Figure-eight fibre lasers with NALM loops consisting of highly nonlinear dispersion shifted fibres for dense wavelength division multiplexing

Abstract

We describe 'Figure-of-Eight' fibre lasers with NALM (Nonlinear Amplifying Loop Mirror) loops of 100 m, 200 m 300 m highly nonlinear dispersion shifted fibre and 50 m photonic crystal fibre. Apart from the NALM loops the rest of the fibre lasers consisted of normal single-mode fibre (SMF28). The fibre lasers produced mode-locked and Q-switched pulses. By varying the length of the NALM loop we generated a variety of short and long stable high peak power and low peak power pulses in the range from 2 ns to 104 ns. The length of the pulses depends on the length of the NALM loop and the pump diode power. By changing the setting of the polarization controllers we can manipulate the amplitude of the pulses, produce high and low pulses, step pulses, double or multiple pulses. The period of the pulses is equal to the round trip time. We present pulse widths, pulse peak power and spectral measurements in dependence of the pump diode power, and discuss the shapes and spectra of the laser pulses with reference to the transmission curves.