Precision Fabrication of D - Shaped Single - Mode Optical Fibers by In Situ Monitoring

A technique has been developed to locally remove, over a distance of several millimeters of fiber length, the cladding layer of single-mode (at the 1300 nm wavelength) optical fibers with 1 pm depth precision by use of mechanical lapping and in situ optical transmission monitoring. A cylinder lap dressed with diamond is used to perform high-pressure mechanical lapping. The in situ monitoring technique is based on the specific different attenuations exhibited by higher order propagating modes (for 633 nm light) as the cylinder penetrates into the fiber. Advantages include relatively rapid overall processing, high lapping rate, good optical surface quality, and 1 y m precision. Experimental results are presented and analyzed by an approximate geometrical-optics model.