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All content in this area was uploaded by Alexander Bortsov on Jul 17, 2018
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Content uploaded by Alexander Bortsov
Author content
All content in this area was uploaded by Alexander Bortsov on Jul 17, 2018
Content may be subject to copyright.
1
Method of manufacturing work pieces for fiber optic on
nitrogen-doped quartz glass
Inventor: Alexander A.Bortsov and etc.
2015-01-10
RU2537450C1Grant
Priority date
2013-09-27
Family: RU (1)
DateApp/Pub NumberStatus
2013-09-27RU2013143694A
2015-01-10RU2537450C1Grant
Abstract
FIELD: optics, resonator, optoelectronic, chemistry.
SUBSTANCE: method of manufacturing workpieces includes supply of mixture of molecular
gas reagents, containing nitrogen, oxygen and silicon atoms into support tube, excitation of
UHF discharge in it, formation of plasma column, provision of its scanning along support
tube and precipitation of products of reaction, taking place in mixture, onto internal surface
of support tube. Mixture of molecular gas reagents is additionally supplied into second
support tube, UHF discharge is excited in it, plasma column is formed, its scanning along
support tube is realised, precipitation of reaction products on internal surface of support
tube, synchronous movement of plasma columns in first and second support tubes,
transmission of power from region of plasma column of second support tube to region of
plasma column of first support tube, measurement and regulation of temperature of first
support tube surface by measurement of transmitted power from region of plasma column
of second support tube to region of plasma column of first support tube depending on
measured temperature, are carried out.
EFFECT: elaboration of mode of manufacturing optical fibres on the basis of nitrogen-
doped quartz glass with provision of stabilisation and smooth control of temperature in
region of plasma column of support tube, with reduction of time for installation of required
tube temperature and with increased accuracy of temperature adjustment.
12 cl, 2 dwg
Images (2)
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Description
TECHNICAL FIELD
The invention relates to the field of fiber optics and, in particular, to the formation of
preforms of optical fibers vapor deposition.
BACKGROUND
A number of fiber structures based on quartz glass and methods for manufacturing optical
fibers of different types (single mode, multimode, police, etc.) and compositions: MCVD
(Modified Chemical Vapour Deposition), OVD (Outside Vapour Deposition), VAD (Vapour-
Phase Axial Deposition), PMCVD (Plasma MCVD), PCVD, POD (Plasma Outside
Deposition), PICVD (Plasma Impulse CVD), SPCVD (Surface Plasma CVD).
A method for manufacturing preforms for optical fibers based on silica glass (Patent US
4,877,938 «Plasma activated deposition of an insulating material on the interior of a tube»
(IPC S03V 37/018; H05B 6/80, published 31.10.1989), comprising a. heating of the support
tube, the support tube over the mixture of molecular gaseous reactants, agitation therein of
a microwave discharge and precipitation of products in the reaction mixture flowing in the
inner surface of the support tube.
The disadvantage of this method is considerable heterogeneity of the longitudinal
supporting surface temperature and as a result, the inability to obtain glass preforms with
the desired quality.
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A method for manufacturing optical fiber preform by plasma chemical heterogeneous
deposition layers of core and cladding on the inner surface of high-quality reference quartz
tube of large diameter from the gas phase under reduced pressure, microwave discharge
on the surface wave in the modulation of the microwave power and the subsequent
collapse of the reference quartz tube with the deposited layers rod-in-blank (RF patent
2112756 "METHOD FOR FABRICATION OF bLANKS FOR OPTICAL FIBER BASED ON
QUARTZ GLASS", IPC S03V 37/018, G02B 6/16, publ. 10.06.1998). It is based on the
formation of quartz preforms of optical fibers, by plasma chemical synthesis quartz glass
layers doped with nitrogen on the inner surface of the quartz tube on the supporting SPCVD
technology (Patent FR 2628730 «Apparatus for making preforms for optical fibres», (IPC
C03B 37/018; G02B 6 / 00, published 06.29.1990) (patents-analogues:. US 4,944,244 and
EP 0333580).
The disadvantage of structures formed preforms and optical fibers based on silica glass is
that it is not defined ratio of silicon and oxygen entering the reactor in the gas mixture. This
makes it impossible to provide a technological mode nitrogen entering the quartz glass to
obtain a predetermined difference Δn of refractive indices of the core and shell.
The closest analogue is the method for manufacturing preforms for optical fibers based on
silica glass disclosed in Russian patent 2433091 "METHOD FOR PRODUCING
PREPARATIONS OF QUARTZ mode optical fiber, DEVICE FOR CARRYING OUT SAID
BLANKS AND MANUFACTURED ACCORDING METHOD" (IPC S03V 37/018, G02B 6 /
16, publ. 10.11.2011), which serves to support tube a mixture of molecular gaseous
reactants therein excite the microwave discharge, the plasma column is formed, it provides
scanning along the support tube and precipitated products showed ekayuschey in the
reaction mixture on the inner surface of the support tube. Thus the support tube is carried
along the measurement of its surface temperature and provide temperature control of the
supporting surface of the tube by changing the power of the plasma column in function of
the measured temperature.
The disadvantages of the prototype are:
- stabilization of the temperature in the region of the plasma column is not fast enough and
precise enough, since it does not apply automatic workpiece temperature control system
and control the temperature of the recording elements constituting the feedback loop;
- there is a substantial longitudinal inhomogeneity of the temperature of the support tube
surface by scanning the plasma column along the tube (under a parameter longitudinal
temperature inhomogeneity is the ratio between the maximum and minimum temperature
values along the longitudinal section of the support tube to the average temperature of the
substrate tube during the passage of the deposition reaction, wherein the longitudinal
surface nonuniformity of temperature the support tube is determined by the temperature of
gases supplied to the tube, the rate of their supply, around a longitudinal temperature
distribution is supporting tube, etc.).;
- no possibility smooth control along the reference tube "length" field of the plasma column
since no along the supporting tube the temperature detection element, there is no feedback
regulating system controls the change is not carried out and the microwave power at the
time when scanning of the plasma column;
- insufficiently high efficiency of the process (in this case, by efficiency is meant the ratio of
useful power expended in heating the core of the support tube, the total consumed
microwave power supplied to the main support tube, part of the microwave power in the
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prior art is consumed excessively because no system for automatically adjusting the
reference temperature tube, and the microwave power loss thus can be more than 80%).
These disadvantages make it impossible to provide a technological mode with the required
parameters and the quality of the nitrogen entering the quartz glass to obtain a
predetermined difference Δn of refractive indices of the core and the cladding in the
transverse and longitudinal sections of the support tube.
SUMMARY OF THE INVENTION
The object of the claimed invention is to provide a technological mode manufacturing
preforms for optical fibers based on nitrogen-doped quartz glass with ensuring stabilization
and smooth control of temperature in the plasma column support tube, preferably in the
range from 1000 ° C to 1950 ° C, the reduction time required to establish the desired
temperature tube (time for establishing the desired temperature of the tube means the time
between the time the microwave power and the instant of time SETdetecting a
predetermined temperature of the tube, the settling time depends on the ambient
temperature, the temperature and velocity fed to the pipe of gases instability microwave
power, etc.) and with high precision adjusting temperature as well as with the possibility of
smoothly control "length" field of the plasma column along the supporting tube and
increasing the overall efficiency of the reaction process, and, as a consequence, a higher
quality ensuring a predetermined distribution of the nitrogen content of the workpieces in
longitudinal and transverse sections.
The problem is solved in that the proposed method for manufacturing preforms for optical
fibers based on silica glass doped with nitrogen, comprises supplying a support tube a
mixture of molecular gaseous reagents containing in its structure nitrogen, oxygen and
silicon, agitation therein microwave discharge, formation plasma column, ensuring it is
scanned along the substrate tube and the deposited products in the reaction mixture flowing
in the inner surface of the support tube. Wherein further the second support tube, a
predetermined next to said first support tube is fed a mixture of molecular gaseous
reactants excite therein discharge microwave, formed plasma column is carried scanning it
along a second support tube, deposition products flowing in the reaction mixture on the
inner surface a second support tube, a synchronous movement of the plasma column in the
first and second support tubes, power transfer from the region of the plasma column of the
second support tube to the plasma region nnogo post first support tube, measuring and
regulating the temperature of the surface of the first support tube by changing the transmit
power from the second region of the plasma column support tube to the area of the plasma
column of the first support tube depending on the measured temperature. Also, the
temperature of the first surface of the support tube can provide regulation and stabilization
of the temperature.
The second support tube advantageously fed with a mixture of molecular gaseous reagents
containing in its structure nitrogen, oxygen and silicon.Wherein the second support tube
advantageously fed with a mixture of molecular gaseous reagents containing the same
composition of gas reactants atoms (nitrogen, oxygen and silicon), and that the composition
of the gaseous reactants fed to the first support tube.
The discharge of microwave is excited in the first support tube, summing from across the
first support tube of the microwave power from the first microwave generator, and a second
microwave generator, and the second support tube excite the microwave discharge,
summing from across the second support tube of the microwave power from the second
microwave generator and third microwave generator. Also, the plasma column scanning
along the first and second support tubes carry the second oscillator changing the
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microwave power on a periodic law, e.g., in the frequency range from 10 to 150
Hz. Changes in transmitted power from the region of the plasma column to the second
support tube of the plasma column of the first support tube is carried out by changing the
third power of the microwave generator.
Between the surface of the first support tube and the surface of the second support tube
may place an attenuator controlled by adjustment of which is carried out by changing the
transmit power of the plasma column of the second support tube to the region of the plasma
column of the first support tube.
Temperature measurement tube first support surface can be carried out with M via
temperature gauges located along the first support tube. It is also possible additional
heating of the first tube by spaced therealong heating elements.
Also further near the first support tube may be pre-set has N additional support tubes, each
of which is then fed to the mixture of molecular gaseous reactants (usually the same as the
first and second tubes), excite discharge of the microwave, formed plasma column provide
its scanning along each additional support tube, the products are precipitated in the reaction
mixture flowing in the inner surface. Thus provide movement of the plasma column in each
of the N additional support tubes, synchronized with the movement of the plasma column in
the first and second support tubes, wherein the N additional support tubes mounted relative
to the first support tube in such a way as to ensure power transmission from the region of
the plasma column to the field plasma column of the first support tube. For controlling the
temperature along the first support tube is additionally used transmit power change from the
region of the plasma column of each of N additional support tubes to the field of the plasma
column of the first support tube depending on the measured temperature. Also, each of the
N additional support tubes and a second support tube is best installed parallel to the first
support tube and on a circle around it.
Thanks to the proposed method due to temperature stabilization in the plasma column by
the transmitted microwave power is a smooth temperature control and more than 30% less
time and establishing a desired temperature by more than 30% of the temperature
adjustment accuracy is improved (as to control the reaction The microwave power used by
the electric field of the second support tube) and more than 30% reduced temperature
nonuniformity longitudinal support tube surface during scanning of the plasma column along
the tube, and it becomes possible to steplessly controlling the "length" (along the support
tube) of the plasma column, and the overall efficiency of the reaction process is increased
by more than 5%.
By stabilizing the temperature in the plasma column by means of the transmitted microwave
electric power inside the support tube of nitrogen improves the distribution of the
workpieces in a longitudinal section (approx .: control and control of nitrogen content with a
relative accuracy of less than 1% over the length of the workpiece (in this case, a precision
refers to the ratio of the maximum value of the nitrogen content of deviations from its
average value to the average nitrogen content in a specified segment length), lead to an
improvement of a number of parameters an optical fiber, for example, to reduce optical
losses by more than 5%) and cross-section, and as a result, provided the desired value of
the difference Δn in refractive index in longitudinal and transverse cross sections of the
workpiece and improves the uniformity of the preform.
List of figures
1 shows a basic embodiment of an apparatus for implementing the method of
manufacturing preforms for optical fibers.
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2 shows a second embodiment of the supplemented said device.
EMBODIMENTS
1 shows a device for performing the claimed method. The apparatus 1 comprises a support
tube of quartz glass into which the mixture of molecular gaseous reactants through the inlet
2 3. Next to the first support tube 1 is placed second bearing tube 19, into which is fed a
mixture of molecular gaseous reactants 2 via splitter 20 and the entrance 21. Apparatus as
also comprises a first microwave generator 4, the second microwave generator 12 and a
third microwave generator 17. the output of the first microwave generator 4 is connected to
the input of divider 5, whose first output is connected to a first input of the third microwave
generator 17, and the second output through the waveguide 6 one with the matching device
8. The output of the second microwave generator 12 is connected to the input of a
modulator 13 controlled by a low frequency generator 16. The output of modulator 13 is
connected to the input of the divider 14, whose first output is connected to the input of the
matching device 15, and the second output - to the input of the matching device 35. The
third output of the microwave generator 17 is connected to interface device 34. For
registration of temperature in different areas of the supporting surface of the tube 1
temperature gauges has 29, 30, 31 and 32, connected respectively to the inputs 1-4
processing unit 28, whose output is connected to the input of the control unit 33. The output
control device 33 is connected to a second input of the third oscillator 17 and microwave
communication 37 with the controlled attenuator 36. As a result, the machine has a
feedback system comprising a processing device 28 and control device 33.
For temperature registration in the various areas of the support tube surface 1 positioned
temperature gauges 29, 30, 31 and 32. The signals from all the temperature measuring
devices 29, 30, 31 and 32 respectively arrive at the inputs 1-4 processing unit 28, whose
output is connected to an input device 33. The control output control unit 33 is connected to
a second input of the third microwave generator 17 whose output is connected to the
matching device 34. As a result of measuring temperature along the surface of the first
support tube by a feedback system, This turns the processing device 28 and control device
33, there is a third power control of the microwave generator and the attenuator 36. By
adjustment of the attenuator 36 and the change in the power of the third generator 17,
connected to the control device 33 feedback, depending on the measured temperature is
carried out by changing the transmit power of the plasma second support pillar 26 of the
tube 19 to the region of the plasma column 10, the first support tube 1, which causes a
change in the temperature region of the plasma column n rvoy support tube.
The apparatus in Figure 2 further comprises adjacent to the first support tube therealong
discrete heating elements 42, 43, 44, 45, e.g., in the form of spiral rings, burners, and the
like), the temperature of which is regulated by appropriate control blocks 38 , 39, 40, and 41
connected to the processing device 28. Using additional heating elements allows to further
improve the possibility of stabilizing the temperature along the first support tube and reduce
the time-to required temperatures.
The process is carried out as follows.
The support tube 1 of quartz glass for receiving the mixture of molecular gaseous reagent 2
under a pressure of several mmHg through the inlet 3. On the one side to the support tube
1 from the first microwave generator 4 through a divider 5, the waveguide 6 and a matching
device 8 is supplied microwave power stream 7. In this case the tube 1 inside the support
surface electromagnetic wave propagates 9 which is reacted with a mixture of molecular
gaseous reactants 2. on the opposite side to the support tube 1 from the second microwave
generator 12 through a modulator 13, a divider 14, a waveguide, and matching device 15 is
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applied another stream of microwave power. In the opposite direction applies a surface
electromagnetic wave, which is reacted with a mixture of molecular gaseous reactants 2. As
a result of the interaction of two surface electromagnetic waves in a mixture of molecular
gaseous reactants into the substrate tube 1 occurs and the discharge is maintained
stationary, forming a plasma column 10.
As a mixture of molecular gaseous reactants 2 use drained oxygen O 2 and nitrogen
N 2 together with the silicon tetrachloride SiCl 4. The mixture of molecular gaseous reactants
2, falling into the region of the plasma column 10, test chemical transformations due to the
appearance of a mixture of molecular gaseous reactant 2-active radicals which are "work
enough" in a mixture of molecular gaseous reactants 2 from unexcited molecules when they
interact with the "hot electrons" plasma (plasma column 10). As a result, silicon tetrachloride
transforms to silicon oxide which is adsorbed by the walls of the support tube and
dookislyaetsya resulting heterogeneous reaction involving nitrogen-containing radicals to
silicon dioxide, forming thus the deposition zone 11 of doped quartz glass.
By changing the input from the second oscillator 12, the microwave power, the position of
the plasma column 10 relative to the support tube 1 and is implemented scan mode
deposition zone 11 along the support tube 1 and thus the layer deposition is carried out
mode at its inner surface. Next to the first support tube 1 is placed a second support tube
19 into which is fed a mixture of molecular gaseous reactants 2 via splitter 20 and through
the inlet 21 under pressure of a few mmHg On one side of the second support tube 19 from
the third microwave generator 17, synchronized with the first microwave generator 4
through a matching device 34 is supplied microwave power flow. Wherein the second inside
support tube 19, an electromagnetic wave propagates surface 25 which interacts with a
mixture of molecular gaseous reactants 2. On the opposite side of the second support tube
from the second microwave generator 12 through a modulator 13, splitter 14 and matching
device 35 is applied another stream of microwave power and surface electromagnetic wave
propagates in the opposite direction, which enters into interaction with a mixture of
molecular gaseous reactants 2. by the reaction of I two surface electromagnetic waves in a
mixture of molecular gaseous reactants in the second support tube 19 occurs and the
discharge is maintained stationary, forming a plasma column 26.
In accordance with a change input from the second microwave generator 12, the power
varies the position of the plasma column 26 along the second support tube 19 and is
implemented in synchronism with the plasma column of the first tube scanning the plasma
column along the second support tube by changing the thickness of the second generator
of a periodic law with a frequency in the range of 10 to 150 Hz, and thus, layer deposition
mode is carried on the inner surface of the second support tube. For example, for the
manufacture of blanks for fiber sheath of undoped silica glass, the core glass doped with
nitrogen, and the magnitude Δn = 0,02 first support tube of 20 mm diameter and a wall
thickness of 2 mm was heated to 1250 ° C temperature. The mixture was fed to a substrate
tube 2 with the chemical composition SiCl 4 + O 2 + N 2at a total pressure of 1 mm Hg 7
microwave power ranges from 1 kW to 5 kW. The required level of doping the glass with
nitrogen is obtained at mass flow ratio [SiCl 4]: [O 2] = 0.92 and [O 2]: [N 2] = 0.5. The ratio
entering the reactor per unit time of oxygen atoms and silicon is 2.2, and the ratio of
nitrogen and oxygen is equal to 2.
This provides a smooth temperature control, typically in the temperature range from 1000 °
C to 1950 ° C, temperature adjustment accuracy is from 0.5 ° C to 25 ° C (note: the
accuracy of a mean temperature difference between workpiece temperature before
adjusting the temperature and after carrying out adjustment), while establishing the desired
temperature - from 1 to 100 seconds, the estimated value of the efficiency - from 15 to 20%.
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For comparison, content expert estimations, in the process prototype longitudinal
inhomogeneity of the temperature of the support tube surface may be from 25 ° C to 250 °
C, time to establish a desired preform temperature - from 100 to 1000 seconds or more, as
in the prior art, there is no automatic temperature control.
In the proposed method, when administered to a temperature control feedback system by
recording and controlling the temperature of the support tube is carried out more
economical consumption of the microwave power; and upon reaching a predetermined
temperature, microwave power is introduced into the support tube is reduced and thereby is
achieved a more economical consumption of the microwave power as a whole in the
substrate tube; the prototype is no system of regulation - and this reduce the microwave
power does not occur;resulting standard values efficiency in the prototype method may be
from 5 to 10%, while in the proposed method: Efficiency - from 15 to 20%.
Thus, by the proposed method is attained significantly better stabilization of the temperature
in the plasma column ensured smooth temperature control, reduce the time of establishing
a desired temperature and increasing the accuracy of its adjustment, a smooth control
along the reference tube "length" field of the plasma column and increase overall process
efficiency reactions, which provides high quality of a given distribution of nitrogen content in
longitudinal and transverse sections of the blanks for the ox horse fibers based on silica
glass doped with nitrogen.
Claims (12)
12. Способ по п.11, отличающийся тем, что каждую из N дополнительных опорных трубок
и вторую опорную трубку устанавливают параллельно первой опорной трубке и по кругу
вокруг нее.
1. 1. A process for manufacturing preforms for optical fibers based on silica glass doped
with nitrogen, comprising feeding into the support tube a mixture of molecular
gaseous reagents containing in its structure nitrogen, oxygen and silicon, the
excitation of the microwave discharge therein, the formation of the plasma column,
ensuring its scanning along the support tube and the precipitation of products in the
reaction mixture flowing in the inner surface of the support tube, characterized in that
it additionally serves a mixture of molecular gaseous reactants into a second a support
tube, a predetermined next to said first support tube excite the second support tube
discharge microwave, formed plasma column is carried scanning it along a second
support tube, deposition products flowing in the reaction mixture on the inner surface
of the second support tube, a synchronous movement of the plasma column in first
and second support tubes, power transfer from the region of the plasma column to the
second support tube of the plasma column of the first support tube, a temperature
measurement surface temperature control and the first support surface of the tube by
changing the transmit power from the second region of the plasma column support
tube to the area of the plasma column of the first support tube depending on the
measured temperature.
2. 2. A method according to claim 1, characterized in that the temperatures
of the first support tube surface temperature regulation provide
stabilization along the first support tube.
3. 3. A method according to claim 1, characterized in that the second
support tube is fed a mixture of molecular gaseous reagents containing in
its structure nitrogen, oxygen and silicon.
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4. 4. A method according to claim 1, characterized in that the second
support tube is fed a mixture of molecular gaseous reagents containing
the same composition of gas reactants atoms as that of the gas reactants
fed to the first support tube.
5. 5. A method according to claim 1, characterized in that the microwave
discharge is excited in the first support tube, summing across a first
support tube of the microwave power from the microwave generator of
the first and second microwave generator, and the second support tube
excite the microwave discharge, summing with different the second ends
of the support tube of the microwave power from the microwave
generator of the second and third microwave generator.
6. 6. A method according to claim 5, characterized in that the scanning of
the plasma column along the first and second support tubes carry the
second oscillator changing the microwave power on a periodic law with a
frequency in the range from 10 to 150 Hz.
7. 7. A method according to claim 6, characterized in that the change in
transmit power from the second region of the plasma column to the
support tube of the plasma column of the first support tube is carried out
by changing the third power of the microwave generator.
8. 8. A method according to claim 1, characterized in that between the
surface of the first support tube and the surface of the second support
tube disposed attenuator controlled by adjustment of which is carried out
by changing the transmit power of the plasma column of the second
support tube to the region of the plasma column of the first support tube.
9. 9. A method according to claim 1, characterized in that the temperature
measurement surface of the first support tube carried by means of
temperature measuring devices M located along the first support tube.
10. 10. The method of claim 1, further comprising heating the first tube by
spaced there along heating elements.
11. 11. A method according to claim 1, characterized in that it further
adjacent to the first support tube pre installed N additional support tubes,
each of which is then fed to the mixture of molecular gaseous reactants
excite the microwave discharge, the plasma column is formed, it provides
an additional scan along each the support tube, precipitated products in
the reaction mixture flowing in the inner surface, thus providing the
movement of the plasma column in each of the N additional support
tubes, synchronized with the movement of plasmas nnyh pillars in the
first and second support tubes, wherein the N additional support tubes
mounted relative to the first support tube in such a way as to ensure
power transmission from the region of the plasma column to the region of
the plasma column of the first support tube, and to control the
temperature along the first support tube is additionally used change
transmit power from the region of the plasma column of each additional
support to the tubes of the plasma column of the first support tube
depending on the measured temperature.
12. 12. A method according to claim 11, characterized in that each of the N
additional support tubes and a second support tube installed parallel to
the first support tube and on a circle around it.
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