Image formation properties and inverse imaging problem in aperture based scanning near field optical microscopy

Aperture based scanning near field optical microscopes are important instruments to study light at the nanoscale and to understand the optical functionality of photonic nanostructures. In general, a detected image is affected by both the transverse electric and magnetic field components of light. The discrimination of the individual field components is challenging as these four field components are contained within two signals in the case of a polarization resolved measurement. Here, we develop a methodology to solve the inverse imaging problem and to retrieve the vectorial field components from polarization and phase resolved measurements. Our methodology relies on the discussion of the image formation process in aperture based scanning near field optical microscopes. On this basis, we are also able to explain how the relative contributions of the electric and magnetic field components within detected images depend on the chosen probe. We can therefore also describe the influence of geometrical and material parameters of individual probes within the image formation process. This allows probes to be designed that are primarily sensitive either to the electric or magnetic field components of light

Theoretical study of lithium niobate slab waveguides for integrated optics applications

International audienceWe report on the theoretical study of lithium niobate slab and wire waveguides with different kinds of cladding (silicon dioxide, sapphire and air). The mode propagation, the light confinement and radiation losses are simulated using a software based on a beam propagation method. We propose from those results lithium niobate waveguide geometries for optical integrated application

The impact of finite-depth cylindrical and conical holes in lithium niobate photonic crystals

International audienceThe performance of lithium niobate (LN) photonic crystals (PhCs) is theoretically analyzed with transmission spectra and band diagrams as calculated by the 3-D Finite-Difference Time Domain (FDTD) method. For a square lattice of holes fabricated in the top surface of an Annealed Proton-Exchange (APE) waveguide, we investigate the influence of both finite hole depth and non-cylindrical hole shape, using a full treatment of the birefringent gradient index profile. As expected, cylindrical holes which are sufficiently deep to overlap the APE waveguide mode (centered at 2.5μm below the surface) produce transmission spectra closely resembling those predicted by simple 2??D modeling. As the hole depth decreases without any change in the cylindrical shape, the contrast between the photonic pass- and stop-bands and the sharpness of the band-edge are slowly lost. We show that this loss of contrast is due to the portion of the buried APE waveguide mode that passes under the holes. However, conical holes of any depth fail to produce well-defined stop-bands in either the transmission spectra or band diagrams. Deep conical holes act as a broad-band attenuator due to refraction of the mode out of the APE region down into the bulk. Experimental results confirming this observation are shown. The impact of holes which are cylindrical at the top and conical at their bottom is also investigated. Given the difficulty of fabricating high aspect-ratio cylindrical holes in lithium niobate, we propose a partial solution to improve the overlap between shallow holes and the buried mode, in which the PhC holes are fabricated at the bottom of a wide, shallow trench previously introduced into the APE waveguide surface

Optical far-field and near-field observations of the strong angular dispersion in a lithium niobate photonic crystal superprism designed for double (passive and active) demultiplexer applications

International audienceWe report on a lithium niobate photonic crystal (PC) superprism device designed for double demultiplexer applications. In fact, the strong angular beam steering cannot only be reached by passively tuning the vavelength but it can also be actively controlled by the Pockels effect enhanced due to the slow light phenomenon. The performance of the passive device is demonstrated by measuring its transmission properties. Optical far field and near-field experiments, corroborated by two-dimensional finite difference time domain (2D-FDTD) calculations, exhibit an angular dispersion of 1.5°/nm. A value as high as 4.3°/nm is expected by improving the PC design as supported by 2D-FDTD simulation

Strong improvement in the photonic stop-band edge sharpness of a lithium niobate photonic crystal slab

International audienceWe report on a photonic crystal PhC etched into a 380 nm thick lithium niobate LN thin film deposited on a MgO substrate by pulsed laser deposition. The transmission properties of this device were assessed by optical near-field measurements and compared to the transmission spectra of the same PhC drilled into bulk LN and calculated by a two dimensional finite-difference time domain method. We show a strong improvement in the transmission properties of the LN PhC by etching it into a thin layer rather than into a 500 m thick wafer. This result appears to be very promising for applications based on LN tunable PhCs. © 2009 American Institute of Physic

Caractérisation optique sub-longueur d'onde de couches minces de niobate de lithium développées pour la nanophotonique

International audienc

Multiplexer/Demultiplexer based on electro-optical control of superprism effect in photonic crystal

International audienc

Stability of the self-assembled polymer film from PAH et PSS

International audienc