Loss Characterization of Waveguides in Lithium Niobate on Insulator

10.1109/OMN.2016.7565837International Conference on Optical MEMS and Nanophotonics (OMN

Single mode photonic crystal vertical cavity lasers

We report the accuracy of the photonic crystal model in describing the characteristics of vertical cavity surface-emitting lasers with lateral optical confinement consisting of a periodic array of etched circular holes. Experiments were carried out to compare predictions of the photonic crystal model to observed modal device characteristics, and the oxide aperture size was optimized to give maximum output power and lower threshold. The role of loss in improving modal properties was also investigated. Optimized lasers exhibit submilliamp threshold current and operate in the fundamental lateral mode for all currents. This work is supported by a National Science Foundation Graduate Research Fellowship and Grant No. 03-35082. The authors thank E. Shyu, E. Yamaoka, S. Lala, and M. Hwang for device characterization and Y. H. Lee for valuable discussions

Improved silicon oxide/polysilicon passivated contacts for high efficiency solar cells via optimized tunnel layer annealing

10.1016/j.solmat.2020.110720Solar Energy Materials and Solar Cells217110720-11072

Focused Ion Beam Nanopatterning for Optoelectronic Device Fabrication

Recent photonic device structures, including distributed Bragg reflectors (DBRs), one-dimensional (1-D) or two-dimensional (2-D) photonic crystals, and surface plasmon devices, often require nanoscale lithography techniques for their device fabrication. Focused ion beam (FIB) etching has been used as a nanolithographic tool for the creation of these nanostructures. We report the use of FIB etching as a lithographic tool that enables sub-100-nm resolution. The FIB patterning of nanoscale holes on an epitaxially grown GaAs layer is characterized. To eliminate redeposition of sputtered materials during FIB patterning, we have developed a process using a dielectric mask and subsequent dry etching. This approach creates patterns with vertical and smooth sidewalls. A thin titanium layer can be deposited on the dielectric layer to avoid surface charging effects during the FIB process. This FIB nanopatterning technique can be applied to fabricate optoelectronic devices, and we show examples of 1-D gratings in optical fibers for sensing applications, photonic crystal vertical cavity lasers, and photonic crystal defect lasers

Loss and index guiding in single mode proton-implanted holey vertical-cavity surface-emitting lasers

Wedge-shaped holes are fabricated in the top mirror of proton-implanted vertical-cavity surface-emitting lasers (VCSELs). A radially symmetric fill factor approach is used to calculate the resulting transverse index profile. To investigate both the index confinement provided by the etched pattern and its effect on optical loss, continuous-wave (CW) and pulsed experiments are performed. Under CW operation, we show proper wedge design leads to improved fundamental-mode output power, decreased threshold, and increased efficiency. We report a significant decrease in threshold under pulsed operation for the etched device compared to an unetched device, indicating a significant reduction in diffraction loss to the fundamental mode due to strong index guiding. Single-mode output is maintained over the entire operating range of the VCSEL due to increased loss for the higher order mode

The effect of dust on transmission and self-cleaning property of solar panels

10.1016/j.egypro.2012.02.051Energy Procedia15421-42

TiO₂ Thin Films Prepared via Adsorptive Self-Assembly for Self-Cleaning Applications

Low-cost controllable solution-based processes for preparation of titanium oxide (TiO₂) thin films are highly desirable, because of many important applications of this oxide in catalytic decomposition of volatile organic compounds, advanced oxidation processes for wastewater and bactericidal treatments, self-cleaning window glass for green intelligent buildings, dye-sensitized solar cells, solid-state semiconductor metal-oxide solar cells, self-cleaning glass for photovoltaic devices, and general heterogeneous photocatalysis for fine chemicals etc. In this work, we develop a solution-based adsorptive self-assembly approach to fabricate anatase TiO₂ thin films on different glass substrates such as simple plane glass and patterned glass at variable compositions (normal soda lime glass or solar-grade borofloat glass). By tuning the number of process cycles (i.e., adsorption-then-heating) of TiO₂ colloidal suspension, we could facilely prepare large-area TiO₂ films at a desired thickness and with uniform crystallite morphology. Moreover, our as-prepared nanostructured TiO₂ thin films on glass substrates do not cause deterioration in optical transmission of glass; instead, they improve optical performance of commercial solar cells over a wide range of incident angles of light. Our as-prepared anatase TiO₂ thin films also display superhydrophilicity and excellent photocatalytic activity for self-cleaning application. For example, our investigation of photocatalytic degradation of methyl orange indicates that these thin films are indeed highly effective, in comparison to other commercial TiO₂ thin films under identical testing conditions

TiO₂ Thin Films Prepared via Adsorptive Self-Assembly for Self-Cleaning Applications

Low-cost controllable solution-based processes for preparation of titanium oxide (TiO₂) thin films are highly desirable, because of many important applications of this oxide in catalytic decomposition of volatile organic compounds, advanced oxidation processes for wastewater and bactericidal treatments, self-cleaning window glass for green intelligent buildings, dye-sensitized solar cells, solid-state semiconductor metal-oxide solar cells, self-cleaning glass for photovoltaic devices, and general heterogeneous photocatalysis for fine chemicals etc. In this work, we develop a solution-based adsorptive self-assembly approach to fabricate anatase TiO₂ thin films on different glass substrates such as simple plane glass and patterned glass at variable compositions (normal soda lime glass or solar-grade borofloat glass). By tuning the number of process cycles (i.e., adsorption-then-heating) of TiO₂ colloidal suspension, we could facilely prepare large-area TiO₂ films at a desired thickness and with uniform crystallite morphology. Moreover, our as-prepared nanostructured TiO₂ thin films on glass substrates do not cause deterioration in optical transmission of glass; instead, they improve optical performance of commercial solar cells over a wide range of incident angles of light. Our as-prepared anatase TiO₂ thin films also display superhydrophilicity and excellent photocatalytic activity for self-cleaning application. For example, our investigation of photocatalytic degradation of methyl orange indicates that these thin films are indeed highly effective, in comparison to other commercial TiO₂ thin films under identical testing conditions