We report a novel experimental setup to perform distributed characterization in intensity and phase of the nonlinear stage of modulation instability by means of a non-invasive experimental setup : a heterodyne time domain reflectometer.
G. Bentini, A. Parini, M. Chiarini, M. Bianconi, A. Cerutti, A. Nubile, S. Sugliani, G. Pennestrì, G. Bellanca, S. Trillo, S. Petrini, M. Gallerani, P. De Nicola, F. Bergamini
In the last few years Programmable Micro Diffraction Gratings (PMDG) have shown the possibility to be applied in many areas, spanning from imaging, to telecommunication, to spectroscopy. These devices were mainly based on Micro-Electro-Mechanical Systems (MEMS) techniques and realized by moveable mirrors and pop-up structures. Although this approach have held a central stage in Micro-Opto-Electro-Mechanical-Systems (MOEMS), they made the realized devices delicate and not useful for some critical environments. In this work we discuss the possibility to fabricate a fully integrated electrically driven PMDG device where, to avoid the presence of moving parts, the electro-optical properties of a suitable substrate material are used. The theoretical approach and the design procedure of a miniaturized PMDG apparatus useful as a generator of synthetic spectra are illustrated and discussed in details.
We study the effects of the induced third-order nonlinearity on backward second-harmonic generation in Penodically
Poled Lithium Niobate (PPLN). We show that self-phase and cross-phase modulation terms induced
by a proper engineering of the domain length can compete with intrinsic quadratic nonlinearity enriching the
dynamics of the system. In particular it allows for self oscillation even with vanishing second-harmonic input.
The transmission properties of a one-dimensional grating with a Kerr nonlinearity, at operating frequencies close to the upper edge of the stop-band, have been investigated using the Finite Difference Time Domain (FD-TD) technique. Results show that the structure exhibits a bistable behavior: transitions from strong reflection to nonlinearity-induced transparency and viceversa are found, leading to high-intensity field localization within the grating. In the limit of shallow gratings, FD-TD results are in good agreement with those based on coupled-mode theory (CMT).
Since the early work of Kelley in 1965, self-focusing in transparent dielectric materials was recognized as one of the mechanisms of optical induced damage in laser materials. Recently the experimental demonstration of stable solitary waves in Quadratic materials has shown that the catastrophic collapse of laser beams can be arrested in materials with a pure second order response. New ways to solve the self- focusing damage mechanism in laser materials can result from such an experimental discovery. Indeed choosing host laser materials with a quadratic nonlinearity can considerably delay the appearance of the laser beam collapse. We present theoretical considerations and numerical calculations on materials design concepts which can in practice resolve the self-focusing collapse in the presence of a quadratic nonlinearity.
Based on cascading of second-order nonlinearities we propose novel schemes for all-optical signal processing exploiting the tensorial nature of the susceptibility. Waves of the same frequency and orthogonal polarizations can interact via the generated second-harmonic, with an indirect energy transfer and the consequent possibility of gain and transistor action, polarization switching, amplitude and phase modulation.
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