Method and apparatus for reduction on optical coupling between pump lasers and photodetectors in optical amplifiers

Abstract

In a first aspect, the present invention comprises an optical filter comprising a fiber having a core and a cladding and a light-absorbing coating applied onto a portion of the fiber cladding, the coating attenuating loosely bound cladding modes. In another aspect, the invention comprises a fiber amplifier apparatus comprising fibers for delivering pump laser light and for monitoring signal light and at least one photodetector optically coupled to a monitoring fiber, wherein either an optical filter is disposed between a monitoring fiber and a photodetector or at least one of the fibers has a core and a cladding and a light-absorbing coating applied onto a portion of the fiber cladding. A method in accordance with the present invention includes providing an optical amplifier having fibers for delivering pump laser light and for monitoring signal light, and applying a light-absorbing coating onto a portion of one of said fibers.

1 . An optical filter comprising:
 an optical fiber comprising:
 a core; and 
 a cladding surrounding the core; and 
   a light-absorbing coating upon a portion of the cladding, wherein the light absorbing coating attenuates a light propagating through the cladding.   
   
   
       2 . The optical filter of  claim 1  wherein a second light propagates through the core, the propagation of the second light not being perturbed by the light-absorbing coating. 
   
   
       3 . The optical filter of  claim 1 , wherein the light-absorbing coating is chosen from the group consisting of marking fluid and marking ink. 
   
   
       4 . The optical filter of  claim 1 , wherein the light and the second light comprise the same wavelength. 
   
   
       5 . The optical filter of  claim 1 , wherein the light is a pump laser light comprising a first wavelength and the second light is a signal light comprising a second wavelength different from the first wavelength. 
   
   
       6 . The optical filter of  claim 1 , wherein the light enters the fiber through a portion of the cladding not having the light-absorbing coating. 
   
   
       7 . An optical filter comprising:
 an optical fiber comprising:
 a core; 
 a cladding surrounding the core; and 
 a first coating surrounding the cladding; and 
   a light-absorbing coating upon a portion of the first coating, wherein the light absorbing coating attenuates a light propagating through the first coating.   
   
   
       8 . The optical filter of  claim 7  wherein a second light propagates through the core, the propagation of the second light not being perturbed by the light-absorbing coating. 
   
   
       9 . The optical filter of  claim 7 , wherein the light-absorbing coating is chosen from the group consisting of marking fluid and marking ink. 
   
   
       10 . The optical filter of  claim 7 , wherein the light and the second light comprise the same wavelength. 
   
   
       11 . The optical filter of  claim 7 , wherein the light is a pump laser light comprising a first wavelength and the second light is a signal light comprising a second wavelength different from the first wavelength. 
   
   
       12 . The optical filter of  claim 7 , wherein the light enters the fiber through a portion of the first coating not having the light-absorbing coating. 
   
   
       13 . A method for reducing inter-fiber optical coupling within an optical amplifier having a first optical fiber optically coupled to a pump laser and a second optical fiber optically coupled to a photodetector, comprising:
 applying a light-absorbing coating to a portion of the length of the second optical fiber.   
   
   
       14 . The method of  claim 13 , further comprising:
 applying a second light-absorbing coating to a portion of the length of the first optical fiber.   
   
   
       15 . The method of  claim 13 , wherein the second optical fiber comprises:
 a core; and   a cladding surrounding the core, wherein the light-absorbing coating is upon a portion of the cladding, wherein the light absorbing coating attenuates a light propagating through the cladding.   
   
   
       16 . The method of  claim 13 , wherein the second optical fiber comprises:
 a core;   a cladding surrounding the core; and   a first coating surrounding the cladding, wherein the light-absorbing coating is upon a portion of the first coating, wherein the light absorbing coating attenuates a light propagating through the first coating.