Ph.D Thesis

Ph.D StudentVodonos Boris
SubjectExperimental Study of the Noise Effect on Pulse Formation
in Mode Locked Lasers Following a Statistical
Mechanics Approach
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROFESSOR EMERITUS Baruch Fischer


This work presents an experimental study of the noise effect on pulse formation in passively mode locked lasers. We follow a novel statistical mechanics approach to mode locking, recently introduced in our group, and demonstrate many of its theoretical predictions.

The statistical mechanics approach emerges as natural tool for studying such a nonlinear many-mode laser system with its inherent noise. This approach is especially powerful for passively mode locked lasers, where generation of short optical pulses is identified as a first-order noise and power dependent phase transition and thus the solution is given to the long-standing question on the origin of power threshold for pulsation self-starting.

Directly controlling the level of the noise in the laser cavity by injection of amplified spontaneous emission from an external noise source we observe the first-order noise-dependent phase transition in the time domain, as well as an abrupt jump in the measured RF power of the detected laser output. The RF power is a natural order parameter distinguishing between pulsed operation and quasi continuous-wave regime.

Our detailed experimental study of multiple pulse formation yields a thermodynamic-like ``phase diagram" with boundaries representing cascaded first-order phase transitions that correspond to abrupt creation and annihilation of pulses and a quantized RF power behavior as system parameters (noise and/or pumping levels) are varied. The theory and the experiment are in excellent agreement, both qualitatively and quantitatively.

Another part of our experimental study is addressed to the self-starting stochastic behavior of passive mode locking. Our quantitative study confirms that pulsation self-starting is a Poisson process that results from an entropic noise-activated switching barrier.