Benjamin Reig

Oxide confinement and high contrast grating mirrors for Mid-infrared VCSELs

A new mid-infrared (MIR) Vertical Cavity Surface Emitting Laser (VCSEL) structure is proposed. We have integrated to the VCSEL structure both an oxide aperture for lateral confinement, and a sub-wavelength high-contrast-grating top mirror. Upon the GaSb-based half-VCSEL, we have grown a metamorphic AlGaAs heterostructure to enable thermal oxidation and grating mirror fabrication steps. A methodology based on optimization and anti-optimization methods has been used to design the optical grating, with improved parameter tolerances regarding processing errors. Finally, we show the complete fabrication of an electrically-pumped MIR monolithic VCSEL structure implementing both oxide confinement and a subwavelength grating top mirror.

A microtip self-written on a vertical-cavity surface-emitting laser by photopolymerization

We present the integration of a self-aligned microtip on a vertical-cavity surface-emitting laser (VCSEL) by near infrared photopolymerization. This one-step fabrication process is triggered by the laser source itself. It is based on the use of photopolymers sensitive at the lasing wavelength and can be applied to VCSEL devices after their process fabrication. We have characterized the fabricated microtips and shown that they focus laser light at few micrometers from the device. The applications of this simple method may concern VCSEL beam shaping as well as the fabrication of microprobes for near-field optical microscopy.

3D optimization of a polymer MOEMS for active focusing of VCSEL beam

We report on the optimized design of a polymer-based actuator that can be directly integrated on a VCSEL for vertical beam scanning. Its operation principle is based on the vertical displacement of a SU-8 membrane including a polymer microlens. Under an applied thermal gradient, the membrane is shifted vertically due to thermal expansion in the actuation arms induced by Joule effect. This leads to a modification of microlens position and thus to a vertical scan of the laser beam. Membrane vertical displacements as high as 8μm for only 3V applied were recently experimentally obtained. To explain these performances, we developed a comprehensive tri-dimensional thermo-mechanical model that takes into account SU-8 material properties and precise MOEMS geometry. Out-of-plane mechanical coefficients and thermal conductivity were thus integrated in our 3D model (COMSOL Multiphysics). Vertical displacements extracted from these data for different actuation powers were successfully compared to experimental values, validating this modelling tool. Thereby, it was exploited to increase MOEMS electrothermal performance by a factor higher than 5.

A miniaturized VCSEL-based system for optical sensing in a microfluidic channel

We report on design and fabrication of a VCSEL-based Micro-Optical-Electrical-Mechanical-System (MOEMS) suited for portable optical biosensors. It is based on a tunable polymer microlens directly integrated on the surface of the VCSEL laser device. We demonstrate that this method leads to a VCSEL focusing at a working distance of ~300μm suitable for optical analysis in a microfluidic channel. Moreover, as the microlens can be vertically moved up to 8μm with an applied power of only 43 mW (3V), a dynamic scan of the laser spot is possible over 100μm. This integrated approach opens new insights for the use of VCSEL arrays in miniaturized optical sensors.

Study of SU-8 reliability in wet thermal ambient for application to polymer micro-optics on VCSELs

We present experimental data on the reliability of SU-8 polymer when used as a core material for the integration of microlenses on vertical-cavity surface-emitting lasers (VCSELs). The respective effects of a hot and humid environment on structural, mechanical and optical properties of this epoxy resist are investigated. High aspect-ratio SU-8 micropillars are found to keep a good surface morphology and a stable optical transmission, as well as a good adherence on the wafer. Thermal cycling is also studied to check material stability under electro-thermal actuation in SU-8 micro-opto-electro-mechanical system (MOEMS). These results are of great importance for the collective integration of low-cost SU-8-based passive or active microlens arrays onto VCSELs wafers for optical interconnects and optical sensing applications.

Polymer optical MEMS integrated on VCSELs for biosensing

We present our recent advances on design and fabrication of polymer optical MEMS that can be directly integrated on VCSELs arrays for dynamic beam focusing. These studies open new insights for the fabrication of compact optical sensors that require a real-time scan of laser beam position.

Vertical integration of an electro-absorption modulator within a VCSEL device

The huge increase of datacom traffic requires laser sources of ever-widening modulation bandwidth. Vertical-Cavity Surface-Emitting Lasers (VCSEL) are strategically relevant given that their wide use for short communication links such as in datacenters and are, in light of recent developments, good candidates to address such demands. We propose to increase the modulation bandwidth by vertically integrating a continuous-wave VCSEL with a high-speed electroabsorption modulator (EAM-VCSEL). We will present our studies on the electrical and optical designs, on the development of optimized fabrication steps and on the microwave characterizations leading to the realization of integrated EAM-VCSEL devices.

Technologies of oxide confinement and high contrast grating mirrors for mid-infrared VCSELs

A new architecture for mid-infrared (MIR) Vertical Cavity Surface Emitting Laser (VCSEL) is proposed and fabricated. The MIR-VCSEL structure includes both a lateral confinement by an oxide aperture, and a high-contrast sub-wavelength grating mirror (HCG mirror) formed by the high contrast combination AlOx/GaAs, and that replaces conventional GaSb/AlAsSb top Bragg mirror. Upon the GaSb-based half-microcavity bottom part, a metamorphic AlGaAs heterostructure was epitaxially grown to enable thermal oxidation and grating mirror fabrication steps on AlGaAs material platform. The optical design of the VCSEL structure and more precisely the HCG mirror has been optimized thanks to an original methodology based on optimization and anti-optimization methods, resulting in improved parameter tolerances regarding processing errors. After all, we show the complete fabrication of an electrically-pumped MIR monolithic VCSEL structure by integrating this new technological bricks.

Polymer MEMS for the active control of VCSEL beam

Beam control of VCSELs (Vertical Cavity Surface Emitting Lasers) is a key topic to integrate these laser diodes in microsystems for instrumentation or biomedical application [1]. We report here on a simple method to control dynamically the beam shape of VCSELs devices. Our approach is based on an electro-thermal actuator including a polymer membrane, a heating electrode and a polymer microlens (fig.1 a). The operation principle is the following: the laser beam waist position can be tune thanks to the membrane vertical displacement induced by varying the applied current. Optical and thermo-mechanical optimizations of membrane geometry have been carried out. These studies point out that a vertical deflection of 2µm should be obtained with a thermal gradient of 100°C [2], leading to a corresponding waist displacement of few hundred microns.