Low loss optical fiber designs and methods for their manufacture

Abstract

The specification describes an improved optical fiber produced by a hybrid VAD/MCVD process. The core of the fiber is produced using VAD and the inner cladding layer has a depressed index and is produced using MCVD. In preferred embodiments, the optical power envelope is essentially entirely contained in VAD produced core material and the MCVD produced depressed index cladding material. Optical loss is minimized by confining most of the optical power to the VAD core where OH presence is low, as well as by maximizing the optical power in the un-doped silica region. The MCVD substrate tube material is essentially devoid of optical power.

1 . Method for the manufacture of optical fiber comprising: 
 (a) preparing an optical fiber preform,    (b) heating the preform to the softening temperature, and    (c) drawing an optical fiber from the preform,    the invention characterized in that the preform comprises:    an inner core region with delta >0.001,    an outer core region with delta −0.001 to 0.0005,    a first cladding region with delta <−0.001,    the invention further characterized in that the inner core region and the outer core region are formed using VAD or OVD.    
   
   
       2 . The method of  claim 1  wherein the first cladding region is formed using MCVD.  
   
   
       3 . The method of  claim 1  wherein the first cladding region is formed by a high purity tube with hydroxyl concentration less than about 50 ppb.  
   
   
       4 . The method of  claim 1  wherein the preform is produced by: 
 i. forming a core rod, the core rod comprising the inner core region and the outer core region,    ii. inserting the core rod into a tube, the tube comprising the first cladding region, and    iii collapsing the tube around the core rod.    
   
   
       5 . The method of  claim 4  wherein the core rod is produced by heating the core body in a furnace to stretching/elongate the core rod.  
   
   
       6 . The method of  claim 4  wherein the core rod is produced by removing the outer surface of the stretched/elongated core rod to a depth of at least 0.15 mm using plasma etching.  
   
   
       7 . The method of  claim 4  wherein the core rod is produced by removing the outer surface of the stretched/elongated, plasma etched core rod to a depth of at least 30 microns using acid etching.  
   
   
       8 . The method of  claim 4  wherein after inserting the core rod into the tube but prior to collapsing the tube, the core rod is dried and etched by heating the assembly in the presence of a drying agent and a source of fluorine.  
   
   
       9 . The method of  claim 8  wherein the drying agent is selected from the group consisting of chlorine gas or CCl 4  and the source of fluorine is selected from the group consisting of SiF 4 , SF 6 , and C 2 F 6 .  
   
   
       10 . The method of  claim 1  wherein the fiber attenuation at 1383 nm is less than 0.4 dB/km.  
   
   
       11 . The method of  claim 10  wherein the fiber attenuation at 1383 nm is less than 0.35 dB/km.  
   
   
       12 . The method of  claim 11  wherein the fiber attenuation at 1383 nm is less than 0.31 dB/km.  
   
   
       13 . The method of  claim 4  wherein the average hydroxyl concentration within a 1 um thick annular region centered about the radius of the core rod-tube interface is less than about 25 ppb.  
   
   
       14 . Method for transmitting a light signal through an optical fiber the light signal having an approximately Gaussian shaped power envelope, the optical fiber comprising: 
 an inner core region with delta >0.001,    an outer core region with delta −0.001 to 0.0005,    a first cladding region with delta <−0.001,    wherein the power envelope is distributed according to:                                                Inner core   50-80%         Outer core   20-40%         First cladding   >5%.                                               
   
   
       15 . Method of  claim 14  wherein the outer core region has index essentially equal to that of undoped silica, except for the germanium diffusion tail that naturally occurs in VAD or OVD soot processing.  
   
   
       16 . An optical fiber comprising: 
 an inner core region with delta >0.001,    an outer core region with delta −0.001 to 0.0005,    a first cladding region with delta <−0.001,    
   
   
       17 . The optical fiber of  claim 16  where the 1550 nm attenuation is less than 0.180 dB/km.  
   
   
       18 . The optical fiber of  claim 17  where the 1550 nm attenuation is less than 0.175 dB/km.  
   
   
       19 . The optical fiber of  claim 16  where the 1383 nm attenuation is less than 0.31 dB/km.  
   
   
       20 . The optical fiber of  claim 16  where the Aeff at 1550 nm is about 80 um2.  
   
   
       21 . The optical fiber of  claim 20  where the cable cutoff wavelength is less than 1260 nm.  
   
   
       22 . The optical fiber of  claim 16  where the Aeff at 1550 nm is >100 um 2 .  
   
   
       23 . The optical fiber of  claim 22  where the cable cutoff wavelength is less than about 1530 nm.  
   
   
       24 . The optical fiber of  claim 23  where the 20 mm diameter macrobending loss is less than 2 dB/m.  
   
   
       25 . The optical fiber of  claim 20  where the outer cladding is fluorine doped.  
   
   
       26 . The optical fiber of  claim 16  where the inner core region has a radius of 2-8 microns.  
   
   
       27 . The optical fiber of  claim 26  where the outer core region has a radius of 3-10 microns.  
   
   
       28 . The optical fiber of  claim 16  where the First cladding has a radius of 5-25 microns.  
   
   
       29 . The optical fiber of  claim 16  wherein the inner core region and the outer core region have a combined radius of 5-12 microns.  
   
   
       30 . An optical fiber preform having a VAD core and an MCVD cladding, the MCVD cladding having at least one depressed index region.  
   
   
       31 . The optical fiber of  claim 17  where the fiber is drawn at speeds of about 15 m/s or higher.  
   
   
       32 . The optical fiber of  claim 16  where the sum of the power-weighted Ge and F concentrations fall within the range of about 1.0 to 2.0 wt %.