Theoretical Analysis And Experimental Study On Laser Pulses Noise

As one of the most important light sources, lasers have been an indispensable device in the optical communication system. The quality of output laser pulse trains directly affects the performance of communication system. Noise is one of the most important parameters to evaluate the laser pulses quality. In the recent years, the characterization of pulse noise has attracted more and more attention. The main works of this dissertation is summarized as follows:1. We have derived the power spectrum of pulse intensity of the pulse trains with all the amplitude noise, timing jitter and pulse width jitter. With the obtained model of the power spectrum, we have theoretically analyzed the contribution of all the amplitude noise, timing jitter and pulse width jitter to the total noise power spectrum. The simulated results show that while the product of pulse width and angular frequency is larger than 1, the pulse width jitter will contribute an amount of noise to the total noise power. Compared to the amplitude noise and timing jitter, the pulse width jitter can not be neglected. 2. We have experimentally studied the noise characterization of laser pulses. A Fabry-Perot Laser Diode with 1550 nm centre wavelength was selected as the light source. The optical pulses with 57.6ps full width at half maximum (FWHM) and 2.0GHz repetition rate were generated by gained-switching technique and measured with an ultrafast photodetector combined with a spectrum analyzer. The characterization of the pulse noise is presented with harmonic spectrum analysis. The third, fifth and seventh harmonics were selected to calculate the pulse width jitter, and the corresponding product of pulse width and angular frequency, 7W, were 1.305, 2.175 and 3.045, respectively. With 25 kHz～5 MHz integration limits, the pulse width jitter was obtained to be 3.08ps. In the condition that pulse width jitter was neglected, the amplitude noise and timing jitter were evaluated to be 2.07% and 3.1 lps, respectively. The comparison of the three noise values indicated that while the product of pulse width and angular frequency is larger than 1, the pulse width jitter would contribute considerable power to the total noise power spectrum, which is consistent well with the theoretical analysis.3. We have also analyzed the influences of the resolution bandwidth of the spectrum analyzer and the offset frequency range on the amplitude noise, the timing jitter and the pulse width jitter. The results indicated that the noise power was small in low offset frequency than that in high one. Both the offset frequency ranges and the resolution bandwidth have little influence on the amplitude noise.