Title

Clock recovery for OTDM and characteristics of actively mode-locked fiber lasers

Date of Completion

January 2004

Keywords

Engineering, Electronics and Electrical|Physics, Optics

Degree

Ph.D.

Abstract

High data rate clock recovery is a key technology for realizing future ultrafast optical time division multiplexed (OTDM) network. In this thesis study, an electric-optic type phase locked loop clock recovery circuit is developed which has the potential to operate at very high speed. Residue jitter free operation up to 80Gb/s has been demonstrated which is in good agreement with the phase noise analysis included in this work. ^ The characteristics of the actively mode-locked fiber lasers is also studied in depth in this thesis work. A time domain circulating pulse model has been proposed to study the pulse width optimization problem as well as the output amplitude equalization problem associated with rational harmonic mode-locking. By proposing a cascaded modulator as the cavity loss modulator, amplitude equalized pulse train operating at 80Gb/s has been obtained, which represents the highest order of rational harmonic mode-locking with amplitude equalized output ever reported so far. The dispersion effect on the detuning characteristics of the mode-locked fiber lasers is also studied. An analytic formula is derived which is capable of predicting the saturation effects associated with large frequency detunings. The analytic results obtained are well supported by both the numerical and the experimental investigations. By using the self-biased LiNbO3 modulator as an artificial intensity dependent loss element, nearly 20dB suppression of the relaxation oscillation noise peak has been demonstrated. Based on the linearized rate equation approach, a theory for the laser AM noise suppression has been developed. The jitter problem for harmonic mode-locked fiber lasers is also studied in the frequency domain. It is shown in this work that the super-mode noise contributes significantly to the timing jitter of the produced pulse train which explains the recent experimental observations well. Finally, as a connection between the clock recovery technique and the mode-locked fiber lasers, we extend the regenerative type mode-locking technique from the traditional harmonic region to the current rational harmonic region. In addition, with the help of a novel external repetition rate doubler based on the polarization maintaining fiber loop mirror, a highly stable pulse train operating at 80Gb/s has been obtained. ^