Intensity Noise in Mode-Locked External Cavity Lasers

Abstract

Effect of spontaneous and carrier density noise on a mode-locked hybrid soliton pulse source (HSPS) utilizing linearly chirped fiber Bragg grating is investigated by using coupled mode-equations. It is found that transform-limited pulses are generated from mode-locked HSPS over a wide tuning range around the fundamental mode-locking frequency without noise and with low level of both spontaneous and carrier densiy noise sources. However, mode-locking is difficult to achieve for large value of spontaneous coupling factor, linewidth enhancement factor, gain saturation parameter and some value of rf and dc currents because of increasing noise. High noise introduces a noise peak in the relative intensity noise (RIN) spectrum making transform-limited pulses unobtainable. Hence, the proper mode-locking range where transform-limited pulses are generated reduces.