Jean-Yves Emery

Lateral modulations in zero‐net‐strained GaInAsP multilayers grown by gas source molecular‐beam epitaxy

Compressive GaInAsP multiple quantum wells (MQW) grown by gas source molecular‐beam epitaxy present altered structural and optical characteristics when tensile GaInAsP barriers are used instead of lattice‐matched ones. An alternate tensile/compressive GaInAsP MQW has been examined by transmission electron microscopy. A strong lateral modulation of thickness, strain, and probably chemical composition was shown. This modulation exhibits pronounced anisotropy, with a periodicity of about 50 nm along the [110] direction. Although its origin is not fully accounted for yet, it seems to allow partial elastic relaxation of tensile layers. Based on this analysis, a schematic description of distortion modulation is proposed.

Gas source molecular beam epitaxy of alternated tensile / compressive strained GaInAsP multiple quantum wells emitting at 1.5 μm

Abstract Compressive and tensile strained GaInAsP layers as well as zero-net strain multiple quantum wells, grown by gas source molecular beam epitaxy, have been investigated. Reflection high energy electron diffraction patterns show two-dimensional growth for compressive strained layers ( Δa a . Three-dimensional growth is observed after a few nanometers for tensile strained layers even for low tensile value ( Δa a . Transmission electron microscopy shows that three-dimensional growth of a tensile strained layer is related to a quasi-periodic composition modulation along the [110] in the epitaxial plane.

Hot phonons and Auger related carrier heating in semiconductor optical amplifiers

We have directly measured the carrier temperature in semiconductor optical amplifiers (SOAs) via spontaneous emission and we demonstrate an unexpectedly high carrier temperature. The direct correlation of the temperature increase with the carrier density suggests Auger recombination as the main heating mechanism. We have developed a model based on rate equations for the total energy density of electrons, holes, and longitudinal-optical phonons. This model allows us to explain the thermal behavior of carrier and phonon populations. The strong heating observed is shown to be due to the combined effects of hot phonon and Auger recombination in the valence band. We also observe an evolution of the Auger process, as the density is increased, from cubic to square dependence with coefficients C/sub 3/ = 0.9 10/sup -28/ cm/sup 6/ s/sup -1/ and C/sub 2/ = 2.4 10/sup -10/ cm/sup 3/ s/sup -1/. This change is explained by the hole quasi-Fermi level entering the valence band.

Direct observation of longitudinal spatial hole burning in semiconductor optical amplifiers with injection

Measurements of spontaneous emission from InGaAsP semiconductor optical amplifiers provide information on both the carrier density and temperature. By spatially resolving the light emitted along the active layer of the device, we find evidence of longitudinal spatial hole burning which results from amplified spontaneous emission in the structure and is modified by the injected optical signal. Under injection, we also observe pronounced asymmetry of the amplified spontaneous emission intensity from the two facets which we relate to the carrier density profile. The experimental results are in good agreement with numerical simulations. An analysis of the measured spectra reveals an unexpected very high temperature (400 K) and its decrease by at least 35 K in the middle of the device when light is injected

Direct measurement of lateral elastic modulations in a zero‐net strained GaInAsP/InP multilayer

A zero‐net strained GaInAsP/InP(001) multilayer grown by gas source molecular beam epitaxy exhibits large interfacial undulations and an orthorhombic modulated distortion, which are attributed to elastic relaxation of tensile layers. It is examined by high resolution transmission electron microscopy in order to directly determine the strain distribution in the (110) plane. The interplanar spacings are found to be laterally modulated along the [110] direction within tensile and compressive layers. The interplanar spacing modulation is perfectly correlated to the interfacial morphology. Therefore, the strain is not homogeneous but concentrated along [110] oriented lines. Large variations of (110) interplanar spacings up to 3.5% have been measured, while the lattice mismatch between tensile and compressive layers is only 2%. The observed strain distribution is qualitatively consistent with an elastic relaxation mechanism of the tensile layer. Different other effects are reviewed. Surface relaxation effects...

Strained quaternary GaInAsP quantum well lasee emitting at 1.5 μm grown by gas source molecular beam epitaxy

Abstract Quantum well structures and separate confinement heterostructure lasers based on strained quaternary Ga 1− x In x As 1− y P y well material were grown by gas source molecular beam epitaxy. The substitution of As for P allows a simultaneous control of wavelength, well width and strain in the structure. Single strained layers in InP show photoluminescence with narrow linewidth (4 to 8 meV). Broad area lasers with strained and unstrained layers have been grown with five quantum wells and identical optical confinement. The strained quaternary structure has a threshold current density of 760 A/cm 2 for L = 400 μm, an internal quantum efficiency of nearly 100%, a waveguide loss of 10 cm -1 and a high T 0 value ( T 0 = 91 K). Single-well structures have a lowest value of 240 A/cm 2 for 3 mm long devices.

Observation of dark-pulse formation in gain-clamped semiconductor optical amplifiers by cross-gain modulation

We have measured the ultrafast simultaneous cross-gain and laser mode dynamics in a gain-clamped semiconductor amplifier perturbed by an intense detuned 150 fs pump pulse. Besides relaxation oscillations, we demonstrate the instantaneous formation of a dark pulse in the laser mode that repeats itself with a period given by the cavity round-trip time. The dark pulse sequence subsequently decays into two-mode beating and is shown to weakly cross modulate the amplifier gain. To describe dark-pulse formation a time- and spatially dependent model based on rate equations is necessary. The experimental results are in reasonable agreement with numerical simulations

First array of 8 CG-SOA gates for large-scale WDM space switches

We report here on an 8 CG-SOA gate array with uniform characteristics for WDM large-scale space switches operating at 1550 nm. The mean fiber-to-fiber gain and noise figure n/sub sp//C/sub 1/ yield 19 dB and 6.6 dB at 200 mA, respectively.

Optical speedup at transparency of the gain recovery in semiconductor optical amplifiers

Experimental demonstration of optical speedup at transparency (OSAT) has been performed on a 1 mm long semiconductor optical amplifiers (SOA). OSAT is a recently proposed scheme that decreases the recovery time of an SOA while maintaining the available gain. It is achieved by externally injecting into the SOA the beam of a separate high power laser at energies around the transparency point. Even though the experimental conditions were not optimal, a beam of 100 mW decreases the recovery time by a third when it is injected in the vicinity of the material transparency point of the device. This acceleration of the device response without detrimental reduction of the gain is found to be effective over a broad wavelength window of about 20 nm around transparency. The injection of the accelerating beam into the gain region is a less efficient solution not only because the gain is then strongly diminished but also because speeding is reduced. This originates from the reduction of the amplified spontaneous emission power in the device, which counterbalances the speeding capabilities of the external laser beam. Another advantage of the OSAT scheme is realized in relatively long SOAs, which suffer from gain overshoot under strong current injection. Simulations show that OSAT decreases the gain overshoot, which should enable us to use OSAT to further speedup the response of long SOAs.

SOA-based optical network components

SOA-based devices provide a family of key components for optical networks, including wavelength conversion, regeneration, space switching and wavelength selection. All these functions require integration of multiple SOAs that calls for efficient combination of monolithic and hybrid integration to reach performances and cost effective solutions. Several examples are presented and discussed.