Patent Application
20090013726
The present invention relates to a glass base material for manufacturing an optical fiber, a manufacturing method thereof, and a method for manufacturing an optical fiber. More particularly, the present invention relates to a method for manufacturing a glass base material having an end shape suitable for drawing of an optical fiber, a glass base material obtained thereby, and a method for manufacturing an optical fiber using the glass base material.
In addition, the present application also relates to the following applications, the contents of which are incorporated herein by reference for designated countries accepting this reference.
Japanese Patent Application No. 2004-159822 (Application date: May 28, 2004)
Japanese Patent Application No. 2004-159848 (Application date: May 28, 2004)
A large-scale glass base material is elongated in an axial direction, particularly, a vertical direction and is divided with predetermined length after being heated in a heating furnace such as an electric furnace, in order to be processed to a glass base material having a diameter suitable for drawing.
As shown in a schematic diagram of
The welding of the dummy rod 3 to one end of the glass base material 1 and the formation of the taper portion 4 on the other end are performed by means of a glass lathe in many cases.
For example, a method for processing a taper shape by means of a glass lathe includes methods disclosed in Patent Documents 1 and 2.
In the glass base material 1 having mechanical cutting faces on its both ends, the dummy rod 3 is connected to the one end and the taper portion 4 is formed on the other end. The glass base material (hereinafter, referred to as “a glass base material for drawing”) having the formed taper portion 4 is attached to a drawing apparatus by making a feeder 5 of the drawing apparatus grip the dummy rod 3 with a scroll chuck 6 as shown in
Next, the taper portion 4 of the glass base material for drawing is set at a predetermined position of the heating furnace 7 to start to be heated, and a leading end of the glass base material for drawing falls by softening the leading end. After the leading end falls, the leading end is caught and passes through a diameter measurement device 8. After that, when its diameter stably reaches desired wire size, coating and curing to an optical fiber 9 are performed by passing the optical fiber 9 through a first dice 10, a first ultraviolet-ray curing apparatus 11, a second dice 12, and a second ultraviolet-ray curing apparatus 13 in the order. After that, the optical fiber is reeled by a capstan (not shown) in a bobbin via a guide pulley 14.
After that, a drawing process becomes a steady state by gradually raising a feed speed and a drawing speed of the feeder 5 up to a regulation speed. The discrimination for a steady state is performed by whether all of the next indices are satisfied. In other words, index 1: a feed speed and a drawing speed reach a regulation speed, index 2: an outside diameter of the optical fiber is stable, and index 3: the prescribed excess length is withdrawn after the outside diameter of the optical fiber is stable. An optical fiber of a steady part drawn in a steady state is utilized as a product. An optical fiber of an unsteady part drawn in an unsteady state before that is discarded as a faulty part.
Here, the above index 3 is required because eccentricity of the drawn optical fiber is reduced due to the index 3. In the drawn optical fiber, the eccentricity is large in an unsteady part in an early stage of the start of drawing, the eccentricity is gradually reduced with the advance of drawing, and the eccentricity is stable at a certain value in a steady part. Therefore, in the unsteady part, a portion with large eccentricity exists even if the outside diameter satisfies specification. Although this outside diameter is within a specification range, the excess length of index 3 is required to exclude an optical fiber portion with large eccentricity from a product.
The interval between the outside-diameter stable point 16 and the eccentric stable point 17 becomes the excess length 18 to be excluded. The eccentricity of optical fiber is expressed with an eccentricity ratio defined in the following Expression.
Eccentricity ratio (%)=[(E02+E902)1/2/{(D0+D90)/2}]*100
In the computation of eccentricity ratio, it is necessary to rotate the optical fiber in an axial direction and measure the profile at two positions of 0° and 90°.
In Expression, E0 is an amount of eccentricity in 0° and E90 is an amount of eccentricity in 90°. Do is an outside diameter of the optical fiber in 0° and D90 is an outside diameter in 90°.
An optical fiber in an unsteady part in an early stage of the start of drawing cannot be used as a product due to eccentricity and thus is discarded. When the discarded optical fiber increases, yield decreases and thus a manufacturing cost increases. Therefore, in order to improve yield, it is necessary to shorten a time in an unsteady part in an early stage of the start of drawing and stabilize quality by realizing a steady state as soon as possible.
In recent years, a glass base material grows in size, in this relation an unsteady part area in an early stage of the start of drawing becomes long, and an amount of the discarded optical fiber also increases. The reason discarding an optical fiber in an unsteady part is that the optical fiber departs from the specification of optical fiber due to the fluctuation of outside diameter, the unevenness of cladding-material, or the like in addition to the above eccentricity. Here, an unsteady part area is shortened and thus yield improves by reducing all or either of values of the above indices.
An object of the present invention is to provide a glass base material having an end shape suitable for drawing, a method for manufacturing the glass base material, and a method for manufacturing an optical fiber, capable of immediately reducing the eccentricity of the optical fiber in an early stage of the start of drawing and of shortening an unsteady part area.
To solve the problem, according to the first aspect of the present invention, there is provided a method for fusing a cylindrical glass base material and manufacturing a glass base material for drawing having a straight base with a substantially constant diameter and a taper portion that is formed on one end of the straight base and of which a diameter becomes narrow as the taper portion departs from the straight base, the manufacturing method including: modifying a center-line displacement amount of a fusing point for a center line of an effective straight base of the glass base material to a predetermined numeric value to form a modified point; and fusing the glass base material at the modified point to form the taper portion. In this way, distortion of the taper portion formed on the glass base material for drawing becomes smaller than that of the original taper portion, and the excess length generated from the start of drawing to a steady state is shortened.
Moreover, as one embodiment, in the above manufacturing method, the modifying includes an operation heating the glass base material with a burner flame while rotating the glass base material by means of a glass lathe. In this way, a precise modification work can be performed.
Moreover, as another embodiment, in the above manufacturing method, the predetermined numeric value is 2.6 mm.
In this way, an effect modifying the glass base material becomes remarkable, and the taper portion with a little distortion can be formed.
Moreover, as another embodiment, in the above manufacturing method, the fusing includes an operation heating the glass base material with a burner flame. In this way, each work of modifying and fusing can be continuously performed.
Moreover, as another embodiment, in the above manufacturing method, the modified glass base material is attached to a drawing apparatus, and the fusing is performed just before drawing. In this way, each work of modifying, fusing, and drawing can be continuously performed. Moreover, since a series of works can be executed at a short time, an effect of modification does not deteriorate.
Moreover, according to the second aspect of the present invention, there is provided a glass base material for drawing having a cylindrical straight base and a taper portion formed on one end of the straight base so that a diameter becomes narrow as the taper portion departs from the straight base, in which the taper portion is formed by fusing a modified point modified so that a center-line displacement amount for a center line of the whole cylindrical glass base material is less than or equal to a predetermined numeric value. In this glass base material, since the excess length generated from the start of drawing to a steady state is short, use efficiency of a raw material becomes high, and thus the optical fiber can be manufactured at low cost.
Furthermore, according to the third aspect of the present invention, there is provided a glass base material for drawing having an effective straight base with an average outside diameter D and a taper portion that is formed on one end of a straight base that is a part of the effective straight base and of which a diameter becomes narrow as the taper portion departs from the straight base, in which a ratio δ/D between the average outside diameter D and a taper portion distortion δ is δ/D<=0.03 when the glass base material for drawing is attached to a drawing apparatus and when a maximum value of a displacement amount of a center of the taper portion for a center of the taper portion side end in the straight base is the taper portion distortion δ.
In this way, the excess length generated from the start of drawing to a steady state is shortened.
Moreover, as one embodiment, in the above glass base material, the end of the straight base is a part having an outside diameter of a value obtained by multiplying a coefficient β in a range of 0.90 to 1.00 (no dimension) by the average outside diameter D. In this way, a reference when measuring distortion δ of the taper portion is prescribed.
Moreover, as another embodiment, in the above glass base material, a length LD of the taper portion is not less than one time of a mean value DM for outside diameters at three to ten points randomly extracted from the vicinity of center in a longitudinal direction of the glass base material in the range of 30 to 60% of overall length of the glass base material. In this way, the start of drawing from the taper portion becomes easy.
Moreover, as another embodiment, in the above glass base material, the taper portion is formed by fusing or grinding. In this way, the glass base material for drawing is prepared and drawing for manufacturing the optical fiber becomes easy.
Moreover, according to the fourth aspect of the present invention, there is provided a method for manufacturing a glass base material for drawing having a straight base with an average outside diameter D and a taper portion that is formed on one end of the straight base and of which a diameter becomes narrow as the taper portion departs from the straight base, the method including drawing the glass base material for drawing in which a ratio δ/D between the average outside diameter D and a taper portion distortion δ is δ/D<=0.03, when the glass base material for drawing is attached to a drawing apparatus and when a maximum value of a displacement amount of a center of the taper portion for a center of the taper portion side end in the straight base is the taper portion distortion δ. In this way, it is possible to manufacture an optical fiber with a predominant optical characteristic at low cost.
According to the present invention, it is possible to immediately and stably reduce eccentricity of the optical fiber in an early stage of the start of drawing and shorten an unsteady part area that is a faulty part of a product.
In this way, it is possible to improve yield of the production of optical fiber and contribute to resource saving and reduction of manufacturing cost.
As shown in
However, although an end of the glass base material is precisely processed by fusing or mechanical grinding, a taper portion without distortion may not be obtained. Thus, as a result of a keen examination, the problem can be solved by measuring a center-line displacement amount (hereinafter, simply referred to as a center-line displacement amount) at a taper portion formation point (a fusing point when being formed by fusing) for a center line of an effective straight base of the glass base material, and fusing and forming the taper portion after modifying the center-line displacement amount to be not more than a predetermined numeric value, before forming the taper portion. In this way, it is possible to immediately reduce and stabilize the eccentricity of optical fiber in an early stage of the start of drawing and shorten excess length.
A method for manufacturing the glass base material of the present invention is to modify a center-line displacement amount at a fusing point for a center line of the glass base material to a value not more than a predetermined numeric value and then fuse the glass base material from the modified point to form the taper portion, and is to fuse the glass base material to form the taper portion after modifying the center-line displacement amount at a fusing point to a value not more than a predetermined numeric value, particularly 2.6 mm before fusing. In this way, it is possible to immediately stabilize the eccentricity of optical fiber in an early stage of the start of drawing to reduce it and shorten excess length. In addition, a fusing point is a point that is a starting end for forming the taper portion.
Moreover, according to the present invention, since the distortion of shape of the taper portion 4 is put in a predetermined number range, a ratio δ/D between distortion δ and an average outside diameter D is δ/D<=0.03.
In this way, it is possible to stably reduce the eccentricity of optical fiber in an early stage of the start of drawing and shorten excess length.
In addition, an end of a straight base of the glass base material for drawing, which is also a starting point of the taper portion, defines a part having an outside diameter made by multiplying a coefficient β by an average outside diameter D. The coefficient β is in a range of 0.90 to 1.00 (no dimension). For example, assuming that β=0.98 and the average outside diameter D=80 mm, the end of straight base is a position reaching an outside diameter=0.98*80=78.4 mm in the vicinity of taper.
The glass base material for drawing including the taper portion is obtained by measuring a ratio δ/D between distortion δ and the average outside diameter D, and a glass base material having distortion exceeding 1.00 mm and a glass base material having δ/D exceeding 0.03 are fused or grinded so as to be put in a predetermined numeric value. The length LD of the taper portion is processed so as to be not less than one time of a mean value DM of the outside diameter. LD less than one time is not preferable because an amount of softening material that does not become a fiber increases at the start of drawing.
In addition, as shown in
Moreover, in a method shown in
As shown in
In addition, the end of straight base of the glass base material for drawing is a starting point of the taper portion, and is a part having an outside diameter obtained by multiplying the coefficient δ by the average outside diameter D. Moreover, the coefficient β is in a range of 0.90 to 1.00 (no dimension).
Moreover, the measurement of distortion of the taper portion uses a preform-shaped measuring device for optical fiber disclosed in Japanese Patent No. 3222777, but is not limited to this if it is an apparatus including a similar function. The glass base material for drawing measured and sorted in this way is provided to drawing processing.
The measurement procedure of distortion δ of the fusing taper portion is as follows. First, an end 21 of the straight base of the glass base material and the distortion evaluating end 22 of the fusing taper portion are determined. An outside diameter is measured at five points adjacent to the center at which the outside diameter is comparatively stable, and a mean value DM for outside diameters is obtained. The end 21 of straight base is a portion of the coefficient β=0.98, that is, a position of which an outside diameter is 0.98*DM.
When the glass base material for drawing is attached to a drawing apparatus, the distortion evaluating end 22 is a position equivalent to the center of a heating furnace heating unit and is a position at which an outside diameter of the taper portion is φ20 mm in
When the formation of taper portion is performed by fusing, the distortion of taper portion largely comes under the influence of a center-line displacement amount of the glass base material before forming the taper portion, particularly, a center-line displacement amount of a taper forming point (a fusing point). Therefore, it is necessary to previously reduce a center-line displacement amount of a fusing point to reduce the distortion of taper portion by fusing. In the present invention, as a result of keen examinations for relation between the center-line displacement amount of fusing point and the distortion of taper portion, there is made clear the center-line displacement amount of fusing point for realizing the distortion not more than a specified value.
The distortion δ/D for the average diameter D and the eccentricity of optical fiber have correlativity, and the eccentricity of optical fiber becomes large and the excess length gets longer when the distortion δ/D exceeds 0.03. For this reason, fusing processing is performed once more so as to be put in a predetermined numeric value when δ/D exceeds 0.03.
Moreover,
When the taper portion is formed by fusing after modifying the glass base material until the center-line displacement amount e<=2.6 mm, it is possible to sufficiently reduce the distortion of taper portion.
The glass base material is modified so that a center-line displacement amount becomes not more than 2.6 mm by attaching the glass base material of an average outside diameter φ62 mm and length 1100 mm having the mechanical cutting face 2 on both ends to a glass lathe including a shape measuring device as shown in
In the glass base material for drawing, a center-line displacement amount between the end of straight base of which an outside diameter is 0.98*DM=60.8 mm and the distortion evaluating end of which the outside diameter of taper portion is Φ20 mm, that is, the distortion of taper portion is extremely small, and δ=0.119 mm and δ/D=0.002 mm. In this manner, since there is drawn the glass base material for drawing made by sufficiently reducing the distortion of taper portion, it is possible to improve yield when manufacturing an optical fiber and thus reduce manufacturing cost of the optical fiber.
The drawing is performed by preparing several kinds of glass base materials with an outside diameter different from one another and respectively forming taper portions by fusing.
The manufacturing cost of optical fiber can be lowered by using the glass base material obtained in a manufacturing method of the present invention, and this method is extremely valid.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-159822 | May 2004 | JP | national |
| 2004-159848 | May 2004 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2005/008540 | 5/10/2005 | WO | 00 | 9/9/2008 |
