Method of forming a grating in a waveguide

Abstract

A refractive-index grating fabricated in an optical fiber having a multilayer coating and a method for making refractive-index patterns such as gratings in optical fibers such that the mechanical properties of the original fiber are preserved. The patterns are written into the optical fiber by partially stripping away the outer coating of the fiber, exposing the core of the fiber through the remainder of the coating with an actinic radiation to form the pattern in the photosensitive core of the fiber, followed by recoating the fiber in the stripped area to provide protection of the newly formed pattern from corruption and to preserve the mechanical properties of the fiber.

What is claimed is:  
     
         1 . A waveguide comprising: 
 a core region sensitive to an actinic radiation; and    a coating having at least an inner layer and a protective layer where said inner layer is at least half as transmissive as absorptive for said actinic radiation.    
     
     
         2 . The waveguide of  claim 1 , wherein the actinic radiation has a wavelength longer than 220 nm.  
     
     
         3 . The waveguide of  claim 1 , wherein the protective layer is less transmissive than absorptive of the actinic radiation.  
     
     
         4 . The waveguide of  claim 1  wherein said protective layer is removable without removing the inner layer.  
     
     
         5 . The waveguide of  claim 4 , wherein said protective layer is removable by mechanical means.  
     
     
         6 . The waveguide of  claim 4 , wherein said protective layer is removable by chemical means.  
     
     
         7 . The waveguide of  claim 1 , wherein said protective layer is dissolvable.  
     
     
         8 . The waveguide of  claim 1 , wherein said inner layer is a polymer.  
     
     
         9 . The waveguide of  claim 8 , wherein said inner layer is polyacrylate.  
     
     
         10 . The waveguide of  claim 8 , wherein said inner layer is Teflon.  
     
     
         11 . The waveguide of  claim 8 , wherein said inner layer is a silicone resin.  
     
     
         12 . The waveguide of  claim 1 , wherein the core region is formed in an optical fiber.  
     
     
         13 . The waveguide of  claim 12 , wherein the core region further comprises a core surrounded by a cladding layer.  
     
     
         14 . A method of forming a grating in an optical waveguide having a core and a coating, the coating having at least an inner layer and a protective layer, comprising the steps of: 
 removing the protective layer of the coating in a selected portion of the waveguide;    forming a pattern within the core of the optical waveguide by illuminating the waveguide with actinic radiation.    
     
     
         15 . The method of  claim 14 , wherein the step of illuminating the waveguide includes illuminating the waveguide in a manner which is non-uniform along the length of the waveguide.  
     
     
         16 . The method of  claim 14 , wherein the step of illuminating the waveguide includes illuminating the waveguide in a manner which is uniform along the length of the waveguide.  
     
     
         17 . The method of  claim 14 , further comprising the steps of: 
 providing a phase mask;    illuminating the waveguide by passing the actinic radiation through the phase mask to form a pattern of regions having varying refraction indexes in the core of the waveguide.    
     
     
         18 . The method of  claim 14 , further comprising the step of recoating the waveguide with a protective layer after forming the pattern in the core.  
     
     
         19 . The method of  claim 18 , wherein the waveguide is recoated with a polymer.  
     
     
         20 . The method of  claim 18 , wherein the waveguide is recoated with polymethacrylate.  
     
     
         21 . The method of  claim 19  wherein the waveguide is recoated with a polymer selected from the group consisting of aliphatic polyacrylates, silesesquioxanes, alkyl-substituted silicones and vinyl ethers.  
     
     
         22 . The method of  claim 14 , wherein the step of illuminating includes illuminating the waveguide with directing Ultra-Violet radiation having a wavelength in a range of 220 nm-390 nm.  
     
     
         23 . The method of  claim 14 , wherein the step of illuminating the waveguide includes illuminating the waveguide with Ultra-Violet radiation having a wavelength of less than 275 nm.  
     
     
         24 . The method of  claim 14 , further comprising the step of loading the waveguide with a material selected from the group consisting of Hydrogen (H 2 ) and its isotopes prior to the step of forming the pattern.  
     
     
         25 . The method of  claim 24 , wherein the isotope of Hydrogen selected to load the waveguide prior to the step of forming the pattern is Deuterium (D 2 ).  
     
     
         26 . A fiber optic refractive index grating formed in an optical fiber, comprising: 
 an optical fiber having a core region surrounded by a cladding layer, the core region being sensitive to actinic radiation;    a coating surrounding the cladding layer, the coating having at least an inner layer and a protective layer, the inner layer being at least partially transparent to actinic radiation and the protective layer being substantially non-transparent to actinic radiation;    a pattern of varying refractive indexes formed in a selected portion of the core region of the optical fiber.    
     
     
         27 . The fiber optic refractive index grating of  claim 26 , wherein the portion of the core region having the pattern has a mechanical breaking strength greater than 50% of the mechanical breaking strength of the remainder of the optical fiber.  
     
     
         28 . The fiber optic refractive index grating of  claim 26 , wherein the portion of the core region having the pattern has a mechanical breaking strength at least 90% of the mechanical breaking strength of the remainder of the optical fiber.  
     
     
         29 . The refractive index grating of  claim 26 , wherein the grating is a Bragg grating.  
     
     
         30 . The refractive index grating of  claim 26 , wherein the grating is a long period grating.  
     
     
         31 . The refractive index grating of  claim 30 , wherein the grating has an average grating period within the range of 10 microns to 2000 microns.  
     
     
         32 . The refractive index grating of  claim 30 , wherein the refractive index of the inner layer is less than the refractive index of the cladding layer.