51,554 research outputs found
An ultrafast reconfigurable nanophotonic switch using wavefront shaping of light in a nonlinear nanomaterial
We demonstrate a new concept for reconfigurable nanophotonic devices
exploiting ultrafast nonlinear control of shaped wavefronts in a multimode
nanomaterial consisting of semiconductor nanowires. Femtosecond pulsed laser
excitation of the nanowire mat is shown to provide an efficient nonlinear
mechanism to control both destructive and constructive interference in a shaped
wavefront. Modulations of up to 63% are induced by optical pumping, due to a
combination of multimode dephasing and induced transient absorption. We show
that part of the nonlinear phase dynamics can be inverted to provide a
dynamical revival of the wavefront into an optimized spot with up to 18%
increase of the peak to background ratio caused by pulsed laser excitation. The
concepts of multimode nonlinear switching demonstrated here are generally
extendable to other photonic and plasmonic systems and enable new avenues for
ultrafast and reconfigurable nanophotonic devices.Comment: 18 pages, 6 figure
Flat systems, equivalence and trajectory generation
Flat systems, an important subclass of nonlinear control systems introduced
via differential-algebraic methods, are defined in a differential
geometric framework. We utilize the infinite dimensional geometry developed
by Vinogradov and coworkers: a control system is a diffiety, or more
precisely, an ordinary diffiety, i.e. a smooth infinite-dimensional manifold
equipped with a privileged vector field. After recalling the definition of
a Lie-Backlund mapping, we say that two systems are equivalent if they
are related by a Lie-Backlund isomorphism. Flat systems are those systems
which are equivalent to a controllable linear one. The interest of
such an abstract setting relies mainly on the fact that the above system
equivalence is interpreted in terms of endogenous dynamic feedback. The
presentation is as elementary as possible and illustrated by the VTOL
aircraft
- ā¦