JPS5851892B2 - Method and apparatus for manufacturing optical glass products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for manufacturing an optical glass article that can be formed from a pultruded stock and that is capable of drawing light waveguide filaments.

Optical waveguides, which are the most promising medium for use in optical communication systems operating in the visible or near-visible spectrum, typically combine a transparent core with a transparent outer layer having a smaller refractive index. It consists of an optical filament surrounded by a material.

However, because strict optical requirements are imposed on transmission media used in optical communication systems, conventional glass fiber optics cannot be used as such transmission media.

This is because traditional glass fiber optics have too much attenuation due to both scattering and impurity absorption.

Therefore, unique methods had to be developed to form very high purity glasses into filaments.

Certain glass manufacturing methods, particularly vapor deposition methods, are commonly used to form optical waveguide materials.

In one such method, raw material vapor is pumped into a heated substrate tube where it reacts and
Forming materials that are deposited in successive layers.

The glass and tube combination so deposited is crushed to form a drawn blank which is subsequently heated and drawn into a light waveguide filament.

In order to obtain uniform deposition along the length of the substrate tube described above, a sequential deposition method (5erial deposition method) was used.
nprocess) is used.

That is, the reactants are fed to the end of the tube, but deposition occurs only in the narrow section of the tube that is heated by the flame.

The flame moves up and down the tube. As the flame moves up the tube, it moves the reactants and thus the glass deposition area along the tube.

In this case, once the flame has completed its upward movement along such a tube, it now moves downward along the tube in preparation for the next glass deposition step which occurs when it moves upward again.

One of the limitations of such sequential deposition methods is that the effective mass deposition rate is relatively low.

One possible way to increase such a deposition rate is to increase the inner diameter of the substrate tube so as to increase the collection surface area, but this is because the heat to deposit the glass is supplied from the outside of the tube. , if the diameter of the tube is increased, the steam temperature at the axis of the tube will be lowered.

Additionally, the flow profile across the tube is such that maximum flow occurs axially within the tube.

Therefore, as the diameter of the tube increases, the reactant vapor flows through the region near the walls of the tube where the reaction temperature is highest, i.e., the soot-like reaction products are more easily collected on the heated region of the tube. The amount of

Therefore, as the diameter of the substrate tube increases, the proportion of soot deposited on the substrate tube decreases accordingly.

In order to increase the effective mass deposition rate in sequential deposition processes of the type described above, according to the invention, a glass-forming vapor mixture is flowed through an elongated hollow cylindrical substrate tube, and the glass-forming vapor mixture is flowed into said tube and introduced into it. heating the vapor mixture with a heat source, the heat source being moved longitudinally with respect to the tube to establish a hot zone within the tube, and at least a portion downstream within the so established hot zone. creating a suspension of migrating particulate material, with at least a portion of the suspension resting on the inner surface of said tube to form a deposit on said inner surface. The method of manufacturing comprises directing the flow of the vapor mixture by flowing a gas flow through the axial region of the tube in the hot zone of the tube, which does not adversely affect the properties of the optical glass article. A method for producing an optical glass article, characterized in that it is confined in an annular channel adjacent to the inner surface of the tube and spaced from the longitudinal axis of the tube, thereby increasing the deposition efficiency of the reaction of said vapor mixture. is provided.

In accordance with the present invention, an axial portion of a suitably supported cylindrical substrate tube is heated to produce an optical glass preform from the hollow cylindrical substrate tube that can be drawn into an optical filament. heating means for forming a hot zone within the tube; means for imparting relative longitudinal motion between the heating means and the substrate tube; and means for directing the moving flow of the vapor mixture to the substrate tube. and a means for introducing it into one end of the
In this case, the vapor mixture may react within the hot zone to form a suspension of particulate material, which suspension is transferred downstream, where at least a portion of the suspension is transferred to the inner surface of the substrate tube. In an apparatus for producing optical glassware that is suspended above the hot zone of the substrate tube, the gas flows through an axial region of the substrate tube, wherein the gas directs the flow of the vapor mixture. means for confining the hot zone in an annular channel adjacent the inner wall of the substrate tube, thereby substantially confining the reaction of the vapor mixture to an annular region adjacent the wall of the substrate tube; An apparatus for manufacturing an optical glass product is provided.

The means for directing the flow of gas through the axial region of the substrate tube described above comprises a tube, preferably a gas guide, located at one end of the cylindrical substrate and terminating at one end in the vicinity of the hot zone. Advantageously, it consists of a baffle tube.

The means for longitudinally moving the tube relative to the substrate tube moves the tube synchronously with the movement of the heating means.

The gas flow exiting the baffle tube forms a gaseous mandrel within the hot zone that confines the vapor mixture in an annular channel adjacent the substrate surface.

Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show a prior art system including a base tube 10 having a handle tube 8 secured to its upstream end and an exhaust tube 12 secured to its downstream end. There is.

Tubes 8 and 12 are chucked onto a conventional glass rotary lathe (not shown) and the combination is rotated as indicated by the arrows.

The handle tube is an inexpensive glass tube with the same diameter as the substrate tube, but it does not form part of the resulting light waveguide and may be omitted.

Hot zone 14 (FIG. 2) is moved through tube 10 by moving heating means 16 as shown schematically by arrows 18a and 18b.

Heating means 16 may comprise any suitable heat source, such as a plurality of burners surrounding tube 10.

Reactants are introduced into the tube 10 through an inlet tube 20 that is connected to multiple gas and vapor sources.

In FIG. 1, the flow meter is represented by a circle surrounding the letter F.

Oxygen source 22 is connected to inlet tube 20 by flow meter 24.
and further connected to reservoirs 32, 34 and 36 by flow meters 26, 28 and 30, respectively.

A boron trifluoride source 38 is connected to tube 20 by a flow meter 40.

Reservoirs 32, 34, and 36 contain normally liquid reactant materials that are introduced into tube 10 by bubbling oxygen or other suitable carrier gas through them. Ru.

Exhaust material is exhausted through exhaust tube 12.

Although not shown, a mixing valve and isolation valve mechanism may be utilized to meter the flow rate and make other necessary adjustments to the composition.

Burner 16 initially moves at a low speed relative to tube 10 in the direction indicated by arrow 18b in the same direction as the reactant flow direction.

The reactants react in hot zone 14 to form a powdery suspension of soot or particulate oxide material, which suspension is conveyed downstream to region 42 of tube 10 by the moving gas.

Generally, 20% and 7% of the reaction products produced in the vapor stream
0%, a soot having the desired glass composition is produced and the soot is deposited on the substrate surface.

It can be seen that substantially no soot is formed in the region 46 of the tube 10 upstream from the hot zone 14.

As burner 16 continues to move in the direction of arrow 18b, hot zone 14 moves downstream such that a portion of soot accumulation 44 extends into the hot zone and is thereby fused into a unitary homogeneous material. A glass layer 48 is formed.

Process parameters such as temperature, flow rates, reactants, etc. are described in the Proceedings of the IEEE.
) 1280 (1974) by J. BoMacChesney.
) et al. and Applied Optics
W, G, Fren in 15 (1976)
It is described in the paper by ch et al.

Also, John Wiley and Sons, Inc.
s, Inc.) (1966) Published by C.F. Powell et al.
Reference is also made to the textbook entitled VaporDeposition).

Tube 10 with burner 16 adjacent to exhaust tube 12
, the temperature of the flame decreases and the burner 16 returns to the inlet end of the tube 10 in the direction of arrow 18a.

Thereafter, additional layers of vitreous material are deposited within tube 10 in the manner described above.

After a layer suitable to act as a jacket and/or base material for the optical waveguide filament has been deposited, the temperature of the glass blank thus formed is lowered to a high silica-containing glass in order to collapse the tube 10. Approximately 2200 in the case of
It is raised to ℃.

This can be accomplished by slowing down the speed of movement of the hot zone.

The glass material can then be drawn according to known techniques to form a light waveguide filament with the desired diameter.

Elevated temperatures are used to optimize the process from a reaction point of view.

In the case of conventional silica-based systems, the temperature of the substrate wall is generally maintained between about 1400'C and 1900C at the location corresponding to the hot zone.

The indicated temperature is the temperature measured by a radiation pyrometer focused on the outer surface of the tube.

One of the factors limiting the deposition rate is the rate at which the deposited soot is sintered to form a transparent glass layer.

For a glass of a certain composition to be deposited, there is a maximum layer thickness of glass that can be sintered using an optimal combination of hot zone width, peak hot zone temperature, and burner travel speed.

If the thickness of the sintered glass layer is kept at a maximum value for different tube diameters, the deposition rate theoretically increases proportionally to the inner diameter of the tube due to the increased surface area. It should be done.

However, due to the flow dynamics and soot particle dynamics properties of the reactant vapor system, the fraction of produced soot that deposits on the substrate tube decreases with increasing tube diameter, thereby reducing the effective A decrease is caused.

According to the invention, it is confined within the hot zone in an annular channel adjacent to the wall of the substrate tube.

For this purpose, as shown in FIG. 3, a portion of the gas supply tube 50 extends into the end of the substrate tube 52 into which the reactants are introduced.

That portion of tube 52 within tube 52 terminates just before the hot zone created by moving heat source 56 .

Tube 50 is mechanically coupled to burner 56 by means represented by dashed line 58 to ensure that tube 50 is maintained at an appropriate distance upstream of hot zone 54.

Alternatively, the heat source and gas supply tube may be fixed and the rotating base tube 52 may be moved.

The inlet end of the tube 52 is connected to the tube 50 by a collapsible member 60, with a rotary seal 62 disposed between the member 60 and the tube 52.

As shown in FIG. 4, which is a cross-sectional view of the hot zone and the adjacent area of tube 52, tube 50
The gas emerging from the tubes 50 and 52 provides an effective mandrel or barrier for reactants flowing in the direction of the arrows, thereby forcing these reactants to the walls of tube 52 in hot zone 54. Confined to adjacent annular channel.

At some distance downstream of the hot zone 54, the gas from the tube 50 continues to act as a barrier to the soot formed in the hot zone, thereby causing the soot to deposit on the walls of the tube 52, as shown at 44'. This will increase the probability of doing so.

Dashed line 66 in FIG. 5 represents the boundary between the gas exiting tube 50 and the reactant vapors entering hot zone 54.

The gas supplied to the hot zone by tube 50 can be any gas that does not have an adverse effect on the resulting optical waveguide preform.

Oxygen is preferred as such a gas.

This is because oxygen satisfies the requirements and is relatively inexpensive.

Alternatively, other gases such as argon, helium, nitrogen, etc. may also be used.

As shown in FIG. 4, the end of the tube 50 is
It is separated from the hot zone by a distance X, which must be large enough to prevent soot deposition thereon.

The distance X will vary depending on parameters such as the width of the burner and the temperature of the hot zone.

The following findings were made for a deposition system in which tubes 50 and 52 have outer diameters of 20 mm and 38 mm, respectively, and their wall thicknesses are 1.6 mm and 2 mm, respectively.

The burner face orifice was placed in a circle with a diameter of 45 mm.

In this system, it was observed that soot would deposit on the tube 50 if the distance X was approximately 13 millimeters.

The mixing of gas and reactant vapor streams flowing through the gas supply or baffle tubes 50 increases with longitudinal distance from the baffle tubes 50.

Benefits of confining the reactant vapors to an annular region proximate the wall of tube 52 may be obtained when distance X is up to about 15 centimeters.

Best results are obtained when distance X is in the range 25-75 millimeters.

The size and shape of tube 50 must be such that substantially laminar flow exists in the hot zone and the region immediately downstream thereof.

The turbulence created by tube 50 will pick up soot particles and carry them downstream to the exhaust tube.

In the conventional deposition methods described above in connection with FIGS. 1 and 2, deposition efficiency decreases as the tube diameter increases beyond a predetermined size.

Generally, increasing the deposition rate with increasing tube diameter can be achieved by increasing the tube diameter to about 30 millimeters.

However, for tubes with diameters greater than 30 mm, the deposition efficiency decreases and it becomes difficult to further increase the deposition rate.

However, the use of baffle tubes confines the reactant vapors to a fixed distance from the inner surface of the substrate tube 52, thereby providing optimal deposition efficiency regardless of the diameter of the substrate tube.

The maximum dimensions of the outer tube 52 are limited by the dimensions of the tube such that the internal holes can be plugged to form a light waveguide preform.

The wall thicknesses of baffle tube 50 and base tube 52 are typically kept relatively small, ie, a few millimeters.

Cylindrical baffle tubes, such as those shown in Figures 3 and 4, are easily manufactured and deliver a body or mandrel of gas to the hot zone of the substrate tube without introducing unduly large turbulence. It was recognized that the system fully demonstrates its functions.

Other shapes, such as those shown in FIG. 6, can also be used to perform this function.

The direction of gas flow from tube 70 is indicated by arrow 72.

To demonstrate the improvement in deposition rate and efficiency, the deposition apparatus was operated both with and without baffle tubes 50, without changing all other process parameters.

A device similar to that shown in FIG. 1 was used to supply the reactant streams, but only one reservoir 32 was used.

Oxygen is flowed into reservoir 32 containing S i CA'4 maintained at 35° C. to provide a flow of approximately 2.5 g 7 min 5 iC4.

The flow rate of BCl3 is 92SCcrrL, and the flow rate is 24
The oxygen flow rate through was 2.451 m.

The substrate tube was a borosilicate glass tube with an outer diameter of 38 mm and a wall thickness of 2 mm.

A borosilicate glass having a composition of approximately 14% B2O3 and 86% 5102 by weight was deposited.

From the flow rates of S i CA'4 and BCl3, the oxide production rate was calculated to be 0.85.9/min S t 02 and 0.2'l/min B2O3.

If no baffle tube is used, the deposition rate is 0.
．． 251 g/min S t 02, and the deposition efficiency is 26.
It was 2%.

Next, the above system has an outer diameter of 20 mm and a diameter of 1.
It was modified by adding a fused silica baffle tube with a wall thickness of 6 millimeters.

The end of the baffle tube is located 5 minutes from the center of the hot zone.
They were separated by a distance of 0 mm.

By using baffle tubes, the deposition rate increased from 0.251.97 minutes to 0.451 g/min and the efficiency increased from 26.2% to 43.2%.

Table I shows the effect on deposition rate and efficiency of varying process parameters.

For Examples 1 to 6 of this table, the base tube is formed from a 38 mm outer diameter borosilicate tube with a wall thickness of 2 mm, and the baffle tube is formed from a 38 mm outer diameter borosilicate tube with a wall thickness of 2 mm. It was constructed of fused silica tubing with a wall thickness of 20 millimeters outside diameter.

During the course of these experiments, multiple glass layers were deposited within the substrate tube in the manner described above.

After 10-30 layers were deposited, the substrate tube was broken and the thickness of each layer was measured under a microscope.

The deposition rate is calculated from the layer thickness, and the deposition efficiency is the deposition rate in g/min divided by the total mass flow of soot entering the tube, assuming 100% oxide conversion. defined.

The best results thus obtained were a deposition rate of 0.691 g/min and an efficiency of 40.3%.

Graded Intex (g
A specific example of manufacturing a raded 1ndex ) type optical waveguide filament is as follows.

A tube made of commercial quality borosilicate glass with an outside diameter of 38 millimeters and a wall thickness of 2 millimeters was cleaned by sequential immersion in hydrofluoric acid, deionized water, and alcohol.

The base tube is approximately 120 cm long, having one end to a 90 cm long, 65 mm outside diameter exhaust tube, and a 60 cm long exhaust tube having the same diameter and wall thickness as the base tube. Each other end is attached to a meter handle tube.

The tube combination is inserted into a lathe with each tube rotatably supported.

The free end of the handle tube is provided with a rotating seal that includes a fused silica baffle with an outside diameter of 20 mm and a wall thickness of 1.6 mm.
A 180 cm long section of tubing is inserted.

The baffle tube is supported at two different points along its length on supports that move with the burner.

The burner moves through the 100 cm length of the base tube at a speed of 25 cm/min.

The burner is heated to 1800°C on the outer surface of the base tube.
is adjusted to give a deposition temperature of

A layer of glass is deposited while the burner is moving, but when the burner reaches the end of its travel it returns to its starting point at a speed of 100 cm/min.

Oxygen flows into the baffle tube at a velocity of 2.551 m.

SiCl+, GeCA'4 and POCl3, respectively
There are three reservoirs containing
maintained at a temperature of

Oxygen in the first and third reservoirs is 0.31 pm each.
and flowing at a rate of 0.561 pm during the entire deposition process. O91 min SiC#, and 0.175ji
/min POCl3 is supplied to the substrate tube.

What is the rate at which oxygen is supplied to the second reservoir, OA? pm to 0
．． increases linearly to 713 pm, so the burner
Ge C14 is supplied to the substrate tube in an amount between O and L5i/min during 0 passes.

That is, during the first pass of the burner along the substrate tube, no GeC14 is supplied to the substrate tube, but the amount of it is 2.0 g 1 minute GeC during the last pass of the burner.
It is increased linearly on another pass through the burner until l4 is supplied to the base tube.

BC71?3 is fed to the substrate tube at a constant speed of 155 (J7!) and bypass oxygen is fed to the substrate tube at a speed of 2.551 m.

During a period of 3 hours and 20 minutes, the burner passes along the substrate tube 50 times, during which time the burner travel speed decreases to 2.5 cm/min and the temperature decreases at the outer surface of the substrate tube. The temperature rises to about 2200°C.

This collapses the base tube into a light waveguide preform with a dense cross section throughout.

The usable length of this preform is approximately 84 centimeters.

The deposition rate is about 0.68.97 minutes and the average deposition efficiency is about 39.5%.

The preform or blank obtained as described above is then heated to a temperature (approximately 2000° C.) such that the material has a sufficiently low viscosity for pultrusion.

This structure is drawn to form approximately 25 kilometers of optical waveguide filament having an outer diameter of approximately 110 μm.

Although specific embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications and changes can be made without departing from the spirit of the present invention and the scope of the claims. It should be understood that modifications and variations are also part of the invention.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an apparatus for depositing a glass layer in a tube; FIG. 2 is a diagram showing a portion of the tube shown in FIG. 1 and showing the conditions observed during the process; FIG. 4 and 5 are cross-sectional views of the apparatus according to the invention, showing the conditions occurring during the process; FIG. Modified baffles that can be used in the device of the invention
Figures 1 and 2 are views showing the ends of the tubes, in which 8 is the handle tube, 10 is the base tube, 12 is the handle tube;
is the exhaust tube, 14 is the hot zone, 16 is the burner,
20 is an inlet tube, 22 is an oxygen supply source, 26-30.
40 is a flow meter, 32 to 36 are reservoirs, 44 is soot accumulation, 4
8 is a glass layer, 50 is a gas supply tube (baffle tube), 52 is a base tube, 56 is a heat source, 56 is a burner, 54 is a hot zone, and 62 is a rotary seal.

Claims (1)

Claims: 1. Flowing a glass-forming vapor mixture through an elongated hollow cylindrical substrate tube, heating the tube and the vapor mixture introduced therein with a heat source, the heat source extending longitudinally with respect to the tube. moving to establish a hot zone within the tube, creating a suspension of particulate material within the hot zone at least a portion of which migrates downstream, and causing at least a portion of the suspension to be deposited on an inner surface of the tube. A method of manufacturing an optical glass article comprising: allowing a deposit to form on the inner surface of the tube; The flow of the vapor mixture is caused to flow through the axial region of the tube to confine the flow of the vapor mixture in an annular channel adjacent to the inner surface of the tube and spaced from the longitudinal axis of the tube. A method for producing optical glass products characterized by increasing the deposition efficiency of the reaction. 2. A method for manufacturing an optical product according to claim 1, wherein the annular channel is formed by inserting another tube into the base tube in a coaxial relationship therewith, and the optical fiber, the outlet end of the inserted tube terminating in front of the hot zone and moving synchronously with the hot zone, causing the flow of gas to exit the end of the inserted tube adjacent the hot zone; Method for manufacturing glass products. 3. A method for manufacturing an optical glass product according to claim 1 or 2, using oxygen as the gas stream. 4. A method for manufacturing an optical glass product according to one of claims 1 to 3, in which the substrate tube is brought to a temperature sufficiently high to close the pores thereof. A method for producing an optical glass product as described above, comprising heating to form the glass product in the form of a drawn stock. 5. A method for manufacturing an optical glass product as claimed in claim 4, wherein the optical drawing material is heated to the drawing temperature of the material and the material is drawn to form a light waveguide filament. A method for manufacturing glass products. 6. To produce an optical glass preform in a hollow cylindrical substrate tube that can be drawn into an optical filament, an axial portion of a suitably supported cylindrical substrate tube is heated to create a hot ink within the tube. heating means for forming a zone; means for imparting relative longitudinal motion between the heating means and the substrate tube; and means for introducing a moving flow of the vapor mixture into one end of the substrate tube. and means for the vapor mixture to react within the hot zone to form a suspension of particulate material, the suspension being transferred downstream where at least a portion of the suspension is within the substrate tube. In an apparatus for producing optical glassware adapted to rest on a surface, the gas is caused to flow through an axial region of the substrate tube in the hot zone of the substrate tube, and the gas directs the flow of the vapor mixture into the hot zone of the substrate tube. means 50 for confining the hot zone in an annular channel adjacent to the inner wall of the substrate tube, thereby substantially confining the reaction of said vapor mixture to an annular region adjacent to the wall of said substrate tube; An apparatus for manufacturing optical glass products, characterized in that: 7. An apparatus for manufacturing optical glass products according to claim 6, wherein the means for causing the gas flow to flow is located at the one end of the cylindrical substrate tube and extends one end from the substrate tube. another tube 50 terminating in the vicinity of said hot zone and means 58 for moving said tube longitudinally relative to said base tube 52 synchronously with the movement of said heating means 56;
Apparatus for producing optical glassware, wherein the gas flow is emitted from the one end of the tube 50. 8. Apparatus for manufacturing optical glass products according to claim 7, wherein oxygen is used as the gas stream.