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We study the electromagnetic force exerted on a pair of parallel slab waveguides by the light propagating through them. We have calculated the dependence of the force on the slab separation by means of the Maxwell–Stress tensor formalism and we have discussed its main features for the different propagation modes: spatially symmetric (antisymmetric) modes give rise to an attractive (repulsive) interaction. We have derived the asymptotic behaviors of the force at small and large separation and we have quantitatively estimated the mechanical deflection induced on a realistic air-bridge structure. [ABSTRACT FROM AUTHOR]

A Fabry-Perot optical microcavity based on liquid crystal infiltration integrated in a waveguide has been designed and fabricated. Careful optimization of the cavity geometry allows designing a device with a simulated resonance peak transmission of 95% with a linewidth of about 1.7 nm. Based on this simulation, a first prototype has been fabricated and tested. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we present the waveguiding properties of a set of mono-dispersed silicon nanocrystal Si-nc superlattices. The measured modal refractive indices (obtained by the m-line technique) of different samples can only be explained by assuming a negative “form birefringence” of about 1% originating from the particular structure of the active core, i.e., a periodical set of parallel planes of two different materials. By means of a simple model for the ordinary and extraordinary refractive indices in this kind of structures, by using the information from TEM images and the nominal growth parameters, and by considering as free parameters the upper size of the diameter of Si-nc, we are able to fit the m-line measurements in a unique way. We also report gain measurements on this set of samples, showing that, under high power pulsed excitation, positive optical gain is observed in samples that provide both good light confinement inside the waveguide and the right Si-nc dimension. [Copyright &y& Elsevier]

We investigate the optical properties of planar waveguides where the core layer is formed by a silicon nanocrystals (Si-nc)/SiO2 superlattice. M-line measurements of the different waveguides yield the mode indices, which can be modeled by assuming anisotropic optical properties of the core layer. This anisotropy is related to the superlattice, i.e., it is a form birefringence. By modeling the m-line measurements with the structural data obtained by transmission electron microscopy analysis, we determine for each waveguide the value of the form birefringence, an upper limit of the nanocrystals size and their refractive index. Values of the form birefringence as high as 1% have been found. [ABSTRACT FROM AUTHOR]

Stimulated emission from silicon-nanocrystal planar waveguides grown via phase separation and thermal crystallization of SiO/SiO2 superlattices is presented. Under high power pulsed excitation, positive optical gain can be observed once a good optical confinement in the waveguide is achieved and the silicon nanocrystals have proper size. A critical tradeoff between Auger nonradiative recombination processes and stimulated emission is observed. The measured large gain values are explained by the small size dispersion in these silicon nanocrystals. [ABSTRACT FROM AUTHOR]

We present experimental evidence for the different mechanisms driving the fluctuations of the local density of states (LDOS) in disordered photonic systems. We establish a clear link between the microscopic structure of the material and the frequency correlation function of LDOS accessed by a near-field hyperspectral imaging technique. We show, in particular, that short- and long-range frequency correlations of LDOS are controlled by different physical processes (multiple or single scattering processes, respectively) that can be--to some extent--manipulated independently. We also demonstrate that the single scattering contribution to LDOS fluctuations is sensitive to subwavelength features of the material and, in particular, to the correlation length of its dielectric function. Our work paves a way towards complete control of statistical properties of disordered photonic systems, allowing for designing materials with predefined correlations of LDOS. [ABSTRACT FROM AUTHOR]

We employ a far-field analysis of the angular emission pattern to experimentally assess the symmetry of localized modes in coupled photonic-crystal cavities. We demonstrate that the spatial distribution of localized modes in photonic-crystal nanocavities may change from a bonding to an antibonding orbital, a feature that is unusual in quantum mechanical coupled systems. Experimental data are confirmed by numerical calculations and interpreted in terms of the peculiar oscillatory behavior of the evanescent waves in photonic-crystal band gaps. [ABSTRACT FROM AUTHOR]

Abstract: In view of the integration within Si-based optical devices, LPCVD (low-pressure chemical vapor deposition) thin-film Si3N4 waveguides have been fabricated on a Si substrate within a CMOS fabrication pilot-line. Different structures (channel, rib and strip-loaded) were designed, fabricated and characterized both optically and structurally to optimize waveguide performances. Geometry, sidewall as well as layer roughness of the waveguides have been investigated by scanning electron microscopy and atomic force microscopy. Optical guided modes have been observed and propagation loss measurements at 632.8 and 780nm have been performed by using the cut-back technique, the insertion loss technique and scattered light collection. The channel waveguides have shown propagation losses of about 0.1–0.2dB/cm. Differences between geometries and lithographic processes have been discussed. Polarization dependence of propagation losses has been investigated too. Optical guided modes have also been measured in the near-infrared range (at 1544nm), where propagation losses are about 4.5–5dB/cm, quite larger with respect to the visible, because of the poorer confinement factor of the optical modes. [Copyright &y& Elsevier]

Abstract: We report on a set of experimental measurements aimed to fully characterize both the spatial and angular pattern of the optical modes of photonic crystal microcavities. By using a confocal microscope we resolve the spatial distribution of the mode on the sample surface. With the same setup, by introducing an iris placed on a translational stage within the collimated beam region of the confocal microscope, we are able to measure the far field angular pattern of the microcavity modes. The experimental data are compared with theoretical predictions obtained by finite difference in time domain calculations and a very good agreement is found. [Copyright &y& Elsevier]

Abstract: We directly investigate, by means of near-field spectroscopy, the spatial distribution of the optical cavity modes of 2D photonic crystal microcavities. Numerical simulations confirm that the photoluminescence maps of quantum dots embedded in the photonic structure qualitatively match the spatial modulation of the electric field intensity. [Copyright &y& Elsevier]

A multi-speckle set-up for dynamic light scattering experiments has been implemented to investigate the relaxation dynamics in the glass-formerat temperatures across the glass transition. When compared to literature data obtained with traditional single-speckle set-ups, the present results clearly show the advantages of the multi-speckle approach in the study of slow dynamics processes in glass-forming materials. This opens the way for new detailed studies of the slow dynamics in glasses using dynamic light scattering, e.g. of ageing processes. [ABSTRACT FROM PUBLISHER]

The article discusses research using multidimensional nanospectroscopic imaging to map local charge recombination heterogeneity in nanowires. The authors note that the importance of optically probing matter with true nanoscale spatial resolution increases as materials' functionality becomes more dependent on local physical and electronic properties. Topics include the authors' methodology for mapping the influence of local trap states within individual nanowires on carrier recombination using multidimensional nanospectroscopic imaging, hyperspectral imaging of indium phosphide nanowires via excitation and collection through the probes, and what the results revealed about the optoelectronic structure along individual nanowires.

Experimental and theoretical investigations of photonic crystal (PhC) structures in silicon nitride/silicon dioxide (Si3N4/SiO2) vertical waveguiding geometry are reported. One-dimensional patterns, either periodic or with cavity layers, are carved onto the channel waveguides by using focused ion beam lithography. Broadband transmittance spectroscopy in the visible and near-infrared frequency ranges is employed to show photonic band gap behavior up to the fourth order. For structures with a cavity layer, resonant peaks appear in transmittance spectra within the photonic gaps, in agreement with theory. The results show the interest of Si3N4/SiO2-based PhC waveguides for photonics applications from the infrared up to the visible range. [ABSTRACT FROM AUTHOR]

The post-fabrication control of evanescent tunnelling in photonic crystal molecules is demonstrated through the combination of selective infiltration and oxidation. By laser non thermal oxidation, we reduce the photonic coupling by more than 30% while by means of water micro-infiltration, we increase it by 28%. Fine-tuning of the photonic coupling is achieved by low-power laser oxidation and forced evaporation, opening the route to post-fabrication control of array of coupled cavities. [ABSTRACT FROM AUTHOR]