0000000000054495
AUTHOR
Emmanuel Picard
On chip shapeable optical tweezers
International audience; Particles manipulation with optical forces is known as optical tweezing. While tweezing in free space with laser beams was established in the 1980s, integrating the optical tweezers on a chip is a challenging task. Recent experiments with plasmonic nanoantennas, microring resonators, and photonic crystal nanocavities have demonstrated optical trapping. However, the optical field of a tweezer made of a single microscopic resonator cannot be shaped. So far, this prevents from optically driven micromanipulations. Here we propose an alternative approach where the shape of the optical trap can be tuned by the wavelength in coupled nanobeam cavities. Using these shapeable …
Near-field spectroscopy of low-loss waveguide integrated microcavities
International audience; A scanning near-field spectroscopy method is used to observe loss reduction and Q-factor enhancement due to transverse-mode profile matching within photonic-crystal microcavities. Near-field measurements performed directly on cavity modes are compared with three-dimensional calculations and quantitative agreement is observed. (c) 2006 American Institute of Physics.
Optical field molding within near-field coupled twinned nanobeam cavities
Twinned high Q nanobeam cavities can be optically coupled while being placed in the optical near-field of each other. They form then a new optical system which supports discrete field maps addressable by wavelength selection.
Tunable optical lattices in the near-field of a few-mode nanophotonic waveguide
Due to the action of the scattering force, particles that are optically trapped at the surface of a waveguide are propelled in the direction of the light propagation. In this work, we demonstrate an original approach for creating tunable periodic arrays of optical traps along a few-mode silicon nanophotonic waveguide. We show how the near-field optical forces at the surface of the waveguide are periodically modulated when two guided modes with different propagation constants are simultaneously excited. The phenomenon is used to achieve stable trapping of a large number of dielectric particles or bacteria along a single waveguide. By controlling the light coupling conditions and the laser wa…
Single-mode room-temperature emission with a silicon rod lattice
The authors experimentally evidence an increase of light emission efficiency at room temperature in a silicon-on-insulator photonic crystal. The photonic crystal is made of a triangular lattice of silicon rods and operates as a single-mode light extractor. It exhibits a luminescence intensity two orders of magnitude higher than silicon-on-insulator substrate. In light of photoluminescence experiments, emission diagram measurements, and finite difference time domain calculations, they identify the different optical properties of the photonic crystal and they demonstrate the existence of at least a fivefold emission efficiency enhancement per surface unit.
Optical tweezing using tunable optical lattices along a few-mode silicon waveguide
International audience; Fourteen years ago, optical lattices and holographic tweezers were considered as a revolution, allowing for trapping andmanipulating multiple particles at the same time using laser light. Since then, near-field optical forces have arousedtremendous interest as they enable efficient trapping of a wide range of objects, from living cells to atoms, in integrateddevices. Yet, handling at will multiple objects using a guided light beam remains a challenging task for current on-chipoptical trapping techniques. We demonstrate here on-chip optical trapping of dielectric microbeads and bacteria usingone-dimensional optical lattices created by near-field mode beating along a f…
Experimental demonstration of Bloch mode parity change in photonic crystal waveguide
We experimentally show coupling between two photonic crystal waveguide Bloch modes having a different parity. A monomode ridge waveguide etched in a silicon-on-insulator substrate and connecting to the photonic crystal waveguide allows us to excite the even Bloch mode. Transmission measurements, performed on a broad spectral range, show the even mode propagation along the defect line. Then, spectrally resolved near-field patterns obtained by using a scanning near-field optical microscope in collection mode for wavelengths, inside and outside the multimode region of the photonic crystal waveguide, clearly demonstrate coupling phenomenon between even and odd modes.
On-chip periodic arrays of optical traps based on the superposition of guided modes in silicon waveguides
Since the pioneering work of Kawata and Tani [1], photonic waveguides have long been regarded as efficient optical conveyor belts for potential lab-on-a-chip applications. Indeed, near-field optical forces arising at the surface of such waveguides lead to efficient on-chip guided propulsion of micro- and even nanoparticles [2], as well as cells and bacteria in liquid solutions [3]. However, achieving stable and precisely controlled optical trapping of particles at the surface of a waveguide has been made possible only recently, and even then, it still requires complex photonic electro-optic tools to produce and handle on-chip standing waves [4].
Sub-wavelength imaging of light confinement and propagation in SOI based photonic crystal devices
A light source is coupled into photonic crystal devices and a near field optical probe is used to observe the electromagnetic field propagation and distribution at a sub-wavelength scale. Bloch modes are clearly observed.
Far- and near-field characterization of a photonic-crystal-based microcavity on silicon-on-insulator
International audience
Extraordinary tuning of a nanocavity by a near-field probe
Abstract We report here an experimental observation of an extraordinary near-field interaction between a local probe and a small-volume solid-state nanocavity. We directly compare the normally observed near-field interaction regime driven by the perturbation theory and then report the extraordinary interaction regime. Subsequently, we show that the cavity can take up to 2 min to recover from this interaction after removing the probe and that leads to an extraordinary blue-shift of the cavity resonance wavelength (∼15 nm) which depends on the probe motion above the cavity and not the position. The reasons for this effect are not fully understood yet but we try to give some explanations.
Bloch mode coupling investigation in silicon-on-insulator W1 photonic crystal waveguide
We report in this paper the study of a W1 photonic crystal waveguide which supports two Bloch modes having different parity. A monomode ridge waveguide etched in a Silicon-On-Insulator substrate and connecting to the photonic crystal waveguide allows us to excite the even Bloch mode. Transmission measurements, performed on a broad spectral range, evidence the even mode propagation along the defect line and experimental spectrum is discussed in light of band diagram and FDTD calculations. Then spectrally resolved near-field patterns obtained by using a scanning near field optical microscope in collection mode for wavelengths inside and outside the multimode region of the photonic crystal wav…
Subwavelength imaging of field confinement in a waveguide-integrated photonic crystal cavity
A photonic crystal microcavity is designed to obtain an original field distribution inside the cavity and the structure is etched inside a silicon-on-insulator waveguide. Spectral location of the photonic band gap and cavity resonance are identified by using transmittance measurements and by analyzing the light collected by a scanning near-field optical microscope probe exactly positioned on the center of the cavity. The results obtained with the two techniques are in very good agreement. Then the near-field distribution above the device is mapped and light confinement inside the cavity is evidenced. Moreover, this confined light presents some remarkable patterns which clearly correspond to…
Bloch Modes Coupling in Photonic Crystal Waveguides
We investigate the properties of Bloch modes inside a photonic crystal waveguide. By using simultaneously a near field optical microscope and a transmittance setup, we demonstrate that Bloch modes having different parity are coupled.
Assembly of microparticles by optical trapping with a photonic crystal nanocavity
International audience; In this work, we report the auto-assembly experiments of micrometer sized particles by optical trapping in the evanescent field of a photonic crystal nanocavity. The nanocavity is inserted inside an optofluidic cell designed to enable the real time control of the nanoresonator transmittance as well as the real time visualization of the particles motion in the vicinity of the nanocavity. It is demonstrated that the optical trap above the cavity enables the assembly of multiple particles in respect of different stable conformations.
Optofluidic taming of a colloidal dimer with a silicon nanocavity
International audience; We report here the optical trapping of a heterogeneous colloidal dimer above a photonic crystal nanocavity used as an on-chip optical tweezer. The trapped dimer consists of a cluster of two dielectric microbeads of different sizes linked by van der Waals forces. The smallest bead, 1 μm in diameter, is observed to be preferentially trapped by the nanotweezer, leaving the second bead untrapped. The rotational nature of the trapped dimer Brownian motion is first evidenced. Then, in the presence of a fluid flow, control of its orientation and rotation is achieved. The whole system is found to show high rotational degrees of freedom, thereby acting as an effective flow-se…
Coupling evanescently low loss Silicon-on-insulator (SOI) ridge waveguides(WGs) including high Q nanocavities: For light control
We have fabricated a multislotted optical nanoresonator with several spatial field distributions which are all addressable by the wavelength. The reported structure consists in an array of evanescently coupled single mode photonic crystal nanocavities. By using a scanning near-field optical microscope, we quantify the morphology of the different optical mode volumes and show that they consist in grids of light confined at the subwavelength scaleOver the last recent years, optical microcavities have proven their ability to slow down, control and even trap light inside an ultra small volume. Several approaches have led to quality factor (Q) records allowing to reach high photon life-time for …
Coupling evanescently low loss Silicon-on-insulator ridge waveguides including high Q nanocavities for light control
Summary form only given. In this work, we propose an innovative way to achieve an air-slotted nanocavities by coupling evanescently low loss Silicon-on-insulator (SOI) ridge waveguides(WGs) including high Q nanocavities exhibiting an ultrasmall modal volume V. We first show that coupling two WGs allows us to achieve a field confinement within the air slot as low as lambda/30 while preserving a high group index of the guided modes. Then we demonstrate that merging such coupled WGs with state-of-the-art high-Q/small V nanocavities is a robust way to achieve a single compact (1 µm × 3 µm) air-slotted resonator on substrate. Finally, we extend the concept to multiple air-slotted resonator syste…
A near-field actuated optical nanocavity
International audience; We demonstrate here that switching and tuning of a nanocavity resonance can be achieved by approaching a sub-micrometer tip inside its evanescent near-field. The resonance energy is tuned over a wide spectral range (Δλ/λ~10-3) without significant deterioration of the cavity peak-transmittance and of the resonance linewidth. Such a result is achieved by taking benefits from a weak tip-cavity interaction regime in which the tip behaves as a pure optical path length modulator.