## Jason W. Fleischer

**Associate Professor of Electrical Engineering**

Ph.D. 1999, University of California, San Diego
My research treats nonlinear optics within the broader context of general wave
physics. The emphasis is on propagation problems that are universal to wave systems,
taking advantage of the fact that optical systems allow easy control of the input
and direct imaging of the output. Using a healthy mix of theory and experiment,
my group studies both basic nonlinear physics and advanced design issues for photonic
applications.

As a prime example, my group is developing an optical hydrodynamics in which the nonlinear
propagation of light is described in terms of the equations for ideal fluid flow. In
this case, the light intensity acts as a fluid density while the direction of the
wavefront gives an effective velocity. Such a fluid interpretation was the
historical starting point for the wave theory of light, as envisioned by Huygens,
but its consequences have been underappreciated in the nonlinear case. For
example, our work on optical shock waves has enabled a nonlinear generalization
of Huygens’ principle: superposition holds when two waves meet, but
the combined field acts as a nonlinear source for new waves. This can be seen
in the figure, in which the circular wavefronts of the individual shocks become
flattened by the collision.

Other examples follow by adding structure to the light. Propagation in waveguide
arrays can be interpreted in terms of solid-state physics, while interactions between
array sites can be described by coarse-grained hydrodynamics. Shock waves
in photonic lattices provide a very efficient way to disperse energy, while the
general behavior relates to waves in granular and molecular media, bubbly fluids,
etc. Similarly, cascaded wave mixing can be viewed as a form of optical turbulence,
and the propagation of statistical light can be treated as a photonic plasma.

There are two primary results of these mappings: 1) optical modeling and observation
of condensed-matter behavior that is difficult, if not impossible, to see by other
means, and 2) a framework for the discovery of new optical physics. This latter
consequence is particularly important, as better understanding of optical dynamics
inevitably leads to the design of new photonic devices. Active areas along
these lines include advanced waveguide systems, improved holographic techniques,
and all-optical image/signal processing.