Control system for optic-fiber coating process based on photoelastic effects

The coating process, of optic-fibers into a polymer matrix is a very difficult and delicate process due to the fragility of the fibers, which can get broken by the stresses and temperature imposed during processing. In this paper we introduce a new control system which is based on measurement of specific power changes in the laser transmitted signal thought the fiber. Those changes are produced by mechanical or thermal stresses on the fiber during processing. Those stresses normally generated by photoelastic effects on the fiber when it is pulled or heated, changing its optical properties. By a meticulous characterization of those effects we are able to establish a real time control system for the coating process, avoiding the deformation or even breaking of the fiber during coating.