JP4082326B2 - Method for measuring surface temperature of article to be heated, heating method using the same, and method for manufacturing optical fiber preform - Google Patents

Description

  The present invention relates to a method for measuring the surface temperature of an article to be heated that can be suitably used particularly when heating glass, a heating method using the method, and a method for manufacturing an optical fiber preform.

As a temperature measurement method during the growth of a porous preform of a glass preform for optical fibers, a method of moving a non-contact thermometer in accordance with the movement of a burner or the growth of a porous body has been proposed (see Patent Document 1). ).
As a plasma CVD apparatus, an apparatus that measures the temperature of an object to be formed with plasma energy using a non-contact thermometer has been proposed (see Patent Document 2).

JP 61-167826 A JP-A-5-190462

Accurately grasping the temperature of the heated article in the part exposed to the heat source is important for adjusting the heating condition and affects the quality of the product produced by heating. . For example, the glass tube SiCl _4, GeCl _4, flow of glass material gas and the oxygen of SiF ₄ and the like, when synthesizing a glass in the MCVD process to deposit inside the glass tube to generate glass particles by heating, GeO ₂ with temperature The reaction efficiency of F-SiO ₂ and the deposition efficiency of glass fine particles change, and the refractive index distribution and the volume of the deposited glass layer change. For this reason, since the synthesis temperature of the MCVD method affects the properties of the glass layer to be produced, it is necessary to strictly control the temperature.

However, when the surface temperature of the article to be heated is measured using a non-contact type thermometer as in the prior art, the temperature of the flame is measured in the area exposed to the heat source, or the glass particles that are not the article to be heated Or measure the light emitted by. In some cases, the temperature is measured finely up and down, but whether it is a measurement error or the actual temperature cannot be determined by temperature measurement only in the region exposed to the heat source. Therefore, it has been difficult to strictly control the temperature of the article to be heated.
In particular, in the case of glass products, there are differences in the size of the required heat zone, the temperature difference between the inside and outside of the heat zone, and the like depending on the type and process of the product. Even if only the maximum temperature of the article to be heated is grasped, the size of the heat zone is not known, so that there is a problem that the heating cannot be appropriately adjusted.

  The present invention solves the above problems, accurately measures the temperature in the region exposed to the heat source of the article to be heated, and grasps and measures the temperature distribution in the heated and heated region. It is an object of the present invention to provide a method for estimating the temperature at a position that is not performed, a heating method for adjusting the heating intensity and the like based on these methods, and a method for manufacturing an optical fiber preform using the same.

The present invention makes it possible to solve the above problems by adopting the following configuration.
(1) Measurement position by simultaneously measuring the surface temperature of at least one location in a region exposed to a heat source of a hollow article to be heated and a plurality of locations in a region that has not been exposed to a heat source but is heated Create a temperature distribution with respect to, and estimate the surface temperature at the position where it is not measured The position where the maximum temperature estimated from the temperature distribution created by the surface temperature measurement method is separated from the position by a certain distance A method for heating an article, wherein at least one selected from heating intensity, heating range, and heating time is adjusted so that the temperature of each position becomes a desired temperature, and the predetermined distance is equal to or greater than the thickness of the article to be heated. .

(2) The method for heating an article according to (1), wherein the certain distance is not more than 50 times the thickness of the article to be heated.
(3) The method for heating an article according to (1) or (2), wherein the article to be heated is glass.
(4) A compound serving as at least one kind of glass raw material is introduced into the hollow quartz glass body, and the glass body is heated by the heating method according to any one of (1) to (3). A method for producing an optical fiber preform, comprising depositing a new glass layer.

In the present invention, the “region exposed to the heat source” is specifically a region directly exposed to flame, and when the heat source is a heater, it is a region facing the heater. In addition, the “region that has not been exposed to the heat source but has been heated” is a portion that has already been heated by the heat source, and has not been directly heated by the heat source, but has been heated by an effect such as heat conduction. Part. The positions of these “region” and “measurement location” are relative to the position of the heat source. When the heat source moves relative to the article to be heated, each “region” and “measurement location” Also move synchronously.
Further, in this specification, the “optical fiber preform” may be a glass body that is drawn as it is to become an optical fiber, and further processed by a method such as stretching, synthesis of a clad portion, collapse, or peripheral grinding. It may be a glass body (optical fiber preform intermediate) that is drawn and then becomes an optical fiber.

  According to the surface temperature measurement method of the present invention, the surface temperature in a region exposed to a heat source with many errors can be measured with high accuracy, and the measurement is performed by creating a temperature distribution with respect to the measurement position. The surface temperature at the missing position can also be estimated. Since the heating method of the present invention adjusts heating based on the result of the measurement method, it is possible to perform appropriate heating according to the type and process of the product, and to improve the quality of the product. According to the method of the present invention, a high-quality optical fiber preform can be manufactured.

The heat source in the present invention is not particularly limited. For example, the heat source may be a flame such as a plasma burner or an oxyhydrogen burner, a heater such as a resistance furnace or an induction furnace, or a laser such as a CO ₂ laser.
The article to be heated is not particularly limited in type or shape, but the present invention is effective when dealing with rod-shaped or tubular shaped articles. An example of the material is glass. Glass tubes and glass rods are heated for the purpose of stretching and flame polishing. In the case of a glass tube, the heating for the collapse (including the rod in collapse that inserts the rod into the glass tube and integrates the glass tube and the rod) for making the glass tube solid is also performed. In addition to glass products, metals, ceramics, and the like can be used as articles to be heated.
The thermometer used in the present invention is not particularly limited as long as it is a non-contact type, and a radiation thermometer, a luminance thermometer, a thermotracer using a two-dimensional arrangement of elements of a radiation thermometer, and the like can be used. . The measurable temperature range is generally room temperature to 3000 ° C.

A method for measuring the surface temperature of an article to be heated in a region exposed to a heat source according to the first invention will be described with reference to the drawings. FIG. 1 is an explanatory view schematically showing how glass particles are deposited in a quartz glass tube by MCVD using a plasma burner as a heat source. Into the glass tube, a glass raw material gas such as SiCl ₄ , GeCl ₄ , SiF ₄ , oxygen as an oxidizing medium, He for adjusting the thermal conductivity and flow velocity of the pipe space, if necessary, are introduced, and a plasma burner The glass tube 1 is heated by 3 to deposit glass fine particles (soot body) on the inner surface of the glass tube. This soot body may be sintered by the same heat source 3 and may be a transparent glass body or may be a soot body. In the figure, the area indicated by A is an "area exposed to a heat source", and there are "areas that are not exposed to a heat source but are heated up" on both sides. While the non-contact type thermometer 2 moves the surface temperature in the region A and the non-contact type thermometer 2 ′ moves in synchronism with the plasma burner 3 at the same time while moving outside the region A, Measure continuously or intermittently. When the plasma burner 3 is used, the area A exposed to the heat source of the article to be heated is usually surrounded by the casing 4, and the temperature in the area A is measured by opening a window 5 in the casing 4. It can be carried out. The glass tube 1 rotates around its axis. The plasma burner 3 and the housing 4 move in parallel with the axis of the glass tube 1.

  If the measurement result is a graph of temperature against time, it will be as shown in FIG. 2 (a) (FIG. 2 (a) is the measurement result in the implementation of the MCVD method with a quartz glass tube having an outer diameter of 34 mm and a wall thickness of 4 mm. The length of the area A is 65 mm, the measurement position is the thermometer 2 in the center of the length direction of the area A, the thermometer 2 ′ is 10 mm from the end of the area A, and the moving speed of the heat source 3 is 100 mm / min. is there). The upper line is the measurement result of the thermometer 2, and the lower line is the measurement result of the thermometer 2 '. That is, the temperature change in a region where the top is exposed to a heat source, and the temperature change in a region where the bottom is not exposed. If you compare the upper and lower lines, you can see that the upper and lower temperatures appear only in the upper line. Since heating at the measurement point of the thermometer 2 raises and lowers the temperature at the measurement point of the thermometer 2 ′ by heat conduction, the two lines in the graph should be the same shape, although there is a time difference and a temperature difference. . Therefore, the upper and lower temperatures that can be seen only in the measurement result of the thermometer 2 are the results (noise) of the influence of the flame and the disturbance of light emitted from the heated glass particles that are not the article to be heated. You may think that it is not above or below the temperature. If the shape of the curve of the measurement result of the thermometer 2 ′ is corrected as shown in FIG. 2B based on the shape of the curve of the measurement result of the thermometer 2 ′, the region A exposed to the heat source of the actual article to be heated. It is possible to obtain a result that can be considered as a change in the inner surface temperature.

In the above description, the two lines of the graph are basically parallel. However, the two measurement points are separated so that the temperature changes at the two points are substantially parallel as shown in FIG. It is preferable not to be too much. If the measurement points of the thermometer 2 and the thermometer 2 ′ are too far apart, the temperature change may not be parallel, and it becomes difficult to estimate the surface temperature in the region exposed to the heat source.
Also, if the surface temperature in the area exposed to the heat source is changing rapidly even though the surface temperature is not changing in the area not exposed to the heat source, it is noise or actual temperature change. The criteria for determining whether (1) the noise component is determined using a Fourier transform filter, (2) the moving average is compared and determined, (3) the time derivatives of both surface temperatures are compared, etc. Can be used. The "moving average", for example refers to those sequentially calculates the average last measured value i pieces of, may be multiplied by a coefficient (a _n) to the respective values so as to increase the weight as near measurements . However, the _{Σa n (= a 1 + a} 2 + ··· + a i) = i.

Next, a temperature measuring method for creating a temperature distribution and estimating a surface temperature according to the second invention will be described. The temperature distribution may be two-dimensional or one-dimensional as long as it is a temperature distribution relative to the positional relationship from the reference position. However, if the article to be heated is a rod-like or tubular article, It is better to create a temperature distribution in one dimension. FIG. 3 shows a temperature distribution created by simultaneously measuring the surface temperature at six points in the longitudinal direction in the implementation of the MCVD method under the same conditions as shown in the description of FIG. As the temperature at the measurement position in the region A, the temperature obtained by the method of the first invention described above is used. From this temperature distribution curve, it can be seen that the temperature at a position not being measured can also be estimated. At this time, if it is measured by a thermotracer, it is possible to directly know the one-dimensional or two-dimensional temperature distribution on the glass tube surface, which is preferable.
By using at least one measurement result in the region exposed to the heat source, which is obtained by the method of the first invention, the accuracy of the temperature distribution and the accuracy of the estimated maximum temperature are improved. The number of measurement points in the region where the temperature is not exposed to the heat source but the temperature is rising is not limited as long as the temperature distribution can be created, and the position of the measurement point is not particularly limited, but it is within the region exposed to the heat source. 3 points or more in total including the measurement points in (preferably at least one part each in the part exposed to the heat source, the area not exposed to the heat source before and after that but the temperature rising). preferable. In addition, it is preferable that measurement points exist on both sides of the region exposed to the heat source. This is because the temperature distribution is not necessarily symmetrical with respect to the heat source.

The heating method of the present invention is characterized in that at least one selected from a heating intensity, a heating range, and a heating time is adjusted based on the measurement result of the surface temperature of the article to be heated by the first and second measuring methods. .
For example, when the heat source is a plasma burner, the heating intensity is adjusted by changing the power supplied to the plasma source, the frequency, the type of gas supplied, the flow rate, and the flow rate. The heating range is adjusted by changing the outflow range of the supplied gas and the relative distance between the burner and the article to be heated. Further, for example, a method of adjusting the size of the flame by changing the pipe through which the gas flows out with a burner as a multiple pipe can be considered. In addition, a method of adjusting the size of the flame outlet using a shutter is also possible. The heating time can be adjusted by changing the relative moving speed of the burner.
When the heat source is an oxyhydrogen burner, the heating intensity is adjusted by changing the flow rate and flow rate of the supplied gas. The heating range is adjusted by changing the outflow range of the supplied gas and the relative distance between the burner and the article to be heated. Multiple tubes and shutters can be used in the same way as plasma burners. The heating time can be adjusted by changing the relative movement speed of the burner.
When the heat source is a heater, the heating intensity is adjusted by changing the power supplied to the heater. The heating range is adjusted by changing the size of the heater and the relative distance between the heater and the article to be heated. The heating time can be adjusted by changing the relative moving speed of the heater.

As one of the heating methods of the present invention, the surface temperature in the region exposed to the heat source of the article to be heated, which is measured by the method of the first invention, is adjusted so as to become a preset desired temperature. There is something. For example, in the manufacture of glass products, it is possible to prevent variations in quality depending on the part by moving the heat source relatively while adjusting the heating so that the surface temperature becomes constant.
As another heating method, there is a method in which the shape of the temperature distribution created in the method of the second invention is adjusted so as to have a desired shape set in advance. Even if the estimated or measured maximum temperature of the surface of the article to be heated is the same, the heating condition varies greatly depending on the shape of the temperature distribution. If you want to narrow or widen the heat zone, or if you want to create a steep temperature difference between the inside and outside of the heat zone There is a shape of temperature distribution according to each. By adjusting the heating state as a form of temperature distribution, not just the heating temperature, it is possible to perform appropriate heating required according to the product and the manufacturing process, and to improve the quality and yield of the product. .
The case where it is desired to widen the heat zone is, for example, the case where the diameter of the glass tube is reduced, the case where a large-diameter glass tube or a columnar glass is processed, and the case where the heat zone is desired to be narrowed are, for example, a thin glass tube or a circle. This is a case where columnar glass or the like is processed (stretched or the like). In addition, when the temperature difference is desired to be steep, for example, there are cases where glass fine particles are deposited in a glass tube by the MCVD method.

  As another heating method, the temperature at the position where the maximum temperature is estimated from the temperature distribution created in the method of the second invention and the temperature at a position at a certain distance from the position are respectively determined in advance. There is one that adjusts to a set desired temperature. By adjusting the temperature at two points instead of one point, the temperature distribution can be adjusted to some extent, which is a simpler method for adjusting the entire temperature distribution as described above. The “certain distance” at this time can be appropriately selected depending on the material, shape, etc. of the article to be heated, but when the article to be heated is solid, it is preferably not less than the distance from the surface to the center of the article, The distance from the surface to the center of the article is preferably 50 times or less. When the article to be heated is hollow, it is preferably not less than the thickness of the article, and preferably not more than 50 times the thickness of the article. If the “certain distance” is too short, the surface temperature obtained is too close to the maximum temperature, so the merit of adjusting the temperature at two points cannot be obtained. However, the temperature is too low, making it difficult to adjust the heating.

A specific example of measuring the temperature at two points and adjusting the temperature is as follows. For example, when a quartz glass pipe having an outer diameter of 34 mm and an inner diameter of 26 mm is heated by a plasma burner moving at 100 mm / min, it is exposed to a heat source. The region that is formed is 60 to 70 mm (varies depending on the fluctuation of the flame) from end to end with the plasma burner as the center. The radiation thermometer 1 measures a temperature T _{1 at} a position corresponding to the center of the burner, and the radiation thermometer 2 measures a temperature T ₂ at a position 80 mm therefrom. The measurement result at this time is schematically shown in FIG. 7A (the upper line is the measurement result of T ₁ and the lower line is the measurement result of T ₂ ). When the variation of T ₁ is corrected in the same manner as T _{2, the result} is as shown in FIG. Specifically, the correction method is as follows.

(1) Comparison of frequency components Fourier transform of T ₁ (t) (temperature T _{1 at} time t) and T ₂ (t) (T ₂ ) to frequency components τ ₁ (ω) and τ ₂ (ω), respectively. Compare the two. Of the components observed at τ ₁ (ω), the frequency component observed at τ ₂ (ω) is filtered and converted to T ₁ (t) to obtain the temperature of the region exposed to the heat source. The frequency component depends on the stability of the temperature T ₂ (t), the measurement accuracy of the radiation thermometer, etc., but is about several mHz to several tens Hz.

(2) Comparison of moving averages The temperature capturing speed is, for example, once every 0.01 second, and this is i times (if the moving speed is 100 mm / min and the moving distance is 0.5 mm, i = 30. i is 5 to 100) On average, T ₁ and T ₂ are compared. In addition to simple averaging, the averaging process may be performed by multiplying each value by a coefficient so as to increase the weight as the measured value is closer as described in paragraph 0014. An example of taking the center value (median value) of the population i times is given.
Furthermore, the moving averages T ₁ ^AVE (t) and T ₂ ^AVE (t) can be continuously compared with the measurement time.
Temperature difference at a certain time t _i ΔT (t _i ) = T ₁ ^AVE (t _i ) −T ₂ ^AVE (t _i )
When, the next time the temperature difference ΔT in the (next time time after about 0.01 seconds ti _{and) t ii (t ii) =} T 1 AVE (t ii) -T 2 AVE (t ii)
When the fluctuation of is large (for example, when the difference is ± 5% or more), it is determined that T ₁ ^AVE (t _ii ) is not a true value,
T ₁ ^AVE (t _ii ) = T ₂ ^AVE (t _ii ) + ΔT (t _i )
Correct as follows.

(3) Comparison of time differentiation dT ₁ (t) / dt and dT ₂ (t) / dt are continuously compared with time.
At a certain time t _a , dT ₁ (t _a ) / dt = k (t _a ) × dT ₂ (t _a ) / dt
And the next time dT ₁ with (next time time after about 0.01 seconds from t _{a and) t b (t b) /} dt = k (t b) × dT 2 (t b) / Dt
And k (t _a ) and k (t _b ) are compared. If the fluctuation is large (eg, ± 5% or more), it is determined that t _b cannot be measured,
_{dT 1 (t b) / dt} = k (t a) × dT 2 (t b) / dt
Then, the temperature T ₁ (t _b ) is corrected.

  Further, when the article to be heated is hollow, a heating method for estimating the internal surface temperature based on the outer surface temperature measured by the first invention or the second invention and adjusting the inner surface temperature to be a desired temperature. You can also take For example, when depositing glass particles by the MCVD method, what is actually important is the temperature inside the glass tube at which the raw material reacts and the glass particles deposit, or the deposited glass particle layer becomes transparent vitrified. This is because the quality of the glass fine particle deposit or the transparent glass film is improved by direct control. The estimation of the internal surface temperature may be calculated from the measured external surface temperature using the thickness and thermal conductivity of the article to be heated, or for the external surface temperature measured in an area not exposed to a heat source. To the internal surface temperature at a position close to the heat source.

As shown in FIG. 4, the correction of the measured temperature, the estimation of the surface temperature, the creation of the temperature distribution, etc. can be performed by inputting the temperature measured by the thermometers 13 and 13 ′ to the data processing means 14 such as a computer. Further, a command based on the temperature or the like obtained here is sent to the control means 15, and the heating intensity of the heat source (the plasma burner 12 in FIG. 4) is heated during the heating of the article so that the control means 15 has an appropriate temperature and temperature distribution. At least one of the heating range and the heating time can be adjusted. The glass tube 11 rotates around its axis, and the plasma burner 12 and the casing move in parallel with the axis of the glass tube 11.
The surface temperature measuring method and heating method of the present invention can be used for the production of optical fiber preforms. Here, the production of the optical fiber preform includes respective steps such as vapor phase etching of the inner surface of the glass tube, production of a glass fine particle deposit, transparent vitrification, diameter reduction, dehydration, flame polishing, and collapse. Among these, in particular, it can be suitably used for the manufacturing process of the glass fine particle deposit by the MCVD method.

Next, the present invention will be described more specifically with reference to examples. The present invention is not limited to the materials, compositions, and production methods described in the following examples.
Example 1
In the trial manufacture of an optical fiber having a profile as shown in FIG. 5, an F-added SiO ₂ pipe having an outer diameter of 42 mm and a wall thickness of 3 mm is prepared as a second depressed portion.
This pipe is cleaned and smoothed by grinding the inner surface by vapor phase etching. At this time, the internal pressure of the pipe is +50 Pa with respect to the external pressure, the heat source is a plasma burner, and the moving speed of the heat source is 100 mm / min.
As shown in Fig. 6 (a), the temperature is measured at 7 points (3 points in the area exposed to the heat source and 4 points in the unexposed area) as shown in Fig. 6 (a). for maximum temperature T _max calculated from the surface temperature distribution, reflecting that in FIG. 6 (a), the indicated black arrows, the variation of the surface temperature T _B of the portion B which are separated by 10mm from the area that is exposed to the heat source by, the maximum temperature determined (specifically in the method of the first invention described above, the relationship between the surface temperature T _B at the point B of the maximum temperature T _max and black arrows, with T _max = T _B + 600 ° C. _Assuming that T _max is estimated), the heating intensity is controlled and adjusted so that the temperature becomes 2000 ° C. According to this method, the inner surface of the pipe can be etched to a uniform diameter, and the wall thickness can be in the range of 2.80 ± 0.03 mm.
On the other hand, when the measured temperature of the part exposed to the heat source is used, the temperature cannot be measured satisfactorily, making it difficult to control the temperature, and the wall thickness varies to about 2.80 ± 0.07 mm. End up.

(Example 2)
In the pipe obtained in Example 1, the GeO ₂ -added SiO ₂ glass layer serving as the ring part and the F-added SiO ₂ glass layer serving as the first depressed part are internally attached by MCVD using a plasma burner as a heat source. To do. At this time, the moving speed of the heat source is 100 mm / min, and the internal pressure of the pipe is such that the differential pressure between the inside and outside of the pipe is within the range of +100 to +400 Pa so that the pressure inside the pipe is uniform at an outer diameter of 42 mm. To control.
The measurement method of the surface temperature and the determination of the maximum temperature are the same as in Example 1. However, unlike in Example 1, the determined maximum temperature, the temperature distribution, and the thickness of the glass pipe performing the MCVD method are used. The temperature of the pipe inner surface is estimated, and control is performed so that the internal temperature becomes constant.
For example, the following control is performed when the GeO ₂ —SiO ₂ layer is internally attached. The outer surface temperature is measured using a radiation thermometer.
(1) From the obtained temperature distribution of the outer surface, the flow rate of the gas flowing through the plasma burner is controlled so that the range of 1900 ° C. or higher is a constant value of 75 mm (FIG. 6B).
(2) From the thickness of the glass film attached by the MCVD method and the thickness of the starting pipe, the total thickness of the pipe when applying a certain layer is obtained. In order to obtain the total wall thickness, it may be measured directly, or if it cannot be measured, it may be calculated from the number of glass layers attached by the MCVD method and the shape of the starting pipe.
(3) The maximum temperature of the glass surface is calculated by computer simulation so that the maximum temperature of the inner surface is 1500 ° C. At this time, the temperature distribution is assumed to have a typical shape, and the desired inner surface temperature is obtained from physical properties such as specific heat and thermal conductivity of the glass.
(4) The power value applied to the plasma burner is controlled so that the calculated maximum temperature differs for each inner layer of the MCVD method.

Of course, the internal attachment may be performed while controlling the shape of the temperature distribution to be a desired shape. In addition, depending on the calculation method of the internal temperature, the internal temperature may be calculated online from the shape of the measured temperature distribution, and the heating condition of the plasma burner may be controlled so that the temperature of the pipe inner surface becomes a desired value.
The variation of the refractive index of the inner layer thus obtained was extremely small, and the variation rate was ± 0.5% or less. On the other hand, in the method of controlling the temperature of the portion exposed to the heat source on the glass surface, it becomes difficult to control due to variations in measured values, and the refractive index fluctuation rate is about ± 1%.

(Example 3)
The pipe obtained in Example 2 is thermally contracted by a plasma burner. At this time, the temperature distribution on the outer surface of the pipe is obtained by the same measurement method as in Examples 1 and 2. Here, the heating intensity and the heating range are controlled so that the maximum temperature is 2300 ° C. and the region where the temperature is 1900 ° C. or higher is 90 mm.
As a result, the outer diameter of the pipe after the diameter reduction was 32.5 mm. Further, the ellipticity of the outer diameter at this time is as good as 0.1% or less. (Here, the ellipticity is defined as {(ab) × 100} / {(a + b) / 2} where a is the length of the major axis and b is the length of the minor axis).

Example 4
In the pipe obtained in Example 3, a glass rod having a region serving as a central core portion and a region serving as a first depressed portion on the outer periphery thereof is inserted, and heated with a plasma burner to integrate the pipe and the rod. The rod in collapse is executed. At this time, the pressure of the gap between the rod and the pipe is set to 1 kPa in absolute pressure, and the heating intensity is controlled by the same method as in Example 1 so that the maximum temperature of the glass surface becomes 1200 ° C.
As a result, an optical fiber preform having an outer diameter of 32 mm and having a central core portion, a first depressed portion, a first ring portion, and a second depressed portion in order from the center was obtained.

A clad portion is synthesized on the outer periphery of the glass rod thus obtained. The cladding portion can be appropriately synthesized by a soot synthesis method such as VAD or OVD, or a rod in collapse method.
An optical fiber preform in which the cladding portion was synthesized was drawn so that the outer diameter of the glass portion was 125 μm to obtain an optical fiber. The transmission characteristic at the wavelength of 1550 nm is
Transmission loss = 0.19dB / km
Dispersion = + 8.0 ps / nm / km
Dispersion slope = + 0.023 ps / nm ² / km
Cut-off wavelength in cable state = 1300nm
PMD = 0.02ps / km ^1/2
Aeff = 44 μm ²
As a result, an optical fiber having a small dispersion slope and good characteristics as a dispersion-shifted fiber was obtained.
Further, in the MCVD method, the variation of each characteristic is small by performing the internalization by accurately controlling the temperature. Regarding the dispersion characteristics, the dispersion value is 8.0 ± 0.5 ps / nm / km and the dispersion slope is + 0.023 ± 0.001 ps / nm ² / km at a fiber length of 20 km.

It is explanatory drawing which shows typically an example of the surface temperature measurement of the glass tube in the glass fine particle deposition process by MCVD method. It is the typical graph which showed the result of having performed the surface temperature measurement shown in FIG. 1 continuously with the temperature with respect to time, The upper line of (a) is the temperature of the thermometer 2 (area | region exposed to the heat source). Change, the lower line shows the temperature change of the thermometer 2 '(region not exposed to the heat source). (B) is the result of correcting the upper line based on the lower line. It is the graph which showed typically the temperature distribution created by measuring surface temperature in six points of a longitudinal direction in the heating of the glass tube by MCVD method. It is explanatory drawing which shows typically an example of the apparatus using the heating method of this invention. It is a figure which shows the profile of the optical fiber prototyped in the Example. (A) is the temperature distribution on the outer surface of the glass tube obtained in Example 1, and (b) is the temperature distribution on the outer surface of the glass tube obtained in Example 2. (A) is a graph schematically showing a measurement result when temperature measurement is performed at two points inside and outside the region exposed to the heat source, and (b) is a graph showing exposure to the heat source corrected based on the result of (a). It is a graph which shows typically the temperature fluctuation in the area | region currently made.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,11 Glass tube 2, 2 ', 13, 13' Non-contact-type thermometer 3, 12 Plasma burner 4 Case 5 Window 14 Data processing means 15 Control means A Area | region exposed to heat source

Claims (4)

  Temperature distribution at the measurement position by simultaneously measuring the surface temperature of at least one location in the area exposed to the heat source of the hollow article to be heated and multiple locations in the area where the temperature is not exposed to the heat source The temperature at the maximum temperature estimated from the temperature distribution created in the surface temperature measurement method created by the surface temperature measurement method that estimates the surface temperature at a position where measurement is not performed, and the temperature at a position away from the temperature A method for heating an article, wherein at least one selected from a heating intensity, a heating range, and a heating time is adjusted so that each has a desired temperature, and the predetermined distance is equal to or greater than a thickness of the article to be heated.   The method for heating an article according to claim 1, wherein the predetermined distance is 50 times or less the thickness of the article to be heated.   The method for heating an article according to claim 1 or 2, wherein the article to be heated is glass.   The compound used as at least 1 type of glass raw material is introduce | transduced inside a hollow quartz glass body, a glass body is heated with the heating method as described in any one of Claims 1-3, and a novel glass layer is formed inside a glass body. A method of manufacturing an optical fiber preform characterized by depositing.

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