Abstract:
A method of manufacturing an optical fiber of the invention includes: preparing a direction changer; drawing the bare optical fiber from an optical fiber preform; providing a coated layer on a periphery of the bare optical fiber; obtaining an optical fiber by curing the coated layer; changing a direction of the bare optical fiber at a position between a bare-optical-fiber formation position and a coated-layer provision position; and measuring the outer diameter of the coated layer; and adjusting the length of the bare optical fiber from a drawing unit to a coating unit by controlling a position of the direction changer based on a measurement value of the outer diameter, the drawing unit forming the bare optical fiber, the coating unit providing the coated layer on the periphery of the bare optical fiber.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from Japanese Patent Application No. 2015-024648 filed on Feb. 10, 2015, the contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a method of manufacturing an optical fiber, an optical fiber manufacturing apparatus, and a control apparatus that controls the manufacturing apparatus. 
         [0004]    2. Description of the Related Art 
         [0005]    Generally, in manufacture of an optical fiber, a method is employed which vertically and downwardly draws an optical fiber from an optical fiber preform along a linear pathway. 
         [0006]    The overall height of the system thereof is limited and becomes a factor that affects the productivity of the manufacturing method. 
         [0007]    Because the height of the system becomes a main factor that limits the productivity, it is necessary to ensure the distance of a bare optical fiber in the system which is required to sufficiently cool the bare optical fiber obtained by drawing it from an optical fiber preform. 
         [0008]    The above-described limitation can be eased by construction of new facilities such as new buildings; however, a huge cost is necessary in order to ease the limitation, if improvement in productivity is required in the future, it will be necessary to construct new facilities at great expense. 
         [0009]    As a method of easing the limitation, a method of using a direction changing device that includes a noncontact retention mechanism and changes the direction in which a drawn fiber is drawn is known. 
         [0010]    This noncontact retention mechanism is a mechanism that contactlessly retains an object by using a pressure of fluid such as air, and a direction changer that is provided with this mechanism can change the direction, in which a bare optical fiber (bare fiber) is drawn, without being in contact with the bare optical fiber. 
         [0011]    By using this direction changer, the direction of a bare optical fiber which is fiber-drawn a optical fiber preform along a first pathway can be changed into a direction along a second pathway (for example, refer to Japanese Patent No. 5571958 and Japanese Unexamined Patent Application, First Publication No. S62-003037). 
         [0012]    Japanese Patent No. 5571958 discloses a method of manufacturing an optical fiber, which uses a direction changing device that changes the direction of a drawn fiber. The instrument has a groove into which an optical fiber is to be introduced, and the groove has an opening formed therein. 
         [0013]    In this method, a gas that is introduced into the instrument is discharged through one flow inlet port, and a direction of an optical fiber is changed in a state where the optical fiber floats due to the pressure of the gas. 
         [0014]    Japanese Unexamined Patent Application, First Publication No. S62-003037 discloses a direction changer, the direction changer has a guide groove that guides a bare optical fiber into, and gas outlet nozzles are formed on the bottom surface and both side surfaces of the guide groove (refer to Example and FIGS. 3 and 4). 
         [0015]    In this manufacturing method using the direction changer, a direction of an optical fiber is changed due to the pressure of the gas blown from four outlet nozzles in a state where the optical fiber floats. 
         [0016]    In order to stabilize an outer diameter (coating diameter) of a coated layer of an optical fiber, it is preferable to suitably control a temperature of a bare optical fiber. 
         [0017]    According to the manufacturing methods disclosed in Japanese Patent No. 5571958 and Japanese Unexamined Patent Application, First Publication No. S62-003037, since the bare optical fiber is retained by the gas pressure in the direction changing device, it is possible to control the temperature of the bare optical fiber by use of the gas. 
         [0018]    However, in the case of adjusting a temperature of the bare optical fiber by control of the amount of gas in the direction changing device, there is the following problem. 
         [0019]    Particularly, there is a concern that the amount of flotation of the bare optical fiber is insufficient and a bare optical fiber thereby comes into contact with the inner surface of the groove of the direction changing device. 
         [0020]    In the case where the bare optical fiber comes into contact with the direction changing device, the bare optical fiber is damaged, and there is a possibility that the strength of the bare optical fiber is degraded. 
       SUMMARY OF THE INVENTION 
       [0021]    Some aspects of the invention were conceived in view of the above-described circumstances and have an object thereof to provide a method of manufacturing an optical fiber, an optical fiber manufacturing apparatus, and a control apparatus that controls the manufacturing apparatus, which can sufficiently ensure an amount of flotation of a bare optical fiber and can control a temperature of the bare optical fiber with a high level of accuracy. 
         [0022]    A first aspect of the invention provides a method of manufacturing an optical fiber, including: preparing a direction changer, the direction changer including a guide groove and an outlet nozzle, the guide groove being configured to guide a bare optical fiber, the bare optical fiber being arranged along and introduced into the guide groove, the outlet nozzle being formed in the guide groove and being configured to cause the bare optical fiber to float; drawing the bare optical fiber from an optical fiber preform, thereby forming the bare optical fiber (drawing step); providing a coated layer made of a resin on a periphery of the bare optical fiber (coating step); obtaining an optical fiber by curing the coated layer (curing step); changing the direction of the bare optical fiber at a position between a position at which the bare optical fiber is formed (the position in the drawing step, a bare-optical-fiber formation position) and a position at which the coated layer is provided on the periphery of the bare optical fiber (the position in the coating step, a coated-layer provision position) by use of the direction changer; measuring an outer diameter of the coated layer; and adjusting the length of the bare optical fiber from a drawing unit to a coating unit by controlling the position of the direction changer based on a measurement value of the outer diameter, the drawing unit forming the bare optical fiber, the coating unit providing the coated layer on the periphery of the bare optical fiber. 
         [0023]    A second aspect of the invention provides a method of manufacturing an optical fiber, including: preparing a direction changer, the direction changer including a guide groove and an outlet nozzle, the guide groove being configured to guide a bare optical fiber, the bare optical fiber being arranged along and introduced into the guide groove, the outlet nozzle being formed in the guide groove and being configured to cause the bare optical fiber to float; drawing the bare optical fiber from an optical fiber preform, thereby forming the bare optical fiber (drawing step); providing a coated layer made of a resin on a periphery of the bare optical fiber (coating step); obtaining an optical fiber by curing the coated layer (curing step); changing the direction of the bare optical fiber at the position between the position at which the bare optical fiber is formed (the position in the drawing step, a bare-optical-fiber formation position) and the position at which the coated layer is provided on the periphery of the bare optical fiber (the position in the coating step, a coated-layer provision position) by use of the direction changer; measuring the drawing velocity of the optical fiber; and adjusting the length of the bare optical fiber from a drawing unit to a coating unit by controlling the position of the direction changer based on a measurement value of the drawing velocity, the drawing unit forming the bare optical fiber, the coating unit providing the coated layer on the periphery of the bare optical fiber. 
         [0024]    A third aspect of the invention provides a method of manufacturing an optical fiber, including: preparing a direction changer, the direction changer including a guide groove and an outlet nozzle, the guide groove being configured to guide a bare optical fiber, the bare optical fiber being arranged along and introduced into the guide groove, the outlet nozzle being formed in the guide groove and being configured to cause the bare optical fiber to float; drawing the bare optical fiber from an optical fiber preform, thereby forming the bare optical fiber (drawing step); providing a coated layer made of a resin on a periphery of the bare optical fiber (coating step); obtaining an optical fiber by curing the coated layer (curing step); changing the direction of the bare optical fiber at the position between the position at which the bare optical fiber is formed (the position in the drawing step, a bare-optical-fiber formation position) and the position at which the coated layer is provided on the periphery of the bare optical fiber (the position in the coating step, a coated-layer provision position) by use of the direction changer; measuring the temperature of the bare optical fiber; and adjusting the length of the bare optical fiber from a drawing unit to a coating unit by controlling the position of the direction changer based on a measurement value of the temperature, the drawing unit forming the bare optical fiber, the coating unit providing the coated layer on the periphery of the bare optical fiber. 
         [0025]    A fourth aspect of the invention provides a control apparatus used in an optical fiber manufacturing apparatus, the manufacturing apparatus including: a drawing unit that forms a bare optical fiber by drawing the bare optical fiber from an optical fiber preform; a coating unit that provides a coated layer made of a resin on a periphery of the bare optical fiber; and a curing unit that cures the coated layer, the control apparatus including: one or more direction changers that change the direction of the bare optical fiber at the position between the drawing unit and the coating unit, each direction changer including a guide groove and an outlet nozzle, the guide groove being configured to guide the bare optical fiber, the bare optical fiber being arranged along and introduced into the guide groove, the outlet nozzle being formed in the guide groove and being configured to cause the bare optical fiber to float; a measurement unit that measures an outer diameter of the coated layer; and a controller that adjusts the position of the direction changers based on a measurement value of the outer diameter measured by the measurement unit, the controller controlling positions of the direction changers and thereby adjusting the length of the bare optical fiber from the drawing unit to the coating unit in accordance with the measurement value. 
         [0026]    A fifth aspect of the invention provides a control apparatus used in an optical fiber manufacturing apparatus, the manufacturing apparatus including: a drawing unit that forms a bare optical fiber by drawing the bare optical fiber from an optical fiber preform; a coating unit that provides a coated layer made of a resin on a periphery of the bare optical fiber; and a curing unit that cures the coated layer, the control apparatus including: one or more direction changers that change the direction of the bare optical fiber at the position between the drawing unit and the coating unit, each direction changer including a guide groove and an outlet nozzle, the guide groove being configured to guide the bare optical fiber, the bare optical fiber being arranged along and introduced into the guide groove, the outlet nozzle being formed in the guide groove and being configured to cause the bare optical fiber to float; a measurement unit that measures the drawing velocity of the optical fiber; and a controller that adjusts the position of the direction changers based on a measurement value of the drawing velocity measured by the measurement unit, the controller controlling positions of the direction changers and thereby adjusting the length of the bare optical fiber from the drawing unit to the coating unit in accordance with the measurement value. 
         [0027]    A sixth aspect of the invention provides a control apparatus used in an optical fiber manufacturing apparatus, the manufacturing apparatus including: a drawing unit that forms a bare optical fiber by drawing the bare optical fiber from an optical fiber preform; a coating unit that provides a coated layer made of a resin on a periphery of the bare optical fiber; and a curing unit that cures the coated layer, the control apparatus including: one or more direction changers that change the direction of the bare optical fiber at the position between the drawing unit and the coating unit, each direction changer including a guide groove and an outlet nozzle, the guide groove being configured to guide the bare optical fiber, the bare optical fiber being arranged along and introduced into the guide groove, the outlet nozzle being formed in the guide groove and being configured to cause the bare optical fiber to float; a measurement unit that measures a temperature of the bare optical fiber; and a controller that adjusts the position of the direction changers based on a measurement value of the temperature measured by the measurement unit, the controller controlling positions of the direction changers and thereby adjusting the length of the bare optical fiber from the drawing unit to the coating unit in accordance with the measurement value. 
         [0028]    A seventh aspect of the invention provides an optical fiber manufacturing apparatus including: a control apparatus according to the above-described fourth aspect; a drawing unit that forms a bare optical fiber by drawing the bare optical fiber from an optical fiber preform; a coating unit that provide a coated layer made of a resin on a periphery of the bare optical fiber; and a curing unit that cures the coated layer. 
         [0029]    An eighth aspect of the invention provides an optical fiber manufacturing apparatus including: a control apparatus according to the above-described fifth aspect; a drawing unit that forms a bare optical fiber by drawing the bare optical fiber from an optical fiber preform; a coating unit that provide a coated layer made of a resin on a periphery of the bare optical fiber; and a curing unit that cures the coated layer. 
         [0030]    A ninth aspect of the invention provides an optical fiber manufacturing apparatus including: a control apparatus according to the above-described sixth aspect; a drawing unit that forms a bare optical fiber by drawing the bare optical fiber from an optical fiber preform; a coating unit that provide a coated layer made of a resin on a periphery of the bare optical fiber; and a curing unit that cures the coated layer. 
       Effects of the Invention 
       [0031]    According to the aspects of the invention, since the path length of the bare optical fiber is adjusted by controlling the position of the direction changer based on a measurement value of an outer diameter of the coated layer an optical fiber production intermediate, the temperature of the bare optical fiber which is introduced into the coating unit is adjusted with a high level of accuracy, and it is possible to maintain the outer diameter of the coated layer within a constant range in the coating unit. 
         [0032]    According to the aspects of the invention, since it is possible to adjust the temperature of the bare optical fiber without varying the flow rate of the gas discharged from the outlet nozzle in the direction changer, it is possible to avoid the bare optical fiber from being in contact with the inner side surface of the guide groove due to a lack of flotation of the bare optical fiber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]      FIG. 1  is a schematic diagram showing the configuration of an optical fiber manufacturing apparatus according to a first embodiment of the invention. 
           [0034]      FIG. 2  is a cross-sectional schematic diagram showing the structure of a direction changer of the manufacturing apparatus shown in  FIG. 1 . 
           [0035]      FIG. 3  is a front view showing a first example of the direction changer. 
           [0036]      FIG. 4  is a front view showing a modified example of the direction changer of the first example shown in  FIG. 3 . 
           [0037]      FIG. 5  is a front view showing a second example of the direction changer. 
           [0038]      FIG. 6  is a front view showing a modified example of the direction changer of the second example shown in  FIG. 5 . 
           [0039]      FIG. 7  is a schematic diagram showing the configuration of an optical fiber manufacturing apparatus according to a second embodiment of the invention. 
           [0040]      FIG. 8  is a schematic diagram showing the configuration of an optical fiber manufacturing apparatus according to a third embodiment of the invention. 
           [0041]      FIG. 9  is a schematic diagram showing the configuration of an optical fiber manufacturing apparatus according to a fourth embodiment of the invention. 
           [0042]      FIG. 10  is a schematic diagram showing the configuration of an optical fiber manufacturing apparatus according to a fifth embodiment of the invention. 
           [0043]      FIG. 11  is a schematic diagram showing the configuration of an optical fiber manufacturing apparatus according to a sixth embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0044]      FIG. 1  is a schematic diagram showing the configuration of a manufacturing apparatus  1 A which serves as an optical fiber manufacturing apparatus according to a first embodiment of the invention. 
         [0045]    The manufacturing apparatus  1 A includes a drawing unit  10 , direction changers  20  ( 20 A,  20 B,  20 C), a coating unit  30 , a curing unit  40 , a measurement unit  50 , a controller  60 , a pick-up unit  70 , a pulley  80 , and a winding unit  90 . 
         [0046]    The direction changers  20 , the measurement unit  50 , and the controller  60  constitute a control apparatus  101 . 
         [0047]    The drawing unit  10  is provided with a heating furnace  11 , an optical fiber preform  2  is heated by the heating furnace  11 , and a bare optical fiber  3  is formed by drawing the heated preform. 
         [0048]    The direction changers  20  change a direction of the bare optical fiber  3 . 
         [0049]    Three direction changers  20  are used in the manufacturing apparatus  1 A. 
         [0050]    The direction changers  20  are each referred to as a first direction changer  20 A, a second direction changer  20 B, and a third direction changer  20 C in order from the upstream side to the downstream side in the fiber drawing direction. 
         [0051]    The first direction changer  20 A changes, by 90 degrees, the direction of the bare optical fiber  3  that is drawn from the optical fiber preform  2  in the downward vertical direction (first pathway L 1 ), as a result, the direction of the bare optical fiber  3  is in the horizontal direction (second pathway L 2 ). 
         [0052]    A plane including the first pathway L 1  and the second pathway L 2  is referred to as P 1 . 
         [0053]    The X-direction is the direction extending in the second pathway L 2  in the plane P 1  and the Y-direction is the direction perpendicular to the plane P 1 . 
         [0054]    The second direction changer  20 B changes the direction of the bare optical fiber  3  by 180 degrees, as a result, the direction of the bare optical fiber  3  is directed to the direction (third pathway L 3 ) opposite to the second pathway L 2 . 
         [0055]    The second direction changer  20 B is movable in the direction in which the second direction changer comes close to or separates from the first direction changer  20 A and the third direction changer  20 C. 
         [0056]    Particularly, the second direction changer  20 B is movable in the X-direction. 
         [0057]    The second direction changer  20 B can move along a guide rail that extends in, for example, the X-direction by use of a driving device such as a motor. 
         [0058]    The third direction changer  20 C changes the direction of the bare optical fiber  3  by 90 degrees, as a result, the direction of the bare optical fiber  3  is in the downward vertical direction (fourth pathway L 4 ). 
         [0059]    The coating unit  30  is configured to coat (coating) the periphery of the bare optical fiber  3  with a coating material such as a urethane acrylate-based resin, thereby forms a coated layer, and an optical fiber production intermediate  4  is obtained. 
         [0060]    The resin coating is, for example, a bilayer coating such that a material used to form a first coated layer having a lower Young&#39;s modulus is applied to the inside thereof and a material used to form a second coated layer having a higher Young&#39;s modulus is applied to the outside thereof. 
         [0061]    The material used to form the resin coating is, for example, an ultraviolet curable resin. 
         [0062]    The coating unit  30  may be configured to independently apply the first coated layer and the second coated layer or may be configured to simultaneously apply the first coated layer and the second coated layer. 
         [0063]    The curing unit  40  is provided with one or more UV lamps  40   a,  is configured to cure the coated layer of the optical fiber production intermediate  4  and thereby form an optical fiber  5 . 
         [0064]    For example, the curing unit  40  includes UV lamps  40   a  which form a plurality of pairs thereof and are provided to sandwich spaces through which the optical fiber production intermediate  4  passes. 
         [0065]    The measurement unit  50  can measure an outer diameter of the coated layer of the optical fiber production intermediate  4 . 
         [0066]    It is preferable that the measurement unit  50  can measure an outer diameter of the coated layer without coming in contact with the optical fiber production intermediate  4 . 
         [0067]    As the measurement unit  50 , for example, a measurement device that includes a light source and a detector can be used. 
         [0068]    By use of this measurement device, the light source (laser light source, or the like) that is provided at, for example, the side position of the optical fiber production intermediate  4  emits light thereto, the detector that is disposed to face the light source receives forward-scattered light from the optical fiber production intermediate, and an outer diameter of the optical fiber production intermediate  4  (that is, an outer diameter of the coated layer) is measured by analyzing a pattern of the received light or the intensity thereof. 
         [0069]    The measurement unit  50  can be provided between the coating unit  30  and the curing unit  40 . 
         [0070]    The measurement unit  50  outputs a measurement signal to the controller  60  based on the measurement value of the outer diameter. 
         [0071]    The controller  60  can control the position of the second direction changer  2013  (position in the X-direction) based on the measurement signal output from the measurement unit  50 . 
         [0072]    The controller  60  controls driving or stopping of, for example, the above-described driving device such as a motor and thereby can determine the position of the second direction changer  20 B in the X-direction. 
         [0073]    The optical fiber  5  is picked up by the pick-up unit  70 , the pulley  80  changes the direction of the optical fiber, and the optical fiber is wound around the winding unit  90 . 
         [0074]    The pick-up unit  70  is, for example, a pick-up capstan, and the pick-up unit determines the drawing speed. 
         [0075]    The drawing speed is greater than or equal to, for example, 1500 m/min. 
         [0076]    The winding unit  90  is a bobbin that winds the optical fiber  5  therearound. 
         [0077]    The outer diameter of the optical fiber preform  2  is greater than or equal to, for example,  100  mm, and the length of the optical fiber  5  manufactured from the optical fiber preform  2  is, for example, several thousands km. 
         [0078]    Hereinbelow, configurations of a direction changer  20  will be described. 
         [0079]    As shown in  FIG. 3 , a direction changer  201  is a first example of the direction changer  20  and can change a direction of the bare optical fiber  3  by 90 degrees. 
         [0080]    The direction changer  201  is formed in a quarter-circular shape (arc) in plan view and has an outer peripheral face  20   a  and a guide groove  21 . The guide groove  21  is formed on and along the entire periphery of the outer peripheral face  20   a.    
         [0081]    The center of the direction changer  201  coincides with the Y-direction, and the direction changer  201  is provided in the attitude in which the radial direction D 1  (refer to  FIG. 2 ) is in the direction along the plane P 1  (refer to  FIG. 1 ). 
         [0082]    Here, the direction along the outer peripheral face  20   a  formed in a circular-arc shape in plan view is referred to as a circumferential direction. 
         [0083]    An outlet nozzle  22  is formed at the bottom of the guide groove  21  and along the guide groove  21 . The outlet nozzle blows fluid (e.g., air) into the guide groove, and the fluid (e.g., air) causes the bare optical fiber  3  which is arranged along and introduced into the guide groove  21  to float. 
         [0084]    The outlet nozzle  22  is formed over the entire guide groove  21 . 
         [0085]    A first end  22   a  (one end) of the outlet nozzle  22  reaches a first end  21   a  (one end) of the guide groove  21 , and a second end  22   b  (the other end) of the outlet nozzle  22  reaches a second end  21   b  (the other end) of the guide groove  21 . 
         [0086]    As shown in  FIG. 2 , the direction changer  201  is configured to be able to discharge fluid (for example, air) of the space (fluid reservoir  25 ) into the guide groove  21  through the outlet nozzle  22 . The space is ensured in the direction changer  201 . 
         [0087]    The direction changer  201  can be configured to introduce the fluid into the fluid reservoir  25  from, for example, the outside and discharge the fluid into the guide groove  21  through the outlet nozzle  22 . 
         [0088]    It is preferable that the guide groove  21  be formed to be inclined with respect to the radial direction D 1  so that the space (length in the Y-direction) between the inner side surfaces  21   c  thereof gradually increases in the radial-outer direction. 
         [0089]    It is preferable that the inclination angles  01  of the two inner side surfaces  21   c  with respect to the radial direction D 1  are equal to each other. 
         [0090]    In the direction changer  201  shown in  FIG. 3 , the bare optical fiber  3  enters the first end  21   a  of the guide groove  21  that is formed in a quarter-circular shape (arc) and exits from the second end  21   b,  and the direction of the bare optical fiber is thereby changed by 90 degrees. 
         [0091]    A fiber inlet portion  23  to which the bare optical fiber  3  enters is a portion including the first end  21   a  of the guide groove  21 , and a fiber outlet portion  24  from which the bare optical fiber  3  exits is a portion including the second end  21   b  of the guide groove  21 . 
         [0092]    A direction changer  202  shown in  FIG. 4  is a modified example of the direction changer  201  and is formed in a three-quarter-circular shape (arc) in plan view. 
         [0093]    Hereinbelow, identical reference numerals are used for the elements which are identical to those of the above description, and the explanations thereof are simplified here. 
         [0094]    The direction changer  202  is configured to include: a body part  29   a  having the same structure as that of the direction changer  201  shown in  FIG. 3 ; and auxiliary parts  29   b  and  29   c,  each of which has the same structure as that of the body part  29   a  and which are consecutively connected to the incoming side and the outgoing side of the body part  29   a.    
         [0095]    Regarding the direction changer  202 , the bare optical fiber  3  enters the guide groove  21  of the body part  29   a  through the fiber inlet portion  23 ′, the direction of the bare optical fiber is changed by 90 degrees by the body part  29   a,  thereafter, the bare optical fiber exits from the body part through the fiber outlet portion  24 ′. Therefore, the basic function of the direction changer  202  is the same as that of the direction changer  201 . 
         [0096]    The direction changers  201  and  202  can change the direction of the bare optical fiber  3  by 90 degrees, and therefore can be used as the first direction changer  20 A and the third direction changer  20 C as shown in  FIG. 1 . 
         [0097]    A direction changer  203  shown in  FIG. 5  is a second example of the direction changer  20  and can change the direction of the bare optical fiber  3  by 180 degrees. 
         [0098]    The direction changer  203  is formed in a semicircular shape in plan view and has an outer peripheral face  20   a  and a guide groove  31 . The guide groove  31  is formed on and along the entire periphery of the outer peripheral face  20   a.    
         [0099]    An outlet nozzle  32  is formed at the bottom of the guide groove  31  and along the guide groove  31 . The outlet nozzle blows fluid (e.g., air) into the guide groove, and the fluid (e.g., air) causes the bare optical fiber  3  to float. 
         [0100]    The outlet nozzle  32  is formed over the entire guide groove  31 . 
         [0101]    The direction changer  203  is configured to be able to discharge fluid into the guide groove  31  through the outlet nozzle  32  from a fluid reservoir  35 . 
         [0102]    In the direction changer  203 , the bare optical fiber  3  enters a first end  31  a (one end) of the guide groove  31  of the semicircular shape and exits from a second end  31   b  (the other end) thereof, and the direction of the bare optical fiber is changed by 180 degrees. 
         [0103]    A fiber inlet portion  33  is a portion including the second end  31  a of the guide groove  31 , and a fiber outlet portion  34  is a portion including the second end  3  lb of the guide groove  31 . 
         [0104]    The cross-sectional configuration of the guide groove  31  is the same as that of the guide groove  21  (refer to  FIG. 2 ). 
         [0105]    A direction changer  204  shown in  FIG. 6  is a modified example of the direction changer  203  and is formed in a three-quarter-circular shape (arc) in plan view. 
         [0106]    The direction changer  204  is configured to include: a body part  39   a  having the same structure as that of the direction changer  203  shown in  FIG. 5 ; and auxiliary parts  39   b  and  39   c,  each of which has the same cross-sectional structure as that of the body part  39   a,  which are consecutively connected to the incoming side and the outgoing side of the body part  39   a,  and which are formed in a one-eighth circular shape (arc) in plan view. 
         [0107]    Regarding the direction changer  204 , the bare optical fiber  3  enters the guide groove  31  of the body part  39   a  through the fiber inlet portion  33 ′, the direction of the bare optical fiber is changed by 180 degrees by the body part  39   a,  thereafter, the bare optical fiber exits from the body part through the fiber outlet portion  34 ′. Therefore, the basic function of the direction changer  204  is the same as that of the direction changer  203 . 
         [0108]    The direction changers  203  and  204  can change the direction of the bare optical fiber  3  by 180 degrees, and therefore can be used as the first direction changer  2013  as shown in  FIG. 1 . 
         [0109]    Next, a method according to a first embodiment of the invention will be described which manufactures an optical fiber in the case of using, for example, the manufacturing apparatus  1 A. 
         [0110]    (Drawing Step) 
         [0111]    In the drawing unit  10 , the optical fiber preform  2  is heated and drawn, and the bare optical fiber  3  is formed. 
         [0112]    (Direction Change by use of Direction Changer) 
         [0113]    The direction of the bare optical fiber  3  that is drawn from the optical fiber preform  2  in the downward vertical direction (first pathway L 1 ) is changed by 90 degrees by the first direction changer  20 A, as a result, the direction of the bare optical fiber  3  is in the horizontal direction (second pathway L 2 ). 
         [0114]    The direction of the bare optical fiber  3  is changed by 180 degrees by the second direction changer  20 B, as a result, the direction of the bare optical fiber  3  is directed to the direction (third pathway L 3 ) opposite to the second pathway L 2 . The direction of the bare optical fiber  3  is changed by 90 degrees by the third direction changer  20 C, as a result, the direction of the bare optical fiber  3  is in the downward vertical direction (fourth pathway L 4 ). 
         [0115]    In the direction changers  20 A to  20 C, as a result of discharging the fluid (for example, air) in the fluid reservoir  25  into the guide groove  21  through the outlet nozzle  22 , it is possible to cause the bare optical fiber  3  to float. 
         [0116]    Particularly, as shown in  FIG. 2 , since a difference in pressure between a deep portion  21   d  of the guide groove  21  and a shallow portion  21   e  thereof increases due to the discharged air, a force in the radial-outer direction of the direction changer is applied to the bare optical fiber  3 , and the bare optical fiber  3  floats. 
         [0117]    (Coating Step) 
         [0118]    In the coating unit  30 , the optical fiber production intermediate  4  is obtained by forming a coated layer by applying a coating material such as a urethane acrylate based resin onto the periphery of the bare optical fiber  3 . 
         [0119]    (Curing Step) 
         [0120]    In the curing unit  40 , the coated layer of the optical fiber production intermediate  4  is cured by irradiating the coating material with UV light by the UV lamp  40   a  or the like, and the optical fiber  5  is thereby formed. 
         [0121]    (Adjustment of Path Length of Bare Optical Fiber  3 ) 
         [0122]    The measurement unit  50  measures an outer diameter of the optical fiber production intermediate  4  (i.e., an outer diameter of the coated layer) and outputs a measurement signal to the controller  60  based on the measurement value. 
         [0123]    The controller  60  controls the position of the second direction changer  20 B in accordance with the measurement value of the outer diameter and thereby adjusts the path length of the bare optical fiber  3 . 
         [0124]    The path length of the bare optical fiber  3  is the length of the bare optical fiber  3  from the drawing unit  10  to the coating unit  30 . 
         [0125]    Particularly, in the case where the outer diameter of the coated layer increases, the controller  60  outputs a measurement signal corresponding to the measurement value, and the controller  60  disposes the second direction changer  20 B at a position close to the first direction changer  20 A and the third direction changer  20 C. 
         [0126]    As a control method, feedback control such as PID control is preferable. 
         [0127]    Accordingly, it is possible to carry out control of the position of the second direction changer  20 B with a high degree of responsiveness. 
         [0128]    When the second direction changer  2013  approaches the first direction changer  20 A and the third direction changer  20 C, since the path length of the bare optical fiber  3  decreases accordingly, the temperature of the bare optical fiber  3  which is introduced into the coating unit  30  relatively increases. 
         [0129]    In the case where the temperature of the bare optical fiber  3  increases, since the thickness of the coated layer formed in the coating unit  30  decreases due to physical properties of the coating material, the outer diameter of the coated layer decreases. 
         [0130]    On the other hand, in the case where the outer diameter of the coated layer decreases, the controller  60  outputs a measurement signal corresponding to the measurement value, and the controller  60  disposes the second direction changer  20 B at the position apart from the first direction changer  20 A and the third direction changer  20 C. 
         [0131]    When the second direction changer  2013  moves separately from the first direction changer  20 A and the third direction changer  20 C, since the path length of the bare optical fiber  3  increases accordingly, the temperature of the bare optical fiber  3  which is introduced into the coating unit  30  relatively decreases. 
         [0132]    In the case where the temperature of the bare optical fiber  3  decreases, since the thickness of the coated layer formed in the coating unit  30  increases, the outer diameter of the coated layer increases. 
         [0133]    The optical fiber  5  is picked up by the pick-up unit  70 , the direction of the optical fiber  5  is changed by the pulley  80 , and the optical fiber  5  is wound around the winding unit  90 . 
         [0134]    According to the manufacturing method, since the path length of the bare optical fiber  3  is adjusted by controlling the position of the second direction changer  20 B based on the measurement value of the outer diameter of the coated layer of the optical fiber production intermediate  4 , the temperature of the bare optical fiber  3  which is introduced into the coating unit  30  is adjusted with a high level of accuracy, and it is possible to maintain the outer diameter of the coated layer within a constant range in the coating unit  30 . 
         [0135]    According to the manufacturing method, it is possible to adjust the temperature of the bare optical fiber  3  without varying the flow rate of the gas discharged from the outlet nozzle  22  in the direction changers  20 A to  20 C. 
         [0136]    Therefore, it is possible to avoid the bare optical fiber  3  from being in contact with the inner side surface  21   c  of the guide groove  21  due to a lack of flotation of the bare optical fiber. 
         [0137]      FIG. 7  is a schematic diagram showing the configuration of a manufacturing apparatus  1 B which serves as an optical fiber manufacturing apparatus according to a second embodiment of the invention. In  FIG. 7 , identical reference numerals are used for the elements which are identical to those of the above-described embodiment, and the explanations thereof are omitted or simplified here. 
         [0138]    The manufacturing apparatus  1 B includes the drawing unit  10 , the direction changers  20  ( 20 A,  20 B,  20 C), the coating unit  30 , the curing unit  40 , a controller  100 , the pick-up unit  70 , the pulley  80 , and the winding unit  90 . 
         [0139]    The direction changers  20 , the pick-up unit  70 , and the controller  100  constitute a control apparatus  102 . 
         [0140]    The pick-up unit  70  serves as a measurement unit that measures a drawing velocity of the optical fiber  5 . 
         [0141]    The controller  100  can control the position of the second direction changer  2013  (position in the X-direction) based on the measurement signal output from the pick-up unit  70 . 
         [0142]    Next, a method according to a second embodiment of the invention will be described which manufactures an optical fiber in the case of using, for example, the manufacturing apparatus  1 B. 
         [0143]    The drawing step, the direction change by use of the direction changer, the coating step, and the curing step are the same as those of the above-described embodiments. 
         [0144]    (Adjustment of Path Length of Bare Optical Fiber  3 ) 
         [0145]    The pick-up unit  70  measures a drawing velocity of the optical fiber  5  and outputs a measurement signal to the controller  100  based on the measurement value. 
         [0146]    The controller  100  controls the position of the second direction changer  2013  in accordance with the measurement value of the drawing velocity and thereby adjusts the path length of the bare optical fiber  3 . 
         [0147]    Particularly, in the case where the drawing velocity of the optical fiber  5  decreases, the controller  100  outputs a measurement signal corresponding to the measurement value, and the controller  100  disposes the second direction changer  20 B at a position close to the first direction changer  20 A and the third direction changer  20 C. 
         [0148]    As a control method, proportional control is preferable. 
         [0149]    When the second direction changer  20 B approaches the first direction changer  20 A and the third direction changer  20 C, since the path length of the bare optical fiber  3  decreases accordingly, the temperature of the bare optical fiber  3  which is introduced into the coating unit  30  relatively increases. 
         [0150]    In the case where the temperature of the bare optical fiber  3  increases, since the thickness of the coated layer formed in the coating unit  30  decreases due to physical properties of the coating material, the outer diameter of the coated layer decreases. 
         [0151]    On the other hand, in the case where the drawing velocity of the optical fiber  5  increases, the controller  100  outputs a measurement signal corresponding to the measurement value, and the controller  100  disposes the second direction changer  20 B at the position apart from the first direction changer  20 A and the third direction changer  20 C. 
         [0152]    When the second direction changer  20 B moves separately from the first direction changer  20 A and the third direction changer  20 C, since the path length of the bare optical fiber  3  increases accordingly, the temperature of the bare optical fiber  3  which is introduced into the coating unit  30  relatively decreases. 
         [0153]    In the case where the temperature of the bare optical fiber  3  decreases, since the thickness of the coated layer formed in the coating unit  30  increases, the outer diameter of the coated layer increases. 
         [0154]    According to the manufacturing method, since the path length of the bare optical fiber  3  is adjusted by controlling the position of the second direction changer  20 B based on the measurement value of the drawing velocity of the optical fiber  5 , it is possible to maintain the outer diameter of the coated layer within a constant range in the coating unit  30 . 
         [0155]    According to the manufacturing method, since it is possible to adjust the temperature of the bare optical fiber  3  in the direction changers  20 A to  20 C without varying the flow rate of the gas, it is possible to avoid the bare optical fiber  3  from being in contact with the inner side surface  21   c  of the guide groove  21  due to a lack of flotation of the bare optical fiber. 
         [0156]      FIG. 8  is a schematic diagram showing the configuration of a manufacturing apparatus  1 C which serves as an optical fiber manufacturing apparatus according to a third embodiment of the invention. In  FIG. 8 , identical reference numerals are used for the elements which are identical to those of the above-described embodiments, and the explanations thereof are omitted or simplified here. 
         [0157]    The manufacturing apparatus IC includes the drawing unit  10 , the direction changers  20  ( 20 A,  20 B,  20 C), the coating unit  30 , the curing unit  40 , a measurement unit  110 , a controller  120 , the pick-up unit  70 , the pulley  80 , and the winding unit  90 . 
         [0158]    The direction changers  20 , the measurement unit  110 , and the controller  120  constitute a control apparatus  103 . 
         [0159]    The manufacturing apparatus  1 C is different from the manufacturing apparatus  1 A shown in  FIG. 1  in that the measurement unit  110  which measures a temperature of the bare optical fiber  3  is used instead of the measurement unit  50  which measures an outer diameter of the coated layer. 
         [0160]    It is preferable that the measurement unit  110  can measure a temperature of the bare optical fiber  3  without coming in contact with the bare optical fiber  3 . 
         [0161]    The measurement unit  110  is, for example, a radiation thermometer. 
         [0162]    The measurement unit  110  can be provided between the third direction changer  20 C and the coating unit  30 . 
         [0163]    The controller  120  can control the position of the second direction changer  2013  (position in the X-direction) based on the measurement signal output from the measurement unit  110 . 
         [0164]    Next, a method according to a third embodiment of the invention will be described which manufactures an optical fiber in the case of using, for example, the manufacturing apparatus IC. 
         [0165]    The drawing step, the direction change by use of the direction changer, the coating step, and the curing step are the same as those of the above-described embodiments. 
         [0166]    (Adjustment of Path Length of Bare Optical Fiber  3 ) 
         [0167]    The measurement unit  110  measures a temperature of the bare optical fiber  3  and outputs a measurement signal to the controller  120  based on the measurement value. 
         [0168]    The controller  120  controls the position of the second direction changer  20 B in accordance with the measurement value of the temperature and thereby adjusts the path length of the bare optical fiber  3 . 
         [0169]    Particularly, in the case where the temperature of the optical fiber production intermediate  4  decreases, the controller  120  outputs a measurement signal corresponding to the measurement value, and the controller  120  disposes the second direction changer  20 B at a position close to the first direction changer  20 A and the third direction changer  20 C. 
         [0170]    As a control method, feedback control such as PID control is preferable. 
         [0171]    When the second direction changer  20 B approaches the first direction changer  20 A and the third direction changer  20 C, since the path length of the bare optical fiber  3  decreases accordingly, the temperature of the bare optical fiber  3  which is introduced into the coating unit  30  relatively increases. 
         [0172]    In the case where the temperature of the bare optical fiber  3  increases, since the thickness of the coated layer formed in the coating unit  30  decreases, the outer diameter of the coated layer decreases. 
         [0173]    On the other hand, in the case where the temperature of the optical fiber production intermediate  4  increases, the controller  120  outputs a measurement signal corresponding to the measurement value, and controller  120  disposes the second direction changer  20 B at the position apart from the first direction changer  20 A and the third direction changer  20 C. 
         [0174]    When the second direction changer  20 B moves separately from the first direction changer  20 A and the third direction changer  20 C, since the path length of the bare optical fiber  3  increases accordingly, the temperature of the bare optical fiber  3  which is introduced into the coating unit  30  relatively decreases. 
         [0175]    In the case where the temperature of the bare optical fiber  3  decreases, since the thickness of the coated layer formed in the coating unit  30  increases, the outer diameter of the coated layer increases. 
         [0176]    According to the manufacturing method, since the path length of the bare optical fiber  3  is adjusted by controlling the position of the second direction changer  20 B based on the measurement value of the temperature of the optical fiber production intermediate  4 , it is possible to maintain the outer diameter of the coated layer within a constant range in the coating unit  30 . 
         [0177]    According to the manufacturing method, since it is possible to adjust the temperature of the bare optical fiber  3  in the direction changers  20 A to  20 C without varying the flow rate of the gas, it is possible to avoid the bare optical fiber  3  from being in contact with the inner side surface  21   c  of the guide groove  21  due to a lack of flotation of the bare optical fiber. 
         [0178]      FIG. 9  is a schematic diagram showing the configuration of a manufacturing apparatus  1 D which serves as an optical fiber manufacturing apparatus according to a fourth embodiment of the invention. In  FIG. 9 , identical reference numerals are used for the elements which are identical to those of the above-described embodiments, and the explanations thereof are omitted or simplified here. 
         [0179]    The manufacturing apparatus ID includes the drawing unit  10 , the direction changers  20  ( 20 A,  20 B,  20 D,  20 E,  20 F), the coating unit  30 , the curing unit  40 , a measurement unit  50 , a controller  130 , the pick-up unit  70 , the pulley  80 , and the winding unit  90 . 
         [0180]    The direction changers  20 , the measurement unit  50 , and the controller  130  constitute a control apparatus  104 . 
         [0181]    The manufacturing apparatus ID is different from the manufacturing apparatus  1 A shown in  FIG. 1  in that the manufacturing apparatus  1 D includes a third direction changer  20 D, a fourth direction changer  20 E, and a fifth direction changer  20 F. 
         [0182]    The third direction changer  20 D changes the direction of the bare optical fiber  3  extending in the horizontal direction (third pathway L 3 ) by 180 degrees, as a result, the direction of the bare optical fiber  3  is directed to the direction (fourth pathway L 5 ) opposite to the third pathway L 3 . 
         [0183]    The fourth direction changer  20 E changes the direction of the bare optical fiber  3  by 180 degrees, as a result, the direction of the bare optical fiber  3  is directed to the direction (fifth pathway L 6 ) opposite to the fourth pathway L 5 . 
         [0184]    The fourth direction changer  20 E is movable in the direction in which the fourth direction changer comes close to or separates from the third direction changer  20 D and the fifth direction changer  20 F. 
         [0185]    Particularly, the fourth direction changer  20 E is movable in the X-direction. 
         [0186]    The fourth direction changer  20 E can move along a guide rail that extends in, for example, the X-direction by use of a driving device such as a motor. 
         [0187]    The fifth direction changer  20 F changes the direction of the bare optical fiber  3  by 90 degrees, as a result, the direction of the bare optical fiber  3  is in the downward vertical direction (sixth pathway L 7 ). 
         [0188]    The controller  130  can control the position of the second direction changer  20 B and the fifth direction changer  20 E (position in the X-direction) based on the measurement signal output from the measurement unit  50 . 
         [0189]    Next, a method according to a fourth embodiment of the invention will be described which manufactures an optical fiber in the case of using, for example, the manufacturing apparatus  1  D. 
         [0190]    (Direction Change by use of Direction Changer) 
         [0191]    The direction of the bare optical fiber  3  that is drawn from the optical fiber preform  2  in the downward vertical direction (first pathway L 1 ) is changed by 90 degrees by the first direction changer  20 A, as a result, the direction of the bare optical fiber  3  is in the horizontal direction (second pathway L 2 ). 
         [0192]    The direction of the bare optical fiber  3  is changed by 180 degrees by the second direction changer  20 B, as a result, the direction of the bare optical fiber  3  is directed to the direction (third pathway L 3 ) opposite to the second pathway L 2 . The direction of the bare optical fiber  3  is changed by 180 degrees by the third direction changer  20 D, as a result, the direction (fourth pathway L 5 ) opposite to the third pathway L 3 . 
         [0193]    The direction of the bare optical fiber  3  is changed by 180 degrees by the fourth direction changer  20 E, as a result, the direction of the bare optical fiber  3  is directed to the direction (fifth pathway L 6 ) opposite to the fourth pathway L 5 . The direction of the bare optical fiber  3  is changed by 90 degrees by the fifth direction changer  20 F, as a result, the direction of the bare optical fiber  3  is in the downward vertical direction (sixth pathway L 7 ). 
         [0194]    (Adjustment of Path Length of Bare Optical Fiber  3 ) 
         [0195]    The measurement unit  50  measures an outer diameter of the optical fiber production intermediate  4  (i.e., an outer diameter of the coated layer) and outputs a measurement signal to the controller  130  based on the measurement value. 
         [0196]    The controller  130  controls the positions of the second direction changer  20 B and the fourth direction changer  20 E in accordance with the measurement value of the outer diameter and thereby adjusts the path length of the bare optical fiber  3 . 
         [0197]    As a control method, feedback control such as PID control is preferable. 
         [0198]    Particularly, in the case where the outer diameter of the coated layer of the optical fiber production intermediate  4  increases, the controller  130  disposes the second direction changer  20 B and the fourth direction changer  20 E at the positions close to the direction changers  20 A,  20 D, and  20 F. In the case where the outer diameter of the coated layer of the optical fiber production intermediate  4  decreases, the controller  130  disposes the second direction changer  20 B and the fourth direction changer  20 E at the positions apart from the direction changers  20 A,  20 D, and  20 F. 
         [0199]    According to the manufacturing method, since the path length of the bare optical fiber  3  is adjusted by controlling the positions of the second direction changer  20 B and the fourth direction changer  20 E, the variation range in the path length of the bare optical fiber  3  increases. 
         [0200]    Consequently, it is possible to carry out adjustment of the outer diameter of the coated layer with a high degree of responsiveness. 
         [0201]    According to the manufacturing method, since it is possible to adjust the temperature of the bare optical fiber  3  in the direction changers  20 A to  20 F without varying the flow rate of the gas, it is possible to avoid the bare optical fiber  3  from being in contact with the inner side surface  21   c  of the guide groove  21  due to a lack of flotation of the bare optical fiber. 
         [0202]      FIG. 10  is a schematic diagram showing the configuration of a manufacturing apparatus  1 E which serves as an optical fiber manufacturing apparatus according to a fifth embodiment of the invention. In  FIG. 10 , identical reference numerals are used for the elements which are identical to those of the above-described embodiment, and the explanations thereof are omitted or simplified here. 
         [0203]    The manufacturing apparatus  1 E includes the drawing unit  10 , the direction changers  20  ( 20 A,  20 B,  20 D,  20 E,  20 F), the coating unit  30 , the curing unit  40 , a controller  140 , the pick-up unit  70 , the pulley  80 , and the winding unit  90 . The direction changers  20 , the controller  140 , and the pick-up unit  70  constitute a control apparatus  105 . 
         [0204]    The controller  140  can controls the positions of the second direction changer  20 B and the fourth direction changer  20 E (position in the X-direction) based on the measurement signal output from the pick-up unit  70 . Next, a method according to a fifth embodiment of the invention will be described which manufactures an optical fiber in the case of using, for example, the manufacturing apparatus  1 E. 
         [0205]    (Adjustment of Path Length of Bare Optical Fiber  3 ) 
         [0206]    The pick-up unit  70  measures a drawing velocity of the optical fiber  5  and outputs a measurement signal to the controller  140  based on the measurement value. 
         [0207]    The controller  140  controls the positions of the second direction changer  20 B and the fourth direction changer  20 E in accordance with the measurement value of the drawing velocity and thereby adjusts the path length of the bare optical fiber  3 . 
         [0208]    Particularly, in the case where the drawing velocity of the optical fiber  5  decreases, the controller  140  and disposes the second direction changer  20 B and the fourth direction changer  20 E at the positions close to the direction changers  20 A,  20 D, and  20 F. In the case where the drawing velocity of the optical fiber  5  increases, the controller  140  disposes the second direction changer  20 B and the fourth direction changer  20 E at the positions apart from the direction changers  20 A,  20 D, and  20 F. 
         [0209]    According to the manufacturing method, since the path length of the bare optical fiber  3  is adjusted by controlling the positions of the second direction changer  2013  and the fourth direction changer  20 E based on the measurement value of the drawing velocity of the optical fiber  5 , it is possible to maintain the outer diameter of the coated layer within a constant range in the coating unit  30 . 
         [0210]    According to the manufacturing method, since it is possible to adjust the temperature of the bare optical fiber  3  in the direction changers  20 A to  20 F without varying the flow rate of the gas, it is possible to avoid the bare optical fiber  3  from being in contact with the inner side surface  21   c  of the guide groove  21  due to a lack of flotation of the bare optical fiber. 
         [0211]      FIG. 11  is a schematic diagram showing the configuration of a manufacturing apparatus IF which serves as an optical fiber manufacturing apparatus according to a sixth embodiment of the invention. In  FIG. 11 , identical reference numerals are used for the elements which are identical to those of the above-described embodiment, and the explanations thereof are omitted or simplified here. 
         [0212]    The manufacturing apparatus  1 F includes the drawing unit  10 , the direction changers  20  ( 20 A,  20 G,  20 H,  20 I,  20 J), the coating unit  30 , the curing unit  40 , the measurement unit  50 , a controller  150 , the pick-up unit  70 , the pulley  80 , and the winding unit  90 . 
         [0213]    The direction changers  20 , the measurement unit  50 , the controller  150  constitute a control apparatus  106 . 
         [0214]    The manufacturing apparatus  1 F is different from the manufacturing apparatus  1 A shown in  FIG. 1  in that the manufacturing apparatus  1 F includes a second direction changer  20 G, a third direction changer  20 H, a fourth direction changer  20 I, and a fifth direction changer  20 J instead of the second direction changer  20 B and the third direction changer  20 C. 
         [0215]    The second direction changer  20 G changes, by 90 degrees, the bare optical fiber  3  that is in the horizontal direction (second pathway L 8 ) by the first direction changer  20 A, as a result, the direction of the bare optical fiber  3  is in the upward vertical direction (third pathway L 9 ). 
         [0216]    The third direction changer  20 H changes the direction of the bare optical fiber  3  by 180 degrees, as a result, the direction of the bare optical fiber  3  is in the downward vertical direction (fourth pathway L 10 ) opposite to the third pathway L 9 . 
         [0217]    The third direction changer  20 H is movable in the direction in which the third direction changer comes close to or separates from the second direction changer  20 G and the fourth direction changer  20 I. 
         [0218]    Particularly, the third direction changer  20 H is movable in the vertical direction. 
         [0219]    The fourth direction changer  201  changes the direction of the bare optical fiber  3  by 90 degrees, as a result, the direction of the bare optical fiber  3  is in the horizontal direction (fifth pathway L 11 ). 
         [0220]    The fifth direction changer  20 J changes the direction of the bare optical fiber  3  by 90 degrees, as a result, the direction of the bare optical fiber  3  is in the downward vertical direction (sixth pathway L 12 ). 
         [0221]    The controller  150  can control the position of the third direction changer  20 H (position in Z-direction) based on the measurement signal output from the measurement unit  50 . 
         [0222]    The Z-direction is perpendicular to both the X-direction and the Y-direction. 
         [0223]    Next, a method according to a sixth embodiment of the invention will be described which manufactures an optical fiber in the case of using, for example, the manufacturing apparatus IF. 
         [0224]    (Direction Change by use of Direction Changer) 
         [0225]    The direction of the bare optical fiber  3  that is drawn from the optical fiber preform  2  in the downward vertical direction (first pathway L 1 ) is changed by 90 degrees by the first direction changer  20 A, as a result, the direction of the bare optical fiber  3  is in the horizontal direction (second pathway L 8 ). 
         [0226]    The direction of the bare optical fiber  3  is changed by 90 degrees by the second direction changer  20 G, as a result, the direction of the bare optical fiber  3  is in the upward vertical direction (third pathway L 9 ). Furthermore, the direction of the bare optical fiber  3  is changed by 180 degrees by the third direction changer  20 H, as a result, the direction of the bare optical fiber  3  is in the downward vertical direction (fourth pathway L 10 ). 
         [0227]    The direction of the bare optical fiber  3 , is changed by 90 degrees by the fourth direction changer  201 , as a result, the direction of the bare optical fiber  3  is in the horizontal direction (fifth pathway L 11 ). The direction of the bare optical fiber  3  is changed by 90 degrees by the fifth direction changer  20 J, as a result, the direction of the bare optical fiber  3  is in the downward vertical direction (sixth pathway L 12 ). 
         [0228]    (Adjustment of Path Length of Bare Optical Fiber  3 ) 
         [0229]    The measurement unit  50  measures an outer diameter of the optical fiber production intermediate  4  (i.e., an outer diameter of the coated layer) and outputs a measurement signal to the controller  150  based on the measurement value. The controller  150  controls the position in the vertical direction of the third direction changer  20 H in accordance with the measurement value of the outer diameter and thereby adjusts the path length of the bare optical fiber  3 . 
         [0230]    According to the manufacturing method, since the path length of the bare optical fiber  3  is adjusted by controlling the position in the vertical direction of the third direction changer  20 H, it is not necessary to ensure a large space in the X-direction in which the direction changer  20  is to be accommodated. 
         [0231]    Accordingly, it is advantageous to reduce the manufacturing apparatus  1 E in size. 
         [0232]    According to the manufacturing method, since it is possible to adjust the temperature of the bare optical fiber  3  in the direction changers  20 A to  20 J without varying the flow rate of the gas, it is possible to avoid the bare optical fiber  3  from being in contact with the inner side surface  21   c  of the guide groove  21  due to a lack of flotation of the bare optical fiber. 
       EXAMPLES 
     Example 1 
       [0233]    The manufacturing apparatus  1 A shown in  FIG. 1  was prepared. 
         [0234]    As the first direction changer  20 A and the third direction changer  20 C, the direction changer  201  shown in  FIG. 3  was used. 
         [0235]    As the second direction changer  20 B, the direction changer  203  shown in  FIG. 5  was used. 
         [0236]    A width of the guide groove  21  was 145 μm. 
         [0237]    A flotation turning radius of the bare optical fiber  3  was approximately 62.5 mm. 
         [0238]    Fluid which is to be introduced into the direction changers  20 A and  2013  is air, and the temperature thereof was at a room temperature (approximately 24° C.). 
         [0239]    The introduction flow rate of air into each of the first direction changer  20 A and the third direction changer  20 C was 100 liters per minute. An introduction flow rate of air into the second direction changer  20 B was 200 liters per minute. 
         [0240]    The first direction changer  20 A was provided at the position at which the temperature of the bare optical fiber  3  becomes approximately 1000° C. 
         [0241]    The bare optical fiber  3  (outer diameter of 125 μm) was obtained by drawing the optical fiber from the optical fiber preform  2  in the drawing unit  10 . 
         [0242]    As a drawing speed and a drawing tension, a common condition (drawing speed of 30 m/second and a drawing tension of approximately 150 gf) was adopted. 
         [0243]    The direction of the bare optical fiber  3  that is drawn from the optical fiber preform  2  in the downward vertical direction (first pathway L 1 ) is changed by the first direction changer  20 A to be in the horizontal direction (second pathway L 2 ). Subsequently, the direction of the bare optical fiber  3  is changed by 180 degrees by the second direction changer  20 B, as a result, the direction of the bare optical fiber  3  is in the direction (third pathway L 3 ) opposite to the second pathway L 2 . Furthermore, the direction of the bare optical fiber  3  is changed by 90 degrees by the third direction changer  20 C, as a result, the direction of the bare optical fiber  3  is in the downward vertical direction (fourth pathway L 4 ). 
         [0244]    In the coating unit  30 , the bare optical fiber  3  was subjected to a coating step using an ultraviolet curable resin, the UV lamp  40   a  irradiated the resin with ultraviolet light in the curing unit  40  and thereby a coated layer was cured, and the optical fiber  5  was obtained. 
         [0245]    The optical fiber  5  passed through the pick-up unit  70  and the pulley  80  and was wound around the winding unit  90 . 
         [0246]    The measurement unit  50  measured an outer diameter of the optical fiber production intermediate  4  (i.e., an outer diameter of the coated layer) and outputs a measurement signal to the controller  60  based on the measurement value. 
         [0247]    The controller  60  adjusted the path length of the bare optical fiber  3  by controlling the position of the second direction changer  20 B in accordance with the measurement value of the outer diameter. 
         [0248]    As a control method, PID control was used. 
         [0249]    In the manufacturing method, flotation of the bare optical fiber  3  was stabilized in the direction changers  20 A to  20 C. 
         [0250]    In the manufacture of the optical fiber, a drawing velocity of the optical fiber  5  varied at ±1 m/second; however, variation in the outer diameter of the coated layer was within ±1 μm, and the diameter was stabilized. 
         [0251]    Thus, as a result of using the direction changers  20 A to  20 C, it was determined that the optical fiber  5  can be manufactured with a high level of yield without damage to the bare optical fiber  3 . 
       Example 2 
       [0252]    The manufacturing apparatus  1 B shown in  FIG. 7  was prepared. 
         [0253]    The pick-up unit  70  measured a drawing velocity of the optical fiber  5  and carried out control such that: in the case where the drawing velocity of the optical fiber  5  decreases, the second direction changer  20 B comes close to the first direction changer  20 A and the third direction changer  20 C; in the case where a drawing velocity of the optical fiber  5  increases, the second direction changer  20 B moves separately from the first direction changer  20 A and the third direction changer  20 C. 
         [0254]    In this Example, the optical fiber  5  was manufactured under the control condition described above, and the condition other than the above-described condition was the same as that of Example 1. 
         [0255]    In the manufacturing method, flotation of the bare optical fiber  3  was stabilized in the direction changers  20 A to  20 C. 
         [0256]    In the manufacture of the optical fiber, a drawing velocity of the optical fiber  5  varied at ±1 m/second; however, variation in the outer diameter of the coated layer was within ±1 μm, and the diameter was stabilized. 
         [0257]    Thus, as a result of using the direction changers  20 A to  20 C, it was determined that the optical fiber  5  can be manufactured with a high level of yield without damage to the bare optical fiber  3 . 
       Example 3 
       [0258]    The manufacturing apparatus ID shown in  FIG. 9  was prepared. 
         [0259]    The direction changer  201  shown in  FIG. 3  was used as the direction changers  20 A and  20 F. 
         [0260]    The direction changer  203  shown in  FIG. 5  was used as the direction changers  20 B,  20 D, and  20 E. 
         [0261]    The first direction changer  20 A was provided at the position at which the temperature of the bare optical fiber  3  becomes approximately 800° C. 
         [0262]    The bare optical fiber  3  (outer diameter of 125 μm) was obtained by drawing the optical fiber from the optical fiber preform  2  in the drawing unit  10 . 
         [0263]    As a drawing speed and a drawing tension, a common condition (drawing speed of 40 m/second and a drawing tension of approximately 150 gf) was adopted. 
         [0264]    The direction of the bare optical fiber  3  that is drawn from the optical fiber preform  2  in the downward vertical direction (first pathway L 1 ) is changed by 90 degrees by the first direction changer  20 A to be in the horizontal direction (second pathway L 2 ). Subsequently, the direction of the bare optical fiber  3  is changed by 180 degrees by the second direction changer  20 B, as a result, the direction of the bare optical fiber  3  is in the direction (third pathway L 3 ) opposite to the second pathway L 2 . Furthermore, the direction of the bare optical fiber  3  is changed by 180 degrees by the third direction changer  20 D, as a result, the direction of the bare optical fiber  3  is in the direction (fourth pathway L 5 ) opposite to the third pathway L 3 . 
         [0265]    The direction of the bare optical fiber  3  is changed by 180 degrees by the fourth direction changer  20 E to be in the direction (fifth pathway L 6 ) opposite to the fourth pathway L 5 . Subsequently, the direction of the bare optical fiber  3  is changed by 90 degrees by the fifth direction changer  20 F to be in the downward vertical direction (sixth pathway L 7 ). 
         [0266]    In the coating unit  30 , the bare optical fiber  3  was subjected to a coating step using an ultraviolet curable resin, the UV lamp  40   a  irradiated the resin with ultraviolet light in the curing unit  40  and thereby a coated layer was cured, and the optical fiber  5  was obtained. 
         [0267]    The optical fiber  5  passed through the pick-up unit  70  and the pulley  80  and was wound around the winding unit  90 . 
         [0268]    The measurement unit  50  measured an outer diameter of the optical fiber production intermediate  4  (i.e., an outer diameter of the coated layer) and outputs a measurement signal to the controller  130  based on the measurement value. 
         [0269]    The controller  130  adjusted the path length of the bare optical fiber  3  by controlling the positions of the second direction changer  20 B and the fourth direction changer  20 E in accordance with the measurement value of the outer diameter. 
         [0270]    As a control method, PID control was used. 
         [0271]    In the manufacturing method, flotation of the bare optical fiber  3  was stabilized in the direction changers  20 A to  20 F. 
         [0272]    In the manufacture of the optical fiber, a drawing velocity of the optical fiber  5  varied at ±1 m/second; however, variation in the outer diameter of the coated layer was within ±1 μm, and the diameter was stabilized. 
         [0273]    Thus, as a result of using the direction changers  20 A to  20 F, it was determined that the optical fiber  5  can be manufactured with a high level of yield without damage to the bare optical fiber  3 . 
       Example 4 
       [0274]    The manufacturing apparatus  1 E shown in  FIG. 10  was prepared. 
         [0275]    The pick-up unit  70  measured a drawing velocity of the optical fiber  5  and carried out control such that: in the case where the drawing velocity of the optical fiber  5  decreases, the second direction changer  20 B and the fourth direction changer  20 E come close to the direction changers  20 A,  20 D, and  20 F; in the case where a drawing velocity of the optical fiber  5  increases, the second direction changer  20 B and the fourth direction changer  20 E move separately from the direction changers  20 A,  20 D, and  20 F. 
         [0276]    In this Example, the optical fiber  5  was manufactured under the control condition described above, and the condition other than the above-described condition was the same as that of Example 1. 
         [0277]    In the manufacturing method, flotation of the bare optical fiber  3  was stabilized in the direction changers  20 A to  20 F. 
         [0278]    In the manufacture of the optical fiber, a drawing velocity of the optical fiber  5  varied at ±1 m/second; however, variation in the outer diameter of the coated layer was within ±1 μm, and the diameter was stabilized. 
         [0279]    Thus, as a result of using the direction changers  20 A to  20 F, it was determined that the optical fiber  5  can be manufactured with a high level of yield without damage to the bare optical fiber  3 . 
       Comparative Example 1 
       [0280]    In this Comparative Example, an optical fiber  5  was manufactured under the same condition as that of Example 1 except that the adjustment of the path length of the bare optical fiber  3  due to control of the position of the second direction changer  20 B is not carried out. 
         [0281]    In the manufacturing method, it was determined that the outer diameter of the coated layer is varied at approximately ±5 μm, and stabilized coating cannot be realized. 
       Comparative Example 2 
       [0282]    In this Comparative Example, an optical fiber  5  was manufactured under the condition of Example  4  except that the adjustment of the path length of the bare optical fiber  3  due to control of the positions of the second direction changer  20 B and the fourth direction changer  20 E is not carried out. 
         [0283]    In the manufacturing method, it was determined that the outer diameter of the coated layer is varied at approximately ±5 μm, and stabilized coating cannot be realized. 
         [0284]    In the above-description, a method of manufacturing an optical fiber of the invention and an optical fiber manufacturing apparatus thereof are described; however, the technical scope of the invention is not limited to the above embodiments, and various modifications may be made without departing from the scope of the invention.