3 research outputs found
Optical Limiter Based on PT-Symmetry Breaking of Reflectionless Modes
The application of parity-time (PT) symmetry in optics, especially
PT-symmetry breaking, has attracted considerable attention as a novel approach
to controlling light propagation. Here, we report optical limiting by two
coupled optical cavities with a PT-symmetric spectrum of reflectionless modes.
The optical limiting is related to broken PT symmetry due to light-induced
changes in one of the cavities. Our experimental implementation is a
three-mirror resonator of alternating layers of ZnS and cryolite with a
PT-symmetric spectral degeneracy of two reflectionless modes. The optical
limiting is demonstrated by measurements of single 532-nm 6-ns laser pulses. At
fluences below 10 mJ/cm2, the multilayer exhibits a flat-top passband at 532
nm. At higher fluences, laser heating combined with the thermo-optic effect in
ZnS leads to cavity detuning and PT-symmetry breaking of the reflectionless
modes. As a result, the entire multilayer structure quickly becomes highly
reflective, protecting itself from laser-induced damage. The cavity detuning
mechanism can differ at much higher limiting thresholds and include
nonlinearity.Comment: 17 pages, 5 figure
A reflective mm-wave photonic limiter
Millimeter wave (mm-wave) communications and radar receivers capable of
processing small signals must be protected from high-power signals, which can
damage sensitive receiver components. Many of these systems arguably can be
protected by using photonic limiting techniques, in addition to electronic
limiting circuits in receiver front-ends. Here we demonstrate, experimentally
and numerically, a free-space, reflective mm-wave limiter based on a multilayer
structure involving a nanolayer of vanadium dioxide (VO2), experiencing a
thermal insulator-to-metal transition. The multilayer acts as a variable
reflector, controlled by the input power. At low input power levels, VO2
remains dielectric, and the multilayer exhibits resonant transmittance. When
the input power exceeds a threshold level, the emerging metallic phase renders
the multilayer highly reflective while dissipating a small portion of the input
power without damage to the limiter. In the case of a Gaussian beam, the
limiter has a nearly constant output above the limiting threshold input.Comment: 18 pages, 6 figures, 3 supplementary figures and 1 supplementary
tabl