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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 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]

Abstract: We present a numerical analysis and preliminary experimental results on one-dimensional Fabry–Perot micro-cavities in Si3N4waveguides. The Fabry–Perot micro-cavities are formed by two distributed Bragg reflectors separated by a straight portion of a waveguide. The Bragg reflectors are composed of a few air slits produced within the Si3N4 waveguides. In order to increase the quality factor of the micro-cavities, we have minimized, with a multiparametric optimization tool, the insertion loss of the reflectors by varying the length of their first pairs (those facing the cavity). To explain the simulation results, the coupling of the fundamental waveguide mode with radiative modes in the Fabry–Perot micro-cavities is needed. This effect is described as a recycling of radiative modes in the waveguide. To support the modelling, preliminary experimental results of micro-cavities in Si3N4 waveguides realized with the focused ion beam technique are reported. [Copyright &y& Elsevier]

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]

Low-pressure chemical-vapor deposition (LPCVD) thin-film Si3N4 waveguides have been fabricated on Si substrate within a complementary metal-oxide-semiconductor (CMOS) fabrication pilot line. Three kinds of geometries (channel, rib, and strip-loaded) have been simulated, fabricated, and optically characterized in order to optimize waveguide performances. The number and optical confinement factors of guided optical modes have been simulated, taking into account sidewall effects caused by the etching processes, which have been studied by scanning electron microscopy. Optical guided modes have been observed with a mode analyzer and compared with simulation expectations to confirm the process parameters. Propagation loss measurements at 780 and 632.8 nm have been performed by both using the cutback technique and measuring the drop of intensity of the top scattered light along the length of the waveguide. Loss coefficients of approximately 0.1 dB/cm have been obtained for channel waveguides. These data are very promising in view of the development of Si-integrated photonics. [ABSTRACT FROM PUBLISHER]

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]

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]

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]