Efficient pulse compression and frequency conversion of phase-modulated laser pulses in engineered quasi-phase-matching gratings

The simultaneous generation of the 2nd and 3rd harmonics of a frequency-chirped pulse in a quadratically nonlinear medium encompassing a quasi-phase-matched grating with linearly varying inverse domain size has been numerically studied. The efficient pulse compression and energy conversion have been analyzed taking into account the group velocity mismatch and dispersion.     

Escaping solitons from a trapping potential

Solitons propagating within a confining potential undergo momentum-dependent scattering and eventually escape for large excitations. We experimentally highlight this phenomenon in the presence of a nonperturbative nonlinear response using self-confined light beams in a reorientational medium.     

Signal readdressing by steering of spatial solitons in bulk nematic liquid crystals

Fully three-dimensional spatial solitons in bulk nematic liquid crystals form self-consistent waveguides that are able to confine a weak, collinear copolarized signal at different wavelengths and with large trapping angles. We use a milliwatt cw source to generate a soliton and, by angular steering of the soliton, spatially readdress the guided signal.     

Optical multisoliton generation in nematic liquid crystals

The nonlocal nonlinearity stemming from molecular reorientation in nematic liquid crystals supports the formation of multiple solitary waves, following the onset of spatial modulational instability from both wide and focused input beams. We report experimental observations of such phenomena at power levels of hundreds of milliwatts in planar cells with a voltage bias.     

Energy localization in photonic crystals of a purely nonlinear origin

We investigate electromagnetic localization in a nonlinear photonic crystal, i.e., a structure with a stop band in its nonlinear spectral response. Taking a one-dimensional model of degenerate two-wave interaction we introduce the concept of parametric nonlinear-gap solitons, that is, strongly localized two-color locked envelopes arising from interplay of two nonlinear effects, which propagate slowly. We discuss the observable signature of these novel localized structures.     

Optical solitons and wave-particle duality

We investigate the propagation of optical solitons interacting with linear defects in the medium. We show that solitons exhibit a wave-particle dualism versus power, i.e., depending on the relative size of soliton and defect, responsible for a soliton trajectory dependent on its waist.     

Robust generation,properties and potential applications of quadratic spatial solitons generated by optical parametric amplification

Quadratic spatial solitary waves are predicted and observed experimentally near degeneracy for Type II optical parametric amplification in bulk KTP, by seeding an intense pump optical field with a control signal at half the pump wave frequency. The self-trapping of light at the two wavelengths has been shown to be insensitive to phase, polarization and magnitude of the control input, and can be exploited in novel schemes for robust all-optical processing.     

Observation of Beam Self-Induced Transition from Positive to Negative Optical Refraction in Nematic Liquid Crystals

We demonstrate that light refraction at a straight interface between an isotropic dielectric and a nematic liquid crystal can change from positive to negative depending on power. The phenomenon relies on the reorientational response and the all-optical rotation of the optic axis, causing in turn variations in walk-off and beam self-steering.     

Second-harmonic generation in surface periodically poled lithium niobate waveguides: on the role of multiphoton absorption

Second-harmonic generation is investigated in lithium niobate channels realized by proton exchange and quasi-phase matched by surface periodic poling. The reduction in conversion efficiency at high powers is interpreted in terms of multiphoton absorption via two-color terms, yielding an estimate of the dominating three-photon process.     

A germanium photodetector array for the near infrared monolithically integrated with silicon CMOS readout electronics

Near infrared (NIR) detectors, operating in the 1.3–1.6 μm region, are key elements in a number of applications ranging from optical communications to remote sensing. InGaAs and Ge are currently the materials of choice for the fabrication of NIR detectors due to their good absorption and transport properties. However, as the required performances increase (bit-rate in optical communications, number of pixels in imaging, etc.), it becomes more and more important to reduce the separation from detectors and driving/biasing and amplifying electronics, by integrating the two components on the same chip.We demonstrate an array of NIR detectors monolithically integrated with standard silicon CMOS readout electronics. The employed low temperature process allowed the integration of the detectors as the last step of chip fabrication. The integrated micro-system consists of a linear array of 120×120 μm² pixels, an analog CMOS multiplexer and a transimpedance amplifier. The chip exhibits a good photoresponse in the NIR, with responsivities as high as 43 V/W at 1.3 μm, dark currents of 1 mA/cm² and inter-pixel cross-talk better than −20 dB.