Abstract:
A deposition burner for an optical fiber preform includes: a first body including a plurality of injection tubes for fusing and emitting raw materials; a second body assembled with the first body in a shape to envelope the outer surface of the first body; a moving member disposed in a vertical orientation between the inner surface of the second body and the outer surface of the first body for moving in a longitudinal direction; and a switch type injection tube opened and closed along the rim of the one end of the first body in response to a movement of the moving member in the longitudinal direction.

Description:
CLAIM OF PRIORITY  
       [0001]     This application claims priority under 35 U.S.C. § 119 to an application entitled “Deposition Burner for Optical Fiber Preform,” filed in the Korean Intellectual Property Office on Dec. 16, 2004 and assigned Serial No. 2004-107073, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to optical fiber and in particular, to a silica glass, i.e., optical fiber preform, and an apparatus for manufacturing the same.  
         [0004]     2. Description of the Related Art  
         [0005]     A common method of manufacturing an optical fiber preform typically includes a vapor-phase deposition method and a sol-gel process. The sol-gel process involves manufacturing silica glass by pouring liquid raw materials into a mold, processing the liquid raw materials into a gel state, and sintering the gel materials. The sintering method is economical, and the composition of a target product can be easily controlled since it is generally performed at a low temperature.  
         [0006]     The vapor-phase deposition method includes a modified chemical vapor deposition (MCVD) method, a vapor phase axial deposition (VAD) method, an outside vapor deposition (OVD) method, etc. The vapor-phase deposition has an advantage in that a high quality optical fiber preform can be obtained but its productivity is low and expensive manufacturing equipments must be used as a solid optical fiber preform is manufactured using a vapor phase reaction at a high temperature, reaching up to around 1800° C., for a long time.  
         [0007]     As shown in  FIGS. 1 and 2 , a deposition burner  10  for the optical fiber preform fuses chemical compounds for forming SiO 2  by a plurality of injection tubes  11  deployed according to a predetermined pattern. The chemical compounds for forming SiO 2  include SiCl 4  and OMCTS. SiO 2  is formed by fusing the chemical compounds in the burner  10  using oxygen and nitrogen gas.  
         [0008]      FIGS. 3 and 4  are schematic diagrams of a deposition equipment for an optical fiber preform  1  using the burner  10 . The chemical compounds fused and emitted through the burner  10  are deposited while flowing around the optical fiber preform  1 , and undeposited SiO 2  and by-products after fusing are discharged to the outside through a discharge unit  19 .  
         [0009]     For conventional deposition burners as described above, if they are in a produced state, it is impossible to change a deposition condition during an optical fiber preform deposition process except independently controlling the amount of supplied gas and the mass flux of oxygen and nitrogen gas used for fusing. In the OVD method, a diameter of the optical fiber preform increases in response to a deposition progress of the optical fiber preform, thereby resulting in a problem in that the deposition cannot be uniformly achieved. This problem is mainly caused by steadily maintaining flames emitted by the conventional deposition burners regardless of the change in the deposition condition accompanied by a gradual increase of the diameter of the optical fiber preform.  
         [0010]     Referring to  FIGS. 3 and 4 , flame  13  emitted from the burner  10  covers and flows around the optical fiber preform  1 , showing a separation phenomenon of unable to maintain a constant flow around the optical fiber preform  1  after going a certain distance away from the burner  10 . Due to this separation phenomenon, when the diameter of the optical fiber preform  1  gradually increases, separation points  17  are grow apart from each other, thereby gradually expanding a region in which the flow of the flame  13  is not uniform.  
         [0011]     As a result, the separation phenomenon is an obstacle preventing an optical fiber preform from being uniformly deposited along the optical fiber preform.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention provides a deposition burner for an optical fiber preform that enables an uniform deposition of the optical fiber preform by changing an injection condition in response to a gradual increase in the diameter of the optical fiber preform.  
         [0013]     In one embodiment, there is provided a deposition burner for an optical fiber preform which includes: a first body including a plurality of injection tubes for fusing and emitting raw materials that are formed at one end thereof; a second body assembled with the first body in a shape of enveloping the outer surface of the first body; a moving member moving in a longitudinal direction and located between the inner surface of the second body and the outer surface of the first body; and a switch type injection tube opened and closed along the rim of one end of the first body in response to a movement of the moving member on the first body in the longitudinal direction.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The above features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:  
         [0015]      FIG. 1  is a cross sectional diagram of a deposition burner for an optical fiber preform according to a prior art;  
         [0016]      FIG. 2  is a plan view of the burner shown in  FIG. 1 ;  
         [0017]      FIGS. 3 and 4  are schematic diagrams of a deposition equipment for an optical fiber preform using the burner shown in  FIG. 1 ;  
         [0018]      FIG. 5  is a cross sectional diagram of a deposition burner for an optical fiber preform according to an embodiment of the present invention;  
         [0019]      FIG. 6  is a plan view of the burner shown in  FIG. 5 ;  
         [0020]      FIG. 7  is a cross sectional diagram of the burner shown in  FIG. 5  after a moving member of the burner has moved; and  
         [0021]      FIGS. 8 and 9  are schematic diagrams of a deposition equipment for an optical fiber preform using the burner shown in  FIG. 5 . 
     
    
     DETAILED DESCRIPTION  
       [0022]     Now, embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the drawings, the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings. For the purposes of clarity and simplicity, well-known functions or constructions are not described in detail as they would obscure the invention in unnecessary detail.  
         [0023]     Referring to FIGS.  5  to  7 , the burner  100  includes a first body  101 , a second body  102 , and the moving member  103 .  
         [0024]     The first body  101  includes a plurality of injection tubes  111 ,  112 ,  113 , and  114  formed at one end thereof and a plurality of inlets  119  formed on the outer surface to feed chemical compounds. The injection tubes are comprised of a first injection tube  111  formed at a center portion of the first body  101 , a plurality of second injection tubes  112  deployed in an outer circumference direction from the first injection tube  111 , a plurality of third injection tubes  113  deployed by at least one row in the outer circumference direction from the second injection tubes  112 , and a plurality of fourth injection tubes  114  deployed in the outer circumference direction from the third injection tubes  113 .  
         [0025]     SiCl 4  and OMCTS are fed into the first injection tube  111 , O 2  and N 2  are fed into the second injection tubes  112 , mixed gas such as CH 4 +O 2  and H 2 +O 2  are fed into the third injection tubes  113 , and O 2 , N 2  and Ar are fed into the fourth injection tubes  114 . The composition of the chemical compounds fed into the injection tubes can be selectively changed by a manufacturer according to the desired characteristic of optical fiber to be manufactured.  
         [0026]     The second body  102  is assembled with the first body  101  to envelop the outer surface of the first body  101  and guides the flame emitted from the burner  100  to maintain a constant shape by being further extended by a predetermined length from the one end of the first body  101 .  
         [0027]     The moving member  103  is assembled between the outer surface of the first body  101  and the inner surface of the second body  102 , which are apart from each other by a predetermined distance.  
         [0028]     The moving member  103  is assembled to move in a longitudinal direction of the first body  101  and a ring-shaped cover plate  131  formed at one end thereof. The cover plate  131  serves to close a space between the outer surface of the first body  101  and the inner surface of the second body  102 , forming a switch type injection tube  135  (shown in  FIG. 7 ) along the outer surface of the first body  101  in response to a movement of the moving member  103 .  
         [0029]     That is, according to the movement of the moving member  103 , the space between the outer surface of the first body  101  at one end and the inner surface of the cover plate  131  is opened, thereby forming another type of an injection tube. For the formation of the switch type injection tube  135 , a slope  115  is formed on the outer surface of the first body  101  at one end, and the inner surface of the cover plate  131  is formed to correspond to the slope  115 . The slope  115  is formed so that its diameter gradually decreases towards the one end of the first body  101 .  
         [0030]     The switch type injection tube  135  is closed in a state in which the outer surface of the first body  101  meets the inner surface of the moving member  103 , and is opened in a state in which the outer surface of the first body  101  is apart from the inner surface of the moving member  103  due to the movement of the moving member  103 . It is preferable that gas emitted from the switch type injection tube  135  is O 2 , N 2  and Ar, and an inlet  119  to feed the gas can be formed on the outer surface of the second body  102 .  
         [0031]     In the state in which the switch type injection tube  135  is closed, the surface of one end of the cover plate  131  contacts the surface of the one end of the first body  101 .  
         [0032]     In order for the flame emitted from the burner  100  to form the constant shape, it is preferable that a discontinuous shape is minimized on the surface of one end of the burner  100 . To achieve this, it is preferable that a boundary line  133  is formed by matching the rim of the first body  101  at one end to the surface end of the cover plate  131 .  
         [0033]     To actuate the moving member  103 , a driving member  139  is assembled with the burner  100 . One end of the driving member  139  is supported by the outer surface of the first body  101 , and the other end is supported by the other end of the moving member  103 . It is preferable that the driving member  139  is made of a metal capable of varying its shape in response to a change in temperature, e.g., a bimetal. The bimetal is constituted by uniting two metals having different rates of thermal expansion, thereby varying its shape according to the difference in the thermal expansion rate caused by temperature change.  
         [0034]     In additional to the bimetal, the driving member  139  can be constituted using a metal having a rate of thermal expansion so that the switch type injection tube  135  can be opened and closed as the moving member  103  moves. As a metal satisfying this condition, there exist an aluminum alloy, a copper alloy, and a zinc alloy.  
         [0035]     It can be understood that a hastelloy series alloy or a quartz material having a low rate of thermal expansion may be used for components, except the driving member  139 , such as the first body  101 , the second body  102 , and the moving member  103 .  
         [0036]     In response to a change in the shape of the driving member  139  due to the surrounding temperature changes while the optical fiber preform is being deposited, the moving member  103  moves to enable the switch type injection tube  135  to open.  
         [0037]      FIG. 8  is a schematic diagram of a deposition device to manufacture an optical fiber preform  201  using the burner  100  described above. In particular,  FIG. 8  shows an initial state of an optical fiber preform process.  FIG. 9  illustrates a state in which a diameter of the optical fiber preform  201  is increased after the optical fiber preform process is performed for a predetermined time period. By-products after fusing, which are emitted from the burner  100  but not deposited on the optical fiber preform  201 , are discharged to the outside through a discharge unit  209 .  
         [0038]     In operation, as the deposition process continues, the diameter of the optical fiber preform  201  is gradually increased, thereby making a distance between the outer surface of the optical fiber preform  201  and the burner  100  closer while increasing the surface area of the optical fiber preform  201  facing the burner  100 . As a result, radiant heat of the optical fiber preform  201  transferred to the burner  100  gradually increases as the deposition process continues.  
         [0039]     An increase in the radiant heat transferred to the burner  100  causes the surrounding temperature of the moving member  139  to be increased as well. This causes the transformation of the moving member  139  to gradually move downward, thus enabling the switch type injection tube  135  gradually open. As more deposition of the optical fiber preform  201  continues, the radiant heat transferred to the burner  100  increases, thereby increasing the size of the switch type injection tube  135 .  
         [0040]     The gas emitted from the switch type injection tube  135  flows around flame  203  emitted from the burner  100 , thereby maintaining the shape of the flame  203  constantly and preventing separation points  207  of the flame  203  from being farther apart from each other as in the prior art. Thus, a region in which the flame  203  discontinuously flows between the separation points  207  is restrained from being extended, thereby maintaining the deposition of the optical fiber preform  201  uniformly.  
         [0041]     As described above, a deposition burner according to the present invention can uniformly maintain the flow of flame flowing around the optical fiber preform even when diameter of the optical fiber preform increases, by opening a switch type injection tube that is activated due to the surrounding temperature of the burner that increases in response to a radiation heat transferred from the optical fiber preform to the burner. Thus, quality of the optical fiber preform is improved by uniformly maintaining the deposition of the optical fiber preform by changing an injection condition to be suited to a change of a deposition condition of the optical fiber preform. In addition, while equipments for a separate control such as a mass flux control are required to respond to the change in the deposition condition in a prior art, the deposition burner according to the present invention changes the injection condition using the switch type injection tube, thereby simplifying a deposition equipment.  
         [0042]     While the invention has been shown and described with reference to a certain preferred embodiment 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.