JP2020532482A - Methods and furnaces for preparing fiber optic preforms using etching and neutralizing gases - Google Patents

Abstract

The method of preparing the optical preform 22 is the step of positioning the optical preform 22 made of silica in the cavity of the furnace 10; the etching gas 42 is defined in the furnace and in the optical preform 22. It comprises a step of passing through at least one of the passages 34 and around the optical preform 22; and a neutralizing gas 50 designed to neutralize the etching gas 42 into the cavity of the furnace. Reactors equipped with etching gas systems and neutralizing gas systems 38, 46 are also disclosed.

Description

priority

This application claims the priority benefit of US Provisional Patent Application No. 62/551372 filed on August 29, 2017, on which the content is relied upon and cited herein in its entirety, October 26, 2017. It claims the benefit of priority to the Dutch Patent Application No. 200811 filed on the same day.

The present disclosure relates to an optical preform furnace, and more particularly to an optical preform furnace equipped with a neutralizing gas system.

In the formation of a multimode optical preform, a centerline etching step may be performed using an etching agent to remove the silica-containing layer of the centerline of the preform. In other embodiments, the co-appliform may form a centerline species during subsequent processing, which adversely affects the performance and yield of the optical fiber drawn from these preforms. There is. To address the seed problems in these preforms, the centerline may be etched with an etching agent that passes through the centerline after the preform has been consolidated.

The etchant used for the centerline is transported to the furnace where the preform is located. In addition to etching the preform, the etching agent may also remove the muffle in the furnace by etching, significantly reducing the useful life of the muffle.

According to one aspect of the present disclosure, the method of preparing an optical preform is the step of locating the optical preform made of silica in the cavity of the furnace; etching gas in the furnace and in the optical preform. It consists of a step of passing through at least one of the defined open passages and around the optical preform; and a step of passing a neutralizing gas designed to neutralize the etching gas into the cavity of the furnace. ..

According to another aspect of the present disclosure, the method of operating the furnace is the step of positioning the optical preform in the muffle of the furnace; first, a fluorine-containing etching gas is placed in the furnace and in the centerline passage of the optical preform. A process of passing a neutralizing gas containing silicon, which is designed to neutralize the etching gas, through the cavity of the furnace at a second molar flow rate, and into the furnace. It comprises a step in which the ratio of the first molar flow rate into the furnace to the second molar flow rate is from about 0 to about 2.

According to yet another aspect of the present disclosure, the furnace assembly comprises a muffle that defines the cavity. The muffle contains silicon. An optical preform is positioned in the cavity. The preform defines an open passage with an entrance opening and an exit opening. The etching gas system is fluid-coupled to the preform and is designed to pass the etching gas through the open passage of the optical preform. The neutralizing gas system is designed to pass the neutralizing gas through the cavity, and the neutralizing gas is designed to neutralize the etching gas.

These and other aspects, purposes, and features of the present disclosure will be understood and recognized by those skilled in the art when reviewing the following specification, claims, and accompanying drawings.

The following is a description of the drawings in the accompanying drawings. The figure is not necessarily drawn to a constant scale, and certain features and fields of view of the figure may be exaggerated at scale and diagram for clarity and brevity.
Schematic of a furnace used to prepare an optical preform, according to at least one example. Schematic flow diagram of an exemplary method of operating the furnace of FIG. 1 according to at least one example. Graph of SiC ₄ and SiO ₂ concentration as a function of temperature

Additional features and advantages of the invention are described in the detailed description below, which will be apparent to those skilled in the art, or as described in the description below, along with the claims and accompanying drawings. Will be recognized by practicing the present invention.

As used herein, the term "and / or" can be used alone or by any one of the listed items when used in a list of two or more items. It means that any combination of any two or more of the listed items can be used. For example, if the composition is described as containing components A, B, and / or C, the composition is A only; B only; C only; A and B combination; A and C combination; Combinations of B and C; or may contain combinations of A, B, and C.

In this document, related terms such as first and second, top and bottom, etc., refer to one entity or action from another entity or action, which actual such relationship or order between such entities or actions. Is also used only to distinguish, not necessarily required or implied.

For the purposes of the present disclosure, the term "bonded" (all in its form: bonded, combined, combined, etc.) broadly refers to two components (electrical or mechanical) that are either direct or indirect to each other. It means the connection of the target). Such a connection may be virtually stationary or virtually movable. Such a connection may be made by the two components (electrically or mechanically) and any additional intermediate members integrally molded with each other, or by the two components. Unless otherwise stated, such connections may be virtually permanent or virtually removable or releasable.

As used herein, the term "about" does not require the quantity, size, formulation, parameters, and other quantities and features to be accurate, but tolerable, conversion factors, rounding. , Measurement error, and other factors known to those of skill in the art, meaning that they may be approximated and / or larger or smaller, as desired. When the term "about" is used in describing the endpoints of a value or range, the disclosure should be understood to include that particular value or endpoint mentioned. Whether or not the endpoints of a number or range in the specification are "approx.", The endpoints of the number or range are modified by the following two embodiments: "approx." And "approx." It is intended to include those that are not modified with. It will be further understood that each endpoint of those ranges is significant both with respect to the other endpoint and regardless of the other endpoint.

Terms such as "substantially" and "substantially", as used herein, and variants thereof are intended to point out that the described features are equal to or nearly equal to a value or description. .. For example, a "substantially flat" surface is intended to mean a surface that is flat or nearly flat. Further, "substantially" is intended to mean that the two values are equal or nearly equal. In some embodiments, "substantially" may mean 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, a noun refers to "at least one" object and should not be limited to "only one" object unless explicitly indicated to be the opposite. Thus, for example, reference to "ingredients" includes embodiments having more than one such ingredient, unless the context clearly indicates otherwise.

With reference to FIG. 1, reference numeral 10 generally refers to the furnace assembly 10. The furnace assembly 10 includes a muffle 14 that defines the cavity 18. The optical preform 22 is positioned within the cavity 18. The optical preform 22 defines an inlet opening 26, an outlet opening 30, and an open passage 34. The etching gas system 38 is fluid-coupled to the optical preform 22 and is made to pass the etching gas 42 through the optical preform 22. The neutralizing gas system 46 is made to pass the neutralizing gas 50 through the cavity 18 of the furnace assembly 10. According to various examples, the neutralizing gas 50 is made to neutralize the etching gas 42.

The furnace assembly 10 is made to provide a heating environment for the optical preform 22. The furnace assembly 10 may be a consolidation furnace, a redraw furnace, or any other type of furnace used in the optical preform 22. The furnace assembly 10 is made to heat the cavity 18 in the muffle 14 to a temperature of about 800 ° C to about 1600 ° C. For example, the furnace assembly 10 has its cavities at about 800 ° C, about 900 ° C, about 1000 ° C, about 1100 ° C, about 1200 ° C, about 1300 ° C, about 1400 ° C, about 1500 ° C, about 1600 ° C, or higher. May be made to heat to temperature. Further, the furnace assembly 10 may be made to heat the cavity 18 to a temperature of about 800 ° C to about 1600 ° C. In one example, the furnace assembly 10 may be made to heat the cavity 18 to a temperature of about 1000 ° C to about 1600 ° C. In various embodiments, the furnace assembly 10 may be made to heat the cavity 18 to a temperature of about 1200 ° C to about 1600 ° C. It should be understood that the cavity 18 may have a uniform temperature over the length of the cavity 18 or may have one or more areas having more heat with respect to the rest of the cavity 18. For example, the cavity 18 is closest to the exit opening 30 of the optical preform 22 and hotter (eg, about 1200) with respect to the temperature closest to the inlet opening 26 of the optical preform 22 (eg, about 1000 ° C. or less). ℃ or higher) may occur.

The muffle 14 is positioned within the furnace assembly 10 such that the optical preform 22 defines a cavity 18 within which the optical preform 22 is located. The muffle 14 may define a furnace exhaust port 60 located towards the top of the muffle 14. The furnace exhaust port 60 may allow pressure equalization in the cavity 18 and its surrounding environment, or removal of various gases generated in the furnace assembly 10. The muffle 14 may consist of a refractory material that accommodates heat within the furnace assembly 10 and protects other components of the furnace assembly 10. According to various examples, the refractory material of muffle 14 may contain silicon. For example, the muffle 14 may consist of quartz, silica and / or other silicon-containing compounds. Although it is shown to include one muffle 14, it should be understood that the furnace assembly 10 may include multiple muffles 14. For example, the furnace assembly 10 may include a sacrificial muffle that is positioned closer to the main muffle and the optical preform 22. As described in more detail below, the use of a muffle 14 refractory material having the same or similar composition as the optical preform 22 will have adverse effects when the etching gas 42 is used. ..

The optical preform 22 is suspended in the muffle 14 by a tube 64 and an integral handle 68. The pipe 64 extends outward from the furnace exhaust port 60 and is coupled to the etching gas system 38. The tube 64 is fluid coupled to the etching gas system 38 and the optical preform 22 so that the etching gas 42 is passed from the etching gas system 38 into the optical preform 22. For example, the tube 64 and the integral handle 68 may be made to impregnate the etching gas 42 into the optical preform 22 and / or to pass the etching gas 42 through the open passage 34. The tube 64 may be made of metal, ceramic and / or other material that can withstand the heat generated by the furnace assembly 10. Further, the tube 64 may be made to resist etching by the etching gas 42. The tube 64 is coupled to the integral handle 68 through the seal 72. The seal 72, like the tube 64, may be made to resist the temperature of the furnace assembly 10 as well as etching by the etching gas 42. The integral handle 68 may be formed by the optical preform 22 or may be attached after the formation of the optical preform 22. The integral handle 68 may serve as a point for holding, moving, or suspending the optical preform 22.

The optical preform 22 may be a fiber optic co-appliform and / or a fiber optic clad preform. Such optical preforms 22 may be utilized in the formation of doped or undoped single-mode or multi-mode optical fibers. According to various examples, the optical preform 22 may be formed by external vapor deposition (OVD). The OVD process for forming the optical preform 22 may include the deposition of the soot on a substrate designed to receive silica or doped silica soot (eg, SiO ₂ and GeO ₂ ). In an exemplary manufacturing process, the optical preform 22 is formed by soot deposition on a bait rod (eg, a ceramic substrate rod designed to receive soot). The bait rod may have a cylindrical, square or other higher order polygonal cross-sectional shape. It should be understood that the optical preform 22 may be doped at this time or flood-doped at a later time. Illustrated dopants would include GeO ₂ , Al ₂ O ₃ , P ₂ O ₅ , Br, Cl and / or F. For example, as part of the suit deposition process to form the optical preform 22, the first few deposition passes (100 micron) of the suit to achieve the desired GeO ₂ SiO ₂ profile near the bait rod. Meter to 500 micrometer soot deposits (eg, in the OVD process) are SiO ₂ optionally doped with a relatively small amount of GeO ₂ (eg, 10-18 mass% GeO ₂ ). This is followed by SiO ₂ soot deposition containing a large amount (eg, about twice the amount) of GeO ₂ . It should be understood that the optical preform 22 may be formed in addition to or in place of it by improved chemical vapor deposition, physical vapor deposition and / or soot pressurization. The soot applied to the bait rod may consist of nanometer and / or micrometer scale particles and / or dopant particles of SiO ₂ . The finished optical preform 22 may have an outer diameter of about 20 mm to about 200 mm. The diameter of the inlet opening 26 may be about 20 mm or less, about 10 mm or less, about 5 mm or less, about 4 mm or less, or about 3 mm or less. For example, the diameter of the inlet opening 26 may be from about 1 mm to about 20 mm, or from about 3 mm to about 10 mm.

The bait rod is then removed from the optical preform 22 to form an open passage 34. The open passage 34 of the optical preform 22 may extend through a portion of the optical preform 22, substantially all or completely, through a portion of the optical preform 22. The open passage 34 may be positioned along the centerline of the optical preform 22. In such an example, the open passage 34 may also be referred to as a centerline passage, an open cavity and / or an open centerline. It should be understood that the bait rods may be positioned off-center of the optical preform 22 or that a large number of bait rods (eg, therefore a large number of open cavities 34) are possible. Removing the bait rod from the optical preform 22 will form an inlet opening 26, an outlet opening 30, and an open passage 34 of the preform 22. Once the bait rod is removed, the optical preform 22 is placed in a consolidation furnace (eg, furnace assembly 10 or another furnace) for drying and consolidation. Drying of the optical preform 22 may be performed by placing the preform 22 in a halogen-containing atmosphere (eg, Cl ₂ ) to remove moisture (ie, OH). The optical preform 22 may then be consolidated (eg, sintered into void-free glass) to form the consolidated optical preform 22. The optical preform may be opaque and / or translucent to visible and invisible light before sintering and solidification, while after solidification, the preform 22 is visible and non-visible. It should be understood that it can be transparent to visible light.

The consolidation optical preform 22 can be drawn directly to the optical fiber, or it can first be further processed in the redraw furnace to crush the open passage 34 before drawing the preform 22 to the optical fiber. it can. According to various examples, the open passage 34 of the optical preform 22 is at least to some extent collapsed before being drawn into the fiber. Crushing of the open passage 34 may be performed at high temperatures (eg, about 1700 ° C. to 2200 ° C.) and, if desired, under vacuum. The crushed preform can also be called a preform cane. In some cases, these canes are referred to as core canes starting with the co-appli form. The optical preform 22 heats the preform 22 at or above the temperature at the softening point of the glass and the deposited material, crushes the preform 22 and opens the inlet opening 26, the outlet opening 30 and the open passage 34. By eliminating it, it may be converted to core cane.

According to various examples, an etching process using an etching gas system 38 and an etching gas 42 may be used to etch a portion of the optical preform 22. In one example, the etching gas 42 may be passed through the optical preform 22 to etch the interior of the preform 22 (eg, the open passage 34). In another example, the etching gas 42 may be passed along the outside of the optical preform 22 to etch the outside of the optical preform 22. Thus, the etching gas 42 may be passed through the furnace assembly 10 at least in the open passage 34 defined in the optical preform 22 and around the optical preform 22. It will be appreciated that in the example where the etching gas 42 is passed outside the optical preform 22, the etching gas 42 may or may not flow through the tube 64 and / or the integrated handle 68. In an example where the etching gas 42 is passed through the open passage 34, the etching gas 42 may be passed before crushing and / or sintering the optical preform 22. The etching gas 42 may be passed in a vapor phase to remove the first few deposition passes (eg, in the OVD manufacturing process) and to a predetermined depth (eg, soot pressurization method). Such features may result in defects in the control of the dopant concentration profile of the optical preform 22 and / or in the optical fiber drawn from the optical preform 22 before the preform 22 is crushed (eg,). It would be convenient to remove the internal and / or external) from the optical preform 22. For example, as part of the suit deposition process, the first few passes of the suit (about 100 micrometers to 500 micrometers) are in an undesired amount near the open passage 34 (eg, low or high relative to the target concentration). ) May have a dopant. In another example, removing the bait rod from the optical preform 22 may result in the formation of anomalies (eg, holes, coarse spots, etc.) on the preform 22 closest to the centerline 34. The anomaly would also be known as the centerline species. The formation of centerline species can adversely affect the performance and yield of the optical fibers drawn from these preforms 22.

The etching of the preform 22 may be performed by passing the etching gas 42 from the etching gas system 38 through the tube 64 into the optical preform 22. When the etching gas 42 is introduced through the open passage 34, the etching gas 42 can effectively etch the open passage 34 of the preform 22. The etching gas 42 is a gas capable of removing crystalline or vitreous oxide materials by chemical action under appropriate conditions (for example, temperature and concentration). According to various examples, the etching gas 42 may contain a fluorine-containing gas, but it will be understood that other etching gases 42 may be utilized without departing from the teachings given herein. .. For example, as _the etching gas _{42, SF 6, SOF 4,} CF 4, SF 6, NF 3, C 2 F 6, C 4 F 8, CHF 3, CClF 3, CCl 2 F 2, CCl 3 F, SiF 4 , And combinations thereof. The etching gas 42 may contain one or more other gases having little or no etching ability. For example, the etching gas 42 may include one or more types of transport gas designed to transport the etching gas 42. For example, the etching gas 42 may include oxygen, helium, nitrogen, argon, and / or other transport gas.

The etching gas system 38 passes through the open passage 34 in about 25 standard conditions cubic centimeters per minute (“sccm”), about 50 sccm or more, about 90 sccm or more, about 150 sccm or more, about 200 sccm or more, about 300 sccm or more, about 500 sccm or more, about 1000 sccm. Etching gas 42 may be passed through the furnace assembly 10 at a flow rate of about 3000 sccm or more. In one example, the flow rate of the etching gas 42 into the furnace assembly 10 is from about 25 sccm to about 10000 sccm, or from about 25 sccm to about 3000 sccm, or from about 25 sccm to about 1000 sccm. The temperature of the etching gas 42 in contact with the optical preform 22 may be about 1700 ° C. or lower, about 1600 ° C. or lower, about 1550 ° C. or lower, about 1500 ° C. or lower, about 1400 ° C. or lower, or about 1300 ° C. or lower. In one example, the temperature of the etching gas 42 in contact with the optical preform 22 is from about 800 ° C to about 1700 ° C, or from about 1000 ° C to about 1600 ° C, or from about 1200 ° C to about 1600 ° C. The etching gas 42 is about 100 micrometers or more, about 200 micrometers or more, about 300 micrometers or more, about 400 micrometers or more, about 500 micrometers or more, about 600 micrometers or more, about 700 micrometers or more from the open passage 34. , About 800 micrometers or more, about 900 micrometers or more, or about 1000 micrometers or more may be passed through the optical preform 22 for a sufficient period of time to be removed. In one example, the etching gas 42 removes from the open passage 34 from about 100 micrometers to about 3000 micrometers, or from about 100 micrometers to about 2000 micrometers, or from about 100 micrometers to about 1000 micrometers. It is passed through the optical preform 22 at a sufficient temperature for a sufficient period of time. It will be appreciated that the thickness removed from the open passage 34 is expressed as a radial distance.

As described above, the etching gas system 38 puts the etching gas 42 into the inlet opening 26 of the optical preform 22, passes it through the open passage 34, and passes it out of the optical preform 22 through the outlet opening 30. May be made. Since the cavity 18 of the furnace assembly 10 is hot closest to the outlet opening 30, excess etching gas 42 (eg, etching gas 42 that has not reacted with the optical preform 22) comes into contact with the muffle 14 and the muffle. Etching of 14 silicon-containing examples may begin. Such an outcome would reduce the useful life of the muffle 14 and would be inconvenient. Therefore, it would be convenient to introduce the neutralizing gas 50 into the muffle 14 and / or closest to the outlet opening 30.

The neutralizing gas system 46 is designed to pass or inject the neutralizing gas 50 into the cavity 18 closest to the outlet opening 30. As described above, the neutralizing gas 50 is made to neutralize the etching effect of the etching gas 42 so that the etching gas 42 is substantially inactive to the muffle 14. In other words, the neutralizing gas 50 may chemically react with the etching gas 42 to neutralize and / or reduce the etching effect of the etching gas 42 on the silicon-containing compound. According to various examples, the neutralizing gas 50 may contain a silicon-containing gas. Examples of the silicon content of the neutralizing gas 50 include SiCl ₄ , Si ₂ Cl ₆ , Si ₂ OCl ₆ , SiHCl ₃ , SiH ₂ Cl ₂ , SiH ₃ Cl, SiBr ₄ , SiH ₄ , SiCl ₃ F, SiCl ₂ F ₂ , SIClF _3, octamethylcyclotetrasiloxane, and Y ≦ 3,1 ≦ X ≦ 4, R is alkyl, aryl or H moiety, _SiR X _{F Y,} and / or at least one of its combinations thereof Will.

The use of the silicon-containing gas in the neutralizing gas 50 is configured to react with the etching gas 42 such that the etching gas 42 reduces and / or drastically reduces the ability of the etching gas 42 to etch the muffle 14. As can be seen from Equation 1, the fluorine-containing example of the etching gas 42 (for example, SF ₆ ) is similar to the silicon-containing example of the muffle 14 and the optical preform 22 (for example, SiO ₂ ) without the neutralizing gas 50. react.

It is shown by Equation 2 that the introduction of the silicon-containing example (for example, SiCl ₄ ) of the neutralizing gas 50 can neutralize the etching effect of the fluorine-containing example (SF ₆ ) of the etching gas 42.

As shown in Equation 3, the introduction of the silicon-containing example (for example, SiCl ₄ ) of the neutralizing gas 50 has no effect on the silicon-containing example (for example, SiO ₂ ) of the muffle 14 from the minimum, and the etching gas 42 It has been shown that the etching effect of the fluorine-containing example (SF ₆ ) can be neutralized preferentially. Such a preferred reaction is believed to occur due to the chemical reaction potential of the vapor phase of the neutralizing gas 50 with respect to the chemical reaction potential of the solid muffle 14.

In the neutralizing gas system 46, the molar ratio of the etching gas 42 entering the furnace assembly 10 to the neutralizing gas 50 entering the furnace assembly 10 is about 0.1 or more, about 0.2 or more, about 0.3 or more, and about 0. .4 or more, about 0.5 or more, about 0.6 or more, about 0.7 or more, about 0.8 or more, about 0.9 or more, about 1.0 or more, about 1.1 or more, about 1.2 Above, about 1.3 or more, about 1.4 or more, about 1.5 or more, about 1.6 or more, about 1.7 or more, about 1.8 or more, about 1.9 or more, about 2.0 or more, The neutralizing gas 50 is made to pass through the furnace assembly 10 at a flow rate such that it is about 3.0 or more, about 4.0 or more, or about 5.0 or more. In one example, the molar ratio of the etching gas 42 entering the furnace assembly 10 to the neutralizing gas 50 entering the furnace assembly 10 is about 0 to about 10, or about 0 to about 5, or about 0 to about 2, or about 0. It is about 1 to 2. In other words, the molar ratio of the etching gas 42 entering the furnace assembly 10 to the neutralizing gas 50 entering the furnace assembly 10 is greater than 0 and less than 2 or greater than 0 and less than or equal to 1.

Here, with reference to FIG. 2, an exemplary method 80 for operating the furnace assembly 10 is shown. Method 80 may begin with step 84, which positions the optical preform 22 within the cavity 18 of the furnace assembly 10. As described above, the optical preform 22 is suspended in the cavity 18 of the muffle 14 through a tube 64 and an integral handle 68. The furnace assembly 10 may be heated to a temperature of about 1000 ° C. or higher. In another example, the furnace assembly 10 may be heated to a temperature of about 1000 ° C to about 1600 ° C. In one example, the furnace assembly 10 is heated to a temperature of about 800 ° C to about 1600 ° C, or about 1000 ° C to about 1600 ° C, or about 1200 ° C to about 1600 ° C.

Next, a step 88 is performed in which the etching gas 42 is passed through at least one of the open passages 34 defined in the furnace assembly 10 and the optical preform 22 and around the optical preform 22. As described above, the etching gas 42 may be passed through the open passage 34, through the tube 64, and / or around the outside of the optical preform 22. The etching gas 42 may be passed through the furnace assembly 10 at a first molar flow rate. In an example in which the etching gas 42 is passed through the optical preform 22, the etching gas system 38 passes the etching gas 42 through the tube 64 through the optical preform 22 and through the inlet opening 26 through the optical preform 22. The etching gas 42 then travels through the centerline passage 34 and through the outlet opening 30 into the cavity 18. The passage of the etching gas 42 has the effect of etching the open passage 34 of the optical preform 22. In an example in which the etching gas 42 is passed around the optical preform 22, the passage of the etching gas 42 has the effect of etching the outside of the optical preform 22.

Next, a step 92 of passing the neutralizing gas 50 through the cavity 18 of the furnace assembly 10 is performed. As described above, the neutralizing gas 50 is made to neutralize the etching gas 42. The neutralizing gas 50 is passed through the cavity 18 closest to the end of the optical preform 22 (eg, the outlet opening 30 of the optical preform 22, the open passage 34). The neutralizing gas 50 may be passed at a second molar flow rate such that the ratio of the first molar flow rate of the etching gas 42 to the second molar flow rate of the neutralizing gas 50 is about 2 or less. In other words, the passage of the neutralizing gas 50 may be a flow rate such that the molar ratio of the etching gas 42 to the neutralizing gas 50 entering the furnace assembly 10 is about 2 or less, or about 1 or less.

The use of this disclosure will present various advantages. First, the use of the neutralizing gas 50 presents a simple and low cost method of extending the availability of the muffle 14. Replacing the muffle 14 in the furnace assembly 10 requires both the new muffle 14 and the downtime of the furnace assembly 10, so increasing the availability of the muffle 14 will only increase the production of the furnace assembly 10. However, the costs associated with the maintenance of the furnace assembly 10 will also be reduced. Second, the use of the neutralizing gas 50 will allow for more aggressive etching of the optical preform 22. For example, it may be convenient to increase the amount or concentration of etching gas 42 passed through the furnace assembly 10 (eg, reduce the etching time and / or the etching depth). According to the present disclosure, the excess etching gas 42 can be neutralized before contacting the muffle 14, so that a higher concentration of etching gas 42 is passed through the preform 22, thereby increasing the useful life of the muffle 14. Etching times could be reduced without a corresponding reduction. Third, since the silicon-containing example of the neutralizing gas 50 has already been used in many manufacturing processes of the optical preform 22, no special gas will necessarily be required to carry out the present disclosure. ..

Here, referring to FIG. 3, a modeling calculation of the equilibrium concentration of SiO ₂ : SF ₆ : SiCl ₄ at a temperature between 1000 ° C. and 1500 ° C. is given. For explanatory calculations, 10 moles of SiO ₂ (eg, representing the example of silica in muffle 14) and 1 mole of SF ₆ (eg, etching gas 42) are given. As can be seen from FIG. 3 and Table 1, increasing the use of SiCl ₄ (eg, neutralizing gas 50) increases the retention of SiO ₂ .

Table 1 shows the calculated concentration of SiO _{2 in} the equilibrium state. SiCl ₄ without, when _SiO 2 / SF ₆ molar ratio is 10, for the etching reaction, SiO ₂ concentration at equilibrium is calculated to be decreased by 15%. The SiO ₂ concentration is calculated to decrease by 5% with respect to a 0.5 SiO ₂ / SF ₆ molar ratio. The SiO ₂ concentration is calculated to decrease by less than 0.2% for a SiO ₂ / SF ₆ molar ratio greater than 1. The results provided show that the addition of SiCl ₄ inhibits SF ₆ etching of SiO ₂ . As a practical matter, this data shows that the introduction of the silicon-containing example of neutralizing gas 50 neutralizes the excess etching gas 42 so that the etching experienced by the silicon-containing example of muffle 14 is reduced. Such a reduction in etching of the muffle 14 results in a corresponding increase in the useful life of the muffle 14.

Table 2 shows the quantitative results of the experimental data. Comparative Example 1 was a silica-based tube (for example, muffle 14) having a length of 1.25 meters and an outer diameter of 6.37 mm. The silica tube had a centerline passage (eg, an open passage 34) with an inner diameter (ID) of 4.00 mm. The silica-based tube of Comparative Example 1 was placed in a tube furnace (for example, furnace assembly 10) so that each end protruded from the tube furnace. This tube furnace had a hot area of 30 cm and had an insulated end cap with a hole in the center into which the silica tube was placed. The temperature of this furnace was maintained at 1125 ° C. Silica is then passed through the open cavity of the silica tube for 120 minutes at flow rates of 0.10 and 0.58 SLPM, respectively, of SF ₆ (eg, etching gas 42) and He (eg, transport gas). The open cavity of the tube was vapor phase etched. Immediately after this process, the silica tubing was purged by continuous flow of He at 0.58 SLPM, the tubing furnace was extinguished and cooled to room temperature. Next, the silica tube was taken out of the tube furnace and weighed with a chemical balance. This silica tube had a mass loss of about 3.9 grams as a result of the SF ₆ etching process. The inner diameter of the silica tube in the tube furnace was measured at several points and etched to about 4.6-4.7 mm (eg, wall thickness of about 0.3 mm to 0.35 mm was removed). It was also found that the inner diameter of the silica tube was slightly recessed (diameter of about 0.1 mm to 0.5 mm) from the etching process. The inner diameter of the part of the silica tube outside the tube furnace remained innocent and was not etched with an inner diameter of 4.00 mm.

The experiment of Example 1 was performed in the same manner as in Comparative Example 1, but contained SiCl ₄ (eg, neutralizing gas 50). In Example 1, the silica-based tube (eg, muffle 14) had a length of 1.25 meters and an outer diameter of 6.37 mm. This silica tube had an open passage (eg, centerline passage 34) with an inner diameter of 4.00 mm. The silica-based tube of Example 1 was placed in a tube furnace (eg, furnace assembly 10) so that each end protruded from the tube furnace. This tube furnace had a high temperature area of 30 cm and had a heat insulating end cap with a hole in the center to put the silica tube inside. The temperature of this furnace was maintained at 1125 ° C. The open cavity of the silica tube is then filled with SF ₆ (eg, etching gas 42), He (eg, transport gas), and SiC at 0.10 SLPM, 0.38 SLPM, and 0.20 SLPM, respectively, for 120 minutes. The open cavity of the silica tube was vapor phase exposed at this temperature by flowing ₄ (eg, neutralizing gas 50). Immediately after this process, the silica tubing was purged by continuous flow of He at 0.58 SLPM, the tubing furnace was extinguished and cooled to room temperature. Next, the silica tube was taken out of the tube furnace and weighed with a chemical balance. This silica tube had a mass loss of about 0.0 grams as a result of the SF ₆ and SiC ₄ exposure process. The inner diameter of the silica tube inside the tube furnace was measured at several places and was solid, unetched, and maintained an inner diameter of 4.00 mm. The inner diameter portion of the silica tube outside the tube furnace also remained innocent and was not etched with an inner diameter of 4.00 mm. These results show that the presence of a silicon-containing gas (eg, neutralizing gas 50) in the vapor phase in the presence of a silica etching gas (eg, fluorine-containing etching gas 42) causes the neutralizing gas to react with the etching gas. Indicates that the etching gas is prevented from etching the silica tube.

Modifications of this disclosure will be recalled to those skilled in the art and those who use the disclosure. Accordingly, the embodiments shown in the drawings and described above are for explanatory purposes only and are not intended to limit the scope of the present disclosure and are to be construed in accordance with the principles of patent law, including the doctrine of equivalents. It will be understood that the scope is defined by the following claims.

Hereinafter, preferred embodiments of the present invention will be described in terms of terms.

Embodiment 1
In the method of preparing optical preforms
The process of locating an optical preform made of silica in a furnace cavity,
Neutralize the etching gas in the furnace, in the open passage defined in the optical preform, and at least one around the optical preform, and in the cavity of the furnace. A method of having a step of passing a neutralizing gas, which is made to be.

Embodiment 2
The step of etching the open passage of the optical preform using the etching gas,
The method according to the first embodiment, further comprising.

Embodiment 3
The process of passing the etching gas is
A step of passing the etching gas through the center line of the optical preform,
The method according to the first embodiment.

Embodiment 4
The step of passing the neutralizing gas through the cavity of the furnace closest to the outlet of the open passage of the optical preform,
The method according to the third embodiment, further comprising.

Embodiment 5
The step of passing the neutralizing gas is
A step of passing the neutralizing gas at a flow rate such that the molar ratio of the etching gas entering the furnace to the neutralizing gas entering the furnace is more than 0 and 2 or less.
The method according to the first embodiment, further comprising.

Embodiment 6
The step of passing the neutralizing gas is
A step of passing a flow in said neutralizing gas such that the molar ratio of the etching gas entering the furnace to neutralization gas entering the furnace is greater than 0 and less than 1, the neutralizing gas includes a SiCl _4, A step in which the etching gas contains SF ₆ .
The method according to embodiment 5, further comprising.

Embodiment 7
The step of heating the furnace to about 1000 ° C. or higher,
The method according to the first embodiment, further comprising.

8th Embodiment
In the method of operating the furnace
The process of positioning the optical preform in the muffle of the furnace,
A step of passing an etching gas containing fluorine at a first molar flow rate in the furnace and in the centerline passage of the optical preform, and a neutralizing gas containing silicon prepared to neutralize the etching gas. In the step of passing the gas through the cavity of the furnace at a second molar flow rate, the ratio of the first molar flow rate into the furnace to the second molar flow rate into the furnace is about 0. The process, which is about 2.
How to have.

Embodiment 9
A step of heating the furnace to a temperature of about 1000 ° C to about 1600 ° C.
The method according to embodiment 8, further comprising.

Embodiment 10
The process of positioning the optical preform in the muffle of the furnace is
The step of positioning the optical preform in a muffle containing silicon,
The method according to embodiment 8, further comprising.

Embodiment 11
The step of passing the neutralizing gas is
A step of passing the neutralizing gas at a second molar flow rate such that the ratio of the first molar flow rate into the furnace to the second molar flow rate into the furnace is more than 0 and 1 or less.
The method according to embodiment 8, further comprising.

Embodiment 12
It is a furnace assembly
Silicon-containing muffle, which defines the cavity,
An optical preform positioned in the cavity that defines an open passage with an inlet opening and an outlet opening,
An etching gas system that is fluid-bonded to the preform and is designed to allow the etching gas to pass through an open passage of the optical preform, and a neutralizing gas that is designed to neutralize the etching gas. Neutralizing gas system designed to pass through cavities,
Furnace assembly with.

Embodiment 13
12. The furnace assembly according to embodiment 12, wherein the optical preform is an optical fiber co-appliform.

Embodiment 14
The etching gas system is designed to allow the etching gas to enter the inlet opening of the optical preform, pass through the open passage of the optical preform, and exit the optical preform through the outlet opening. , The furnace assembly according to embodiment 12.

Embodiment 15
The furnace assembly according to embodiment 14, wherein the neutralizing gas system is made to pass the neutralizing gas closest to the outlet opening.

Embodiment 16
The furnace assembly according to embodiment 12, wherein the optical preform is a consolidated optical preform.

Embodiment 17
The furnace assembly according to embodiment 12, wherein the etching gas contains a fluorine-containing gas.

Embodiment 18
The furnace assembly according to embodiment 17, wherein the fluorine-containing gas comprises at least one of SF ₆ , NF ₃ , and SOF ₄ .

Embodiment 19
The furnace assembly according to embodiment 12, wherein the neutralizing gas comprises a silicon-containing gas.

20th embodiment
The silicon-containing gases are SiCl ₄ , Si ₂ Cl ₆ , Si ₂ OCl ₆ , SiHCl ₃ , SiH ₂ Cl ₂ , SiH ₃ Cl, SiBr ₄ , SiH ₄ , SiCl ₃ F, SiCl ₂ F ₂ , SICl F ₃ , Octa. tetramethylcyclotetrasiloxane, and Y ≦ 3,1 ≦ X ≦ 4, R is alkyl, aryl or H moiety, _SiR X _{F Y} comprises at least one of, the furnace assembly of embodiment 19.

10 Reactor Assembly 14 Muffle 18 Cavity 22 Optical Preform 26 Inlet Opening 30 Outlet Opening 34 Open Passage 38 Etching Gas System 42 Etching Gas 46 Neutralizing Gas System 50 Neutralizing Gas 60 Reactor Exhaust Port 64 Pipe 68 Integrated Handle 72 Seal

Claims (10)

In the method of preparing an optical preform in a furnace assembly with a muffle that defines the cavity.
A step of positioning an optical preform made of silica in the cavity of a muffle of the furnace assembly, wherein the muffle contains silica.
In order to etch the preform, an etching agent in the form of an etching gas is passed through the furnace assembly, and the etching agent is passed through an open passage defined in the optical preform. A step of etching an open passage defined in the optical preform and a step of passing a neutralizing gas through the cavity of the muffle of the furnace assembly, the neutralizing gas is an open passage in the preform. The process of passing the neutralizing gas through the muffle cavity of the furnace assembly closest to the outlet of the open passage of the optical preform, which is designed to neutralize the etchant exiting the.
Have
The etching _{gas, SF 6, SOF 4, CF} 4, SF 6, NF 3, C 2 F 6, C 4 F 8, CHF 3, CClF 3, CCl 2 F 2, CCl 3 F, SiF 4, and Including one or more combinations
The neutralizing gas is SiCl ₄ , Si ₂ Cl ₆ , Si ₂ OCl ₆ , SiHCl ₃ , SiH ₂ Cl ₂ , SiH ₃ Cl, SiBr ₄ , SiH ₄ , SiCl ₃ F, SiCl ₂ F ₂ , SICl F ₃ , Octa. tetramethylcyclotetrasiloxane, and Y ≦ 3,1 ≦ X ≦ 4, R is alkyl, aryl or H moiety, including _SiR X _{F Y,} and / or silicon compound is at least one of its combinations, Method. The method of claim 1, wherein the etching gas is passed through the cavity of the muffle in a vapor phase. The etching gas is as follows:
− Approximately 25 standard conditions cubic centimeters per minute (“sccm”),
− About 50 sccm or more,
-Approximately 90 sccm or more,
-Approximately 150 sccm or more,
-Approximately 200 sccm or more,
-Approximately 300 sccm or more,
-Approximately 500 sccm or more,
-About 1000 sccm or more, or-About 3000 sccm,
The method according to claim 1, wherein one of the flow rates is passed through the cavity of the muffle. The etching gas is passed through the muffle cavity at a flow rate of about 25 sccm to about 10000 sccm, or about 25 sccm to about 3000 sccm, or about 25 sccm to about 1000 sccm, and / or the temperature of the etching gas is about 1700 ° C. or less. , About 1600 ° C or lower, about 1550 ° C or lower, about 1500 ° C or lower, about 1400 ° C or lower, or about 1300 ° C or lower, and / or the temperature of the etching gas in contact with the optical preform is from about 800 ° C. About 1700 ° C, or about 1000 ° C to about 1600 ° C, or about 1200 ° C to about 1600 ° C.
The method according to any one of claims 1 to 3. The etching gas has a thickness of about 100 micrometers or more, about 200 micrometers or more, about 300 micrometers or more, about 400 micrometers or more, about 500 micrometers or more, about 600 micrometers or more, and about 700 from the open passage. It is passed through an open passage in the optical preform and removed from the open passage for a sufficient period of time such that micrometer or more, about 800 micrometers or more, about 900 micrometers or more, or about 1000 micrometers or more is removed. The method according to any one of claims 1 to 4, wherein the thickness is represented by a radial distance. At a temperature sufficient for the etching gas to remove from the open passage from about 100 micrometers to about 3000 micrometers, or from about 100 micrometers to about 2000 micrometers, or from about 100 micrometers to about 1000 micrometers. The method of claim 5, wherein the method is passed through an open passage in the optical preform for a sufficient period of time. The method according to any one of claims 1 to 6, wherein the neutralizing gas is passed through the cavity of the muffle so that the etching gas is substantially inert to the muffle of the furnace assembly. The etching gas is passed through the cavity of the muffle and through the centerline passage of the optical preform at a first molar flow rate.
The neutralizing gas is passed through the muffle cavity at a second molar flow rate so as to neutralize the etching gas, and into the muffle cavity with respect to the second molar flow rate into the muffle cavity. The ratio of the first molar flow rate is about 0 to about 2.
The method according to any one of claims 1 to 7. 8. The method of claim 8, further comprising heating the furnace assembly to a temperature of about 1000 ° C to about 1600 ° C. In the step of passing the neutralizing gas, the ratio of the first molar flow rate into the muffle cavity to the second molar flow rate into the muffle cavity is more than 0 and 1 or less. The method according to claim 8 or 9, further comprising the step of passing the neutralizing gas at the second molar flow rate.

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