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Optical Phase Conjugation

Optical Phase Conjugation is a third order non linear peculiar phenomenon occurring in many non linear crystals. Its principles and applications are reviewed.

Nicolas Fressengeas

@fresseng · 10 years ago

Photorefractivity

This is a basic lecture on photorefractivity: its principle as a low power optical non linearity are shown and applications are reviewed

Nicolas Fressengeas

@fresseng · 10 years ago

Champs et propagation

Nicolas Fressengeas

@fresseng · 10 years ago

InterCell: a Software Suite for Rapid Prototyping and Parallel Execution of Fine Grained Applications

InterCell is an open and operational software suite for implementation, code generation and interactive simulation of fine grained parallel computational models. This article describes the software architecture, some use cases from physics and cortical networks as well as first performance measurements.

Nicolas Fressengeas

@fresseng · 10 years ago

Photorefractive effect in InP:Fe under Gaussian illumination at telecommunication wavelengths

Nicolas Fressengeas

@fresseng · 10 years ago

InterCell: a Software Suite for Rapid Prototyping and Parallel Execution of Fine Grained Applications

InterCell is an open, operational software suite for implementation, code generation and interactive simulation of fine grained parallel computational models. This article describes the software architecture, some use cases from physics and cortical networks as well as first performance measurements.

Nicolas Fressengeas

@fresseng · 10 years ago

Optimized sub-wavelength grating mirror design for mid infrared wavelength range

Several subwavelength grating mirrors have been designed for VCSEL application in mid-infrared wavelength range (λ = 2.3 µm). These mirrors are automatically optimized thanks to a global algorithm which maximizes a specially defined quality factor for VCSEL top mirrors. Three different designs based on Si/SiO2, AlGaSb/GaSb and GaAs/AlOx are simulated and exhibit bandwidth as large as 206 nm. Also, the bandwidth is polarisation selective with a TM reflection coefficient higher than 99.9 % while TE coefficient is kept below 90 %. These reflectors present several fabrication solutions with a trade off between technological limitations, tolerances in regard to the fabrication error and mirror quality.

Nicolas Fressengeas

@fresseng · 10 years ago

Optimized sub-wavelength grating mirror design for mid-infrared wavelength range

We present the design of a sub-wavelength grating mirror optimized for integration in mid-IR VCSEL. The definition of a quality factor adapted to VCSEL requirements and maximized by an optimization algorithm allowed us to obtain a polarization selective and high reflectivity structure showing several percent of tolerance. The design of the SGM mirror can easily be adapted to the technological constraints of the manufacturers by adjusting the limitations defined for the automated optimization process. Indeed, the comparison between different technological constraints shows that a better accuracy of the etching process results in an increase of the quality of the mirror.

Nicolas Fressengeas

@fresseng · 10 years ago

Optimized sub-wavelength grating mirror design for mid-infrared wavelength range

Several designs of sub-wavelength grating mirrors adapted to mid-infrared operation are reported with several percents of tolerance for the grating fabrication. These designs have been automatically optimized by the use of a genetic-based algorithm to maximize a quality factor defined to meet the requirements of a VCSEL cavity mirror. These mirrors are devoted to an integration in VCSEL operating near λ=2.3 µm, with a large bandwidth, very high reflectivity coefficient for transverse magnetic mode only, polarization selectivity and a thickness as low as 2 µm.

Nicolas Fressengeas

@fresseng · 10 years ago

Optimized sub-wavelength grating mirror design for mid-infrared wavelength range

Nicolas Fressengeas

@fresseng · 10 years ago

Optimized subwavelength grating mirror design for mid-infrared wavelength range

Nicolas Fressengeas

@fresseng · 10 years ago

Optimized GaAs High Contrast Grating Design and Fabrication for Mid-infrared Application at 2.3 μm

A GaAs high contrast grating design has been optimized for a mid-infrared VCSEL application through the use of an optimization algorithm. Reflection spectra of an experimental grating with dimensions within the computed tolerances are in a correct agreement with the simulations.

Nicolas Fressengeas

@fresseng · 10 years ago

Experimental control of steady state photorefractive self-focusing in InP:Fe at infrared wavelengths

This paper reports an experimental study of the self-focusing process in iron doped indium phosphide at an 1.06 micron wavelength, identifying the influence of temperature, beam intensity and background illumination \RefereeOne{for two different iron dopings}. We point out that the iron ionization ratio is at the origin of different qualitative behavior previously reported and we show that it is possible to reproduce the said behaviors in the same crystal by applying a uniform illumination, allowing their eventual control for dynamic wave-guiding.

Nicolas Fressengeas

@fresseng · 10 years ago

Robust design of subwavelength grating mirror for mid-infrared VCSEL application

We present the design of a Si/Si3N4 subwavelength grating mirror optimized for an integration in mid-infrared VCSEL. The definition of a quality factor adapted to VCSEL requirements and maximized by an optimization algorithm allowed us to obtain a polarization selective and high reflectivity structure. The robustness with respect to fabrication error has been enhanced thanks to a precise study of the grating dimension tolerances.

Nicolas Fressengeas

@fresseng · 10 years ago

Mid-infrared sub-wavelength grating mirror design: tolerance and influence of technological constraints

High polarization selective Si/SiO2 mid-infrared sub-wavelength grating mirrors with large bandwidth adapted to VCSEL integration are compared. These mirrors have been automatically designed for operation at λ = 2.3 µm by an optimization algorithm which maximizes a specially defined quality factor. Several technological constraints in relation with the grating manufacturing process have been imposed within the optimization algorithm and their impact on the optical properties of the mirror have been evaluated. Furthermore, through the tolerance computation of the different dimensions of the structure, the robustness with respect to fabrication errors has been tested. Finally, it appears that the increase of the optical performances of the mirror imposes a less tolerant design with severer technological constraints resulting in a more stringent control of the manufacturing process.

Nicolas Fressengeas

@fresseng · 10 years ago

Interface states effects in GaN Schottky diodes

Current voltage (I-V) and capacitance voltage (C-V) measurements have been performed versus temperature on GaN Schottky diodes. The results show an increase of the Schottky barrier height ϕb and a decrease of the ideality factor n both with the increase of the temperature. We show that this behavior originates in the existence of an interface state density distribution, which is determined via the analysis of the temperature dependence of the I-V measurements, and allows the tunneling of the carriers from the semiconductor to the metal. Those interface states are shown to be responsible for interface inhomogeneities which result in two Gaussian voltage dependent Schottky barrier distributions. We show also that, in the presence of this interface state distribution, C-V measurements, without the correction of the built in voltage by taking into account the effect of both the high values of the ideality factor and series resistance, lead to erroneous values of the Schottky barrier height ϕb.

Nicolas Fressengeas

@fresseng · 10 years ago

Robust design of Si/Si3N4 high contrast grating mirror for mid-infrared VCSEL application

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.

Nicolas Fressengeas

@fresseng · 10 years ago

Gaussian Beams

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.

Nicolas Fressengeas

@fresseng · 10 years ago

Optimized Si/SiO2 high contrast grating mirror design for mid-infrared wavelength range: robustness enhancement

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.

Nicolas Fressengeas

@fresseng · 10 years ago

Robust design for parameter tolerant GaAs High Contrast Grating mirror for mid infrared VCSEL application

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.

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