Spontaneous Symmetry Breaking in a Coherently Driven Nanophotonic Bose-Hubbard Dimer.

We report on the first experimental observation of spontaneous mirror symmetry breaking (SSB) in coherently driven-dissipative coupled optical cavities. SSB is observed as the breaking of the spatial or mirror Z_{2} symmetry between two symmetrically pumped and evanescently coupled photonic crystal nanocavities, and manifests itself as random intensity localization in one of the two cavities. We show that, in a system featuring repulsive boson interactions (U>0), the observation of a pure pitchfork bifurcation requires negative photon hopping energies (J<0), which we have realized in our photonic crystal molecule. SSB is observed over a wide range of the two-dimensional parameter space of driving intensity and detuning, where we also find a region that exhibits bistable symmetric behavior. Our results pave the way for the experimental study of limit cycles and deterministic chaos arising from SSB, as well as the study of nonclassical photon correlations close to SSB transitions.

N6L pseudopeptide interferes with nucleophosmin protein-protein interactions and sensitizes leukemic cells to chemotherapy.

NPM1 is a multifunctional nucleolar protein implicated in several processes such as ribosome maturation and export, DNA damage response and apoptotic response to stress stimuli. The NPM1 gene is involved in human tumorigenesis and is found mutated in one third of acute myeloid leukemia patients, leading to the aberrant cytoplasmic localization of NPM1. Recent studies indicated that the N6L multivalent pseudopeptide, a synthetic ligand of cell-surface nucleolin, is also able to bind NPM1 with high affinity. N6L inhibits cell growth with different mechanisms and represents a good candidate as a novel anticancer drug for a number of malignancies of different histological origin. In this study we investigated whether N6L treatment could drive antitumor effect in acute myeloid leukemia cell lines. We found that N6L binds NPM1 at the N-terminal domain, co-localizes with cytoplasmic, mutated NPM1, and interferes with its protein-protein associations. N6L toxicity appears to be p53 dependent but interestingly, the leukemic cell line harbouring the mutated form of NPM1 is more resistant to treatment, suggesting that NPM1 cytoplasmic delocalization confers protection from p53 activation. Moreover, we show that N6L sensitizes AML cells to doxorubicin and cytarabine treatment. These studies suggest that N6L may be a promising option in combination therapies for acute myeloid leukemia treatment.

Leftward oculomotor prismatic training induces a rightward bias in normal subjects.

Wedge prisms shifting the visual field laterally create a mismatch between the straight ahead position signalled by vision and that encoded by extraretinal and head-on-trunk proprioceptive information. Short-term adaptation to left-deviating prisms in normal subjects results in a visuomotor attentional bias towards the right-hand side (aftereffect). Prismatic adaptation (PA) is usually induced through a training consisting in repeated ballistic movements of the dominant arm towards visual targets, while participants are wearing prismatic goggles. The present study demonstrates that an original oculomotor PA procedure with leftward deviating prisms-without pointing movements and only consisting in repeated gaze shifts towards visual targets-can induce a rightward bias in normal subjects as assessed by visual straight ahead and line bisection tasks (Experiments 1 and 2). We show that oculomotor PA induces a bias in line bisection similar to that reported after visuomotor PA (Experiment 2). We suggest that a conflict between retinal, extraretinal and proprioceptive information about the straight ahead location causes the observed effects. In follow-up experiments 3, 4, and 5, we demonstrate that neither eye deviation without prisms nor shift of the visual field without eye deviation induces PA biases. We propose that an optimal integration model of visual and proprioceptive inputs can best account for the observed results.

Asymmetric mode scattering in strongly coupled photonic crystal nanolasers.

We investigate the basic mechanism of nonlinear mode competition in two semiconductor-coupled nanocavities operating in the laser regime. For this, we study energy transfer between bonding (in-phase) and anti-bonding (out-of-phase) modes of the system formed by two strongly coupled photonic crystal nanolasers. We experimentally observe mode switching from the blue-detuned to the red-detuned mode as the pump power is increased. A semi-classical description in terms of mean-field equations allows us to explain this phenomenon as stimulated scattering due to carrier population oscillations in the cavities at the mode splitting frequency. We predict such asymmetrical mode interaction to be universal in arrays of optically coupled semiconductor micro and nanocavities.

Ultra-compact III‒V-on-Si photonic crystal memory for flip-flop operation at 5 Gb/s.

We report on a photonic crystal (PhC) nanolaser based on the heterogeneous integration of a III-V PhC nanocavity on SOI, configured to operate as a Set-Reset Flip-Flop (SR-FF). The active layer is a nanobeam cavity made of a 650 nm × 285 nm InP-based wire waveguide evanescently coupled to 500 nm × 220 nm SOI wire waveguides, demonstrating a record-low footprint of only 6.2 µm2. Injection locking enables optical bistability allowing for memory operation with only 6.4 fJ/bit switching energies and <50 ps response times. Bit-level SR-FF memory operation was evaluated at 5 Gb/s with PRBS-resembling data patterns, revealing error free operation with a negative power penalty.

Modulation contrast optimization for wavelength conversion of a 20 Gbit/s data signal in hybrid InP/SOI photonic crystal nanocavity.

Photonic crystal cavity-based switching is studied both theoretically and experimentally in order to identify the best configuration to maximize "wavelength conversion" efficiency. In particular, it is shown that an enhanced contrast can be reached when the probe is blueshifted with respect to the resonance. The use of an InP/SOI hybrid photonic crystal nanocavity is reported for the first time for all-optical error-free "wavelength conversion" at 20 Gbit/s with a nonreturn to zero on-off keying signal.

Temporal ringdown of silicon-on-insulator racetrack resonators.

Ring-down temporal measurements of silicon-on-insulator wire racetrack resonators are performed with 150 fs input pulses using a parametric process in a nonlinear crystal to gate and amplify the weak output pulses. We measure the cavity round trip time and the quality factor of these all-pass filters and find excellent agreement with continuous wave spectroscopic measurements as well as with an analytic model built using numerical solutions for the fully vectorial waveguide modes.

Coupling light into a slow-light photonic-crystal waveguide from a free-space normally-incident beam.

We present a coupler design allowing normally-incident light coupling from free-space into a monomode photonic crystal waveguide operating in the slow-light regime. Numerical three-dimensional calculations show that extraction efficiencies as high as 80% can be achieved for very large group indices up to 100. We demonstrate experimentally the device feasibility by coupling and extracting light from a photonic crystal waveguide over a large group-index range (from 10 to 60). The measurements are in good agreement with theoretical predictions. We also study numerically the impact of various geometrical parameters on the coupler performances.

Uniformity of the lasing wavelength of heterogeneously integrated InP microdisk lasers on SOI.

We report a high lasing wavelength uniformity of optically pumped InP-based microdisk lasers processed with electron-beam lithography, heterogeneously integrated with adhesive bonding on silicon-on-insulator (SOI) waveguide circuits and evanescently coupled to an underlying waveguide. We study the continuous wave laser emission coupling out of the SOI via a grating coupler etched at one side of the waveguide, and demonstrate a standard deviation in lasing wavelength of nominally identical devices on the same chip lower than 500 pm. The deviation in the diameter of the microdisks as low as a few nanometers makes all-optical signal processing applications requiring cascadability possible.

Enhancement of a nano cavity lifetime by induced slow light and nonlinear dispersions.

We start from a 2D photonic crystal nanocavity with moderate Q-factor and dynamically increase it by two order of magnitude by the joint action of coherent population oscillations and nonlinear refractive index.

High quality beaming and efficient free-space coupling in L3 photonic crystal active nanocavities.

We report on far-field measurements of L3 photonic crystal (PhC) cavities with high quality beaming. This is achieved by means of the so-called "band folding" technique, in which a modulation of the radius of specific holes surrounding the cavity is introduced. Far-field patterns are measured from photoluminescence of quantum wells embedded in the PhC. A very good agreement between experimental results and simulated radiation patterns has been found. Laser effect is demonstrated in the beaming cavity with a threshold comparable to the regular one. In addition, free-space input coupling to this cavity has been achieved. In order to fully analyze the coupling efficiency, we generalize the approach developed in S. Fan, et al., [J. Opt. Soc. Am. A 20, 569 (2003)], relaxing the hypothesis of mirror symmetry. The obtained coupling efficiencies are about 15% with quality factors (Q) exceeding 10(4). These results further validate the "folding" technique on L3 cavities for nanocavity realization with efficient free-space coupling and high Q factors.

Nanocavity linewidth narrowing and group delay enhancement by slow light propagation and nonlinear effects.

Slow light induced by coherent population oscillations and cavity dispersive nonlinear response are combined achieving 2 orders of magnitude enhancement of the group delay and an equivalent decreasing of the spectral linewidth of a L3 two-dimensional photonic crystal nanocavity.

Hybrid III-V semiconductor/silicon nanolaser.

Heterogeneous integration of III-V compound semiconductors on Silicon on Insulator is one the key technology for next-generation on-chip optical interconnects. In this context, the use of photonic crystals lasers represents a disruptive solution in terms of footprint, activation energy and ultrafast response. In this work, we propose and fabricate very compact laser sources integrated with a passive silicon waveguide circuitry. Using a subjacent Silicon-On-Insulator waveguide, the emitted light from a photonic crystal based cavity laser is efficiently captured. We study experimentally the evanescent wave coupling responsible for the funneling of the emitted light into the silicon waveguide mode as a function of the hybrid structure parameters, showing that 90% of coupling efficiency is possible.

Enhanced efficiency of the second harmonic inhomogeneous component in an opaque cavity.

In this Letter, we experimentally demonstrate the enhancement of the inhomogeneous second harmonic conversion in the opaque region of a GaAs cavity with efficiencies of the order of 0.1% at 612 nm, using 3 ps pump pulses having peak intensities of the order of 10 MW/cm(2). We show that the conversion efficiency of the inhomogeneous, phase-locked second harmonic component is a quadratic function of the cavity factor Q.

Cardiac complications and mortality rates in diabetic patients following non-cardiac surgery in an Australian teaching hospital.

This retrospective study of diabetic patients undergoing non-cardiac surgery has identified that a greater number of patients are at risk of cardiac complications and death in the perioperative period than had previously been suggested. As well as insulin-dependent diabetic patients and patients with elevated creatinine (> 178 micromol/l) as previously found, our study suggests that non-insulin-dependent diabetic patients and patients with creatinine > 120 micromol/l are also at increased risk of cardiac complications and death following non-cardiac surgery. This increases by a factor of six those diabetic patients at risk of perioperative complications from non-cardiac surgery and also increases the number of patients with renal failure similarly at risk. The study confirms similar risks of cardiac complications and death to other recently published data and suggests ongoing comparisons will contribute to quality assurance activities in anaesthesia and surgery.

Continuous-wave operation of photonic band-edge laser near 1.55 microm on silicon wafer.

We report on the continuous-wave operation of a band edge laser at room temperature near 1.55 mum in an InGaAs/InP photonic crystal. A flat dispersion band-edge photonic mode is used for surface normal operation. The photonic crystal slab is integrated onto a Silicon chip by means of Au/In bonding technology, which combines two advantages, efficient heat sinking and broad band reflectivity.

Fast thermo-optical excitability in a two-dimensional photonic crystal.

We experimentally demonstrate excitability in a semiconductor two-dimensional photonic crystal. Excitability is a nonlinear dynamical mechanism underlying pulselike responses to small perturbations in systems possessing one stable state. We show that a band-edge photonic crystal resonator exhibits class II excitability, resulting from the nonlinear coupling between the high-Q optical mode, the charge-carrier density, and the fast (sub-micros) thermal dynamics. In this context, the critical slowing down of the electro-optical dynamics close to the excitable threshold can delay the optical response by an amount comparable to the duration of the output pulse (5 ns). The latter results from a short thermal dynamical excursion along a high local intensity manifold of the phase space.

Nonadiabatic dynamics of the electromagnetic field and charge carriers in high-Q photonic crystal resonators.

We address, both experimentally and theoretically, phase and amplitude dynamics of the electromagnetic field in a two-dimensional photonic crystal when femtosecond pulses are injected. We demonstrate that the usual adiabatic approximation underlying the dynamics of field and carriers in a semiconductor resonator is no longer valid, since in general the photon lifetime cannot be neglected with respect to the carrier recombination lifetime. Parameter regions where adiabaticity is broken are shown, and the ubiquity of the observed dynamical scenario in the new generation of active photonic microresonators is predicted.

Tuning a two-dimensional photonic crystal resonance via optical carrier injection.

We report on wide wavelength tuning through optical injection of carriers of a photonic resonance observed in reflectivity at 1543 nm in an InP-based two-dimensional photonic crystal slab. An 8-nm blueshift, which represents 20 times the resonance linewidth, is observed when a 4-kW/cm2 intense optical pump is incident on the sample. An analytical model that we developed, based on a coupled-mode nonlinear approach, allows us to describe this phenomenon in detail.