Dynamics of Partially Coherent Solitons

                 

Principal Investigator

Darran Edmundson

Optical Sciences Centre Research School of Physical Sciences and Engineering

Co-Investigators

Nail Akhmediev

Ole Bang

Optical Sciences Centre

Research School of Physical Sciences and Engineering

Wieslaw Krolikowski

Laser Physics Centre Research School of Physical Sciences and Engineering

Project

x12 - VPP

A ray of light refracts towards the normal as it enters

a medium having a higher refractive index. This

phenomena is exploited in optical fibers where laser pulses are transversely confined by the relatively higher refractive index in the fiber core. The optimal index profile is selected by design and then the "waveguide" is permanently fixed in the glass during fabrication.
In the presence of intense laser light, the refractive index of many nonlinear materials increases in proportion to the light intensity. Thus, one can imagine a suitably shaped beam travelling through an otherwise uniform index block and inducing its own optical waveguide. Such a self-trapped beam is known as a spatial soliton. Over the last decade spatial solitons have been studied extensively in view of their potential for realizing all-optical photonic devices.
While work in the field to date has focused on coherent solitons, recent experiments with photorefractive crystals have renewed theoretical interest in the physics of incoherently coupled beams. The overall aim of our project is quite general: to understand the effect of incoherence on the propagation of 2-dimensional beams in nonlinear bulk media. Our mathematical model consists of an infinite number of 2D nonlinear Schroedinger (NLS) equations coupled to the refractive index potential induced by the total beam intensity.

 
           
                 

   
                 

What are the results to date and the future of the work?

Much of 1998 was spent in developing, debugging and testing of a robust numerical code; only in the last quarter have we finally begun production simulations. With the integrity of the solver now established, we are investigating how the power threshold for collapse of a 2D Gaussian beam is affected by beam coherence. We plan to continue with these dynamical studies as well as initiate a search for stable beams in saturable nonlinear media.

                 
Appendix A -

                 

     

What computational techniques are used?

The solver uses a split-operator technique to solve a system of (many) coupled 2D NLS equations. Computations are memory intensive as rectangular spatial meshes of 512x512 for each of 256 individual NLS equations (1 Gb) are necessary in the limit of large beam incoherence. The code makes efficient use of the VPP as the majority of the cpu time used is spent performing 2D FFTs. Vectorization is typically greater than 90%.

     
- Appendix A