Finely tunable 1.55 µm emitting VeCSELs for embedded and compact optical and microwave systems

International audienceCompact wavelength-tunable laser sources are important for the development of optical based system units which can be used for numerous applications, ranging from optical communications, optical sensors, and even microwave photonics and high resolution spectroscopy. In most cases, large mode-hop-free wavelength tuning is of high interests to increase system performances and versatilities. In the metrology area, a small but very accurate wavelength tuning is required to fulfill system requirements. Thanks to their long cavity, VeCSELs offer the opportunity to get small laser wavelength linewidth, and shot noise limited behavior (class-A lasers). In this work we summarize the objectives and the preliminary results of the ANR Astrid HYPOCAMP project (HYbrid Polarisation controlled and mOnolithic tunable vertical Cavity surface emitting lAsers, for eMbedded and comPact optical and microwave systems), which is lead by FOTON in partnership with IPR (Rennes), CNRS-LAAS (Toulouse), CNRS-LPN (Marcoussis) and Telecom Bretagne. The project aims to develop a compact, reliable and low cost monolithic and versatile technology for the realization of tunable V(e)CSEL lasers, emitting in the 1.55 µm range (InP-based technology). In Fig.1 the optically-pumped external-cavity version of the device is presented

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

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

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

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

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

Design and Fabrication of GaInAsP/InP VCSEL with two a-Si/a-SiNx Bragg reflectors

International audienceWe report on the design and fabrication of a 1.55-μm wavelength Vertical Cavity Surface Emitting Lasers (VCSELs) which consists of two dielectric Bragg mirrors and a InGaAsP-based active region. The dielectric materials are amorphous silicon and amorphous silicon nitride. Layers of such materials have been deposited by magnetron sputtering and analyzed in order to determine their optical properties. A large refractive index difference of 1.9 is found between these materials. Distributed Bragg Reflectors (DBRs) 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 maximum reflectivity of 99.5% at 1.55-μm and a large spectral bandwidth of 800nm are reached with only four and a half periods of a-Si/a-SiNx. The VCSEL was fabricated by metallic bonding process. This method allows to bond an InP-based active region as the gain medium on a Si substrate thanks to the formation of a Au–In alloy. This process is performed at a low temperature of 240◦C without damaging the optical properties of the microcavity. This VCSEL has been characterized by an optical pumping experiment with a low and a high-density optical power and a laser emission has been obtained at room-temperature

Increase of charge-carrier redistribution efficiency in a laterally organized superlattice of coupled quantum dots

We report the observation of enhanced charge-carrier redistribution in laterally organized and coupled InAs/InP quantum dots (QDs). We show that a periodic organization appears in the QD plane for a high in-plane QD density (QDD). This organization enhances the lateral coupling between the dots, which is evidenced by photoluminescence and magnetophotoluminescence experiments. Electronic inter-QD lateral coupling results in an improved charge-carrier distribution at low temperature, as shown by electroluminescence on high QDD QD lasers. We conclude that the inter-QD tunneling occurs via the tunneling of excited states through the wetting layer, and discuss the prospects of using coupled QDs for improving the quantum efficiency and dynamical properties of QD lasers

Lamb mode-coupling constant in quantum-dot semiconductor lasers

International audienceIn 1964, W. E. Lamb introduced a mode-coupling constant C to characterize the stability of a dual-mode laser. Considering quantum-dot semiconductor lasers, we calculate analytically C in the framework of a rate-equation model, which includes both the homogeneous broadening of the quantum-dot emission and the dot-to-dot carrier exchange due to wetting-layer-assisted lateral coupling. Although first established using fully symmetric laser parameters for both modes, this result is then extended numerically to nonsymmetric parameters and shows that C remains unchanged when the gain/losses are adjusted so that the two laser modes are brought to oscillate simultaneously. Finally, C is shown to depend on two parameters only encompassing the pumping, the gain material mainly through the homogeneous broadening and the dot-to-dot carrier exchange, and the cavity design. Above laser threshold, the analytic result predicts a stable dual-mode behavior whatever the conditions but with a margin that decreases drastically close to lasing threshold or at small beating frequencies