Liquid crystal micro-cells for tunable VCSELs

International audienceWe recently demonstrated the tunability of a VCSEL with an intra-cavity liquid crystal layer. This demonstration was made on a macroscopic-sized sample with optical pumping. For a further development of this solution, it is necessary to place the liquid crystal on microscopic VCSEL chips. We developed a microtechnology process which makes it possible to fabricate liquid crystal micro-cells in a collective process

Impact of the capping layers on lateral confinement in InAs/InP quantum dots for 1.55 um laser applications srudied by magneto-photoluminescence.

We have used magnetophotoluminescence to study the impact of different capping layer material combinations (InP, GaInAsP quaternary alloy, or both InP and quaternary alloy) on lateral confinement in InAs/InP quantum dots (QDs) grown on (311)B orientated substrates. Exciton effective masses, Bohr radii, and binding energies are measured for these samples. Conclusions regarding the strength of the lateral confinement in the different samples are supported by photoluminescence at high excitation power. Contrary to theoretical predictions, InAs QDs in quaternary alloy are found to have better confinement properties than InAs/InP QDs. This is attributed to a lack of lateral intermixing with the quaternary alloy, which is present when InP is used to (partially) cap the dots. The implications of the results for reducing the temperature sensitivity of QD lasers are discussed. ©2005 American Institute of Physic

Growth of quantum wires for long-wavelength VCSEL with a polarized laser emission

International audienceWe report continuous-wave operation at room temperature for a 1.55-µm VCSEL where the active region is made up of quantum-well. Now, self-organized quantum wires grown on InP substrate is used to obtain polarized laser emission

Design of InGaAs/InP 1.55μm vertical cavity surface emitting lasers

International audienceThe design of an electrically pumped InGaAs quantum well based vertical cavity surface emitting laser (VCSEL) on InP substrate is presented. Such optically pumped VCSELs have already been demonstrated. To design electrically pumped VCSEL, three simulations steps are needed: optical simulation gives access to the electric field repartition, to design the active zone and the Bragg mirrors. Thermal simulation is helpful to design metallic contacts while the energy band diagram is obtained by electrical simulation to design the buried tunnel junction useful for carrier injection. All these simulations are compared to experiment

Si wafer bonded of a-Si/a-SiNx distributed Bragg reflectors for 1.55-µm wavelength vertical cavity surface emitting lasers

International audienceAmorphous silicon (a-Si) and amorphous silicon nitride (a-SiNx) layers deposited by magnetron sputtering have been analyzed in order to determine their optical and surface properties. A large value of ~1.9 of index difference is found between these materials. Distributed Bragg reflectors (DBR) based on these dielectric materials quarter wave layers have been studied by optical measurements and confronted to theoretical calculations based on the transfer matrix method. A good agreement has been obtained between the experimental and expected reflectivity. A maximum reflectivity of 99.5% at 1.55 µm and a large spectral bandwidth of 800 nm are reached with only four and a half periods of a-Si/a-SiNx. No variation of the DBR reflectivity has been observed with the time nor when annealed above 240°C and stored during few months. This result allows to use this DBR in a metallic bonding process to realize a vertical cavity surface emitting laser (VCSEL) with two dielectric a-Si/a-SiNx DBR. This bonding method using AuIn2 as the bonding medium and Si substrate can be performed at a low temperature of 240°C without damaging the optical properties of the microcavity. The active region used for this VCSEL is based on lattice-matched InGaAs/InGaAsP quantum wells and a laser emission has been obtained at room-temperature on an optically pumped device

Self-assembled InAs quantum dots grown on InP (3 1 1)B substrates: Role of buffer layer and amount of InAs deposited

International audienceThe formation of InAs quantum dots by Stransky–Krastanow method on (3 1 1)B InP substrates has been studied. On Al0.48In0.52As alloy lattice matched on InP, large changes of the quantum dot structural characteristics have been observed as a function of the amount of InAs deposited and of the arsenic pressure during the InAs quantum dot formation. Small quantum dots (minimum diameter=20 nm) in very high density (1.3×1011 quantum dots per cm2) have been achieved in optimized growth conditions. These results are interpreted from the strong strain field interaction through the substrate at high density and from the InAs surface energy evolutions with the Arsenic pressure. The effect on quantum dot characteristics of the arsenic pressure during the growth of Al0.48In0.52As buffer layers has also been investigated. Despite the importance of this parameter on the Al0.48In0.52As clustering, weak changes have been observed

Design and fabrication of a tunable InP-based VCSEL using a electro-optic index modulator

International audienceWe present the first vertical surface emitting laser (VCSEL) operating at 1.55-μm comprising a electro-optic modulator inside its cavity. This material consists of nematic liquid crystal dispersed in a polymer material (nano-PDLC). This first VCSEL exhibits a 10 nm tuning range and an excellent side-mode suppression ratio higher than 20 dB over the whole spectral range. The device is formed by a conventional InP-based active region with an epitaxial and a dielectric Bragg mirror. The nano-PDLC layer length, close to 6 μm, is in agreement with a tunable laser emission without mode-hopping. Another decisive advantage, compared to mechanical solutions, is the tuning response time which is close to a few 10 μs to scan the full spectral range, making this device appropriate for some access network functions. This first version is optically pumped and requires 170 volts to obtain a 10 nm tunability

Réalisation d’un laser à faible courant de seuil, avec des boites quantiques InAs/InP organisées et couplées latéralement

Nous présentons ici la réalisation d’un laser à faible courant de seuil avec des boites quantiques (QDs) organisées et couplées InAs/InP sur subsstrat (311)B pour une émission à 1.55 m. En effet, pour des hautes densités de QDs, une organisation périodique apparaît dans le plan. Cette organisation renforce le couplage latéral inter-boites. Des expériences de magnéto-photoluminescence permettent de mettre en évidence ces effets de couplage. Ce couplage améliore l’injection des porteurs. Une émission laser avec des faibles courants de seuil est obtenue avec de telles boites

Characterization of InAs quantum wires on (001) InP: toward the realization of VCSEL structures with a stabilized polarization

International audienceVertical cavity surface emitting lasers (VCSELs) operating at 1.55-µm are of great interests in optical telecommunication applications. Their circular, spectral and spatial single mode laser beam is essential points for an efficient fiber coupling and high frequency modulation. Moreover, their low-cost production and the possibility to test each laser directly on the wafer represent great advantages for production applications. In contrast with edge emitting lasers, VCSEL present an important polarization instability, which may increase the bit error rate in data transmission. Different solutions have been proposed for controlling the polarization, from patterning the output mirror or by using a birefringent material on top of the mirror, which do complicate the device technology. In this contribution, we propose to use a gain material presenting an important polarization anisotropy like quantum wires in order to fix the polarization of the emitting VCSEL

InAs quantum wires on InP substrate for VCSEL applications

International audienceQuantum dash based vertical cavity surface emitting lasers (VCSEL) on InP substrate are presented. Single and close stacking layers were successfully grown with molecular beam epitaxy. Optimized quantum dash layers exhibit a strong polarized 1.55 µm photoluminescence along the [1-10] crystallographic axis. Continuous wave laser emission is demonstrated at room temperature for the first time on a quantum dash VCSEL structure on InP susbtrate. The quantum dash VCSEL laser polarization appears stable on the whole sample and with excitation, no switching is observed. Its polarization is mainly oriented along [1-10], an extinction coefficient of 30 dB is measured. Those preliminary results demonstrate the interests of quantum dashes in the realization of controlled and stable polarization VCSEL device