Search

Excitability, encountered in numerous fields from biology to neurosciences and optics, is a general phenomenon characterized by an all-or-none response of a system to an external perturbation of a given strength. When subject to delayed feedback, excitable systems can sustain multistable pulsing regimes, which are either regular or irregular time sequences of pulses reappearing every delay time. Here, we investigate an excitable microlaser subject to delayed optical feedback and study the emergence of complex pulsing dynamics, including periodic, quasiperiodic, and irregular pulsing regimes. This work is motivated by experimental observations showing these different types of pulsing dynamics. A suitable mathematical model, written as a system of delay differential equations, is investigated through an in-depth bifurcation analysis. We demonstrate that resonance tongues play a key role in the emergence of complex dynamics, including non-equidistant periodic pulsing solutions and chaotic pulsing. The structure of resonance tongues is shown to depend very sensitively on the pump parameter. Successive saddle transitions of bounding saddle-node bifurcations constitute a merging process that results in unexpectedly large regions of locked dynamics, which subsequently disconnect from the relevant torus bifurcation curve; the existence of such unconnected regions of periodic pulsing is in excellent agreement with experimental observations. As we show, the transition to unconnected resonance regions is due to a general mechanism: the interaction of resonance tongues locally at an extremum of the rotation number on a torus bifurcation curve. We present and illustrate the two generic cases of disconnecting and disappearing resonance tongues. Moreover, we show how a pair of a maximum and a minimum of the rotation number appears naturally when two curves of torus bifurcation undergo a saddle transition (where they connect differently). [ABSTRACT FROM AUTHOR]

We investigated the dark current components of thin planar InGaAs photodiodes grown by metalorganic vapor-phase epitaxy for optical nano-resonators. Owing to their high electric field enhancement, nano-resonators make it possible to substantially reduce the thickness of the active region to about 100?nm all the while maintaining high quantum efficiency. In the present study, to cover a broad spectral band, we combined several resonance peaks induced by guided-mode resonances in a given spectral range. This type of geometry allowed us to introduce InAlAs at the edge of a thin InGaAs active region in order to drastically reduce both the diffusion current and the generation/recombination current. We found that, in such devices, tunneling dark current components increase as the thickness of the active layer is reduced and dominate the reverse dark current. By optimizing the epitaxial stack, while keeping its total thickness constant (the optical properties of the nano-resonator remained unchanged), we showed that we are already able to achieve a specific detectivity of up to 1 × 1013?cm √Hz W-1 for λ = 1.55 μm&. [ABSTRACT FROM AUTHOR]

We investigate infrared detection at room temperature using non-degenerate two-photon absorption in a nanostructured indium phosphide photodiode. We designed the detector structure to achieve a good nonlinear absorption by combining three major ideas: first, we use the non-degenerate two-photon absorption process, which is known to be more efficient than the previously used degenerate two-photon absorption. Second, we ensured a correct spatial overlap of our pump field with our signal field. Third, we optimized the nanostructuration to increase the signal field amplitude locally within the active medium of the device. The resulting device consists of a PIN junction embedded between a back-reflecting gold mirror and a top grating. We experimentally characterized our diode with regard to reflectivity and two-photon absorption generated photocurrent for a continuous-wave pump and a nanosecond pulsed signal of around 3.39 μm. Owing to the nanostructuration, the generated photocurrent shows a gain of 24 with respect to the bulk response of InP. [ABSTRACT FROM AUTHOR]

We present a detailed experimental analysis on mid-infrared superradiant emission from highly doped quantum wells. The emission originates from the radiative decay of intersubband plasmon excitations, which are electrically injected by directly contacting the two-dimensional electron gas. For the experiment, we processed an InGaAs/AlInAs quantum well into a three terminal field effect transistor with a leaky gate. Depending on the current pathway, we observe either a purely thermal excitation (source to drain injection) or a combination between thermal and resonant excitations (gate to source and drain injection). The scaling of the optical power with the density of electrons in the channel is in excellent agreement with the superradiant nature of the plasmon decay. [ABSTRACT FROM AUTHOR]

Ultrafast switching with low energies is demonstrated using InP photonic crystal nanocavities embedding InGaAs surface quantum wells heterogeneously integrated to a silicon on insulator waveguide circuitry. Thanks to the engineered enhancement of surface non radiative recombination of carriers, switching time is obtained to be as fast as 10 ps. These hybrid nanostructures are shown to be capable of achieving systems level performance by demonstrating error free wavelength conversion at 10 Gbit/s with 6 mWswitching powers. [ABSTRACT FROM AUTHOR]

Instrumented nanoindentation is used in conjunction with scanning transmission electron microscopy to evaluate the mechanical resistance at the bonding interface of a 450 nm thick InP membrane bonded oxide-free to Si. Indentation using a Berkovich tip is shown to cause the planes in InP to rotate by as much as 16°. The shear stress resulting from this rotation causes the InP membrane to buckle, forming a debonded blister around the indented zone. The geometry of this blister is used to compute the surface bond energy of InP bonded oxide-free to Si. An average surface bonding energy of 585 mJ m-2 is reported. [ABSTRACT FROM AUTHOR]

A plasmonic microcavity providing broadband control of spontaneous emission for large and sparse semiconductor quantum dots emitting at telecommunications wavelengths is proposed. By designing and fabricating such a cavity, we demonstrate a broadband Purcell effect with spontaneous emission enhancement over a broad spectral range of Δλ≃20 nm with a 3.9-fold maximum enhancement, as well as inhibition over Δλ≃100 nm around 1.3 μm. The broadband feature relaxes the constraint on spectral matching between the dot emission and the cavity mode, favourable for implementing efficient non-classical light sources or nanoscale lasers. [ABSTRACT FROM AUTHOR]