Device and method for VAD deposition of optical fiber preform

Abstract

The invention relates to a device for VAD deposition of an optical fiber preform. A lifting rotating motor is arranged above a reaction cavity; the top of the target rod is connected with a lifting rotating motor, and the bottom extends into the reaction cavity; the blowtorch mechanism comprises a core layer blowtorch which is provided with an upward inclined jet orifice and is connected with a feeding system; the image shooting unit shoots image data of a core layer deposition area; the visual system is connected with the image shooting unit and processes the image data to obtain a deposition angle, and the deposition angle is an included angle between the axis of the target rod and a connecting line between the lowest point of core layer deposition and the center of the jet orifice of the core layer blowtorch; a thermodetector measures the temperature of the deposition end face of the core layer; and the PID controller is connected with the visual system, the thermodetector, the feeding system and the lifting rotating motor, and performs closed-loop adjustment based on the deposition angle, the temperature, the raw material flow of the feeding system and the lifting speed of the target rod. The lifting speed control stability is improved from the aspects of the core layer deposition end face temperature and the relative position of the core layer and the blow lamp, and therefore the product quality is improved.

Description

Technical Field

[0001] The present application relates to the field of optical fiber preform manufacturing, and in particular to a device and method for VAD deposition of optical fiber preform. Background Art

[0002] In the current optical fiber preform manufacturing process, the quality of the core rod determines the quality of the optical fiber. In the VAD deposition process, it is crucial to control the stability of the growth surface shape and the uniformity of the outer diameter of the loose body preform to ensure the quality of the optical fiber.

[0003] The stability of the growth surface shape and the uniformity of the outer diameter of the loose body preform rod depend on various deposition process conditions, such as flame temperature, temperature of the deposition end surface, exhaust speed, preform rod lifting speed, relative position of the deposition end surface and the blowtorch, etc.

[0004] The temperature of the SOOT deposition surface also has a great influence on the growth rate of the powder rod. If the core surface temperature is too high, the density of the powder rod will increase, reducing the deposition rate. At the same time, the temperature has a very large impact on the conversion rate of GeO2. When the temperature is too high, GeO2 will decompose into GeO and cause a decrease in the relative refractive index difference. The relative refractive index difference is usually increased by increasing the GeCl4 flow rate, but this will lead to an increase in cost. At the same time, too high or too low temperature will also affect the density of the powder rod, thereby affecting the stability of the deposition rate.

[0005] In some related technologies, the core layer diameter is continuously detected by a laser rangefinder, which is fed back to the PLC unit after processing and compared with the set core layer diameter to control the lifting speed of the rotating boom, thereby ensuring that the core layer diameter of the deposited preform powder rod is always uniform. However, the laser rangefinder is affected by the flame, and measuring objects with a flame atmosphere affects the measurement accuracy. In addition, the dust is large during the powder rod deposition process and will adhere to the rangefinder window, affecting the distance measurement accuracy.

[0006] In some related technologies, the distribution image of the outer diameter is collected by a CCD detector and transmitted to an image processing component. After the area S1 of the core layer deposition area is greater than a preset value, the PID controller is used to control the target rod lifting speed to increase. However, the core layer deposition area is an irregular area, and the boundary between the core layer and the middle layer is affected by the blowtorch angle, flame temperature, and the flame shape of the core layer and the middle layer. The shape is constantly changing, the area cannot be calculated more accurately, and the core layer deposition process has a time lag effect, so it is difficult to accurately control using the area as a feedback signal.

[0007] In some related technologies, the power of the laser receiving end is detected and the position of the torch is adjusted to stabilize the growth of the core rod and ensure the stability of the axial size. However, frequent adjustment of the position of the torch will cause the position of the deposition point to change continuously. The change of the deposition position will change the bottom shape of the deposition point, which in turn will cause the fluctuation of the laser feedback power, resulting in the re-adjustment of the torch. The entire control system is not easy to reach a steady state, which is not conducive to the stability of the deposition growth rate. Summary of the invention

[0008] The embodiments of the present application provide a device and method for VAD deposition of optical fiber preform, which improves the stability of lifting speed control from the aspects of core layer deposition end surface temperature and the relative position of the core layer and the blowtorch, thereby improving product quality.

[0009] In a first aspect, a device for VAD deposition of optical fiber preform is provided, comprising:

[0010] A reaction chamber, which is used for performing a deposition reaction and has a lifting and rotating motor disposed above it;

[0011] A target rod, the top of which is connected to the lifting and rotating motor, and the bottom of which extends into the reaction chamber;

[0012] The blowtorch mechanism comprises a core blowtorch with a spray port inclined upward and connected to a feed system;

[0013] An image capturing unit, which is used to capture image data of the core layer deposition area;

[0014] A visual system connected to the image capturing unit and used to process the image data to obtain a deposition angle, which is the angle between the line between the lowest point of the core layer deposition and the center of the core layer torch jet and the target rod axis;

[0015] A temperature measuring instrument, which is used to measure the temperature of the core layer deposition end surface;

[0016] The PID controller is connected to the vision system, the temperature measuring instrument, the feeding system and the lifting and rotating motor, and is used to perform closed-loop regulation based on the deposition angle, temperature, the raw material flow rate of the feeding system and the lifting speed of the target rod.

[0017] In some embodiments, the image capturing unit includes an industrial camera, a base, and a four-degree-of-freedom platform, and the industrial camera is mounted on the base via the four-degree-of-freedom platform for adjustment in the X, Y, Z directions and rotational directions.

[0018] In some embodiments, two observation windows are provided on the reaction chamber, and the image capturing unit and the temperature measuring instrument face the two observation windows respectively.

[0019] In some embodiments, the top of the target rod is connected to a suspension rod via a chuck, and the suspension rod is connected to the lifting and rotating motor.

[0020] In some embodiments, the visual system is further used to process the image data to obtain the core layer diameter and the core layer shape;

[0021] The PID controller is also used to perform closed-loop regulation based on the core layer diameter and core layer shape, and the raw material flow rate of the feeding system.

[0022] In a second aspect, a method for preparing an optical fiber preform by using the VAD deposition optical fiber preform device as described above is provided, comprising:

[0023] Comparing the deposition angle obtained by the visual system with an angle threshold to obtain an angle deviation;

[0024] If the angle deviation is within the first angle deviation range, the lifting speed of the target rod is not adjusted;

[0025] If the angle deviation is outside the first angle deviation range and within the second angle deviation range, the lifting speed of the target rod is adjusted by the PID controller based on the lifting stable speed of the target rod, the basic speed of the angle influencing factor, the weight of the angle influencing factor, the basic speed of the temperature influencing factor, and the weight of the temperature influencing factor;

[0026] Compare the temperature obtained by the thermometer with the temperature threshold to obtain the temperature deviation;

[0027] If the temperature deviation is within the first temperature deviation range, the raw material flow rate of the feeding system corresponding to the core layer burner is not adjusted;

[0028] If the temperature deviation is outside the first temperature deviation range and within the second temperature deviation range, the oxygen flow rate is adjusted by the PID controller;

[0029] If it is outside the second temperature deviation range, the hydrogen flow rate is adjusted through the PID controller.

[0030] In some embodiments, the first angle deviation range is -0.2° to +0.2°;

[0031] The second angle deviation range is -0.5°~+0.5°;

[0032] The first temperature deviation range is -5℃~+5℃;

[0033] The second temperature deviation range is -10°C to +10°C.

[0034] In some embodiments, if the angle deviation is outside the second angle deviation range, manual intervention is performed.

[0035] In some embodiments, if the temperature deviation exceeds a set alarm temperature, manual intervention is performed.

[0036] In some embodiments, the image data is processed to obtain the core diameter and the core shape;

[0037] If the core layer shape is inconsistent with the preset shape, an alarm will be sounded and the machine will be shut down;

[0038] If the core shape is consistent with the preset shape, the core diameter is compared with the preset diameter;

[0039] If it is smaller than the preset diameter, the PID controller is used to adjust the raw material flow rate of the feeding system corresponding to the core layer burner;

[0040] If it is larger than the preset diameter, the PID controller is used to adjust the raw material flow of the feeding system corresponding to the core layer burner.

[0041] The beneficial effects of the technical solution provided by this application include:

[0042] The embodiment of the present application provides a device and method for VAD deposition of optical fiber preform rods. The present application eliminates or greatly reduces the influence of flame on the image data captured by the image capture unit through the image processing function, thereby improving the detection accuracy. The present application detects the angle between the lowest point of the core layer deposition and the core layer torch through the visual system, measures the temperature of the core layer deposition end face through the thermometer, and achieves the purpose of stabilizing the control of the lifting speed by controlling the angle between the lowest point of the core layer deposition and the core layer torch, as well as controlling the temperature of the core layer deposition end face and other factors, thereby achieving the goal of stabilizing the growth rate of the preform rod, improving the control accuracy of the growth rate, and controlling the temperature stability of the core layer deposition end face, which not only ensures the stability of the core layer density, but also reduces the influence of density changes on the growth rate of the powder rod, and at the same time can improve the conversion rate of GeO2, realize the precise control of the relative refractive index difference, ensure the stability of the relative refractive index difference, and ultimately improve the product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0044] Figure 1 Schematic diagram of a device for VAD deposition of optical fiber preform provided in an embodiment of the present application.

[0045] In the figure: 1. reaction chamber; 2. lifting and rotating motor; 3. target rod; 4. outer cladding torch; 5. inner cladding torch; 6. core layer torch; 7. feeding system; 8. image capture unit; 9. visual system; 10. thermometer; 11. PID controller; 12. chuck; 13. suspension rod; 14. observation window. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0047] See also Figure 1 As shown, the embodiment of the present application provides a device for VAD deposition of optical fiber preform, the reaction chamber 1 is used for deposition reaction, a lifting and rotating motor 2 is arranged above the reaction chamber 1, the top of the target rod 3 is connected to the lifting and rotating motor 2, and the bottom extends into the reaction chamber 1 to connect to the preform loose body soot, the lifting and rotating motor 2 can drive the target rod to drive the preform loose body to rotate and lift upward; the blowtorch mechanism includes an outer cladding blowtorch 4, an inner cladding blowtorch 5 and a core layer blowtorch 6 to deposit the outer cladding, inner cladding and core layer of the optical fiber preform respectively, the injection ports of the outer cladding blowtorch 4, the inner cladding blowtorch 5 and the core layer blowtorch 6 are inclined upward and form a certain angle with the horizontal, the outer cladding blowtorch 4, the inner cladding blowtorch 5 and the core layer blowtorch 6 are arranged in sequence from top to bottom, and the outer cladding blowtorch 4, the inner cladding blowtorch 5 and the core layer blowtorch 6 are respectively connected to independent feeding systems 7.

[0048] A high-resolution visual system 9 is arranged outside the reaction chamber 1. The visual system 9 is connected to an image capturing unit 8. The image capturing unit 8 is installed on a column independent of the reaction chamber. The image capturing unit 8 is used to monitor the deposition process in real time and capture image data of the core layer deposition area. The visual system 9 is used to process the image data through feature point matching, edge search, position correction, and calculation of the gradient amplitude and gradient direction of the pixel points, so as to accurately locate the lowest point of the core layer deposition, and suppress the image edge noise interference through image denoising and smoothing filtering, eliminate or greatly reduce the influence of flame and high temperature on the detection result, and ensure the accuracy of the detection result. Finally, the angle between the line connecting the lowest point of the core layer deposition and the center of the injection port of the core layer blowtorch 6 and the axis of the target rod 3 is calculated, so as to obtain the deposition angle. A thermometer 10 is arranged outside the reaction chamber 1, and the temperature of the core layer deposition end face is measured by the thermometer 10.

[0049] The PID controller 11 is connected to the vision system 9 , the temperature measuring instrument 10 , the feeding system 7 and the lifting and rotating motor 2 , and is used to perform closed-loop regulation based on the deposition angle, temperature, the raw material flow rate of the feeding system 7 and the lifting speed of the target rod 3 .

[0050] The present application eliminates or greatly reduces the influence of the flame on the image data captured by the image capturing unit 8 through the image processing function, thereby improving the detection accuracy. The present application detects the angle between the lowest point of the core layer deposition and the core layer torch 6 through the visual system 9, measures the temperature of the core layer deposition end face through the thermometer 10, and achieves the purpose of stabilizing the control of the lifting speed by controlling the angle between the lowest point of the core layer deposition and the core layer torch 6, and controlling the temperature of the core layer deposition end face and other factors, thereby achieving the goal of stabilizing the growth rate of the preform rod, improving the control accuracy of the growth rate, and controlling the temperature stability of the core layer deposition end face, which not only ensures the stability of the core layer density, but also reduces the influence of density changes on the growth rate of the powder rod, and at the same time can improve the conversion rate of GeO2, realize the precise control of the relative refractive index difference, ensure the stability of the relative refractive index difference, and ultimately improve the product quality.

[0051] In the present application, the image capture unit 8 includes an industrial camera, a base, and a four-degree-of-freedom platform. The industrial camera is mounted on the base through the four-degree-of-freedom platform to adjust the X, Y, Z directions and the rotation direction. Among them, the industrial camera can directly use the CCD, and the four-degree-of-freedom platform can ensure that the industrial camera rotates and moves around the X, Y, and Z directions to match the field of view of the visual system 9 and meet the control requirements. The vertical direction can be the Z direction, and the X and Y directions can constitute a horizontal plane.

[0052] The thermometer 10 is installed on a bracket erected on the ground, and detects the temperature through an observation window. By setting up an air cooling and water cooling system to cool the image capture unit and the thermometer body, the thermometer 10 can simultaneously measure the temperature of multiple points and the average temperature of multiple areas. Compared with ordinary point-shaped temperature sensors, it can more accurately feedback the temperature of the deposition area. In this application, the temperature of the core layer deposition end surface can be selected as a representative of the temperature of one point on the end surface. The thermometer 10 transmits the temperature of the core layer deposition end surface to the PID controller through communication.

[0053] Further, see Figure 1 As shown, two observation windows 14 are provided on the reaction chamber 1 , and the image capturing unit 8 and the temperature measuring instrument 10 face the two observation windows 14 respectively.

[0054] Further, see Figure 1 As shown, the top of the target rod 3 is connected to the suspension rod 13 through a chuck 12 , and the suspension rod 13 is connected to the lifting and rotating motor 2 .

[0055] Furthermore, the visual system 9 is also used to process the image data to obtain the core layer diameter and core layer shape; the PID controller 11 is also used to perform closed-loop regulation based on the core layer diameter and core layer shape and the raw material flow of the feeding system 7.

[0056] Closed-loop control of the core layer diameter and core layer shape can ensure the consistency of product quality.

[0057] The present application also provides a method for preparing an optical fiber preform by using a VAD deposition device for an optical fiber preform, which comprises the following steps:

[0058] 101: The target rod 3 is lowered to the initial deposition position by the lifting and rotating motor 2, and the rotation is started.

[0059] The core layer burner 6, the inner cladding burner 5 and the outer cladding burner 4 are sequentially ignited, the cavity door is closed, the air supply and exhaust valves are opened to appropriate openings, and the lifting and rotating motor 2 drives the target rod 3 to start rotating at an initial speed (as an example, such as 50r / min). At this time, the upward lifting speed of the lifting and rotating motor 2 is zero.

[0060] 102: According to the preset formula, the raw material flow rate of the feeding system 7 of the core layer, the inner cladding layer and the outer cladding layer is set, and the product after the hydrolysis reaction begins to be deposited on the target rod. At this time, it is in the speed control mode, and the constant speed is increased according to the preset formula. The initial speed is zero. As the deposition proceeds, the shape of the bottom of the core layer is gradually formed, and as the given flow rate tends to be stable, the deposition speed gradually increases, and the speed fluctuation gradually decreases and tends to be stable. For example, as an example, the deposition increase speed is about 2.0 mm / min when stable, and this speed can be used as the deposition stabilization speed.

[0061] 103: When the powder stick has entered the stable growth stage, the system switches to the angle control mode. The deposition angle θ obtained by the visual system 9 is compared with the angle threshold to obtain the angle deviation. Specifically, the angle deviation is obtained by subtracting the angle threshold from the deposition angle θ.

[0062] If the angle deviation is within the first angle deviation range, the lifting speed of the target rod 3 is not adjusted, and the target rod 3 is lifted at the deposition stable speed.

[0063] If the angle deviation is outside the first angle deviation range and within the second angle deviation range, the lifting speed of the target rod 3 is adjusted by the PID controller 11 based on the stable lifting speed of the target rod 3, the basic speed of the angle influencing factor, the weight of the angle influencing factor, the basic speed of the temperature influencing factor, and the weight of the temperature influencing factor.

[0064] If the angle deviation is outside the second angle deviation range, it means that the deposition process is abnormal and the shape of the bottom core layer may be deformed. Then the angle control mode is switched to the manual control mode for manual intervention, and an alarm is issued to remind the operator to intervene. After manual intervention, when the angle returns to the control range, the angle control mode can be switched back to the angle control mode.

[0065] The above-mentioned angle threshold, first angle deviation range, and second angle deviation range can be set according to actual needs.

[0066] For example, as an example, the first angle deviation range is -0.2° to +0.2°; the second angle deviation range is -0.5° to +0.5°.

[0067] Among them, see Figure 1 As shown, when the lifting is too fast, the lowest point of the core layer deposition is biased upward, and the angle deviation is positive. When the lifting is too slow, the lowest point of the core layer deposition is biased downward, and the angle deviation is negative.

[0068] When the angle deviation is between -0.2° and +0.2°, no adjustment is required; when the angle deviation is between -0.5° and -0.2° or between +0.2° and +0.5°, the lifting speed of the target rod 3 is adjusted by the PID controller 11. When the angle deviation is less than -0.5° or greater than +0.5°, manual intervention is performed.

[0069] Based on the lifting stable speed of the target rod 3, the basic speed of the angle influencing factor, the weight of the angle influencing factor, the basic speed of the temperature influencing factor, and the weight of the temperature influencing factor, the lifting speed of the target rod 3 is adjusted by the PID controller 11, specifically:

[0070] Lifting speed V = deposition stability speed V0 + angle influencing factor basic speed V 01 × Angle influence factor weight Q 01 × Angle influence factor P ID feedback percentage P 01 +Temperature Factor Base Speed ​​V 02 × Temperature influence factor weight Q 02 ×Temperature influence factor P ID feedback percentage P 02 .

[0071] Among them, the angle influencing factor P ID feedback percentage P 01 and temperature influence factors P ID feedback percentage P 02 The value range is -100% to +100%, which is specifically fed back by the PID controller.

[0072] Through the above PID closed control, the lifting speed V is determined by the angle and temperature, that is, by the deposition angle θ and the core layer deposition end surface temperature. The angle influencing factor weight Q 01, Temperature influence factor weight Q 02 、Angle influence factor basic speed V 01 and temperature factors affecting the base speed V 02 Can be assigned in advance.

[0073] In order to further reduce the interference of flame on detection, the data transmitted from the visual system is filtered in the software. The median average filtering method is used in this system, which can eliminate the sampling value deviation caused by accidental pulse interference.

[0074] 104: The temperature measuring instrument 10 performs online temperature detection on the core layer deposition end face in real time. No temperature control is performed in the bottom formation stage, and only the temperature of the powder rod core layer matrix is ​​monitored. The fuel hydrogen and oxygen flow rates are adjusted through the formula to make the temperature of the core layer matrix gradually approach the temperature threshold. When entering the stable growth stage and the temperature is stable and close to the temperature threshold, the temperature control mode is turned on.

[0075] The temperature acquired by the thermometer 10 is compared with the temperature threshold to obtain the temperature deviation. Specifically, the temperature deviation is obtained by subtracting the temperature threshold from the temperature.

[0076] If the temperature deviation is within the first temperature deviation range, the raw material flow rate of the feeding system 7 corresponding to the core layer burner 6 is not adjusted.

[0077] If the temperature deviation is outside the first temperature deviation range and within the second temperature deviation range, the oxygen flow rate is adjusted by the PID controller 11.

[0078] If the temperature is outside the second temperature deviation range, the hydrogen flow rate is adjusted by the PID controller 11 .

[0079] If the temperature deviation exceeds the set alarm temperature, manual intervention is performed.

[0080] The above-mentioned temperature threshold, first temperature deviation range, second temperature deviation range, and alarm temperature can be set according to actual needs.

[0081] For example, as an example, the first temperature deviation range is -5°C to +5°C; the second temperature deviation range is -10°C to +10°C.

[0082] 105: When the effective length of the powder rod reaches the preset length, the system exits the angle control mode and the temperature control mode, enters the manual control mode, maintains a constant speed to lift the rod, the core layer burner stops firing, cuts off the flow of the feeding system, and then the inner and outer layer burners stop firing in turn. When all the burners are extinguished, it enters the cooling stage. After 15 minutes, the cooling is completed, the formula is completed, and the deposition process is completed. The powder rod is moved out of the deposition chamber and transported to the next sintering process.

[0083] Furthermore, the method also includes: processing the image data to obtain the core layer diameter and the core layer shape; if the core layer shape is inconsistent with the preset shape, an alarm is issued and the machine is shut down; if the core layer shape is consistent with the preset shape, the core layer diameter is compared with the preset diameter; if it is smaller than the preset diameter, adjustment is made through the PID controller 11 to increase the raw material flow rate of the feeding system 7 corresponding to the core layer blowtorch 6; if it is larger than the preset diameter, adjustment is made through the PID controller 11 to reduce the raw material flow rate of the feeding system 7 corresponding to the core layer blowtorch 6.

[0084] By comparing the core layer shape with the preset shape in real time, it is possible to monitor whether the appearance shape of the powder rod meets the requirements. When an abnormality occurs, an early warning shutdown or manual intervention is issued to ensure product consistency and promote further improvement of VAD's powder rod product quality indicators such as outer diameter, density and uniformity.

[0085] In the description of the present application, it should be noted that the terms "upper", "lower", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. Unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0086] It should be noted that, in this application, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0087] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A device for VAD deposition of optical fiber preform, characterized in that: It includes: A reaction chamber (1) is used for carrying out a deposition reaction, and a lifting and rotating motor (2) is arranged above the reaction chamber; A target rod (3), the top of which is connected to the lifting and rotating motor (2) and the bottom of which extends into the reaction chamber (1); A blowtorch mechanism, comprising a core layer blowtorch (6) with a spray port inclined upward and connected to a feed system (7); An image capturing unit (8) for capturing image data of a core layer deposition area; A visual system (9) connected to the image capturing unit (8) and used to process the image data to obtain a deposition angle, wherein the deposition angle is the angle between a line connecting the lowest point of the core layer deposition and the center of the jet port of the core layer torch (6) and the axis of the target rod (3); A temperature measuring instrument (10) for measuring the temperature of the core layer deposition end surface; A PID controller (11) is connected to the visual system (9), the temperature measuring instrument (10), the feeding system (7) and the lifting and rotating motor (2), and is used to perform closed-loop regulation based on the deposition angle, temperature, the raw material flow rate of the feeding system (7) and the lifting speed of the target rod (3).

2. The VAD deposition device for optical fiber preform according to claim 1, characterized in that: The image capture unit (8) comprises an industrial camera, a base, and a four-degree-of-freedom platform. The industrial camera is mounted on the base via the four-degree-of-freedom platform to perform adjustment in the X, Y, Z directions and the rotation direction.

3. The VAD deposition device for optical fiber preform according to claim 1, characterized in that: The reaction chamber (1) is provided with two observation windows (14), and the image capturing unit (8) and the temperature measuring instrument (10) are respectively facing the two observation windows (14).

4. The VAD deposition device for optical fiber preform according to claim 1, characterized in that: The top of the target rod (3) is connected to a suspension rod (13) via a chuck (12), and the suspension rod (13) is connected to the lifting and rotating motor (2).

5. The VAD deposition device for optical fiber preform according to claim 1, characterized in that: The visual system (9) is also used to process the image data to obtain the core layer diameter and core layer shape; The PID controller (11) is also used to perform closed-loop regulation based on the core layer diameter and core layer shape and the raw material flow rate of the feeding system (7).

6. A method for preparing an optical fiber preform by using the VAD deposition optical fiber preform device as claimed in claim 1, characterized in that: It includes: Comparing the deposition angle obtained by the visual system (9) with an angle threshold to obtain an angle deviation; If the angle deviation is within the first angle deviation range, the lifting speed of the target rod (3) is not adjusted; If the angle deviation is outside the first angle deviation range and within the second angle deviation range, the lifting speed of the target rod (3) is adjusted by a PID controller (11) based on the lifting stable speed of the target rod (3), the basic speed of the angle influencing factor, the weight of the angle influencing factor, the basic speed of the temperature influencing factor, and the weight of the temperature influencing factor; Comparing the temperature obtained by the thermometer (10) with the temperature threshold to obtain a temperature deviation; If the temperature deviation is within the first temperature deviation range, the raw material flow rate of the material supply system (7) corresponding to the core layer burner (6) is not adjusted; If the temperature deviation is outside the first temperature deviation range and within the second temperature deviation range, the oxygen flow rate is adjusted by a PID controller (11); If the temperature is outside the second temperature deviation range, the hydrogen flow rate is adjusted by the PID controller (11).

7. The method according to claim 6, characterized in that: The first angle deviation range is -0.2°~+0.2°; The second angle deviation range is -0.5°~+0.5°; The first temperature deviation range is -5℃~+5℃; The second temperature deviation range is -10°C to +10°C.

8. The method according to claim 6, characterized in that: If the angle deviation is outside the second angle deviation range, manual intervention is performed.

9. The method according to claim 6, characterized in that: If the temperature deviation exceeds the set alarm temperature, manual intervention is performed.

10. The method according to claim 6, characterized in that: Processing the image data to obtain the core diameter and core shape; If the core layer shape is inconsistent with the preset shape, an alarm will be sounded and the machine will be shut down; If the core shape is consistent with the preset shape, the core diameter is compared with the preset diameter; If it is smaller than the preset diameter, the PID controller (11) is used to adjust the flow rate of the raw material of the feeding system (7) corresponding to the core layer burner (6); If it is larger than the preset diameter, the PID controller (11) is used to adjust the raw material flow rate of the feeding system (7) corresponding to the core layer burner (6).

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