Holey optical fiber with random pattern of holes and method for making same

Abstract

A random array of holes is created in an optical fiber by gas generated during fiber drawing. The gas forms bubbles which are drawn into long, microscopic holes. The gas is created by a gas generating material such as silicon nitride. Silicon nitride oxidizes to produce nitrogen oxides when heated. The gas generating material can alternatively be silicon carbide or other nitrides or carbides. The random holes can provide cladding for optical confinement when located around a fiber core. The random holes can also be present in the fiber core. The fibers can be made of silica. The present random hole fibers are particularly useful as pressure sensors since they experience a large wavelength dependant increase in optical loss when pressure or force is applied.

1 - 21 . (canceled) 
   
   
       22 . A method for making a random hole optical fiber, comprising the steps of:
 a) heating a fiber preform containing a gas generating material that generates gas bubbles when heated; and   b) drawing the heated fiber preform so that the bubbles are drawn into tubes.   
   
   
       23 . The method of  claim 22  wherein the gas generating material is a compound of elements comprising silicon and nitrogen. 
   
   
       24 . The method of  claim 22  wherein the gas generating material is provided in the preform in the form of a liquid precursor. 
   
   
       25 . (canceled) 
   
   
       26 . The method of  claim 22  further comprising the step of supplying oxygen to the interior of the preform. 
   
   
       27 . The method of  claim 22  wherein the preform comprises a glass powder combined with the gas generating material. 
   
   
       28 . The method of  claim 22  wherein the gas bubbles are generated by oxidation of the gas generating material. 
   
   
       29 - 32 . (canceled) 
   
   
       33 . The method of  claim 23 , wherein the gas generating material comprises silicon nitride. 
   
   
       34 . The method of  claim 23 , wherein the gas generating material comprises silicon nitrate. 
   
   
       35 . The method of  claim 22 , wherein the gas generating material comprises silicon carbide. 
   
   
       36 . A method for making a holey optical fiber, comprising the steps of:
 a) providing a fiber perform comprising an optical material and a second material which is a compound of elements comprising silicon and nitrogen; and   b) drawing the fiber preform into the holey optical fiber such that the second material causes bubbles to remain in the holey optical fiber once the holey optical fiber is formed.   
   
   
       37 . The method of  claim 36 , wherein the second material comprises silicon nitride. 
   
   
       38 . The method of  claim 37 , wherein the silicon nitride comprises less than 1% by weight of the optical material and the second material. 
   
   
       39 . The method of  claim 38 , wherein the silicon nitride comprises 0.01-0.5% by weight of the optical material and the second material. 
   
   
       40 . The method of  claim 39 , wherein the silicon nitride comprises 0.04-0.1% by weight of the optical material and the second material. 
   
   
       41 . The method of  claim 36 , wherein the second material comprises silicon nitrate. 
   
   
       42 . The method of  claim 36 , wherein the bubbles in the holey optical fiber form a random distribution. 
   
   
       43 . The method of  claim 42 , wherein the random distribution varies along a length of the holey optical fiber. 
   
   
       44 . The method of  claim 36 , wherein the bubbles are of varying sizes in the holey optical fiber. 
   
   
       45 . A method for forming an optical fiber, the method comprising:
 (a) providing a preform; and   (b) forming the optical fiber from the preform so as to form a holey region with a random and non-uniform array of holes, wherein the random and non-uniform array of holes varies along a length of the optical fiber.   
   
   
       46 . The method of  claim 45 , wherein the holes contain a gas. 
   
   
       47 . The method of  claim 46 , wherein the gas consists substantially of N 2 . 
   
   
       48 . The method of  claim 46 , wherein the gas consists substantially of CO 2 . 
   
   
       49 . The method of  claim 46 , wherein the gas consists substantially of carbon monoxide. 
   
   
       50 . The method of  claim 46 , wherein the gas consists substantially of nitrogen oxides. 
   
   
       51 . The method of  claim 46 , wherein the gas includes at least one of N 2 , CO 2 , carbon monoxide, and nitrogen oxides. 
   
   
       52 . The method of  claim 46 , wherein the gas consists substantially of an inert gas. 
   
   
       53 . A method of making an optical fiber having a first material with a first index of refraction and a surrounding second material with a second index of refraction that is lower than the first index of refraction, the method comprising:
 (a) locating said first material within said second material;   (b) trapping gas in said second material to randomly locate gas bubbles in said second material so as to increase the porosity of said second material to lower the second index of refraction as compared to the index of retraction of said first material; and   (c) drawing said first and second materials to stretch said bubbles and to form the optical fiber in which said second material guides light along said first material.   
   
   
       54 . The method of  claim 53 , wherein said bubbles are located within said second material prior to said first material being located within said second material. 
   
   
       55 . The method of  claim 53 , wherein said bubbles are created by a gas generating material. 
   
   
       56 . The method of  claim 55 , wherein said gas generating material is a solid. 
   
   
       57 . The method of  claim 55 , wherein said gas is trapped by locating said gas generating material within said second material and causing said gas generating material to decompose to create said bubbles. 
   
   
       58 . The method of  claim 55 , wherein said gas is trapped by locating said gas generating material within said second material and causing said gas generating material to oxidize to create said bubbles. 
   
   
       59 . The method of  claim 53 , wherein the gas bubbles consist substantially of N 2 . 
   
   
       60 . The method of  claim 53 , wherein the gas bubbles consist substantially of CO 2 . 
   
   
       61 . The method of  claim 53 , wherein the gas bubbles consist substantially of carbon monoxide. 
   
   
       62 . The method of  claim 53 , wherein the gas bubbles consists substantially of nitrogen oxides. 
   
   
       63 . The method of  claim 53 , wherein the gas bubbles include at least one of N 2 , CO 2 , carbon monoxide, nitrogen oxides and an inert gas. 
   
   
       64 . The method of  claim 53 , wherein the gas bubbles consist substantially of an inert gas. 
   
   
       65 . A method of making optical fiber having a core with a first index of refraction and a cladding with a second index of refraction that is lower than the first index of refraction, the method comprising:
 (a) locating said core within said cladding;   (b) trapping gas in said cladding to randomly locate bubbles in said cladding so as to increase the porosity of said cladding, thereby lowering the second index of refraction as compared to the first index of refraction; and   (c) drawing said core and cladding to stretch said bubbles and to form said optical fiber in which the said cladding guides light along said core.   
   
   
       66 . The method of  claim 65 , wherein said bubbles are located within said cladding prior to said core being located within said cladding. 
   
   
       67 . The method of  claim 65 , wherein said bubbles are created by a gas generating material. 
   
   
       68 . The method of  claim 67 , wherein said gas generating material is a solid. 
   
   
       69 . The method of  claim 67 , wherein said gas is trapped by locating said gas generating material within said cladding and causing said gas generating material to decompose to create said bubbles. 
   
   
       70 . The method of  claim 67 , wherein said gas is trapped by locating said gas generating material within said cladding and causing said gas generating material to oxidize to create said bubbles. 
   
   
       71 . The method of  claim 65 , wherein the gas bubbles consist substantially of N 2 . 
   
   
       72 . The method of  claim 65 , wherein the gas bubbles consist substantially of CO 2 . 
   
   
       73 . The method of  claim 65 , wherein the gas bubbles consist substantially of carbon monoxide. 
   
   
       74 . The method of  claim 65 , wherein the gas bubbles consist substantially of nitrogen oxides. 
   
   
       75 . The method of  claim 65 , wherein the gas bubbles include at least one of N 2 , CO 2 , carbon monoxide, nitrogen oxides and an inert gas. 
   
   
       76 . The method of  claim 65 , wherein the gas bubbles consist substantially of an inert gas.