Patent Application
20080013901
The above and other features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:
Hereinafter, preferred embodiments of the present invention are described with reference to the accompanying drawings. In the following description, the same elements are designated by the same reference numerals although they are illustrated in different drawings. For the purposes of clarity and simplicity, a detailed description of known functions and configurations incorporated herein is omitted when it may make the subject matter of the present invention rather unclear.
Process (a) (S11) is a process of growing a primary soot preform along a longitudinal direction of a start member on the start member through soot deposition.
The deposition chamber 130 has a cylindrical shape comprising an internal space. Further, the deposition chamber 130 is provided with an exhaust port 135 at one side thereof, and the first and second burner 140 and 150 are installed at an other side of the deposition chamber 130 opposite the one side.
In a preparation process before process (a) (S11), a start member 110 is installed inside the deposition chamber 130. A primary soot preform 120a is grown along a longitudinal direction of the start member 110 from an end thereof through soot deposition. The primary soot preform 120a includes a core 122a positioned at a center thereof and an inner clad 124a formed directly on an outer circumference of the core 122a. The core 122a has a relatively high refractive index, and the inner clad 124a surrounding the core 122a has a relatively low refractive index. At the beginning of the soot deposition, soot is deposited on the end of the start member 110 using the second burner 150 to form a ball. When the ball reaches a predetermined size by continuously depositing the soot, the core 122a and the inner clad 124a are simultaneously formed on the ball using the first and second burner 140 and 150. In a case where the primary soot preform 120a is grown directly on an end of the start member 110 without the formation of the ball, the start member 110 and the primary soot preform 120a may be separated from each other, or cracks may be produced in the primary soot preform 120a due to the weight of the primary soot preform 120a. The start member 110 simultaneously rotates about the center and moves away from the first and second burner 140 and 150 during the soot deposition. The start member 110 is rotated about a central axis 112 thereof as the center such that the primary soot preform 120a has rotational symmetry. Further, the start member 110 is moved away from the first and second burner along the central axis 112 thereof such that the primary soot preform 120a is continuously grown toward the first and second burner 140 and 150. Along the central axis 112 of the start member 112, in a preferred embodiment, the growth direction of the primary soot preform 120a is downward and the reverse direction thereof is upward. The upward movement of the start member 110 is servo-controlled using a sensor. That is, the sensor measures a growth size selected from the group consisting of a diameter or a length, and the start member 110 is moved upwardly if the growth size of the primary soot preform 120a approaches a predetermined value. Thus, the start member 110 is automatically moved upward depending on the growth size of the primary soot preform 120a.
The first burner 140 has a central axis inclined at an acute angle with respect to the central axis 112 of the start member 110, and jets flames toward an end of the primary soot preform 120a such that the core 122a is downwardly grown from the end of the primary soot preform 120a. A glass raw material S (SiCl4, GeCl4, POCl3, CF4, BCl3 or the like), a fuel gas GFuel containing hydrogen, an oxidation gas Goxygen containing oxygen, and the like are provided to the first burner 140. Soot is produced in accordance with a chemical reaction in which the glass raw material is hydrolyzed within the flames jetted from the first burner 140, and the like. Further, the produced soot is deposited on the primary soot preform 120a.
Hydrolysis reaction formulas of SiO2 and GeO2, which are main oxides constituting the soot, are shown as the following Chemical Formulas 1 and 2. At this time, the reaction temperature is in the range of 700 to 900° C.
SiCl4+2H2O→SiO2+4HCl (1)
GeCl4+2H2O→GeO2+4HCl (2)
The second burner 150 is upwardly spaced apart from the first burner 140, and a central axis of the second burner 150 is inclined at an acute angle with respect to the central axis 112 of the start member 110. The second burner 150 jets flames toward an outer circumferential surface of the core 122a such that the inner clad 124a is grown on the outer circumferential surface of the core 122a. A glass raw material S (SiCl4, GeCl4, POCl3, CF4, BCl3 or the like), a fuel gas GFuel containing hydrogen, an oxidation gas Goxygen containing oxygen, and the like, are provided to the second burner 150. Soot is produced in accordance with a chemical reaction in which the glass raw material is hydrolyzed within the flames jetted from the second burner 150, and the like. Further, the produced soot is deposited on the primary soot preform 120a.
The supply quantities or kinds of the glass raw materials S respectively provided to the first and second burners 140 and 150 are controlled to be different from each other, so that the core 122a has a refractive index higher than the inner clad 124a. For example, GeO2 and P2O5 within glass increase a refractive index, and B2O3 and F decrease it. Soot that has not been deposited on the primary soot preform 120a from among the soot produced by the first and second burners 140 and 150 is exhausted to the outside through the exhaust port 135.
Process (b) (S12) is a process of dehydrating the primary soot preform 120a. That is, the primary soot preform 120a is heated in a chlorine (Cl2) atmosphere so that OH group and impurities existing inside the primary soot preform 120a are removed.
In a preparation process before process (b) (S12), the primary soot preform 120a is installed inside the furnace 200. Cl2 and He gas is provided to the inside of the furnace 200 through the inflow port 220, and the primary soot preform 120a is heated using the heater 210. Preferably, the input of the He gas is 20 to 50 splm, and the input of the Cl2 gas is 2 to 5 vol % of that of the He gas. For example, the primary soot preform 120a may be heated at 1130° C. for 120 minutes under an atmosphere of the Cl2 gas of 1.0 splm and the He gas of 25 splm.
Process (c) (S13) is a process of obtaining a primary vitrified soot preform by sintering the primary dehydrated soot preform 120a.
Process (d) (S14) is a process of stretching the primary vitrified optical fiber preform 120b by heating it using a heat source that does not use hydrogen. That is, in order to reduce the diameter of the primary vitrified optical fiber preform 120b and to extend the length thereof, an end of the primary vitrified optical fiber preform 120b is stretched in a state where the primary vitrified optical fiber preform 120b is softened. The primary vitrified optical fiber preform 120b is stretched to a predetermined diameter wherein a diameter ratio of a core and clad of a final product is determined by that of the optical fiber. The heat source that does not use hydrogen includes an electric furnace, a plasma heater and the like.
Referring to
Further, in a preparation process before process (d) (S14), the diameter of the primary vitrified optical fiber preform 120b is measured with respect to the entire length thereof using the outer diameter measuring device 340 to produce a measurement result, and the upwardly moving speed of the second chuck 325 and the furnace 330 are adjusted in accordance with the measurement result.
Referring to
Thereafter, the stretched primary vitrified optical fiber preform 120c is cut to be divided into two cut primary optical fiber preforms 120c, and one cut primary optical fiber preform 120c of the two, to which the first dummy rod 310 is attached, is used in the following processes.
Process (e) (S15) is a process of obtaining a secondary soot preform by growing an outer clad on the cut primary optical fiber preform 120c by soot deposition along a central axis direction thereof. The outer clad has a refractive index higher than the inner clad 124b of the cut primary optical fiber preform 120c and lower than the core 122b thereof. The outer clad is formed directly on the outer circumference of the inner clad 124b of the primary cut optical fiber preform 120c.
The deposition chamber 410 has a cylindrical shape with an inner space, and is provided with an exhaust port 415 at a top of the deposition chamber 410. The burner 420 is positioned opposite to the exhaust port 415 with the cut primary optical fiber preform 120c therebetween. An outer clad 126a is grown on an outer circumference of the cut primary optical fiber preform 120c through a second soot deposition using the burner 420. During the second soot deposition, the cut primary optical fiber preform 120c rotates and simultaneously moves along the central axis thereof. The cut primary optical fiber preform 120c is rotated about the central axis 117 as a center such that a secondary opaque soot preform 125a resulting from the second soot deposition has rotational symmetry. Further, the secondary soot preform 125a is obtained by repeatedly reciprocating the cut primary optical fiber preform 120c along the central axis 117 thereof. In a preferred embodiment, the burner 420 is fixed.
A raw material S containing SiCl4, which is a glass forming substance, a fuel gas GFuel containing hydrogen or CH4, and an oxidation gas GOxygen containing oxygen, and the like are provided to the burner 420. Soot is produced in accordance with a chemical reaction in which the raw material S is hydrolyzed within flames jetted from the burner 420, and a produced soot is deposited on an outer circumferential surface of the cut primary optical fiber preform 120c. Soot produced by the burner 420 that has not been deposited on the outer circumferential surface of the cut primary optical fiber preform 120c is exhausted to the outside through the exhaust port 415 of the deposition chamber 410.
In an alternative preferred embodiment, the burner 420 is repeatedly reciprocated along a path parallel to the central axis 117 of the cut primary cut optical fiber preform 120c.
Process (f) (S16) is a process of obtaining a secondary vitrified optical fiber preform 125b by dehydrating and sintering the secondary soot preform 125a. That is, the secondary soot preform 125a is heated in a Cl2 gas atmosphere to perform a dehydrating process for eliminating OH group and impurities, which exist inside the secondary soot preform 125a, and the secondary soot preform 125a is simultaneously sintered under He gas atmosphere to perform a process of vitrifying the secondary soot preform 125a.
Preferably, the input of the He gas is 10 to 20 splm, and the input of the Cl2 gas is 1 to 4 vol % of that of the He gas. For example, the secondary soot preform 125a may be heated at 1500° C. for 300 minutes under an atmosphere of the Cl2 gas of 0.375 splm and the He gas of 15 splm.
Conventionally, a secondary soot preform is not dehydrated but sintered. However, the secondary soot preform 125a is dehydrated and sintered in the present invention to produce a secondary transparent soot perform 125b so that there is reduced loss due to the OH group of a macro-bending-insensitive optical fiber manufactured hereafter.
Thereafter, the secondary optical fiber preform 125b manufactured through the aforementioned method is drawn as a macro-bending-insensitive optical fiber through a process that will be described below. The macro-bending-insensitive optical fiber has the same configuration and diameter ratio as the secondary transparent optical fiber preform 125b. The core of the macro-bending-insensitive optical fiber becomes a transmission medium of an optical signal, the inner clad functions to trap the optical signal within the core, and the outer clad functions to increase the diameter of the macro-bending optical fiber. Further, the diameter ratio of the core, inner clad and outer clad of the macro-bending optical fiber is identical with that of the core 122b, inner clad 124b and outer clad 126b of the secondary transparent optical fiber preform 125b.
The furnace 510 heats an end of the secondary transparent optical fiber preform 125b, which has installed inside the furnace 510, at 2000 to 2500° C. to melted the end. Although a macro-bending-insensitive optical fiber 128 drawn from the secondary transparent optical fiber preform 125b has the same configuration as the secondary optical fiber preform 125b, the diameter of the macro-bending-insensitive optical fiber 128 is much smaller than that of the secondary transparent optical fiber preform 125b. Further, in order to prevent the inside of the furnace 510 from being oxidized due to heat, an inert gas is flowed inside the furnace 510.
The cooling device 520 cools the heated macro-bending-insensitive optical fiber 128 drawn from the furnace 510.
The coater 530 applies an ultraviolet curable resin to the macro-bending-insensitive optical fiber 128 passing through the cooling device 520, and the ultraviolet curing device 540 cures the ultraviolet curable resin by radiating ultraviolet rays thereon.
The capstan 550 pulls the macro-bending-insensitive optical fiber 128 with a pre-determined force such that the macro-bending-insensitive optical fiber 128 is continuously drawn from the secondary transparent optical fiber preform 125b while maintaining a pre-determined diameter thereof.
The macro-bending-insensitive optical fiber 128 passing through the capstan 550 is wound around the spool 560.
A loss of an optical fiber in a wavelength of 1383 nm is greatly influenced by the ratio D/d of a diameter d of a core and a diameter D of an inner clad in the macro-bending-insensitive optical fiber. In the macro-bending insensitive optical fiber 128, the maximum loss value in a wavelength of 1310 to 1625 nm is 0.46 dB/km or less, and an OH loss is maintained as 0.320 dB/km or less through the double dehydration (processes (b) and (f) (S12 and S16)) in the process of manufacturing the macro-bending-insensitive optical fiber 128 and D/d of 3.9 or more. Further, a loss value in the wavelength of 1383 mm does not increase even after the macro-bending-insensitive optical fiber 128 has passed through H2 aging, and the loss value in the wavelength of 1383 nm is less than that in a wavelength of 1310 nm even 14 days after the H2 aging.
As described above, there is an advantage in that, since an optical fiber according to the present invention has little OH loss and a low connection loss, it has a good compatibility with an existing LWPF. Further, since the optical fiber meets a transmission characteristic required in a CWDM optical subscriber network and has a small macro-bending loss, it is suitable for even building an optical subscriber network in an environment where bending is excessive.
While the invention has been illustrated and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-59533 | Jun 2006 | KR | national |
