1 DESCRIPTION DRAWING METHOD FOR BARE OPTICAL FIBER, MANUFACTURING METHOD FOR OPTICAL FIBER, AND OPTICAL FIBER TECHNICAL FIELD The present invention relates to a drawing method for a bare optical fiber, a manufacturing method for an optical fiber using the drawing method, and an optical fiber obtained using the manufacturing method for an optical fiber, and it particularly relates to a drawing method for a bare optical fiber for manufacturing optical fiber with a lower absorption loss due to OH groups, and a manufacturing method for an optical fiber using the drawing method, and an optical fiber obtained using the manufacturing method for an optical fiber. The present application claims priority to Japanese Patent Application No. 2003-387746 filed on November 18,2003 and Japanese Patent Application No. 2004-279452 filed on September 27,2004, the details of which are incorporated herein. BACKGROUND ART Recently, optical fiber, which is applicable to coarse wavelength division multiplexing (hereafter, abbreviated as "CWDM") transmission, with a lower loss in the band of wavelength 1380 nm (absorption loss due to OH groups), has attracted attention. The optical fiber with a lower absorption loss due to OH groups enables structuring an inexpensive CWDM transmission system; and in addition, the production cost is also substantially equal to that of typical single mode fiber. Consequently, the optical fiber has a great cost merit, so many companies proceed with research and 2 development and products are commercialized. When hydrogen diffuses into an optical fiber, it causes increased absorption loss due to OH groups, making so it necessary to prevent hydrogen penetration into the optical fiber. For drawing the bare optical fiber in the manufacturing of the optical fiber, a means to prevent hydrogen penetration into the bare optical fiber is provided. FIG. 7 is a schematic diagram showing a manufacturing device for an optical fiber used in a conventional manufacturing method for an optical fiber. In FIG. 7, a reference symbol 31 indicates a drawing furnace. An optical fiber preform 32 is mounted inside the drawing furnace 31 to be axially movable, and a lower end of the optical fiber preform 32 is drawn. In the manufacturing of the optical fiber, first, optical fiber preform 32 containing as a main component silica-based glass is placed within the drawing furnace 31, and its end is heated to approximately 2000°C at high temperature in an inert gas atmosphere, such as argon (Ar) or helium (He), and is drawn, thereby obtaining a bare optical fiber 33 with an external diameter of 125 jam. Subsequently, the bare optical fiber 33 is sent to a mechanism to slowly cool the optical fiber, such as an annealing furnace 34 (hereafter, referred to as "annealing mechanism"), the cooling speed of the bare optical fiber 33 is changed and the optical fiber is slowly cooled. The bare optical fiber 33 drawn out to the outside of the annealing furnace 34 is cooled to a temperature suitable to the formation of a coating layer for a next process. In the cooling process, it is naturally cooled in an atmosphere surrounding the bare optical fiber 34 or is forcibly cooled by supplying cooling gas, such as helium or nitrogen gas, using a cooling cylinder 35. The bare optical fiber 33 cooled in the cooling process is coated with a coating 3 layer made of ultraviolet ray curable resin, and which is made of a primary coating layer and a secondary coating layer, by a resin coating device 36 and a UV lamp 37 for the purpose of protecting the bare optical fiber 33, thereby obtaining an optical fiber 38 with an external diameter of 250 urn. In addition, the optical fiber 38 is turned to another direction by a turning pulley 39, and is wound onto a winding drum 42 via a drawer 40 and a dancer roller 41. Furthermore, a method for providing a coating layer onto the bare optical fiber 33 is not only a method where after a resin for the primary coating layer formation and a resin for the secondary coating layer are applied by a single resin applicator 36, the resins are cured by a single UV lamp 37, as; shown in FIG. 7, but with a method where after a resin for primary coating layer formation knd a resin for secondary coating layer are applied by two different resin applicators, the resins are cured by a single UV lamp, and another method where after a resin for primary coating layer formation is applied by a first resin applicator, the resin is cured by a first UV lamp, and after a resin for the secondary coating layer is applied by a second resin applicator, a resin cured by a second UV lamp can also be used. In the conventional manufacturing method for an optical fiber, in order to reduce Rayleigh scattering and to reduce loss at a wavelength of 1550 run (for example, refer to Patent Documents 1 to3), or in order to control the increase in absorption loss caused by OH groups, it tends to slow the cooling speed and to cool the bare optical fiber 33 drawn out to me outside of me drawing furnace 31, by adjusting the drawing speed in a temperature region corresponding to the purpose, respectively, or by prolonging the annealing time. As described above, when annealing is performed in the drawing the bare optical fiber 33, residual OH groups in the optical fiber preform 32 diffuse and hydrogen is thermally dissociated from the OH groups. In addition, diffusion of the dissociated 4 hydrogen increases. Increased absorption loss due to the OH groups or the combination of a non-bridging oxygen hole center (hereafter, abbreviated as "NBOHC") in the optical fiber and hydrogen results in increased absorption loss due to the OH groups. Means to resolve the problem are proposed, for example, in Patent Documents 4 to 6. In Patent Document 4, ah optical fiber preform having a substrate tube, a cladding layer inside the substrate tube and a core layer inside the cladding layer, and a barrier layer established between the substrate tube and the cladding layer, and a manufacturing method for an optical fiber using the optical fiber preform are proposed. The barrier layer is formed by depositing a substance with a low OH diffusion coefficient between the substrate tube and the cladding layer, and the penetration of the residual OH groups within the substrate tube to the cladding layer is prevented. In Patent Document 5, a manufacturing method for an optical fiber is proposed where a first cladding with an external diameter "D" is deposited so as to surround a core with an external diameter "d" using a vapor-phase axial deposition method; a porous core rod satisfying a relational expression, D/d > 4.0, is formed; the porous core rod is dehydrated and the OH group concentration is reduced to 0.8 wtppb or less and vitrified to form a core rod; the transparent core rod is heated and elongated; a second core rod is deposited surrounding the core rod after elongating using the vapor-phase deposition method; the second clad is dehydrated so as to reduce the OH group concentration to 50 wtppm or less; it is vitrified to form an optical fiber preform; and after the optical fiber preform is drawn, it is maintained in a heavy hydrogen atmosphere for a pre-determined time. In Patent Document 6, in a manufacturing method for an optical fiber where raw material gas is reacted and a glass fine particle aggregate is obtained, and the glass fine 5 particle aggregate is sintered to vitrify it, a method via a first heating process to pre-dehydrate the glass fine particle aggregate and next, a second heating process to increase the temperature to a vitrification temperature, within the temperature range of 950 to 1,250°C where the glass fine particle aggregate is not remarkably contracted, substantially in the oxygen gas atmosphere containing 1 mol% to 20 mol% of chlorine or chlorine compound, is proposed. The manufacturing methods for optical fibers proposed in Patent Documents 4 to 6 have a problem where an absorption loss due to OH groups increases depending upon drawing conditions for the optical fiber. Further, there is another problem where a production cost increases. Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2002-338289 Patent Document 2: Japanese Unexamined Patent Application, First Publication No. 2002-321936 Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2000-335933 Patent Document 4: Japanese Unexamined Patent Application, First Publication No. 2002-535238 Patent Document 5: Japanese Unexamined Patent Application, First Publication No. 2002-187733 Patent Document 6: Japanese Patent No. 2,549,615 DISCLOSURE OF INVENTION Problems to be Solved by the Invention The present invention has considers the above-described circumstances, and has 6 an object of providing a drawing method for a bare optical fiber where production cost is reduced and a loss at the 1380 nm wavelength band is low, a manufacturing method for an optical fiber using the method, and an optical fiber obtained using the manufacturing method for an optical fiber. ' Means for Solving the Problem In order to resolve the problem, the present invention provides a drawing method for a bare optical fiber, comprising the steps of: melting an optical fiber preform using a heating device and drawing the bare optical fiber; and naturally cooling down the bare optical fiber or forcibly cooling down the bare optical fiber by a cooling device after the heating and melting step, wherein a temperature history during the drawing the optical fiber preform to obtain the bare optical fiber in the heating device satisfies a relational expression: T < -0.01X + 12 where a time period when the heated and molten portion of the optical fiber preform heated and molten by the heating device reaches 1800°C or higher is T (min) and a OH group concentration in a cladding layer of the optical fiber preform is X (wtppm). In the drawing method for a bare optical fiber, when the OH group concentration in the cladding layer of the optical fiber preform before the heating and fusing step is X (wtppm) and a thermal dissociation coefficient from the OH groups during drawing is Y (wt%), it is preferable to satisfy a relational expression, Y < -8 x 10"5X + 0.06. The present invention provides a manufacturing method for an optical fiber, comprising the steps of: melting an optical fiber preform using a heating device and drawing the bare optical fiber; naturally cooling down the bare optical fiber or forcibly cooling down by a cooling device after the heating and melting step; applying a coating material around the circumference of the bare optical fiber cooled to a pre-determined temperature in the 7 cooling step; and curing the coating material and to obtain the optical fiber. It is preferable that the cooling step comprises the steps of accelerating a cooling speed of the bare optical fiber to 6000°C/sec or faster until the external diameter of the bare optical fiber becomes constant after the bare optical fiber during drawing becomes less than 1800°C. It is preferable that the cooling step comprises the step of accelerating the cooling speed of the bare optical fiber faster than that by air after the external diameter of the bare optical fiber during drawing becomes constant. The present invention provides an optical fiber manufactured using the above manufacturing method for an optical fiber. It is preferable for the optical fiber with the composition in which the loss at a wavelength of 1383 nm is 0.31 dB/km or less. Advantageous Effect of the Invention With the manufacturing method for an optical fiber of the present invention, an optical fiber with a lower loss at a wavelength band of 1380 nm can be obtained without dehydrating the cladding layer of the optical fiber preform. Therefore, the manufacturing process can be reduced. Concurrently, manufacturing time and manufacturing cost can be reduced. Further, even in the case in which dehydration is performed, a hydrogen amount to be generated due to the heat-free from the residual OH groups can be reduced by adjusting the OH group concentration in the residual cladding layer according to the degree of the dehydration and variation in the concentration of residual OH groups due to manufacturing variation. In addition, the diffusion of the generated hydrogen can be lessened, so a loss at the 1380 nm wavelength band can be adjusted, enabling improved 8 yield. As a result, manufacturing costs can be reduced. BRIEF DESC]|UPTION OF DRAWINGS FIG. 1 is a diagram showing OH group concentration distribution at a relative position from the center of an optical fiber preform and an OH group concentration distribution at a relative position' from the center of a bare optical fiber obtained by drawing an optical fiber preform. FIG 2 is a graph showing the concentration distribution of hydrogen generated from OH groups due to thermal dissociation at a relative position from the center of an optical fiber preform and a concentration distribution of hydrogen generated from OH groups due to thermal dissociation at a relative position from the center of a bare optical fiber obtained by drawing the optical fiber preform. FIG. 3 is a graph showing the temperature change of a molten portion of an optical fiber preform. FIG. 4 is a graph showing the wavelength loss characteristics of an optical fiber. FIG. 5 is a graph showing the concentration distribution of hydrogen generated from OH groups due to thermal dissociation at a relative position from the center of an optical fiber preform, and a concentration distribution of hydrogen generated from OH groups due to thermal dissociation at a relative position from the center of a bare optical fiber obtained by drawing the optical fiber preform, and a region affecting loss at a wavelength of 13 83 nm according to tile relationship with the intensity of an incident light. FIG. 6 is a schematic diagram showing a manufacturing device for an optical fiber used for the present invention. [ FIG. 7 is a schematic diagram showing a conventional manufacturing device for an optical fiber used for the conventional manufacturing method for an optical fiber. 9 Description of Reference symbols 1 ... drawing furnace, 2 ... optical fiber preform, 3 ... bare optical fiber, 4 ... annealing furnace, 5 ... cooling cylinder, 6 1.. resin coating device, 7 ... UV lamp, 8 ... optical fiber, 9 ... turning pulley, 10 ... drawer, 11 ... dancer roller, 12 ... winding drum DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The manufacturing method for an optical fiber embodying the present invention is described hereafter, with reference to the drawings. As a cause to increase loss in the 1380 ran wavelength band of the optical fiber, diffusion of residual OH groups in an optical fiber preform, diffusion of hydrogen generated from OH groups due to thermal dissociation, and a difference between a recombination rate of NBOHC and a binding rate of hydrogen and NBOHC per temperature can be cited. First, in order to examine the cause of an increase in the loss in the 1380 nm wavelength band of the optical fiber, the following two relationships were examined: (1) The relationship between the OH group concentration distribution at a relative position from the center of an optical fiber preform and the OH group concentration distribution at a relative position from the center of a bare optical fiber obtained by drawing the optical fiber preform; and (2) The relationship between the concentration distribution of hydrogen generated from OH groups due to thermal dissociation at a relative position from the center of an optical fiber preform and the concentration distribution of hydrogen generated from OH groups due to thermal dissociation at a relative position from the center of a bare optical fiber obtained by drawing the optical fiber preform. FIG. 1 is a graph showing the OH concentration distribution at a relative position 10 from center of the optical fiber preform and the OH concentration distribution at a relative position from the center of the bare optical fiber obtained by fusion drawing the optical fiber preform. FIG. 2 is a graph showing the concentration distribution of hydrogen generated from OH groups due to thermal dissociation at a relative position from the center of the optical fiber preform and the concentration distribution of hydrogen generated from OH groups due to thermal dissociation at a relative position from the center of the bare optical fiber obtained by drawing the optical fiber preform. Comparing the optical fiber preform and the bare optical fiber according to FIG. 1, there is no great change in the OH group concentration distribution at the relative position from the center, respectively. In other words, although drawing of the bare optical fiber causes diffusion of OH groups, its effect on the transmission loss is small. When the optical fiber preform and the bare optical fiber is compared according to FIG. 2, the concentration distributions of hydrogen generated due to OH groups at the relative position from the respective center greatly changed. In other words, drawing of the bare optical fiber causes the significant diffusion of hydrogen generated from OH groups due to thermal dissociation. As described above, the increase of the loss in the 1380 nm wavelength band of the optical fiber is greatly affected by the diffusion of hydrogen generated from OH groups due to thermal dissociation more than by the diffusion of residual OH groups in the optical fiber preform, because a diffusion coefficient of hydrogen (see Y. Namihira, K. Mochizuki and K. Kuwazuru, "Temperature dependence of the hydrogen-diffusion constant in optical fibers", Opt. Lett., Vol. 9, No. 95