Creating the conditions so that matter naturally self-arranges at the nanoscale under a homogeneous excitation is an exciting challenge for the development of efficient and cost-effective processes. Sub-micrometer periodic templates can be formed spontaneously on materials by low-energy ion sputtering or with lasers. In the latter case, the formation of self-organized grating-like structures requires a high temperature rise and generally results from interactions with ultrashort laser pulses. Recently, a few studies have dealt with self-formed periodic patterns of metal nanoparticle assemblies, but they only reported changes in the spatial and size distributions of metal nanoparticles deposited on surfaces prior to interaction with femtosecond lasers. Here, we show that metal nanoparticles can grow in a selforganized manner within a waveguide illuminated from free-space by a continuous wave visible laser. We report the conditions that give rise to the generation of such 1D nanoparticle gratings and describe the parameters that influence the grating characteristics. We explain the mechanisms involved in the formation of such nanostructures on the basis of interference phenomena between the incident wave and guided modes.
Measurements of optical tweezers forces on biological micro-objects can be used to develop innovative biodiagnostics
methods. In the first part of this report, we present a new sensitive method to determine A, B, D types of red blood cells.
Target antibodies are coated on glass surfaces. Optical forces needed to pull away RBC from the glass surface increase
when RBC antigens interact with their corresponding antibodies. In this work, measurements of stripping optical forces
are used to distinguish the major RBC types: group O Rh(+), group A Rh(+) and group B Rh(+). The sensitivity of the
method is found to be at least 16-folds higher than the conventional agglutination method. In the second part of this
report, we present an original way to measure in real time the wall thickness of bacteria that is one of the most important
diagnostic parameters of bacteria drug resistance in hospital diagnostics. The optical tweezers force on a shell bacterium
is proportional to its wall thickness. Experimentally, we determine the optical tweezers force applied on each bacteria
family by measuring their escape velocity. Then, the wall thickness of shell bacteria can be obtained after calibrating
with known bacteria parameters. The method has been successfully applied to indentify, from blind tests, Methicillinresistant
Staphylococcus aureus (MRSA), including VSSA (NCTC 10442), VISA (Mu 50), and heto-VISA (Mu 3)
Hole arrays metallic filters can be made independent to polarization at normal incidence. However they may lose this
property for a non-normal incidence, being dependent to both polar and azimuthal incident angles. These variations of
the filter characteristics according to light orientation and polarization are not desirable for most optical applications.
Yet, for specific geometric parameters, high-stability can be obtained for cruciform-holes Ag-SiO2 filters. In this article, we propose a review of cross-holes metallic filters, working with CMOS-compatible materials in the visible range. We find out the main geometrical parameters impacting the filters sensitivity to the incident angles and polarization and link their role to spectral stability. We give proper design rules to realize stable filters which may lead to optical sensors with very low spectral variations whatever the incidence and the polarization of the source.
In the present paper, we will show how diffractive microstructures can lead to efficient lenses which present several advantages with respect to other proposed solutions. Also, they only require wavelength-scale resolution and not very small nanostructuring. Nevertheless we obtain comparable performances as plasmonics lenses and we show that the diffraction phenomenon which is at the origin of the observed effects can indeed lead to efficient focusing in the Fresnel region. The structures we proposed in this paper consist of pairs of parallel metallic nanowires fabricated by direct laser writing technique. The fabrication set-up is based on a metallic photoreduction initiated by two photon absorption using a nanosecond Q-Switched Nd-YAG laser. We show for instance experimentally that this pair of metallic nanowires separated by 2 μm when irradiated with an unpolarized light (at λ=546 nm) lead to a focusing at 2 μm with a diffraction limited resolution and an intensity enhancement at the focusing point of about 2.2 times the incoming intensity. Two different theoretical models were used to corroborate our experimental measurement. The first one is the diffraction theory based on the Rayleigh-Sommerfeld integral and the second one is the well kwon FDTD simulations, which are in very good agreement with experiments and confirm the origin of the focusing process. In addition they show that, in the case of our microstructures, plasmonic effects do not contribute to the focusing process. Finally, we propose a 2D array of microlenses based on a grid of metallic nanowires separated by a distance D. This device has slightly the same lens characteristics as a pair of metallic nanowires but with an intensity enhancement higher than 5, and thus may present practical interest in view of applications.
We study the rotation of photo-driven Archimedes screw with multiple blades. The micron-sized Archimedes screws are
readily made by the two-photon polymerization technique. Free-floating screws that are trapped by optical tweezers
align in the laser irradiation direction, and rotate spontaneously. In this study we demonstrate that the rotation speeds of
two-blade-screws is twice the rotation speed of one-blade-screw. However, more complex 3-blade-screws rotate slower
than 2-blade-screws due to their limited geometry resolution at this micron scale.
Ion-exchanged devices on glass have been successfully used to realize passive and active integrated optic devices for sensor and telecom applications. Nowadays, research is focused on the reduction of the chip dimensions with an increase of the number of different function integrated. In this paper we present how the use of two stacked optical layers can allow realizing efficient and compact pump duplexer for ion-exchanged hybrid erbium doped waveguide amplifier. Indeed our complete theoretical study of the device shows that excess losses lower than - 0.1 dB and crosstalk lower than -20 dB can be achieved.
A chemical system consisting of a metallic salt, a water-soluble polymeric matrix and a photosensitive specie absorbing
at two-photon, has been used to produce metal deposition upon exposure to a femtosecond laser. We show that this
technique can be used to fabricate 2D and 3D metallic structures with gold and silver. We illustrate the potential use of
this technique for the fabrication of optical diffractive structures and we report on the first observations of spectral
filtering effects in the near vicinity of micro/nano structures.
We are using the technique of two-photon induced photoprecipitation to fabricate gold and silver nanostructures. Gold and silver nanoparticles are produced in solution as well as in thin films. In both cases an absorption peak associated with the plasmon resonance is clearly observed and is found to vary as particles grow. In addition, we show that this technique also permits the fabrication of 2D and 3D metallic nanostructures with a good quality. The potential for optical applications is discussed and illustrated on some examples. In particular, we observe high efficiency luminescence and strong tunable diffusion.
Ion exchange on glass substrates has proved to be an efficient low cost and high performance technology to realise integrated optic devices. Among structures developed thanks to this technology, those presenting both surface and buried waveguides are of great interest. In this paper, we first describe a fabrication process of selectively buried ion exchange waveguides. Its principle is based on a two step ion exchange process. First a surface waveguide is realised by a thermal exchange of Ag\+-Na\+. Then a mask is deposited on the back side of the optical wafer perpendicularly to the axis of the waveguide. Finally a second step assisted by an external electric field is performed. Then we report the performances of this method through the measurement of the burying depth evolution. When the mask is wide enough, the burying depth varies from 2 μm above the middle of the mask to 12 μm in the unmasked region. The transition is 3 mm long and therefore avoid any excess losses. For this structure, no deformation of the fundamental mode has been observed. Finally, the first results of use of these selectively buried waveguides to realize Bragg filters with a surface grating is presented through a comparison of measured reflexion spectra.
The engineering of functionalized polymers for second order nonlinear optical applications is shortly described and discussed. The ways of chromophore orientation are also discussed with a special emphasis on static field poling. Practical application applications of these polymers are overviewed and an integrated optical amplifier is described in more details.
Nowadays, optical telecommunication systems require an increasing bit-rate. For this reason Dense Wavelength Division Multiplexing (DWDM) systems are currently under development. They need optical sources with a narrow and stable emission spectrum in the C band which should also integrate several emission wavelengths. Glass waveguide lasers enable both the sharp linewidth of optical fiber lasers and the integration possibilities of semiconductor lasers. In this paper, the realization of ion-exchanged waveguide DFB lasers on glass substrates is presented. Phosphate Er-Yb-codoped glass integrated lasers are first investigated for different doping concentrations. The characteristics of these lasers are then compared : each one have low threshold and exhibit single mode output power of several milliwatt for 100 mW launched pump power. The effect of a passivation layer is then studied. Its modelling and experiment shows that the emitted power can be increased by reducing pump scattering losses. Thanks to the use of silver ion exchange technology, a high index increase is obtained which induces an important variation of the waveguide's effective index with its width. Thus, the emission of 15 channels roughly placed on the 100 GHz ITU grid is demonstrated.
Nonlinear M-line spectroscopy is based on the analysis of the nonlinear change in the shape of the dark line associated with the excitation of guided waves. This is an easy technique for the determination of Kerr properties of thin films, which can constitute optical waveguides. Full spatiotemporal nonlinear modeling tools have been developed recently for nonlinear waveguide couplers, which are used for the determination of the complex nonlinear coefficient of organic polymers.
The nonlinear M-line technique is based on the analysis of the nonlinear change in the shape of the dark line associated with the excitation of guided waves. It is an easy technique for the determination of Kerr properties of thin films which can constitute optical waveguides. Full spatio-temporal nonlinear modelization tools have been developed recently for nonlinear waveguide couplers which are used for the determination of the complex nonlinear coefficient of new organic materials.
We present a simplified modal analysis of a Kerr-type grating coupler that rigorously takes into account the groove depth of the grating. These nonlinear grating couplers exhibit optical bistability. A comparison between the bistable loops obtained from this simplified method and a previously published rigorous method is performed.
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