Vertical-cavity surface-emitting lasers (VCSELs) have gained great attention as an attractive light source for short-distance optical communication systems, optical interconnects optical storage and laser printing. The proven potentials and flexibility of these optoelectronic devices have recently attracted much attention from other fields of application such as microsensors and biomedical instrumentation.
Due to this new interest, derivate functionalities have now to be developed to further extend the integration capabilities of the VCSELs in microsystems.
Two aspects have to be addressed in this prospect: the adaptation of the laser source to the microsystem and the diversification and/or association of other optical functionalities.
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Based on a strong experience on materials, the group has developed tools and know-how of the molecular beam epitaxy : selectable wavelength in-situ reflectometry for growth monitoring, complex VCSEL structures (double-cavity VCSEL), and new material system for laser applications (GaAsN, InGaAsN)
Epitaxial structure of a double cavity VCSEL
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Cross section of an oxide-confined
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The current VCSEL fabrication technology is based on the both optical and electrical confinements realized by an AlOx layer formed selectively in the vertical structure by oxidizing an dedicated Al(Ga)As film. One can then obtain by this method stable lateral single-mode behaviour, while keeping operating currents around a few mA, meeting better the requirements of optical sensors and systems. |
Integrated detectors for VCSELs
The LAAS’ photonics group has developed since a few years integrated detectors based on the same geometry than a VCSEL. Detectors and VCSELs can be then directly integrated on the same semiconductor substrate, which is of first importance for monitoring the emitted light in a transceiver. Dual VCSEL/detector devices are currently planned to be implemented.
Schematic of a cross-section and top view
of the VCSEL/Schottky contact emitter/detector device |
The integration of VCSEL with an “optical-guiding” structure such as photonics crystal (PCs) is one other strong motivation for the future. This concept is very promising and opens a new field of possibilities to combine optical functions.
AlOx technology
The oxidation of a dedicated AlAs layer in the VCSEL structure enables an efficient optical and electrical confinement within the laser cavity. This technology is a standard today for VCSELs based on AlGaAs material systems.
The challenging point of this technique is nevertheless the uniformity and accuracy of the oxide depth into the structure, in order to obtain a reproducible active small diaphragm diameter, thus fixing the optimized performances of the laser.
View of processed VCSELs arrays
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 Light-current characteristics
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Polymer micro-optics for photonics integration
The control of beam divergence is crucial for VCSEL integration in optical microsystems. With this aim, a novel deposition method using a silicon cantilever-based spotter has been developed at LAAS to fabricate integrated polymer microlenses. We have demonstrated that the optical quality, the dimensions and the focal lengths of such microlenses are suitable for VCSEL collimation. Integration on VCSELs devices using self-alignment properties on cylindrical patterns is under progress. (LAAS project MIOPY) [ Optics Express Vol. 15, Issue 11, pp. 6900-6907, 2007].
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SEM image of various size polymer microlenses deposited using the microcantilever-based spotter
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3D Microscopic image of microlenses arrays self-aligned on SU-8 micropillars (diameters from 30 to 220µm) Insert : SEM image of a microlens self-aligned on a 30µm-diameter pillar |
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Projects :
- FunFACS - Fundamentals, Functionalities and Applications of Cavity Solitons - (IST-FET-STREP 2004-2007)
- Optonanogen - Integrated OPTO-NANOmechanical Biosensor for functional GENomic Analysis - (IST-2002-2005)
- OSA 131 - Multi-standard transmitter micro-module working at 1.31 µm and 10 Gbit/s - (RMNT - French Research Network in Micro and Nano Technologies) (2004-2005)
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