טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentKatz Michael
SubjectPulse Stability and Fluctuations in Passively Mode-Locked
Lasers with Noise
DepartmentDepartment of Electrical Engineering
Supervisors Professor Emeritus Baruch Fischer
Dr. Omri Gat
Full Thesis textFull thesis text - English Version


Abstract

Passively mode locked lasers are the prime source of ultra-short light pulses, nowadays reaching the few femto-seconds regime, A recently developed Statistical Light-Mode Dynamics (SLD) theory is based on the observation that a multi-mode laser is a many-body dynamical system of interacting light modes, subject to external noise. SLD has shown, that for a particular relation between the laser parameters passive mode locking can be analyzed by means of an equilibrium statistical mechanics, with noise playing the role of temperature.

In the present work we extend the results of SLD theory to a broad class of passively mode locked lasers with arbitrary, unrestricted parameters, constituting a prototype for non-equilibrium statistical mechanics system that cannot be directly analyzed by standard methods.

The gain balance methods developed in this work is based on the decomposition of the steady state intra-cavity waveform into noisy (background) and ordered (pulse) components, comparable in energy, coupled via a common sharing of the laser gain resources.

The method is applied to several laser systems: fast saturable absorber and slow saturable absorber configurations, and multi-pulse mode locking scenario. One of the important practical outcomes of our theory is closed form expressions for the destabilization threshold of mode locked pulses, from which follows the minimal value of the total intra-cavity power required for mode locking. We analyze the dependence of the mode locking phenomena in the whole laser parameters space, and find the optimal regions that maximize the mode locked pulse power and stability.

We also analyze the statistical properties of the mode-locked laser pulses, which are important for many practical applications. The developed approach allows to take into account the stochastic back-action of the background on the mode-locked pulse and leads to discovery of new features in the fluctuation dynamics- oscillations in the autocorrelation functions of the pulse power and frequency, and an enhancement of the phase jitter.

The pulse stability and fluctuations are also analyzed in the limit of the spontaneous emission noise inherent to the laser operation.

The theoretical results are corroborated by direct numerical simulations of the stochastic equations and an experimental investigation of the pulse stability in a fiber based, non-linear polarization rotation mode-locked laser. We have measured the dependence of the mode-locking threshold on the laser parameters and found good agreement with the theoretical predictions.