Superlocalization Reveals Long-Range Synchronization of Vibrating Soliton Molecules.

We implement a superlocalization method in the time domain that allows the observation of the external motion of soliton molecules in a fiber ring cavity laser with unprecedented accuracy. In particular, we demonstrate the synchronization of two oscillating soliton molecules separated by several nanoseconds, with intermolecular oscillations following the same pattern as the intramolecular motion of the individual molecules. These experimental findings indicate an interplay between the different interaction mechanisms that coexist inside the laser cavity, despite their very different characteristic ranges, timescales, strengths, and physical origins.

Heterodyne interferometry applied to the characterization of nonlinear integrated waveguides.

We demonstrate that heterodyne interferometry makes it possible to accurately measure minute nonlinear phase shifts with little constraint on the propagation loss or chromatic dispersion. We apply this technique to characterize the effective nonlinearity of silicon nitride rib waveguides in the normal and anomalous dispersion regimes.

2D Waveguided Bessel Beam Generated Using Integrated Metasurface-Based Plasmonic Axicon.

Near-field imaging of the propagation of a diffraction-free Bessel-type beam in a guided wave configuration generated by means of a metasurface-based axicon lens integrated on a silicon waveguide is reported. The operation of the axicon lens with a footprint as small as 11 µm2 is based on local engineering of the effective index of the silicon waveguide with plasmonic nanoresonators. This generic approach, which can be adapted to different types of planar lightwave circuit platforms, offers the possibility to design nano-engineered optical devices based on the use of plasmonic resonators to control light at the nanoscale.

Saturable plasmonic metasurfaces for laser mode locking.

Metamaterials are artificial materials made of subwavelength elementary cells that give rise to unexpected wave properties that do not exist naturally. However, these properties are generally achieved due to 3D patterning, which is hardly feasible at short wavelengths in the visible and near-infrared regions targeted by most photonic applications. To overcome this limitation, metasurfaces, which are the 2D counterparts of metamaterials, have emerged as promising platforms that are compatible with planar nanotechnologies and thus mass production, which platforms the properties of a metamaterial into a 2D sheet. In the linear regime, wavefront manipulation for lensing, holography, and polarization control has been achieved recently. Interest in metasurfaces operating in the nonlinear regime has also increased due to the ability of metasurfaces to efficiently convert incident light into harmonic frequencies with unusual polarization properties. However, to date, the nonlinear absorption of metasurfaces has been mostly ignored. Here, we demonstrate that plasmonic metasurfaces behave as saturable absorbers with modulation performances superior to the modulation performance of other 2D materials and exhibit unusual polarimetric nonlinear transfer functions. We quantify the link between saturable absorption, the plasmonic resonances of the unit cell and their distribution in a 2D metasurface, and finally provide a practical implementation by integrating the metasurfaces into a fiber laser cavity operating in pulsed regimes driven by the metasurface properties. As such, this work provides new perspectives on ultrathin nonlinear saturable absorbers for applications where tunable nonlinear transfer functions are needed, such as in ultrafast lasers or neuromorphic circuits.

Improving the transmittance of an epsilon-near-zero-based wavefront shaper.

Although epsilon-near-zero (ENZ) metamaterials offer many unconventional ways to play with light, the optical impedance mismatch with surroundings can limit the efficiency of future devices. We report here on the improvement of the transmittance of an ENZ wavefront shaper. In this Letter, we first address the way to enhance the transmittance of a plane wave through a layer of ENZ material, thanks to a numerical optimization approach based on the transfer matrix method. We then transpose the one-dimensional approach to a two-dimensional case where the emission of a dipole is shaped into a plane wave by an ENZ device with a design that optimizes the transmittance. As a result, we demonstrate a transmittance efficiency of 15% that is four orders of magnitude higher than previous devices proposed in the literature for wavefront shaping applications. This Letter aims to pave the way for future efficient ENZ devices by offering new strategies to optimize the transmittance through ENZ materials.

Integrated plasmonic nanotweezers for nanoparticle manipulation.

We numerically demonstrate that short gold nanoparticle chains coupled to traditional SOI waveguides allow conceiving surface plasmon-based nanotweezers. This configuration provides for jumpless control of the trapping position of a nano-object as a function of the excitation wavelength, allowing for linear repositioning. This novel feature can be captivating for the conception of compact integrated optomechanical nanoactuators.

Lower bound for the spatial extent of localized modes in photonic-crystal waveguides with small random imperfections.

Light localization due to random imperfections in periodic media is paramount in photonics research. The group index is known to be a key parameter for localization near photonic band edges, since small group velocities reinforce light interaction with imperfections. Here, we show that the size of the smallest localized mode that is formed at the band edge of a one-dimensional periodic medium is driven instead by the effective photon mass, i.e. the flatness of the dispersion curve. Our theoretical prediction is supported by numerical simulations, which reveal that photonic-crystal waveguides can exhibit surprisingly small localized modes, much smaller than those observed in Bragg stacks thanks to their larger effective photon mass. This possibility is demonstrated experimentally with a photonic-crystal waveguide fabricated without any intentional disorder, for which near-field measurements allow us to distinctly observe a wavelength-scale localized mode despite the smallness (~1/1000 of a wavelength) of the fabrication imperfections.

Delocalization of Nonlinear Optical Responses in Plasmonic Nanoantennas.

Remote excitation and emission of two-photon luminescence and second-harmonic generation are observed in micrometer long gold rod optical antennas upon local illumination with a tightly focused near-infrared femtosecond laser beam. We show that these nonlinear radiations are emitted from the entire antenna and the measured far-field angular patterns bear the information regarding the nature and origins of the respective nonlinear processes. We demonstrate that the nonlinear responses are locally induced by a propagating surface plasmon at the excitation frequency, enabling thereby a polariton-mediated spatial tailoring and design of coherent and incoherent nonlinear responses.

Generation of two-dimensional plasmonic bottle beams.

By analogy to the three dimensional optical bottle beam, we introduce the plasmonic bottle beam: a two dimensional surface wave which features a lattice of plasmonic bottles, i.e. alternating regions of bright focii surrounded by low intensities. The two-dimensional bottle beam is created by the interference of a non-diffracting beam, a cosine-Gaussian beam, and a plane wave, thus giving rise to a non-diffracting complex intensity distribution. By controlling the propagation constant of the cosine-Gauss beam, the size and number of plasmonic bottles can be engineered. The two dimensional lattice of hot spots formed by this new plasmonic wave could have applications in plasmonic trapping.

Polarization beam splitting using a birefringent graded photonic crystal.

The use of a birefringent graded photonic crystal (GPhC) is proposed for the realization of an efficient polarization beam splitter. This approach allows decoupling the two functions of efficient light injection for both polarizations and TE/TM beam splitting. A smooth light polarization splitting is naturally achieved due to the different curved trajectories followed within the graded medium by the TE and TM waves. A 160 nm operating bandwidth with insertion loss around 1 dB and interpolarization crosstalk below -15 dB is predicted by a finite difference time domain simulation. The unusually exploited electromagnetic phenomena are experimentally evidenced by scanning near-field optical measurements performed on samples fabricated using the silicon on insulator photonics technology. These experimental works open perspectives for the use of birefringent GPhCs to manage polarization diversity in silicon photonic circuits.

Cosine-Gauss plasmon beam: a localized long-range nondiffracting surface wave.

A new surface wave is introduced, the cosine-Gauss beam, which does not diffract while it propagates in a straight line and tightly bound to the metallic surface for distances up to 80 µm. The generation of this highly localized wave is shown to be straightforward and highly controllable, with varying degrees of transverse confinement and directionality, by fabricating a plasmon launcher consisting of intersecting metallic gratings. Cosine-Gauss beams have potential for applications in plasmonics, notably for efficient coupling to nanophotonic devices, opening up new design possibilities for next-generation optical interconnects.

Near-field observation of beam steering in a photonic crystal superprism.

The optical near-field technique is applied to provide a direct experimental observation of the refracted beam propagation inside a photonic crystal structure displaying a superprism effect. The obtained results show a 35° light beam angle deviation for a wavelength variation from 1500 to 1600 nm. The experimentally determined beam divergence is in good agreement with modeling predictions and previously performed transmittance experiments. A marked self-collimation propagation over a broad 20 nm wide spectral range centered at λ=1550 nm is experimentally demonstrated. The developed technique opens promising perspectives for the invisibility cloaking structures investigation.

Optical near-field microscopy of light focusing through a photonic crystal flat lens.

We report here the direct observation by using a scanning near-field microscopy technique of the light focusing through a photonic crystal flat lens designed and fabricated to operate at optical frequencies. The lens is fabricated using a III-V semiconductor slab, and we directly visualize the propagation of the electromagnetic waves by using a scanning near-field optical microscope. We directly evidence spatially, as well as spectrally, the focusing operating regime of the lens. At last, in light of the experimental scanning near-field optical microscope pictures, we discuss the lens ability to focus light at a subwavelength scale.