Passive Temperature-Compensating Technique for Microstructured Fiber Bragg Gratings

The thermal drift of the characteristic wavelength of fiber Bragg gratings (FBGs) photowritten in the core of microstructured fibers (MOFs) is significantly reduced by inserting a liquid of suitable refractive index into their holes. For instance, the spectral range of variations is divided by a factor of 4 over a temperature range larger than 20\degree C in a six-hole MOF, and the maximum sensitivity is reduced. Such passive FBG temperature compensation technique is of great interest for applications involving accurate sensing free of thermal effects

Covariance Fitting Interferometric Phase Linking: Modular Framework and Optimization Algorithms

Interferometric phase linking (IPL) has become a prominent technique for processing images of areas containing distributed scaterrers in SAR interferometry. Traditionally, IPL consists in estimating consistent phase differences between all pairs of SAR images in a time series from the sample covariance matrix of pixel patches on a sliding window. This paper reformulates this task as a covariance fitting problem: in this setup, IPL appears as a form of projection of an input covariance matrix so that it satisfies the phase closure property. Given this modular formulation, we propose an overview of covariance matrix estimates, regularization options, and matrix distances, that can be of interest when processing multi-temporal SAR data. In particular, we will observe that most of the existing IPL algorithms appear as special instances of this framework. We then present tools to efficiently solve related optimization problems on the torus of phase-only complex vectors: majorization-minimization and Riemannian optimization. We conclude by illustrating the merits of different options on a real-world case study

SMART SECURITY MANAGEMENT IN SECURE DEVICES

International audienceAmong other threats, secure components are subjected tophysical attacks whose aim is to recover the secret information theystore. Most of the work carried out to protect these components generally consists in developing protections (or countermeasures) taken one byone. But this “countermeasure-centered” approach drastically decreasesthe performance of the chip in terms of power, speed and availability.In order to overcome this limitation, we propose a complementary approach: smart dynamic management of the whole set of countermeasuresembedded in the component. Three main specifications for such management are required in a real world application (for example, a conditionalaccess system for Pay-TV): it has to provide capabilities for the chip todistinguish between attacks and normal use cases (without the help of ahuman being and in a robust but versatile way); it also has to be basedon mechanisms which dynamically find a trade-off between security andperformance; all these mecanisms have to formalized in a way which isclearly understandable by the designer. In this article, a prototype whichenables such security management is described. The solution is based ona double-processor architecture: one processor embeds a representativeset of countermeasures (and mechanisms to define their parameters) andexecutes the application code. The second processor, on the same chip,applies a given security strategy, but without requesting sensitive datafrom the first processor. The chosen strategy is based on fuzzy logic reasoning to enable the designer to describe, using a fairly simple formalism,both the attack paths and the normal use cases. A proof of concept hasbeen proposed for the smart card part of a conditional access for Pay-TV,but it could easily be fine-tuned for other applications

Tilted Fiber Bragg Grating photowritten in microstructured optical fiber for improved refractive index measurement

International audienceWe report what we believe to be the first Tilted short-period Fiber Bragg Grating photowritten in a microstructured optical fiber for refractive index measurement. We investigate the spectral sensitivity of Tilted Fiber Bragg Grating to refractive index liquid inserted into the holes of a multimode microstructured fiber. We measure the wavelength shift of the first four modes experimentally observed when calibrated oils are inserted into the fiber holes, and thus we determine the refractive index resolution for each of these modes. Moreover, a cross comparison between experimental and simulation results of a modal analysis is performed. Two simulation tools are used, respectively based on the localized functions method and on a finite element method. All results are in very good agreement

Three-hole microstructured optical fiber for efficient Fiber Bragg Grating refractometer

International audienceWe present a photosensitive three-hole microstructured optical fiber specifically designed to improve the refractive index sensitivity of a standard Fiber Bragg Grating (FBG) sensor photowritten in the suspended Ge-doped silica core. We describe the specific photowriting procedure used to realize gratings in such a fiber. We then determine their spectral sensitivity to the refractive index changes of material filling the holes surrounding the core. The sensitivity is compared to that of standard FBGs photowritten in a six-hole fiber with a larger core diameter. We demonstrate an improvement of the sensitivity by two orders of magnitude and reach a resolution of 3 x 10-5 and 6 x 10-6 around mean refractive index values of 1.33 and 1.40, respectively

Barriers and opportunities of fast-growing biobased material use in buildings

Limiting global warming to 1.5°C requires immediate and drastic reductions in greenhouse gas (GHG) emissions. A significant contributor to anthropogenic global GHG emissions is the production of building materials. Biobased materials offer the potential to reduce such emissions and could be deployed in the short term. Timber construction has received the main attention from policy and industry. However, the implementation of timber construction at the global scale is constrained by the availability of sustainably managed forest supplies. A viable alternative is fast-growing plants and the use of agricultural waste products. These can be deployed faster and are better aligned to local supplies of biomass and demands from the building sector. Fast-growing materials are generally able to achieve net-cooling impacts much faster due to their short rotation periods. The GHG emissions due to the production of biogenic building material can be compensated by regrowth of the new (replacement) plant and, overall, this will absorb CO2 from the atmosphere. A range of biogenic materials can be promoted and used as insulation materials and structural materials. Policy relevance Materials play an important part of the transition to a low carbon society, especially as many existing construction materials have large amounts of ‘embodied carbon’ in their manufacture. Given the need to rapidly reduce GHG emissions, public policies can promote a rapid transition to low carbon biogenic materials. The use of fast-growing biogenic materials for use in construction products can create carbon-neutral or even carbon-negative products. The use of biogenic materials in construction materials delivers larger GHG savings than their use in other sectors (e.g. biofuels). The use of these materials can be scaled up quickly due to their short rotation period. An integrated policy approach is needed that provides synergy between the energy, industry, housing and agriculture sectors to encourage the use of biobased materials.ISSN:2632-665

Barriers and opportunities of fast-growing biobased material use in buildings

Limiting global warming to 1.5°C requires immediate and drastic reductions in greenhouse gas (GHG) emissions. A significant contributor to anthropogenic global GHG emissions is the production of building materials. Biobased materials offer the potential to reduce such emissions and could be deployed in the short term. Timber construction has received the main attention from policy and industry. However, the implementation of timber construction at the global scale is constrained by the availability of sustainably managed forest supplies. A viable alternative is fast-growing plants and the use of agricultural waste products. These can be deployed faster and are better aligned to local supplies of biomass and demands from the building sector. Fast-growing materials are generally able to achieve net-cooling impacts much faster due to their short rotation periods. The GHG emissions due to the production of biogenic building material can be compensated by regrowth of the new (replacement) plant and, overall, this will absorb CO2 from the atmosphere. A range of biogenic materials can be promoted and used as insulation materials and structural materials

SOS An innovative secure system architecture

International audience`Smart On Smart' (SOS) is a project launched in 2008 and funded by the `Agence Nationale pourla Recherche'. This project aims at helping the partnershipformed by Trusted Logic, Viaccess, LIP6, and the CEA-LETI to study aninnovative secure system architecture. This architecture is based on twoparts. The first one called the host system is in charge of the mainapplication and processes the sensitive data. Connected to the host system thesecond part called the audit system is strictly dedicated to thesecurity strategy response of the whole system.The underlying idea is that such an architecture will help to build abetter secure system. For instance it becomes possible to improve theintelligence of the security policy to be able to differentiate a normalerror behaviour from a suspect one. Since the whole system's securityreliability is adjustable it becomes also possible to maximise theperformance when nonsensitive data are processed. Non repeatablebehaviour and response of the system under attack could be alsoprogrammed in order to counter the attacker.One of the main tasks is to define a hardware architecture correspondingto this concept for which a safe boundary has to be established between thetwo systems. The software part and in particular the way thesecurity policy is implemented on the audit system is also a non obvioustask especially because the overhead due to this additional auditsystem has to be the lowest possible in order to be cost-effective.We are building a proof of concept around a pay TV application. Additionalhardware features are used to emulate fault injection attacks for thedemo. We are building the hardware model on an FPGA board provingalso that such an architecture fits an FPGA based system

VLTI status update: a decade of operations and beyond

We present the latest update of the European Southern Observatory's Very Large Telescope interferometer (VLTI). The operations of VLTI have greatly improved in the past years: reduction of the execution time; better offering of telescopes configurations; improvements on AMBER limiting magnitudes; study of polarization effects and control for single mode fibres; fringe tracking real time data, etc. We present some of these improvements and also quantify the operational improvements using a performance metric. We take the opportunity of the first decade of operations to reflect on the VLTI community which is analyzed quantitatively and qualitatively. Finally, we present briefly the preparatory work for the arrival of the second generation instruments GRAVITY and MATISSE.Comment: 10 pages, 7 figures, Proceedings of the SPIE, 9146-1