Multimode optical fiber for high rate LAN, method for manufacturing the same, and test bed thereof

Abstract

Disclosed is a method for manufacturing a multimode optical fiber for high data rate LAN using MCVD, which includes a deposition process for forming a clad layer and a core layer, doped with an additive for controlling a refractive index, on an inner wall of a quartz tube by injecting a deposition gas into the quartz tube and applying heat to outside of the quartz tube; and a collapse process, which is repeatedly conducted N times, for filling up a gap in the quartz tube by applying heat of a temperature over a deposition temperature to the quartz tube after the core layer is completely deposited. In the method, together with an N−1 th collapse process, an etching process of injecting a reaction gas for etching into the quartz tube is conducted in order to eliminate a portion of which refractive index is transformed due to evaporation of the additive.

1 . A method for manufacturing a multimode optical fiber using MCVD (Modified Chemical Vapor Deposition), comprising: 
 a deposition process for forming a clad layer and a core layer, to which an additive for controlling a refractive index is doped, on an inner wall of a quartz tube by injecting a deposition gas into the quartz tube and applying heat to outside of the quartz tube; and    a collapse process, which is repeatedly conducted N times, for filling up a gap in the quartz tube by applying heat of a temperature over a deposition temperature to the quartz tube after the core layer is completely deposited,    wherein, together with an N−1 th  collapse process, an etching process of injecting a reaction gas for etching into the quartz tube is conducted in order to eliminate a portion of which refractive index is transformed due to evaporation of the additive.    
     
     
         2 . The method for manufacturing a multimode optical fiber according to  claim 1 , wherein the additive for controlling a refractive index is GeO 2 .  
     
     
         3 . The method for manufacturing a multimode optical fiber according to  claim 1  or  2 , wherein the reaction gas for etching is O 2  and C 2 F 6 .  
     
     
         4 . The method for manufacturing a multimode optical fiber according to  claim 3 , 
 wherein a collapse rate at the N−1 th  collapse process is set to 2.5 to 4.5 mm 2 /s, and    wherein a flow ratio of O 2  to C 2 F 6  is in the range of 2.5 to 30.    
     
     
         5 . The method for manufacturing a multimode optical fiber according to  claim 3 , 
 wherein a flow rate of O 2  is in the range of 50 to 120 sccm, while a flow rate of C 2 F 6  is in the range of 4 to 20 sccm.    
     
     
         6 . The method for manufacturing a multimode optical fiber according to  claim 1  or  2 , wherein a positive pressure is applied to inside of the quartz tube during the collapse process.  
     
     
         7 . The method for manufacturing a multimode optical fiber according to  claim 6 , wherein the positive pressure is in the range of 0 to 10 mmWC.  
     
     
         8 . A multimode optical fiber for an optical LAN (Local Area Network), which has a core diameter of 50±3 μm, transmits a signal of 1-gigabit (Gb) level at 850 nm and 1300 nm, and has a transmission distance more than 600 m at both wavelengths, 
 wherein, among DMD (Differential Mode Delay) features at 850 nm, a maximum time delay difference at the entire area of a core is within 2.0 ns/km, and    wherein a maximum time delay difference in a range where a radial offset is 5 to 18 μm is within 2.0 ns/km.    
     
     
         9 . The multimode optical fiber according to  claim 8 , wherein an optical fiber having a transmission distance more than 600 m and 2000 m at 850 nm and 1300 nm respectively is characterized in that: 
 among DMD features at 850 nm, a maximum time delay difference at the entire area of a core is within 2.0 ns/km,    a maximum time delay difference in a range where a radial offset is 5 to 18 μm is within 1.0 ns/km, and    all time delay differences of the core except for a center is more than 0.4 ns/km.    
     
     
         10 . A multimode optical fiber for an optical LAN, which has a core diameter of 62.5±3 μm, transmits a signal of 1-gigabit (Gb) level at 850 nm and 1300 nm, and has a transmission distance more than 300 m and 500 m at 850 nm and 1300 nm respectively, 
 wherein, among DMD features at 850 nm, a maximum time delay difference at the entire area of a core is within 5.0 ns/km, and    wherein a maximum time delay difference in a range from a core center to a point where a radial offset is 16 μm is within 3.5 ns/km.    
     
     
         11 . A multimode optical fiber for an optical LAN, which has a core diameter of 50±3 μm or 62.5±3 μm, transmits a signal of 1-gigabit (Gb) level at 850 nm and 1300 nm, and has a transmission distance more than 500 m and 1000 m at 850 nm and 1300 nm respectively, 
 wherein, among DMD features at 850 nm, a maximum time delay difference at the entire area of a core is within 3.0 ns/km,    wherein a maximum time delay difference in a range from a core center to a point where a radial offset is 16 μm is within 2.0 ns/km, and    wherein all time delay differences of the core except for the center is more than 0.4 ns/km.    
     
     
         12 . A multimode optical fiber for an optical LAN, which has a core diameter of 50±3 μm, transmits a signal of 10-gigabit (Gb) level at 850 nm, and has a transmission distance more than 300 m, 
 wherein, among DMD features at 850 nm, a maximum time delay difference at the entire area of a core is within 0.3 ns/km, and    wherein a maximum time delay difference in a range where a radial offset is 5 to 18 μm is within 0.3 ns/km.    
     
     
         13 . The multimode optical fiber according to  claim 12 , wherein an optical fiber having a transmission distance more than 500 m is characterized in that: 
 a maximum time delay difference at the entire area of a core is within 0.15 ns/km, and    a maximum time delay difference in a range where a radial offset is 5 to 18 μm is within 0.15 ns/km.    
     
     
         14 . A test bed for evaluating transmission characteristics of a multimode optical fiber used for a gigabit level optical transmission system, comprising: 
 a light source and a photo-detector substantially connected to both ends of an optical fiber sample to be tested;    a fiber shaker provided to at lease one side of the optical fiber sample to give shaking thereto;    a bit error rate tester connected to the light source and the photo-detector for detecting an error of an optical signal;    a visual analyzer connected to the photo-detector for visually displaying a waveform of a received light;    an optical powermeter for measuring an output level of the received light; and    a variable optical attenuator combined to one side of the optical fiber sample for the purpose of attenuating control of the optical signal.