Search results for "photonics"
showing 10 items of 802 documents
Accurate expansion of cylindrical paraxial waves for its straightforward implementation in electromagnetic scattering
2017
Abstract The evaluation of vector wave fields can be accurately performed by means of diffraction integrals, differential equations and also series expansions. In this paper, a Bessel series expansion which basis relies on the exact solution of the Helmholtz equation in cylindrical coordinates is theoretically developed for the straightforward yet accurate description of low-numerical-aperture focal waves. The validity of this approach is confirmed by explicit application to Gaussian beams and apertured focused fields in the paraxial regime. Finally we discuss how our procedure can be favorably implemented in scattering problems.
New photonic devices for ultrafast pulse processing operating on the basis of the diffraction-dispersion analogy
2008
The space-time analogy is a well-known topic within wave optics that brings together some results from beam diffraction and pulse dispersion. On the above basis, and taking as starting point some classical concepts in Optics, several photonic devices have been proposed during the last few years with application in rapidly evolving fields such as ultrafast (femtosecond) optics or RF and microwave signal processing. In this contribution, we briefly review the above ideas with particular emphasis in the generation of trains of ultrafast pulses from periodic modulation of the phase of a CW laser source. This is the temporal analogue of Fresnel diffraction by a pure phase grating. Finally, we ex…
Extraordinary nonlinear transmission modulation in a doubly resonant acousto-optical structure
2017
International audience; Acousto-optical modulators usually rely on coherent diffraction of light by a moving acoustic wave, leading to bulky devices with a long interaction length. We propose a subwavelength acousto-optical structure that instead relies on a double resonance to achieve strong modulation at near-infrared wavelengths. A periodic array of metal ridges on a piezoelectric substrate defines cavities that create a resonant dip in the optical transmission spectrum. The ridges simultaneously support large flexural vibrations when resonantly excited by a radio-frequency signal, effectively deforming the cavities and leading to strongly nonlinear acousto-optical modulation. The nano-o…
Characterization of opal photonic hetero-crystals by light scattering
2006
Spectra of the light scattered in the heterogeneous photonic crystal based on the thin triple-film opal, which was prepared by successive, convective force-assisted crystallisation of colloidal suspensions containing spheres of 374, 474 and again 374 nm in diameter, have been studied in the wavelength range of low order photonic bandgaps. If the ballistic regime of light propagation is preserved, the forward scattered light becomes the subject of the diffraction attenuation, whereas the backscattered light experiences both the diffraction enhancement and attenuation. A variety of possible configurations of scattered light measurements have been examined and corresponding spectra of scattere…
Light Propagation in Heterogeneous Opal-Based Photonic Crystals
2006
Ballistic light propagation in the heterogeneous photonic crystals based on the thin triple-film opal have been studied in the wavelength range of low order photonic bandgaps. Since the scattered light experiences the diffraction attenuation, the spectra and the angle diagrams of the transmitted and forward scattered light have been used to identify the effect of heterostructuring.
Subwavelength surface waves with zero diffraction
2011
We identified nanostructured devices sustaining out-of-plane nondiffracting beams with near-grazing propagation and a transverse beamwidth clearly surpassing the diffraction limit of half a wavelength. This type of device consists of a planar multilayered metal-dielectric structure with a finite number of films deposited on a solid transparent substrate. We assumed that the nondiffracting beam is launched from the substrate. The construction of the subwavelength diffraction-free beam is attended by plane waves which are resonantly transmitted through the stratified medium. Therefore, light confinement and wave amplification occurs simultaneously. We performed an optimization process concern…
Experimental observation of temporal dispersion gratings in fiber optics
2017
We experimentally demonstrate a temporal analog to the diffraction optical grating in the Fraunhofer formalism. Using amplitude and phase temporal periodic modulations, we show that the accumulation of dispersion in fiber optics induces the development of temporally well-separated sidebands similar to the spatial orders of diffraction that are commonly observed in an optical grating operating in the far field.
Devil’s vortex-lenses
2009
In this paper we present a new kind of vortex lenses in which the radial phase distribution is characterized by the "devil's staircase" function. The focusing properties of these fractal DOEs coined Devil's vortex-lenses are analytically studied and the influence of the topological charge is investigated. It is shown that under monochromatic illumination a vortex devil's lens give rise a focal volume containing a delimited chain of vortices that are axially distributed according to the self-similarity of the lens.
Determinant role of the edges in defining surface plasmon propagation in stripe waveguides and tapered concentrators
2012
International audience; In this paper, we experimentally show the effect of waveguide discontinuity on the propagation of the surface plasmon in metal stripes and tapered terminations. Dual-plane leakage microscopy and near-field microscopy were performed on Au stripes with varied widths to imag29e the surface plasmon intensity distribution in real and reciprocal spaces. We unambiguously demonstrate that edge diffraction is the limiting process determining the cutoff conditions of the surface plasmon mode. Finally, we determine the optimal tapered geometry leading to the highest transmission.
Tunable dual-wavelength thulium-doped fiber laser in the range from 2067 to 2073.5 nm
2017
A tunable dual-wavelength lineal cavity Tm-doped fiber laser is presented. The generation of the laser lines is based on the use of cascaded fiber Bragg gratings and a Hi-Bi fiber optic loop mirror.