High-energy femtosecond figure-eight fiber laser

A simple figure-8 fibre laser that generates femtosecond pulses with large pulse energy is reported. The pulsewidth is 125 fs and pulse energy is 0.5 nJ. The high energy is achieved by pulse stretching effect by using an erbium-doped fibre in the amplifier with normal dispersion and the narrow pulsewidth is obtained by means of a long length of dispersion shifted fibre. Furthermore, the pulses are made stable by introducing a gradual twist to the dispersion shifted fibre. The central wavelength and the spectral width of the pulses can be tuned by simply adjusting the polarisation-controllers in the loop. No additional components are required. (C) 1997 Elsevier Science B.V.