JP2645716B2 - Optical fiber drawing apparatus and drawing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber drawing apparatus and a drawing method in which an optical fiber in a high temperature state immediately after drawing is efficiently cooled and sent to a resin coating apparatus. .

<Prior Art> When an optical fiber preform in the form of a transparent vitrified rod is heated and drawn to a predetermined diameter, generally, the primary coating and the secondary coating of the resin are simultaneously and continuously performed.

As shown in FIG. 4, which shows the concept of the main part of such a conventional drawing apparatus, a core tube 102 into which an optical fiber preform 101 is fed has a furnace body 103 together with a carbon heater 103 surrounding it.
It is held at 104. A purge gas introduction pipe 106 for supplying an inert gas such as nitrogen into the drawing furnace 105 is connected to an upper end portion of the furnace body 104 in order to prevent oxidative consumption of the furnace tube 102 and the carbon heater 103. And the furnace body 104
A seal ring 107 is attached to the upper end of the optical fiber preform 101 for sliding contact with the outer peripheral surface of the optical fiber preform 101, and a shutter 108 is provided at the lower end of the furnace body 104 to keep the inside of the drawing furnace 105 in an inert gas atmosphere. ing. The optical fiber 109 drawn in the drawing furnace 105 reaches the coating die 111 through the inside of the cooling tube 110, and is subjected to, for example, a primary coating of an ultraviolet curable resin. At the lower end of the cooling cylinder 110, a cooling gas introduction pipe 112 for guiding a cooling gas into the cooling cylinder 110 is connected, so that the optical fiber 109 in a high temperature state immediately after drawing is cooled. It has become. The ultraviolet curable resin that has passed through the coating die 111 together with the optical fiber 109 is cured by being irradiated with ultraviolet light in the ultraviolet curing device 113 and integrated with the optical fiber 109.

At the lower end of the ultraviolet curing device 113, a purge gas introduction pipe 114 such as nitrogen gas is connected to remove the presence of oxygen that hinders the curing of the ultraviolet curing resin. A shutter 115 for reducing the outflow of the purge gas is provided at the upper end of the shutter. Further, downstream of the ultraviolet curing device 113, a coating die 116 for secondary coating and a resin curing device 117 using the coating die 116 are sequentially disposed, and the optical fiber strand 118 with the secondary coating is an optical fiber core. The wire 119 is wound by a winding device (not shown) via a direction changing roller 120 as a line 119.

<Problems to be Solved by the Invention> Usually, the drawing speed of an optical fiber depends on the curing speed of a coating resin. In other words, with the current technology, it is possible to make the drawing speed of the optical fiber faster than the curing speed of the coating resin. Speed is of paramount importance. By the way, ultraviolet curable resins are much better than conventional coating materials such as thermoplastic resins in terms of curing speed and handleability, and are therefore expected to be extremely excellent coating materials. With the increase in drawing speed due to the use of the ultraviolet curable resin, it is necessary to rapidly cool the high-temperature optical fiber 109 immediately after drawing and send it to the coating die 111 as shown in FIG.

Therefore, conventionally, helium gas having good thermal conductivity is continuously supplied from the cooling gas introduction pipe 112 into the cooling cylinder 110, but as a result of consuming a large amount of expensive helium gas, optical fiber production There was a disadvantage that the cost was increased. Although it is known that the consumption of helium gas is suppressed by narrowing the opening at the upper end of the cooling cylinder 110, helium gas is consumed to a greater or lesser extent, and some improvement is expected. Was rare.

<Means for Solving the Problems> The configuration of the optical fiber drawing apparatus of the present invention includes a drawing furnace for heating an optical fiber preform, and an outer periphery of an optical fiber provided below the drawing furnace and drawn from the drawing furnace. An optical fiber drawing device having a coating device for coating a surface with a resin, wherein a seal ring provided at an upper end opening of the drawing furnace and in which the optical fiber preform slides and contacts, between the drawing furnace and the coating device. A cooling cylinder having an upper end hermetically connected to a lower end opening of the drawing furnace, and a helium gas supply communicating with at least one of the cooling cylinder and the drawing furnace to fill the inside with helium gas. Means, and cooling means disposed around the cooling cylinder to cool the optical fiber via the cooling cylinder and the helium gas. Having substantially no helium gas outlet other than toward the cooling cylinder, and having a fiber outlet port open to the atmosphere below the cooling cylinder, The outlet is provided with means for detecting mixing of air from the outlet, and the helium gas supply means is provided with control means for limiting the flow rate of helium.

On the other hand, in the optical fiber drawing method of the present invention, the optical fiber preform is heated and drawn in a drawing furnace, and a resin is coated on the outer peripheral surface of the drawn optical fiber by using a drawing coating device below the drawing furnace and wound. In the method of drawing an optical fiber wound by an apparatus, the upper end opening of the drawing furnace is opened under an inert atmosphere using the drawing furnace and a cooling cylinder airtightly connected to the lower end opening of the drawing furnace, and the optical fiber The preform is set in a drawing furnace, the upper end opening is sealed by sliding the optical fiber preform against a seal ring at the upper end opening, and helium gas is supplied from at least one place of the drawing furnace and the cooling cylinder. The entire lever is filled with helium gas, air entrapment is detected below the cooling cylinder, and based on this information, the optical fiber preform is reduced in the drawing furnace while the flow rate of helium supplied is minimized. Inside In the cooling cylinder portion, the drawn optical fiber and the helium gas filling the inside are cooled by the cooling means arranged around the cooling cylinder, and then drawn downward. The outer peripheral surface of the drawn optical fiber is coated with a resin using a coating device, and is wound by a winding device.

<Operation> The optical fiber preform supplied into the drawing furnace is drawn by heating and sent to the coating apparatus side. On the other hand, the inside of the drawing furnace and the inside of the cooling cylinder integrated therewith are filled with helium gas by the helium gas supply means, and the helium gas leaks from the opening at the upper end of the drawing furnace by the seal ring that slides on the optical fiber preform. And the atmosphere of the helium gas is ensured in the drawing furnace and the cooling cylinder without replenishing the helium gas. The optical fiber passing through the inside of the cooling cylinder is efficiently cooled by the cooling means through the cooling cylinder and the helium gas having good thermal conductivity, and is coated with the resin by the coating device.

On the other hand, in the optical fiber drawing method according to the present invention, the optical fiber preform is heated and drawn in a drawing furnace, and a resin is applied to the outer peripheral surface of the drawn optical fiber by using a draw coating device below the drawing furnace. A method for drawing an optical fiber which is coated and wound by a winding device, wherein the drawing furnace and a cooling tower which is connected to the lower end opening of the drawing furnace in an airtight manner are used. The opening is opened, the optical fiber preform is set in a drawing furnace, the optical fiber preform is slid into contact with a seal ring at the upper end opening, the upper end opening is sealed, and the drawing furnace and the cooling tower are cooled. Helium gas is supplied from at least one place and the whole is filled with helium, and the optical fiber preform is heated and drawn with the helium gas filled inside in the drawing furnace part, and drawn in the cooling tower part. Cooled optical fiber and helium filled inside the cooling tower After cooling by disposed cooling means around through, characterized in that the wound coated with retractor resin on the outer circumferential surface of 該線 pull optical fiber using a drawer coating device downward.

<Embodiment> As shown in Fig. 1 showing a schematic structure of an embodiment of an optical fiber drawing apparatus according to the present invention, a core tube 12 into which an optical fiber preform 11 is fed is provided together with a carbon heater 13 surrounding the furnace. It is held by the body 14. At the upper end of the furnace body 14,
A seal ring 16 that is in sliding contact with the outer peripheral surface of the optical fiber preform 11 and seals the inside of the drawing furnace 15 is attached, and an upper end of a cooling cylinder 19 whose lower end is air-tightly connected to a coating device 18 having a coating die 17 is The lower end of the furnace body 14 is airtightly connected. A cooling liquid passage pipe 20 connected to a cooling liquid supply device (not shown) is spirally wound around the outer peripheral surface of the cooling cylinder 19, and a high-temperature optical fiber drawn by heating in a drawing furnace 15.
While passing through the cooling tube 19, the optical fiber 21 is cooled down to a temperature at which the resin can be coated by the coating device 18. For this reason, a shutter 22 is provided at the lower end of the furnace body 14 to prevent the influence of the radiant heat in the drawing furnace 15 from affecting the cooling cylinder 19 side. In the present embodiment, the cooling liquid passage pipe 20 is spirally wound around the outer peripheral surface of the cooling cylinder 19, but the inside of the wall of the cooling cylinder 19 may be formed to be hollow, and the cooling liquid may pass therethrough. In short, any structure may be used as long as the optical fiber 21 can be efficiently cooled via the helium gas.

A curing device 23 is hermetically connected to the coating device 18 for the primary coating via a connection tube 24.In this embodiment, a coating device 25 for the secondary coating and a curing device 26 are further connected in series. Connected to The curing device 23 for the primary coating and the coating device 25 for the secondary coating are provided with a cooling cylinder 28 in which a cooling liquid flow pipe 27 having the same configuration as the above-described cooling liquid flow pipe 20 is spirally wound.
Similarly, the coating device 25 for secondary coating and the curing device 26 are airtightly connected via a connection tube 30. The upper end of an extension cylinder 31 having a shutter 29 at the lower end is hermetically connected to the curing device 26, and in the present embodiment, an ultraviolet curing resin is used as the coating resin.
At the lower end of the cooling cylinder 28, a light-shielding ring 33 for preventing stray light is attached because it is necessary to prevent ultraviolet light from the curing device 23 for primary coating from entering the coating die 32 for secondary coating.

A helium gas supply pipe 34 connected to a helium gas supply source (not shown) communicates with a lower end of the cooling cylinder 19, and the optical fiber preform 11, the optical fiber 21, and the optical fiber element from the drawing furnace 15 to the extension cylinder 31. The transport path of the wire 35 and the optical fiber core 36 is filled with helium gas. For this reason,
In this embodiment, an oxygen detector 38 is provided in the extension cylinder 31 and communicates via a suction pipe 37, and an opening / closing valve provided in the helium gas supply pipe 34 based on a detection signal from the oxygen detector 38.
The opening and closing operation of 39 is adjusted by the control device 40.

Therefore, as shown in FIGS. 2 and 3 showing the state of the helium gas being filled in the extension tube 31, a case where the helium gas 41 is present in the extension tube 31 more than the position of the suction pipe 37 (see FIG. 2), a control device is provided via an oxygen detector 38.
40 judges that oxygen is not present in the extension cylinder 31, closes the on-off valve 39, and stops the supply of the helium gas 41. On the other hand, when the helium gas 41 is present in the extension tube 31 slightly less than the position of the suction pipe 37 (see FIG. 3), the control device 40 sends oxygen to the extension tube 31 via the oxygen detector 38. When it is determined that the helium gas exists, the helium gas 41 is supplied into the cooling cylinder 19 using the on-off valve 39.

Thereby, the consumption of the helium gas 41 can be minimized, and at least the path from the drawing furnace 15 to the curing device 26 can be always maintained in the helium gas atmosphere. For this reason, in the present embodiment, no oxygen is present in the atmosphere in which the resin is cured by the curing devices 23 and 26, and the disadvantage that the curing speed of the ultraviolet resin is reduced does not occur. In addition, since the resin is coated before the optical fiber 21 comes into contact with air, it is possible to reduce the influence of moisture which largely affects the transmission loss of the optical fiber 21. Also, as is well known, the helium gas 41 has a significantly higher thermal conductivity than other gases, so that the optical fiber 21 is efficiently cooled while passing through the cooling cylinder 19.

During the replacement of the optical fiber preform 11, it is impossible to maintain the hermeticity of the drawing furnace 15 by the seal ring 16;
An inert gas introduction passage 42 connected to an inert gas supply source such as nitrogen (not shown) is connected to an upper end of the optical fiber preform 14.
During the replacement of 11, an inert gas such as nitrogen having almost no difference in specific gravity from outside air is supplied from the inert introduction passage 42 into the drawing furnace 15, and the helium gas 41 from the helium gas supply pipe 34 is supplied.
Is stopped to prevent wasteful consumption of expensive helium gas 41.

The optical fiber core 36 to which the secondary coating has been applied by the coating device 25 and its curing device 26 is wound up by a winding device (not shown) via a direction changing roller 43. In the present embodiment, the on-off valve 39 is controlled to open and close according to the filling amount of the helium gas 41 in the extension cylinder 31, but the amount of leakage of the helium gas 41 per unit time is checked in advance,
In response to this, the opening of the on-off valve 39 may be kept constant.

<Effect of the Invention> According to the optical fiber drawing apparatus of the present invention, a cooling cylinder having a cooling means at the lower end of the drawing furnace is air-tightly joined and a gap between the upper end of the drawing furnace and the optical fiber preform is sealed with a seal ring. Since the inside of the drawing furnace and the cooling cylinder is maintained in a helium gas atmosphere having a high thermal conductivity by the helium gas supply means, there is almost no consumption of helium gas serving as a cooling medium in the cooling cylinder. Thus, the optical fiber can be efficiently cooled by the cooling means, and the efficiency of heating the optical fiber preform increases, so that the heat source of the heater can be reduced in size. Further, since the flow of gas in the drawing furnace is almost eliminated, the fluctuation in the diameter of the optical fiber can be reduced.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a schematic structure of an embodiment of an optical fiber drawing apparatus according to the present invention, FIGS. 2 and 3 are enlarged views showing a state of helium gas at a lower end portion of the extension tube, respectively. FIG. 1 is a conceptual diagram illustrating an example of a conventional optical fiber drawing apparatus. Also, in the reference numerals in the figure, 11 is an optical fiber preform, 12 is a furnace tube, 13
Is a carbon heater, 14 is a furnace body, 15 is a drawing furnace, 16 is a seal ring, 19 is a cooling cylinder, 20 is a coolant flow pipe, 21 is an optical fiber, 22, 29 are shutters, 34 is a helium gas supply pipe, 37
Is a suction pipe, 38 is an oxygen detector, 39 is an on-off valve, 40 is a control device, and 41 is helium gas.

Claims (2)

(57) [Claims] 1. An optical fiber drawing apparatus comprising: a drawing furnace for heating an optical fiber preform; and a coating device provided below the drawing furnace and coating a resin on an outer peripheral surface of an optical fiber drawn from the drawing furnace. In the above, a seal ring provided at an upper end opening of the drawing furnace and in which the optical fiber preform slides, and an upper end provided between the drawing furnace and the coating device and hermetically sealed to a lower end opening of the drawing furnace. A helium gas supply means for communicating with at least one of the cooling cylinder and the drawing furnace to fill the interior with helium gas; and a cooling cylinder disposed around the cooling cylinder and connected to the cooling cylinder. A cooling means for cooling the optical fiber via the cylinder and the helium gas, and the drawing furnace has a helium gas discharge port substantially in addition to the cooling cylinder. A fiber outlet that is open to the atmosphere below the cooling cylinder, and a means for detecting entry of air from the outlet into the fiber outlet. Wherein the helium gas supply means has a control means for limiting a flow rate of helium. 2. An optical fiber in which an optical fiber preform is heated and drawn in a drawing furnace, a resin is coated on an outer peripheral surface of the drawn optical fiber by using a drawing coating device below the drawing furnace, and the fiber is wound by a winding device. In the drawing method, the upper end opening of the drawing furnace is opened under an inert atmosphere using the drawing furnace and a cooling cylinder airtightly connected to the lower end opening of the drawing furnace, and the optical fiber preform is drawn into the drawing furnace. Set
At the upper end opening, the optical fiber preform is slid into contact with a seal ring to seal the upper end opening, and helium gas is supplied from at least one place of the drawing furnace and the cooling cylinder, and the whole is filled with helium gas. Detecting the entrainment of air below the cooling cylinder and heating the optical fiber preform together with the helium gas filling the interior in the drawing furnace part while minimizing the flow rate of helium supplied based on this information. After drawing, the drawn optical fiber and the helium gas filling the inside thereof are cooled by cooling means disposed around the drawn optical fiber through the cooling tube, and then drawn downward using a draw coating device. A method of drawing an optical fiber, comprising coating an outer peripheral surface of the optical fiber with a resin and winding the resin with a winding device.