13,697 research outputs found
Evidences of evanescent Bloch waves in Phononic Crystals
We show both experimentally and theoretically the evanescent behaviour of
modes in the Band Gap (BG) of finite Phononic Crystal (PC). Based on
experimental and numerical data we obtain the imaginary part of the wave vector
in good agreement with the complex band structures obtained by the Extended
Plane Wave Expansion (EPWE). The calculated and measured acoustic field of a
localized mode out of the point defect inside the PC presents also evanescent
behaviour. The correct understanding of evanescent modes is fundamental for
designing narrow filters and wave guides based on Phononic Crystals with
defects.Comment: 8 pages, 3 figure
Dynamics and tolerance to external optical feedback of III-V/Si hybrid lasers with dispersive narrowband mirror
We report how external cavity III-V/Si hybrid lasers operate in regimes of ultra-damped relaxation oscillations or in unstable regimes as consequence to the dispersive mirror, non-zero linewidth enhancement factor and four-wave mixing in the gain medium. Tolerance to external optical feedback is also discussed
Dynamic regimes and damping of relaxation oscillations in III-V/Si external cavity lasers
We report how external cavity IIIV/Si hybrid lasers operate in regimes of ultradamped relaxation oscillations or in turbulent and selfpulsing regimes. The different regimes are reached by detuning the lasing wavelength respect to the mirror effective reflectivity peak and are the consequence of the dispersive narrow band reflectivity of the silicon photonics mirror, the linewidth enhancement factor and fourwave mixing in the gain medium
Evanescent modes in Sonic Crystals: Complex relation dispersion and supercell approximation
Evanescent modes in complete sonic crystals (SC) and SC with point defects
are reported both theoretically and experimentally in this paper. Plane wave
expansion (PWE) and, in general, methods have been used to
calculate band structures showing gaps that have been interpreted as ranges of
frequencies where no real exists. In this work, we extend PWE to solve the
complex problem applied to SC, introducing the supercell
approximation for studying one vacancy. Explicit matrix formulation of the
equations is given. This method enables the calculation of complex
band structures, as well as enabling an analysis of the propagating modes
related with real values of the function , and the evanescent modes
related with imaginary values of . This paper shows theoretical
results and experimental evidences of the evanescent behavior of modes inside
the SC band gap. Experimental data and numerical results using the finite
elements method are in very good agreement with the predictions obtained using
the method.Comment: 15 pages, 3 figure
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