Mordechai (Moti) Segev

Visiting Lecturer with Rank of Professor
Ph.D. 1990, Technion, Israel Institute of Technology

The research is my group is in the general area of nonlinear optics and quantum electronics. Our current projects have to do with solitons, nonlinear frequency conversion, nonlinear guided waves, nonlinear dynamics, and photorefractive materials. Our research is both theoretical and experimental, and all our students are required to learn both aspects.



Above, a naturally diffracted beam. Below, a soliton, a self-guided beam.

Over the last few years we have studied spatial solitons: beams of light that never diffract and interact with each other like particles do. We have made many contributions in this area. Two years ago, we discovered incoherent solitons, that is, solitons upon which the phase is fully random and which can be generated using light from an incoherent source. We have demonstrated that an incoherent white light beam, that is, a "pulse" that is both temporally and spatially incoherent, can self-trap in a noninstantaneous nonlinear medium, and form a soliton. In this experiment the self-trapped beam originated from an incandescent light bulb that emitted light at the entire visible spectrum. Then, we went on to demonstrate self-trapping of dark incoherent "beams," that is, one-dimensional or two-dimensional "voids" nested in a spatially incoherent beam. Subsequently, we have laid out the theoretical foundations of this new kind of soliton. These were the first incoherent solitons demonstrated in nature, in any physical system.

Another discovery was that solitons interacting in a three-dimensional nonlinear medium conserve angular momentum and can capture each other in a spiraling orbit. Another important result was our demonstration of multimode solitons and composite solitons. Other contributions we have made in the general area of solitons were our prediction and first experimental observation of photorefractive solitons, and of several different families of such solitons (for example, screening solitons). A more recent result has to do with our prediction of necklace-ring solitons in Kerr media.

Another direction includes the prediction of a new effect that combines nonlinear optics and nonlinear transport phenomena: the photorefractive Gunn effect. Another project has to do with phase-transition phenomena in nonlinear self-oscillators. Yet another project targets the spontaneous formation of crystalline waveguides in metastable material systems, which shows how light can influence the clustering and macroscopic crystalline polarization at the vicinity of a phase transition.

Some of our work also has an applied aspect. For example, we have invented a new scheme for nonlinear frequency conversion in waveguides, by using soliton-induced waveguides that allow for a wide range of wavelength tunability.

Self-trapping of white light. Incoherent beams can be trapped in any noninstantaneous nonlinearity.