Direct bonding has been a major key technology in many fields nowadays. From microelectronic to optoelectronic technologies, it became a technique used for mass production technology in many different applications. Direct bonding of silicon or silicon dioxide is now a well known process. In this article, we explore this technology through the transfer of a crystalline multilayer made of III-V materials (AlGaAs/GaAs) from its native GaAs substrate upon a fused silica substrate (SiO2). The goal of this work is to explore the conception of crystalline Bragg mirrors with low mechanical loss and high optical quality for precision measurement applications. We present the main results obtained for each step of the transfer process. Various experiment such as AFM characterization have been performed on the wafers to probe surface quality. Chemical wet etching with different experimental conditions have been tested to remove the GaAs substrate. We discuss the main challenges of the process, especially the bonding of two rather different materials from the thermo-mechanic point of view. Focus is also made on the chemistry used in the wet etching part to have a selective etching between GaAs and AlGaAs.
The thermal oxidation of an Al-rich AlGaAs buried layer is a common established technique used to improve
the performances of some optoelectronic devices, like VCSEL or optical waveguides, in terms of electro-optical
confinement. This oxidation technique is usually proceeding laterally, which allows achieving good results but leads to
some difficulties on the control of the shape and size of the oxidized areas. In this work, a new technology to oxidize
GaAs/AlAs epitaxial structures which avoids these limitations is presented. This method consists of an oxidation through
the top of the sample, allowing in consequence a total control of the shape of oxidation by means of photolithography.
For this purpose the method has two steps: first, the intentional creation of defects in the top GaAs layer, in order to
make it possible the oxidant species diffusion through this material, and second the planar oxidation of the AlAs layer. In
this paper this technique is thoroughly studied: different methods to create defects in the GaAs layer have been analysed,
and the optimization of the procedure has been achieved leading to a uniform oxidation and a reduced lateral oxidation
spreading. Finally a comparison between the experiments and simulations has been realized in order to provide an
explanation for this type of vertical oxidation. This innovating technique allows addressing separately the electrical and
optical operating aspects of optoelectronic devices, thus opens to novel structures with controlled transverse optical
behaviour.
We present an optical microsystem aimed to be integrated into a nanomechanical biosensor for functional genomic analysis. The operation principle is based on a sub-nanometer resolution optical measurement of a cantilever deflection caused by a surface stress when the target nucleic acid sample hybridises to the nucleic acid probe on the active side of the cantilever. The resulting deflection, of the order of nanometers, is measured by an optical system, in which a laser beam reflects off the back of the cantilever to a position sensitive photo-detector. We report in this paper on the design, fabrication and test of the optical head associated with an optical coupling system which enables detection of the presence of target nucleic acid on the cantilever by amplifying the deflection caused by the stress.
VCSELs (Vertical Cavity Surface Emitting Lasers) are nowadays more and more exploited in optoelectronic applications, monitoring their lasing power in a compact and low cost manner becomes crucial. To collect and control the output light, an external photodetector associated with an optical microlens array can be used. Integrated solutions based on the use of a bulk or QW photodetection section added in single-or double-cavity structures have also been proposed. Here, we have investigated a simpler solution based on a standard VCSEL array. Light emitted by a VCSEL has been electrically detected by adjacent VCSELs located in the same array, using in plane optical waveguiding of spontaneous emission in the intrinsic central zone of the devices. We show that the detected photocurrent can be related to the power of the emitting VCSEL. Signal intensity has been studied as a function of VCSELs distance. This method could lead to a more efficient way to monitor VCSEL emission.
We present here a design of a coupling element aimed to be integrated into a nanomechanical biosensor for functional genomic analysis. The operation principle is based on a sub-nanometer resolution optical measurement of a cantilever deflection caused by a surface stress when the target nucleic acid sample hybridizes to the nucleic acid probe on the active side of the cantilever. The resulting deflection, of the order of nanometers, is measured by an optical system, in which a laser beam reflects off the back of the cantilever to a position sensitive photo-detector. We study in this paper three polymer optical coupling systems which could allow to detect the presence of target nucleic acid on the cantilever by amplifying the deflection caused by the stress.
The increasing interest for high-speed, compact and low cost devices for optoelectronic applications such as bi-directional optical interconnects, optical imaging or telemetry has recently led to focus on the ability for the vertical-cavity surface-emitting lasers to be used as resonant cavity enhanced photodetectors for dual-purpose applications. Here we present results on design, fabrication and characterization of an oxide-confined 830nm top-emitting laser for self-aligned emission and photodetection. In this single-cavity GaAs-based device, submitted alternatively to forward and reverse bias, the oxide layer is not only used to obtain a single mode emission but also to enable decoupling between a small surface emission and a large surface detection. However the optical path is observed to change because of the refractive index difference between the oxidized and non-oxidized zones of the structure. This leads to a detrimental blue-shift on the wavelength of the Fabry-Perot cavity mode. In this work, we demonstrate this effect in photodetection by the means of spatially localized photocurrent and reflectance spectra measurements. These results show that the photocurrent is correctly collected in the whole device despite of the presence of an oxide layer. The results obtained on selective etching for optimisation of this dual-purpose device are presented.
This paper discusses secure architecture and protocols of managing Intellectual Property Rights in distributed content databases in a close environment. This discussion has been conducted within the European project AQUARELLE. This paper presents a short survey of watermarking technologies and focuses on functionalities offered by such techniques. We propose the terms of watermarking, fingerprinting and monitoring. For our implementation, we have worked with the Universite catholique de Louvain (UCL). This work is joint work with Jean-Francois Delaigle. Next we focus mainly on keys issues, and conclude that a trusted third party is needed to establish a verification service of watermarks. Next the DHWM key exchange is presented, based on the simple idea that watermarking and verification can be separated. This scheme uses the Diffie-Hellman key-exchange protocol. Next some hints on the implementation of the scheme and on its correctness are given.
Bragg reflectors of three geometrical configurations are considered analytically and experimentally to solve the problem of cracking which develops due to thermal stress between the two materials used. The Bragg reflectors are based on (Ca,Sr)F2 and (Ga,Al)As and are grown by means of molecular beam epitaxy. Three geometrical solutions are considered: (1) three material combinations within quarter-wave structures; (2) mixed reflectors of GaAs-(Ca,Sr)F2 and GaAs-AlAs in shifted Bragg reflectors with reduced layer thicknesses; or (3) generalized Bragg structures based on asymmetrical geometries. The absolute or relative fluoride thicknesses in the structures can be reduced by means of the proposed configurations. Effective heteroepitaxial reflectors are set forth that have crack-free surface morphologies because the structures of the generalized Bragg reflectors reduce the stress inherent in the devices.
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