Large mode area fibers for high power applications

We review our recent work toward designing large mode area fibers for high power applications. We show that appropriately designed doped multimode fib ers can be used to provide robust single-mode output when used in fiber las er cavities. Single-mode (SM) fiber mode field diameters of similar to 35 m u m are demonstrated with record SM pulse energies of 0.5 mJ at 1550 nm wit h a repetition rate of 200 Hz. Energies approaching I mJ are obtained with a slight compromise in mode quality. A modification in the laser cavity res ults in a passively modelocked laser giving femtosecond pulses with nanojou le energies. (C) 1999 Academic Press.