Yassine Hadjar

Waveguide-coupled nanowire as an optical antenna

We study the optical coupling between a gold nanowire and a silver ion-exchanged waveguide, with special emphasis on the nanowire antenna radiation pattern. We measure the radiation patterns of waveguide-coupled gold nanowires with a height of 70 nm and width of 50 or 150 nm in the 450-700 nm spectral range for TE and TM polarizations. We perform a systematic theoretical study on the wavelength, polarization, nanowire size, and material dependences on the properties of the radiation pattern. We also give some elements concerning absorption and near-field. Experiments and calculations show localized plasmon resonance for the polarization orthogonal to the wire (far-field resonance at 580 nm for the smallest wire and 670 nm for the widest). It is shown that a great variety of radiation patterns can be obtained, together with a high sensitivity to a change of one parameter, particularly near-resonance.

Stable 120-mW green output tunable over 2 THz by a second-harmonic generation process in a KTP crystal at room temperature

We report on 120-mW directly measured cw power at 532 nm from a tunable alpha -distributed-feedback laser diode near 1.064 microm frequency doubled in a KTP crystal operating room temperature inside a ring cavity. Our experimental setup allows us to scan frequencies up to 2 THz in the green-light domain and thus is extremely useful for iodine spectroscopy. We show good agreement between experimental results and theoretical predictions for the second-harmonic generation process.

Bidimensional near-field sampling spectrometry

We report on a concept of compact optical Fourier-transform spectrometer based on bidimensional (2D) spatial sampling of a confined interferogram. The spectrometer consists of a nanostructured glass surface on which two light beams interfere in total internal reflection. Subwavelength spatial sampling of the interferogram near field is achieved by introducing a tilt angle between a 2D array of optical nanoantennas and the interferogram pattern. The intensity distribution of the scattered light is recorded on a 2D CCD camera, and a one-dimensional Fourier transform of the interferogram is used to recover the input light spectrum. Experimental results show a wide spectral bandwidth in the visible range, down to 380 nm, with spectral resolution of 1.6 nm around 780 nm.

Compact interferometer transducer based on surface plasmon phase resonance.

We propose a new monolithic interferometric configuration and implement a novel method for spectroscopic phase shift detection of surface plasmon resonance (SPR) sensors. The interference pattern is obtained using a nonpolarizing beam splitter cube with two attached right angle prisms in such a way that each interference field undergoes two total internal reflections (TIR) at prisms/air interface and one attenuated total reflection (ATR) through surface plasmon interaction. The evanescent part of the interferogram around the Zero optical path difference (ZOPD) is sampled and detected in the far field, thanks to a bidimensional array of scattering optical near-field probes deposited on the corresponding prism surface. A Fourier transform of the sampled interferogram is performed to measure the input light wavelength, while a direct comparison of the interferogram in TM and TE polarization modes allows us to determine the differential phase shift induced by the SPR layer. The phase shift measurement is made possible thanks to a remarkable time stability of the interferogram in the glass bulk. By tuning the input laser wavelength around the resonance, we show a good agreement between experimental and theoretical calculations for both amplitude and phase spectral responses.

CoBiSS: Compact Bidimensional Sampling Spectrometer

Novel technology for static Fourier spectrometer based on 2D angle-tilted array of nanostructured glass surface on which light beams interfere in total internal reflection. Near field subwavelength spatial sampling is achieved by tilt angle control.

Far field scattering by a waveguide-coupled nanowire

We study both experimentally and numerically far-field radiation patterns of single metallic nanowires coupled to weak confined optical waveguides. The radiation pattern resulting from the interaction of the nanowire and the optical mode depends strongly on the mode properties (polarization and wavenumber) and on the antenna properties (material and size). To investigate these phenomena we compare the electric far-field distributions computed with different numerical methods (Greens tensor technique, rigourous coupled wave method, Fourier modal method). We also compare simulated results to experimental measurements obtained over a large spectral domain ranging from 400 nm to 1000 nm. This study should be useful for optimizing nanostructured photonic circuits elements.