No abstract

A tantalum pentoxide-based (Ta 2 O 5 -based) micro-ring alloptical modulator was fabricated. The refractive index inside the micro-ring cavity was modified using the Kerr effect by injecting a pumped pulse. The transmittance of the ring resonator was controlled to achieve all-optical modulation at the wavelength of the injected probe. When 12 GHz pulses with a peak power of 1.2 W were coupled in the ring cavity, the transmission spectrum of the Ta 2 O 5 resonator was redshifted by 0.04 nm because of the Kerr effect. The relationship between the modulation depth and gap of the Ta 2 O 5 directional coupler is discussed. An optimized gap of 1100 nm was obtained, and a maximum buildup factor of 11.7 with 84% modulation depth was achieved. The nonlinear refractive index of Ta 2 O 5 at 1.55 μm was estimated as 3.4 × 10 −14 cm 2 /W based on the Kerr effect, which is almost an order of magnitude higher than that of Si 3 N 4 . All results indicate that Ta 2 O 5 has potential for use in nonlinear waveguide applications with modulation speeds as high as tens of GHz.

In silicon quantum dots (Si-QDs), the sub-bandgap cross-absorption-modulation (XAM) has been preliminarily observed and confirmed as a new kind of wavelength conversion process to enable ultrafast optical switching. By using the Si-QD doped Si-rich SiC x micro-ring resonator waveguide with a quality factor of 1.710 4 under an optimized gap spacing of 700 nm away from the bus waveguide, the XAM effect induces a wavelength-converted picosecond all-optical switching between pump and probe signals, which is attributed to a specific free-carrier absorption at probe wavelength caused by the two-photon-absorption induced carriers. The non-degenerate pump-probe analysis also shows a weak Kerr nonlinearity related ultrafast switching response from the changing envelope of the XAM probe pulse at red-shifted wavelength. These observations declare that the nano-scale Si-QDs can provide sufficiently large XAM effect to enable the ultrafast all-optical switching capability for pulsed optical logic applications. To confirm, the Si-QDs doped Si-rich SiC x waveguide modulator based 1.2 Gbit/s all-optical format inversion of a PRZ-OOK data-stream is demonstrated for the first time.

Investigation was conducted on bauxite mixed with Li2CO3 as alkali metal catalysts for biodiesel production. Bauxite contains a high percentage of Si and Al compounds among products. Because of the high expense of commercial materials (SiO2, Al2O3) that makes them not economical, the method was very recently improved by replacing commercial materials with Si and Al from bauxite. This is one of the easiest methods for preparing heterogeneous transesterification catalysts, through one-pot blending, grinding bauxite with Li2CO3, and heating at 800 °C for 4 h. The prepared solid-base alkali metal catalyst was characterized in terms of its physical and chemical properties using X-ray powder diffraction and field-emission scanning electron microscopy (FE-SEM). The optimal conditions for the transesterification procedure are to mix methanol oil by molar ratio 9:1, under 65 °C, with catalyst amount 3 wt.%. The procedure is suitable for transesterifying oil to fatty acid methyl ester in the 96% range.

Polarization-manipulated all-optical format inversion of a 12.5 Gbit s−1 pulsed return-to-zero on-off-keying (PRZ-OOK) data stream is demonstrated through the nonlinear Kerr switching-induced wavelength conversion process.