Near-field optical forces arise from evanescent electromagnetic fields and can be advantageously used for on-chip
optical trapping. In this work, we investigate how evanescent fields at the surface of photonic cavities can efficiently trap
micro-objects such as polystyrene particles and bacteria. We study first the influence of trapped particle’s size on the
trapping potential and introduce an original optofluidic near-field optical microscopy technique. Then we analyze the
rotational motion of trapped clusters of microparticles and investigate their possible use as microfluidic micro-tools such
as integrated micro-flow vane. Eventually, we demonstrate efficient on-chip optical trapping of various kinds of bacteria.
Proc. SPIE. 7608, Quantum Sensing and Nanophotonic Devices VII
KEYWORDS: Resonators, Microscopy, Photonic crystals, Near field scanning optical microscopy, Near field, Geometrical optics, Signal detection, Optical microcavities, Near field optics, Photonic nanostructures
The fundamentals of the near-field interaction between a subwavelength tip and a photonic-crystal
nanocavity are investigated experimentally and theoretically. It is shown experimentally that the cavity
resonance is tuned without any degradation by the presence of the tip and that the reported near-field
interaction is strongly related to the field distribution within the nanostructure. From the interaction between
the probe and the cavity, we will show a new kind of microscopy.
Ultrahigh Q/V lineic silicon Fabry Perot (FP) microcavities relying on silica substrate have been fabricated. Two cavities
designs are studied based respectively on cavity mode losses recycling and on mirrors with tapered sections. The
experimental evolution of cavities characteristics are studied as a function of sample temperature. The authors achieve a
quality factor of 58000 for a modal volume of 0.6 (λ/n)3.
Short microcavities consisting of two identical tapered hole mirrors etched into silicon-on-insulator ridge waveguides are investigated. They are designed for operating at telecom wavelength. We describe theoretically and experimentally two different ways to boost quality factors to some thousands. In one hand, we investigate the adaptation of mode profile to suppress mismatch losses. In an other hand, we explore the recycling of the losses. We obtained quality factor up to 3000, which opens the route to WDM applications.
Investigations of polarizations effects in second-harmonic generation of a one-dimensional photonic crystal based on gallium nitride were performed for the fundamental beam incident on the surface of the photonic crystal. The angle of incidence, the azimuthal rotation angle of the photonic crystal, the frequency, and the polarization behaviour for strongly enhanced second-harmonic generation agree well with the identified position and polarization of the resonant Bloch modes. Along the direction, giant enhancements of 7500 times in the second-harmonic conversion have been obtained in the one-dimensional photonic crystal by comparison with the unpatterned GaN layer. The combined role of the resonant coupling of the fundamental field and of the second-harmonic field has been observed as the polarization of the fundamental beam is rotated.
We report on third-harmonic (TH) generation emitted from 1D photonic slabs etched into Silicon-on-Insulator (SOI) planar waveguides, as compared to the bare waveguide and (100) Silicon bulk responses. 130-fs laser pulses at ~ 810 nm and ~1550 nm have been chosen as a pump to excite TH signals in reflection and diffraction directions. The measured angles of in-plane diffracted third-harmonic beams agree with those predicted by nonlinear diffraction equations. The nonlinear reflectance as a function of the angle of incidence and azimuthal orientation of the structure has been measured. The near-infrared measurements have revealed that, whenever the pump frequency is resonant with a photonic mode, a substantial enhancement of the harmonic signal occurs. This nonlinear mechanism is in principle a very sensitive spectroscopic tool in determining and mapping the photonic band diagram of the system above the light line. The agreement between experimental data and ad hoc simulations of the nonlinear behavior of the system sheds new light on the nonlinear optical response of these nanostructured materials.
The second-harmonic field generated has been measured in reflection from the surface of one-dimensional and two-dimensional photonic crystals etched into a GaN layer. A very large second-harmonic enhancement is observed when simultaneously the incident beam at the fundamental frequency w excites a resonant Bloch mode and the second-harmonic field generated is coupled into a resonant Bloch mode at 2w. A smaller, but still substantially enhanced, second-harmonic generation level was also observed when the fundamental field was coupled into a resonant mode, while the second-harmonic field was not. By using calculated and experimental equifrequency surfaces, it is possible to identify the geometrical configurations that will allow quasi-phase matching to be satisfied - and observed experimentally in the available wavelength tuning range of the laser. The extended transparency window of III-nitride wide-bandgap semiconductors, coupled with large non linearities, is an appealing feature pointing towards the control and manipulation of light in photonic structures.
We study adiabatic mode transformations in waveguides that rely on subwavelength holes with progressively-varying dimensions. The variation synthesizes an artificial material with a gradient effective index. Two devices are presented, a microcavity with short tapers incorporated at the four reflector extremities, and a taper between a conventional waveguide and a photonic crystal waveguide.