Optical fiber preform manufacturing apparatus and optical fiber preform manufacturing method

Abstract

To prevent a resonance phenomenon in a burner hood from occurring in the step of depositing glass soot while flexibly corresponding to various gas supply conditions.SOLUTION: An apparatus for manufacturing an optical fiber preform includes: a reaction vessel having an arranged start base material; a burner for emitting flame including glass soot toward the start base material in the reaction vessel; a burner hood for orienting the flame to the start base material; and a control mechanism for movably supporting at least one of the burner and the burner hood along the direction of movement of the flame to control a relative position between the burner and the burner hood in the direction of movement.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an apparatus for manufacturing an optical fiber preform and a method for manufacturing an optical fiber preform. [Background technology]

[0002] Some optical fiber preform manufacturing equipment, such as OVD equipment, has a burner hood surrounding the burner. The burner hood is an effective means of directing the gas emitted from the burner and preventing or converging the flame and compounds. However, in burners equipped with a burner hood, depending on the supply conditions of gases such as raw material gas, resonance can occur inside the burner hood, resulting in problems such as a drop in flame temperature due to turbulence in the airflow and noise levels exceeding environmental standards. Therefore, the occurrence of resonance has been a factor that reduces the flexibility of the supply conditions of gases such as raw material gas. For example, in relation to countermeasures against resonance in a burner, Patent Document 1 discloses a combustion device having a structure in which a communication pipe is provided at the starting point of the flame to communicate with the atmosphere. Also, Patent Document 2 discloses a combustion device in which an air passage is provided on the side of the combustion tube and a protruding plate is provided on the inner wall of the combustion tube. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 55-014445 [Patent Document 2] Japanese Patent Application Publication No. 04-121552 Summary of the Invention [Problem to be solved by the invention]

[0004] The techniques described in Patent Documents 1 and 2 are both targeted at burners and burner hoods that are larger than those of optical fiber preform manufacturing equipment such as OVD equipment. Therefore, if the above-mentioned techniques are applied as is to match the size of the burner in an OVD equipment, for example, fine processing must be performed on the burner hood, etc. Furthermore, in optical fiber preform manufacturing equipment, the supply conditions of the raw material gas may be changed as needed, so it is difficult to obtain a resonance prevention structure optimized for each gas supply condition, such as the raw material gas, using the above-mentioned techniques that require processing on the burner hood, etc.

[0005] Therefore, in view of the above-mentioned problems of the conventional technology, the present invention aims to provide an optical fiber preform manufacturing apparatus and an optical fiber preform manufacturing method that can flexibly respond to various gas supply conditions while preventing the occurrence of resonance phenomena within the burner hood during the glass soot deposition process. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided an optical fiber preform manufacturing apparatus comprising: a reaction vessel in which a starting substrate is placed; a burner that emits a flame containing glass soot toward the starting substrate within the reaction vessel; a burner hood that directs the flame toward the starting substrate; and an adjustment mechanism that supports at least one of the burner and the burner hood so that they can move freely along the direction of flame progression, and adjusts the relative positions of the burner and the burner hood in the direction of flame progression.

[0007] According to another aspect of the present invention, there is provided a method for manufacturing an optical fiber preform, in which a flame containing glass soot released from a burner in a reaction vessel is directed and sprayed onto a starting substrate by a burner hood, the method comprising the steps of supporting at least one of the burner and the burner hood so that it can move freely along the direction of the flame, and adjusting the relative positions of the burner and the burner hood in the direction of the flame. [Effects of the Invention]

[0008] According to the present invention, an optical fiber preform manufacturing apparatus and an optical fiber preform manufacturing method are provided that can flexibly respond to various gas supply conditions while preventing the occurrence of resonance phenomena within the burner hood during the glass soot deposition process. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view showing the overall configuration of a manufacturing apparatus according to a first embodiment. [Figure 2] FIG. 3 is an enlarged cross-sectional view illustrating a position adjustment mechanism in the manufacturing apparatus according to the first embodiment. [Figure 3] FIG. 2 is a block diagram showing a schematic configuration of a control system of the manufacturing apparatus according to the first embodiment. [Figure 4] 6 is a flowchart showing an example of a process for adjusting the relative positions of a burner hood and a burner in the manufacturing apparatus according to the first embodiment. [Figure 5] 4 is a flowchart showing an example of a process during glass soot formation in the manufacturing apparatus according to the first embodiment. [Figure 6] 10 is a flowchart showing an example of a process for determining an adjustment policy for the relative position of a burner hood and a burner in a manufacturing apparatus according to a second embodiment. [Figure 7] 10 is a flowchart showing an example of a process for adjusting the relative position of a burner hood and a burner in a manufacturing apparatus according to a third embodiment. [Figure 8] FIG. 10 is a diagram showing the relationship between changes in gas flow rate and noise intensity in an example. [Figure 9] FIG. 1 is a diagram showing the relationship between the distance from the central axis of the flame and the temperature at a position 200 mm away from the tip of the burner along the direction of flame progression, for each gas flow rate, in an example. [Figure 10] FIG. 10 is a diagram showing the temperature distribution at the center of the flame when the amounts of methane and premixed oxygen supplied to the burner are changed in the example. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings described below, parts having the same functions are designated by the same reference numerals, and repeated description thereof will be omitted.

[0011] [First embodiment] 1 is a schematic cross-sectional view showing the overall configuration of a manufacturing apparatus 100 according to this embodiment. The manufacturing apparatus 100 includes a reaction vessel 101, a burner 102, a burner hood 103, a position adjustment mechanism 104, a slide mechanism 105, and an exhaust mechanism 106.

[0012] The burner 102 is disposed so as to protrude into the reaction vessel 101 from a side wall 101a on the air intake side of the reaction vessel 101 via a slide mechanism 105. The burner 102 forms a flame F with a combustion gas supplied from a combustion gas supply device 110 described later in accordance with instructions from a control unit 200 described later, hydrolyzes a glass raw material gas supplied from a raw material gas supply device 111 described later in the flame F to form glass soot, and blows the flame F containing glass particles onto a target rod 108 serving as a starting substrate to deposit the glass particles and form the optical fiber preform 10.

[0013] A raw material gas is supplied to the burner 102 from a raw material gas supply device 111 (described later) via a raw material gas supply line (not shown). The raw material gas is, for example, a gas containing silicon tetrachloride (SiCl4). Octamethylcyclotetrasiloxane (OMCTS) may be used as the raw material gas instead of silicon tetrachloride (SiCl4). The raw material gas may further contain methane, oxygen, nitrogen, hydrogen, etc.

[0014] Furthermore, combustion gas is supplied to the burner 102 from a combustion gas supply device 110 (described later) via a combustion gas supply line (not shown). Examples of the combustion gas include gas containing methane, hydrogen, and oxygen. In this embodiment, the combustion gas used is methane premixed with oxygen at a predetermined volume ratio.

[0015] A seal gas is supplied to the burner 102 from a seal gas supply device 112 (described later) via a seal gas supply line (not shown). Examples of the seal gas include gases containing nitrogen and oxygen.

[0016] The burner hood 103 is disposed at a distance from the tip of the burner 102, i.e., the outlet of the flame F. The burner hood 103 is a member for directing and spraying the flame F emitted from the burner 102 toward the target rod 108. In this embodiment, the burner hood 103 is a cylindrical member with openings formed at both ends.

[0017] The position adjustment mechanism 104 adjusts the relative position between the burner 102 and the burner hood 103. Figure 2 is an enlarged cross-sectional view illustrating the position adjustment mechanism 104 in the manufacturing apparatus 100 according to this embodiment. The position adjustment mechanism 104 supports the burner hood 103 so that it can move freely along the direction A of progression of the flame F (X-axis direction).

[0018] In Figure 2, the distance between the outlet of the flame F at the tip of the burner 102 and the opening surface on the inlet side of the burner hood 103 is D1. The distance D1 can be adjusted by the position adjustment mechanism 104. The length of the burner hood 103 in the traveling direction A is L. Point P is the temperature measurement position of the flame F in this embodiment. The distance from the tip of the burner 102 to point P is D2.

[0019] The slide mechanism 105 is connected to the burner 102 and the position adjustment mechanism 104, and moves the burner 102 and the position adjustment mechanism 104 back and forth in the vertical direction (Z-axis direction) along the guide rail 105a.

[0020] The exhaust mechanism 106 is provided via an exhaust port 106a provided in the side wall 101b opposite to the side wall 101a. The exhaust mechanism 106 has an exhaust hood 106b around the exhaust port 106a to collect exhaust gas after combustion by the burner 102 into the exhaust port 106a. The exhaust hood 106b is provided over almost the entire movable range of the burner 102 in the vertical direction.

[0021] The exhaust mechanism 106 also has a pump and a valve 106c (not shown), and by driving the pump in accordance with instructions from the control unit 200 (described later), a flow of gas G1 can be formed from the intake side of the reaction vessel 101 to the exhaust side, thereby exhausting the inside of the reaction vessel 101. That is, excess glass soot that could not be deposited on the optical fiber preform 10 is collected by the pump through the exhaust hood 106b and exhausted by the exhaust mechanism 106. This makes it possible to stabilize the flame F of the burner 102.

[0022] The manufacturing apparatus 100 also includes a rotation mechanism 107 on the ceiling 101c side of the reaction vessel 101. The rotation mechanism 107 is connected to one end of a target rod 108 serving as a starting substrate. The rotation mechanism 107 rotates the target rod 108 in a rotation direction R around the longitudinal direction of the target rod 108 as the rotation axis in accordance with instructions from a control unit 200 (described later). The other end of the target rod 108 is rotatably connected to a predetermined position on the bottom 101d of the reaction vessel 101.

[0023] A core 10a is formed in advance on the outer periphery of a target rod 108, which is a starting substrate. In the OVD process, glass soot is deposited on the target rod 108 on which the core 10a has already been formed, thereby forming a cladding 10b on the outer periphery of the core 10a. In this way, an optical fiber preform 10 is manufactured.

[0024] 3 is a block diagram showing a schematic configuration of a control system according to this embodiment. The control unit 200 is a control device having a CPU (Central Processing Unit) 201 that executes various processing operations such as calculations, controls, and determinations, and a ROM (Read Only Memory) 202 that stores various control programs executed by the CPU 201. The control unit 200 also has a RAM (Random Access Memory) 203 that temporarily stores input data and data currently being processed by the CPU 201, and a non-volatile memory 204 such as an HDD (Hard Disk Drive) or SSD (Solid State Drive).

[0025] In addition, the control unit 200 is connected to an input operation unit 205 including a keyboard or various switches for inputting predetermined commands or data, and a display unit 206 (for example, a display such as a liquid crystal display or an organic EL display) for displaying various information including the input and setting status of the manufacturing apparatus 100.

[0026] The control unit 200 is connected to the burner 102, position adjustment mechanism 104, slide mechanism 105, exhaust mechanism 106, rotation mechanism 107, combustion gas supply device 110, raw material gas supply device 111, seal gas supply device 112, noise sensor 113, and temperature sensor 114 via drive circuits 207a to 207j, respectively.

[0027] The combustion gas supply device 110 supplies the flow rate controlled combustion gas to the burner 102 via a combustion gas supply line (not shown) in accordance with instructions from the control unit 200 .

[0028] The raw material gas supply device 111 supplies the raw material gas, the flow rate of which is controlled, to the burner 102 via a raw material gas supply line (not shown) in accordance with an instruction from the control unit 200 .

[0029] The seal gas supply device 112 follows instructions from the control unit 200 to supply a flow-controlled seal gas to the burner 102 via a seal gas supply line (not shown).

[0030] The noise sensor 113 is a sensor that measures the volume of noise generated inside the reaction vessel 101 when the flame F is emitted from the burner 102. The noise sensor 113 in this embodiment is disposed outside the reaction vessel 101.

[0031] The temperature sensor 114 is a sensor that measures the temperature distribution of the flame F inside the reaction vessel 101. The temperature sensor 114 of this embodiment is disposed outside the reaction vessel 101.

[0032] Next, we will explain the principle behind the occurrence of the resonance phenomenon in the burner hood 103. As shown in Figures 1 and 2, the burner hood 103 of this embodiment has a cylindrical shape and an open tube shape with both an inlet and an outlet open.

[0033] Vibrations are permitted in the direction of gas inflow and outflow near the opening of the burner hood 103. Therefore, when resonance occurs inside the burner hood 103, the vicinity of this opening becomes the antinode of the standing wave. The resonance frequency f inside the burner hood 103 is approximately expressed by the following equation (1). f=nv / 2L (1) Here, n is an integer representing the number of resonance nodes, v is the speed of sound in the gas inside the hood, and L is the length of the hood. From this equation (1), the resonance wavelength λ is expressed by the following equation (2). λ=2L / n (2)

[0034] It is possible to obtain a more accurate resonant wavelength by applying a simple aperture correction to equation (2) that takes into account the aperture diameter of the burner hood 103. It is also generally known that the antinode of the standing wave is located slightly outside the aperture.

[0035] From the above-mentioned principle, one of the causes of the resonance phenomenon in the burner hood 103 is that the air column in the hood is vibrated near the hood opening edge, which can be the antinode of the standing wave.

[0036] Furthermore, in the burner hood 103 installed near the burner 102, one of the causes of vibration in the air column is a sudden temperature change caused by a chemical reaction of gas within the flame F generated by the burner 102. In other words, when a steep temperature gradient occurs in the space where a combustion reaction or the like occurs, the change in the volume of the gas generates a pressure wave. This pressure wave causes the vibration of the air column.

[0037] As an example, consider the case where a premixed flame of methane is formed in the burner 102. In a stoichiometric premixed flame of 1 mol of methane and 1 mol of air, most of the combustion reaction is completed in the order of approximately 1 msec, and this reaction region is observed from the outside as a pale blue inner flame.

[0038] For example, when gas is supplied at a flow rate of 15 m / sec at room temperature, a steep temperature change occurs over a travel distance of approximately 15 mm, and pressure changes occur in this space due to the expansion of the gas. The temperature of the flame changes depending on the gas mixture ratio, but the temperature at which a flame can be maintained is said to be 1500 K or higher for methane. The burning speed of gas also changes depending on the gas mixture ratio; for example, if the methane mixture ratio is increased above the stoichiometric ratio, the burning speed slows down and the temperature changes more gradually along the direction of gas movement.

[0039] Considering the pressure fluctuations in the air column inside the burner hood 103, resonance is likely to occur at points where temperature changes due to gas reactions occur, which can be the starting point of resonance. In other words, resonance is more likely to occur the closer you are to the opening of the burner hood, the greater the temperature change, and the more narrow the space in which the temperature change occurs.

[0040] The operation of the manufacturing apparatus 100 configured as described above will be described below with reference to the drawings.

[0041] 4 is a flowchart showing an example of a process for adjusting the relative positions of the burner hood 103 and the burner 102 in the manufacturing apparatus 100 according to this embodiment. Note that this process is merely an example and can be changed as desired.

[0042] First, the control unit 200 acquires manufacturing conditions for the optical fiber preform 10 to be manufactured (step S101). The control unit 200 acquires the manufacturing conditions stored in the ROM 202 or the RAM 203 based on, for example, lot information of the optical fiber preform 10 to be manufactured inputted from the input operation unit 205.

[0043] Next, the control unit 200 controls the burner 102, the combustion gas supply device 110, the raw material gas supply device 111, and the seal gas supply device 112 based on the manufacturing conditions acquired in step S101 (step S102), and starts combustion in the burner 102.

[0044] Next, the control unit 200 measures the volume of noise at a predetermined position in the reaction vessel using the noise sensor 113 (step S103).

[0045] Next, the control unit 200 determines whether the measured value of the noise is equal to or less than a predetermined threshold value (step S104).

[0046] Here, if the control unit 200 determines that the measured value of the noise is equal to or less than the predetermined threshold value (step S104: YES), the process proceeds to step S106.

[0047] On the other hand, if the control unit 200 determines that the measured value of the noise exceeds the predetermined threshold (step S104: NO), the process proceeds to step S105.

[0048] In step S105, the control unit 200 controls the driving of the position adjustment mechanism 104 to move the burner hood 103 a predetermined distance along the direction of travel of the flame F, thereby adjusting the relative position between the burner hood 103 and the burner 102. Thereafter, the processing returns to step S103.

[0049] The processes from step S103 to step S105 are repeated until the measured noise value falls below the predetermined threshold.

[0050] In step S106, the control unit 200 determines whether or not to change the manufacturing conditions based on the time that has elapsed since combustion started under the current manufacturing conditions.

[0051] Here, if the control unit 200 determines that the manufacturing conditions are to be changed (step S106: YES), the process proceeds to step S107.

[0052] On the other hand, if it is determined that the manufacturing conditions are not to be changed (step S106: NO), the process proceeds to step S108.

[0053] In step S108, the control unit 200 determines whether or not combustion by the burner 102 should be terminated.

[0054] Here, if the control unit 200 determines that combustion should be terminated (step S108: YES), the process proceeds to step S109. On the other hand, if the control unit 200 determines that combustion should not be terminated (step S108: NO), the control unit 200 continues combustion, and the process returns to step S103.

[0055] In step S109, the control unit 200 stops combustion in the burner 102 and ends the process. Specifically, the control unit 200 controls the combustion gas supply device 110, the raw material gas supply device 111, and the seal gas supply device 112 to stop the gas supply. By the process of Fig. 4, the size of the gap between the tip of the burner 102 and the opening surface on the inlet side of the burner hood 103 is adjusted to a value that can suppress the occurrence of the resonance phenomenon.

[0056] Fig. 5 is a flowchart showing an example of a process for forming glass soot in the manufacturing apparatus 100 according to this embodiment. The process in Fig. 5 is executed after the process in Fig. 4 described above. Note that this process is merely an example and can be changed as desired.

[0057] First, the control unit 200 acquires the manufacturing conditions stored in the ROM 202 or the RAM 203 based on the lot information of the optical fiber preform 10 to be manufactured inputted from the input operation unit 205 (step S201). The manufacturing conditions include the type and flow rate of the gas to be supplied, the rotation speed of the target rod 108, the heating temperature and heating time by the burner 102, etc.

[0058] Next, the control unit 200 controls a driving mechanism (not shown) to place the target rod 108 at a predetermined position in the reaction vessel 101 (step S202).

[0059] Next, the control unit 200 starts the manufacturing glass soot forming process based on the manufacturing conditions acquired in step S201 (step S203). In the glass soot forming process, the control unit 200 controls the rotation mechanism 107 to rotate the target rod 108 in the rotation direction R with the longitudinal direction of the target rod 108 as the rotation axis.

[0060] In the glass soot forming process, the control unit 200 controls the combustion gas supply device 110 to form a flame F using the combustion gas, and controls the raw material gas supply device 111 to hydrolyze the glass raw material gas in the flame F to form glass particles, and then blows the flame containing these particles onto the target rod 108.

[0061] Next, the control unit 200 determines whether the weight of the optical fiber preform 10 measured by a weight scale (not shown) has reached a target value (step S204).

[0062] Here, if the control unit 200 determines that the weight of the optical fiber preform 10 has reached the target value (step S204: YES), the process proceeds to step S206.

[0063] On the other hand, if the control unit 200 determines that the weight of the optical fiber preform 10 has not reached the target value (step S204: NO), the process proceeds to step S205.

[0064] In step S205, the control unit 200 determines whether the time elapsed since the start of the glass soot forming process has reached the end time.

[0065] Here, if the control unit 200 determines that the elapsed time has reached the end time (step S205: YES), the process proceeds to step S206.

[0066] On the other hand, if the control unit 200 determines that the elapsed time has not reached the end time (step S205: NO), the control unit 200 continues the glass forming process under the same conditions until the end time is reached.

[0067] In step S206, the control unit 200 ends the glass soot forming process, and ends the processing of FIG.

[0068] Specifically, the control unit 200 controls the combustion gas supply device 110, the raw material gas supply device 111, and the seal gas supply device 112 to stop the gas supply. The control unit 200 also controls the rotation mechanism 107 to stop the rotation of the target rod 108. Then, the control unit 200 drives the target rod 108 to carry out the optical fiber preform 10 having the glass soot deposited on its surface from the reaction vessel 101.

[0069] In conventional OVD equipment, when resonance occurs inside the burner hood 103, the gas flow becomes turbulent, and the dispersion of the flame leads to a decrease in the soot sintering temperature, causing cracks in the base material. Also, the dispersion of the synthesized silica particles leads to a decrease in the silica adhesion rate to the base material, slowing down the synthesis rate, and other problems arise, resulting in reduced production efficiency.

[0070] In consideration of the above-mentioned problems, the manufacturing apparatus 100 according to this embodiment applies a method of adjusting the distance (clearance) between the burner 102 and the burner hood 103 based on the principle of resonance and the phenomenon that occurs when the resonance occurs. In particular, by using the correlation between the strength of the resonance and the noise level as an index for determining whether the clearance adjustment is satisfactory or not, it has become possible to make appropriate adjustments even under complex gas conditions.

[0071] Furthermore, in manufacturing using an OVD device, in addition to combustion gases, multiple gases, such as raw materials for SiO2 synthesis and inert gases used as raw material carriers and seal gases, are injected and mixed within the flame F generated by the burner 102, causing reactions, making accurate calculations difficult. For this reason, it is extremely effective to use the noise level generated by the burner 102 as an indicator for adjustments to suppress resonance in the burner 102 of the OVD device.

[0072] The manufacturing apparatus 100 described in the above embodiment can also be configured as in the following second and third embodiments. In each embodiment, the same reference numerals as those in the first embodiment indicate the same objects. Explanations of the parts common to the first embodiment will be omitted, and differences will be described in detail.

[0073] [Second embodiment] This embodiment differs from the first embodiment in that it supports the user's manual adjustment work by displaying instruction information on the screen (display unit 206) that shows adjustment guidelines for the relative position of the burner 102 and the burner hood 103.

[0074] 6 is a flowchart showing an example of a process for determining a policy for adjusting the relative positions of the burner hood 103 and the burner 102 in the manufacturing apparatus 100 according to this embodiment. Note that this process is merely an example and can be changed as desired.

[0075] First, the control unit 200 starts combustion in the burner 102 based on the gas supply conditions input by the user via the input operation unit 205 (step S301).

[0076] Next, the control unit 200 measures the volume of noise at a predetermined position in the reaction vessel 101 using the noise sensor 113 (step S302).

[0077] Next, the control unit 200 stops combustion in the burner 102 (step S303). Specifically, the control unit 200 controls the combustion gas supply device 110, the raw material gas supply device 111, and the seal gas supply device 112 to stop the gas supply.

[0078] Next, the control unit 200 determines a policy for adjusting the relative position of the burner 102 and the burner hood 103 based on the noise measurement value of the noise sensor 113 (step S304). Specifically, by storing a table of correspondence relationships between gas supply conditions, noise measurement values, and relative positions in the ROM 202, RAM 203, etc. in advance, the control unit 200 can refer to the table based on the gas supply conditions and the noise measurement values ​​and determine the optimal position for reducing noise.

[0079] Then, the control unit 200 displays instruction information indicating the adjustment policy for the relative position determined in step S304 on the screen of the display unit 206 (step S305), and the processing of FIG. 6 ends.

[0080] According to the manufacturing apparatus 100 of this embodiment, the user can easily adjust the position of the burner hood 103 by manually operating the position adjustment mechanism 104 by referring to the instruction information displayed on the screen of the display unit 206.

[0081] [Third embodiment] This embodiment differs from the first embodiment in that the relative positions of the burner hood 103 and the burner 102 are automatically adjusted based on data of the temperature distribution measured by the temperature sensor 114 without using the noise sensor 113.

[0082] 7 is a flowchart showing an example of an automatic adjustment process for the relative positions of the burner hood 103 and the burner 102 in the manufacturing apparatus 100 according to this embodiment. Note that this process is merely an example and can be changed as desired. For example, similar to the case of FIG. 4, a temperature measurement process by the temperature sensor 114 and a position adjustment process by the position adjustment mechanism 104 may be executed every time the manufacturing conditions are changed at predetermined intervals.

[0083] First, the control unit 200 acquires manufacturing conditions for the optical fiber preform 10 to be manufactured (step S401). The control unit 200 acquires the manufacturing conditions stored in the ROM 202 or the RAM 203 based on, for example, lot information of the optical fiber preform 10 to be manufactured inputted from the input operation unit 205.

[0084] Next, the control unit 200 controls the burner 102, the combustion gas supply device 110, the raw material gas supply device 111, and the seal gas supply device 112 based on the manufacturing conditions acquired in step S401 (step S402), and starts combustion in the burner 102.

[0085] Next, the control unit 200 measures the temperature distribution of the flame F using the temperature sensor 114, starting from the tip of the burner 102 (step S403).

[0086] Next, the control unit 200 stops combustion in the burner 102 (step S404). Specifically, the control unit 200 controls the combustion gas supply device 110, the raw material gas supply device 111, and the seal gas supply device 112 to stop the gas supply.

[0087] Next, the control unit 200 analyzes the temperature distribution measured in step S403, and identifies a region in which the temperature gradient exceeds a predetermined threshold in the direction A of progression of the flame F (step S405).

[0088] Then, the control unit 200 controls the driving of the position adjustment mechanism 104 to move the burner hood 103 based on the position identified in step S405, thereby adjusting the relative position between the burner hood 103 and the burner 102 (step S406), and ends the processing of Figure 7.

[0089] According to this embodiment, the distance between the tip of the burner 102 and the opening surface on the inlet side of the burner hood 103 is adjusted to a value that can suppress the occurrence of the resonance phenomenon according to the temperature distribution of the flame. Specifically, the relative positions of the burner hood 103 and the burner 102 are adjusted so that the region where the temperature gradient in the direction of flame progression exceeds a predetermined value is located between the inlet of the burner hood 103 and the burner. It is preferable that the position where a steep temperature gradient occurs is located slightly outside the inlet of the burner hood 103, avoiding a region that could become an antinode of a pressure standing wave due to combustion.

[0090] [Example] 8 to 10, an example of equipment adjustment when methane is burned by the burner 102 will be described. In this example, a glass tube with an inner diameter of 45 mm and a length of 100 mm was used as the burner hood 103. The initial position of the opening on the inlet side of the burner hood 103 was set 4 mm away from the tip of the burner 102.

[0091] FIG. 8 shows the relationship between changes in gas flow rate and noise intensity in this example. The horizontal axis represents the flow rate (L / min) of methane (CH4) that constitutes the combustion gas, and the vertical axis represents the flow rate (L / min) of premixed oxygen (O2) that is premixed with the methane. The symbols "x," "△," and "◯" in the graph qualitatively represent the strength of the resonance that occurred when methane and premixed oxygen were introduced into the burner 102. The strength of the resonance is ranked in order from smallest to largest: "◯," "△," and "x." FIG. 8 shows that the strongest resonance occurred when the methane flow rate was 18 (L / min) and the premixed oxygen flow rate was 20 (L / min).

[0092] Figure 9 shows the relationship between the distance from the center of the burner 102 and the temperature for each gas flow rate in this example. Figure 9 shows the case where gas is supplied at a predetermined volumetric flow rate, and the temperature is measured at a predetermined temperature measurement position at a distance of 200 mm from the tip of the burner 102 along the flame propagation direction, while the distance from the central axis of the flame F is changed. The symbols "△", "◯", and "□" in the graph represent cases where the flow rates (L / min) of the premixed oxygen O2 are 16, 20, and 24, respectively. Figure 9 shows that the drop in flame temperature is particularly large under the gas supply conditions marked with "◯" in the figure, where the strongest resonance occurs.

[0093] 10 is a diagram showing the temperature distribution at the center of the flame when the amounts of methane and premixed oxygen supplied to the burner 102 are changed. Table 1 shows the noise level measured under each condition at a position about 1 m away from the burner 102, outside the chamber wall of the manufacturing apparatus 100. [Table 1]

[0094] The strength of the resonance within the burner hood 103 is related to the volume of noise generated by the burner hood 103. As shown in Figure 10, as the mixture ratio of methane to premixed air approaches the stoichiometric ratio, the flame temperature increases and the highest temperature point of the flame tends to move closer to the hood opening edge. As this change makes resonance more likely to occur, the noise level around the equipment also increases; for example, as shown in Table 1, in the graph for volumetric flow ratio R4, a maximum noise level of over 100 dB was detected.

[0095] In contrast, by adjusting the distance D1 (clearance) between the burner 102 and the inlet opening of the burner hood 103 so that the maximum noise level falls to less than 80 dB, close to the level when the equipment is stopped, under any of the gas conditions (volumetric flow ratios R1 to R4) in the figure, it was possible to eliminate the resonance phenomenon within the burner hood 103. In this case, the distance between the burner 102 and the inlet opening of the burner hood 103 was 29 mm, and it was confirmed that the inlet of the burner hood 103 was positioned in a relatively stable position after the flame temperature peaked.

[0096] It should be noted that the above-described embodiments are merely examples of specific implementations of the present invention, and the technical scope of the present invention should not be construed as being limited thereby. In other words, the present invention can be implemented in various forms without departing from its technical concept or main features.

[0097] [Modified embodiment] In the above-described embodiment, a case has been described in which only the burner hood 103 is moved along the direction A of flame advance, but the method of adjusting the relative position of the burner 102 and the burner hood 103 is not limited to this. For example, only the burner 102 may be moved, or both the burner 102 and the burner hood 103 may be moved to adjust the relative position. In other words, the position adjustment mechanism 104 may be configured to support at least one of the burner 102 and the burner hood 103 so that they can move freely along the direction of advance, and to adjust the relative position of the burner 102 and the burner hood 103 in the direction of flame advance.

[0098] In the above-described embodiment, the manufacturing apparatus 100 is of a vertical type, but the manufacturing apparatus 100 to which the present invention can be applied is not limited to a vertical type, and may be of a horizontal type.

[0099] In the above embodiment, the burner hood 103 is described as being cylindrical, but the burner hood 103 does not necessarily have to be perfectly cylindrical. For example, the burner hood 103 may be tapered in part or all of the direction of flame travel, or may be formed so that the cross section of the burner hood 103 relative to the direction of gas travel is polygonal. Furthermore, the burner hood 103 may be formed by combining multiple plate materials.

[0100] In addition, in the above-described embodiment, the burner hood 103 is open at both ends, but it may be open at only one end. In this case, too, the relative positions of the burner 102 and the burner hood 103 can be changed by moving at least one of the burner 102 and the burner hood, thereby achieving the same effect as the above-described embodiment.

[0101] Furthermore, in the above-described first embodiment, the relative position is adjusted using the noise sensor 113, and in the third embodiment, the relative position is adjusted using the temperature sensor 114. However, the relative position may also be adjusted by combining both the noise sensor 113 and the temperature sensor 114. [Explanation of symbols]

[0102] 10. Optical fiber preform (glass soot preform) 10a Core part 10b Cladding part 100...Manufacturing equipment 101 Reaction vessel 101a...1st side wall 101b...Second side wall 101c··Ceiling 101d...Bottom 102 Burner 103 Burner Hood 104...Position adjustment mechanism 106 Exhaust mechanism 106a···Exhaust port 106b···Exhaust hood 106c Valve 107 Rotation mechanism 108···Target Rod 110 Combustion gas supply device 111 Raw material gas supply device 112 Seal gas supply device 113 Noise sensor 114 Temperature sensor 200 Control unit 201 CPU 202···ROM 203 RAM 204 Non-volatile memory 205 Input operation section 206...Display section 207a to 207j Drive circuit

Claims

1. a reaction vessel in which the starting substrate is placed; a burner that projects a flame containing glass soot toward the starting substrate within the reaction vessel; a burner hood for directing the flame toward the starting substrate; an adjustment mechanism that supports at least one of the burner and the burner hood so as to be freely movable along the direction of flame advance and adjusts the relative position of the burner and the burner hood in the direction of flame advance; a noise sensor for measuring the magnitude of noise generated from the burner; a control device that controls the adjustment of the relative position in the adjustment mechanism based on the magnitude of the noise; An optical fiber preform manufacturing apparatus comprising:

2. The burner hood is disposed at a distance from the flame outlet of the burner in the traveling direction, the adjustment mechanism adjusts the distance between the discharge port and the burner hood in the traveling direction.

2. The optical fiber preform manufacturing apparatus according to claim 1,

3. Further comprising a display, the control device causes the display device to display instruction information indicating an adjustment policy for the relative position in the adjustment mechanism based on the magnitude of the noise.

3. The optical fiber preform manufacturing apparatus according to claim 1, wherein the optical fiber preform is a tubular member.

4. Further provided is a temperature sensor for measuring the temperature distribution of the flame, the control device controls the adjustment of the relative position in the adjustment mechanism based on the temperature distribution.

3. The optical fiber preform manufacturing apparatus according to claim 1, wherein the optical fiber preform is a tubular member.

5. The relative position is adjusted based on a resonance wavelength of a pressure wave generated in the burner hood by the flame and the temperature distribution.

5. The optical fiber preform manufacturing apparatus according to claim 4.

6. The relative position is adjusted so that a region in which a temperature gradient in the traveling direction exceeds a predetermined value is located between an inlet of the burner hood and the burner.

6. The optical fiber preform manufacturing apparatus according to claim 4, wherein the optical fiber preform is made of a fluororesin.

7. A method for manufacturing an optical fiber preform, in which a flame containing glass soot emitted from a burner in a reaction vessel is directed toward a starting substrate by a burner hood, a step of supporting at least one of the burner and the burner hood so as to be freely movable along a direction in which the flame advances, and adjusting the relative positions of the burner and the burner hood in the direction in which the flame advances; measuring the magnitude of noise generated from the burner with a noise sensor; Equipped with 4. The method for manufacturing an optical fiber preform, wherein, in the step of adjusting the relative position, the relative position is adjusted based on the magnitude of the noise.

8. In the step of adjusting the relative position, the burner hood is disposed at a distance from the flame outlet of the burner in the traveling direction, and at least one of the burner and the burner hood is moved along the traveling direction to adjust the distance between the outlet and the burner hood in the traveling direction.

8. The method for manufacturing an optical fiber preform according to claim 7.

9. further comprising a step of measuring the temperature distribution of the flame with a temperature sensor; In the step of adjusting the relative position, the relative position is adjusted to a position where a temperature gradient of the flame in the traveling direction is equal to or less than a predetermined value.

9. The method for manufacturing an optical fiber preform according to claim 7 or 8.

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