Catastrophic optical damage of high power InGaAs/AlGaAs laser diodes

Producción CientíficaThe defects generated by the catastrophic optical degradation (COD) of high power laser diodes have been examined using cathodoluminescence (CL). Discontinuous dark lines that correspond to different levels of damage have been observed along the ridge. Finite element methods have been applied to solve a physical model for the degradation of the diodes that explicitly considers the thermal and mechanical properties of the laser structure. According to this model, the COD is triggered by a local temperature enhancement that gives rise to thermal stresses leading to the generation of dislocations. Damage is initially localized in the QW, and when it propagates to the waveguide layers the laser ends its life.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13

Proprietes structurales et electroniques des super-reseaux a-periodiques GaAs/GaAlAs

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Philosophies of Difference: A Critical Introduction to Non-philosophy

In this first English translation of his work, Laruelle explores the major European thinkers from Nietzsche to Derrida to define his own 'non-philosophical' project. A crucial text in the development of Francois Laruelle's oeuvre and an excellent starting point for understanding his broader project, "Philosophies of Difference" offers a theoretical and critical analysis of the philosophers of difference after Hegel and Nietzsche. Laruelle then uses this analysis to introduce a new theoretical practice of non-philosophical thought. Rather than presenting a narrative historical overview, Laruelle provides a series of rigorous critiques of the various interpretations of difference in Hegel, Nietzsche and Deleuze, Heidegger and Derrida. From Laruelle's innovative theoretical perspective, the forms of philosophical difference that emerge appear as variations upon a unique, highly abstract structure of philosophical decision, the self-posing and self-legitimating essence of philosophy itself. Reconceived in terms of philosophical decision, the seemingly radical concept of philosophical difference is shown to configure rather the identity of philosophy as such, which thus becomes manifest as a contingent and no longer absolute form of thinking. The way is thereby opened for initiating a new form of thought, anticipated here with the development of a key notion of non-philosophy, the Vision-in-One. Originally published in French as Les philosophies de la difference, ©Presses Universitaires de France, 1986. This English language edition translated by Rocco Gangle

Optical characterizations of “P-down” bonded InP pump lasers

International audienceWe investigate the effects of the assembly process and its parameters on the optical polarization in InP pump lasers for telecommunications. Different measurements were performed for this study, such as degree of polarization of the laser emission below and above the threshold current, as well as the evaluation of the induced strain in the materials by measuring the degree of linear polarization of the photo-luminescence. We demonstrate that the soldering process parameters can affect the emission polarization both below and above the laser threshold current

DOP characterization of oxide-confined GaAs based VCSEL operating at 850 nm

International audienc

Optical Characterizations of VCSEL for Emission at 850 nm with Al Oxide Confinement Layers

International audienceIn-plane micro-photoluminescence (mu-PL) and micro-reflectivity measurements have been performed at room temperature by optical excitation perpendicular to the surface of two different structures a complete vertical surface-emitting laser (VCSEL) structure and a VCSEL without the upper p-type distributed Bragg reflector (P-DBR). The two structures were both laterally oxidized and measurements were made on the top of oxidized and unoxidized regions. We show that, since the photoluminescence (PL) spectra consist of the cumulative effect of InGaAs/AlGaAs multi-quantum wells (MQWs) luminescence and interferences in the DBR, the presence or not of the P-DBR and oxide layers can significantly modify the spectrum. mu-PL mapping performed on full VCSEL structures clearly shows oxidized and unoxidized regions that are not resolved with visible light optical microscopy. Finally, preliminary measurements of the degree of polarization (DOP) of the PL have been made on a complete VCSEL structure before and after an oxidation process. We obtain an image of DOP measured by polarization-resolved mu-PL. These measurements allow us to evaluate the main components of strain

Mechanical strain mapping of GaAs based VCSELs

International audienceWe report an investigation of the strain field in mesa structures for oxide-confined vertical-cavity surface-emitting lasers (VCSELs) using the polarization-resolved micro-photoluminescence (PL) measurement of the degree of polarization (DOP) at room temperature. The DOP of the PL is correlated with the spatial distribution of the embedded anisotropic strain in a VCSEL structure. Measurements normal to (100) surfaces of the samples and from (110) cross-sectional planes were performed. The effect of two processes required in the fabrication of GaAs-based VCSELs was studied: the plasma etching of the P-doped distributed Bragg reflector and the wet oxidation process used to control current flow and lateral optical confinement. The DOP method allows very sensitive measurements of the mechanical strain (on the order of 10 - 5) accumulated in VCSEL devices even during different steps of the fabrication process