Restoring robust binary switching operation and exceptional point using long-period grating-assisted parity-time symmetric couplers

International audienceThe impact of imbalance in waveguides propagation constants among Parity-Time symmetric coupled waveguides and/or of a complex-valued coupling coefficient is assessed. The narrow tolerance found implies that attempts to tightly control waveguides parameters appear as elusive because of fabrication technology limitations, calling for more feasible mitigation avenues. It is shown that a grating-assisted Parity-Time symmetric coupler design restores both technologically robust binary switching operation and exceptional point. In addition the proposed design is compatible with birefringence compensation techniques providing polarization-independent operation as well as coupling and/or gain-loss profile modulation techniques that extend the control of switching operation in the Parity-Time symmetric phase. Using wavelength as an additional tuning parameter near exceptional points opens promising avenues for manipulating the trajectory on Riemann sheets in topological photonics applications

Coupled oscillator ensembles with loss and gain: a graph approach of PT symmetry

International audienceWe present a approach aimed at generalizing Parity-Time symmetry to mesoscopic ensembles of coupled oscillators with gain and loss, with inspiration from graph-theoretic tools. We globally minimize the imaginary part of the eigenvalues for small gain/loss and describe how couplingsadopt some topologies. We also discuss recent results on distributed-feedback laser diodes operating at 1550 nm and having both real and imaginary index modulation. We notably study their resistance to optical feedback

Electrically injected parity-time symmetric distributed feedback laser diodes (DFB) for telecom applications

The new paradigm of parity-time symmetry in quantum mechanics has readily been applied in the field of optics with numerous demonstrations of exotic properties in photonic systems. In this work, we report on the implementation of single frequency electrically injected distributed feedback (DFB) laser diodes based on parity-time symmetric dual gratings in a standard ridge waveguide configuration. We demonstrate enhanced modal discrimination for these devices as compared with index or gain coupled ones, fabricated in the same technology run. Optical transmission probing experiments further show asymmetric amplification in the light propagation confirming the parity-time symmetry signature of unidirectional light behavior. Another asset of these complex coupled devices is further highlighted in terms of robustness to optical feedback

Over-wavelength pitch sized diffraction gratings for augmented reality applications

International audienceWaveguide based optical combiners for augmented reality (AR) glasses are integrating several surface relief gratings (SRG) whose pitch sizes can be as small as 200 nm for the blue wavelength. All SRG components exploit the first diffraction order to couple in and out or to deviate the light. We present SRG using higher diffraction orders featuring over-wavelength pitch sizes. Our gratings use the edge wave (EW) diffraction phenomenon to steer light in the preferred far field direction

Bulletin Bibliographique

Ce bulletin bibliographique réunit plus d’une centaine de recensions d’ouvrages pour l’année 2011. Il fait appel aux principales disciplines de connaissance des faits religieux, telles que la sociologie, l’histoire, l’ethnologie ou la philosophie. Les multiples religions du monde sont appréhendées dans divers moments et contextes en même temps que les systèmes d’idées et d’usages avec lesquelles elles composent ou s’affrontent dans l’espace public. Outre les comptes rendus, plusieurs notes critiques reviennent sur la production du savoir : le sens des mots-clés d’hier et d’aujourd’hui dans les dictionnaires savants sur les phénomènes religieux ; les anthropologues et la religion en France et dans le monde ; l’histoire et la sociologie des mouvements messianiques et millénaristes ; les raisons de l’effervescence pentecôtiste au Nigeria ; les enjeux de l’engagement congréganiste dans l’éducation italienne du XIXe siècle