Abstract:
Disclosed is a monitoring system and method of monitoring optical-fiber drawing systems. The scattering monitor includes: a scattering monitor housing provided on a path drawing an optical fiber and having holes aligned on the upper and lower ends of the scattering monitor housing with the optical fiber passing there-through; a reflecting plate surrounding the optical fiber in the scattering monitor housing; a light condenser for converging light reflected from the reflecting plate; and, a light detector for detecting converged light and generating a corresponding electrical signal.

Description:
CLAIM OF PRIORITY  
       [0001]    This application claims priority to an application entitled “ Scattering Monitor In Optical Fiber Drawing Systems, ” filed in the Korean Intellectual Property Office on Jul. 29, 2002 and assigned Serial No. 2002-44758, the contents of which are hereby incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention generally relates to an optical fiber. In particular, the present invention relates to an optical-fiber drawing system for drawing an optical fiber from an optical fiber pre-form.  
           [0004]    2. Description of the Related Art  
           [0005]    In a typical optical-fiber drawing process, an optical fiber pre-form is softened to its melting point and then pulled or drawn into a thin bare optical fiber. This bare optical fiber (also referred to as “bare glass”) is hot enough to be sensitive to external contaminants before it is coated. Therefore, the bare optical fiber must be protected from contaminants such as atmospheric dust. To this end, gas or air is blown towards the bare optical fiber. Further, the bare optical fiber is cooled by passing it through a cooling apparatus. The cooled bare optical fiber is then coated.  
           [0006]    [0006]FIG. 1 illustrates a side view of an optical-fiber drawing system according to the conventional art. In FIG. 1, a furnace  120 , a cooler  140 , a coating applicator  150 , an ultra-violet (UV) curer  170  and a capstan  180  are shown.  
           [0007]    The furnace  120  is hot enough to maintain a temperature of at least 2,000° C. thus softening the end of an optical pre-form in order to generate a bare optical fiber  130  from the softened pre-form.  
           [0008]    The cooler  140  cools the optical fiber to a temperature suitable for coating the bare optical fiber  130  and includes a cooling tube for cooling gas, i.e., helium, through which to flow. Further, a coolant such as cooling water, liquid nitrogen, or the like is circulated through a spacing between the inner and outer walls of the cooling tube so as to insulate the cooler  140 .  
           [0009]    The coating applicator  150  is provided with a path filled with atmospheric gas, through which the bare optical fiber passes. The coating applicator  150  has a retainer in which liquid coating material fed from its storage tank (not shown) is contained. The bare optical fiber is coated in the course of passing through the retainer. The coating material, like various types of UV curable resin, is curable under UV radiation. Alternatively, a thermosetting resin may be used as the coating material.  
           [0010]    The UV curer  170  cures the coating material coated on a circumference of the bare optical fiber, i.e., the UV curable resin under UV radiation.  
           [0011]    The capstan  180  pulls the cured bare optical fiber  160  under a predetermined force so that the cured bare optical fiber can be drawn continuously at a constant diameter.  
           [0012]    The optical fiber  160  has a very small diameter of 125±0.2 μm. Consequently, when the drawn optical fiber has a non-uniform profile resulting from accidental scratching, a microstructure defect of the optical fiber pre-form, unstable coating pressure, etc., during drawing at a high speed, a scattering phenomenon may be created in the optical fiber. If this scattering phenomenon becomes large enough for detection during a megascopic check, most operators may be able to cope with it. In fact, it is difficult to observe a minute scattering phenomenon without the aid of any tool, which acts as a factor of quality failures. In addition, as this scattering phenomenon is dependent on an observing angle, it is difficult to measure precisely.  
         SUMMARY OF THE INVENTION  
         [0013]    Accordingly, the present invention is to provide a scattering monitor in optical-fiber drawing systems, in which quality improvement as well as productivity improvement can be promoted, by monitoring a scattering phenomenon resulting from a non-uniform profile of the optical fiber during an optical-fiber drawing process.  
           [0014]    In one embodiment of the present invention, there is provided a monitoring system for an optical-fiber drawing system, including: a scattering monitor housing provided on a path drawing the optical fiber defining holes aligned on the upper and lower ends of the scattering monitor housing; a reflecting plate surrounding the optical fiber in the housing; a light condenser for converging light reflected from the reflecting plate; and, a light detector for detecting converged light and generating a corresponding electrical signal.  
           [0015]    Preferably, the embodiment provides a controller for measuring the power of the electrical signal and comparing it to a predetermined reference value, that when exceeded, warns an operator of an abnormality. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a side view of an optical-fiber drawing system according to the conventional art;  
         [0017]    [0017]FIG. 2 is a side view of an optical-fiber drawing system according to a preferred embodiment of the present invention;  
         [0018]    [0018]FIG. 3 is a schematic plan view of a scattering monitor of the optical-fiber drawing system; and,  
         [0019]    [0019]FIG. 4 is a schematic front view of a scattering monitor of the optical-fiber drawing system. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    In accordance with the present invention, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same element, although depicted in different drawings, will be designated by the same reference numeral or character. For the purposes of clarity and simplicity, a detailed description of known functions and configurations incorporated herein will be omitted as it may make the subject matter of the present invention unclear.  
         [0021]    [0021]FIG. 2 is a side view of an optical-fiber drawing system according to a preferred embodiment of the present invention. FIG. 3 is a schematic plan view of a scattering monitor of the optical-fiber drawing system. FIG. 4 is a schematic front view of a scattering monitor of the optical-fiber drawing system.  
         [0022]    As shown, the optical-fiber drawing system comprises a furnace  220 , a cooler  240 , a coating applicator  250 , a scattering monitor  270 , an ultra-violet (UV) curer  320 , a capstan  330  and a controller  310 .  
         [0023]    The furnace  220  maintains a temperature of at least 2,000° C. and softens the end of an optical pre-form. The softened pre-form is generated into a bare optical fiber  230 .  
         [0024]    The cooler  240  cools the bare optical fiber  230  to a temperature suitable for coating. The cooler  240  includes a cooling tube (not shown) for a cooling gas, like helium, through which to flow. Further, a coolant such as cooling water, liquid nitrogen, or the like is circulated through a spacing between the inner and outer walls of the cooling tube so as to insulate the cooler  240 .  
         [0025]    The coating applicator  250  is provided with a path filled with atmospheric gas, through which the bare optical fiber passes. The coating applicator  250  has a retainer in which liquid-coating material fed from its storage tank (not shown) is contained. The bare optical fiber  230  is coated in the course of passing through the retainer. This coating material, like various types of UV curable resin, has is curable under UV radiation. Alternatively, thermosetting resin may be used for the coating material.  
         [0026]    The scattering monitor  270  has a sealed housing which can communicate with its external what? through the upper and lower holes  272  and  274 . The coated bare optical fiber  260  passes through the housing  270 , specifically, from the upper hole  272  to the lower hole  274 . The diameter of the upper and lower holes  272  and  274 , respectively, are slightly larger than that of the optical fiber  260 , thereby preventing external light from penetrating the housing through the upper and lower holes  272  and  274 , respectively.  
         [0027]    Referring to FIGS. 3 and 4, the scattering monitor housing  270  is mounted with a reflecting plate  280 , a light condenser  290 , and a light detector  300 .  
         [0028]    The reflecting plate  280  is provided with reflecting film on its inner surface. The reflecting plate  280  is provided as a hollow cylinder in the shape of the letter C. The open portion faces the light condenser. The reflecting plate  280  is installed to surround the optical fiber  260 , enabling scattered light radiated from the circumferential surface of the optical fiber to be reflected through the opening.  
         [0029]    The light condenser  290  converges scattered light reflected from the reflecting plate  280 . The light condenser  290  consists of a convex lens, an aspherical lens, or a combination thereof.  
         [0030]    The light detector  300  functions to detect the converged scattered light, and to transform it into an electrical signal that is outputted to the controller  310 . The light detector  300  consists of a photodiode, a CCD camera, a CdS cell or the like.  
         [0031]    The controller  310  measures scattering levels by the measure of the power of the electrical signal, and then determines a non-uniform profile of the optical fiber  260  on the basis of the measured results. In the controller  310 , an acceptable reference power value is predetermined, and checked against the measured power value to see if it is greater than the reference power value. If the measured power value is greater than the reference power value, the controller  310  can function either to stop drawing the optical fiber or to alert the occurrence of an abnormal operation using a warning device (not shown). In addition, the controller  310  can display the power value of the electrical signal on a display monitor (not shown), so as to allow an operator to check the abnormal operation in real time.  
         [0032]    The UV curer  320  provides UV radiation to the surface of the optical fiber to cure the coating material coated on the optical fiber. Additionally, UV rays incidental to the optical fiber are scattered out of the optical fiber due to a non-uniform profile of the optical fiber  260 .  
         [0033]    The capstan  330  pulls the optical fiber  260  with a given force so that the optical fiber can be continuously drawn from the optical fiber pre-form at a constant diameter.  
         [0034]    As seen above, the scattering monitor in optical-fiber drawing systems according to the present invention has an advantage because it can promote quality improvement and productivity improvement by monitoring a scattering phenomenon resulting from a non-uniform profile of the optical fiber during the optical-fiber drawing process.  
         [0035]    While the invention has been shown and described with reference to a 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. Therefore, this invention is not to be limited unduly to the embodiment set forth herein, but it is to be defined by the appended claims and the equivalents thereof.