Stephane Tisserand

Titanium implantation in bulk and thin film amorphous silica

Both bulk and thin film amorphous silica implanted with titanium were investigated. We studied the induced modifications of the microstructure and the consequences on the optical properties. We determined the refractive index profile of implanted materials from guided wave measurements and we show that it matches the distribution of titanium. An increase in refractive index of up to 0.9 can be obtained by high dose implantation. A study of thermal annealing in air shows that the implanted materials exhibit low optical losses.

Resonant metamaterial absorbers for infrared spectral filtering: quasimodal analysis, design, fabrication, and characterization

We present a modal analysis of metal–insulator–metal (MIM)-based metamaterials in the far infrared region. These structures can be used as resonant reflection bandcut spectral filters that are independent of the polarization and direction of incidence. We show that this resonant reflection dip is due to the excitation of quasimodes (modes associated with a complex frequency) leading to quasi-total absorption. We have fabricated large area samples made of chromium nanorod gratings on top of Si/Cr layers deposited on silicon substrate. Measurements by Fourier transform spectrophotometry show good agreement with finite element simulations. A quasimodal expansion method is applied to obtain a minimal resonant model that fits well full wave simulations and that highlights excitation conditions of the modes.

Ion implanted integrated optics (I3O) technology for planar lightwave circuits fabrication

The Ion Implanted Integrated Optics (I3O) technology, using titanium ion implantation in bulk silica to fabricate passive compact planar lightwave circuits (PLCs), is presented in this paper. Its advantages are described and compared with other waveguide fabrication technologies. It is demonstrated that the guided electromagnetic field can be tailored by adjusting the titanium ion dose either to fit the guided mode of standard single-mode fibers or to allow a sharp radius of curvature of bent waveguides.

Transmission enhancement through square coaxial aperture arrays in metallic film: when leaky modes filter infrared light for multispectral imaging.

The diffractive behavior of arrays of square coaxial apertures in a gold layer is studied. These structures exhibit a resonant transmission enhancement that is used to design tunable bandpass filters for multispectral imaging in the 7-13 μm wavelength range. A modal analysis is used for this design and the study of their spectral features. Thus we show that the resonance peak is due to the excitation of leaky modes of the open photonic structure. Fourier transform infrared (FTIR) spectrophotometry transmission measurements of samples deposited on Si substrate show good agreement with numerical results and demonstrate angular tolerance of up to 30 degrees of the fabricated filters.

Analysis of diffraction gratings via their resonances

We analyze diffraction gratings via their resonances by a direct determination of the eigenmodes and the complex eigenfrequencies using a finite element method (FEM), that allows to study mono‐ or bi‐periodic gratings with a maximum versatility : complex shaped patterns, with anisotropic and graded index material, under oblique incidence and arbitrary polarization. In order to validate our method, we illustrate an example of a four layer dielectric slab, and compare the results with a specific method that we have called tetrachotomy, which gives us numerically the poles of the reflection coefficient (which corresponds to the eigenfrequencies of the structure).

Resonances determination in microstructured films embedded in multilayered stacks

Our approach consists in finding the eigenmodes and the complex eigenfrequencies of structures using a finite element method (FEM), that allows us to study mono- or bi-periodic gratings with a maximum versatility : complex shaped patterns, with anisotropic and graded index material, under oblique incidence and arbitrary polarization. In order to validate our method, we illustrate an example of a four layer dielectric slab, and compare the results with a specific method that we have called tetrachotomy, which gives us numerically the poles of the reflection coefficient (which corresponds to the eigenfrequencies of the structure). To illustrate our method, we show the eigenvalues of one- and two-dimensional gratings.

Bulk silica NIR blazed transmission gratings made by Silios technologies

In order to study the dark universe (energy and matter), EUCLID space mission will collect near infrared spectra and images of millions of galaxies. This massive measurement survey requires a slitless spectroscopic channel including GRISMs (for “Grating pRISMs”) in NISP (Near Infrared SpectroPhotometer). Very special technical specifications are required for the grating manufacturing: large aperture, low groove frequency and blaze angle, line curvature. In addition, it has to withstand space environment. Therefore, in the frame of a R&D project funded by the CNES, we developed bulk silica gratings in close collaboration with the French company SILIOS Technologies. SILIOS delivered two resin-free blazed gratings with curved lines engraved directly into the fused silica substrate of 80mm and 108mm useful aperture. At LAM, we measured very high optical performances of these prototypes: <80% transmitted efficiency, <30nm RMS wavefront error, groove shape and roughness very close to theory and uniform over the useful aperture. In this paper, we give specifications of these gratings, we describe the manufacturing process developed by SILIOS Technologies, we present briefly optical setups and models allowing optical performances verifications at LAM and we show very encouraging results obtained on the two gratings.

Transformation optics PML and quasi-mode analysis: Application to diffraction gratings

This paper presents the Perfectly Matched Layers (PMLs) in the framework of transformation optics as a complexvalued change of coordinates. PMLs provide the suitable operator extensions required for the leaky mode computation of open waveguides and the quasi-mode computation of scattering problems. Quasi-modes of diffraction gratings are considered here together with a numerical use of this spectral analysis.

Development of diffractive antireflection structures on ZnSe for high power CO2 laser applications

The unavoidable absorption of thin films used in antireflective coatings forms a permanent bottleneck in the development of optics for high power laser applications. A valid alternative would be the micro-structuring of the optics surface, realizing a diffraction grating which emulates the functioning of an Anti-Reflection thin film layer. Due to the absence of film material, this diffractive structure would not contribute to the overall absorption of the optics. This paper investigates the practical limits of this strategy, applied to zinc selenide as low absorption infrared substrate material.

Laser damage on diffractive optics

Laser damage studies are made on a phase mirror used for laser beam shaping in high power laser applications. The phase mirror is composed of a glass substrate with defined patterns to encode a phase, on top of which a multilayer mirror is deposited. We describe in this paper the LIDT obtained (at 1064nm, 6ns) and the laser damage test procedure, adapted to the geometry, that has been used. A morphologic analysis of the damage sites is made with Nomarski and Atomic Force Microscopy, to obtain information on the damage initiation and its localization on the structured component. The results are completed with simulations of the electric field within the multilayer by using a wave propagation computer code. We obtain localization and values of the light intensification occurring in the structure, that we correlate to experimental measurements.