C-band spectrum and L-band spectrum negatively affect the performance of the optical fiber 10, particularly in the L-band spectrum. When using CO as the reducing agent, CO2 may form within the fiber and affect the attenuation. The absorption peak at 1583 nm arises when CO is used as the reducing agent and may result from the CO or from other structural effects in the silica caused by carbon or CO. The absorption peak at 1583 nm affects the overall performance of the resulting fiber.
The method 40 disclosed herein utilizes a non-carbon based reducing agent during the moat formation of the manufacturing process to reduce oxygen-rich hydrogen aging defects in the optical fiber 10. The non-carbon based reducing agent is SiCl4. The use of the non-carbon based reducing agent reduces attenuation (1) at a water peak, generally at a wavelength of about 1383 nm, (2) within the C-band spectrum, generally at a wavelength of about 1547 nm, and (3) within the L-band spectrum, generally at a wavelength of about 1583 nm. Using the non-carbon based reducing agent reduces or avoids oxygen-rich hydrogen aging defects without forming carbon dioxide CO2, thereby reducing or eliminating undesirable absorption peaks in the L-band and/or the C-band. Moreover, the optical fiber 10 produced via the method 40 herein has a TTP at 1383 nm at 23° C. of less than 100 hours upon exposure to a H2-containing gas atmosphere having a total pressure of 1 atm and containing a partial pressure of 0.01 atm H2 and a partial pressure of 0.99 atm N2. The TTP is determined using the method set forth herein associated with Table 1. As noted above, low values of TTP signify a low concentration of oxygen-rich hydrogen aging defects in the cladding region(s) of the optical fiber.
As previously noted, the third stage 46 of the manufacturing process involves doping the porous cladding soot blank 170 with fluorine to form a trench inner cladding region (e.g., the moat 26) of a profile of the optical fiber 10 (e.g., step 136). Generally, the moat index is less than an index of the core 12. There is sufficient power in the trench region or moat 26 that any defects in the moat 26 generally contribute to the aging behavior of the optical fiber 10. When the optical fiber 10 is exposed to hydrogen, if no reducing agent is used, absorption peaks at or about 1383 nm and 1550 nm are formed. The conventional method of using CO to reduce oxygen-rich hydrogen aging defects results in CO2 formation or other contaminating or structural effect in the optical fiber 10 and may cause an absorption peak at or about 1583 nm, in the L-band, and, to a lesser extent, at or about 1547 nm in the C-band, as illustrated in
In the process disclosed herein, the SiCl4 interacts with the porous cladding soot blank 170 to reduce, or eliminate, the oxygen-rich hydrogen aging defects without forming carbon dioxide CO2 or other residual contaminating or structural effect associated with CO in the optical fiber 10.
As a result, the absorption peak at or about 1583 nm is avoided, and consequently, attenuation within the L-band transmission spectrum is reduced. The SiCl4 makes the optical fiber 10 insensitive to hydrogen aging, or at least reduces hydrogen aging sensitivity, while simultaneously reducing or eliminating the absorption peaks in the C-band and the L-band that are known to occur when CO is used as a reducing agent.
The use of SiCl4 as the reducing agent, rather than a carbon-based reducing agent, does not form the absorption peaks in the C-band and the L-band. Moreover, the SiCl4 also assists with reducing water, or SiOH, within the optical fiber 10. The use of SiCl4 eliminates the absorption peaks at or about 1583 nm and 1547 nm and reduces the water peak at or about 1383 nm.
The use of SiCl4 during processing produces an optical fiber 10 with low attenuation at or about each of 1383 nm, 1547 nm, and 1583 nm. Due to the exposure to SiCl4 during the formation of the moat 26, the optical fiber 10 exhibits an attenuation <0.16 dB/km at 1583 nm and an incremental peak or attenuation above a baseline at 1583 nm less than 0.0005 dB/km. In certain aspects, the optical fiber 10 may exhibit the incremental attenuation above the baseline at 1583 nm due to the CO2 absorption of less than 0.0005 dB/km. The baseline is a best-fit attenuation over the C- and L-bands exclusive of a wavelength range centered near 1583 nm. The best fit of attenuation is a function of wavelength between about 1530 nm (e.g., a lower end of C-band) and about 1625 nm (e.g., an upper end of L-band) exclusive of the range between about 1570 nm and about 1590 nm. The baseline considers that there is no absorption at 1583 nm and produces a smooth curve across wavelengths from 1550 nm and 1625 nm, in accordance with standard spectroscopic measurements.
Further, the attenuation may be monotonically increasing between about 1570 nm and about 1600 nm, or may be monotonically increasing between about 1570 nm and about 1590 nm. The monotonically increasing attenuation is a property of the SiCl4-treated optical fiber 10 that is absent in a comparative CO-treated fiber. Additionally or alternatively, the optical fiber 10 may exhibit an attenuation <0.16 dB/km at 1583 nm and an incremental attenuation above baseline at 1583 nm less than 0.0003 dB/km. Further, the optical fiber 10 exhibits an attenuation <0.5 dB/km at 1383 nm.
The moat-forming third stage 46 of the manufacturing process affects the overall performance of the resulting optical fiber 10. The exposure to the non-carbon reducing agent reduces attenuation of the optical fiber 10 to improve the performance of the optical fiber 10. By using SiCl4, the attenuation in both the C-band and the L-band spectrum is reduced, which improves optical transmission and overall performance through each of these regions.
Referring again to
Conversely, decreasing the draw speed increases the time, which may result in a decrease in the concentration of alkali metal oxide in the core 12 of the optical fiber 10 as the alkali metal oxide diffuses further into the cladding 14 of the optical fiber 10. Moreover, increasing the draw furnace temperature may increase the diffusion rate, decreasing the concentration of alkali metal oxide in the core 12 and increasing the concentration of alkali metal oxide in the cladding.
Referring again to
The outer cladding region 28 generally has a refractive index less than the core 12 and greater than the moat 26. In various examples, the doping of the outer cladding region 28 is sufficient to achieve a relative refractive index delta % between the maximum value of the core 12 and the minimum value of the cladding 14 of, for example, between about 0.3% and about 0.4%. In the outermost cladding layer (e.g., the outer cladding region 28), the fluorine wt. % may be slightly less and be between about 0.1 wt. % and about 0.5 wt. % to achieve a relative refractive index within the preferred range and to minimize stress effects that arise when an optical fiber is drawn from preform 50. The fluorine-doped porous overclad soot blank 190 is then sintered and consolidated to form the preform 50 (step 100).
The preform 50 created through the various stages 42, 44, 46, 48 is then drawn into the optical fiber 10 to have the selected dimensions and properties (step 102). The method 40 described herein forms an alkali-doped silica optical fiber 10, which has an attenuation at 1583 nm following exposure to a H2-containing atmosphere containing 1 vol. % H2 and 99 vol. % N2 for one week at 23° C. of less than 0.16 dB/km and an incremental attenuation above baseline at 1583 nm less than 0.0005 dB/km, as well as an attenuation at 1547 nm of less than <0.16 dB/km and an incremental attenuation above baseline at 1547 nm less than 0.0003 dB/km. Further, the optical fiber 10 results from drawing the preform 50 formed from the method 40 exhibits an attenuation <0.5 dB/km at 1383 nm.
Referring still to
The final draw process to draw the preform 50 into the optical fiber 10 (step 102) is conducted in a similar manner (
The draw system 200 may include a cooling system 218. Once the optical fiber 10 is drawn from the preform 50, the optical fiber 10 may be cooled in a cooling tube or another device. The cooling system 218 may be coupled to, or alternatively, spaced apart from an exit of the furnace 180. The optical fiber 10 may subsequently be coated by a coating system 220, which may apply a polymeric-based coating material to an outside surface of the optical fiber 10. It is also contemplated that the coated optical fiber 10 may pass through a coating curing apparatus within the coating system 220. The coated optical fiber 10 may be wound onto a reel or spool 222.
The draw system 200 is illustrated as having the controller 212, which may have a microprocessor or a processor 224, a memory 226, and other control circuitry. The memory 226 may store instructions 228 executable by the processor 224. It is contemplated that any digital and/or analog processing circuitry and memory storage medium may be employed.
The controller 212 may modify the manufacturing processes, such as, for example, by adjusting a drawing speed of the draw system 200, modifying the temperature of the furnace 180, and/or modifying the draw tension applied to the optical fiber 10. The draw system 200 may utilize various drawing mechanisms and/or pulleys to provide the selected draw tension to the optical fiber 10 as the optical fiber 10 is drawn through the draw system 200.
Referring to
Referring to
Additionally, the optical fiber 10 has the TTP hydrogen aging value of less than 100 hours upon exposure at 23° C. to a H2-containing gas atmosphere having a total pressure of 1 atm and containing a partial pressure of 0.01 atm H2 and a partial pressure of 0.99 atm N2. Further, due to the exposure to SiCl4 during the formation of the moat 26, the optical fiber 10 exhibits an attenuation <0.16 dB/km at 1583 nm and an incremental attenuation above baseline at 1583 nm less than 0.0005 dB/km. Additionally or alternatively, the optical fiber 10 may exhibit an attenuation <0.16 dB/km at 1547 nm and an incremental attenuation above baseline at 1547 nm less than 0.0003 dB/km. For example, the optical fiber 10 may exhibit an attenuation <0.16 dB/km at 1547 nm and an incremental attenuation above baseline at 1547 nm of less than 0.0003 dB/km. Moreover, the optical fiber 10 may exhibit an attenuation <0.5 dB/km at 1383 nm. It is contemplated that cathodoluminescence or 240 nm absorption measurement processes could be utilized to determine whether the preform 50 was made with the method 40.
Currently, optical fibers 10 may transmit at a wavelength at or about 1550 nm and/or at about 1580 nm. Communication technology may use wavelength division multiplexing, allowing multiple wavelength channels situated on the same optical fiber 10. In such configurations, both the C-band transmission spectrum and the L-band transmission spectrum may be utilized. Removing the absorption peak from the L-band spectrum decreases the attenuation in the L-band and, consequently increases the performance of the optical fiber 10. The method 40 disclosed herein decreases attenuation while mitigating the absorption peaks at or near 1547 nm and 1583 nm as well as the water peak at or near 1383 nm.
Use of the disclosed process provides for a variety of advantages. For example, the non-carbon reducing agent reduces water (OH) formation and contaminant or structure defects associated with carbon-containing reducing agents in the optical fibers 10. Additionally, the non-carbon reducing agent may be SiCl4, which reduces the formation of SiOH in the optical fiber 10, thereby lowering the water peak. Further, the use of SiCl4 reduces or avoids absorption peaks in the C-band, at or about 1547 nm, and in the L-band, at or about 1583 nm. Moreover, the use of SiCl4 decreases attenuation, which positively affects the performance of the optical fiber 10. Further, the non-carbon reducing agent reduces or eliminates the oxygen-rich hydrogen aging defects in the optical fiber 10, which decreases attenuation. Additional benefits or advantages may be realized and/or achieved.
The device and method disclosed herein is further summarized in the following paragraphs and is further characterized by combinations of any and all of the various aspects described therein.
According to a first aspect, a method of manufacturing a preform of an optical fiber where the optical fiber has a core region and a cladding region includes forming a porous cladding soot blank by depositing silica soot on a core cane. The core cane includes a core portion having a composition corresponding to at least a portion of the core region of the optical fiber and a concentration of an alkali metal oxide in a core portion of the core cane is between 0.1 wt. % and 1.5 wt. %. The method includes exposing the porous cladding soot blank to a fluorine-doping precursor in the presence of SiCl4, the fluorine-doping precursor doping the porous cladding soot blank with fluorine to form a fluorine-doped porous cladding soot blank. The exposing comprises providing a flow of the fluorine-doping precursor to the porous cladding soot blank. The method includes consolidating the fluorine-doped porous cladding soot blank in presence or absence of a fluorine-doping precursor to form a consolidated fluorine-doped cladding cane, the consolidating comprising exposing the fluorine-doped porous cladding soot blank to SiCl4. The composition of the core portion of the core cane comprises silica doped with an alkali metal oxide.
According to a second aspect, a method includes applying a fluorine doped silica glass outer cladding layer to a consolidated fluorine-doped cladding cane to form an optical fiber preform.
According to a third aspect, SiCl4 is present up to a minimum density of about 1.6 g/cm3 in a consolidating step.
According to a fourth aspect, a method includes forming a porous overclad soot blank by depositing silica soot on a consolidated fluorine-doped cladding cane, exposing the porous overclad soot blank to the fluorine-doping precursor in an absence of SiCl4, and consolidating the porous overclad soot blank to form a preform, the preform comprising a cladding portion having a composition corresponding to a cladding region of an optical fiber.
According to a fifth aspect, a cladding portion comprises a depressed-index cladding portion surrounding the core portion and an outer cladding portion surrounding the depressed-index cladding portion, the depressed-index cladding portion having a first concentration of fluorine and the outer cladding portion having a second concentration of fluorine, the second concentration of fluorine being less than the first concentration of fluorine.
According to a sixth aspect, a depressed-index cladding portion has a relative refractive index Δ3 with a minimum relative refractive index Δ3min in a range from −0.80% to −0.30% and an outer cladding portion has a relative refractive index Δ4 such that Δ4−Δ3min>0.05%.
According to a seventh aspect, a depressed-index cladding portion comprises a first concentration of chlorine and an outer cladding portion comprises a second concentration of chlorine, the second concentration of chlorine being less than the first concentration of chlorine.
According to an eighth aspect, a method of manufacturing an optical fiber where the optical fiber has a core region and a cladding region includes forming an alkali-doped core cane. The alkali-doped core cane includes a portion having a composition corresponding to at least a portion of the core region of the optical fiber. The method includes forming a porous cladding soot blank by depositing silica soot on the alkali-doped core cane and exposing the porous cladding soot blank to a fluorine-doping precursor. The fluorine-doping precursor dopes the silica soot with fluorine to form a fluorine-doped porous cladding soot blank. The step of exposing comprises providing a flow of the fluorine-doping precursor to the porous cladding soot blank. The method includes consolidating the fluorine-doped porous cladding soot blank in the absence or presence of the flow of the fluorine-doping precursor to form a fluorine-doped cladding cane, the fluorine-doped cladding cane having a portion with a composition corresponding to the cladding region of the optical fiber. The step of exposing comprises exposing the porous cladding soot blank to the fluorine-doping precursor in the presence of SiCl4 or the step of consolidating comprises exposing the fluorine-doped porous cladding soot blank to SiCl4.
According to a ninth aspect, a step of exposing comprises exposing a porous cladding soot blank to a fluorine-doping precursor in the presence of SiCl4 and a step of consolidating comprises exposing a fluorine-doped porous cladding soot blank to SiCl4 According to a tenth aspect, a method includes drawing an optical fiber from a preform comprising a fluorine-doped cladding cane. The optical fiber exhibits an attenuation <0.16 dB/km at 1583 nm. The attenuation monotonically increases between about 1570 nm and about 1590 nm.
According to an eleventh aspect, a step of forming an alkali-doped core cane comprises evaporating an alkali halide precursor and flowing it through a substrate tube, traversing a heating burner on an outside of the substrate tube with the alkali halide vapor flowing through the tube allowing alkali to dope the inside of the substrate tube and diffusing through the tube wall, and collapsing the substrate tube to form a portion of the core cane. The portion of the core cane has a the composition having an alkali concentration between 0.1 wt. % and 1.5 wt. %.
According to a twelfth aspect, a portion with a composition corresponding to a cladding region of an optical fiber has a relative refractive index Δ3 with a minimum relative refractive index
Δ3min<−0.30%.
According to a thirteenth aspect, a method includes forming an outer cladding region by depositing silica soot on a fluorine-doped cladding cane to form a porous overclad soot blank. The outer cladding region hays a relative refractive index Δ4 such that Δ4−Δ3min>0.05%. The method includes consolidating the porous overclad soot blank to form a preform and drawing an optical fiber from the preform. The optical fiber exhibits an attenuation <0.16 dB/km at 1583 nm and an incremental attenuation above baseline at 1583 nm less than 0.0005 dB/km.
According to a fourteenth aspect, a step of consolidating the porous overclad soot blank comprises exposing a porous overclad soot blank to a fluorine-doping precursor in the absence of SiCl4.
According to a fifteenth aspect, when present in a step of exposing or a step of consolidating, the SiCl4 is provided in a gas atmosphere and a concentration of the SiCl4 in the gas atmosphere is between 0.1 vol. % and 15 vol. %.
According to a sixteenth aspect, an optical fiber includes a core region, the core region comprising silica glass doped with an alkali metal oxide. A cladding region surrounds and is directly adjacent to the core region. The cladding region comprises a depressed-index cladding region surrounding the core region. The depressed-index cladding region comprises silica glass doped with a first concentration of fluorine. The depressed-index cladding region has a relative refractive index Δ3 with a minimum relative refractive index Δ3min in a range from −0.80% to −0.30%. The cladding region includes an outer cladding region surrounding and directly adjacent to the depressed-index cladding region. The outer cladding region comprises silica glass doped with a second concentration of fluorine less than the first concentration of fluorine. The outer cladding region has a relative refractive index Δ4 such that Δ4−Δ3min>0.05%. The optical fiber has a time-to-peak (TTP) hydrogen aging value at 23° C. of less than 100 hours upon exposure of the optical fiber to a gas atmosphere having a total pressure of 1 atm and containing a partial pressure of 0.01 atm H2 and a partial pressure of 0.99 atm N2. The optical fiber exhibits an attenuation <0.16 dB/km at 1583 nm and the attenuation monotonically increases between about 1570 nm and about 1600 nm.
According to a seventeenth aspect, a core region has an alkali metal oxide concentration between 0.5 wt. % and 1.5 wt. %.
According to an eighteenth aspect, an alkali metal oxide includes at least one of K2O, Na2O, LiO2, Rb2O, and Cs2O.
According to a nineteenth aspect, an optical fiber exhibits an attenuation <0.16 dB/km at 1547 nm and an incremental attenuation above baseline at 1547 nm less than 0.0003 dB/km.
According to a twentieth aspect, an optical fiber exhibits an attenuation <0.5 dB/km at 1383 nm.
According to a twenty first aspect, a preform is configured to be drawn into an optical fiber of any of the preceding aspects.
While exemplary embodiments and examples have been set forth for the purpose of illustration, the foregoing description is not intended in any way to limit the scope of disclosure and appended claims. Accordingly, variations and modifications may be made to the above-described embodiments and examples without departing substantially from the spirit and various principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.
This application claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 63/283,604 filed on Nov. 29, 2021, the content of which is relied upon and incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63283604 | Nov 2021 | US |
