M.Sc Thesis

M.Sc StudentShapira Yuval
SubjectInteraction between Solitons in Nonlinear Fiber Bragg
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROF. Moshe Horowitz
Full Thesis textFull thesis text - English Version


Fiber Bragg gratings (FBGs) have revolutionized the fields of optical communications and optical sensing. The success of these devices lies in their nearly-ideal properties such as extremely narrow bandwidth, low loss, compatibility with fiber systems, and the ability to tailor easily the grating structure according to specifications.

Although most current applications of FBGs are based on their linear properties, the nonlinear properties of FBGs have a very promising potential to generate and manipulate light waves of moderate power that are required for optical metrology and for optical frequency conversion such as second harmonic generation and optical parametric oscillation. Among the different nonlinear effects, a special attention has been devoted to the propagation of solitary waves in FBGs which are called Bragg or gap solitons. Bragg solitons exhibit a much richer behavior than solitons of the nonlinear Schrödinger equation (NLS). Bragg solitons can propagate with extremely low velocity and interactions between them can be obtained on length scales on the order of centimeters.

In this thesis we concentrate on studying novel Bragg soliton interactions and their applications. Prior to this work the interaction between solitons was studied mainly numerically for a limited range of parameters. However, these studies didn't provide an intuitive physical interpretation of the interaction phenomena. During our research we have discovered new types of interactions between Bragg solitons in nonuniform gratings and have identified the physical mechanisms behind them. Based on the newly discovered effects we were able to theoretically demonstrate a set of all-optical logic gates and a memory device that enables controllable trapping and releasing of optical pulses. These devices are made of 15cm-long nonuniform FBGs.

We have shown that Bragg soliton interactions can induce frequency shifts for the interacting solitons. Because of the high frequency selectivity of FBGs, these changes can alter the propagation direction of the interacting solitons. It was previously shown that an initially moving Bragg soliton can be trapped by a localized defect. We have shown that soliton interaction induces effective force on the interacting solitons. This force can be utilized for release of the trapped optical pulse.

Another contribution of our work is a design of a novel experimental setup for investigating Bragg solitons propagation and their interactions. We discuss the main challenges to successful experiments and propose practical methods to overcome these challenges. We have implemented part of this experimental setup in our lab. Preliminary results are summarized in this thesis.