A Lanczos Method for Approximating Composite Functions

We seek to approximate a composite function h(x) = g(f(x)) with a global polynomial. The standard approach chooses points x in the domain of f and computes h(x) at each point, which requires an evaluation of f and an evaluation of g. We present a Lanczos-based procedure that implicitly approximates g with a polynomial of f. By constructing a quadrature rule for the density function of f, we can approximate h(x) using many fewer evaluations of g. The savings is particularly dramatic when g is much more expensive than f or the dimension of x is large. We demonstrate this procedure with two numerical examples: (i) an exponential function composed with a rational function and (ii) a Navier-Stokes model of fluid flow with a scalar input parameter that depends on multiple physical quantities

Couplage entre modes et bruit d'intensité de partition de lasers à fibre multifréquences

session Affiches, thème 3 « Amplificateurs et lasers à fibre » [A-Th3-2]National audienceL'utilisation de sources optiques peut permettre la génération de signaux radiofréquences sur une gamme très étendue et est particulièrement adaptée dans le cas de signaux à hautes fréquences (> 10 GHz). Dans cet article, nous présentons des sources lasers à deux fréquences et dont l'écart entre les longueurs d'ondes est ajustable dans le domaine micro-onde (de 1 à 50 GHz). Nous montrons l'influence de l'écart en fréquence sur le couplage des modes

Measurement of Intensity Noise Correlation between Lines of Spatially Distributed Multi-Wavelength Fiber Lasers

conference 6389 « Active and Passive Optical Components for Communications VI », topic: Communications/ITCom, session: Posters [ 6389 46]International audiencePhotoinscription of superstructured Bragg gratings in Er-Yb codoped fiber is a promising and cost-effective approach to produce high-quality multi-wavelength fiber lasers for various applications like radio-over-fiber systems, fiber-optic sensors or low-cost WDM testing source. However, a good understanding of the noise properties of the laser source is required before these applications can be addressed. Previous modeling has shown that these devices are similar to compact cascades of single wavelength DFB fiber lasers in which the modes at each wavelength are almost nonoverlapping along the fiber. In this paper, we further examine the independence of each channel by performing relative intensity noise (RIN) measurements on a multi-wavelength fiber laser, a dual-polarization fiber laser and a dualwavelength fiber laser. In each case, we estimate the correlation between the laser lines. From RIN measurements performed on each channel of a multi-wavelength laser, as well as on the full spectrum, we compute an average degree of correlation between the RIN of neighboring lines and observed no correlation in most of the cases. Moreover, each channel displays a single relaxation frequency which is different from those of the other channels. On the other hand, we observed strong partition noise, with negative correlation, between polarization modes of a single wavelength fiber laser. Finally, we measured the RIN of the two modes of a dual-wavelength fiber laser with modes having a greater overlap than the multi-wavelength laser. The results show that the lines share two common relaxation frequencies, an indication of a dynamic link between them

All Optical Up-Conversion of WLAN signal in 60 GHz Range with Side-Band Suppression

International audienc

Les réacteurs à neutrons rapides refroidis au gaz

Les réacteurs à neutrons rapides refroidis au gaz sont l’un des six types de réacteurs retenus par le forum international GIF, comme candidat possible à la quatrième génération. Cette note rappelle l’historique du développement de cette filière et fait le point en 2014 sur son état d’avancement. Les points forts de la filière sont rappelés. Pour les points faibles, qui sont principalement le développement du combustible et la faible inertie thermique en cas de perte du débit de refroidissement, un état des lieux est effectué quant à l’avancement de la R&D correspondante

Relative Intensity Noise of Multi-wavelength Fiber Laser

International audienceRelative intensity noise of a six-channel multiwavelength distributed Fabry-Perot fibre laser is compared to the noise of a singlemode distributed feedback fibre laser. The noise characteristics of individual channels are similar to that of the singlemode laser, offering a low-cost and compact solution for wavelength multiplexing applications without noise penalty