Frequency shifted feedback and frequency comb generation in an Er³⁺-doped laser

The temporal and spectral characteristics are reported of an Er3+ -doped fibre laser incorporating frequency shifted feedback. The output of the free running laser was found to be either continuous-wave or train of driven relaxation oscillations depending on cavity loss. The performance is described and a simple theoretical model is used to predict the main features. Under cavity matching conditions, a train of pulses was generated with a repetition rate equal to the roundtrip time. Injection seeding of the laser generated a discrete comb of optical frequencies for applications in optical metrology