U.S. patent number RE30,635 [Application Number 06/079,847] was granted by the patent office on 1981-06-02 for method of producing internally coated glass tubes for the drawing of fibre optic light conductors.
This patent grant is currently assigned to U.S. Philips Corporation. Invention is credited to Dieter Kuppers, Hans Lydtin, Ludwig Rehder.
United States Patent |
RE30,635 |
Kuppers , et al. |
June 2, 1981 |
**Please see images for:
( Certificate of Correction ) ** |
Method of producing internally coated glass tubes for the drawing
of fibre optic light conductors
Abstract
In the reactive deposition of the core material from a gas which
is passed through the tube onto the inner wall of the tube by means
of a plasma zone, while a relative motion is effected in the axial
direction between the tube and a plasma-producing device, the rate
of precipitation is increased without impairing the quality of the
core material coat, the reactive deposition being effected at a
pressure of from 1 to 100 Torr and a temperature zone being
superimposed on the plasma zone.
Inventors: |
Kuppers; Dieter (Aachen,
DE), Lydtin; Hans (Stolberg, DE), Rehder;
Ludwig (Aachen, DE) |
Assignee: |
U.S. Philips Corporation
(Tarrytown, NY)
|
Family
ID: |
5925814 |
Appl.
No.: |
06/079,847 |
Filed: |
September 28, 1979 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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610570 |
Sep 5, 1975 |
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Reissue of: |
852068 |
Nov 16, 1977 |
04145456 |
Mar 20, 1979 |
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Foreign Application Priority Data
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Sep 14, 1974 [DE] |
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2444100 |
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Current U.S.
Class: |
427/573; 138/145;
138/177; 204/164; 385/124; 427/167; 427/231; 427/237; 427/255.18;
427/255.19; 427/255.24; 427/575; 65/391; 65/417 |
Current CPC
Class: |
C03B
37/0183 (20130101) |
Current International
Class: |
C03B
37/018 (20060101); B05D 003/06 (); C23C
011/00 () |
Field of
Search: |
;427/38,39,163,167,231,237,255 ;65/3A,DIG.7,DIG.9 ;138/145,177
;204/164 ;350/96.31 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Powell, C. F., et al., Vapor Deposition The Electrochemical
Society, John Wiley and Son, Inc., New York (1966), p.
424..
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Primary Examiner: Smith; Ronald H.
Assistant Examiner: Page; Thurman K.
Parent Case Text
BACKGROUND OF THE INVENTION
This is a continuation of application Ser. No. 610,570, filed Sept.
5, 1975, now abandoned.
Claims
What is claimed is:
1. A method of producing internally coated glass tubes for drawing
fiber optic light conductors which consists of a core and a jacket
of glasses which have a mutually different refractive index,
comprising the steps of introducing into a glass tube surrounded by
a resonator a reactive gas mixture consisting of SiCl.sub.4 and
oxygen at a pressure of about 1 to 100 Torr, adding GeCl.sub.4 to
the gas mixture moving the tube relative to the resonator to form
.[.a.]. non-isothermal plasma zone within the tube, and heating the
tube to a temperature between 800.degree. C.-1200.degree. C. to
form a coating free of soot-like particles and consisting of a
plurality of layers of SiO.sub.2 doped with an increasing content
of GeO.sub.2.
2. A method as claimed in claim 1 wherein the gas mixture consists
of about 96% by volume of oxygen and 4% by volume of
SiCl.sub.4.
3. A method as claimed in claim 2 wherein up to 0.4% by volume of
germanium tetrachloride (GeCl.sub.4) is added to the reactive gas
mixture. .Iadd.
4. A method of producing internally coated glass tubes, for drawing
fibre-optic light conductors which consist of a core and a jacket
of glasses which have a mutually different refractive index,
comprising the steps of introducing into a glass tube surrounded by
a resonator a reactive gas mixture comprising SiCl.sub.4 and oxygen
at a pressure of about 1 to 100 Torr, moving the tube relative to
the resonator 2 and heating the tube to a temperature between
800.degree. C.-1200.degree. C. while activating the resonator to
form a nonisothermal plasma zone within the tube, whereby a coating
free of soot-like particles and consisting of a plurality of layers
of SiO.sub.2 is formed. .Iaddend. .Iadd.5. A method of producing
internally coated glass tubes, as claimed in claim 4, further
comprising the step of adding a dopant-forming compound to the gas
mixture. .Iaddend. .Iadd.6. A method of producing internally coated
glass tubes, as claimed in claim 5, wherein the dopant-forming
compound is one or more compounds from the group consisting of
TiCl.sub.4 AlCl.sub.3, and GeCl.sub.4. .Iaddend. .Iadd.7. A method
of producing internally coated glass tubes, as claimed in claim 5
or 6 wherein the dopant-forming compound is added to the gas
mixture at a constant rate. .Iaddend.
.Iadd. A method of producing internally coated glass tubes, as
claimed in claim 9, wherein the dopant-forming compound is added to
the gas
mixture at an increasing rate. .Iaddend. .Iadd.9. A method of
producing internally coated glass tubes, as claimed in claim 5 or 6
wherein the dopant-forming compound is added to the gas mixture at
a varying rate. .Iaddend. .Iadd.10. A method of producing
internally coated glass tubes, as claimed in claim 9, wherein the
dopant-forming compound is added to the
gas mixture at a decreasing rate. .Iaddend. .Iadd.11. A method of
producing internally coated glass tubes, as claimed in claim 9,
wherein the dopant-forming compound is added to the gas mixture at
a rate which will produce a coating whose index of refraction
increases toward a central axis of the tube. .Iaddend. .Iadd.12. A
method of producing coatings on walls of glass comprising the steps
of:
contacting at least a portion of the wall of the glass with a
mixture of a gaseous glass-forming compound and gaseous oxygen at a
pressure of about 1 to 100 Torr;
forming a plasma zone in the gas mixture in contact with the glass
wall portion;
heating the glass wall portion, to a temperature which is above the
temperature necessary to produce substantially stress-free coating
layers on the heated tube wall portion but which is below the
temperature at which there is substantial reaction of the mixture
in the gas phase, to produce a nonisothermal plasma zone; and
thereby causing a heterogeneous reaction to occur on the glass wall
resulting in the deposit on the glass wall of a glass coating.
.Iaddend.
.Iadd.13. A method as claimed in claim 12, characterized in that
the glass wall is in the form of a tube and further comprising the
step of causing relative movement between the plasma zone and the
tube. .Iaddend. .Iadd.14. A method as claimed in claim 13,
characterized in that the coating and the gas mixture are on the
inside of the tube, and the glass-forming compound is a silicon
tetrahalide. .Iaddend. .Iadd.15. A method as claimed in claim 14,
characterized in that the tube is heated to a temperature which is
not greater than 1200.degree. C. and not below 800.degree. C.
.Iaddend. .Iadd.16. A method as claimed in claim 15, characterized
in that the plasma is formed by means of a high frequency field or
a microware resonator. .Iaddend. .Iadd.17. A method as claimed in
claim 16, characterized in that a dopant-forming compound is added
to the gas mixture. .Iaddend. .Iadd.18. A method of producing a
fiber-optic light conductor comprising the steps of:
producing an internally coated glass tube as claimed in claim 17;
and
drawing the internally coated glass tube to form a a fiber-optic
light conductor. .Iaddend.
Description
The invention relates to a method for producing internally coated
glass tubes, consisting of a core and a jacket of glasses which
have a mutually different refractive index, by means of a reactive
deposition of the coating from a gas mixture which is passed
through the tube and which is brought to reaction in the tube.
The tubes produced in this manner are heated to a temperature which
is suitable for drawing and thereafter drawn to such an extent that
the diameter is reduced until the coating is brought to coincidence
and a light conductor of the required diameter is obtained.
Light conductors consist of a light-conducting core which is
embedded in a jacket of a lower refractive index. The core may, for
example, consist of quartz glass which has been doped with a few
percent of a metal oxide which increases the refractive index and
the jacket of undoped quartz glass.
For the doping of the core glass TiO.sub.2, GeO.sub.2 and Al.sub.2
O.sub.3 may, for example, be used. In the so-called self-focussing
fibre optic light conductors a parabolic change in the refractive
index across the radius is obtained by means of a continuous change
in the grades of doping. According to a known method such
internally coated quartz glass tubes are produced in which gaseous
SiCl.sub.4 and oxygen or a mixture of SiCl.sub.4, TiCl.sub.4 and
oxygen are passed through a tube brought there to reaction in the
gas phase by means of high frequency energization and probably
precipitated at least partly as a soot-like glass coat, which must
thereafter be melted or sintered. There is a danger that gases are
trapped which later on might form light-scattering centers. The
heat treatment makes the formation of a doping profile as required
for self-focussing fibre optic light conductors difficult, owing to
blurring due to diffusion.
The tube may consist of non-doped quartz glass. In this method a
uniform relative motion in .Iadd.an .Iaddend.axial direction may be
caused between the tube and a high frequency pulse which envelopes
the tube .[.a.]..Iadd.. A .Iaddend.uniform distribution of the
deposit is enhanced by the fact that the tube is rotated during the
coating procedure.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method of the
aforementioned kind in which the rate of deposition is relatively
large, in which coatings of a good quality are obtained and
.[.that.]. .Iadd.in which .Iaddend.the deposition is not the result
of a homogeneous reaction in the gas phase but of a heterogeneous
reaction on the wall. According to the invention this object is
realized by means of a method which is characterized in that in the
tube a non-isothermal plasma zone is produced for the activation of
the reactive deposition while a relative motion is caused between
the tube and the equipment which produces the plasma, and a
temperature zone in which the tube is heated to such a temperature
that the deposited coatings are stress-free is superimposed on the
plasma zone and that deposition takes place at a pressure of
between 1 and 100 Torr.
In this respect a non-isothermal plasma is understood to mean a
zone in which the kinetic energy of the gas particles is small
compared with the energy of the excited electronic states. In spite
of the low translational energy, many dissociated and ionised
particles are available, which are favourable for the reaction and
promote it.
With the method according to the invention well-adhering, crackfree
or substantially crackfree coatings are formed on the tube wall.
This is probably explained by the fact that in the method according
to the invention the precipitation of the doped quartz glass takes
.Iadd.place .Iaddend.mainly .[.place.]. on the tube wall and no or
practically no soot-like particles are formed in the gas
atmosphere. However it appeared that at pressures over 100 Torr the
non-isothermal plasma gradually changes into an isothermal plasma
and that the reactive deposition also takes place in gas while
glass soot is formed.
The method according to the invention also enables the direct
reactive deposition on a quartz wire or quartz rod which is
arranged inside the tube.
With the method according to the invention deposition rates of from
2500 .mu.m/hour can be attained. The method according to the
invention makes it .[.therefore.]. possible .Iadd.therefore,
.Iaddend.to obtain in an economic way a uniform deposition over
long tube lengths.
In the method according to the invention a heating up of the tube
(temperature zone) of greater length is superimposed on the plasma
zone. The temperature shall then not be chosen that high that a
homogeneous gas reaction could take place, but it must at least be
chosen that high that the deposited coatings are stress-free.
Heating of the tube to a temperature of between 800.degree. C. and
1200.degree. C., for example in the GeCl.sub.4 /oxygen system, does
not or to only a small extent affect the deposition rate. In the
temperature zone the consistency of the deposited coating is
favourably influenced on the one hand because, at the chosen
temperatures the mobility of the deposited matter is still
sufficient to obtain a stress-free coat and on the other hand
because the embedding of gaseous reaction products is avoided.
At temperatures which are too low, in general below 800.degree. C.
gases such as chlorine produced during the reaction may be trapped.
At temperatures over 1200.degree. C. reaction in the gas phase
.Iadd.also .Iaddend.takes .[.also.]. place while soot-like
particles are formed at the same time.
The plasma may be produced in any way, known in the art, for
example by the inductive or capacitive coupling of a high frequency
field or in a microwave resonator.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be further explained with reference to the
drawing and the following examples.
In the drawing
FIG. 1 is a diagrammatic representation of a device for performing
the method according to the invention;
FIG. 2 shows the attenuation of a fibre optic light conductor drawn
from a tube produced according to the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
A tube 1, for example made of quartz is moved to a heating device
2, for example an electric heating coil in the direction indicated
by arrows. The heating device 2 is enveloped by a resonator 3 by
means of which a plasma 4 can be produced in the gas mixture passed
through the quartz tube 1.
In the reactive deposition a coating 5 is directly formed on the
inner wall of the tube 1.
EXAMPLE I
The deposition of non-doped SiO.sub.2. A gas mixture consisting of
SiCl.sub.4 and oxygen was passed through a quartz tube 1 (length
150 cm, outer diameter=8 mm, inner diameter=6 mm) at a throughput
of 545 cm.sup.3 /minute. The mixture consisted of 7 volume %
SiCl.sub.4 and 93 volume % oxygen. The pressure in tube 1 was 12
Torr. The wall temperature was kept at 1000.degree. C. The tube 1
was passed at a speed of 0.17 cm per minute through the device,
formed by heating device 2 having a length of 500 mm and resonator
3 having a length of 30 mm, while a plasma 4 was produced by a 2.45
GHz generator. An SiO.sub.2 coating having a thickness of 130 .mu.m
was formed directly on the tube wall. A gas phase reaction together
with the formation of soot-like particles did not take place. The
reaction efficiency in the plasma 4 is then almost 100%. The
coating formed adheres well and is homogeneous. The gas mixture was
measured in scm.sup.3 (standard cubic centimeters). 1 scm.sup.3 is
one cm.sup.3 of the gas, where P=760 mm and T=0.degree. C.
EXAMPLE II
The deposition of an SiO.sub.2 -coat doped with GeO.sub.2. A
mixture of SiCl.sub.4 and oxygen, consisting of 4 volume %
SiCl.sub.4 and 96 volume % oxygen was used to which increasing
linearly with time, GeCl.sub.4 was added until the content of
GeCl.sub.4 was 0.4% by volume. The pressure was 10 Torr. The wall
temperature was kept at 960.degree. C. The throughput was 40
scm.sup.3 /minute and the duration of the test was 2 hrs. A
well-adhering SiO.sub.2 coat doped with GeO.sub.2 was obtained. The
coating consisted of 940 single layers of an increasing GeO.sub.2
content .Iadd.toward a central axis of the tube.Iaddend.. The
resonator 3 was moved forward and backward along the tube in this
test at 60 cm/min.
EXAMPLE III
A mixture of 0.4 volume % AlCl.sub.3, 4 volume % SiCl.sub.4 and
.Badd.95.6 volume % oxygen was passed through the quartz tube at a
throughput of 42 scm.sup.3 per minute (length and diameter as in
Example I). The pressure in the tube 1 was 15 Torr. The wall
temperature of the tube 1 was kept at 950.degree. C. A plasma 4 as
in Example I was produced. (Power 180 W, frequency 2.45 GHz). The
reaction efficiency was approximately 100%. The tube was passed
through the device 2-3 at a speed of 60 cm per minute while the
resonator 3 was moved forward and backward along the tube 1. A
homogeneous, adhering coat 5 was obtained. The total thickness of
the coating was 150 .mu.m.
FIG. 2 shows the total attenuation in dB per km as a function of
the wavelength in micrometer of a fiber optic light conductor which
was obtained by drawing at 1900.degree. C. of an internally coated
tube according to Example II. The core diameter was 25 .mu.m and
the fiber diameter was 100 .mu.m. The difference in the refractive
indexes were approximately 5 o/oo.
By means of the method according to the invention a coating profile
which has a certain refractive index in proportion to the doping
can be obtained as shown above at a progressive change of the
doping share. When a suitable profile is chosen the tube forms in
an ideal manner a basic product for the production of monomode,
multimode and self-focussing fiber optics.
.Iadd.Dopant-forming compounds which may be used in the method
according to the invention are, for example, GeCl.sub.4,
TiCl.sub.4, and AlCl.sub.3 which oxidize to form the dopants
GeO.sub.2, TiO.sub.2, and Al.sub.2 O.sub.3, respectively.
* * * * *