50 research outputs found
Polymeric waveguides using oxidized porous silicon cladding for optical amplification
No full textWe report on a new hybrid approach to realize optical slab waveguides for optical amplification purposes. The structure consists of a dye-doped polymer core (PMMA) deposited over an oxidized porous silicon (PS) cladding layer formed on a silicon wafer. The very low refractive index (n = 1.16) achievable in the cladding allows obtaining monomodal behavior with high confinement factors (GTE = 96%) even for very thin cores (400 nm). Optically excited guided luminescence shows stimulated emission, strong line narrowing and a clear threshold and superlinear behavior with pump energy. By means of the variable stripe length (VSL) technique, values of net optical gain up to 113 dB/cm (constant over 3 mm) and absolute amplification values up to 34 dB have been measured at 694 nm when pumping with 80 mJ/cm2 energy pulses. These results validate the use of oxidized PS as a cladding layer in silicon photonics
Fabrication and optimization of rugate filters based on porous silicon
No full textWe report an experimental study of porous silicon-based rugate filters. Possible optimisations that can improve different features of the filters are investigated. We demonstrate sidelobe attenuation by means of half-apodization of the structures with a sinusoidal window. Reduction of interference ripples are experimentally observed through the insertion of index-matching layers on the boundaries of the structure. The superposition of two different designs to obtain a multi-stop-band filter is also demonstrated. We show the possibility of controlling the bandwidth of the stop-bands by varying the index contrast. All the results are discussed and compared with numerical calculations. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Vertical coupling of laser glass microspheres to buried silicon nitride ellipses and waveguides
No full textWe demonstrate the integration of Nd3+ doped barium-titanium-silicate microsphere lasers with a silicon nitride photonic platform. Devices with two different geometrical configurations for extracting the laser light to buried waveguides have been fabricated and characterized. The first configuration relies on a standard coupling scheme, where the microspheres are placed over strip waveguides. The second is based on a buried elliptical geometry whose working principle is that of an elliptical mirror. In the latter case, the input of a strip waveguide is placed on one focus of the ellipse, while a lasing microsphere is placed on top of the other focus. The fabricated elliptical geometry (ellipticity = 0.9) presents a light collecting capacity that is 50% greater than that of the standard waveguide coupling configuration and could be further improved by increasing the ellipticity. Moreover, since the dimensions of the spheres are much smaller than those of the ellipses, surface planarization is not required. On the contrary, we show that the absence of a planarization step strongly damages the microsphere lasing performance in the standard configuration
Tunneling escape process from a spin-polarized two-dimensional electron system
No full textIn this work, we have numerically integrated in space and time the effective-mass nonlinear Schrödinger equation for an electron wave packet in a double barrier heterostructure. Considering both polarized and unpolarized magnetic phases, we have studied the tunneling escape process from the two-dimensional electron gas. Due to the nonlinear effective-mass equation, it is found that the charge trapped dynamically in the quantum well produces a reaction field, which modifies the tunneling escape process in the quantum well. At different electronic sheet densities, we have shown the possibility of having magnetic phase-dependent tunneling rates. © 2001 Elsevier Science Ltd
Mechanical oscillations in lasing microspheres
No full textThis is the preprint version of the paper available at: https://dx.doi.org/10.1063/1.4997182
A. Toncelli, N. E. Capuj, B. Garrido, M. Sledzinska, C. M. Sotomayor-Torres, A. Tredicucci, D. Navarro-Urrios. Mechanical oscillations in lasing microspheres. Journal of Applied Physics, 2017, 122:
Waveguiding, absorption and emission properties of dye-impregnated oxidized porous silicon
No full textThe waveguiding, absorption and emission properties of oxidised porous silicon waveguides when impregnated with Nile Blue have been studied. We present m-line measurements before and after the impregnation showing that the effective indices of the modes remain the same. When performing guided luminescence experiments, a structured emission band is measured. Using the refractive index profile extracted from m-line measurements it has been possible to simulate the emission lineshape assuming the observation of an interference pattern formed across the waveguide. We demonstrate that these oscillations appear because in the first hundreds of nanometers the dye concentration is several orders of magnitude higher than in the rest of the sample. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA
Structural and light-emission modification in chemically-etched porous silicon
No full textAfter electrochemical etching, we have made a study of the effects generated on p +-type porous silicon layers when they are left in presence of the electrolyte for different post-etching times. Using an interferometric technique, we have monitored the change of its porosity during the post-etch process due to a chemical dissolution mechanism. These data are complemented with a study of photoluminescence and transmission electron microscopy measurements for different post-etching times. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Far-field characterization of the thermal dynamics in lasing microspheres
No full textThis work reports the dynamical thermal behavior of lasing microspheres placed on a dielectric substrate while they are homogeneously heated-up by the top-pump laser used to excite the active medium. The lasing modes are collected in the far-field and their temporal spectral traces show characteristic lifetimes of about 2 ms. The latter values scale with the microsphere radius and are independent of the pump power in the studied range. Finite-Element Method simulations reproduce the experimental results, revealing that thermal dynamics is dominated by heat dissipated towards the substrate through the medium surrounding the contact point. The characteristic system scale regarding thermal transport is of few hundreds of nanometers, thus enabling an effective toy model for investigating heat conduction in non-continuum gaseous media and near-field radiative energy transfer
Optical gain in conjugated polymer hybrid structures based on porous silicon waveguides
No full textThe fabrication and optical characterization of a hybrid waveguide formed by a MDMO-PPV semiconductor layer deposited on a porous silicon cladding is reported. Evidence of amplified spontaneous emission is observed when the intensity of the excitation pump pulses is higher than a certain threshold. A net gain coefficient of about 50 ± 8 cm-1 is estimated, which is similar to those reported for other PPV derivate conjugated polymers. The demonstration of positive optical gain in these hetero-structures is very promising because new photonic structures could be envisaged due to the versatility of the porous silicon cladding
