M.Sc Thesis

M.Sc StudentWillinger Amnon
SubjectThe Roles of Random Birefringence and Stimulated Raman
Scattering on the Performances of Narrow Band
Fiber Parametric Amplifiers for the Use
of Tunable Optical Delay Eleme
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROFESSOR EMERITUS Gad Eisenstein


Research activities in many leading laboratories have addressed the need for all optical tunable delay lines. The main thrust in this direction employs controllable group velocities - a research field that is known as slow and fast light propagation. Many possible applications have been suggested including potential optical buffers, optical control of microwave signals, sensing and a general increase in light - matter interaction.

Many optical media using numerous optical processes have been used to demonstrate slow and fast light, but the best results in terms of available bandwidth and tuning range are obtained with narrow-band optical parametric amplifier (NB-OPA) in optical fibers. This is the case where a strong pumping wave generates a narrow region in the optical spectrum in which there is gain, and with it a change in the effective group velocity of the amplified signal. However, since practical fibers have imperfections and since the process is very sensitive to many propagation parameters, a detailed model is required to explain the performance and to predict the ultimate capabilities and limitations of this device.

The subject of this thesis work is to present a comprehensive model, which combines the various coupled nonlinearities that govern NB-OPA in the presence of fiber imperfections such as random birefringence and longitudinal variations of linear and nonlinear parameters. After presenting a summary of these fiber impairments, together with presenting the dominant nonlinear effects in optical fibers - Kerr effect and Stimulated Raman Scattering (SRS) - this work dwells on the interaction between all of the different phenomena, under conditions that make the fiber a narrow-band optical parametric amplifier. A comprehensive physical model is developed and its behavior is examined in simulations.

The last part of this work consists of experimental measurements taken with the fiber based NB-OPA. The first set of experiments is made up of gain measurements, where a strong pumping wave amplifies a low-rate signal wave. These are used to map the parametric gain spectrum and to characterize the specific optical fiber used. The second set of experiments tests the ability to control the delay of a 10 Gbit/s data signal (at a specific wavelength), by changing its gain level using the pumping wave power. A nice rage of delay values is attainable, but with rising gain the signal suffers more distortions and thus a limit is set to the amount of clean delay that can be supplied.