Patent ID: 7957438

Claim:
A method of monitoring light comprising: launching a beam of light into an end of a single mode optical fiber having a core having a refractive index n 1 and having a cladding surrounding the core, having a refractive index n 2 , wherein n 1 >n 2 , wherein a first portion P 1 of the beam launched into the end of the single mode fiber is launched into the core at a first end face of the optical fiber, and wherein a second portion P 2 of the beam of light is launched directly into the cladding at the first end face of the optical fiber, and wherein P 2 /P 1 >0.05; detecting along a side of the optical fiber adjacent the cladding at a first location near the end of the fiber with a photodetector disposed along side of the fiber, a portion of light P3 that was launched into the fiber, wherein the portion of light P 3 includes more than 0.5% of P 2 and no more than 0.003% of P 1 ; and controlling the beam of light based on the P 2 /P 1 .