Optical tweezing using tunable optical lattices along a few-mode silicon waveguide.

Fourteen years ago, optical lattices and holographic tweezers were considered as a revolution, allowing for trapping and manipulating multiple particles at the same time using laser light. Since then, near-field optical forces have aroused tremendous interest as they enable efficient trapping of a wide range of objects, from living cells to atoms, in integrated devices. Yet, handling at will multiple objects using a guided light beam remains a challenging task for current on-chip optical trapping techniques. We demonstrate here on-chip optical trapping of dielectric microbeads and bacteria using one-dimensional optical lattices created by near-field mode beating along a few-mode silicon nanophotonic waveguide. This approach allows not only for trapping large numbers of particles in periodic trap arrays with various geometries, but also for manipulating them via diverse transport and repositioning techniques. Near-field mode-beating optical lattices may be readily implemented in lab-on-a-chip devices, addressing numerous scientific fields ranging from bio-analysis to nanoparticle processing.

On chip shapeable optical tweezers.

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 tweezers, we present micromanipulation of polystyrene microspheres trapped on a silicon chip. These results show that coupled nanobeam cavities are versatile building blocks for optical near-field engineering. They open the way to much complex integrated tweezers using networks of coupled nanobeam cavities for particles or bio-objects manipulation at a larger scale.

Tuning of an active photonic crystal cavity by an hybrid silica/silicon near-field probe.

The influence of a near-field tip on the spectral characteristics of a resonant mode of an active photonic crystal micro-cavity was investigated. The wavelength shift of the mode was theoretically and experimentally demonstrated and evaluated as a function of the nature and the position of the tip above the cavity. Experiment showed that the shift induced is ten times higher with a Si-coated silica probe than with a bare silica tip: a shift until 2 nm was reached with Si-coated tip whereas the shift with bare silica tip is in the range of the tenth of nanometer, for wavelengths around 1,55 microm.

Ultra-High Q/V Fabry-Perot microcavity on SOI substrate.

We experimentally demonstrate an ultra high Q/V nanocavity on SOI substrate. The design is based on modal adaptation within the cavity and allows to measure a quality factor of 58.000 for a modal volume of 0.6(lambda/n)(3) . This record Q/V value of 10(5) achieved for a structure standing on a physical substrate, rather than on membrane, is in very good agreement with theoretical predictions also shown. Based on these experimental results, we show that further refinements of the cavity design could lead to Q/V ratios close to 10(6).

3.3-microm microcavity light emitter for gas detection.

A room-temperature resonant-cavity light source emitting at 3.327 microm is presented. It combines a CdHgTe light-emitting layer, grown by molecular beam epitaxy, and two evaporated YF(3)-ZnS Bragg mirrors. The emitter is optically pumped by a commercial low-power GaAs laser diode. Compared with an unprocessed sample, this microcavity device shows a drastic (10-fold) linewidth reduction, a 3.3-fold intensity increase at 3.327 microm , and a 2.4-fold angular-spread decrease. The emitted optical power is 15 microW , and the device is used as a light source in a basic gas-detection setup. Measurements of a butane-propane mixture in the 1 to 5x 10(-3) bar range with a 5-cm-long single-path gas cell are demonstrated.