JPS6283339A - Formation of coating on optical fiber - Google Patents

Abstract

PURPOSE:To form a film contg. pulverized particles sticking to a film for an optical fiber at a decreased ratio on the fiber by forming said coating on the fiber by a cold wall hot fiber CVD method. CONSTITUTION:The optical fiber 20 is online drawn out through a CVD furnace in such a manner that the fiber is protected by the film deposited by evaporation thereon. The fiber 20 is introduced through a gas isolation chamber 26 in which an inert gas is filled into a reaction chamber 21. The greater part of the chamber 21 is filled with a vacuum bottle 213 for forming a cylindrical channel 214 around the fiber 20. The diameter of the channel 214 is as small as about 3mm, a reactive gas passes near the fiber 20 and reacts efficiently with the fiber in a cold wall hot fiber treatment. The fiber on which the film is formed is taken out through a liquid isolation chamber 27. The undesirable particles deposited on the fiber are removed and the film having no defects and pinholes is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD OF THE INVENTION The present invention relates generally to fiber coatings and, more particularly, to a method and furnace for forming high-speed, corrosion-resistant and sealing coatings on optical fibers on-line. .

[Prior art and its problems]

It is well known that bare, uncoated optical fibers are susceptible to corrosion by various chemicals, including water.

Cracks and scratches in the surface of optical fibers cause areas that are susceptible to chemical attack.

These are particularly noticeable when the fiber is stressed. Therefore, optical fibers are typically coated with wear-resistant coatings to prevent scratching of the fibers.

However, optical fiber surfaces typically have microclutches created during fiber manufacturing that can also be corroded by water. Therefore, in many applications, to prevent sudden fiber breaks due to water corrosion,
It is important to apply a hermetic coating to the fiber. Like the wear-resistant coating, the sealing coating must be formed on-line while the fiber is being drawn to protect the fiber before it is wound onto the take-up spool. Therefore, there is a need for a process that can deposit sealing, wear-resistant coatings at rates consistent with optical fiber production, ie, on the order of 1 to 10 meters per second.

Uses optical fiber. Shaft logging (borehole)
logging) operation, the optical fiber is
Must be able to withstand water at 00°C and 20,000 psi. Furthermore, the weight of the equipment attached to the optical fiber and the weight of the metal cable used to support the equipment can cause up to 3% strain in the metal cable and optical fiber. Under such temperatures, pressures, and strains, uncoated fibers are known to break in seconds.

Therefore, there is a need for a sealing coating that can protect optical fibers under these harsh conditions.

U.S. Patent Application i3 filed March 30, 1982
No. 63.722 presents a coating containing silicon and carbon that has proven to be a hermetic coating under the harsh conditions encountered by optical fibers in shaft logging.

As shown in that application, silane (Si
By adding H4,) it is possible to increase the reaction rate and obtain thicker coatings than without silane. However, chemical resistance testing in which the fiber was immersed in hydrofluoric acid showed that chemical resistance increased as the amount of silicon in the coating decreased. Additionally, high-speed break tests showed that the fiber strength increased slightly as the amount of silicon in the coating decreased. However, decreasing the proportion of silane in the reactants reduces the thickness of the coating produced. Said U.S. Application No. 363
．． As shown in No. 722, by removing Si town,
It has been found that a coating that is not airtight is produced. It is speculated that the coating was too thin to be airtight.

Therefore, there is a need for a method and furnace capable of achieving ultra-high deposition rates that do not unduly reduce the thickness of the produced film and that also reduce the amount of silicon. Such a method should be capable of depositing strongly adherent coatings on-line, pinhole-free, on optical fibers at profitable withdrawal speeds. Increasing the draw speed in production processes requires implementing a process with an order of magnitude higher carbon deposition rate on the optical fiber compared to the aforementioned US Pat. No. 363.722.

FIG. 1 shows a conventional CVD furnace suitable for coating optical fibers. This furnace is disclosed in Japanese Patent Application Laid-Open No. 75945/1983. The CVD furnace has a reaction chamber 11 with a reactant inlet 12 and an outlet 13. The CVD furnace further includes a fiber inlet 14 and a fiber outlet to form an on-line path for the optical fiber 10 through the reactor. It has an outlet 15. In order to prevent the reaction gas from escaping from the fiber inlet 14 or the fiber outlet 15, gas isolation chambers (gas seals) 16 and 17 are provided at the fiber inlet 14 and the fiber outlet 15.
and is provided. The gas isolation chambers 16 and 17 each have an inlet 111 and 112 through which an inert gas is supplied, and an opening 18 and 19 through which the fiber 10 is drawn out. The gas isolation chambers 16 and 17 are protected against scratches caused by the optical fiber 10 passing through the fiber inlet and outlet ports,
and/or as a seal at the fiber inlet and outlet to prevent contamination.

Figure 1 of the above-mentioned JP-A-Sho is a hot wall.
l) A heating coil 110 is used to heat the walls of the reaction chamber 11 for Cv0 treatment. However, the above-mentioned JP-A-Sho discloses that other heating methods can also be used, including RF heating, laser heating of the fiber, and providing a reaction chamber sufficiently close to the elution point. In this last case, the fiber is drawn from the freeform where the fiber is hot enough for cold wall, hot fiber CVD coating to occur.

Unfortunately, however, the use of gas isolation chambers at both ends of the reaction chamber allows ambient gas to be introduced into the reaction chamber by the moving fiber. This problem primarily occurs at the opening 18 within the gas isolation chamber 16.

As the fiber is drawn through the reaction chamber, ambient gas on the fiber surface is drawn into the reaction chamber through the gas isolation chamber 16. If the draw speed is slow and the gas isolation chamber 16 is long enough, this air layer has time to diffuse away from the fiber before it enters the reaction chamber, so that a negligible amount of ambient gas is removed. is drawn into the reaction chamber. However, in many applications, the upper isolation chamber 16 is
The culm is not long enough to clear the gas on the fiber before it traverses the entire gas isolation chamber.

[Purpose of the invention]

The present invention has been made to obviate the above-mentioned disadvantages and provides a deposition method that does not draw unacceptable amounts of ambient gas into the reaction chamber and that does not deposit undesirable particles on the optical fiber. , forming a coating on the fiber with high wear resistance and sealing properties.

[Summary of the invention]

The fiber coating process according to the present invention includes hot fiber and cold wall coating.
old wall) CVD process,
The heat for D is provided by a hot fiber rather than a hot reactant gas. In hot reactant gas coating processes, heat is typically provided by heating coils that heat the walls of the CVO reaction chamber. Such hot wall treatments have several drawbacks.

Since the walls are the hottest part of the reaction chamber, much of the coating process is carried out on the wall soil. Therefore, a coating is formed on the wall,
This coating reduces heat transfer into the reaction chamber, can cause wall spalling, and can also cause undesirable particle deposition on the fiber.

More importantly, hot fiber CVD processing has been found to produce superior coatings with fewer defects, pinholes, and particulates attached to the coating than hot wall CVD processing. The high temperature fiber produces a thermal envelope,
This thermal envelope is theorized to create a pressure gradient on the particles in the gas in the reactor, away from the fiber. This kind of pressure gradient is called thermophoresis (ther
mophoresis). As a result of this pressure gradient, particles within the reaction chamber are inhibited from moving toward the hot fiber and cannot be deposited onto the hot fiber. CVD
This gradient causes particles that are produced away from the surface of the hot fiber or detached from the wall to
Cannot be deposited on fiber.

In the preferred embodiment of hot fiber processing, the high temperature of the fiber is at a weltdown point where the fiber has not yet cooled below the temperature required for the CVD reaction.
This can be achieved by placing the reaction chamber sufficiently close to the int or neckdoe+n point).

Here, the elution point refers to the fiber preform (prif
The point at which the preform is heated to a temperature sufficient to pull it out from the ors. The preform is a rod with a diameter of several centimeters. Generally, optical fibers are made by heating the end, or elution point, of a preform. At the elution point, the preform is nearly dissolved and becomes a thick viscous liquid at that point. The fiber is then drawn out of this liquid region. Since the elution point is relatively high temperature, many CVD processes can be performed using this heat source.

By using this heat source, the expense and complexity of an additional second heat source to heat the fiber can be avoided. Furthermore, methods such as RF heating and laser heating as disclosed in the above-mentioned Japanese Patent Application Publication No. 54-151947 are not suitable for heating optical fibers because the fibers are very thin, non-conductive, and transparent. Not particularly appropriate. Another advantage of using heat from the elution point is that the newly drawn fiber is not subject to the stresses that would occur if the fiber were cooled before being reheated to a temperature that would pass it through a CVD reaction. That's true. Additionally, the newly drawn fiber has an initial surface with poorly formed bonds that increases the bond strength of the coating formed near the elution point.

This hot fiber CVD process uses a reaction chamber with an air isolation chamber at one end and a liquid isolation chamber at the other end. The reactants supplied to the reaction chamber are selected to deposit a sealing coating on the fiber. In one embodiment used to produce a fiber with a silicon wear coating on the outside of the sealing coating, liquid silicone is used as the liquid in the liquid isolation chamber. Other coating materials, explicitly provided as liquids, may also be used in the liquid isolation chamber.

The use of at least one liquid isolation chamber is important to achieve high withdrawal speeds (of the order of 10 m/s). When gas isolation chambers are used at both ends of the reaction chamber, as in conventional FIG. 1, it is very difficult to prevent ambient air from being drawn into the reaction chamber by the moving fibers. Intake port 12.111.112. and by a flow controller controlling the flow of gas through the outlet 13.
The increase in gas flow into the reaction chamber 1 caused by the intake of ambient gas through the frontage 18 is compensated by the increase in the gas flow through the frontage 19. Figures 3A-3C illustrate the relationship between fiber withdrawal speed and the diameter of the isolation chamber opening with respect to the ambient gas drawn in by the moving fiber. As shown in comparison to FIGS. 3B and 3A, some of the ambient gas drawn in by the moving fiber tends to be drawn through the isolation chamber. In FIGS. 3A to 3C, line 325 is the locus of the point where the gas flow rate is zero, and the shaded area 315 is
The gas is shown moving downward with the fiber. The fiber in FIG. 3B is drawn faster than the fiber in FIG. 3A, so the gas drawn in FIG. 3B is carried farther. Therefore, an increase in fiber drawing speed increases the amount of gas carried by the fiber across the opening 18, and at high speeds ambient gas is carried into the reaction chamber. In many CVD processes where the ambient gas is air,
The amount of oxygen drawn into the reaction chamber by the moving fiber significantly reduces the quality of the coating deposited in the CVD reaction.

First, by lengthening the gas isolation chamber 16 to increase the time that the fiber passes through the gas isolation chamber 16, it appears possible to suppress ambient gas from entering the reaction chamber.

That is, the entrained air can diffuse away from the fiber and the inert gas (flowing out of the opening 18)
This increases the amount of time it takes for the material to be carried out of the opening 18. However, in hot fiber processing where high temperatures are obtained by placing the reaction chamber near the elution point, the length of the upper isolation chamber is limited because the reaction chamber must be near the elution point. At a withdrawal speed of 1 m/s, the reaction chamber must be located at around 15c+++ from the elution point. Furthermore, to avoid damage to the gas isolation chamber 16, this isolation chamber must not be located too close to the elution point.

These constraints limit the length of the upper isolation chamber to values inadequate to prevent the moving fiber from drawing ambient gas into the reaction chamber. This problem is found to occur over a wide range of speeds in hot fiber processing using heat from the elution point. In the above process, the rate of fiber cooling is
At a given reaction temperature, the reaction chamber must have a distance to the elution point that increases approximately linearly with the withdrawal rate, which is largely independent of the withdrawal rate. However, the characteristic distance over which the ambient air carried by the fiber is drawn also increases with the drawing speed in a boron-linear relationship;
The problem of entrained air is largely independent of withdrawal speed.

Increasing the flow rate of inert gas through the inlet 111 and into the gas isolation chamber 16 and/or decreasing the diameter of the opening 18 sufficiently will increase the flow rate of the inert gas through the fiber It also appears to generate sufficient shear flow behind the fiber to dislodge the entrained ambient gas layer from the fiber before it enters the reaction chamber. However, according to Bernoulli's equation, the relative motion between the fiber and the inert gas flowing through the aperture 18 creates a force on the fiber that tends to pull the fiber toward the end of the aperture.

The fiber is drawn into the edge of the opening and its contact with the walls of the isolation chamber 16 causes scratches.
The fiber must be tensioned to generate a restoring force toward the center of the aperture 18 that is greater than the force toward the edges of the aperture 18 to avoid being exposed to the force. Unfortunately, however, the increase in tension on the fiber required to offset the increase in Bernoulli force increases the amount of surface defects in the fiber. Therefore, the air drawn in may simply reduce the diameter of the opening 18 and/or
It cannot be removed from the fiber by increasing the flow rate of inert gas through 11. It is also possible to increase the diameter of the opening 18 to provide room for vibration of the fiber so that the fiber does not come into contact with the surrounding area of the opening 18. However, as shown in FIG. 3C, this increase in diameter also increases the amount of gas drawn, thus negating the benefit of the increased flow rate of inert gas through the intake port 111.

A liquid seal (isolation chamber) is advantageous because it inhibits the moving fiber from drawing in gas after its passage. Typically, in optical fiber processing, the upper isolation chamber should be a gas isolation chamber to avoid scratches and chemical reactions with the hot, freshly drawn fiber.

However, the bottom isolation chamber may be liquid if the CVD coating is not damaged or chemically attacked by the liquid in the isolation chamber.

CV using two gas isolation chambers as in the conventional Figure 1
In chamber D, the increase in gas flow into the reaction chamber 11 due to the gas being drawn through opening 18 is compensated by the increase in gas flow through opening 19 due to the drawn gas. On the other hand, if at least one of the two gas isolation chambers is a liquid isolation chamber, the gas is transported through one isolation chamber to compensate for changes in gas flow through the other isolation chamber. I can't. In a system with one gas isolation chamber and one liquid isolation chamber, velocity changes will slightly change the gas flow rate through the opening in the gas isolation chamber, but in other systems controlled by the flow controller. With respect to the input and output ports, a slight change in gas flow rate creates a pressure change in the reaction chamber and gas isolation chamber sufficient to reproduce the previous gas flow rate at the opening of the gas isolation chamber. This pressure change reduces the tendency of faster moving fibers to transport ambient gas through the gas isolation chamber.

In hot fiber CvD processes for depositing carbon or carbon-containing coatings on optical fibers, the reaction rate has been observed to be maximum at a temperature Tm between the temperature of the elution point and typical room temperature. As a result, essentially all coatings are
It has been observed that the fiber is deposited while within a relatively narrow temperature range near the TM. For CVD coating treatment using reactive methylacetylene, the Tm is 1400°C.
That's about it. In a system that uses the heat at the elution point as the heat source for the hot fiber, at a withdrawal speed of 1 m/s, the coating is deposited in the reaction chamber by several cl! Generate at a distance within I. Increasing the withdrawal speed does not significantly affect the thickness of the deposited film as long as the reaction chamber covers the entire distance over which more or less full deposition is performed. In such CvD processes where carbon coatings are deposited on the fibers, the carbon coatings have been found to be too thin to be hermetic.

There is a need in the prior art to provide a coating method that deposits a carbon coating of sufficient thickness to provide a hermetic seal, as described. In order to achieve carbon deposition rapidly and with sufficient thickness, it has been found necessary to use a carbon source containing triple-bonded carbon atoms. Acetylene can be used, but typically the acetylene is fed to a vessel containing acetone since pure acetythelene decomposes on the feed line at a rate of about 15 pounds per square inch or more. The amount of acetone supplied to the reaction chamber together with acetylene is sufficiently large to have an adverse effect on the film produced. Therefore, methylacetylene has been found to be the preferred choice of triple bond carbon source.

A small amount of oxygen getter should be included in the reaction gas to combine with the small amount of oxygen that is emitted from the optical fiber or drawn into the reaction chamber through the gas isolation chamber during the CVD coating. A particularly useful choice of oxygen getter is silane. This is because it not only has a high affinity for oxygen, but also prevents reaction products such as tar from impairing equipment operation. When methylacetylene is the only reactant, a tar-like film is deposited on the walls of the reaction chamber. Due to the effect of thermophoresis, this reaction product is not deposited on the fiber. However, the deposition on the walls of the reaction chamber often requires time-consuming removal and cleaning of the reaction chamber. More importantly, these reaction products are produced in the vicinity of the fiber inlet and reaction chamber outlet to a thickness sufficient to prevent gas flow even in a single treatment. This causes the fiber to be rubbed and scratched by the end of the fiber inlet. In addition, the deposits may be thick enough that the diameter of the fiber inlet is small enough, or the deposits near the outlet are quite thick (and the fiber is in contact with one or both of these deposits). A small amount of a silicon-containing reactant, e.g. silane (approximately 2 of the reactant volume)
%), the reaction products are turned into a light powder, which is moved away from the fiber by thermophoresis and more easily ejected from the reaction chamber outlet.

[Embodiments of the invention]

FIG. 2 is a cross-sectional view of a CVO furnace in which the present invention can be practiced, having one gas isolation chamber and one liquid isolation chamber. That is, a cross-sectional view of a chemical vapor deposition furnace suitable for on-line deposition of coatings on fiber 20 and for depositing carbon coatings on optical fibers, particularly at fast withdrawal speeds. In the case of optical fiber, the fiber is drawn on-line through a Cv-mouth furnace where it is protected by a deposited coating before being wound onto a take-up reel. The furnace includes a reaction chamber 21 with a pair of isolated chambers 26 and 2 at each end.
It is terminated with 7. The reaction chamber 21 has a reactant intake port 22
and a discharge port 23. Fiber openings 24, 28 and 29 in isolation chambers 26 and 27 allow the fibers to be drawn on-line through the reaction chamber for chemical vapor deposition of the coating.

The reaction chamber is arranged vertically with a gas isolation chamber 26 at the top, so that the weight of the fibers is distributed through the openings 24, 28 .
This avoids creating a sag that would tend to bring the fiber into contact with the wall defining the fiber. In the horizontal vapor deposition process, this sagging gas isolation chamber 26 is used. The bottom isolation chamber is a liquid isolation chamber 27 having an inlet 212 for admitting liquid therein. Most of the reaction chamber 21 is filled with a vacuum bottle 213 that forms a cylindrical channel 214 around the fiber 20. The diameter of the channel is approximately 31 mm. The narrowness of the channel allows the reactant gas or gases to pass in close proximity to the fiber and efficiently react with the fiber in cold-wall hot fiber processing. In other embodiments, to further maintain cylindrical symmetry in the device, each inlet and each outlet are connected to a cylindrical gas transport channel that supplies gas to or leaves the furnace with cylindrical symmetry. . Additionally, an inert gas is supplied through another inert gas inlet 220 located directly above the isolation chamber 27 to prevent the reaction gas from reacting with the liquid in the isolation chamber 27 .

In optical fiber deposition, this process is a cold-wall hot fiber process, where a temperature gradient is created,
This creates a pressure gradient across the particles within the reaction chamber through thermophoresis, and thus the particles are inhibited from depositing onto the fiber. The fiber is drawn from a preform mounted vertically above the furnace. Heat the bottom of the preform to the elution point with an RF heater operating at about 2300°C. The fiber is pulled online through a reaction chamber for CvD deposition of the coating. High fiber temperatures are obtained by locating the furnace sufficiently close to the elution point. The fiber is maintained at an elevated temperature during entry into a reaction chamber where chemical vapor deposition occurs on the surface of the fiber. Vacuum bin 213 reduces the cooling rate, thereby increasing the time that the fiber temperature remains within the temperature range where a sufficient CVD coating will occur.

1 meter per second of carbon coating thick enough to create a sealing coating
An extremely fast coating process is required to deposit fibers at fiber draw rates of . Generally, a carbon source containing at least one triple bonded carbon should be used as the reactant. Although acetylene has been found to react sufficiently quickly, it is preferable to use methylacetylene since it must be stored in a container containing acetone. The latter carbon source does not allow the introduction of acetone into the reaction chamber. The presence of acetone is undesirable because it provides oxygen that can enter the fiber coating.

In processes using methylacetylene, deposition essentially only occurs when the fiber is in the temperature range between 800°C and 1400°C. At a drawing speed of 1 m/s and in the temperature range mentioned above, the fiber cools in the reaction chamber with a displacement of a few c111. The reaction chamber is close enough to the elution point (
, it is important that the fiber remains within the above temperature range during passage through the reaction chamber. Preferably, the fiber is within the above temperature range while the fiber is within channel 214. This requires that the top of channel 214 be about 15 cm or less from the elution point for a 1 m/sec withdrawal process. In order to keep the top of the gas isolation chamber 26 far enough away from the elution point so that the gas isolation chamber 26 is not damaged by the high temperatures generated at the elution point, the length of the gas isolation chamber 26 and the opening of the outlet 23 must be adjusted. The length of the adjacent reaction chamber regions 223 may each be about 2 cm.

Isolation chamber 27 is chosen to be a liquid isolation chamber to prevent ambient gas from being drawn into reaction chamber 21 by the moving fiber. Flow controllers 216 , 217 .

218 and 219 are the intake port 22 and the discharge port 23, respectively.
, inert gas intake 220. and controlling gas flow through intake 211. The amount of gas flowing from isolation chamber 26 to the reaction chamber through opening 24 is equal to the difference between the flow rate through controller 217 and the sum of the flow rates through controllers 216 and 219.

Similarly, the gas flow rate through opening 28 is the difference between the flow rate through controller 218 and the flow rate through opening 24 .

Accordingly, the average flow rate through openings 24 and 28 is determined by flow controllers 216-219. Note that this is independent of fiber draw speed. 1, in which the degree of freedom added by the opening 19 in the bottom gas isolation chamber allows the flow rate through the opening 18 to be limited to the outlet 13 and the intake 1.
2. cannot be determined by controlling the flow rate through 112 and 113.

Changes in fiber velocity slightly change the flow rate through opening 28, but these small changes change the pressure within the gas isolation chamber as it is reset to the flow rate commanded by the flow controller. . Therefore, the flow rate through opening 28 is not affected by fiber velocity. This means that every second
It is important to have the ability to prevent drawing ambient gas into the reaction chamber at withdrawal rates exceeding m. Additionally, to maintain a constant fiber diameter despite preform changes, fiber draw speeds are typically up to 3
The above is important in producing a uniform coating since the 0% change is made. This improved deterrent to ambient gas being drawn in makes the gas isolation chamber shown in FIG.
It allows the use of larger openings 2B (diameter >3+uw) compared to the individual furnace openings i8 (of the order of 0.3 to ll1l11).

If a silicone buffer coating is desired in addition to the sealing coating,
The liquid in the bottom isolation chamber should be silicone. In this case, it is necessary that the fiber be sufficiently cooled so that the silicone coating produced is not adversely affected by the temperature of the fiber. This requires that the fiber be cooled after passing through channel 214 where the CVD reaction occurs. To provide this cooling, a non-thermal insulation portion 224 of the reaction chamber is included below the thermal insulation bin 213. For a 1 m/sec process using silicone as the liquid in the bottom isolation chamber, the length of thermal insulation 224 should be on the order of 0.75 m.

The use of a triple bond carbon source increases the reaction rate so much that a diluent gas needs to be supplied with the carbon source reactant. Preferably, the diluent is helium or hydrogen;
The low atomic weight of the diluent gas increases its velocity and heat transfer to the reactant gas, allowing the hot fiber to heat the reactant gas more effectively. For coating at 1 m/sec, methylacetylene is supplied from the intake port 22 at 0.6 liters/min. Diluted H 2 , or He, is supplied through intake 220 at 0.6 liters per minute to dilute the reactant gas and prevent it from reacting with the liquid in isolation chamber 27 . N2 is supplied from the intake port 211 at 1 liter per minute, and gas is discharged from the outlet 23 at 1.5 liters per minute. The resulting total flow rate exiting through opening 28 is 0.7 liters per minute.

In CVD processes using methylacetylene, the air drawn in with the fiber should be prevented from reaching the outlet to avoid the risk of creating an explosive mixture. In CVD processes where air is allowed to reach the outlet, gas isolation chamber 26 may be removed from the reaction chamber. in this case,
Area 223 near the outlet serves as a gas isolation chamber. The upward flow of gas within the narrow channel 214 prevents this air from entering the channel 214. Therefore, channel 2
14 is a region where the CVD reaction can occur without being affected by the drawn-in air. For example, in the process of depositing silicon nitride on optical fiber, silane and ammonia reactants are supplied through reactant inlet 22. As air is removed from channel 214, silicon nitride is deposited in that region. In area 223, area 2
Oxygen in the air drawn into 23 reacts with the silane to form a powder. This powder is not deposited on the fiber but is discharged from the discharge port 23. As a result, oxygen drawn into region 223 does not cause the CVD process to occur in this region.

〔Effect of the invention〕

As is clear from the above description, the present invention is a hot fiber cold wall Cvo furnace, which is provided with a gas isolation chamber and a liquid isolation chamber, and which eliminates undesirable particle deposition on the fiber. , defects, and pin-pole-free coatings can be formed on the fiber.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a conventional optical fiber coating furnace having a pair of gas isolation chambers, FIG. 2 is a sectional view of an optical fiber coating furnace in which the present invention can be practiced, and FIG. 3A. Figures 3B and 3C illustrate the relationship between gas isolation chamber diameter and fiber withdrawal speed with respect to ambient gas being drawn in by the moving fiber. 11: Reaction chamber. 12, 13.111.112: Gas intake or outlet. 16, 17: Gas isolation room. 14, 15.18.19: Opening. 21: Reaction chamber. 26: Gas isolation room. 27: Liquid isolation chamber. 24, 28.29: Opening. 22, 23.220.221: Gas intake or outlet. 216, 217.218.219: Flow rate controller.

Claims (1)

[Claims] Cold wall hot fiber chemical vapor deposition (CVD)
) A method for forming an optical fiber coating, the method comprising: forming an optical fiber coating.