Method of manufacturing optical fiber and apparatus of manufacturing the same

A method of manufacturing an optical fiber includes drawing an optical fiber preform and forming a bare optical fiber, disposing a coating layer formed of a resin on an outer circumference of the bare optical fiber, and curing the coating layer and obtaining an optical fiber. A direction of the bare optical fiber is changed by a direction changer in any position from drawing the optical fiber to disposing the coating layer, and the direction changer includes a guide groove which guides the bare optical fiber.

CROSS REFERENCE TO RELATED APPLICATIONS

Priority is claimed on Japanese Patent Application No. 2014-266308, filed on Dec. 26, 2014, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method of manufacturing an optical fiber and an apparatus of manufacturing the same.

Description of Related Art

FIG. 15is a schematic view showing a schematic configuration of an example of an apparatus of manufacturing an optical fiber of the related art.

The manufacturing apparatus includes a drawing unit10which forms a bare optical fiber3from an optical fiber preform2, a cooling unit120which cools the bare optical fiber3, a coating unit30which disposes a coating layer on the bare optical fiber3and forms an optical fiber intermediary body4, and a curing unit40which cures the coating layer of the optical fiber intermediary body4to be an optical fiber5.

During manufacturing the bare optical fiber, the bare optical fiber3is obtained by drawing the optical fiber preform2at the drawing portion10. After cooling the bare optical fiber3at the cooling portion120, a coating layer made of a resin is provided at an outer surface of the bare optical fiber3at the coating portion30. The bare optical fiber3in which the coating layer is cured at the curing unit40is wound by winding means70through a pulley50and a take-up unit60.

The bare optical fiber3obtained by drawing the optical fiber preform2is drawn toward a vertically lower direction along a linear path.

In the manufacturing method, there is a restriction on the height of the entire system as a factor affecting productivity. The reason that the height of the system is a main factor which restricts productivity is because it is necessary to ensure a distance for sufficiently cooling a bare optical fiber which is obtained by drawing the optical fiber preform.

When a new facility including a building is built, the restriction can be relaxed; however, an enormous cost is required for building a new facility, and when it is required that productivity is further improved in the future, it is necessary that a new facility will be built at higher cost.

As a method of relaxing the restriction, a method is included in which a direction changer including a non-contact retaining mechanism is used.

The non-contact retaining mechanism is for holding a target to be in a noncontact state using the pressure of a fluid such as air, and in the direction changer including the fluid bearing, it is possible to perform direction change with respect to the bare optical fiber without being in contact with the bare optical fiber (a bare fiber).

By using the direction changer, it is possible to change the direction of the bare optical fiber which is subjected to the fiber drawing from the optical fiber preform along the first path to conform to a second path (for example, refer to Japanese Patent No. 5571958 and Japanese Unexamined Patent Application, First Publication No. S62-003037).

In Japanese Patent No. 5571958, a manufacturing method is disclosed in which an apparatus for direction change including a groove into which an optical fiber is introduced and an opening formed in the groove is used. In this method, gas introduced to the apparatus is blown out from the opening through one inflow port, and the direction of the optical fiber is changed in a state where the optical fiber is floated due to the pressure of the gas.

A direction changer disclosed in Japanese Unexamined Patent Application, First Publication No. S62-003037 includes a guide groove which guides a bare optical fiber, and a blowout port for gas which is formed on a lower surface and both side surfaces of the guide groove (refer to Examples, andFIGS. 3A to 4). In the manufacturing method using the direction changer, the direction of the optical fiber is changed in a state where the optical fiber is floated due to the pressure of the gas blown out from four blowout ports.

However, in the manufacturing method described in the above-described Japanese Unexamined Patent Application, it is not easy to stably float the bare optical fiber in a tool for the direction changer.

The present invention has been made in consideration of the above-described circumstances and to provide a method of manufacturing an optical fiber and an apparatus of manufacturing an optical fiber capable of stably floating the bare optical fiber.

SUMMARY OF THE INVENTION

A first aspect of the present invention is a method of manufacturing an optical fiber including, drawing an optical fiber preform and forming a bare optical fiber; disposing a coating layer formed of a resin on the outer circumference of the bare optical fiber; and curing the coating layer and obtaining an optical fiber. A direction of the bare optical fiber is changed by a direction changer in any position from drawing the optical fiber to disposing the coating layer, the direction changer includes a guide groove which guides the bare optical fiber, a blowout port of a fluid which floats the bare optical fiber wired along the guide groove is formed along the guide groove in the guide groove, when a direction of the bare optical fiber is changed by the direction changer, the fluid is introduced into the guide groove from the blowout port and the bare optical fiber is floated and a Reynolds number of the fluid is in a range of 1200-3500, and the Reynolds number in an inlet wire portion of the bare optical fiber to the guide groove and an outlet wire portion from the guide groove is greater than the Reynolds number in an intermediate portion between the inlet wire portion and the outlet wire portion.

In a second aspect of the present invention according to the method of manufacturing an optical fiber of the first aspect described above, the Reynolds number is controlled by measuring a flotation amount of the bare optical fiber is measured and adjusting an introduced flow volume of the fluid to the direction changer based on a measurement value of the flotation amount.

In a third aspect of the present invention according to the method of manufacturing an optical fiber of the first aspect or the second aspect described above, the Reynolds number is adjusted such that a width of the blowout ports in the inlet wire portion and the outlet wire portion is set to be smaller than the blowout port in the intermediate portion.

In a fourth aspect of the present invention according to the method of manufacturing an optical fiber of the first aspect or the second aspect described above, an internal space for transferring the fluid to the blowout port is ensured inside the direction changer, the internal space has a first space which is in communication with the blowout ports in the inlet wire portion and the outlet wire portion and a second space which is in communication with the blowout port in the intermediate portion, and by adjusting an supply of the fluid to the first space and the second space, the Reynolds number of the fluid in the inlet wire portion and the outlet wire portion is set to be greater than the Reynolds number of the fluid in the intermediate portion.

In a fifth aspect of the present invention according to the method of manufacturing an optical fiber of the first aspect or the second aspect described above, an internal space for transferring the fluid to the blowout port is ensured inside the direction changer, the internal space has a first space which is in communication with the blowout port in the inlet wire portion, a second space which is in communication with the blowout port in the intermediate portion, and a third space which is in communication with the blowout port in the outlet wire portion, and by adjusting an supply of the fluid at the first space to the third space, the Reynolds number of the fluid in the inlet wire portion and the outlet wire portion is set to be greater than the Reynolds number of the fluid in the intermediate portion.

In a sixth aspect of the present invention according to the method of manufacturing an optical fiber of the first aspect or the second aspect described above, a narrow portion which is in communication with the blowout ports in the inlet wire portion and the outlet wire portion is formed inside the direction changer, and a pressure loss at the time of blowing out the fluid in the inlet wire portion and the outlet wire portion is greater than the pressure loss in the intermediate portion, thereby, the Reynolds number of the fluid in the inlet wire portion and the outlet wire portion is set to be greater than the Reynolds number of the fluid in the intermediate portion.

A seventh aspect of the present invention is an apparatus of manufacturing an optical fiber including a drawing portion configured to draw an optical fiber perform and form a bare optical fiber, a coating portion configured to dispose a coating layer formed of a resin on an outer circumference of the bare optical fiber, ad a curing portion configured to cure the coating layer. A direction changer which changes a direction of the bare optical fiber is disposed in any position from the drawing portion to the coating portion, the direction changer includes a guide groove which guides the bare optical fiber, a blowout port of a fluid which floats the bare optical fiber wired along the guide groove is formed along the guide groove in the guide groove, and in the blowout port, the Reynolds number in an inlet wire portion of the bare optical fiber to the guide groove and an outlet wire portion from the guide groove is greater than the Reynolds number in an intermediate portion between the inlet wire portion and the outlet wire portion.

In an eighth aspect of the present invention according to the apparatus of manufacturing an optical fiber of the seventh aspect described above, the Reynolds number of the fluid in the inlet wire portion and the outlet wire portion can be set to be greater than the Reynolds number of the fluid in the intermediate portion such that a width of the blowout ports in the inlet wire portion and the outlet wire portion is set to be smaller than the blowout port in the intermediate portion.

In an ninth aspect of the present invention according to the apparatus of manufacturing an optical fiber of the seventh aspect described above, an inner space portion which transports the fluid to the blowout port is ensured inside the direction changer, and the inner space portion can include a first space portion which is in communication with the blowout port of the inlet wire portion and the outlet wire portion, and a second space portion which is in communication with the blowout port of the intermediate portion.

In a tenth aspect of the present invention according to the apparatus of manufacturing an optical fiber of the seventh aspect described above, an inner space portion which transports the fluid to the blowout port is ensured inside the direction changer, and the inner space portion can include a first space portion which is in communication with the blowout port of the inlet wire portion, a second space portion which is in communication with the blowout port of the intermediate portion, and a third space portion which is in communication with the blowout port of the outlet wire portion.

In the eleventh aspect of the present invention according to the apparatus of manufacturing an optical fiber of the seventh aspect described above, a narrow portion which is in communication with the blowout ports in the inlet wire portion and the outlet wire portion is formed inside the direction changer, and a pressure loss as the time of blowing out fluid in the inlet wire portion and the outlet wire portion is greater than the pressure loss in the intermediate portion, thereby, the Reynolds number of the fluid in the inlet wire portion and the outlet wire portion is set to be greater than the Reynolds number of the fluid in the intermediate portion.

According to the aspects of the present invention described above, when the fluid is introduced into the guide groove from the blowout port of the direction changer to float the bare optical fiber, a Reynolds number of the fluid is in a range of 1200-3500, thereby, it is possible to stably float the bare optical fiber.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a schematic view showing a schematic configuration of a manufacturing apparatus1A which is a first embodiment of an apparatus of manufacturing an optical fiber according to the present invention.

The manufacturing apparatus1A includes a drawing unit10, direction changers20(20A and20B), a position sensor80, a coating unit30, a curing unit40, and a control unit90.

A reference numeral “2a” is a tip end portion of a diameter reduced portion (neck-down) of the optical fiber preform2which is heated and melted.

The drawing unit10includes a heating furnace11, and forms the bare optical fiber3by heating the optical fiber preform2using a heating furnace11and by drawing the optical fiber preform2.

The direction changers20(20A and20B) change the direction of the bare optical fiber3. In the manufacturing apparatus1A, two direction changers20are used. The respective direction changers20are referred to as the first direction changer20A and the second direction changer20B from upstream to downstream in a drawing direction.

The first direction changer20A among the two direction changers20changes the direction of the bare optical fiber3which is drawn out to a vertically downward direction from the optical fiber preform2to a horizontal direction, and the second direction changer20B changes the direction of the bare optical fiber3to the vertically downward direction.

The coating unit30applies (coats) a coating material such as a urethane acrylate-based resin onto the outer circumference of the bare optical fiber3to be the coating layer, and thus obtains the optical fiber intermediary body4.

The resin coating, for example, is two-layer coating in which a material for a primary coating layer having a low Young's modulus is applied to the inside, and a material for a secondary coating layer having a high Young's modulus is applied to the outside. The used material, for example, is an ultraviolet curing resin.

The coating unit30may have a configuration in which the primary coating layer and the secondary coating layer are separately coated, or may have a configuration in which the primary coating layer and the secondary coating layer are simultaneously coated.

The curing unit40includes one or a plurality of UV lamps40a, and forms the optical fiber5by curing the coating layer of the optical fiber intermediary body4. The curing unit40, for example, includes a plurality of pairs of UV lamps40awhich are disposed by interposing a space therebetween through which the optical fiber intermediary body4passes

As the position sensor80, for example, a laser-type position sensor can be employed. The position sensor80can detect a position of the bare optical fiber3. The position sensor80can measure a flotation amount of the bare optical fiber3at the second direction changer20B based on the positional information of the bare optical fiber3.

The position sensor80outputs a detection signal to the control unit90based on the information regarding the detected position of the bare optical fiber3.

Although it is not shown, the position sensor for the first direction changer20A can be disposed at a position between the first direction changer20A and the second direction changer20B.

The position sensor can measure a flotation amount of the bare optical fiber3at the second direction changer20A based on the positional information of the bare optical fiber3.

The position sensor also outputs a detection signal to the control unit90based on the information regarding the detected position of the bare optical fiber3.

The control unit90can control the Reynolds number (Re number) at each of the direction changers20A and20B by adjusting the introduced flow volume of the fluid flowed to each of the direction changers20A and20B based on the detection signal. The control unit90can control the introduced flow volume of the fluid by, for example, adjusting an opening degree of an on-off valve provided on an introduction path introducing the fluid to the direction changers20A and20B.

The optical fiber5changes the direction thereof by a pulley50and is taken up by a take-up unit60and is wound by winding means70.

The take-up unit60, for example, is a take-up capstan, and determines a fiber drawing speed. The fiber drawing speed, for example, is greater than or equal to 1500 m/min.

The winding means70is a winding bobbin which winds the optical fiber5.

An outer diameter of the optical fiber preform2, for example, is greater than or equal to 100 mm, and the length of the optical fiber5prepared from one optical fiber perform2, and for example, is a few thousand km.

First, the direction will be defined. As shown inFIG. 1, a surface including a linear path line (a first path L1) of the bare optical fiber3before being subjected to direction change by the direction changer20A and a linear path line (a second path L2) of the bare optical fiber3after being subjected to the direction change of 90° by the direction changer20A is referred to as “P1”. An X direction is a direction along the second path L2in the surface P1, and a Y direction is a direction perpendicular to the surface P1.

The optical fiber preform2is in a state of being suspended in the vertically downward direction, and the direction of the bare optical fiber3which is drawn out from the optical fiber preform2is toward a vertically lower portion. For this reason, in the disposition of the first direction changer20A, accuracy in a disposing position of the direction (the Y direction) perpendicular to the surface P1including the first path L1along a vertical direction and the second path L2along a horizontal direction is important.

The reason that accuracy in the positioning of the Y direction is important is because when the bare optical fiber3is in contact with an inside surface21cof the guide groove21of the direction changer20, the strength of the bare optical fiber3decreases as shown inFIG. 2, and thus it is necessary to reliably separate the bare optical fiber3from the inside surface21c.

In the manufacturing apparatus1A, the direction of the bare optical fiber3is changed to a third path L3along the vertical direction by the second direction changer20B, and thus in the disposition of the second direction changer20B, accuracy in the disposing position of the direction (the Y direction) perpendicular to the surface P1including the second path L2and the third path L3is required.

The resin coating is generally performed with respect to the vertically downward bare optical fiber, and thus disposition accuracy in the Y direction which is the direction perpendicular to a surface including the path L3introduced to the coating unit30and the path L2before the direction change is important.

Furthermore, the direction of the bare optical fiber to be subjected to the resin coating is not limited to the vertically downward direction. The direction may be a direction along the second path insofar as the coating can be performed.

Hereinafter, a specific structure of the direction changer20will be described.

A direction changer201shown inFIG. 3A, is a first example of the direction changer20and is able to change the direction of the bare optical fiber3by 90°. Therefore, the direction changer201can be used as the direction changers20A and20B shown inFIG. 1.

The direction changer201is in the shape of one quarter circle in a plan view, and the guide groove21is formed over the entire circumferential length in an outer circumferential surface20a. The direction changer201allows a central axis direction to be coincident with the Y direction, and disposes a radial direction D1(refer toFIG. 2) in a posture directed towards the direction along the surface P1(refer toFIG. 1). Here, a direction along the outer circumferential surface20awhich is in the shape of an arc in a plan view is referred to as a circumferential direction.

A blowout port22for the fluid (air or the like) which floats the bare optical fiber3wired along the guide groove21is formed in a lower portion of the guide groove21along the guide groove21. The blowout port22is formed over the entire length of the guide groove21.

As shown inFIG. 2, the direction changer201is configured to discharge the fluid (for example, air) in a space (a fluid storing portion25) ensured in the direction changer201into the guide groove21through the blowout port22.

The direction changer201, for example, can be configured to introduce the fluid to the fluid storing portion25from the outside, and to discharge the fluid into the guide groove21through the blowout port22.

It is preferable that the guide groove21is formed to be inclined with respect to the radial direction D1such that a distance between the inside surfaces21cand21c(a dimension in the Y direction) gradually increases towards an outer portion in the radial direction. It is preferable that the two inside surfaces21cand21chave the same inclination angle θ1with respect to the radial direction D1.

In the direction changers20A to20C, the fluid (for example, air) in the fluid storing portion25is discharged into the guide groove21through the blowout port22, and thus it is possible to float the bare optical fiber3. Specifically, a pressure difference between a deep portion21dand a shallow portion21eof the guide groove21increases due to the discharged air, and thus the bare optical fiber3is floated by applying a force of the outer portion in the radial direction to the bare optical fiber3.

In the above case, according to conditions, Karman vortex is generated at an outer side in the radial direction to the bare optical fiber3. When the Karman vortex is generated, pressure fluctuations occur and the bare optical fiber3is oscillated. Due to the oscillation, the bare optical fiber3is possibly in contact with the inside surface21c.

The strength of the bare optical fiber3may decrease when contacting the inside surface21cof the guide groove21, and thus it is necessary to reliably separate the bare optical fiber3from the inside surface21c.

Therefore, the Karman vortex needs to be canceled or to be small enough to reduce the vibration of the bare optical fiber3.

In the direction changer201, in order to reduce the Karman vortex, the Re number just before the fluid contacts the bare optical fiber3is defined.

The Re number is an index indicating a laminar flow and turbulence of a flow, and when the Re number gets smaller, the flow becomes a laminar flow and less Karman vortex is generated. In contrast, when the Re number gets larger, the flow becomes a laminar flow and more Karman vortex is easily generated.

The Re number does not need to be constant in a circumferential direction of the direction changer201, and as appropriate, the Re number can be optimized in each of the sections located in different positions in the circumferential direction. Therefore, the oscillation of the bare optical fiber3can be reduced.

As to the Re number, it is desirable to optimize values at an inlet wire portion (a portion including a part in which the bare optical fiber3moves into the guide groove) and an outlet wire portion (a portion including a part in which the bare optical fiber3moves out from guide groove) of the bare optical fiber3in the direction changer. Therefore, it is possible to improve the stability of the bare optical fiber3when it is floated.

In the direction changer201shown inFIG. 3A, the bare optical fiber3moves into a first end21aof the guide groove21in the shape of one quarter circle and moves out from a second end21b, and thus is subjected to the direction change of 90°. An inlet wire portion23into which the bare optical fiber3moves is a portion including the first end21aof the guide groove21, and an outlet wire portion24from which the bare optical fiber3moves out of is a portion including the second end21bof the guide groove21.

FIG. 3Bis a diagram in which the blowout port22is developed. As shown in this drawing, the blowout port22includes an intermediate portion26having a constant width (a constant dimension in the Y direction) over a predetermined length range of the guide groove21, a first end portion27including the first end22aof the blowout port22, and a second end portion28including the second end22bof the blowout port22.

The first end portion27extends along the guide groove21while the width of the first end portion27is narrowed towards the first end21aof the guide groove21from one end of the intermediate portion26. The second end portion28extends along the guide groove21while the width of the second end portion28is narrowed towards the second end21bof the guide groove21from the other end of the intermediate portion26.

The first end22aof the blowout port22reaches the first end21aof the guide groove21, and the second end22breaches the second end21b.

The first end portion27and the second end portion28, for example, are portions in a circumferential direction range corresponding to 10° to 30°.

In the direction changer201shown inFIG. 3A, the first end portion27may be in a range in which a position of 0° is a starting end and a position of 10° to 30° is a terminating end in a range of 90°. In addition, the second end portion28may be in a range in which a position of 60° to 80° is the starting end and a position of 90° is the terminating end in the range of 90°. In this example, each of the first end portion27and the second end portion28is in a circumferential direction range corresponding to 11.1% to 33.3% of the entire blowout port22.

In a direction changer203shown inFIG. 5A, a first end portion37may be in a range in which a position of 0° is the starting end and a position of 20° to 30° is the terminating end in a range of 180°. In addition, a second end portion38may be in a range in which a position of 150° to 160° is the starting end and a position of 180° is the terminating end in the range of 180°. In this example, each of the first end portion37and the second end portion38is in a circumferential direction range corresponding to 11.1% to 16.7% of the entire blowout port22.

It is difficult for the first end portion27and the second end portion28to have a high flow rate in a range close to the first end21aand the second end21b, and thus a portion including the first end21aand the second end21bmay be excluded.

In an example shown inFIG. 8, the first end portion27may be a portion excluding a circumferential direction range (inFIG. 8, for example, a range of greater than or equal to 0° and less than 5°) including the first end21a. In addition, the second end portion28may be a portion excluding a circumferential direction range (inFIG. 8, for example, a range of greater than 85° and less than or equal to 90°) including the second end21b.

That is, the first end portion27may be in a range in which a position of 5° is the starting end and a position of 10° to 30° is the terminating end in a range of 90°. In addition, the second end portion28may be in a range in which a position of 60° to 80° is the starting end and a position of 85° is the terminating end in the range of 90°.

In this example, each of the first end portion27and the second end portion28is in a circumferential direction range corresponding to 5.5% to 27.8% of the entire blowout port22.

In an example shown inFIG. 9, the first end portion37may be a portion excluding a circumferential direction range (inFIG. 9, for example, less than 10°) including a first end31a. In addition, the second end portion38may be a portion excluding a circumferential direction range (inFIG. 9, for example, a range of greater than 170° and less than or equal to 180°) including a second end31b.

That is, the first end portion37may be in a range in which a position of 10° is the starting end and a position of 20° to 30° is the terminating end in a range of 180°. In addition, the second end portion38may be in a range in which a position of 150° to 160° is the starting end and a position of 170° is the terminating end in the range of 180°.

In this example, each of the first end portion37and the second end portion38is in a circumferential direction range corresponding to 5.5% to 11.1% of the entire blowout port22.

It is not possible to comprehensively determine a difference between the minimum width of the first end portion27and the second end portion28and the width of the intermediate portion26since the difference depends on other designs, but the difference is at least on the order of a few μm to a few dozen μm.

A difference between the minimum width of the first end portion27and the second end portion28, and the width of the intermediate portion26, for example, is able to be 2 μm to 10 μm. By setting the difference to be in the range described above, it is possible to ensure the blowing-out flow rate of the fluid in the first end portion27and the second end portion28, and it is possible to increase a ratio of the blowing-out flow rate in the first end portion27and the second end portion28to the blowing-out flow rate in the intermediate portion26.

It is preferable that the maximum width of the first end portion27and the second end portion28and the width of the intermediate portion26are equal to each other.

The minimum width of the first end portion27and the second end portion28can be 70% to 98% with respect to the width of the intermediate portion26. The minimum width of the first end portion27and the second end portion28is preferably 80% to 95%, and is more preferably 85% to 90%, with respect to the width of the intermediate portion26.

By setting the ratio of the minimum width of the first end portion27and the second end portion28to the width of the intermediate portion26to be in the range described above, it is possible to ensure the blowing-out flow rate of the fluid in the first end portion27and the second end portion28, and it is possible to increase a ratio of the blowing-out flow rate in the first end portion27and the second end portion28to the blowing-out flow rate in the intermediate portion26.

Furthermore, in the first end portion27, the second end portion28, and the intermediate portion26shown inFIG. 3B, both side edges are linear, and when the width of the first end portion27, the second end portion28, and the intermediate portion26is narrowed towards the first end21aand the second end21b, both of the side edges may be curved.

In the direction changer201shown inFIGS. 3A, 3B, The width of the first end portion27and the second end portion28(for example, an average width or the minimum width) is narrowed, and thus the width of the blowout port22is narrowed in the inlet wire portion23and the outlet wire portion24which are both end portions of the guide groove21.

For this reason, in the inlet wire portion23and the outlet wire portion24, a pressure loss at the time of blowing out the fluid from the blowout port22increases compared to the other portion (in this example, a portion between the inlet wire portion23and the outlet wire portion24, that is, a portion in a length range corresponding to the intermediate portion26), and thus the blowing-out flow rate in the inlet wire portion23and the outlet wire portion24is faster than the lowest flow rate of the fluid in the other portion.

The blowing-out flow rate of the fluid in the inlet wire portion23and the outlet wire portion24may be faster than an average flow rate (or the highest flow rate) of the fluid in the intermediate portion26.

In comparison to the flow rate of the fluid in the intermediate portion26, the flow rate of the fluid in the inlet wire portion23and the outlet wire portion24is the average value or the highest value.

Since the blowing-out flow rate of the fluid increases at the inlet wire portion23and the outlet wire portion24, the Re number increases compared to the other portion (in this example, a portion including a length corresponding to the intermediate portion26).

A direction changer202shown inFIG. 4is a modification example of the direction changer201, and is in the shape of a three-quarter circle in a plan view. Hereinafter, the same reference numerals are applied to configurations identical to the configurations described above, and the description thereof will be omitted.

The direction changer202has a structure in which on an incoming line side and an outgoing line side of a main body portion29ahaving the same structure as that of the direction changer201shown inFIG. 3A, auxiliary portions29band29crespectively having the same structure as that of the main body portion29aare continuously disposed.

The direction changer202has a basic function identical to that of the direction changer201since the bare optical fiber3moves into the guide groove21of the main body portion29afrom the inlet wire portion23, and moves out through the outlet wire portion24after the direction thereof is changed by 90° in the main body portion29a.

The direction changers201and202are able to change the direction of the bare optical fiber3by 90°, and thus are able to be used as the direction changers20A and20B shown inFIG. 1.

The direction changer203shown inFIG. 5Ais a second example of the direction changer20, and is able to change the direction of the bare optical fiber3by 180°. The direction changer203is in the shape of a semicircle in a plan view, and a guide groove31is formed over the entire circumferential length in the outer circumferential surface20a.

A blowout port32of the fluid (air or the like) which floats the bare optical fiber3is formed in a lower portion of the guide groove31along the guide groove31. The blowout port32is formed over the entire length of the guide groove31.

The direction changer203is configured to discharge the fluid in the guide groove31from the fluid storing portion35through the blowout port32.

In the direction changer203, the bare optical fiber3moves into a first end31aof the guide groove31which is in the shape of a semicircle, and is subjected to direction change of 180° by moving out from a second end31b. An inlet wire portion33is a portion including the first end31aof the guide groove31, and an outlet wire portion34is a portion including the second end31bof the guide groove31.

The sectional shape of the guide groove31is the same as the sectional shape of the guide groove21(refer toFIG. 2).

As shown inFIG. 5B, the blowout port32includes an intermediate portion36having a constant width (a constant dimension in the Y direction) over a predetermined length range of the guide groove31, a first end portion37including the first end32aof the blowout port32, and a second end portion38including the second end32bof the blowout port32.

The first end portion37extends along the guide groove31while the width of the first end portion37is narrowed towards the first end31aof the guide groove31from one end of the intermediate portion36. The second end portion38extends along the guide groove31while the width of the second end portion38is narrowed towards the second end31bof the guide groove31from the other end of the intermediate portion36.

The first end32aof the blowout port32reaches the first end31aof the guide groove31, and the second end32breaches the second end31b.

The width of the first end portion37and the second end portion38(for example, an average width or the minimum width) is narrowed, and thus the width of the blowout port32is narrowed in the inlet wire portion33and the outlet wire portion34which are both end portions of the guide groove31.

For this reason, in the inlet wire portion33and the outlet wire portion34, the blowing-out flow rate of the fluid from the blowout port32is faster than the lowest flow rate of the fluid in the other portion (an intermediate portion36).

The blowing-out flow rate of the fluid in the inlet wire portion33and the outlet wire portion34may be faster than an average flow rate (or the highest flow rate) of the fluid in the intermediate portion36.

Since the blowing-out flow rate of the fluid increases at the inlet wire portion33and the outlet wire portion34, the Re number increases compared to the other portion (in this example, a portion including a length corresponding to the intermediate portion36).

A direction changer204shown inFIG. 6is a modification example of the direction changer203, and is in the shape of a three-quarter circle in a plan view.

The direction changer204has a structure in which on an incoming line side and an outgoing line side of a main body portion39ahaving the same structure as that of the direction changer203shown inFIG. 5A, auxiliary portions39band39crespectively having the same sectional structure as that of the main body portion39awhich are in the shape of an eighth circle in a plan view are continuously disposed.

The direction changer204has a basic function identical to that of the direction changer203since the bare optical fiber3moves into the guide groove31of the main body portion39afrom the inlet wire portion33, and moves out through the outlet wire portion34after the direction thereof is changed by 180° in the main body portion39a.

Next, a first embodiment of a manufacturing method of an optical fiber of the present invention will be described by using a case where the manufacturing apparatus1A is used as an example.

In the drawing unit10, the optical fiber preform2is heated and drawn, and thus the bare optical fiber3is formed.

(Direction Change of Direction Changer)

The bare optical fiber3which is drawn out to the vertically downward direction (the first path L1) from the optical fiber preform2is directed towards a horizontal direction (the second path L2) due to direction change of 90° of the first direction changer20A.

The bare optical fiber3is directed towards the vertically downward direction (the third path L3) due to direction change of 90° of the second direction changer20B.

In the direction changers20A and20B, the fluid (for example, air) in the fluid storing portion25is discharged into the guide groove21through the blowout port22, and thus it is possible to float the bare optical fiber3. Specifically, a pressure difference between the deep portion21dand the shallow portion21eof the guide groove21increases due to the discharged air, and thus the bare optical fiber3is floated by applying a force of the outer portion in the radial direction to the bare optical fiber3.

The position sensor80outputs a detection signal to the control unit90based on the information regarding the detected position of the bare optical fiber3.

The control unit90controls the introduced flow volume of the fluid flowed to each of the direction changers20A and20B based on the detected signal. The control unit90can control the introduced flow volume of the fluid by, for example, adjusting an opening degree of an on-off valve provided on an introduction path introducing the fluid to the direction changers20A and20B.

In particular, the control unit90controls the introduced flow volume of the fluid to be decreased when the flotation amount of the bare optical fiber3increases. As a result, the Re numbers at the direction changers20A and20B are decreased. The control unit90controls the introduced flow volume of the fluid to be increased when the flotation amount of the bare optical fiber3decreases. Therefore, the Re number at each of the direction changers20A and20B increases.

As a control method, a feedback controller such as a proportional-integral-derivative (PID) controller is preferable. Therefore, the introduced flow volume of the fluid can be controlled with satisfactory responsiveness

The position sensor for the first direction changer20A can be disposed at a position between the first direction changer20A and the second direction changer20B. In this case, the flotation amount of the bare optical fiber3at the first direction changer20A is measured based on the positional information of the bare optical fiber3obtained at this position sensor. Based on the measurement results thereof, the control unit90can control the Re number of the first direction changer20A.

In this case, the control of the Re number at the second direction changer20B is performed based on the positional information of the bare optical fiber3obtained at the position sensor80. In particular, the flotation amount of the bare optical fiber3at the second direction changers20B is measured based on the information obtained at the position sensor80. Based on the measurement results, the control unit90controls the Re number of the second direction changer20B.

In the coating unit30, the coating material such as a urethane acrylate-based resin is applied (coated) onto the outer circumference of the bare optical fiber3and becomes the coating layer, and thus the optical fiber intermediary body4is obtained.

In the curing unit40, the coating layer of the optical fiber intermediary body4is cured by irradiation of a UV lamp40a, and the optical fiber5is formed.

The optical fiber5is wound by the winding means70through the pulley50and the take-up unit60.

As shown inFIG. 2, the flotation amount of the bare optical fiber3inside the guide groove21depends on the flow rate of the fluid.

The inside surfaces21c,21care inclined such that a width gradually increases towards an outer portion in the radial direction. Therefore, when the flotation amount of the bare optical fiber3increases, a gap between the bare optical fiber3and the inside surface21cincreases, and the contact between the bare optical fiber3and the inside surface21chardly occurs.

However, practically, when the flotation amount of the bare optical fiber3increases, the strength of the bare optical fiber3often decreases and the cause thereof is estimated as the contact between the bare optical fiber3and the inside surface21c.

The inventors of the present application found the followings after consideration of causes and solutions of the above phenomenon.

In the guide groove21, by setting the Re number of the fluid flow just before the bare optical fiber3to be 1200-3500, floatation of the bare optical fiber3can be stabilized.

When the Re number exceeds 3500, due to pressure fluctuations which is likely to be caused by an influence of Karman vortex of the fluid flow generated in the rear of the bare optical fiber3, the flotation amount of the bare optical fiber3changes (temporal oscillation or fluctuation of the flotation amount of the bare optical fiber3) occurs.

Due to the variation of the flotation amount, the bare optical fiber3is in contact with the inside surfaces21c,21cwith some frequencies, and the strength of the optical fiber5may decrease by the contact.

FIG. 7is a diagram showing an example of fluctuation of a flotation position.

Regarding the flotation amount, the manufacturing apparatus1A of the bare optical fiber shown inFIG. 1is used and positional data of the bare optical fiber3is obtained by the position sensor80disposed at a position between the direction changer20B and the coating unit30(the third path L3).

With reference toFIG. 7, it is found that a flotation position of a component in an X-direction fluctuates much greater than a flotation position of a component in a Y-direction as the time elapses. It appears that a position in the Y-direction is stable; however, the fluctuation of the flotation position is approximately ±10 μm. Usually, since a gap between the bare optical fiber3and an inside surface21cof the guide groove21is a few tens μm, the fluctuation of the flotation position in the Y-direction is not also a small fluctuation.

When the Re number is under 1200, the fluid flow becomes almost like a laminar flow. However, since a fluid-flow rate is slow, a sufficient flotation amount of the bare optical fiber3, due to the variation of the drawing tension, the flotation position of the bare optical fiber3is shifted in a depth direction of the guide groove21and the bare optical fiber3contacts the surface21c. As a result, the strength of the bare optical fiber3is decreased.

In contrast, when the Re number of the fluid flow is 1200-3500, a certain amount of flotation amount of the bare optical fiber3is secured and the temporal stability of the flotation amount is obtained, and drawing can be performed without causing products to include a serious defect.

A Re number at the direction changer20can be calculated as shown below.
Re number=density of gas to be used [kg/m3]×fluid-flow rate [in/sec]×representative length [m]/viscosity of gas to be used [Pa·s]

Regarding a representative length, since the inclination of the inside surfaces21c,21cis very small, the inside surface21c,21cis assumed to be parallel each other, and a representative length between the two plates.

Here, the Re number is introduced as an index to represent stability of the flotation amount. Therefore, the Re number does not need to be strictly precise, and an upper-class index is used. In other words, when a distance between the two plates is d [m], the representative length is set2d[m].

In addition, with regard to the fluid-flow rate [m/sec], a measurement position is at a bottom side of the guide groove21in a turning position of the bare optical fiber3. For example, a fluid-flow position is follows: fluid-flow position=turning radius (center position of the bare optical fiber3)−radius of the bare optical fiber3. An outer diameter of the bare optical fiber3is, for example, 125 μm.

A cross-section of the guide groove21at this position is calculated, and based on an introduced flow volume [m3/sec] of the fluid to a direction changer20as follows, fluid-flow rate [m/sec]=introduced flow volume [m3/sec]/cross-section of fluid passage [m2], the fluid-flow rate is calculated.

Here, in the density of gas to be used and the viscosity of gas to be used, values at a temperature of used gas to be used (generally, a normal temperature and approximately 20° C.) are employed.

As a specific structure of the direction changer, for example, structures which are described in Japanese Patent No. 5571958 or Japanese Unexamined Patent Application, First Publication No. S62-003037 can be used. The structure of the direction changer20is not particularly limited to these two structures, and other structures may be used.

For example, when a non-contact retaining mechanism described in Japanese Patent No. 5571958 is used, in the direction changer, a direction of the bare optical fiber3is changed by 90° at the turning radius of 62.5 mm. A width of the guide groove21(i.e., the width of the guide groove21at a position of an innermost periphery of the bare optical fiber3in a floating state) is 145 μm. A diameter of the bare optical fiber3is 125 μm. An introduced flow volume of the air is 100 L/min with respect to the direction changer.

The turning radius is determined by a relation between a fluid-flow rate and drawing tension. Here, the turning radius is a radius when a certain drawing tension is set under a structure or a manufacturing condition of a specific direction changer.

Viscosity of air (20° C.)=1.822×10′5Pa·s

Since the Re number falls into a range of 1200 to 3500, the above conditions can be determined as the conditions in a stable state.

In addition, the Re number of the fluid flow does not need to be constant at the entire circumferential direction (the entire blowout port) of the direction changer20, and as appropriate, the Re number can be optimized in each of the sections located in different positions in the circumferential direction.

For example, an inlet wire position and an outlet wire position of the bare optical fiber3to and from the direction changer20are on a contact interface of the bare optical fiber3and the fluid flow. The contact interface is an interface between a portion where the bare optical fiber3contacts the fluid flow and a portion where the bare optical fiber3does not contact the fluid flow.

Furthermore, it is necessary to correct the positional shift between a tip end portion of the optical fiber at the manufacturing apparatus1A and the direction changer20(center shift) by the fluid flow in any way. Therefore, in addition to a condition to obtain stability of the floatation amount at a normal portion excluding an incoming line position and an outgoing line position, a condition for correct the positional shift needs to be added.

For example, inFIG. 1, the optical fiber cannot be moved in a radial direction, and thus the a tip end portion2aof a diameter reduced portion (neck-down) of the optical fiber preform2which is heated and melted, the coating unit30, the take-up unit60, the pulley50, and the winding means70are able to act as a fixed end when the optical fiber is horizontally oscillated.

Regarding the direction changer20, in order to correct a positional shift of a path line of the bare optical fiber3, it is desirable to increase the flotation amount in the inlet wire portion23and the outlet wire portion24.

Therefore, as shown inFIG. 8, the Re number is adjusted to a large value as long as there is no influence of Karman vortex. In other words, the Re number is preferable to be at least in a range of 2500-3500.

As a result, the oscillation of the bare optical fiber3can be decreased, and also the flotation stability in the inlet wire portion23and the outlet wire portion24of the direction changer20can be obtained. In addition, a large allowable range of a positional correction in the inlet wire portion23and the outlet wire portion24can be secured. Accordingly, the decrease of the strength of the bare optical fiber3due to the contact between the bare optical fiber3and the inside surface21c,21ccan be reduced.

In order to increase the flotation amounts at the inlet wire portion23and the outlet wire portion24, the Re number is set greater than the Re number at the other portion (in this example, a portion between the inlet wire portion23and the outlet wire portion24, that is, a portion in a length range corresponding to the intermediate portion26).

In the direction changer201shown inFIGS. 3A and 3B, the width of the first end portion27and the second end portion28(for example, an average width or the minimum width) is narrowed, and thus the width of the blowout port22is narrowed in the inlet wire portion23and the outlet wire portion24which are both end portions of the guide groove21.

For this reason, in the inlet wire portion23and the outlet wire portion24, a pressure loss at the time of blowing out the fluid from the blowout port22increases compared to the other portion (in this example, a portion between the inlet wire portion23and the outlet wire portion24, that is, a portion in a length range corresponding to the intermediate portion26), and thus the blowing-out flow rate in the inlet wire portion23and the outlet wire portion24is faster than the lowest flow rate of the fluid in the other portion.

The blowing-out flow rate of the fluid in the inlet wire portion23and the outlet wire portion24may be faster than an average flow rate (or the highest flow rate) of the fluid in the intermediate portion26.

Therefore, the Re number at the inlet wire portion23and the outlet wire portion24can be greater than the Re number at the other portion (in this example, a portion including a length corresponding to the intermediate portion26).

As described above, the flow rate of the fluid increases in the inlet wire portion23and the outlet wire portion24, and thus a pressure difference between a deep portion21d(seeFIG. 2) and a shallow portion21eof the guide groove21increases, a force in a direction (an outer portion in a radial direction) in which the bare optical fiber3is floated increases due to Bernoulli effect. In addition, based on the Navier-Stokes principle considering viscosity, an effect positioning the bare optical fiber3closer to a center of the guide groove21(a center in the Y-direction) increases. For this reason, a shift in a path line position is corrected.

In addition, a flotation amount of the bare optical fiber3increases in the inlet wire portion23and the outlet wire portion24. Thus, a gap between an inside surface21cof the guide groove21and the bare optical fiber3is widened, and an acceptable amount with respect to the shift in the path line position increases.

For this reason, it is possible to relax a requirement for accuracy in a disposing position of the direction changer20. For example, it is possible to set disposing position required accuracy to be on a μm-order to 0.5 mm order (a few hundred μm order), and it is possible to relax a requirement for accuracy of at least a few hundred times.

Accordingly, a disposing operation of the direction changer20becomes easy, and damage which is caused by bringing the bare optical fiber3in contact with the inside surface21cof the guide groove21is prevented, and thus it is possible to manufacture the optical fiber5with a sufficient yield.

Further, it is possible to adjust the blowing-out flow rate of the fluid in the inlet wire portion23, the outlet wire portion24, and the intermediate portion26. Thus it is possible to ensure the blowing-out flow rate of the fluid for floating the bare optical fiber3in the intermediate portion26. In addition, it is possible to set a sufficient blowing-out flow rate of the fluid for adjusting the path line position in the inlet wire portion23and the outlet wire portion24and for adjusting the flotation amount of the bare optical fiber3. Accordingly, it is possible to reduce the operating cost without wasting the fluid.

Regarding an adjustment of an installing position of the direction changers20A and20B with respect to the X-direction, the same accuracy as in the Y-direction is not necessary. It is because that regarding the X-direction, for example, a flotation position of the bare optical fiber is finely adjustable by adjusting the number in a range of 1200-3500.

Therefore, in the X-direction, if disposition accuracy is in a range capable of ensuring the stability of the flotation amount of the bare optical fiber3by at least adjusting the blowing-out flow rate of the fluid, the disposition accuracy may be low compared to the disposition accuracy in the Y-direction. In other words, it is desirable that if it can be avoided a state that the bare optical fiber3does not float as a result of decreasing the Re number by reducing the blowing-out flow rate of the fluid in order to adjust a position in an X-direction.

FIG. 8shows an Re number distribution in a circumferential direction of the direction changer201(refer toFIGS. 3A and 3B) which changes the direction of the bare optical fiber3by 90°.FIG. 9shows an Re number distribution in a circumferential direction of the direction changer203(refer toFIGS. 5A and 5B) which changes the direction of the bare optical fiber3by 180°. In the measurement, a wind gauge SAV-26A manufactured by Kansai Tech Co., Ltd. is used, but the wind gauge is not particularly limited. The amount of the fluid (air) introduced to the direction changer201is suitably adjusted such that the amount does not exceed a measurement upper limit of the wind gauge. Here, based on the measured wind-speed distribution, the distribution is converted to a wind speed at a position where the Re number is calculated and regarded as the actual introduced flow volume of the fluid, and converted to an Re-number distribution.

As shown inFIG. 8, in the direction changer201(refer toFIGS. 3A and 3B) which changes the direction of the bare optical fiber3by 90°, the measurement is performed at a plurality of positions in the circumferential direction every 5°. In this example, a position of 0° is an incoming line position, and a position of 90° is an outgoing line position.

As shown in this drawing, the Re number is maximized in a position close to the incoming line position and the outgoing line position (a position of 10° and 80°), and the Re number is minimized in a position separated from the incoming line position and the outgoing line position (a position of 35° and 55°).

The Re number in a position of 10° is the highest value of the blowing-out Re number of the fluid in the inlet wire portion23of the direction changer201(refer toFIGS. 3A and 3B). The wind speed in a position of 80° is the highest value of the blowing-out Re number of the fluid in the outlet wire portion24of the direction changer201.

The Re number in a position of 35° and 55° is the lowest value of the blowing-out Re number of the fluid in the intermediate portion26of the direction changer201.

The blowing-out Re number (the highest value) in the inlet wire portion23and the outlet wire portion24is approximately 1.8 times the lowest value of the blowing-out Re number in the intermediate portion26.

As shown inFIG. 9, in the direction changer203(refer toFIGS. 5A and 5B) which changes the direction of the bare optical fiber3by 180°, the measurement is performed at a plurality of positions in the circumferential direction every 10°. In this example, a position of 0° is an incoming line position, and a position of 180° is an outgoing line position.

As shown in this drawing, the Re number is maximized in a position close to the incoming line position and the outgoing line position (a position of 20° and 160°), and the Re number is minimized in a position separated from the incoming line position and the outgoing line position (a position of 70°).

The Re number in a position of 20° is the highest value of the blowing-out flow rate of the fluid in the inlet wire portion33of the direction changer203(refer toFIGS. 5A and 5B). The Re number in a position of 160° is the highest value of the blowing-out flow rate of the fluid in the outlet wire portion34of the direction changer203.

The Re number in a position of 70° is the lowest value of the blowing-out Re number of the fluid in the intermediate portion36of the direction changer203.

The blowing-out Re number (the highest value) in the inlet wire portion33and the outlet wire portion34is approximately 1.8 times the lowest value of the blowing-out Re number in the intermediate portion36.

Hereinafter, practically, a concrete method setting the Re numbers so that the numbers are different in each of the plurality of areas in a circumferential direction is described.

1. Adjusting Re Number by Adjusting Width of Blowout Port22

In the direction changer201shown inFIGS. 3A and 3B, the width of the first end portion27and the second end portion28(for example, an average width or the minimum width) is narrowed, and thus the width of the blowout port22is narrowed in the inlet wire portion23and the outlet wire portion24which are both end portions of the guide groove21.

For this reason, in the inlet wire portion23and the outlet wire portion24, a pressure loss at the time of blowing out the fluid from the blowout port22increases compared to the other portion (in this example, a portion between the inlet wire portion23and the outlet wire portion24, that is, a portion in a length range corresponding to the intermediate portion26), and thus the blowing-out flow rate in the inlet wire portion23and the outlet wire portion24is faster than the lowest flow rate of the fluid in the other portion.

As shown inFIG. 8, at the inlet wire portion23and the outlet wire portion24, the blowing-out flow rate of the fluid becomes faster, the Re numbers increase compared to the another portion (in this example, a portion having a length range corresponding to the intermediate portion26).

2. Adjusting Re Number by Providing Multiple Inner Spaces

The direction changer205shown inFIG. 10is a third example of the direction changer20, and is able to change the direction of the bare optical fiber3by 180°. The direction changer205is in the shape of a semicircle in a plan view, and is configured to discharge the fluid in the guide groove31from a fluid storing portion45through a blowout port42.

The shape of the blowout port42is not particularly limited, and for example, the width may be constant over the length direction of the guide groove31.

The fluid storing portion45is partitioned into a first fluid storing portion45A (a first space) and a second fluid storing portion45B (a second space) by the partition wall41.

The first fluid storing portion45A is in communication with a first end portion47and a second end portion48of the blowout port42, and the second fluid storing portion45B is in communication with an intermediate portion46of the blowout port42.

A first supply port43A which supplies the fluid to the first fluid storing portion45A and a second supply port43B which supplies the fluid to the second fluid storing portion45B are formed on a side surface of the direction changer205.

In the direction changer205, a flow volume of the fluid supplied to the fluid storing portions45A and45B through the supply ports43A and43B is adjusted, and thus it is possible to set inner pressures of the fluid storing portions45A and45B to be independent from each other. For this reason, it is possible to set the blowing-out flow rate of the fluid in the first end portion47and the second end portion48and the blowing-out flow rate of the fluid in the intermediate portion46to be independent from each other.

For this reason, it is possible to set the blowing-out flow rate of the fluid in the inlet wire portion33and the outlet wire portion34to be faster than the lowest blowing-out flow rate of the fluid in the other portion in circumferential direction (the intermediate portion46).

Since the blowing out flow rate of the fluid becomes fast at the inlet wire portion33and the outlet wire portion34, an Re number thereof becomes faster than an Re number at the other portion (the intermediate portion46) in the circumferential direction.

A direction changer206shown inFIG. 11is a fourth example of the direction changer20, and is able to change the direction of the bare optical fiber3by 180°. The direction changer206is in the shape of a semicircle in a plan view and is configured to discharge the fluid in the guide groove31from a fluid storing portion55through a blowout port52.

The fluid storing portion55is partitioned into first to third fluid storing portions55A to55C by partition walls51A and51B.

The first fluid storing portion55A (a first space) is in communication with a first end portion57of the blowout port52, the second fluid storing portion55B (a second space) is in communication with an intermediate portion56of the blowout port52, and the third fluid storing portion55C (a third space) is in communication with a second end portion58of the blowout port52.

A first supply port53A which supplies the fluid to the first fluid storing portion55A, a second supply port53B which supplies the fluid to the second fluid storing portion55B, and a third supply port53C which supplies the fluid to the third fluid storing portion55C are formed on a side surface of the direction changer206.

In the direction changer206, the flow volume of the fluid supplied to the fluid storing portions55A to55C through the supply ports53A to53C is adjusted, and thus it is possible to set the blowing-out flow rate of the fluid in the first end portion57and the second end portion58and the blowing-out flow rate of the fluid in the intermediate portion56to be independent from each other.

For this reason, it is possible to set the blowing-out flow rate of the fluid in the inlet wire portion33and the outlet wire portion34to be faster than the lowest blowing-out flow rate of the fluid in the other portion in the circumferential direction (the intermediate portion56).

Since the blowing out flow rate of the fluid becomes fast at the inlet wire portion33and the outlet wire portion34, an Re number thereof becomes faster than an Re number at the other portion (the intermediate portion56) in the circumferential direction.

3. Adjusting Re Number by Providing Narrow Portion

A direction changer207shown inFIG. 12is a fifth example of the direction changer20and is able to change the direction of the bare optical fiber3by 90°.

The direction changer207is in the shape of one quarter circle in a plan view and is configured to discharge the fluid in a guide groove61from a fluid storing portion65through a blowout port62.

As shown inFIG. 13A, narrow portions69and69in which the width of a flow path is narrowed by the fluid storing portion65are formed between the fluid storing portion65and the guide groove61in a circumferential direction range in which communication occurs with a first end portion67and a second end portion68of the blowout port62.

As shown inFIG. 13B, the narrow portion69is not formed in a circumferential direction range in which communication occurs with an intermediate portion66of the blowout port62.

For this reason, in the circumferential direction range corresponding to the first end portion67and the second end portion68, a pressure loss at the time of blowing out the fluid increases compared to the circumferential direction range corresponding to the intermediate portion66.

In the direction changer207, the narrow portions69and69are formed in the range corresponding to the first end portion67and the second end portion68, and thus in the inlet wire portion23and the outlet wire portion24, the blowing-out flow rate of the fluid from the blowout port62is faster than the lowest flow rate of the fluid in the other portion (the intermediate portion66).

Since the blowing out flow rate of the fluid becomes fast at the inlet wire portion23and the outlet wire portion24, an Re number thereof becomes faster than an Re number at the other portion (the intermediate portion26) in the circumferential direction.

FIG. 14is a schematic view showing a schematic configuration of a manufacturing apparatus1B which is a second embodiment of the manufacturing apparatus of an optical fiber according to the present invention.

The manufacturing apparatus1B is different from the manufacturing apparatus1A shown inFIG. 1in that the manufacturing apparatus1B includes three direction changers20(20A,20C, and20D). Hereinafter, the second embodiment of the manufacturing method of an optical fiber of the present invention will be described.

In the manufacturing apparatus1B, the bare optical fiber3which is drawn out from the optical fiber preform2to the vertically downward direction (the first path L1) is directed towards the horizontal direction (the second path L2) due to direction change of 90° of the first direction changer20A.

The bare optical fiber3is directed towards a direction opposite to the second path L2(a third path L4) due to direction change of 180° of the second direction changer20C and is directed towards the vertically downward direction (a fourth path L5) due to direction change of 90° of a third direction changer20D.

The bare optical fiber3is subjected to the resin coating in the coating unit30and the coating layer is cured by the curing unit40, and thus the optical fiber5is obtained.

The optical fiber5is wound by the winding means70through the pulley50and the take-up unit60.

EXAMPLES

As the direction changers20A and20B, the direction changer201shown inFIGS. 3A and 3Bwas used. A width of the guide groove21is uniform in a depth direction.

A turning radius was approximately 62.5 mm. The width of the guide groove21(i.e., the width of the guide groove21at a position of an innermost periphery of the bare optical fiber3in a floating state) is 145 μm.

Re numbers (calculated values) of the direction changers20A and20B were approximately 2248.

The fluid introduced to the direction changers20A and20B was air, and the temperature thereof was room temperature (approximately 24° C.).

An introduced flow volume of the air was 100 liters/minute with respect to each of the direction changers20A and20B.

The first direction changer20A was disposed in a position in which the temperature of the bare optical fiber3was approximately 1000° C.

When the direction changers20A and20B were disposed, a centering (position adjustment of the path line) was performed in an accuracy of a μm-order by a centering device using a laser.

The optical fiber preform2was drawn by the drawing unit10, and thus the bare optical fiber3(an outer diameter of 125 μm) was obtained. As a drawing speed and drawing tension, general conditions (a drawing speed of 30 m/second, and drawing tension of approximately 150 gf) were adopted.

The bare optical fiber3which was drawn out from the optical fiber preform2to the vertically downward direction (the first path L1) was subjected to direction change to the horizontal direction (the second path L2) by the first direction changer20A, and then was subjected to the direction change to the vertically downward direction (the third path L3) by the second direction changer20B. The length of the second path L2was approximately 1 m.

In the coating unit30, the bare optical fiber3was coated with an ultraviolet curing resin and irradiated with ultraviolet rays by the UV lamp40ain the curing unit40, the coating layer was cured, and thus the optical fiber5was obtained.

The optical fiber5was wound by the winding means70through the pulley50and the take-up unit60.

While manufacturing the optical fiber5from the optical fiber preform2, an air supply to the direction changers20A and20B is reduced and the Re number (a calculated value) is adjusted to be 1200.

In addition, while manufacturing the optical fiber5from the optical fiber preform2, an air supply to the direction changers20A and20B is increased and the Re number (a calculated value) is adjusted to be 3500.

In the manufacturing method, in both conditions, it was confirmed that the bare optical fiber3was not damaged by the direction changers20A and20B, and the optical fiber5was able to be manufactured with a sufficient yield.

In the manufacturing apparatus1A shown inFIG. 1, an introduced flow volume of the fluid to the direction changers20A and20B was controlled by using the position sensor80and the control unit90.

In other words, by the position sensor80, the positional information of the bare optical fiber3(flotation amount in the second direction changer20B) is obtained to output a detected signal to the control unit90, and an introduced flow volume of the fluid to the direction changers20A,20B is controlled by the control unit90.

As a control method, a PID controller is employed. Other conditions are in line with Example 1 to manufacture the optical fiber5.

While manufacturing the optical fiber5, variation of a linear speed is ±50 m/min at maximum, and variation of the drawing tension is ±25 gf at maximum.

However, in the direction changers20A,20B, since the flow volume of the air was controlled in a range of the Re number of 1200-3500, the flotation amount of the bare optical fiber3was ±0.05 mm and stable.

In the manufacturing method, it was confirmed that the bare optical fiber3was not damaged by the direction changers20A and20B, and the optical fiber5was able to be manufactured with a sufficient yield.

In the manufacturing apparatus1A shown inFIG. 1, as the direction changers20A and20B, a direction changer201having an Re-number profile shown inFIG. 8is used. The width of the intermediate portion26in the blowout port22is 50 μm, and the minimum width of the first end portion27and the second end portion28is 45 μm.

As shown inFIG. 2, an inclination angle θ1of the inside surface21cof the guide groove21with respect to the radial direction D1was 0.5°. A turning radius was approximately 62.5 mm.

The Re number at a portion excluding the inlet wire portion23and the outlet wire portion24(i.e., a portion corresponding to the intermediate portion26) was 2200, and the Re number at the inlet wire portion23and the outlet wire portion24was 2500. The inlet wire portion23and the outlet wire portion24are portions in a circumferential direction corresponding to a range having an angle of 30° from each end.

When the direction changers20A and20B were disposed, a thread having an outer diameter of 0.5 mm was used instead of the bare optical fiber3, and was centered by visual contact (position adjustment of the path line).

In the manufacturing method, it was confirmed that the bare optical fiber3was not damaged by the direction changers20A and20B, and the optical fiber5was able to be manufactured with a sufficient yield.

The optical fiber5was manufactured by using the manufacturing apparatus1B shown inFIG. 14as follows.

As the first direction changer and the third direction changer20A and20D, the direction changer201having the same specification as that used in Example 1 was used.

As the second direction changer20C, the direction changer205shown inFIG. 10was used.

An Re number at the inlet wire portion33and the outlet wire portion34is set to 3000. An Re number at an area corresponding to the intermediate portion46is set to 1800.

When the direction changers20A and20B were disposed, a thread having an outer diameter of 0.5 mm was used instead of the bare optical fiber3, and was centered by visual contact (position adjustment of the path line).

In the manufacturing method, it was confirmed that the bare optical fiber3was not damaged by the direction changers20A,20C, and20D, and the optical fiber5was able to be manufactured with a sufficient yield.

In the manufacturing apparatus1A shown inFIG. 1, the optical fiber5was manufactured by the same method as that in Example 1 except that the direction changer207shown inFIGS. 12 to 13Bwas used in the direction changers20A and20B instead of the direction changer201

An Re number at the inlet wire portion23and the outlet wire portion24is set to 3500. An Re number at an area corresponding to the intermediate portion26is set to 3000.

When the direction changers20A and20B were disposed, a thread having an outer diameter of 0.5 mm was used instead of the bare optical fiber3, and was centered by visual contact (position adjustment of the path line).

In the manufacturing method, it was confirmed that the bare optical fiber3was not damaged by the direction changers20A and20B, and the optical fiber5was able to be manufactured with a sufficient yield.

Comparative Example 1

The optical fiber5was manufactured by using the manufacturing apparatus1A shown inFIG. 1by the same method as that in Example 1 except that the Re number was 4000.

When manufacturing the optical fiber5, the fluctuation of a flotation position of the bare optical fiber3as inFIG. 7was shown.

In the manufacturing method, breaking which was considered to be caused by bringing the bare optical fiber3in contact with the inside surface of the guide groove occurred. Thus, the manufacturing yield was not sufficient.

Comparative Example 2

The optical fiber5was manufactured by using the manufacturing apparatus1A shown inFIG. 1by the same method as that in Example 1 except that the Re number was 1000.

When manufacturing the optical fiber5, the fluctuation of a flotation position of the bare optical fiber3as inFIG. 7was shown.

In the manufacturing method, breaking which was considered to be caused by bringing the bare optical fiber3in contact with the inside surface of the guide groove occurred. Thus, the manufacturing yield was not sufficient.