Abstract:
A diffusion barrier attached to the cladding layer prevents significant diffusion of a Raman active gas out of the holes in a holey fiber or photonic band gap fiber.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part (CIP) of copending U.S. application Ser. No. 09/907,241 filed Jul. 17, 2001 (now U.S. Pat. No. 6,496,634 issued Dec. 17, 2002), the above application being incorporated herein by reference in its entirety including incorporated material. 
    
    
     FIELD OF THE INVENTION 
     The field of the invention is the field of optical fibers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a sketch of a cross section of the optical fiber of the invention. 
     FIG. 2 shows a sketch of the system of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Copending U.S. application Ser. No. 09/907,241 filed Jul. 17, 2001 (now U.S. Pat. No. 6,496,634 issued Dec. 17, 2002), includes a detailed description of an optical fiber having fluid filled holes for Raman amplification of light. FIG. 1 shows a sketch of a cross section of the optical fiber  10  of the invention. The fiber  10  comprises a core region  12  and a cladding region  14  surrounding the core region. The core region contains a plurality of holes  16  elongated in the axial direction of the fiber. The center region and/or the holes  16  contain a Raman active fluid material  18 . Such Raman active fluids include but are not limited to: hydrogen containing gases such as molecular hydrogen and methane; deuterium containing gases such as molecular deuterium and deuterated methane; and halogen containing gases such as tetrafluoromethane. The improvement of the present invention over U.S. application Ser. No. 09/907,241 comprises a diffusion barrier material  19  which prevents the Raman active material  18  from diff-using out of the fiber. 
     Optical fibers will have a useful life measured in decades, and the material of the cladding  14  is usually fused silica. Fused silica has a relatively open structure which allows diffusion of material such as hydrogen. Such diffusion of the Raman active material  18  will necessarily reduce the Raman gain if the fluid pressure in the fiber changes. Materials for a diffusion barrier  19  such as non metallic materials silicon nitride and borosilicate glass, or metals such as aluminum allow much less diffusion, so that the time for significant diffusion of hydrogen out of the core of the fiber will be lengthened. For purposes of this specification, significant diffusion has occurred when the pressure of the Raman active material  18  drops sufficiently to significantly reduce the Raman gain in the fiber. FIG. 1 shows the diffusion barrier material surrounding the cladding material, but the diffusion barrier may be part of the cladding layer or between the cladding material and the core. 
     FIG. 2 shows a sketch of the system of the invention. Light output from one or more lasers or other sources of light  22  is introduced into the fiber of the invention  20  by an optical apparatus  24  as is known in the art. Optical apparatus  26  is used to conduct light from the fiber  20  to detectors, signal splitters, demodulators, etc  28  as are known in the art. Control apparatus  26  controls the light generator  22  and optical apparatus  24 . 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.