RIN in mode-locked external cavity semiconductor lasers

The relative intensity noise (RIN) of a mode-locked hybrid soliton pulse source (HSPS) utilising a linearly chirped uniform fibre Bragg grating, is investigated, taking into account spontaneous noise, by using coupled-mode equations. It is shown that low noise does not affect the operation of device and therefore transform-limited pulses are generated over a wide tuning range around the fundamental frequency. However, for large values of linewidth enhancement factor, spontaneous coupling factor and gain saturation parameter, transform-limited pulses are not obtained over a wide tuning range because of increasing noise. Hence, the proper mode-locked range reduces. It is also shown that RIN reduction is possible by using linearly chirped uniform gratings as compared to unchirped gratings.