M.Sc Thesis

M.Sc StudentGrinberg Pavel
SubjectEffects of Noise in Actively Mode-Locked Multi-Pulse
Fiber Lasers
DepartmentDepartment of Electrical and Computer Engineering
Supervisors PROF. Moshe Horowitz
Full Thesis textFull thesis text - English Version


Harmonically mode-locked erbium-doped fiber lasers can generate ultra-low jitter pulses with high repetition rates of tens of gigahertz. These features are important for one of the main applications in optical communications, optical sampling, and for scientific research. One of the main problems of these lasers is pulse dropout. When a laser is harmonically mode-locked, several pulses propagate in its cavity. Some of the pulses may be dropped from the cavity due to imperfect modulation and environmental instabilities, leading to system errors in optical communications or other potential applications. Since the response time of erbium-doped amplifier is very low, the saturation is affected by a large number of pulses and it is insensitive to dropout of several pulses. In this work we study the recovery duration of solitonic pulses from accidental dropout. We examine the characteristic times for the pulse recovery both theoretically and experimentally, and suggest a method to accelerate the recovery by slightly increasing the laser gain. The gain is increased by perturbing all pulses in the cavity so that they experience a higher loss. The gain increase will shorten the recovery time of the dropped pulses.

In the second part of this work we study the behavior of actively mode-locked lasers with complex modulation forms, studied in the framework of statistical lightmode dynamics (SLD) theory where the noise - internal and externally injected - plays an important role. It appears that in the absence of dispersion and nonlinearity, the waveform can be decomposed as a superposition of the master equation eigenstates, which occupation is determined according to some statistical distribution closely resembling Bose-Einstein distribution, where the additive gain plays the role of the chemical potential. This statistical distribution was qualitatively verified by an experiment in which different loss were applied to different pulses in the cavity by using a structured modulation. It was theoretically predicted and experimentally verified that the distribution of the intracavity energy among the different pulses behaves in accordance with the equipartition theorem in statistical physics at high noise levels, while the energy is equally divided between the pulses. Beside the thermodynamic-like phenomena of the pulses we theoretically studied possible effects in case that the fields of different pulses overlap. Like in quantum mechanics, we envision double well, many well and periodic potential structures, with interesting properties.