A Si/Si3N4 high contrast grating mirror has been designed for a VCSEL integration in mid-infrared (λ = 2.65 µm). The use of an optimization algorithm which maximizes a VCSEL mirror quality factor allowed the adjustment of the grating parameters while keeping large and shallow grating pattern. The robustness with respect to fabrication error has been enhanced thanks to a precise study of the grating dimension tolerances. The final mirror exhibits large high reflectivity bandwidth with a polarization selectivity and several percent of tolerance on the grating dimensions.

This is a set of two documents useful for a lecture on Gaussian Optics : - one is a set of slides that can be projected for a lecture - the other one is a handout useful for students following the lecture Both are complementary, not identical.

A high reflectivity and polarization selective high contrast grating mirror has been designed with the use of an automated optimization algorithm. Through a precise study of the tolerance of the different lengths of the structure, the robustness with respect to the fabrication errors has been enhanced to high tolerance values between 5 % and 210 %. This adjustment of the dimensions of the structure leads to a 250 nm large bandwidth mirror well adapted for a VCSEL application at λ = 2.65 µm and can easily be scaled for other wavelengths.

Grating structures made of materials which provide a high optical index contrast between the grating slabs and the surrounding medium have shown many extraordinary properties. The resonance of Bloch modes between the two grating interfaces and their coupling can be adjusted to obtain different and very promising properties in a large range of applications such as broadband mirrors, high-Q filters, planar lenses, circular polarizer... The development of VCSEL devices based on GaSb for a mid-infrared emission is still limited today at 2.6 µm. The high performances of high contrast grating (HCG) mirrors combined with a good polarization selectivity and a thickness lower than 2 µm should be very promising characteristics to enhance electrical, thermal and optical properties of VCSEL devices emitting above 2.3 µm and would allow spectroscopic measurements of polluting gas in the 2-3 µm wavelength range. In this paper, we present the design of a GaAs HCG to replace the top Bragg mirror of mid infrared based VCSEL. A robust optimization algorithm is used to find the best dimensions of the HCG structure for a VCSEL application. Thus, the homemade algorithm searches not only for the most efficient mirror but also for a robust design structure with large tolerances with respect to the errors of fabrication on the grating dimensions.

High contrast gratings (HCG) have drained recently highly attractive perspectives for VCSEL devices through the wide potentialities for obtaining unique optical properties with these integrable optical elements, in contrast to conventional Bragg reflectors. Since most of the HCG approaches on III-V based photonic devices are based on semiconductor/air-gap structures, strong limitations are foreseen for the integration in practical lasers. We proposed to exploit the high refractive index contrast available in the AlOx/GaAs system for which the oxide is formed with the mature thermal wet oxidation technique. High reflective and polarization selective mirrors can thus been achieved monolithically by means of a VCSEL compatible process technology, in a wide spectral range from near to mid infrared. Jointly, the AlOx lateral confinement scheme is proposed for implementation in mid infrared emitters. We present in this paper the fabrication and performances of AlOx/GaAs HCG operating between 2.3 and 2.6 μm and their integration within oxide-confined mid-infrared electrically pumped 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.

The InGaN ternary alloy has the potentiality to achieve high efficiency solar cells. Indeed the bandgap of the InGaN alloy covers the whole solar spectrum including the visible region by changing the Indium composition. The InGaN alloy also counts among its advantages a relatively low effective mass of electrons and holes, their high mobilities, high absorption coefficients as well as radiation tolerance. These very promising characteristics give the possibility to design and develop next-generation high-efficiency thin films solar cells, based on multijunction technology. However, the main drawback is the difficulty of p-doping and the high defects density in these III-Nitride alloys. In this report, we develop a novel and rigorous optimization approach based on state-of-the-art optimization algorithms, to design an optimal multijunction solar cell based on InGaN alloys. This approach allows to automatically determine the values of the cell parameters, among which are the geometries of the active layers, their doping and defect levels, to maximize its efficiency within the possibilities of actual device fabrication. We have found that the use of this rigorous optimization approach is necessary because of the high dependence of the cell efficiency on the device geometry, doping and defects, particularly concerning the top and bottom P layers properties

A time resolved study of the behavior of a single beam in photorefractive iron doped indium phosphide is provided down to the microsecond range, showing that infrared beam bending does occur on the microsecond time scale for moderate beam intensities. Two distinct time scales are evidenced, the behavior of which are the sign of two different photorefractive mechanisms.

This paper shows how partial differential problems can be solved thanks to cellular computing and an adaptation of the Least Squares Finite Elements Method. As cellular computing can be implemented on distributed parallel architectures, this method allows the distribution of a resource demanding differential problem over a computer network.

A GaAs/AlOx high contrast grating structure design which exhibits a 99.5% high reflectivity for a 425nm large bandwidth is reported. The high contrast grating (HCG) structure has been designed in order to enhance the properties of mid-infrared VCSEL devices by replacing the top Bragg mirror of the cavity. A robust optimization algorithm has been implemented to design the HCG structure not only as an efficient mirror but also as a robust structure against the imperfections of fabrication. The design method presented here can be easily adapted for other HCG applications at different wavelengths.

This paper focuses on the determination of the bandgap energy bowing parameter of strained and relaxed InxGa1−xN layers. Samples are grown by metal organic vapor phase epitaxy on GaN template substrate for indium compositions in the range of 0

Mid-infrared Vertical cavity surface emitting lasers (MIR-VCSEL) are very attractive compact sources for spectroscopic measurements above 2μm, relevant for molecules sensing in various application domains. A long-standing issue for long wavelength VCSEL is the large structure thickness affecting the laser properties, added for the MIR to the tricky technological implementation of the antimonide alloys system. In this paper, we propose a new geometry for MIR-VCSEL including both a lateral confinement by an oxide aperture, and a high-contrast sub-wavelength grating mirror (HCG mirror) formed by the high contrast combination AIOx/GaAs in place of GaSb/A│AsSb top Bragg reflector. In addition to drastically simplifying the vertical stack, HCG mirror allows to control through its design the beam properties. The robust design of the HCG has been ensured by an original method of optimization based on particle swarm optimization algorithm combined with an anti-optimization one, thus allowing large error tolerance for the nano-fabrication. Oxide-based electro-optical confinement has been adapted to mid-infrared lasers, byusing a metamorphic approach with (Al) GaAs layer directly epitaxially grown on the GaSb-based VCSEL bottom structure. This approach combines the advantages of the will-controlled oxidation of AlAs layer and the efficient gain media of Sb-based for mid-infrared emission. We finally present the results obtained on electrically pumped mid-IR-VCSELs structures, for which we included oxide aperturing for lateral confinement and HCG as high reflectivity output mirrors, both based on AlxOy/GaAs heterostructures.

Indium Phosphide is a material of primary relevance in the field of opto-electronics since it supersedes conventional materials such as AsGa for electron mobility and heat conduction for instance. It is often doped with iron to reduce its conductivity and enhance its light dependent conduction properties.Indium Phosphide is well known for its two carrier band transport conduction mechanism, where both electrons and holes play a significant role. Its transport mechanisms have been heavily investigated, especially in the dark. Light induced charge transport, on the contrary, has beeninvestigated at the end of the XX th century as far as periodic illumination stemming from beam interference is concerned. More recently, non periodic illumination was tackled. Both have shown the existence of a particular intensity, named the resonance intensity, at which charge transportis enhanced and around which it changes behavior. Both have in common the small modulation hypothesis where ligh intensity is assumed not to deviate too far from its mean value. InP:Fe being a electro-optic material, this resonance mechanism has been shown to be at the heartof a light induced refractive index modulation, leading to light self-focusing. However, a one beam illumination is far from the small modulation hypothesis. Experiments indeed show that the very notion of resonance intensity no longer holds. They also show a behavior-reversal intensity. Itsvalue is different from that of the resonance intensity, but remains to be explained. We attempt here a theoretical study of the two carrier band transport model in InP:Fe, in the simplifying framework of one single space dimension alongside the time dimension. Our originalapproach is to rule out all conventional approximations, aiming to justify each of them mathematically with precise numerical values. Once this is done, we go on to a simplified model of two carrier transport in InP:Fe, for which basic simulation will be undertook and checked against experimentalresults. The mathematical method undertook here is know as multi-scale modeling. It is needed because of the presence of largely varying orders of magnitudes in the parameters of the two carrier band transport model.

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.

The design and optimization of novel structures is an essential part of the next-generation solar cells development. Indeed, the technological steps involved in the development of high-performance solar cells involve a huge set of interdependent physical and geometrical parameters: layers thicknesses, dopings, compositions, and defect characteristics. In this work, we propose a new open-source and free solar cell optimizer: SLALOM À for SoLAr ceLl multivariate OptiMizer À that implements a rigorous multivariate approach, which improves from the one-parameter-at-a-time procedure that is traditionally used in the field to a state-of-the-art multivariate approach. Applied to indium gallium nitride (InGaN) solar cells, it shows its potential to become a useful tool for the development of novel solar cells. SLALOM is implemented to be extended to any semiconductor simulation engine. Several models for solar cells have been implemented in SLALOM, including, for instance, InGaN. One can adapt these models to any solar cell technology by changing the parameter set, the here proposed generic code structure remaining unchanged.

This work is devoted to the design of high contrast grating mirrors taking into account the technological constraints and tolerance of fabrication. First, a global optimization algorithm has been combined to a numerical analysis of grating structures (RCWA) to automatically design HCG mirrors. Then, the tolerances of the grating dimensions have been precisely studied to develop a robust optimization algorithm with which high contrast gratings, exhibiting not only a high efficiency but also large tolerance values, could be designed. Finally, several structures integrating previously designed HCGs has been simulated to validate and illustrate the interest of such gratings.

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