RESUMO
Self-assembled two-dimensional (2D) colloidal crystals (CCs) are utilized in various optical devices, lasers, biosensors, and light harvesting applications. Optical design tuning capabilities, in terms of sphere refractive index and diameter size, can influence the optical characteristics for the close-packed single-layer or multilayer structures. Often transmission dips in 2D CCs are observed, which cannot be explained by Bragg diffraction as it does for 3D photonic crystals. In this work, an analytical attempt to accurately model the transmission dips observed in the 2D CCs optical spectra is presented, aiming to explain the origin of these dips. The formation of a broad dip was studied experimentally as well. A less than 1% mismatching error was found between experiment and theory for the two blaze peak positions as well as for the transmission intensity ratio. Finally, the 2D CCs were integrated in mesostructured solar cells as light trapping structures.
RESUMO
Self-assembled two-dimensional colloidal crystals (CCs) are critical components in many optical and optoelectronic devices. Such structures usually exhibit various types of disorder, which sometimes can be beneficial for the desired applications. However, disorder poses challenges to the modeling of two-dimensional structures. In this work, two-dimensional CCs employed in optoelectronic devices, especially dye-sensitized solar cells, are investigated. scanning electron microscope (SEM) images were used to quantify the disorder in the studied structures. As a basis for simulations, disordered model patterns were generated with properties extracted from the SEM images of prepared samples. Optical modeling was performed with a finite-difference time-domain simulator. The simulated transmission data are consistent with the experimentally measured spectra.
RESUMO
In this work, we propose a micro-scale modulator architecture with compact size, low insertion loss, high extinction ratio, and low energy/bit while being compatible with the silicon-on-insulator (SOI) platform. This is achieved through the utilization of epsilon-near-zero (ENZ) effect of indium-tin-oxide (ITO) to maximize the attainable change in the effective index of the optical mode. It also exploits the ITO layer in a hybrid plasmonic ring resonator which further intensifies the effect of the changes in both the real and imaginary parts of the effective index. By electrically inducing carriers in the indium tin oxide (ITO), to reach the ENZ state, the resonance condition shifts, and the losses of the hybrid plasmonic ring resonator increases significantly. This mechanism is optimized to maximize the extinction ratio and minimize the insertion loss. The proposed structure is designed to maximize the coupling to and from standard SOI waveguide, used as access ports. In addition, the operational region is reconfigurable by changing the bias voltage.
RESUMO
In-plane Fabry-Perot cavities based on deeply etched Bragg mirrors are used in many microphotonic applications including sensing, telecom, and swept laser devices. A main limitation to their performance is the small free spectral range (FSR) and low finesse. The FSR limits the dynamic range or the wavelength tuning range, while the linewidth limits the resolution. In this work, we propose coupled Fabry-Perot micro-cavities that greatly enhance the FSR, besides reducing the linewidth, which lead to higher finesse and better performance. The proposed structure is modeled and etched on Si substrate to a depth of 150 µm using the deep reactive ion etching technology. Optical measurements indicate an enhanced FSR of more than 140 nm and a quality factor of 3152 using coupled cavities as compared to only 9 nm FSR for a single cavity of the same length. The over-etching and surface roughness, being the main effective fabrication tolerances, are modeled and extracted from the measurements.
