Optical sensing based on phase interrogation with a Young's interference hologram using a digital micromirror device.

We propose a new holographic interferometric technique of phase interrogation for nanophotonic sensors, allowing to reach low phase noise and fluctuation by using a digital micromirror device spatial light modulator. With the spatial light modulator, both beam shaping and phase shifting interferometry can be simultaneously managed, hence enabling the interrogation of nanophotonic devices with a common-path heterodyne Young's interference experiment. The efficiency of the technique is illustrated in the particular case of temperature sensing using Tamm plasmon photonic crystals. The hologram sensor allows to probe resonant structures with deep attenuation at resonance, such as resonant structures at critical coupling or with phase singularities.

Super Bound States in the Continuum on a Photonic Flatband: Concept, Experimental Realization, and Optical Trapping Demonstration.

In this Letter, we theoretically propose and experimentally demonstrate the formation of a super bound state in a continuum (BIC) on a photonic crystal flat band. This unique state simultaneously exhibits an enhanced quality factor and near-zero group velocity across an extended region of the Brillouin zone. It is achieved at the topological transition when a symmetry-protected BIC pinned at k=0 merges with two Friedrich-Wintgen quasi-BICs, which arise from the destructive interference between lossy photonic modes of opposite symmetries. As a proof of concept, we employ the ultraflat super BIC to demonstrate three-dimensional optical trapping of individual particles. Our findings present a novel approach to engineering both the real and imaginary components of photonic states on a subwavelength scale for innovative optoelectronic devices.

Low-voltage, broadband graphene-coated Bragg mirror electro-optic modulator at telecom wavelengths.

We demonstrate a graphene based electro-optic free-space modulator yielding a reflectance contrast of 20% over a strikingly large 250nm wavelength range, centered in the near-infrared telecom band. Our device is based on the original association of a planar Bragg reflector, topped with an electrically contacted double-layer graphene capacitor structure employing a high work-function oxide shown to confer a static doping to the graphene in the absence of an external bias, thereby reducing the switching voltage range to +/-1V. The device design, fabrication and opto-electric characterization is presented, and its behavior modeled using a coupled optical-electronic framework.

Time-lapse scanning surface plasmon microscopy of living adherent cells with a radially polarized beam.

We report on a fibered high-resolution scanning surface plasmon microscope for long term imaging of living adherent cells. The coupling of a high numerical aperture objective lens and a fibered heterodyne interferometer enhances both the sensitivity and the long term stability of this microscope, allowing for time-lapse recording over several days. The diffraction limit is reached with a radially polarized illumination beam. Adherence and motility of living C2C12 myoblast cells are followed for 50 h, revealing that the dynamics of these cells change after 10 h. This plasmon enhanced evanescent wave microscopy is particularly suited for investigating cell adhesion, since it can not only be performed without staining of the sample but it can also capture in real time the exchange of extracellular matrix elements between the substrate and the cells.

Plasmon-based tomographic microscopy.

The imaging principle of the scanning surface plasmon microscope (SSPM) springs from the high sensitivity of surface plasmons to modifications of material properties near the dielectric-metal interface. In this paper, we show that tomographic techniques can be applied to SSPM imaging of dielectric objects to reach resolutions beyond the diffraction-limited half-wavelength scale. Furthermore, this high resolution is not limited to the multiple scattering regime. Finally, we conclude that SSPM is less sensitive to noise because it provides higher contrast ratio than other far-field microscopies.

Guided wave microscopy: mastering the inverse problem.

Surface plasmon microscopy is widely recognized for its high sensitivity to nanoscale dielectric or metallic structures confined in a close neighborhood of a gold surface. Recently, its coupling to high-numerical-aperture objective lenses pushed its resolution down to the diffraction limit. Here, we show that the same microscope configuration can be used to excite standing guided waves in asymmetric slabs, which definitely extends the range of applications of this type of microscopy from nano- to microscale structure imaging. We demonstrate experimentally on PPMA films that the V(Z) response of a scanning surface plasmon microscope can be Fourier inverted in order to obtain the reflectivity curve R(ν). When the guided waves are excited, R(ν) shows a finite number of sharp peaks corresponding to quantified guiding modes from which one can extract both the refractive index (RI) and the thickness of the layer at the point focused by the microscope. This device can thus be used to reconstruct RI and thickness contours of dielectric samples with a high spatial resolution.

Modeling of the scanning surface plasmon microscope.

We propose a family of exact solutions of Maxwell's equations to model some aspects of the imaging process involved in the scanning surface plasmon microscope (SSPM). More precisely, we compute the SSPM response of a spherical nanoparticle immobilized close to a thin gold layer and illuminated by a tightly focused spot. We discuss the influence of parameters such as the defocus and the width of the gold layer on the image contrast. We show that this microscopy combines a subwavelength spatial resolution together with high sensitivity to small changes in dielectric properties on the nanoparticle.

Deciphering the internal complexity of living cells with quantitative phase microscopy: a multiscale approach.

The distribution of refractive indices (RIs) of a living cell contributes in a nonintuitive manner to its optical phase image and quite rarely can be inverted to recover its internal structure. The interpretation of the quantitative phase images of living cells remains a difficult task because (1) we still have very little knowledge on the impact of its internal macromolecular complexes on the local RI and (2) phase changes produced by light propagation through the sample are mixed with diffraction effects by the internal cell bodies. We propose to implement a two-dimensional wavelet-based contour chain detection method to distinguish internal boundaries based on their greatest optical path difference gradients. These contour chains correspond to the highest image phase contrast and follow the local RI inhomogeneities linked to the intracellular structural intricacy. Their statistics and spatial distribution are the morphological indicators suited for comparing cells of different origins and/or to follow their transformation in pathologic situations. We use this method to compare nonadherent blood cells from primary and laboratory culture origins and to assess the internal transformation of hematopoietic stem cells by the transduction of the BCR-ABL oncogene responsible for the chronic myelogenous leukemia.

Diffraction phase microscopy: retrieving phase contours on living cells with a wavelet-based space-scale analysis.

We propose a two-dimensional (2-D) space-scale analysis of fringe patterns collected from a diffraction phase microscope based on the 2-D Morlet wavelet transform. We show that the adaptation of a ridge detection method with anisotropic 2-D Morlet mother wavelets is more efficient for analyzing cellular and high refractive index contrast objects than Fourier filtering methods since it can separate phase from intensity modulations. We compare the performance of this ridge detection method on theoretical and experimental images of polymer microbeads and experimental images collected from living myoblasts.

High-resolution surface-plasmon imaging in air and in water: V(z) curve and operating conditions.

We present what are believed to be the first images obtained with a far-field high-resolution scanning surface-plasmon microscope in an aqueous medium. Measurements of V(z), the output response of the microscope, versus defocus z give a signature of the surface-plasmon propagation. V(z) is strongly conditioned by the laser beam diameter and the objective's numerical aperture, and we show how the operating mode (in air and in water) must be chosen to maximize the surface-plasmon field and to minimize diffraction (edge) effects.