Electrical and Photoconductivity Properties of Al/CdFe2O4/p-Si/Al Photodiode

In the present study, we have investigated the effects of illumination intensity on the optical and electrical characteristics of the Al/CdFe2O4/p-Si/Al photodiode. A thin film of CdFe2O4 was fabricated using the sol-gel spin coating method that allows good thickness control and low-cost manufacturing as compared to alternative techniques. The current-voltage (I-V) of the Al/CdFe2O4/p-Si/Al photodiode was measured in the dark and under different illumination intensities. The photocurrent increased with higher luminous intensity and its sensitivity has a strong dependence on the reverse bias rising from 1.08⁎10-7 A under dark conditions to 6.11⁎10-4 A at 100 mW/cm2 of illumination. The parameters of the photodiode such as ideality factor and barrier height were calculated using the thermionic emission model. The ideality factor of the Al/CdFe2O4/p-Si/Al photodiode was found to be 4.4. The barrier height was found to be 0.88 eV. The capacitance-voltage (C-V) characteristics measured at different frequencies have strongly varied with frequency, decreasing with frequency. Consequently, the resulting interface density (Dit) value of the Al/CdFe2O4/p-Si/Al photodiode also decreased with higher frequency. Similarly, the fitted series resistance of the Al/CdFe2O4/p-Si/Al photodiode has declined with higher frequency.

End Face Damage and Fiber Fuse Phenomena in Single-Mode Fiber-Optic Connectors

The evolution of both the core melting and fiber fuse phenomena in a single-mode fiber-optic connector was studied theoretically. Carbon black was chosen as a light-absorbent material. A thin absorbent layer with a thickness of 1 μm order was assumed to be formed between the fiber end faces in the connector. When a high-power laser operating at 1.48 or 1.55 μm was input into the connector, the temperature on the fiber core surface increased owing to heat conduction from the light-absorbent material. The heat flow process of the core, which caused the core to melt or the fiber fuse phenomenon, was theoretically calculated with the explicit finite-difference method. The results indicated that initial attenuation of less than 0.5 dB was desirable to prevent core fusion in the connectors when the input 1.48 μm laser power was 1 W. It was found that a core temperature of more than 4000 K was necessary to generate and maintain a fiber fuse.

Fabric Defect Detection Using Local Homogeneity Analysis and Neural Network

In the textile manufacturing industry, fabric defect detection becomes a necessary and essential step in quality control. The investment in this field is more than economical when reduction in labor cost and associated benefits are considered. Moreover, the development of a wholly automated inspection system requires efficient and robust algorithms. To overcome this problem, in this paper, we present a new fabric defect detection scheme which uses the local homogeneity and neural network. Its first step consists in computing a new homogeneity image denoted as H-image. The second step is devoted to the application of the discrete cosine transform (DCT) to the H-image and the extraction of different representative energy features of each DCT block. These energy features are used by the back-propagation neural network to judge the existence of fabric defect. Simulations on different fabric images and different defect aspects show that the proposed method achieves an average accuracy of 97.35%.

Concept of Bee-Eyes Array of Fresnel Lenses as a Solar Photovoltaic Concentrator System

This paper presents a proposal of a new configuration of an optical concentrator for photovoltaic application which may enhance the efficiency of solar cells. Bee-eyes array Fresnel lenses concentrator proposed here provide high concentration factor which is greater than1000x at the 20th zone. In addition, the system also provides room for increasing the number of zones to achieve the high concentration factor if needs arise. The transmission efficiency greater than 90% has been achieved with f-number of ≥1.25. Mathematical relations derived to obtain flux distribution at the absorber plane and the transmission efficiency as well as the position of the solar cell were used in the ray tracing simulations for 6, 18, 36, 60, 90, 126, 168, 216, 270, and 330 suns concentration systems. A transmission efficiency is linearly decreasing with the increase in the number of arrays in which the transmission efficiency of 94.42% was recorded at the array of 6 suns and 74.98% at 330 suns.

Highly Effective Crosstalk Mitigation Method Using Counter-Propagation in Semiconductor Optical Amplifier for Remodulation WDM-PONs

Remodulation-induced crosstalk mitigation in WDM-PON using remodulation approach is presented in this paper. Utilizing all-optical signal processing, the proposed method has been able to significantly improve system performance in terms of bit error rate (BER) and bit rate distance product. Moreover, the proposed method could be used for both baseband and modulated downstream electrical signals.

Graphene Embedded Modulator with Extremely Small Footprint and High Modulation Efficiency

By embedding graphene sheet in the silicon waveguide, the overall effective mode index displays unexpected symmetry and the electrorefraction effect has been significantly enhanced near the epsilon-near-zero point. An eight-layer graphene embedded Mach-Zehnder Modulator has been theoretically demonstrated with the advantage of ultracompact footprint (4 × 2 μm2), high modulation efficiency (1.316 V·μm), ultrafast modulation speed, and large extinction ratio. Our results may promote various on-chip active components, boosting the utilization of graphene in optical applications.

Wet Chemical Preparation of Nanoparticles ZnO:Eu3+ and ZnO:Tb3+ with Enhanced Photoluminescence

ZnO doped with Eu3+ and Tb3+ had been successfully prepared by wet chemical method with the assistance of microwave. The influence of reaction conditions such as temperature, time, content of Eu3+, Tb3+ ion, and annealing treatment on the structure and luminescent characteristics was studied. The analysis of energy dispersive spectroscopy (EDS) and photoluminescence spectra measurements indicated that Eu3+ and Tb3+ exist in host lattice and create the new emission region compared to ZnO crystalline host lattice. The field emission scanning electron microscope (FE-SEM) studies show the Eu3+, Tb3+ doped ZnO nanoparticles have a pseudohexagonal shape. The particle size was 30–50 nm for ZnO:Eu3+ and 40–60 nm for ZnO:Tb3+. Photoluminescence excitation (PLE) and photoluminescence (PL) spectra at room temperature have been studied to recognize active centers for characteristic luminescence of ZnO:Eu3+ and ZnO:Tb3+. The characteristic luminescent lines of Eu3+ (5D0-7Fj) and Tb3+ (5D4-7Fj) were determined. It has been demonstrated that the wet chemical synthesis method with microwave assistance can strongly enhance the luminescent intensity of nanoparticles ZnO:Eu3+ in red and ZnO:Tb3+ in green.

A New Design for All-Normal Near Zero Dispersion Photonic Crystal Fiber with Selective Liquid Infiltration for Broadband Supercontinuum Generation at 1.55 μm

A new design of all-normal and near zero flattened dispersion based on all-silica photonic crystal fibers (PCFs) using selectively liquid infiltration technique has been proposed to realize smooth broadband supercontinuum generation (SCG). The investigation gives the details of the effect of different geometrical parameters along with the infiltrating liquids on the dispersion characteristics of the fiber. Numerical investigations establish a dispersion value of −0.48 ps/nm/km around the wavelength of 1.55 μm. The optimized design has been found to be suitable for SCG around the C band of wavelength with flat broadband wavelength band (375 nm bandwidth) and smooth spectrum with only a meter long of the PCF. The proposed structure also demonstrates good tunable properties that can help correct possible fabrication mismatch towards a better optimization design for various optical communication systems.

Simulation and Measurement of Solar Harvesting Enhancement of Silver Plasmonic Nanoparticles on GaSb Nanodots

The performance of a plasmonic antireflection layer which can be utilized for deep-space radiationresistant GaSb solar cells is investigated numerically and experimentally. The layer consists of nanodots made by plasma etching of a GaSb substrate and subsequent physical vapor deposition of Ag nanoparticles on the nanodot tips, in a partially ordered configuration determined by the plasma energy level. This technique is readily applicable to patterning of silicon. We measure the substrate reflectivity and model the reflection and absorption of the substrates using the 3D finite difference time domain (FDTD) method, which are realistically imported as 3D layers from the scanning electron microscopy (SEM) images. The variation of the height of the Ag nanoparticles on top of the GaSb pillars shows that the plasmonic effect remarkably enhances the absorption. The presence of GaSb pillars enhances absorption and tunes the maximum absorption wavelength peak.

Heat Conduction Modeling of Fiber Fuse in Single-Mode Optical Fibers

The unsteady-state thermal conduction process in single-mode optical fiber was studied theoretically with the explicit finite-difference method. We assumed that the vitreous silica optical fiber underwent pyrolysis at elevated temperatures to form SiOx (x~1). We also proposed a model in which the optical absorption coefficient of the core layer increased with increasing molar concentration of SiOx. The core-center temperature changed suddenly and reached over 3×104 K when a 1.064-μm laser power of 2 W was input into a short core layer of 40 μm length, which was heated at 2923 K. This thermal wave, that is, a fiber fuse, increased in size and propagated toward the light source at a rate of about 0.54 m/s. The calculated propagation velocity of the fiber fuse was in agreement with the experimental value. Moreover, the average temperature of the radiated region of the core layer gradually approached a temperature of about 5700 K. It was found that the final average temperature was close to the experimentally reported values.