Frédéric Genty

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.

Fabrication and Characterization of GaSb-Based Monolithic Resonant-Cavity Light-Emitting Diodes Emitting Around 2.3 μm and Including a Tunnel Junction

In this paper, the process of fabrication of GaSb-based electrically injected resonant-cavity LEDs near 2.3 mum is detailed. The electrical and optical properties of these diodes operating in continuous wave at room temperature are also presented. The different tested monolithic structures have similar designs with two doped AlAsSb/GaSb Bragg mirrors and an active region with eight GaInAsSb quantum wells. Performances of devices containing or not an n++-InAsSb/p++-GaSb tunnel junction (TJ) can be compared. The large improvements of electrical resistance as well as output power, observed when a TJ is included, demonstrate all the advantages to use such a technology for the realization of electrically injected vertical cavity structures emitting in the mid-IR on GaSb substrate.

Morphological recognition with the addition of multi-band fluorescence excitation of chlorophylls of phytoplankton

The recognition of aquatic organisms plays a crucial role in the monitoring of the pollution and for the adoption of rapid preventive actions. A compact microscopic optical imaging system is proposed in order to acquire and treat the multibands fluorescence of several pigments in phytoplankton organisms. Two algorithms for automatic recognition of phytoplankton were proposed with a minimum number of calibration parameters. The first algorithm provides a morphological recognition based on “watershed” segmentation and Fourier descriptors, while the second one builds fluorescence pigment images by “k-means” partition of intensity ratios. The operation of these algorithms was illustrated by the study of two different organisms: a cyanobacteria (Dolichospermum sp.) and an alga (Cladophora sp.). The family and the genus of these organisms were then classified into a database which is independent of the size, the orientation and the position of the specimens in the images.

Analysis of NO 2 absorption cross-sections at high temperature for the developement of post-combustion gases optical sensor

Nitrogen dioxide is a well-known pollutant which has effect on human health, with pulmonary problems, and on the atmosphere chemistry, where it is responsible for acid rains for example. Consequently, current European standards impose very low NO2 emission thresholds in exhaust gases. Thus, there is a need for novel sensors able to monitor small NO2 concentrations for real time adjustments of engines performances. In this perspective, absorption spectroscopy is a method of great interest as it has been largely used in the past to measure NO2 concentration in air atmosphere. Such measurements require the knowledge of the NO2 absorption cross-sections. As the atmosphere is a “cold” environment, these data is only known up to 25°C. The first purpose of this study is then, to measure the absorption cross-sections of NO2 at higher temperatures, i.e. up to 150°C. Then, based on these results, absorption measurements were performed on hot gas mixtures containing very small concentrations of NO2 (<;5ppm). A resolution close to one part per million was observed.

Automatic recognition system of aquatic organisms by classical and fluorescence microscopy

Blooming of algae and more generally phytoplankton in water ponds or marine environments can lead to hyper eutrophication and lethal consequences on other organisms. The selective recognition of invading species is investigated by automatic recognition algorithms of optical and fluorescence imaging. On one hand, morphological characteristics of algae of microscopic imaging are treated. The image processing lead to the identification the genus of aquatic organisms and compared to a morphologic data base. On the other hand, fluorescence images allow an automatic recognition based on multispectral data that identify locally the ratio of different photosynthetic pigments and gives a unique finger print of algae. It is shown that the combination of both methods are useful in the recognition of aquatic organisms.

Room temperature, Sb-based monolithic EP-VCSEL at 2.3 μm including 2 n-type DBR

We demonstrate a 2.3 mum emission at RT under quasi-CW operation from a Sb-based monolithic VCSEL. The structure is composed of 2 n-doped AlAsSb/GaSb DBR, a type-I GaInAsSb/AlGaAsSb QWs active region and a tunnel junction.

Continuous-wave operation up to 350K of optically-pumped antimony-based midinfrared VCSELs

We report on the growth by MBE and characterization of optically-pumped mid-infrared Vertical Cavity Surface Emitting Lasers (VCSELs), where the optical cavity is formed by a semiconductor Sb-based Bragg mirror, an air gap and a high reflectivity dielectric concave mirror. These lasers operate between 2 μm and 2.5 μm in continuous wave regime at room temperature with a circular TEM00 beam. Two different fabrication processes are tested and the properties of the corresponding devices are compared.