טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentSourani Yael
SubjectThe Dynamics of Wavelength Switching and Tuning by Mode
Locking of Fiber Lasers
DepartmentDepartment of Electrical Engineering
Supervisor Professor Emeritus Baruch Fischer
Full Thesis textFull thesis text - English Version


Abstract

This work deals with methods and implementations of multi-wavelength fiber lasers. The thesis is divided into three parts with three experimental systems that present two main mechanisms for the achievement of the multi-wavelength operation. All systems are in the form of a ring fiber laser with Erbium-doped fiber as the gain medium, active mode locking and Fiber Bragg Gratings (FBGs). The main difference between the systems is the structure of the used FBGs. The first part examines a system with multiple uniform FBGs, the second part examines a system with one or multiple sampled FBGs and the third part examines a system with chirped FBG. The active mode locking, in the form of amplitude modulator or phase modulator, has a key role in the operation of the laser. Besides producing a pulse train at high repetition rates, it is also used to select and switch the operating wavelength.

The first method uses several FBGs with different reflected wavelengths, each grating determines a different cavity length and therefore a different mode-locked frequency. The selection of the wavelength is performed by applying the corresponding modulation frequency. This method is presented in the first and second parts. The second method uses a highly dispersive component to differentiate among the different wavelengths, and presented in the second and third parts. The FBGs in both methods have several roles as well, where the first and obvious one is to determine the operating wavelength. The more subtle role, in the first method is to form a multi-length cavity, demonstrated by multiple uniform and sampled FBGs, and in the second method is to introduce high dispersion to the system, demonstrated by the chirped FBG system.

Even though the system and the working mechanism are different in the various parts, similar behavior and limitations are encountered during the laser steady state and transit operation. The switching properties, which are carefully studied in the first part, are also important for parts two and three.