A. De Rossi

Electrically assisted self-confinement and waveguiding in planar nematic liquid crystal cells

We report on spatial soliton formation and self/cross waveguiding in planar cells containing a nematic liquid crystal in the presence of an externally applied voltage. Self-confinement and cross-induced guidance are demonstrated with an Argon ion laser (514 nm) and a helium–neon probe (633 nm), respectively, over millimeter lengths and with milliwatt pump powers.

Temporal solitons and pulse compression in photonic crystal waveguides

We demonstrate soliton-effect pulse compression in mm-long photonic crystal waveguides resulting from strong anomalous dispersion and self-phase modulation. Compression from 3ps to 580fs, at low pulse energies(~10pJ), is measured via autocorrelation.

Highly efficient four wave mixing in GaInP photonic crystal waveguides.

We report highly efficient four wave mixing in InGaP photonic crystal waveguides. Conversion efficiencies of -52.5dB for two ~1mW CW signals, and -38.8dB for a 1.4mW CW probe and a 14.4mW pulsed pump were demonstrated.

Continuous-wave second-harmonic generation in modal phase matched semiconductor waveguides

We report the observation of continuous-wave second-harmonic generation in a modalphase-matched GaAs/AlGaAs waveguide. The heterostructure has been designed to generate a second-harmonic signal via a type-II process with a fundamental signal around 1.55 μm. Continuous wave conversion enables a quantitative estimation of the conversion efficiency. In our case, η=30%±5% W−1 cm−2 is found experimentally.

Second-harmonic generation through optimized modal phase matching in semiconductor waveguides

We report optical second-harmonic generation (SHG) through modal phase matching in GaAs/AlGaAs semiconductor waveguides. Using femtosecond pulses, both type-I and type-II SHG is demonstrated for fundamental wavelengths near 1.55 μm.

Top grating index-coupled distributed feedback quantum cascade lasers

We report on the modeling and design of top grating distributed feedback (DFB) quantum cascade lasers (QCLs). A low loss, index-coupled, DFB design that is very robust against technological spreads is proposed. Strong DFB coupling conditions are obtained while maintaining a high laser output power. Following this design, DFB QCL lasers with InP cladding layers and InGaAs∕AlInAs active regions have been fabricated. Room temperature monomode QCLs with 30dB side mode suppression ratios are demonstrated over a 4–8μm wavelength range.

Theory of slow light enhanced four-wave mixing in photonic crystal waveguides

The equations for Four-Wave-Mixing in a Photonic Crystal waveguide are derived accurately. The dispersive nature of slow-light enhancement, the impact of Bloch mode reshaping in the nonlinear overlap integrals and the tensor nature of the third order polarization are therefore taken into account. Numerical calculations reveal substantial differences with simpler models, which increase with decreasing group velocity. We predict that the gain for a 1.3 mm long, unoptimized GaInP waveguide will exceed 10 dB if the pump power exceeds 1 W.

Time-Wavelength Reflectance Maps of Photonic Crystal Waveguides: A New View on Disorder-Induced Scattering

We investigate the impact of disorder on the propagation of photonic crystal waveguide modes using phase-sensitive optical low-coherence reflectometry.Combined with a suitable numerical processing, this technique reveals a considerable amount of information that we cast as time-wavelength reflectance maps. By comparing measurements on different samples, we easily identify inter-mode scattering and propagation losses mediated by slow leaky modes. We also characterize the dispersive behaviour of point defects. Our results verify previous theoretical predictions about the general group velocity scaling of losses and the dominant role of backscattering.

Intracavity sum-frequency generation in GaAs quantum cascade lasers

Emission of coherent light at 5.75 μm wavelength has been obtained by intracavity frequency doubling of a GaAs-based quantum cascade laser. This nonlinearity originates from the second-order susceptibility of the bulk material hosting the heterostructure and can be exploited by growing the quantum cascade laser on a 〈111〉 substrate.

Efficient second-harmonic generation in birefringently phase-matched GaAs/Al(2)O(3) waveguides.

We report efficient second-harmonic generation of femtosecond pulses in birefringently phase-matched GaAs/Al(2)O(3) waveguides pumped at 2.01mum. By use of pump pulses of ~200-fs duration and type I interaction, practical second-harmonic average powers of up to ~650muW were obtained, with an average input power of ~50muW. Waveguides of four different widths and two different lengths were investigated, and a normalized conversion efficiency of greater than 1000%W(-1)cm(-2) was obtained for a 1-mm waveguide. Measurements of pump and second-harmonic spectra provided clear evidence of phase matching and depletion of the pump spectrum. The measured bandwidth of the second harmonic was ~1.3nm. From the measurements of transmitted pump power at the phase-matching wavelength, pump depletions of more than 80% were recorded.