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International audience; Tomographic diffraction microscopy is a three-dimensional quantitative optical imaging technique in which the sample is numerically reconstructed from tens of holograms recorded under different angles of incidence. We show that combining the measurement of the amplitude, the phase, and the polarization of the field scattered by the sample with an approximate knowledge of the sample permittivity allows reconstruction of spatially complex samples up to 50 nm resolution. This technique should be particularly useful for imaging objects made of known materials.

International audience

Hybrid bonding of III-V layers on silicon is demonstrated implementing an ultra-thin SiO2 atomic layer deposited - ALD - layer as the intermediate bonding layer. X-ray photoelectron spectroscopy characterization of the SiO2 layers evidences that the plasma enhanced - PE - ALD process activates the surfaces with OH dangling bonds. These dangling bonds ensure the surface activation which is necessary for oxide-mediated bonding. The optimized ALD process parameters have been established in order to produce a void-free InP/Si hybrid interface. This hybrid interface is structurally and mechanically characterized. ALD processing is of great interest for hybrid bonding on Si since it offers simultaneously three advantages: a very thin and controlled thickness, an activated surface and a conformal deposition when already patterned silicon layers have to be considered within operating devices. Display Omitted An ALD SiO2 layer is proposed for InP on Si bonding.The ALD SiO2 layer activation with hydroxyl groups is measured by XPS.The ALD SiO2 layer activation is evidenced by bonding an InP membrane on Si at 300°C.

National audience

A nano-scale analogue to the double cantilever experiment that combines instrumented nano-indentation and atomic force microscopy is used to precisely and locally measure the adhesion of InP bonded on sub-100 nm patterned Si using oxide-free or oxide-mediated bonding. Surface-bonding energies of 0.548 and 0.628 J m(-2), respectively, are reported. These energies correspond in turn to 51% and 57% of the surface bonding energy measured in unpatterned regions on the same samples, i.e. the proportion of unetched Si surface in the patterned areas. The results show that bonding on patterned surfaces can be as robust as on unpatterned surfaces, provided care is taken with the post-patterning surface preparation process and, therefore, open the path towards innovative designs that include patterns embedded in the Si guiding layer of hybrid III-V/Si photonic integrated circuits.

International audience

While the resolution of fluorescence microscopy has undergone a significant improvement in the recent years, reaching a few tens of nanometers, that of marker-free microscopes remains stuck at several hundreds of nanometers.

International audience

A multiscale approach has been developed in order to simulate the etch process of InP in an inductive coupled plasma (ICP) Cl2/Ar plasma discharge. The model consists of three modules: a global kinetic model of the Cl2/Ar plasma discharge, a sheath model, and a 2-D Monte-Carlo etching model. The densities and the fluxes of all neutral and charged species considered in the reaction scheme as well as the electron temperature are calculated from the global model. The angular and energy distribution functions of ions are computed from the sheath model. The output parameters of both the global kinetic model and the sheath model in terms of particle fluxes, ion angular distribution function and ion energy distribution function are used as input parameters in the 2-D etching model. The latter allows tracking in time the evolution of the etched surface. The ultimate goal of the multiscale approach is to predict the etch rate, the etched surface chemical composition, and the etch profile as a function of the operating conditions (power, pressure, gas flow rates, etc). In this paper, the results from the global model are first compared to the measurements carried out in the ICP etching tool, showing a satisfactory agreement. The etching model is then used to simulate the etching of narrow trench and small-diameter hole in InP. The mechanisms involved in the development of undercut below the mask and in the bowing effect are analyzed. The comparison between simulated and experimental etch profiles evidences the important role of Cl adsorption probability on the development of the undercut, and the significant impact of the redeposition of the etched species on the etch rate variation and on the narrowing in the bottom of the etched hole/trench.

International audience; We report the 3D mapping of strain and tilts of crystal planes in an extended InP nanostructured layer bonded onto silicon, measured without sample preparation. Our approach takes advantages of 3D x-ray Bragg ptychography combined to an optimized inversion process. The excellent agreement with the sample nominal structure validates the reconstruction while the evidence of spatial fluctuations hardly observable by other means, underlines the specificities of Bragg ptychography.

We experimentally demonstrate, by etching a “doubly periodic” pattern in a high-index material (Ta2O5), that guided-mode resonance filters can exhibit polarization independent peaks with a Q factor of 5600. Beyond this promising result, complementary characterizations give us some leads to rectify the energy repartition between reflection, transmission, and losses.

International audience; Total internal reflection microscopy is mainly used in its fluorescence mode and is the reference technique to image fluorescent proteins in the vicinity of cell membranes. Here, we show that this technique can easily become a phase microscope by simply detecting the coherent signal resulting from the interference between the field scattered by the probed sample and the total internal reflection. Moreover, combining several illumination angles permits generating synthetic aperture reconstructions with improved resolutions compared to standard label-free micro-scopy techniques. Total internal reflection fluorescence (TIRF) microscopy is the reference technique to study the membrane dynamics and organization in biological cells [1,2]. Its main advantage is the ability to illuminate with a high axial sectioning the sample, typically over a thin slice of about 100 nm, by taking benefit from a total internal reflection (TIR) configuration. The sample is deposited on a glass substrate, and by illuminating through the substrate above the critical angle, an evanescent wave is created at the interface to locally probe the sample. Compared to standard wide-field fluorescence microscopy, images with highly improved contrast are provided, since the background signal stemming from the volume of the sample can be suppressed. The preferred TIRF configuration nowadays uses a high numerical aperture (NA) immersion objective both to illuminate above the critical angle and collect the fluorescence signal. Using fluorophores as contrast agents, however, presents some drawbacks, as their addition is invasive and induces the increased risk of photobleaching and phototoxicity to the cell [3]. Long-term studies are thus difficult to achieve. The spe-cificity of labeling is, moreover, at the same time the main advantage and the main limitation of fluorescence imaging, since the lack of structural images can be detrimental to the interpretation of the results. Therefore, there is a clear need for a high-resolution technique able to probe cell membranes without the constraint of incorporating a fluorescent label. Two main approaches have been used so far to perform label free imaging in TIR with a high NA objective. The first approach uses a spatially incoherent source (such as a light bulb or LED) to illuminate the sample simultaneously with all angles above the critical value imposed by the glass substrate and the sample immersion medium (usually water) [4,5]. As the sample refractive index is higher than that of water, TIR is frustrated at locations where the sample is close to the interface, which modulates the reflected intensity and is the source of contrast in the resulting image. The second approach uses a laser beam focused in the back focal plane (BFP) of the objective at the edge of the NA [6,7]. The focused beam is scanned along a circle in the BFP, so that the sample is illuminated in TIR by a rotating collimated beam, and the integration time of the camera is set to match the rotation period of the beam. The totally reflected beam is blocked in a plane conjugated with the BFP to detect only the scattered intensity and obtain dark-field imaging. Both approaches have a high temporal resolution, and the second one claims an improved resolution at the price of some sample distortions in the image. In this Letter, we propose a label-free TIR microscopy technique that keeps the same setup simplicity as the previous approaches, but permits besides to perform phase imaging and improve the resolution through synthetic aperture generation. The core idea of the technique is that the intensity detected in TIR microscopy can directly give access to the phase and the amplitude of the field scattered by the probed sample. Assuming the scalar approximation, the detected intensity I can be written as I ˆ jE r ‡ E s j 2 ˆ jE r j 2 ‡ jE s j 2 ‡ E r E s ‡ E r E s , (1) where E r is the field reflected by the interface in TIR, and E s is the field backscattered by the sample. As in TIR the sample is illuminated over a very thin slice and is usually of very weak contrast in biology, we can assume E r is very strong compared to E s , and neglect jE s j 2 in Eq. (1). Since E r is close to the edge Letter Vol. 43, No. 9 /

Optical delay lines are key building blocks for all-optical signal processing. Photonic crystal structures can demonstrate efficient group velocity reduction, together with a wide-bandwidth and reduced high-order group velocity dispersion. Theses structures also offer the ability for 2D integration within photonic integrated circuits. This paper presents the performances of photonic crystal structures engineered for slowing down the light, and discuss the actual limitation encountered due to fabrication imperfections. To cite this article: A. Talneau, C. R. Physique 10 (2009).

We report simulation and experiment results of modal behaviors of photonic crystal (PhC) tapers on InP-based materials designed to improve coupling efficiency of the PhC waveguide mode into a cleaved-facet single-mode fiber. The modal distributions of transmitted power are simulated by two-dimensional finite difference time domain (2D-FDTD) calculation and the measured far-field patterns are in agreement with these calculations. The 34.4 mum-long PhC taper with Gaussian curve geometry is demonstrated to have an enhancement of coupling efficiency by a factor of four compared to the direct coupling from a W3 PhC defect waveguide.

International audience; We investigate the impact of disorder on the propagation of photonic crystal waveguide modes using phase-sensitive optical low-coherence reflectometry.Combined with a suitable numerical processing, this technique reveals a considerable amount of information that we cast as time-wavelength reflectance maps. By comparing measurements on different samples, we easily identify inter-mode scattering and propagation losses mediated by slow leaky modes. We also characterize the dispersive behaviour of point defects. Our results verify previous theoretical predictions about the general group velocity scaling of losses and the dominant role of backscattering.

The issue of extracting guided modes from a standard light-emitting heterostructure similar to those of visible or near-infrared light-emitting diodes is considered with respect to the role of lattices and of the amount of omnidirectionality in the extraction performances. Triangular lattices are first-order natural candidates. We examine first whether they can be made omnidirectional thanks to a grating + coupler combination initially proposed by Fehrembach et al (2001), whereby the short periodicity concentrates emission in few in-plane modes, and the double periodicity extracts it. We then examine lattices that directly extract, for a Ga(Al)As system on a GaAs substrate, with a specific 3-D mode decay calculation. We compare triangular and Archimedean lattices experimentally and point out the role of photonic strength also through a spectrally and angularly resolved experiment.

Nous decrivons une tentative originale pour resoudre le probleme de l'accord de phase pour la conversion de frequences optiques dans des composants semiconducteurs. La possibilite d'implementer une grande birefringence intrinseque dans des semiconducteurs artificiels bases sur des composes ayant la structure cubique de la blende de zinc est d'abord discutee theoriquement. Les premiers resultats concernant la croissance epitaxiale et la caracterisation optique de superreseaux d'ultracourte periode sont presentes ensuite.

The development of two-dimensional chemically assisted ion beam etching model of GaAs by Cl2∕Ar+ allowed the authors to analyze the role of some critical parameters of etch process on the morphology of trench and mesa structures. In a fact, the simulation results show that the etch rate variation with substrate temperature Ts reveals three regimes: For Ts TM a fast decrease of the etch rate is observed because of the high decrease of the coverage rate of Cl, ξ, on the gallium sites with the substrate temperature. On the other hand, the increase of the Cl2 flow rate allows to improve the anisotropy and contributes to the elimination of both the mi...

Oxide-free bonding of III-V-based materials for integrated optics is demonstrated on both planar Silicon (Si) surfaces and nanostructured ones, using Silicon on Isolator (SOI) or Si substrates. The hybrid interface is characterized electrically and mechanically. A hybrid InP-on-SOI waveguide, including a bi-periodic nano structuration of the silicon guiding layer is demonstrated to provide wavelength selective transmission. Such an oxide-free interface associated with the nanostructured design of the guiding geometry has great potential for both electrical and optical operation of improved hybrid devices.

Tomographic diffractive microscopy is a three-dimensional imaging technique that reconstructs the permittivity map of the probed sample from its scattered field, measured both in phase and in amplitude. Here, we detail how polarization-resolved measurements permit us to significantly improve the accuracy and the resolution of the reconstructions, compared to the conventional scalar treatments used so far. An isotropic transverse resolution of about 100 nm at a wavelength of 475 nm is demonstrated using this approach.

Progresses in the design of well-defined electronic band structure and dedicated functionalities rely on the high control of complex architectural device nano-scaled structures. This includes the challenging accurate description of strain fields in crystalline structures, which requires non invasive and three-dimensional (3D) imaging methods. Here, we demonstrate in details how x-ray Bragg ptychography can be used to quantify in 3D a displacement field in a lithographically patterned silicon-on-insulator structure. The image of the crystalline properties, which results from the phase retrieval of a coherent intensity data set, is obtained from a well-controlled optimized process, for which all steps are detailed. These results confirm the promising perspectives of 3D Bragg ptychography for the investigation of complex nano-structured crystals in material science.

International audience

Tomographic diffractive microscopy is a marker-free optical digital imaging technique in which three-dimensional samples are reconstructed from a set of holograms recorded under different angles of incidence. We show experimentally that, by processing the holograms with singular value decomposition, it is possible to image objects in a noisy background that are invisible with classical wide-field microscopy and conventional tomographic reconstruction procedure. The targets can be further characterized with a selective quantitative inversion.

International audience; Oxide-mediated bonding of III-V layers on Silicon is demonstrated through ultra-thin –one monolayer-SiO2 ALD layer. XPS characterization of the SiO2 ALD layer evidences its surface activation with –OH dangling bonds, and allows determining the optimized ALD process parameters for a void-free bonded interface.

We report in this paper results obtained from characterizations of photonic band gap waveguide, using near field optical microscopy. We will show evidence of a Bloch wave propagating within our W1 photonic crystal waveguides (PCWs) structure, using a 2D Fourier transform approach. The processed image will then be compared to simulations obtained from plane wave method. This comparison exhibits that near-field measurements, using tapered optical fibers as probes, are mainly sensitive to the electric field propagating within the structure.

Lasing of triangular and square lattice photonic crystal, waveguides on InP substrate is investigated around the 1.5-/spl mu/m wavelength by optical pumping. The lattice period of the fabricated structures is varied over a very large scale, thereby allowing a detailed exploration of the laser behaviors in the cases of micrometer width waveguides. A genuine distributed feedback (DFB) laser emission is observed in the gap for W2-3 waveguides in the /spl Gamma/M direction of a triangular lattice. A different behavior is obtained for W3 waveguides in the /spl Gamma/K direction of the same lattice as well as for W1 and W3 waveguides in the /spl Gamma/X direction of a square lattice. The laser emission is found to occur at the /spl Gamma/ point of the Brillouin zone (wavevector k=0) when the emission frequency is outside the gap. The DFB-like laser emission is intrinsically single mode in this case. Plane wave calculations show that the field distributions of the two DFB components are radically different. The emitting mode is well localized in the guide core while the non-lasing mode spreads over the whole crystal.

Chemically assisted ion beam etching of GaAs-based materials using Cl2 reactive gas was has been experimentally and theoretically examined. The primary effort was the design of an etching system for high reproducibility and improved throughput. Characteristics of the etching process, i.e., etch rate, etch profiles, and surface morphology as a function of etching parameters, i.e., substrate temperature, Cl2 flow rate, ion current density, and energy are reported. In addition, we have analyzed the etched surfaces qualitatively by Auger electron spectroscopy, and quantitatively by atomic force microscopy. The developed process yielded stoichiometric and smooth GaAs surfaces. Moreover, in order to understand the mechanism of the Cl2 etching reaction with GaAs, a simulation of the etch profile evolution with time as function of etching parameters was carried out. Simulations were compared with experimentally derived data and were found to be in good agreement. Finally, the developed process was successfully ap...

We have experimentally investigated the modal behaviour and the polarization dependence of the transmission through single-missing-row photonic crystal (PC) straight guides, bends and combiners, fabricated on InP substrate. A photonic crystal-based taper has been included to funnel light in these strongly confined structures. Two-dimensional finite-difference time-domain simulations have been performed and favorably compared with the measurements. It is found that the scattering process occurring at a bend/combiner transition plays a key role on the overall transmission.

A planarization technique has been developed to embed in a very thin (

We report on results of the fabrication and optical measurements of silicon on insulator (SOI) nanostructures designed for photonic applications. Patterning has been done by electron beam lithography and reactive ion etching with an SF6 and CHF3 gas mixture. Both one dimensional (1D) and two dimensional (2D) photonic lattices were studied by measuring dispersion curves above the light cone. Lateral Fabry-Perot resonators were also fabricated in a waveguide geometry, showing strong dependence of the transmission intensity as a function of the silicon filling factor and the number of air gaps in the Bragg-like mirrors.

International audience

International audience

International audience

Oxide-free bonding of indium phosphide epitaxial layers onto silicon-on-insulator (SOI) offers good thermal and electrical contact. These properties are retained if guidance engineering of the resulting stack is performed by nanostructuring the silicon layer to produce a lower effective index layer. We discuss the optical characterization of such a system by a simple prism deviation method for a thin stack, or diffraction to the air for a more multimode stack, adding a superperiod to the nanostructure.

International audience

Direct bonding of Yttrium Iron Garnet on Si without any intermediate layer is demonstrated and characterized using Scanning Transmission Electron Microscopy. Such geometry of the hybrid stack with no layer in between the magneto-optic garnet film and the Si guiding layer opens the route for highly efficient hybrid isolators.

An heteroepitaxial bonded III-Von Si nanopatterned waveguide is demonstrating a wavelength selective behavior thanks to a super-periodicity added to its sub-wavelength, below band-gap, structuration. Effective Medium Theory has been implemented for modal effective index determination, allowing a quick and nevertheless detailed investigation of the role of a large number of geometrical parameters. Such nanostructured waveguides offer the versatility for designing complex geometries required for hybrid advanced optical functions on silicon.

A n-InP/n-Si isotype heterojunction is fabricated using direct oxide-free bonding, to study electrical transport in this hybrid material system. The band alignment is first evaluated numerically and a theoretical I(V) curve is discussed. The diode is then fabricated and the experimental I(V) curve is compared against theory.

Hybrid silicon photonics offers novel opportunities to control light propagation with nanostructured media on the silicon side. In the specific case of oxide-free heteroepitaxial bonding of III-V layers on silicon, it is particularly crucial to assess the role of nanostructures in the post-bonding situation. We propose here a method of internal light source and integrated prism deviation to evaluate the effective index of small sub-wavelength periodic shallow holes that are completely embedded and do not lend themselves to alternative such as e.g. ellipsometry. We achieve a precision $\Delta n < 0.01$ , a good accuracy both for the understanding and optimization of optical components performances. Measured data are in good agreement with the theoretical expectation, as obtained using an improved homogenization strategy and further confirmed by 3D Bloch mode calculation.

Directly bonded, oxide-free, InP-based epitaxial layer bonding onto nanopatterned silicon-on-insulator structures was performed and result in waveguides with an embedded effective medium. Such a medium ensures flexible form of optical confinement and could also assist heat and electric current transfer optimally to the silicon layer since there is a remarkable absence of oxide, thanks to careful surface preparation processes. The fabricated waveguides, which embed buried 1-D (trenches) or 2-D (holes forming a photonic crystal) nanopatterns have been measured by two techniques. Either the classical end-fire technique, or the “internal light source” technique used for III-V-based photonic crystal waveguides, with a layer that contains several quantum wells. Propagation losses due to scattering in the nanopatterned area are retrieved by both methods and consistently point toward a ~20 cm-1 loss level. A critical assessment is made of this result. Other local probe techniques allowed by the internal probe methods are reported that could help qualifying thermal transfer at these oxide-free interfaces.

Deep etching of a sub-wavelength grating in a high index material Ta"2O"5 guiding layer has been developed for high angular tolerance narrow band grating-waveguide reflective filters operating around 1550nm. Holes with accurate size and smooth as well as vertical sidewalls have been obtained thanks to an intermediate Ge mask layer. A very narrow linewidth down to @[email protected]=0.28nm is measured on a 3mmsq large Ta"2O"5 grating filter close to the targeted 0.21nm linewidth of the ideal structure.

We compare the merit of various longitudinal mode selection mechanism in distributed feedback laser for application as arrayed sources in the wavelength-division multiplexing context. Phase-shifted and complex-coupled laser arrays have been fabricated and characterized. We propose that the dispersion on the emitted wavelengths is strongly correlated to the field localization along the cavity. By comparison of the dispersion values measured within the laser arrays, we can conclude that the complex grating with gain is the best suitable mechanism for high wavelength accuracy and stability, due to the strong and distributed localization of the field in the gain sections of each period of the grating.

We present here the design, fabrication, and static as well as dynamic characteristics of a ten-wavelength, 200-GHz channel spacing emitter for wavelength-division multiplexing applications. The source is based on the monolithic integration on InP of a ten distributed Bragg reflector laser array with a square-shaped transmission response PHASAR. The specific design of the PHASAR is detailed. The continuous-wave operation-one channel at a time-demonstrates a high monomode stability with a rejection better than 32 dB for all channels and all injected currents; the 200-GHz channel spacing can be reached with an accuracy better than 25 GHz. High-speed characteristics demonstrate a 6.5-GHz direct modulation bandwidth at -3 dB for a 70-mA current in the 900-/spl mu/m-long active section. The chirp measured for a 2.5-Gb/s modulation with a 10-dB extinction ratio is less than 1.5 /spl Aring/ for every wavelength.