Title of Invention

A METHOD OF SOOT OVERCLADDING OF CORE ROD

Abstract The invention is related generally to the field of manufacturing of optical fibre preform and more particularly to overcladding of core rod. The current methods of overcladding are time consuming and it is difficult to achieve accepable levels of uniformity of preform surface. The method of present invention provides for high deposition rate of soot overcladding, by employing multi-phase speed regime for traversing of core rod over the burners. The method enhancing the thermophoresis effect, whereby increasing the rate of deposition of soot. The initial non-uniform speed regime also leads to initial high deposition rate. The strategy of shiftingthe starting point of successive traverse in each set of traverses during uniform speed regime has the beneficial effect of obtaining a uniform surface of overcladding. Due to increase in demand for optical fibers worldwide, large size preforms are needed. The method of the present invention helps in manufacturing these preforms economically.
Full Text FORM 2
THE PATENT ACT 1970
(39 of 1970)
&
The Patents Rules, 2003
PROVISIONAL/COMPLETE SPECIFICATION
( See section 10 and rule 13 )
1. TITLE OF THE INVENTION: A novel method of soot overcladding of core rod

2. APPLICANT (S)
a. NAME : Sterlite Optical Technologies Limited
b. NATIONALITY : Indian company registered under the Indian Companies Act, 1956.
c. ADDRESS : E-2, Waluj MIDC, Aurangabad 431 136, Maharashtra State, India
3. PREAMBLE TO THE DISCRETION




The following specification particularly describes the invention and the manner in which it is to be
performed.





A novel method of soot overcladding of core rod
Field of invention
The field of present invention generally relates to production of optical fiber preforms. More particularly, it relates to a novel method for soot overcladding of optical fiber preform.
Background of the Invention
Optical fibers are inherently versatile as a transmission medium for all forms of information, be it voice, video or data. The optical fiber is drawn from an optical fiber preform, which is manufactured by different methods of chemical vapor deposition (CVD). The optical fiber preform comprises a central core rod and an outer overcladding. The core rod itself comprises a core and part of cladding of the fiber. Separate methods are deployed for the manufacture of the core rod and the overcladding.
The core rod is prepared by methods known to persons skilled in the art, such as modified chemical vapor deposition (MCVD), plasma chemical vapor deposition (PCVD), outer vapor deposition (OVD) and vapor axial deposition (VAD). The overcladding applied to the core rod is carried out by methods also known to persons skilled in the art, such as glass tube jacketing (sleeving), OVD soot overcladding, VAD soot overcladding and plasma overcladding.
The manufacture of optical fiber preform can be done by any combination of core rod preparation methods and overcladding preparation methods. The optical fiber of predetermined
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dimension is drawn from the optical fiber preform by subjecting one end of the glass preform to a high temperature, for example, above 2000 °C. The different methods employed in the manufacture of these optical fiber preform are described in by Tingye Li in Optical Fiber Communications, Academic Press, 1985.
Several processes exist for applying soot overcladding to the core rod. In an OVD method, a flame hydrolysis burner deposits soot glass particles on the surface of a core rod that traverses at predetermined speeds over the plurality of burners. The chemical reaction in the formation of soot particles involves SiCl4, Oxygen (O2) gases as reactants and a burner that uses oxyhydrogen gas for flame. SiCl4 vapor reacts with O2 and with the help of oxyhydrogen flame forms sub micrometer sized SiO2 glass particles. This reaction is expressed as:
SiCl4 (g) + 2H2 (g) + O2 (g) ===* Si02 (s) + 4 HCL (g)
Equation(l)
The above mentioned deposition process is continued till the desired amount of glass particles has been deposited. The core rod with the deposited porous soot is then moved into a sintering furnace, where the deposited porous soot layer is dried in a chlorine atmosphere and then consolidated to form a solid glass optical fiber preform in a helium atmosphere at about 1500 °C.
The solid glass optical fiber preform is drawn in to an optical fiber that comprises of core and clad. With the increase in the demand for optical fibers worldwide, there is a need for preparation of larger
preform, which should be done economically. In order to develop
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an economically viable process, the deposition rate of soot must be increased to complete the fabrication process in lesser time, thereby increasing the productivity.
The deposition rate of soot is generally measured in grams/minute and strongly depends on the core rod diameter and temperature gradient within the gas stream in which the soot particles are entrained. The deposition rate is governed by thermophoresis effect. Under the thermophoresis effect, soot particles from the hotter region of the gas stream move towards the cooler parts (Tingye Li, ref. No. 1). Thermophoresis effect and the resultant rates of deposition of soot depend on the temperature gradient. The temperature gradient itself is depends upon the speed of traverse and also the distance between the core rod surface and the burner.
Thermophoresis effect tends to drive the soot particles towards the outer surface of the core rod, which is usually cooler than the surrounding gas stream. As the diameter of the soot overcladding grows with increasing soot deposition, the distance between the burner and the outer surface of the core rod reduces. This causes the temperature at the outer surface of the core rod to be close to that of the surrounding gas stream. This in turn results in a low temperature gradient and reduction in thermophoresis effect, ultimately reducing the rate of deposition. Thus the deposition rate reduces when the distance between core rod surface and burner reduces below certain level.
The temperature of the core rod surface is inversely proportional to
the speed of the traverse. At lower traverse speeds, the temperature
of the core rod surface is higher. As a consequence, the
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thermophoresis effect is lower due to the reduction in temperature gradient, resulting in lower rates of deposition.
The thermophoresis effect therefore has a direct impact on the preform manufacturing process time.
Different patents disclose several methods for soot deposition that are practiced in the industry related to the art of the present invention, however these methods do not always meet the required higher deposition rate along with preform quality, which is required to meet the required fiber specification.
The Japanese Laid-open patent application No.64-9821 describes a method in which a high deposition rate is achieved by traversing the core rod at given amplitude in the lengthwise direction. The traversing is invariably repeated between the two stop positions. One of the disadvantages of this method is that it causes irregularities on the surface of preform.
According to the method disclosed in the Japanese Patent Application No. 53-70449, the gases blown out from the slit of a burner cannot be maintained under the same conditions throughout the length of deposition. A disadvantage of this method is that it causes non-uniform deposit at locations on rod disposed near individual burners or between adjacent burners.
According to the methods disclosed in the Japanese Laid-open patent applications Nos. 56-12120528, 57-183330 and 58-9835 core and clad layers are formed by a single step. However, the
drawback of this method is that there is a possibility of damaging
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the downstream preform portion during handling process, when an elongated preform with a large diameter is manufactured.
The Japanese Laid-open patent application No. 49-84258 describes a method in which a single burner is used to deposit soot. An advantage of this method is that it is simple, however the severe disadvantage is that it causes the splitting of soot porous body caused by the reduction in the mechanical strength of the layer which is the effect of the low value of the E quantity of heat generated during the process.
The Japanese Laid-open Patent Application No. 3-2288454 describes a method wherein a plurality of burners of the same design are disposed in spaced relationship of equal intervals and the starting position of traverse movement of burners is changed at every next traverse. This leads to longitudinal non-uniformity of soot deposition on the surface of the preform.
US Patent No. US 5958102 describes a method in which plurality burners are used for high deposition rate and which method engages a detector to find the non-uniformity of the surface. This method attempts to achieve uniformity of the preform surface by using an additional single burner. This is done by either by changing the traverse speed of the additional single burner or by changing gas flow to the burner. However this method has disadvantages that it has a complex design, and entails high cost due to sophisticated monitoring requirements and due to modification to be carried out in the existing apparatus. The time delay between the measurement of diameter and change in speed
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or gas flows will not be always same due to dynamic factor involved in the instrumentation.
The non-uniform surface of the optical fiber preform has the drawback that it results in the fiber diameter variation during the process of drawing of optical fiber, which leads to change in optical fiber characteristics like mode field diameter (MFD). The method for removing the irregular surface of the preform is by using grinding apparatus, which is explained in US Pat. No 6467310. However, this method has the disadvantage that it leads to material wastage due to grinding the non-uniform surface of the preform.
Summary and objectives of the invention
The method of present invention provides for high deposition rate of soot overcladding, by employing multi-phase speed regime for traversing of core rod over the burners. The method enhances the thermophoresis effect, whereby increasing the rate of deposition of soot. The initial non-uniform speed regime also leads to initial high deposition rate. The strategy of shifting the starting point of successive traverses in each set of traverses during uniform speed regime has the beneficial effect of obtaining a uniform surface of overcladding.
Objects and advantages of the invention:
Accordingly, the objects and advantages of the present invention are described below:
An object of the present invention is to provide a method for high
rate of the soot deposition for optical fiber preform. Another object
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of the present invention is a method to achieve the uniformity of surface to acceptable level for the optical fiber preform. Yet another object of the present invention is to provide a method to manufacture the optical fiber preform, which when drawn in to optical fiber will provide acceptable optical fiber properties like optical fiber diameter and mode field diameter (MFD). Still another object of the present invention is a method to reduce the manufacturing time in the soot overcladding process of optical fiber preform. A further object of the present invention is to provide a method to improve efficiency of the chemicals. A still further object of the present invention is to provide a method to reduce the material wastage occurring during manufacturing and post-manufacturing processes.
Other objects and advantages of the present invention will be more readily understood from the following detailed description of specific embodiments thereof when read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE FIGURES:
Figure 1 is the schematic representation of the set up of the optical
fiber core rod soot overcladding process.
Figure 2A shows the traverse speed regime of a typical conventional process.
Figure 2B shows a linear profile (Profile A) of the first phase of the multi-phase speed regime of the present invention.
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Figure 2C shows a non-liner profile (Profile B) of the first phase of the multi-phase speed regime of the present invention.
Figure 2D shows another non-liner profile (Profile C) of the first phase of the multi-phase speed regime of the present invention.
Figure 2E shows yet another non-liner profile (Profile D) of the first phase of the multi-phase speed regime of the present invention.
Figure 3 shows the regime of starting and end positioning of traverse motion in the second phase of traverse motion.
Figure 4 shows rates of deposition in g/min for a conventional process and for the process of the present invention using Profile A of Figure 2B.
DETAILED DESCRIPTION OF THE INVENTION: The principles and features of the present invention will be readily apparent from the following detailed description, when read in conjunction with the accompanying drawings.
As discussed in the earlier sections, the soot deposition methods generally comprise traversing a core rod over burners, and passing the soot forming gases through the burners to form soot. The core rod is repeatedly traversed over the burners whereby the soot gets deposited over the surface of the core rod to form the overcladding. The core rod with the soot overcladding obtained at the end of the soot deposition process is generally termed as soot porous body.
As shown in Figure 1, the general setup of a soot deposition
method of the present invention comprises a core rod 1 that is
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mounted on a glass-working lathe 2 between the two chucks 3 & 4, and over a plurality of burners 5. The burners facilitate the passage of gas mixture 6 comprising the oxyhydrogen gas to provide a flame and reactant gases such as SiCl4 required for soot formation. The entire setup is enclosed in a controlled cabinet 7 that has an exhaust facility 8 to let out the exhaust gases.
The preferred embodiment of the invention is now described. In the preferred embodiment of the invention two burners 5 are used. The core rod 1 is rotated continuously about its longitudinal axis at a speed, preferably above 60 rpm. At the same time, the core rod 1 traverses longitudinally over the burners 5 that are stationary.
With the help of the heat provided by the burner, SiCl4 reacts with O2 to form soot particles that are deposited in the form of overcladding 9 over the core rod 1 by the action of thermophoresis. The speed of longitudinal traverse of the core rod over the burner is of crucial importance to the rate of deposition of the soot and the quality of the preform obtained.
One of the key features of the present invention is the novel multiphase traverse speed regime adopted during the process as shown in Figures 2A, 2B, 2C, 2D, and 2E. The advantage of this key feature is that it allows the deposition of soot at a very high speed in the initial stages of the soot deposition process. This advantageously leads to a reduction in the overall time of the process of soot overcladding deposition, as explained later.
In the preferred embodiment, the multi-phase traverse speed
regime, referred to simply as speed regime hereinafter, comprises
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two distinct phases. The first phase of the speed regime, referred to hereinafter simply as first phase, is characterized by very high traverse speeds that are gradually reduced during the entire first phase. A reduction profile, Profile A of Figure 2B, selected from a group comprising various profiles (as indicated in Figures 2B-2E) is used in the preferred embodiment. The second phase of the speed regime, referred to hereinafter simply as second phase, is carried out at relatively low longitudinal traverse speed that marks the end of the first phase. The longitudinal traverse speed during the entire second phase is maintained at a predetermined constant level.
The speed of traverse at the start of the first phase is set at a very high level, preferably greater than 5000 mm/min and more preferably greater than 9000 mm/min.
During the first phase, the speed of traverse during each subsequent traverse is set at a predetermined level wherein the speed of each traverse is generally lower than the immediately previous traverse. For determining speed of any given traverse during the first phase, the following empirical equation is used:
S = I - (I-E) x (P/T)n Equation (2)
Wherein
S is the set traverse speed for any given traverse of the first phase,
I is the traverse speed of the first traverse of the first phase
of the speed regime,
E is the traverse speed of the last traverse of the first phase
of the speed regime,
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P is the sequential number of any given traverse for which speed is being calculated,
T is the total number of traverses for first phase speed regime, n is a constant that has a predetermined value ranging between 0.1 to 5, preferably between 0.5 and 3.
It is important to note that by adopting higher traverse speed at start, any part of the external surface of the core rod will be in contact with the flame for a relatively shorter amount of time, than if the traverse speeds were to be lower. Therefore during the first phase the speed regime, the temperature of surface of core rod is relatively low in comparison with the temperature of the surrounding gases and soot, thereby enhancing the thermophoresis effect. This helps the soot particles to get deposited on the surface of core rod at a deposition rate that is higher than if low traverse speeds were used.
It is also important to note that in this case the density of soot is lower as a direct result of high deposition rate. The traverse speed at the start of the first phase is set at a value which is determined such that the density of soot overcladding does not fall below the threshold density required to maintain the integrity of the soot overcladding formation.
During the first phase, the diameter of the soot overcladding
portion increases very fast due to enhanced thermophoresis effect
thereby resulting in the relatively larger surface area on which soot
deposition for each successive traverse can occur. At the start of
the first phase, the rate of increase of the diameter of soot
overcladding portion is advantageously higher due to the higher
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deposition rates. But at the same time, because of the combination of the rotational and longitudinal traverse movement of the core rod 1 relative to the burner, the outer surface of soot overcladding portion is not uniform. The effect is more pronounced at higher traverse speeds. As the effect of the gradual lowering of the traverse speeds during the first phase, the uniformity of the outer surface of the soot overcladding portion improves as more time is afforded to the soot to get deposited. Nevertheless, the level of uniformness of the outer surface of the soot overcladding portion achieved at the end of the first phase is not at levels acceptable to the industry.
The speed at the end of the first phase is preferably less than 3000 mm/min and more preferably less than 2000 mm/min.
During the second phase, the core rod 1 traverses at uniform traverse speed which is attained at the end of the first phase. A special start point regime for the location of end of the core rod with respect to the location of the burners is adopted in the entire second phase in order to attain at the end of the second phase, a soot porous body of an acceptable level of surface uniformness.
As shown in Figure 3, the start and end points of the individual
traverse cycles in the second phase are so arranged that ripples or
areas of low overall deposition of soot attained at the end of the
first phase of the traverse speed regime get filled out with each
successive traverse of the second phase. This operation is carried
out in plurality of sets of traverses, each set comprising preferably
three to five or more traverses, more preferably three, wherein the
distance x by which the starting points of successive consecutive
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traverses within the set are adjusted by taking into consideration the magnitude of the traverse speed and rotation speed of the core rod and can be determined by persons reasonably skilled in the art. The start point for the first traverse in any given set of traverses is same for all of the plurality of sets.
The process is continued till the soot porous body meets predetermined weight and diameter requirements.
As an advantageous feature of the present invention, at the end of the second phase of the traverse speed regime, a soot porous body of acceptable level of surface uniformness is achieved.
Another advantageous feature of the present invention is the reduction in the wastage of raw materials during the process of soot deposition and also of the soot porous body obtained at the end of the process described in the invention. As the deposition rate increases, there is less of the soot that finds its way out of the exhaust thereby reducing its wastage. In some of the processes, uniformness of the final surface of the soot porous body is achieved by grinding of the non-uniform surface. The method of the present invention does not require this, thereby leading to saving of the soot porous body material.
Figure 4 shows a comparison between the deposition rates for a typical example of the present invention and one of the conventional methods. Maintaining the traversing speed at a constant value as adopted in conventional process (Figure 2A) results in the deposition rate profile named as DR A (observed for
conventional profile of Figure 2A) in Figure 4, whereas the process
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of the present invention (Figures 2B-2E) results in the deposition rate profile to take the form similar to that shown in deposition rate profile named as DR B (observed for Profile A of Figure 2B) in Figure 4.
It is observed as a further advantageous feature of the present invention that the optical fiber drawn from the soot porous body of the present invention is without bare fiber diameter variation and mode field diameter variation.
It is observed that with high traversing rate during the initial deposition time and subsequently reducing traversing rate resulted in the increase in the deposition rate that reflected in the decreasing in the fabrication time of the preform. The SiCl4 deposition efficiency is also increased due to higher deposition rate.
In other embodiments of the present invention, the speed reduction profiles as shown in Figures 2C, 2D, or 2E are adopted.
The following example is provided in order to more clearly illustrate the present invention, and while being illustrative, is in no way meant to be construed as limiting the scope of the present invention.
Example:
A preform was fabricated using several speed regimes that have been discussed the foregoing sections. The total fabrication time and the size of the perform, calculated in terms of the diameters achieved was noted. During the deposition, the flow rates of SiCl4, H2, and 02 were kept constant at 200 gm/min, 200 litres/min,
and 83 litres/min respectively. The total amount of the raw

material fed into the system was also noted. It was observed that the speed regime disclosed by this invention led to saving in the total fabrication time and the amount of raw material required to manufacture performs of substantially the same size. Results of the work are presented in Table 1.

Type 1 E T N Avg Deposition Rate Fabrication time (minutes) Weight (Kg)
Conventional 18 1055 211
Profile A 12000 1500 300 1 23 826 165
Profile B 10000 1600 200 2 22.4 848 170
Profile C 10000 1500 250 3 22.7 837 167
Profile D 10500 1400 280 0.5 22 864 173
Table 1
Table 1 also provides values for the parameters used in Equation 1 for the first phase of the speed regime and also a typical constant speed used in the conventional methods. The table provides a comparison of the fabrication time and also the deposition rates achieved for various embodiments described herein can be made. It is observed that a rate of deposition of approximately 22-23 g/min is achieved for the method described in the present invention in comparison with the approximately 18 g/min that is observed with a typical conventional method. This represents an approximately 28% increase in the deposition rate.
It is also observed that the fabrication time for various embodiments of the present invention is approximately 800 to 865 minutes compared to the approximately 1050 minutes required for
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a typical conventional method. This represents a reduction in fabrication time of approximately 18%-23% over a typical conventional method.
It was further observed that using the method described in the preferred embodiment of the present invention, the total amount of raw material used was approximately 165-180 kg as compared to 210 kg required for a typical conventional method. This represents a saving of approximately 18% in raw material quantity.
While the invention has been described with reference to preferred embodiments, those skilled in the art will appreciate that certain substitutions, alterations and omissions may be made without departing from the spirit of the invention. Accordingly, the foregoing description is meant to be exemplary only and should not limit the scope of the invention set forth in the following claims.
In the view of the above detailed description of the present invention, any person reasonably skilled in the art will understand that the present invention basically comprises the following items:
1. A novel method of soot overcladding of core rod comprising the steps of:
a. mounting said core rod on chucks of a movable
lathe
b. rotating said core rod about longitudinal axis
thereof at a predetermined rotational speed, and
c. traversing the mounted core rod over a burner
assembly comprising a single burner or a plurality
of burners, wherein said burners from said burner
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assembly emit chemical reactant gases forming soot
and a flame, wherein said traversing is carried out in a multi-phase speed regime, whereby a high deposition rate of soot is achieved.
2. A hovel method as described in item 1 wherein said traversing in said multiphase speed regime comprises the steps of:
a. setting a first traverse speed of the first traverse for
the first phase of said multi-phase speed regime at
a predetermined level in the speed range from about
4000 mm/min to about 12000 mm/min, preferably
at about 5000 mm/min, more preferably at about
9000 mm/min,
b. adjusting and setting further respective traverse
speeds for respective subsequent traverses at
suitable values, wherein each of said suitable values
is lower than that for respective immediately previous
traverse, and traversing with each of said further
respective traverse speeds for respective traverses,
c. continuing step b above until reaching an end value
of traverse speed in the range from about 1000
mm/min to about 4000 mm/min, preferably lower
than about 3000 mm/min, more preferably lower
than about 2000 mm/min,
d. carrying out a required number of longitudinal
traverses of a second phase of said multi-phase speed
regime with said end value of traverse speed of step c
above till weight and diameter of soot porous body
reaches a predetermined level, wherein said required
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number of longitudinal traverses is grouped into predetermined number of sets of traverses of said second phase, wherein a first traverse of each of said sets of traverses has a predetermined starting point, wherein starting point of each of subsequent traverse in each of said sets of traverses is shifted forward by a predetermined distance, wherein the number of traverses in each said set of traverses is predetermined, which is preferably three. V
3. A novel method as described in item 2, wherein said multiphase speed regime comprises a suitable combination of a plurality of sets of traverses organized in a suitable order, wherein said sets of traverses are carried out with speeds selected from a group comprising uniform speeds, non-uniform increasing speeds, non-uniform decreasing speeds, wherein the rate of increase or decrease of speed is linear or non-linear, and wherein variation of speed is gradual stepwise or continuous.
4. A novel method as described in items 1 to 3, wherein said multi-phase speed regime comprises a combination of at least a first phase and a second phase, wherein said first phase comprises traversing with a plurality of traverses with non-uniform speeds and said second phase comprises traversing with a plurality of traverses with uniform speeds.
5. A novel method as described in items 1 to 4, wherein said non-uniform speed has a linear or non-linear variation, such that each of the subsequent traverse from said plurality of traverses with non-uniform speed has a speed value lower than that of respective immediately previous traverse.
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6. A novel method as described in item 5, wherein said linear or non-linear variation is carried out in stepwise or continuous mode.
7. A novel method as described in item 1, wherein said chemical reactant gases comprise SiCl4.
8. A novel method of soot overcladding of a core rod, substantially as hereinbefore described and illustrated in examples and accompanying drawings.
Other Publications:
1. Optical Fiber Communications, (Academic Press 1985) Tingye Li., Fiber fabrication pp 75-77
2. Soot over cladding process for enlarging modified chemical vapor deposition preform, Heikki Ihalainen et al., Opt. Engg, Vol. 34 No. 9 September 1995, pp-2538-2542.
3. The effect of thermophoresis on particle deposition in a tungsten low pressure chemical vapor deposition reactor, B. S. MacGibbon et al., J. Electrochem. Soc, 146 (8) pp-2901-2905 (1999)
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We claim:
1. A novel method of soot overcladding of core rod comprising
the steps of:
a. mounting said core rod on chucks of a movable lathe
b. rotating said core rod about longitudinal axis thereof
at a predetermined rotational speed, and
c. traversing the mounted core rod over a burner
assembly comprising a single burner or a plurality of
burners, wherein said burners from said burner
assembly emit chemical reactant gases forming soot
and a flame,
wherein said traversing is carried out in a multi-phase speed regime, whereby a high deposition rate of soot is achieved.
2. A novel method as claimed in claim 1 wherein said traversing
in said multiphase speed regime comprises the steps of:
a. setting a first traverse speed of the first traverse for the
first phase of said multi-phase speed regime at a
predetermined level in the speed range from about
4000 mm/min to about 12000 mm/min, preferably at
about 5000 mm/min, more preferably at about 9000
mm/min,
b. adjusting and setting further respective traverse
speeds for respective subsequent traverses at suitable
values, wherein each of said suitable values is lower
than that for respective immediately previous traverse, and
traversing with each of said further respective traverse
speeds for respective traverses,
c. continuing step b above until reaching an end value of
traverse speed in the range from about 1000 mm/min
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to about 4000 mm/min, preferably lower than about 3000 mm/min, more preferably lower than about 2000 mm/min, d. carrying out a required number of longitudinal traverses of a second phase of said multi-phase speed regime with said end value of traverse speed of step c above till weight and diameter of soot porous body reaches a predetermined level, wherein said required number of longitudinal traverses is grouped into predetermined number of sets of traverses of said second phase, wherein a first traverse of each of said sets of traverses has a predetermined starting point, wherein starting point of each of subsequent traverse in each of said sets of traverses is shifted forward by a predetermined distance, wherein the number of traverses in each said set of traverses is predetermined, which is preferably three.
3. A novel method as claimed in claim 1, wherein said multiphase speed regime comprises a suitable combination of a plurality of sets of traverses organized in a suitable order, wherein said sets of traverses are carried out with speeds selected from a group comprising uniform speeds, non-uniform increasing speeds, non-uniform decreasing speeds, wherein the rate of increase or decrease of speed is linear or non-linear, and wherein variation of speed is gradual stepwise or continuous.
4. A novel method as claimed in claims 1 to 3, wherein said multi-phase speed regime comprises a combination of at least a first phase and a second phase, wherein said first phase comprises traversing with a plurality of traverses with
22

non-uniform speeds and said second phase comprises traversing with a plurality of traverses with uniform speeds.
5. A novel method as claimed in claims 1 to 4, wherein said non-uniform speed has a linear or non-linear variation, such that each of the subsequent traverse from said plurality of traverses with non-uniform speed has a speed value lower than that of respective immediately previous traverse.
6. A novel method as claimed in claim 5, wherein said linear or nonlinear variation is carried out in stepwise or continuous mode.
7. A novel method as claimed in claim 1, wherein said chemical reactant gases comprise SiCl4.
8. A novel method of soot overcladding of a core rod, substantially as hereinbefore described and illustrated in examples and accompanying drawings.
Dated this 28th Day of February 2005

(Sharadchandra Dattatraya Tase) Patent Agent for the Applicant Registration Number IN/PA 879
To, .
The Controller of Patents
Patents Office Branch at Mumbai,
Todi Industrial Estate,
Sun Mills Compound,
Lower Parel (w), Mumbai 400 013
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Documents:

221-MUM-2005-ABSTRAC(28-2-2005).pdf

221-MUM-2005-ABSTRACT(18-7-2011).pdf

221-mum-2005-abstract(23-1-2009).pdf

221-MUM-2005-ABSTRACT(GRANTED)-(2-9-2011).pdf

221-MUM-2005-AGREEMENT(18-7-2011).pdf

221-MUM-2005-AGREEMENT(25-9-2008).pdf

221-MUM-2005-ASSIGNMENT(23-1-2009).pdf

221-MUM-2005-ASSIGNMENT(28-2-2005).pdf

221-MUM-2005-CANCELLED PAGES(18-7-2011).pdf

221-mum-2005-claims(23-1-2009).pdf

221-MUM-2005-CLAIMS(28-2-2005).pdf

221-MUM-2005-CLAIMS(4-8-2009).pdf

221-MUM-2005-CLAIMS(AMENDED)-(4-8-2009).pdf

221-MUM-2005-CLAIMS(AMENDED)-18-7-2011).pdf

221-MUM-2005-CLAIMS(GRANTED)-(2-9-2011).pdf

221-mum-2005-claims.doc

221-mum-2005-claims.pdf

221-mum-2005-correspondance-received.pdf

221-MUM-2005-CORRESPONDENCE (27-6-2011).pdf

221-MUM-2005-CORRESPONDENCE(22-9-2008).pdf

221-MUM-2005-CORRESPONDENCE(23-1-2009).pdf

221-MUM-2005-CORRESPONDENCE(4-10-2006).pdf

221-MUM-2005-CORRESPONDENCE(8-7-2011).pdf

221-MUM-2005-CORRESPONDENCE(IPO)-(12-8-2008).pdf

221-MUM-2005-CORRESPONDENCE(IPO)-(5-9-2011).pdf

221-mum-2005-description (complete).pdf

221-mum-2005-description(complete)-(23-1-2009).pdf

221-MUM-2005-DESCRIPTION(COMPLETE)-(28-2-2005).pdf

221-MUM-2005-DESCRIPTION(GRANTED)-(2-9-2011).pdf

221-MUM-2005-DESCRRIPTION COMPELET(28-2-2005).pdf

221-MUM-2005-DRAWING(28-2-2005).pdf

221-MUM-2005-DRAWING(GRANTED)-(2-9-2011).pdf

221-mum-2005-drawings.pdf

221-MUM-2005-FORM 1(18-7-2011).pdf

221-MUM-2005-FORM 1(22-9-2008).pdf

221-MUM-2005-FORM 1(23-1-2009).pdf

221-MUM-2005-FORM 1(28-2-2005).pdf

221-mum-2005-form 13(15-5-2008).pdf

221-mum-2005-form 13(18-7-2011).pdf

221-mum-2005-form 13(22-9-2008).pdf

221-MUM-2005-FORM 13(4-8-2009).pdf

221-mum-2005-form 13-(18-7-2011).pdf

221-mum-2005-form 18(5-10-2006).pdf

221-mum-2005-form 2(23-1-2009).pdf

221-mum-2005-form 2(28-2-2005).pdf

221-MUM-2005-FORM 2(COMPLETE)-(28-2-2005).pdf

221-MUM-2005-FORM 2(GRANTED)-(2-9-2011).pdf

221-MUM-2005-FORM 2(TITLE PAGE)-(18-7-2011).pdf

221-MUM-2005-FORM 2(TITLE PAGE)-(23-1-2009).pdf

221-MUM-2005-FORM 2(TITLE PAGE)-(28-2-2005).pdf

221-MUM-2005-FORM 2(TITLE PAGE)-(GRANTED)-(2-9-2011).pdf

221-MUM-2005-FORM 26(18-7-2011).pdf

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221-MUM-2005-FORM 3(22-9-2008).pdf

221-MUM-2005-FORM 3(23-1-2009).pdf

221-MUM-2005-FORM 3(28-2-2005).pdf

221-MUM-2005-FORM 5(18-7-2011).pdf

221-MUM-2005-FORM 5(22-9-2008).pdf

221-MUM-2005-FORM 5(23-1-2009).pdf

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221-mum-2005-form-2.doc

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221-MUM-2005-MARKED COPY(18-7-2011).pdf

221-MUM-2005-REPLY TO EXAMINATION REPORT(4-8-2009).pdf

221-MUM-2005-REPLY TO HEARING(18-7-2011).pdf

221-MUM-2005-SPECIFICATION(AMENDED)-(18-7-2011).pdf

221-MUM-2005-SPECIFICATION(AMENDED)-(22-9-2008).pdf

abstract1.jpg


Patent Number 248869
Indian Patent Application Number 221/MUM/2005
PG Journal Number 36/2011
Publication Date 09-Sep-2011
Grant Date 02-Sep-2011
Date of Filing 28-Feb-2005
Name of Patentee STERLITE TECHNOLOGIES LIMITED
Applicant Address E-2, WALUJ MIDC, AURANGABAD 431136
Inventors:
# Inventor's Name Inventor's Address
1 SANKET SHAH E1/E2/E3, MIDC, WALUJ, AURANGABAD 431136
2 JINESH SHAH E1/E2/E3, MIDC, WALUJ, AURANGABAD 431136
3 SANTISWARUP TRIPATHY C/O STERLITE OPTICAL TECHNOLOGIES LIMITED, E-2, WALUJ MIDC, AURANGABAD 431136
PCT International Classification Number C03B37/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA