JPS6335577B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an optical fiber manufacturing apparatus, and particularly to an optical fiber manufacturing apparatus that measures various characteristic values of the optical fiber and controls various control parameters during manufacturing to produce an optical fiber with desired characteristics. The present invention relates to a manufacturing device capable of manufacturing with high precision. PRIOR ART AND PROBLEMS TO BE SOLVED BY THE INVENTION Conventional methods for manufacturing optical fibers are usually divided into a manufacturing process of a preform, which is a base material, and a drawing process, in which the preform is heated and drawn.
Typical conventional manufacturing methods include the internal attachment method, the so-called MCVD method, and the VAD method. Figures 1a and b schematically show the MCVD process,
Figure 2 schematically shows the VAD manufacturing process. first,
In the process shown in FIG. 1, dopants (e.g. Ge, P, B) and halides (e.g.
GeCl ₄ , POCl ₃ , BBr ₃ ) are vaporized in oxygen.
The flow rates of these gases are controlled by controlling the flow rate of oxygen, which is a carrier gas, using a mask low controller MFC. The vaporized gas is guided into a quartz pipe 3 which is rotated at a constant speed by a glass lathe 1. This quartz pipe 3 is heated externally by an oxyhydrogen flame burner 2, as a result of which the halides are oxidized in the glass pipe.
A thin quartz glass film containing Ge, P, B, etc. is attached to the inner surface of the pipe 3, and opaque quartz glass particles are attached to the inner surface of the quartz pipe 3 downstream of the gas. The oxyhydrogen flame outside the quartz pipe is slowly moved in the same direction as the gas flow, melting the opaque glass adhering to the inner surface and turning it into transparent glass. After a sufficient amount of transparent quartz film 4 to become the core of the optical fiber is deposited on the inner surface of the quartz pipe (the first
Figure b), the quartz pipe is heated to about 1900℃,
It is crushed by heat and becomes a rod-shaped preform 5. When this is heated in an electric furnace 6 and drawn, an optical fiber 7 is obtained. The other VAD manufacturing process shown in FIG. 2 consists of steps such as soot deposition, dehydration, and sintering. Glass fine particles 11 are generated by oxidation and hydrolysis reaction in an oxyhydrogen flame by an oxyhydrogen torch 10,
The lower end of a suitable glass rod 12 is sprayed (FIG. 2a). The glass fine particles 11 form a fine powder preform 13 that looks like solidified white powder, and grow in the axial direction. That preform 13
is rotated so that it is uniform and has a constant outer diameter, and is slowly pulled upward. Next, the fine powder preform 13 is heated to 1500° C. in a carbon furnace 14 or the like, and sintered into a transparent preform 15. In the two manufacturing methods exemplified above, the refractive index distribution can be changed, for example, by controlling the flow rate of GeCl ₄ , but if you want to realize a complex refractive index distribution, it is necessary to control the amount of impurities mixed in from time to time using a computer. There is. Regarding such control,
Attempts have been made to feed back changes in the characteristics of the finished fiber, that is, the fiber removed from the production line, to the manufacturing side in some way, but it is not possible to provide information on the various characteristics of the preform or fiber at the time of manufacture to the manufacturing side. Attempts have not been made to provide feedback to various manufacturing control parameters on the manufacturing side to better control preform or fiber properties. Recently, with the international standardization of the cross-sectional dimensions of optical fibers used in optical communications, various characteristics such as the cross-sectional dimensions and refractive index distribution within the core of fibers manufactured by optical fiber manufacturing companies and their related organizations have been changed. It is becoming important to manufacture fibers with highly accurate characteristics by precisely measuring the values and reflecting them in the control of various control parameters during manufacturing. Figure 3 shows the structure of the optical fiber. Quartz core 21 and cladding 22 and plastic cladding 2
The transmission characteristics of the optical fiber made up of the three fibers differ depending on the refractive index distribution within the core 21 and other quantities.
Other quantities include the core diameter, cladding diameter, non-circularity of the core and cladding, eccentricity, etc., and hereinafter these will be collectively referred to as cross-sectional dimensions. The following two methods are known for measuring the cross-sectional dimensions of optical fibers. (a) After irradiating laser light or ordinary light from one end of the fiber, observing the light propagating from the other end using a microscope or equivalent optical means, and signal processing the information obtained. A method of measuring by displaying it on a TV monitor or plotter. (b) The core diameter, cladding diameter, and A method to measure refractive index distribution. Figure 4 shows a fiber fusing device that utilizes the fluorescence phenomenon described in method (b). In this device, the side surface of a fiber 31 is irradiated with an ultraviolet light beam 32 from a He-Cd laser, and from this method a two-field microscope is installed with objective lenses 33 and 33' that form an angle of 90 degrees to each other in a direction of ±45 degrees. TV camera 3 through 34
At step 5, it receives light from the fluorescence phenomenon in the fiber and reflected light from the cladding. After processing the signal from such light with a digitizer 36, it is displayed on the TV monitor 3.
7 shows the position of the core. in this case,
Since the purpose is to fusion splice fibers together, the ultraviolet beam is configured to be able to irradiate the connection point between both fibers, and an electrode (not shown) for fusion splicing the fibers by electric discharge is placed between the fibers. located around the area. The position sensing device mentioned here is
Although it is possible to measure various characteristics of fibers non-destructively, since the purpose is limited to connecting fibers, information on the measured characteristic values can be used for various types of manufacturing in time-to-time manufacturing equipment. The idea of using it to control parameters never occurred. Furthermore, in the case of conventional manufacturing equipment, if it is found in post-manufacturing measurements that a fiber with characteristics deviating from the desired specifications has been produced, it is wasteful to discard it. This invention measures various characteristic values of the optical fiber during manufacturing, and continuously feeds back this information to various control parameters on the manufacturing side for control, thereby producing optical fibers with highly accurate desired characteristics. It is an object of the present invention to provide an optical fiber manufacturing apparatus and a manufacturing method thereof that can manufacture fibers. This makes it possible to quickly produce high-precision fibers with excellent properties that could not be achieved with conventional equipment. Means for Solving the Problems In order to achieve the above-mentioned object, the manufacturing apparatus disclosed in the present application utilizes the fluorescence phenomenon of the fluorescent substance doped in the core of the fiber to determine the physical properties of the optical fiber. It is equipped with a measurement means that continuously measures, a signal processing means that processes the measurement results, and a control means that feeds back information from the signal processing means online to change control parameters during manufacturing. . Embodiment FIG. 5 shows a block diagram of an optical fiber manufacturing apparatus according to the invention of the present application. A preform 41 made in a preform manufacturing section 40 is heated in a heating drawing section 42, and a drawn fiber 43 is sent to a characteristic measuring section 44. Measuring part 4
4 measures physical quantities related to the cross-sectional dimension and refractive index distribution of the fiber, and after signal processing, feeds the data back to the preform manufacturing section 40 and/or heating wire drawing section 42 to influence the cross-sectional dimension and refractive index distribution. Control manufacturing parameters. Preform manufacturing section 40 and heating wire drawing section 42
When the preform is not incorporated into one manufacturing device, that is, when a preform made in advance in the preform manufacturing section 44 is heated and drawn, only feedback control in the drawing process is possible. In the case of preform manufacturing, it is desirable to configure a manufacturing apparatus as shown in FIG. The preform 41 made in the preform manufacturing section 40 is measured in the characteristic measuring section 44', and the preform 4
Physical quantities related to the refractive index distribution, etc. of the optical system 1 are measured, and after signal processing, these data are fed back to the preform manufacturing section 40, and manufacturing parameters that affect the refractive index distribution, etc. are controlled. Next, an example of the measuring sections 44, 44' is shown in FIG. Ultraviolet light emitted from an ultraviolet light source S (for example, a He-Cd laser, an ultraviolet lamp, etc.) is focused by a condensing lens _L1 and is applied from the side perpendicular to the axis of the fiber 51. In this case, it is desirable to irradiate light with a spot diameter smaller than the diameter of the cladding 52 of the fiber 51 in consideration of the luminous efficiency of the light source for reasons described later. By irradiating the fiber, a portion of the light energy is absorbed by the core 53, and as a result, the core 53
Ge atoms contained within emit fluorescence. This fluorescent light and the light passing through the cladding 52 are observed by a one-field optical system 54 consisting of an objective lens _L2 and a television camera TVC. tv camera
The signal from TVC is analog/digital converter 5
5, and is converted into digital data by frame memory 56.
Data is stored from the initially set direction, and then the one-field optical system 54 is rotated by a predetermined angle (for example, 90 degrees) by the driving means 60, and the signal from the television camera TVC is converted from analog to digital again. The data from the direction after rotation is digitally converted by the device 55 and stored in the frame memory 56. Using observation data from the two fields of view before and after the rotation stored in the frame memory 56, these patterns are displayed in a superimposed manner on the television monitor 58. Although cross-sectional dimensions can be measured from the pattern on a television monitor, more detailed measurements and measurements of the refractive index distribution within the core require signal processing by a computer. In other words, by selecting a vertical line that passes through the center of the pattern and knowing the boundary between the core and cladding from the brightness distribution on that line, the core diameter can be measured, and by knowing the boundary between the cladding and air, the cladding Diameter can be measured. The degree of non-circularity and eccentricity can be determined from information on the core diameter and cladding diameter observed from two fields of view before and after rotation, or from two or more external fields for greater accuracy. The refractive index distribution within the core can be measured by more precisely observing the luminance distribution within the core and around the core. The reason for this is that the distribution of Ge atoms within the core reflects the refractive index distribution, which appears as the spatial distribution of fluorescence within the core. The measurement results of the refractive index distribution and cross-sectional dimensions described above can be outputted to the printer 59. In the measurement section shown in Fig. 7, in order to obtain the same measurement effect as a multi-view optical system with a single-view optical system, the fiber is fixed as described above.
It is necessary to either rotate the one-field microscope, or to keep the optical system fixed and configure the fiber itself to be rotatable. Also, as mentioned above and explained below,
Considering the economic efficiency of the configuration of the measuring section, it is desirable to configure the optical system so that the ultraviolet rays are irradiated onto the fiber to be measured using the condenser lens _L1 with a spot diameter smaller than the cladding diameter (for example, 125 μm). For example, if the ultraviolet light spot diameter is a large value of 150 μm and the laser light power of the ultraviolet light source is required to be about 4 mV, the optical power density [light power / [π × (radius) ² ]] is approximately
0.23×10 ^-3 mW/(μm) ² . If the same optical power density is required, by setting the ultraviolet light spot diameter to a small value of 50 μm, the required optical power will be 0.45 mW. Reducing the optical power makes it possible to use a low-cost ultraviolet light source, and in addition to being economical, lower output is advantageous in terms of the guaranteed lifetime of the ultraviolet light source. However, since the spot of the ultraviolet light is smaller than the cladding diameter, there is a possibility that the cladding diameter etc. cannot be measured because the light from the outer periphery of the cladding cannot be detected. Although it is possible that some light may wrap around the unirradiated areas due to light diffraction, it is necessary to take the following precautions just to be sure. That is, the spot and the fiber are configured to be relatively movable. For this purpose, the fiber 61 is fixed and the spot 62 is moved as shown in FIG. 8a, or conversely, the spot 62' is fixed and the fiber 61' is moved as shown in FIG. 8b. Configure it so that it can be moved. Next, FIG. 9 shows an arrangement similar to the measuring section shown in FIG. 7 using a two-field optical system. The light rays from the ultraviolet light source S are focused by a condenser lens _L1 and irradiated onto the fiber 51 to be measured from the side perpendicular to the axis. The fluorescence of Ge due to this irradiation and the transmitted light in the cladding are observed using a two-field microscope 65. The ones shown in FIG. 9 are objective lenses L ₂ , L ₃ , L ₄ ,
It consists of reflecting mirrors M ₁ and M ₂ and a light wave combining prism P. The output light from the microscope 65 is added to the television camera TVC66.
The output signal is subjected to predetermined signal processing by a digitizer 67 and then displayed on a television monitor TVM 68. Information such as the refractive index distribution and cross-sectional dimensions can be obtained from the luminescence intensity distribution displayed through signal processing by a computer. The production of optical fibers is usually divided into a process for producing a preform, which is a base material, and a drawing process, in which the preform is heated and drawn. Transmission loss, bandwidth, refractive index distribution, etc. are determined in the former process, while characteristics such as the shape and strength of the cladding are determined in the latter process. An example of the preform manufacturing section 40 shown in FIGS. 5 and 6 will be described with reference to the program diagram shown in FIG. 10. Gas supply section G including a mechanism for controlling the amount of material gas
The material gas from is sent to the first preform forming section P1 . The preliminary preform formed here is sent to the second preform forming section P2 , where a transparent preform PF is formed. The heat sources H1 and H2 heat the first and second forming parts P1 and P2 , respectively, and
The driving section D1 drives the heat source H1, the first forming section P1 , and the second forming section P2 at predetermined speeds, respectively, as necessary. The rotation drive section RD rotates the first forming section P1 at a predetermined speed, and the second drive section D2 drives the second heat source. The manufacturing method of the MCVD process will be explained using each block in FIG. 10 as follows. A material gas whose flow rate is controlled is supplied from the gas supply section G, heated by the first heating source H1 while being rotated by the rotation drive section RD, and sent to the quartz pipe in the first forming section P1. Quartz pipe and first heating source H1
are configured to move relatively at a predetermined speed by the first driving means D1, and a deposited layer is formed within the quartz pipe. After the deposited layer of a predetermined thickness is formed, the quartz pipe is sent to the second forming section P1, heated by the second heating source H2, and formed into a transparent preform PF. At this time, the second heat source H2 is also moved along the second forming portion P2 at a predetermined speed as necessary. Further, if necessary, the quartz pipe in the second forming portion P2 is also moved at a predetermined speed by the first driving means D1. Preform PF leaving the second forming part P2
The measuring section 44' shown in FIG. 2 drive unit D1,
D2, first and second heat sources H1, H2, rotation drive unit
It is fed back to the RD in the form of a control signal. Similarly, the manufacturing method of the VAD process will be briefly explained using each block in FIG. The oxyhydrogen torch 10 and carbon furnace 14 in FIG. 2 correspond to the first and second heat sources, respectively. Fine glass particles adhere to the seed rod 12 (FIG. 2a) provided in the first preform forming section P1 to form a fine powder preform. This is heated by the second heating source H2, and a transparent preform PF is formed in the second forming section P2. An example of the heating wire drawing section 42 shown in FIG. 11 and FIG. 5 is shown using a block diagram.
2 is drawn while heating to obtain an optical fiber 73. Drawing requires a high temperature of 2000°C or higher, and the optimal temperature for drawing is controlled from time to time to a predetermined temperature, taking into consideration the strength of the optical fiber, transmission loss, fiber diameter, etc. If there are many scratches on the preform surface, there is a risk that they will remain on the optical fiber surface after drawing, and to avoid this situation, the drawing temperature must be set sufficiently high. However, on the other hand, if the drawing temperature is too high, color centers may occur due to oxygen defects, foaming of additives may occur, and losses will increase. A coating treatment section is applied to prevent scratches from physical contact with the outside world on the surface of the optical fiber after it has been drawn.
A plastic film with a thickness of about 5 to 100 μm is applied using PC. The optical fiber, which has been coated and has increased strength, is wound up at the winding section PD. that time,
A feedback signal is created by utilizing the characteristic data measured by the measuring section 44, and is sent as a control signal to the heating section H and winding section PD via the feedback circuit 71, so that the drawing conditions can be precisely set at any time during the drawing of the optical fiber. Control. The configuration of the control system has been described above in FIGS. 10 and 11, and yet another control system is shown in FIG. 12. FIG. 12 shows a block diagram of an optical fiber manufacturing apparatus employing a configuration that combines the control systems shown in FIGS. 5 and 6. In FIG. 12, blocks and portions that are the same as or correspond to those in FIGS. 5 and 6 are given the same reference numerals. The physical characteristics of the manufactured optical fiber 43 are continuously measured in a measuring section 44, and information based on the measurement results is fed back to the preform manufacturing section 40 and the heating wire drawing section 42 in the form of a control signal. In addition to this control, the physical characteristics of the preform 41 sent from the preform manufacturing section 40 are continuously measured by another measuring section 44', and information based on the measurement results is similarly sent to the preform manufacturing section 40 as a control signal. It will be returned in the form of By adopting the configuration of the control system shown in FIG. 12, it is possible to manufacture optical fibers under more precise control in an optical fiber manufacturing apparatus that consistently manufactures preforms and optical fibers. For example, the refractive index distribution within the preform is continuously measured, and the measurement results are reflected in the flow rate control of the material gas that controls the amount of impurities in the preform and the heating temperature control in the preform manufacturing department. The cross-sectional dimensions such as the core diameter and cladding diameter of the optical fiber are continuously measured in the same way, and the measurement results are reflected in the control of the heating temperature of the heating wire drawing section and the drawing speed, so that the optical fiber is manufactured. As a result, there is an advantage that optical fibers having desired characteristics can be manufactured with higher precision. According to the manufacturing apparatus and manufacturing method of the present application having the control system configuration described above, problems that have conventionally occurred during manufacturing can be solved, such as low refractive index in the core peripheral area (boundary between the core and the cladding). Manufacturing using high-precision control eliminates skirting, that is, the refractive index does not change significantly at the boundary between the core and cladding, and eliminates irregularities in the refractive index distribution (impurity distribution) around the core. Solved by Note that even if a light source other than a laser beam source, such as an ultraviolet lamp, is used as the ultraviolet light source of the measurement unit shown in Fig. 5, the same measurement effect as when using a laser beam source can be achieved by simple modification of the optical system. You can get it. Effects of the Invention In the optical fiber manufacturing method and apparatus according to the present invention, the physical characteristics of the optical fiber are measured using the fluorescence phenomenon of the fluorescent material doped into the core of the fiber. Therefore, not only the important characteristics such as the refractive index distribution within the core and the core diameter can be measured with high precision, but also the outer diameter of the cladding.
Based on this, manufacturing parameters can be controlled. As a result, the noncircularity and eccentricity of the core can be controlled with high precision, and an optical fiber having desired high performance characteristics can be manufactured.

[Brief explanation of the drawing]

Figures 1a and 1b schematically show the conventional MCVD process, Figure 2 generally shows the AD process schematically, and Figure 3 generally shows the structure of the optical fiber. 4 is a schematic diagram showing a conventional fiber fusion device, FIG. 5 is a block diagram of an optical fiber manufacturing device according to the present invention, FIG. 6 is a preform manufacturing device according to the present invention, and FIG. 7 is a schematic diagram showing a conventional fiber fusion device. 8A and 8B are schematic diagrams showing the relative relationship between the fiber and the ultraviolet beam spot diameter, and FIG. 10 is a block diagram of the preform manufacturing section of the present invention, and FIG. 11 is a block diagram of the heating wire drawing section of the present invention.
FIG. 2 is a block diagram of yet another embodiment of the manufacturing apparatus according to the present invention. In the figure, 1... Glass lathe, 2... Oxyhydrogen flame burner, 3... Quartz pipe, 4... Sediment layer, 5
... Preform, 6 ... Electric furnace, 7 ... Optical fiber, 10 ... Oxyhydrogen torch, 11 ... Glass fine particles, 12 ... Glass rod, 13 ... Fine powder preform, 14 ... Carbon furnace, 15 ... ...Transparent preform, 21... Core, 22... Clad, 2
3... Covering material, 31... Fiber, 32... Ultraviolet light beam, 33, 33'... Objective lens, 34
...Two-field microscope, 35...Television camera, 36
...Digitizer, 37...TV monitor, 40...
...Preform manufacturing department, 41...Preform,
42... heating wire drawing section, 43... fiber, 4
4,44'...Characteristics measurement section, _L1 ...Condensing lens,
S... Ultraviolet light source, 51... Fiber, 52... Clad, 53... Core, 54... Single field optical system, 55... Analog/digital converter, 5
6... Frame memory, 57... Computer,
58...TV monitor, 59...Printer, 60
...driving means, 61, 61'... fiber, 62,
62'...spot, 65...two-field microscope,
66...TV camera, 67...Digitizer, 6
8...TV monitor, D1, D2...Drive unit, G
...Gas supply section, H1, H2...Heating source, P...
Transparent preform, P1, P2...forming part, RD
... Rotation drive section, 70 ... Feedback circuit, F ... Preform delivery section, H ... Heating section, PC ... Coating processing section, PD ... Winding section, 71 ... Feedback circuit, 7
2... preform, 73... optical fiber. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. Manufacture of an optical fiber comprising a heating means for heating a preform, which is a base material of the optical fiber, under predetermined control, and a drawing means for drawing the optical fiber at a controlled drawing speed. In the apparatus, a measuring means for measuring the physical characteristics of the optical fiber by utilizing a fluorescence phenomenon of a fluorescent substance doped into the core of the fiber when drawing the optical fiber, and a signal calculation process for calculating the measurement results. and a feedback circuit for feeding back an information signal from the signal processing means to at least one of the heating means and the drawing means. 2. A material gas and a carrier gas are passed through a rotating quartz pipe, heated at a first temperature by a second heating means running on the outer wall surface of the pipe to form a deposited layer of glass on the inner wall surface of the pipe, and then the first further comprising a deposition method preform manufacturing unit configured to heat the quartz pipe at a second temperature higher than the temperature of 1 to form a preform, and feed back an information signal from the signal processing means to the preform manufacturing unit. further comprising a second feedback circuit,
Based on the information signal, the rotation speed of the quartz pipe, the amount of the material gas, the amount of the carrier gas,
2. The fiber manufacturing apparatus according to claim 1, wherein at least one of the first temperature and the running speed of the second heating means is controlled. 3 Heating a rotating seed rod at a first temperature, spraying glass fine particles onto the lower end of the seed rod by oxidation and hydrolysis reaction of the material gas to form a fine powder preform, and heating the fine powder preform at a second temperature. The method further includes an axial preform manufacturing section configured to heat and sinter with a swept second heating means to form a transparent preform, and feeds back information signals from the signal processing means to the preform manufacturing section. Further comprising a second feedback circuit, the rotational speed of the seed rod, the first temperature, the amount of the material gas, the second temperature, and the sweep speed of the second heating means are adjusted based on the information signal. The optical fiber manufacturing apparatus according to claim 1, characterized in that the apparatus is configured to control at least one of the optical fibers. 4. Any one of claims 1 to 3, wherein the measuring means comprises a one-field microscope and a television camera, and the signal calculation processing means comprises a digitizer, a television monitor, and a computer. The optical fiber manufacturing apparatus described in . 5. Claims 1 to 3, characterized in that the measuring means comprises a two-field microscope and a television camera, and the signal calculation processing means comprises a digitizer, a television monitor, and a computer.
The optical fiber manufacturing apparatus according to any one of the items. 6. In an optical fiber manufacturing method in which an optical fiber is manufactured by heating a preform, which is a base material of the optical fiber, with a heating means and drawing the preform at a variable drawing speed with a tension control means, during drawing of the optical fiber. The physical characteristics of the optical fiber are continuously measured by a measuring means by utilizing the fluorescence phenomenon of the fluorescent substance doped in the core of the fiber, and the measurement results are processed by a signal processing means to obtain the signal. A light source characterized in that an information signal from the arithmetic processing means is fed back to the heating control means and the tension control means through a feedback circuit to cause the heating control means to perform heating control and the tension control means to perform tension control. Method of manufacturing fiber. 7. In the preform, material gas and carrier gas are passed through a rotating quartz pipe, and the outer wall surface of the pipe is heated by a heating means running at a first temperature.
A deposited layer of glass is formed on the inner wall surface of the pipe, and then the quartz pipe is heated at a second temperature higher than the first temperature to be formed in the preform forming section, and information from the signal processing means is A signal is returned to the preform forming section via a second feedback circuit, and based on the information signal, the rotational speed of the quartz pipe, the amount of the material gas, the amount of the carrier gas, and the first and second temperatures are determined. The method for manufacturing an optical fiber according to claim 6, characterized in that at least one of the running speeds of the second heating means is controlled. 8 Heating the rotating seed rod at a first temperature, spraying glass fine particles onto the lower end of the seed rod by oxidation and hydrolysis reaction of the material gas to form a fine powder preform, and heating the fine powder preform at a second temperature. A transparent preform is formed in a preform manufacturing unit that is heated and sintered by a second heating means that is swept;
An information signal from the signal processing means is fed back to the preform manufacturing unit via a third feedback circuit, and based on the information signal, the rotational speed of the seed rod, the first and second temperatures, and the material are determined. amount of gas,
7. The method of manufacturing an optical fiber according to claim 6, further comprising controlling at least one of the sweep speeds of the heating means.