Active fibers from sol-gel derived granulated silica: state of the art and potential

In the recent past we have studied the granulated silica method as a versatile and cost effective way of fiber preform production. We have used the sol-gel technology combined with a laser-assisted remelting step to produce high homogeneity Rare Earth or Transition Metal - activated microsized particles for the fiber core. For the fiber cladding pure or index-raised granulated Silica has been employed. Silica glass tubes, appropriately filled with these granular materials, are then drawn to fibers, eventually after an optional quality enhancing vitrification step. The process offers a high degree of compositional flexibility with respect to dopants; it further facilitates to achieve high concentrations even in cases when several dopants are used. By this "rapid preform production" technique, that is also ideally suited for the preparation of microstructured optical fibers, several fibers ranging from broadband emitters, PCFs and large mode area fibers have been produced and will be presented here.