Resonant optical trapping in microfluidic-integrated hollow photonic crystal cavities

The recent years have highlighted the potential of photonic nanostructures to extend the capabilities of optical tweezers and to perform advanced optical manipulations. In this context, two-dimensional photonic crystal cavities have been regarded as promising candidates owing to their high quality factors and low mode volumes. The work presented in this thesis reports the setting up of a complete experimental platform and the demonstration of optical trapping using the field confined in a planar photonic crystal cavity. In this work, cavities formed by a large circular defect, 700 nm in the diameter, in a triangular lattice are studied. These cavities possess a high quality factor (up to 7000 in air, around 2000 in water) and a central region where the confined field overlaps with the immersion medium. This feature offers a singular advantage for the maximization of the interaction between the cavity field and a particle as compared with standard photonic crystal cavity. An ultra-thin PDMS microfluidic membrane (≈170 μm) is developed for the reliable immersion of the hollow cavities and the control of the flow of nanoparticles to be trapped. The hollow cavities are then integrated within a microchannel within the membrane. The characterization and excitation of the cavities is then performed on the developed optical bench. Fluorescent imaging of the polystyrene particles is performed along with position tracking. The micro manipulation of the particles in the neighborhood of the cavity is realized through a combination of microfluidic valves and optical tweezers. Based on this experimental platform, the resonant optical trapping of 250 and 500 nm polystyrene particles is demonstrated. Trapping times of the order of several tens of minutes are obtained at sub-milliwatt optical powers. Further investigations are then performed on the perturbation of the cavity mode induced by the presence of a particle. This perturbation is experimentally observed in the form of a resonance wavelength shift of more than two cavity mode linewidth in the case of a 500 nm particle. Finally, the existence of back-action between the trapped particle and the cavity mode is experimentally evidenced. The later allows to observe the presence of two distinct trapping regimes. A qualitative understanding of these regimes is proposed based on a finite element method analysis.

Single particle detection, manipulation and analysis with resonant optical trapping in photonic crystals

Nicolas Maxime André Descharmes, Ulagalandha Perumal Dharanipathy, Zhaolu Diao, Romuald Houdré, Mario Lucien Henri Tonin

We demonstrate a resonant optical trapping mechanism based on two-dimensional hollow photonic crystal cavities. This approach benefits simultaneously from the resonant nature and unprecedented field overlap with the trapped specimen. The photonic crystal structures are implemented in a 30 mm x 12 mm optofluidic chip consisting of a patterned silicon substrate and an ultrathin microfluidic membrane for particle injection and control. Firstly, we demonstrate permanent trapping of single 250 and 500 nm-sized particles with sub-mW powers. Secondly, the particle induces a large resonance shift of the cavity mode amounting up to several linewidths. This shift is exploited to detect the presence of a particle within the trap and to retrieve information on the trapped particle. The individual addressability of multiple cavities on a single photonic crystal device is also demonstrated.

Royal Society of Chemistry2013

Observation of Backaction and Self-Induced Trapping in a Planar Hollow Photonic Crystal Cavity

Nicolas Maxime André Descharmes, Ulagalandha Perumal Dharanipathy, Zhaolu Diao, Romuald Houdré, Mario Lucien Henri Tonin

The optomechanical coupling between a resonant optical field and a nanoparticle through trapping forces is demonstrated. Resonant optical trapping, when achieved in a hollow photonic crystal cavity is accompanied by cavity backaction effects that result from two mechanisms. First, the effect of the particle on the resonant field is measured as a shift in the cavity eigenfrequency. Second, the effect of the resonant field on the particle is shown as a wavelength-dependent trapping strength. The existence of two distinct trapping regimes, intrinsically particle specific, is also revealed. Long optical trapping (> 10 min) of 500 nm dielectric particles is achieved with very low intracavity powers (< 120 mu W). DOI: 10.1103/PhysRevLett.110.123601

American Physical Society2013

Refractive multiple optical tweezers for parallel biochemical analysis in micro-fluidics - art. no. 64830A

Jean-Marc Fournier, Fabrice Merenda, Johann Rohner, René Salathé, Horst Vogel

We present a multiple laser tweezers system based on refractive optics. The system produces an array of 100 optical traps thanks to a refractive microlens array, whose focal plane is imaged into the focal plane of a high-NA microscope objective. This refractive multi-tweezers system is combined to micro-fluidics, aiming at performing simultaneous biochemical reactions on ensembles of free floating objects. Micro-fluidics allows both transporting the particles to the trapping area, and conveying biochemical reagents to the trapped particles. Parallel trapping in micro-fluidics is achieved with polystyrene beads as well as with native vesicles produced from mammalian cells. The traps can hold objects against fluid flows exceeding 100 micrometers per second. Parallel fluorescence excitation and detection on the ensemble of trapped particles is also demonstrated. Additionally, the system is capable of selectively and individually releasing particles from the tweezers array using a complementary steerable laser beam. Strategies for high-yield particle capture and individual particle release in a micro-fluidic environment are discussed. A comparison with diffractive optical tweezers enhances the pros and cons of refractive systems.

2007