High precision simulation of a mode locked ring laser using SOA and fiber for generation of λ=1.55µm pulse train

A fiber ring laser with a semiconductor optical amplifier (SOA) as active component is investigated using a hybrid model. The SOA is studied using a newly-established 4^th-order time-domain algorithm, which includes the nonlinear effects of carrier depletion and recovery, as well as gain dispersion. Comparison with existing analytical results shows that this algorithm can attain a relative precision of a few parts per thousand (~10^-3) or better, which is essential for predicting waveform of optical pulse. The transmission in other parts of the ring laser is carried out in frequency domain. Our model predicts a pulse width of ~10ps with a 10GHz external modulation, and reveals higher stability, better waveform, as well as easier locking conditions with dispersion-compensating fiber (DCF). A diffraction-limited Gaussian pulse train can be obtained, with its carrier frequency effectively red-shifted due to band-pass filter. All these are in good agreement with our experimental observations.