Ph.D Thesis

Ph.D StudentShumakher Evgeny
SubjectSlow and Fast Light Propagation in Optical Fibers and
Semiconductor Optical Amplifiers:
Basic Limits and Applications in
Microwave Photonics
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROFESSOR EMERITUS Gad Eisenstein


Recent years have seen a surge in research aimed at gaining continuous control over the group velocity of propagating light. Numerous systems based on nonlinearities in optical fibers and periodic structures, electro-magnetically induced transparency in gaseous media and semiconductor optical amplifiers have been demonstrated. A new term has been coined to describe the above phenomena - “slow and fast light”. Although many initially envisioned applications may prove impractical, the field poses many interesting fundamental research questions and holds promise of benefit for some important electrical engineering concepts.

The main goal of this research is to advance the understanding of the physics behind several key slow light mechanisms and to identify possible applications of the above, particularly in the context of the microwave photonics.

The first element explored is based on stimulated Brillouin scattering in optical fibers. Especially attractive due to its simplicity, the mechanism suffers from narrow natural bandwidth which causes pattern-related distortions in digital data. These were found to be detrimental in co-defining the experienced delay. We have also demonstrated an elaborate characterization methodology that allows comprehensive prediction of the slow-light effect on the delayed digital bit-stream.

The second mechanism studied is based on Raman assisted narrow band optical parametric amplification in fibers whose main merit is sufficient and tunable bandwidth, suitable to accumulate very high bit-rate data. The existing analytical framework is extremely useful in describing the amplifiers behavior under the regular conditions of broadband parametric gain, but offers little assistance in the case of narrow band parametric interaction. This is due to substantial contribution of stimulated Raman scattering to phase matching conditions, increased sensitivity to zero dispersion wavelength variations along the fiber and polarization mode dispersion effects. The different effects have been comprehensively modeled and tested in the laboratory. High bit-rate data propagation in this slow light system was also modeled and demonstrated experimentally.

The third mechanism characterized is based on Coherent Population Oscillations in a semiconductor optical amplifier. Despite being inherently limited to delays of less than a microwave signal cycle, this is probably the most mature slow light technology as well as the one that lends itself more easily to miniaturization. We have conducted both experimental and theoretical characterization of noise contributions due to such phase shifter and provided guidelines for optimizing its operational conditions. In the applicative domain, an original optoelectronic oscillator has been constructed in which an SOA based phase-shifter availed continuous frequency tunability.