Optical Trapping and Fast Discrimination of Label-Free Bacteriophages at the Single Virion Level.

There is a recent resurgence of interest in phage therapy (the therapeutic use of bacterial viruses) as an approach to eliminating difficult-to-treat infections. However, existing approaches for therapeutic phage selection and virulence testing are time-consuming, host-dependent, and facing reproducibility issues. Here, this study presents an innovative approach wherein integrated resonant photonic crystal (PhC) cavities in silicon are used as optical nanotweezers for probing and manipulating single bacteria and single virions with low optical power. This study demonstrates that these nanocavities differentiate between a bacterium and a phage without labeling or specific surface bioreceptors. Furthermore, by tailoring the spatial extent of the resonant optical mode in the low-index medium, phage distinction across phenotypically distinct phage families is demonstrated. The work paves the road to the implementation of optical nanotweezers in phage therapy protocols.

Ultra-wide-band structural slow light.

The ability of using integrated photonics to scale multiple optical components on a single monolithic chip offers key advantages to create miniature light-controlling chips. Numerous scaled optical components have been already demonstrated. However, present integrated photonic circuits are still rudimentary compared to the complexity of today's electronic circuits. Slow light propagation in nanostructured materials is a key component for realizing chip-integrated photonic devices controlling the relative phase of light and enhancing optical nonlinearities. We present an experimental record high group-index-bandwidth product (GBP) of 0.47 over a 17.7 nm bandwidth in genetically optimized coupled-cavity-waveguides (CCWs) formed by L3 photonic crystal cavities. Our structures were realized in silicon-on-insulator slabs integrating up to 800 coupled cavities, and characterized by transmission, Fourier-space imaging of mode dispersion, and Mach-Zehnder interferometry.

Hybrid PDMS/glass microfluidics for high resolution imaging and application to sub-wavelength particle trapping.

We demonstrate the fabrication of a hybrid PDMS/glass microfluidic layer that can be placed on top of non-transparent samples and allows high-resolution optical microscopy through it. The layer mimics a glass coverslip to limit optical aberrations and can be applied on the sample without the use of permanent bonding. The bonding strength can withstand to hold up to 7 bars of injected pressure in the channel without leaking or breaking. We show that this process is compatible with multilayer soft lithography for the implementation of flexible valves. The benefits of this application is illustrated by optically trapping sub-wavelength particles and manipulate them around photonic nano-structures. Among others, we achieve close to diffraction limited imaging through the microfluidic assembly, full control on the flow with no dynamical deformations of the membrane and a 20-fold improvement on the stiffness of the trap at equivalent trapping power.

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

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 × 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.

Statistics of the disorder-induced losses of high-Q photonic crystal cavities.

We analyze and compare the effect of fabrication disorder on the quality factor of six well-known high-index photonic crystal cavity designs. The theoretical quality factors for the different nominal structures span more than three orders of magnitude, ranging from 5.4 × 10(4) to 7.5 × 10(7), and the defect responsible for confining light is introduced in a different way for each structure. Nevertheless, among the different designs we observe similar behavior of the statistics of the disorder-induced light losses. In particular, we show that for high enough disorder, such that the quality factor is mainly determined by the disorder-induced losses, the measured quality factors differ marginally - not only on average as commonly acknowledged, but also in their full statistical distributions. This notably shows that optimizing the theoretical quality factor brings little practical improvement if its value is already much larger than what is typically measured, and if this is the case, there is no way to choose an alternative design more robust to disorder.

Observation of backaction and self-induced trapping in a planar hollow photonic crystal cavity.

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 µW).

Complex-coupled photonic crystal THz lasers with independent loss and refractive index modulation.

Compared to near infra-red photonic crystal (PhC) band-edge lasers, achieving vertical emission with quantum cascade (QC) material operating in the THz range needs dedicated engineering because the TM polarized emission of QCLs favors in-plane emitting schemes and the currently used double plasmon waveguide, prevents vertical light extraction. We present an approach with independent refractive index and extraction losses modulation. The extraction losses are obtained with small extracting holes located at appropriate positions. The modal operation of the PhC is shown to critically depend on the external losses introduced. Very high surface emission power for optimum loss extractor design is achieved.

Refractive index sensing with an air-slot photonic crystal nanocavity.

We investigate an air-slot photonic crystal cavity for high-precision refractive index sensing. The high quality factor approximately 2.6x10(4) of the cavity, along with a strong overlap between the resonant mode and the hollow core region, allows us to achieve an experimental sensitivity of 510nm per refractive index unit (RUI) and a detection limit below 1x10(-5)RUI. The device has a remarkably low sensing volume of 40aliters, holding less than 1x10(6)molecules.

Off-chip beam steering with a one-dimensional optical phased array on silicon-on-insulator.

Optical phased arrays are versatile components enabling rapid and precise beam steering. An integrated approach is followed in which a 1D optical phased array is fabricated on silicon-on-insulator. The optical phased array consists of 16 parallel grating couplers spaced 2 mum apart. Steering in one direction is done thermo-optically by means of a titanium electrode on top of the structure using the phased array principle, while steering in the other direction is accomplished by wavelength tuning. At a wavelength of 1550 nm, continuous thermo-optical steering of 2.3 degrees and wavelength steering of 14.1 degrees is reported.

Experimental observation of slow mode dispersion in photonic crystal coupled-cavity waveguides.

We experimentally investigate the dispersion curve of an integrated silicon-on-insulator coupled-cavity waveguide in a photonic crystal environment using a technique based on far-field imaging. We show that a chain of eight coupled cavities of a moderate Q factor can form a continuous dispersion band characterized by extremely flat dispersion and a group index of 105+/-20 within a 2.6 nm wavelength range. The experimental results are well reproduced by theoretical calculations based on the guided-mode expansion method.

Terahertz quantum cascade lasers based on two-dimensional photonic crystal resonators.

We demonstrate high spectral control from surface emitting THz Quantum Cascade Lasers based on a two-dimensional photonic crystal cavity. The perforated top metallic contact acts as an in plane resonator in a tight double-metal plasmonic waveguide providing a strong optical feedback without needing three-dimensional cavity features. The optical far-field patterns do not exhibit the expected symmetry and the shape of the cavity mode. The difference is attributed to a metal surface plasmon mediated light outcoupling mechanism also responsible for the relatively low extraction efficiency.

Terahertz photonic crystal quantum cascade lasers.

We combine photonic crystal and quantum cascade band engineering to create an in-plane laser at terahertz frequency. We demonstrate that such photonic crystal lasers strongly improve the performances of terahertz quantum cascade material in terms of threshold current, waveguide losses, emission mode selection, tunability and maximum operation temperature. The laser operates in a slow-light regime between the M saddle point and K band-edge in reciprocal lattice. Coarse frequency control of half of a terahertz is achieved by lithographically tuning the photonic crystal period. Thanks to field assisted gain shift and cavity pulling, the single mode emission is continuously tuned over 30 GHz.

Design, fabrication and optical characterization of quantum cascade lasers at terahertz frequencies using photonic crystal reflectors.

We designed, fabricated and characterised electrically injected quantum cascade lasers with photonic crystal reflectors emitting at terahertz frequencies (3.75 THz). These in-plane emitting structures display typical threshold current densities of 420 A/cm2 and output powers of up to 2 mW under pulsed excitation. The emission characteristics are shown to be robust, as with increasing current the emission remains singlemode with no drift in wavelength, this results from the narrow reflectivity band of the photonic crystal reflectors.