טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentAriel Lipson
SubjectMultiple Pulses in High Power Fiber Lasers
DepartmentDepartment of Electrical Engineering
Supervisor Full Professor Orenstein Meir


Abstract

Fiber lasers have gained much attention in the last decade as a quality source for optical communications. Their very short and well-profiled pulses, low noise and great stability make them an attractive option for transmitters and sampling sources. The laser, being based on erbium doped fiber amplifier (EDFA), fits well the desired wavelength of work (1550nm), which shows minimum loss for propagating pulses in fibers. Moreover their fiber cavity allows easy connection to further appliances and make the system more compact as a whole.

As the digital communications frequencies sky rocket, the need for shorter pulses rises as well. The shorter the pulses the more one can condense in a time frame and more information can be delivered. But both the propagation and detection of these pulses becomes more difficult and being so return-to-zero (RZ) pulses are more attractive since they allow shorter duty cycle and better margins. Mode-locking of fiber lasers allow such RZ pulses to develop, reaching pulses as short as a few femtosecond (10-15 seconds) with low gitter and high stability.

The main disadvantage of fiber lasers is their low repetition rate due to their lengthy cavity. Typical lengths are over a few meters yielding widely spaced modes (tens of Mhz and less) that when mode locked turn into low repetition rated pulses. The need for long cavities arises from the length of the EDFA (low amplification per meter) and dispersion management. The ability to create only Mhz pulses doesn’t fit well the communications demand for over 10Ghz pulses and much work is needed in this field.

The work in this thesis is based on the stretched-pulse laser. We introduce the laser, its physical setup, pulse dynamics and an analytical model for its behavior. Much work has been done building the laser and measuring its unique properties. We show work done on developing passive cavity arrangements in order to enhance the laser repetition rate and demonstrate successful results. Simulations of the cavity show how random optical amplitude and phase evolve into a well-defined pulse. Further work is done to investigate the injection mode-locking technique on our laser.