Effect of noise on mode-locked soliton pulse source

ABSTRACT EFFECT OF NOISE ON MODE-LOCKED HYBRID SOLÎTON PULSE SOURCE DO?RU, Nuran Ph. D. in Electrical and Electronics Engineering Supervisor: Prof. Dr. M. Sadettin ÖZYAZICI May 2003,120 pages The noise of hybrid soliton pulse source (HSPS) utilizing different fiber Bragg gratings (FBGs) such as uniform, Gaussian, linearly chirped uniform and linearly chirped Gaussian apodized are described by using electric field approach when HSPS is mode-locked. The HSPS system is made up of a multi-quantum well (MQW) semiconductor laser, a fiber and a FBG. The HSPS is modeled by a time-domain solution of the coupled-mode equations including spontaneous emission noise. These equations are converted into the transfer matrix form by using the piecewise-uniform approach. Relative intensity noise (RIN) is calculated using numerical solutions of these equations. Although transform-limited pulses over a wide tuning range around the fundamental mode-locking frequency are obtained from mode-locked HSPS with linearly chirped uniform and linearly chirped Gaussian apodized FBGs with low noise, mode-locked HSPS with uniform and Gaussian apodized FBGs can generate transform-limited pulses only over a limited tuning range. However, noise increases with increasing linewidth enhancement factor, gain saturation parameter and spontaneous coupling factor. A high noise level that generates a noise peak at the mode-locking frequency in the RIN spectrum makes the transform limited pulses unobtainable at the mode-locking frequency and therefore proper mode-locking range reduces. Noise is also extremely sensitive to the RF and DC currents. Carrier noise is important as spontaneous noise and inclusion of this noise source into the rate equations is necessary for accurate analysis of the noise. It is also found that RIN inreduction is possible for the mode-locked HSPS by selecting a suitable apodization function such as Gaussian and linear chirp rate. Keywords: Hybrid soliton pulse source, mode-locked laser, fiber Bragg grating, multi-quantum well laser, relative intensity noise, spontaneous noise, carrier noise. IV