Composition variation in Al-based dilute nitride alloys using apertureless scanning near-field optical microscopy.

We use apertureless scanning near-field optical microscopy to study the phase separation in chemical beam epitaxy grown Al0.1Ga0.9NxAs1-x alloys. Pits attributed to nitrogen-clustering observed on the Al0.1Ga0.9NxAs1-x surface grown at 420 °C become larger at higher growth temperatures, and 3D islands appear on the surface at 565 °C. Atomic force microscopy phase measurements reveal a composition difference between the islands and the pits, whereas the sample grown at 420 °C appears to be homogeneous. Confocal Raman spectra show that all the N atoms are bonded to Al instead of Ga. Using apertureless scanning near-field optical microscopy, the luminescence of a gold tip is mapped over the surface of the sample grown at 565 °C. We extract the shift of the tip's surface plasmon resonance and determine the variation in the refractive index between the islands and the pits to be close to 0.2. Numerical simulations of the tip luminescence while in contact with the sample predict a similar variation of ∼0.3 in the refractive indices between AlGaAs islands and AlN pits, a substantially smaller value than the difference in the bulk refractive indices of the two media (∼1.8), which we attribute to a convolution of material distribution in an uneven topography. The excellent agreement between simulation and experiments supports the hypothesis of nitrogen-clustering in the pits.

Second harmonic generation in AlGaAs photonic wires using low power continuous wave light.

We report modal phase matched (MPM) second harmonic generation (SHG) in high-index contrast AlGaAs sub-micron ridge waveguides, by way of sub-mW continuous wave powers at telecommunication wavelengths. We achieve an experimental normalized conversion efficiency of ~14%/W/cm2, obtained through a careful sub-wavelength design supporting both the phase matching requirement and a significant overlap efficiency. Furthermore, the weak anomalous dispersion, robust fabrication technology and possible geometrical and thermal tuning of the device functionality enable a fully integrated multi-functional chip for several critical areas in telecommunications, including wavelength (time) division multiplexing and quantum entanglement.

Temperature dependent photoluminescence properties of InAs/InP quantum dashes subjected to low energy phosphorous ion implantation and subsequent annealing.

We report on the impact of phosphorous ion-implantation-induced band gap tuning on the temperature dependent photoluminescence (PL) properties of InAs/InP quantum dashes (QDas). The high temperature range carriers' activation energy, extracted from Arrhenius plots, is found to decrease from 238 to 42 meV when the ion implantation dose increases from 10(11) cm(-2) to 5 x 10(14) cm(-2) which is consistent with the observed emission energy blueshift increase with increasing the ion implantation doses. This effect is attributed to the As/P exchange which reduces the carrier confining potential depth. For intermediate ion implantation doses the reduced carrier confining potential barrier combined with the non-uniform intermixing process, that causes an increased QDas size dispersion, result in anomalous temperature-dependent PL properties. Indeed, the temperature induced PL emission energy redshift measured between 10 K and 300 K is found to be strongly affected by the carrier redistribution within the broadened localized QDas states.

Observation of PT-symmetry breaking in complex optical potentials.

In 1998, Bender and Boettcher found that a wide class of Hamiltonians, even though non-Hermitian, can still exhibit entirely real spectra provided that they obey parity-time requirements or PT symmetry. Here we demonstrate experimentally passive PT-symmetry breaking within the realm of optics. This phase transition leads to a loss induced optical transparency in specially designed pseudo-Hermitian guiding potentials.

Fabrication of silicon nitride waveguides for visible-light using PECVD: a study of the effect of plasma frequency on optical properties.

This paper presents work aimed at optimizing the fabrication of silicon nitride Si(x)N(y) thin-film visible-light planar waveguides using plasma-enhanced chemical vapour deposition (PECVD). The effects of plasma frequency, precursor gas ratio, and thermal annealing in relation to waveguide optical properties (refractive index, propagation losses) are studied. Experimental results over a wide range of precursor gas ratios show convincingly that waveguides fabricated using low-frequency PECVD have lower propagation losses in the visible range compared to waveguides of equal refractive index fabricated with high-frequency PECVD.

Optical spatial solitons at the interface between two dissimilar periodic media: theory and experiment.

Discrete spatial solitons traveling along the interface between two dissimilar one-dimensional arrays of waveguides were observed for the first time. Two interface solitons were found theoretically, each one with a peak in a different boundary channel. One evolves into a soliton from a linear mode at an array separation larger than a critical separation where-as the second soliton always exhibits a power threshold. These solitons exhibited different power thresholds which depended on the characteristics of the two lattices. For excitation of single channels near and at the boundary, the evolution behavior with propagation distance indicates that the solitons peaked near and at the interface experience an attractive potential on one side of the boundary, and a repulsive one on the opposite side. The power dependence of the solitons at variable distance from the boundary was found to be quite different on opposite sides of the interface and showed evidence for soliton switching between channels with increasing input power.

Power-dependent switching of nonlinear trapping by local photonic potentials.

We study experimentally and numerically the nonlinear scattering of wave packets by local multisite guiding centers embedded in a continuous dielectric medium as a function of the input power and angle of incidence. The extent of trapping into the linear modes of different sites is manipulated as a function of both the input power and the angle of incidence, demonstrating power-controlled switching of nonlinear trapping by local photonic potentials.

Inhomogeneous broadening and alloy intermixing in low proton dose implanted InAs/GaAs self-assembled quantum dots.

In this work, low-temperature photoluminescence (PL) and photoluminescence excitation (PLE) experiments have been carried out to investigate the optical and electronic properties of InAs/GaAs quantum dots (QDs) subjected to room-temperature proton implantation at various doses (5 × 10(10)-10(14) ions cm(-2)) and subsequent thermal annealing. The energy shift of the main QD emission band is found to increase with increasing implantation dose. Our measurements show clear evidence of an inhomogeneous In/Ga intermixing at low proton implantation doses (≤5 × 10(11) ions cm(-2)), giving rise to the coexistence of intermixed and non-intermixed QDs. For higher implantation doses, a decrease of both the PL linewidth and the intersublevel spacing energy have been found to occur, suggesting that the dot-size, dot-composition and dot-strain distributions evolve towards more uniform ones.

Nonlinear scattering and trapping by local photonic potentials.

We experimentally study the nonlinear scattering by local photonic structures embedded in continuous Kerr media and demonstrate nonlinear trapping in guiding structures and resonant transmission in antiguiding structures. An intuitive physical picture is presented and verified in simulations.