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- All Subjects: Electrical Engineering
Description
Dual-wavelength laser sources have various existing and potential applications in wavelength division multiplexing, differential techniques in spectroscopy for chemical sensing, multiple-wavelength interferometry, terahertz-wave generation, microelectromechanical systems, and microfluidic lab-on-chip systems. In the drive for ever smaller and increasingly mobile electronic devices, dual-wavelength coherent light output from a single semiconductor laser diode would enable further advances and deployment of these technologies. The output of conventional laser diodes is however limited to a single wavelength band with a few subsequent lasing modes depending on the device design. This thesis investigates a novel semiconductor laser device design with a single cavity waveguide capable of dual-wavelength laser output with large spectral separation. The novel dual-wavelength semiconductor laser diode uses two shorter- and longer-wavelength active regions that have separate electron and hole quasi-Fermi energy levels and carrier distributions. The shorter-wavelength active region is based on electrical injection as in conventional laser diodes, and the longer-wavelength active region is then pumped optically by the internal optical field of the shorter-wavelength laser mode, resulting in stable dual-wavelength laser emission at two different wavelengths quite far apart. Different designs of the device are studied using a theoretical model developed in this work to describe the internal optical pumping scheme. The carrier transport and separation of the quasi-Fermi distributions are then modeled using a software package that solves Poisson's equation and the continuity equations to simulate semiconductor devices. Three different designs are grown using molecular beam epitaxy, and broad-area-contact laser diodes are processed using conventional methods. The modeling and experimental results of the first generation design indicate that the optical confinement factor of the longer-wavelength active region is a critical element in realizing dual-wavelength laser output. The modeling predicts lower laser thresholds for the second and third generation designs; however, the experimental results of the second and third generation devices confirm challenges related to the epitaxial growth of the structures in eventually demonstrating dual-wavelength laser output.
ContributorsGreen, Benjamin C (Author) / Zhang, Yong-Hang (Thesis advisor) / Ning, Cun-Zheng (Committee member) / Tao, Nongjian (Committee member) / Roedel, Ronald J (Committee member) / Arizona State University (Publisher)
Created2011
Description
A proposed visible spectrum nanoscale imaging method requires material with permittivity values much larger than those available in real world materials to shrink the visible wavelength to attain the desired resolution. It has been proposed that the extraordinarily slow propagation experienced by light guided along plasmon resonant structures is a viable approach to obtaining these short wavelengths. To assess the feasibility of such a system, an effective medium model of a chain of Noble metal plasmonic nanospheres is developed, leading to a straightforward calculation of the waveguiding properties. Evaluation of other models for such structures that have appeared in the literature, including an eigenvalue problem nearest neighbor approximation, a multi- neighbor approximation with retardation, and a method-of-moments method for a finite chain, show conflicting expectations of such a structure. In particular, recent publications suggest the possibility of regions of invalidity for eigenvalue problem solutions that are considered far below the onset of guidance, and for solutions that assume the loss is low enough to justify perturbation approximations. Even the published method-of-moments approach suffers from an unjustified assumption in the original interpretation, leading to overly optimistic estimations of the attenuation of the plasmon guided wave. In this work it is shown that the method of moments approach solution was dominated by the radiation from the source dipole, and not the waveguiding behavior claimed. If this dipolar radiation is removed the remaining fields ought to contain the desired guided wave information. Using a Prony's-method-based algorithm the dispersion properties of the chain of spheres are assessed at two frequencies, and shown to be dramatically different from the optimistic expectations in much of the literature. A reliable alternative to these models is to replace the chain of spheres with an effective medium model, thus mapping the chain problem into the well-known problem of the dielectric rod. The solution of the Green function problem for excitation of the symmetric longitudinal mode (TM01) is performed by numerical integration. Using this method the frequency ranges over which the rod guides and the associated attenuation are clearly seen. The effective medium model readily allows for variation of the sphere size and separation, and can be taken to the limit where instead of a chain of spheres we have a solid Noble metal rod. This latter case turns out to be the optimal for minimizing the attenuation of the guided wave. Future work is proposed to simulate the chain of photonic nanospheres and the nanowire using finite-difference time-domain to verify observed guided behavior in the Green's function method devised in this thesis and to simulate the proposed nanosensing devices.
ContributorsHale, Paul (Author) / Diaz, Rodolfo E (Thesis advisor) / Goodnick, Stephen (Committee member) / Aberle, James T., 1961- (Committee member) / Palais, Joseph (Committee member) / Arizona State University (Publisher)
Created2013
Description
This thesis summarizes the research work carried out on design, modeling and simulation of semiconductor nanophotonic devices. The research includes design of nanowire (NW) lasers, modeling of active plasmonic waveguides, design of plasmonic nano-lasers, and design of all-semiconductor plasmonic systems. For the NW part, a comparative study of electrical injection in the longitudinal p-i-n and coaxial p-n core-shell NWs was performed. It is found that high density carriers can be efficiently injected into and confined in the core-shell structure. The required bias voltage and doping concentrations in the core-shell structure are smaller than those in the longitudinal p-i-n structure. A new device structure with core-shell configuration at the p and n contact regions for electrically driven single NW laser was proposed. Through a comprehensive design trade-off between threshold gain and threshold voltage, room temperature lasing has been proved in the laser with low threshold current and large output efficiency. For the plasmonic part, the propagation of surface plasmon polariton (SPP) in a metal-semiconductor-metal structure where semiconductor is highly excited to have an optical gain was investigated. It is shown that near the resonance the SPP mode experiences an unexpected giant modal gain that is 1000 times of the material gain in the semiconductor and the corresponding confinement factor is as high as 105. The physical origin of the giant modal gain is the slowing down of the average energy propagation in the structure. Secondly, SPP modes lasing in a metal-insulator-semiconductor multi-layer structure was investigated. It is shown that the lasing threshold can be reduced by structural optimization. A specific design example was optimized using AlGaAs/GaAs/AlGaAs single quantum well sandwiched between silver layers. This cavity has a physical volume of 1.5×10-4 λ03 which is the smallest nanolaser reported so far. Finally, the all-semiconductor based plasmonics was studied. It is found that InAs is superior to other common semiconductors for plasmonic application in mid-infrared range. A plasmonic system made of InAs, GaSb and AlSb layers, consisting of a plasmonic source, waveguide and detector was proposed. This on-chip integrated system is realizable in a single epitaxial growth process.
ContributorsLi, Debin (Author) / Ning, Cun-Zheng (Thesis advisor) / Zhang, Yong-Hang (Committee member) / Balanis, Constantine A (Committee member) / Yu, Hongbin (Committee member) / Arizona State University (Publisher)
Created2012
Description
Studying charge transport through single molecules tethered between two metal electrodes is of fundamental importance in molecular electronics. Over the years, a variety of methods have been developed in attempts of performing such measurements. However, the limitation of these techniques is still one of the factors that prohibit one from gaining a thorough understanding of single molecule junctions. Firstly, the time resolution of experiments is typically limited to milli to microseconds, while molecular dynamics simulations are carried out on the time scale of pico to nanoseconds. A huge gap therefore persists between the theory and the experiments. This thesis demonstrates a nanosecond scale measurement of the gold atomic contact breakdown process. A combined setup of DC and AC circuits is employed, where the AC circuit reveals interesting observations in nanosecond scale not previously seen using conventional DC circuits. The breakdown time of gold atomic contacts is determined to be faster than 0.1 ns and subtle atomic events are observed within nanoseconds. Furthermore, a new method based on the scanning tunneling microscope break junction (STM-BJ) technique is developed to rapidly record thousands of I-V curves from repeatedly formed single molecule junctions. 2-dimensional I-V and conductance-voltage (G-V) histograms constructed using the acquired data allow for more meaningful statistical analysis to single molecule I-V characteristics. The bias voltage adds an additional dimension to the conventional single molecule conductance measurement. This method also allows one to perform transition voltage spectra (TVS) for individual junctions and to study the correlation between the conductance and the tunneling barrier height. The variation of measured conductance values is found to be primarily determined by the poorly defined contact geometry between the molecule and metal electrodes, rather than the tunnel barrier height. In addition, the rapid I-V technique is also found useful in studying thermoelectric effect in single molecule junctions. When applying a temperature gradient between the STM tip and substrate in air, the offset current at zero bias in the I-V characteristics is a measure of thermoelectric current. The rapid I-V technique allows for statistical analysis of such offset current at different temperature gradients and thus the Seebeck coefficient of single molecule junctions is measured. Combining with single molecule TVS, the Seebeck coefficient is also found to be a measure of tunnel barrier height.
ContributorsGuo, Shaoyin (Author) / Tao, Nongjian (Thesis advisor) / Bennett, Peter (Committee member) / Ning, Cun-Zheng (Committee member) / Yu, Hongbin (Committee member) / Arizona State University (Publisher)
Created2012
Description
This thesis mainly focuses on the study of quantum efficiency (QE) and its measurement, especially for nanowires (NWs). First, a brief introduction of nano-technology and nanowire is given to describe my initial research interest. Next various fundamental kinds of recombination mechanisms are described; both for radiative and non-radiative processes. This is an introduction for defining the internal quantum efficiency (IQE). A relative IQE measurement method is shown following that. Then it comes to the major part of the thesis discussing a procedure of quantum efficiency measurement using photoluminescence (PL) method and an integrating sphere, which has not been much applied to nanowires (NWs). In fact this is a convenient and useful approach for evaluating the quality of NWs since it considers not only the PL emission but also the absorption of NWs. The process is well illustrated and performed with both wavelength-dependent and power-dependent measurements. The measured PLQE is in the range of 0.3% ~ 5.4%. During the measurement, a phenomenon called photodegradation is observed and examined by a set of power-dependence measurements. This effect can be a factor for underestimating the PLQE and a procedure is introduced during the sample preparation process which managed to reduce this effect for some degree.
ContributorsChen, Dongzi (Author) / Ning, Cun-Zheng (Thesis advisor) / Zhang, Yong-Hang (Committee member) / Yu, Hongbin (Committee member) / Arizona State University (Publisher)
Created2012
Description
In this work, I worked on the synthesis and characterization of nanowires and belts, grown using different materials, in Chemical Vapor Deposition (CVD) system with catalytic growth method. Through this thesis, I utilized the Photoluminescence (PL), Secondary Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD) analyses to find out the properties of Erbium Chloride Silicate (ECS) and two segment CdS-CdSe samples. In the first part of my research, growth of very new material, Erbium Chloride Silicate (ECS), in form of core/shell Si/ECS and pure ECS nanowires, was demonstrated. This new material has very fascinating properties for new Si based photonic devices. The Erbium density in those nanowires is which is very high value compared to the other Erbium doped materials. It was shown that the luminescence peaks of ECS nanowires are very sharp and stronger than their counterparts. Furthermore, both PL and XRD peaks get sharper and stronger as growth temperature increases and this shows that crystalline quality of ECS nanowires gets better with higher temperature. In the second part, I did a very detail research for growing two segment axial nanowires or radial belts and report that the structure type mostly depends on the growth temperature. Since our final step is to create white light LEDs using single axial nanowires which have three different regions grown with distinct materials and give red, green and blue colors simultaneously, we worked on growing CdS-CdSe nanowires or belts for the first step of our aim. Those products were successfully grown and they gave two luminescence peaks with maximum 160 nm wavelength separation depending on the growth conditions. It was observed that products become more likely belt once the substrate temperature increases. Also, dominance between VLS and VS is very critical to determine the shape of the products and the substitution of CdS by CdSe is very effective; hence, CdSe growth time should be chosen accordingly. However, it was shown two segmented products can be synthesized by picking the right conditions and with very careful analyses. We also demonstrated that simultaneous two colors lasing from a single segmented belt structures is possible with strong enough-pumping-power.
ContributorsTurkdogan, Sunay (Author) / Ning, Cun-Zheng (Thesis advisor) / Tao, Meng (Committee member) / Yu, Hongbin (Committee member) / Arizona State University (Publisher)
Created2012
Description
Multiport antennas offer greater design flexibility than traditional one-port designs. An antenna array is a special case of a multiport antenna. If the antenna's inter-element spacing is electrically small, the antenna is capable of achieving superdirectivity. Superdirective antenna arrays are known to be narrow band and have low radiation resistance which leads to low radiation efficiency and high VSWR. However, by increasing the self-impedance of the antenna elements, the radiation resistance is increased but the bandwidth remains narrow. A design methodology is developed using the ability to superimpose electric fields and multi-objective optimization to design antenna feed networks. While the emphasis in this dissertation is on antenna arrays and superdirectivity, the design methodology is general and can be applied to other multiport antennas. The design methodology is used to design a multiport impedance-matching network and optimize both the input impedance and radiation pattern of a two-port superdirective antenna array. It is shown that the multiport impedance-matching network is capable of improving the input impedance of the antenna array while maintaining high directionality. The antenna design is critical for the methodology to improve the bandwidth and radiation characteristics of the array. To double the bandwidth of the two-port impedance matched superdirective antenna array, a three-port Yagi-Uda antenna design is demonstrated. The addition of the extra antenna element does not increase the footprint of the antenna array. The design methodology is then used to design a symmetrical antenna array capable of steering its main beam in two directions.
ContributorsArceo, Diana (Author) / Balanis, Constantine A (Thesis advisor) / Aberle, James T., 1961- (Committee member) / Moeller, Karl (Committee member) / Palais, Joseph (Committee member) / Arizona State University (Publisher)
Created2012
Description
Nanophotonics studies the interaction of light with nanoscale devices and nanostructures. This thesis focuses on developing nanoscale devices for optical modulation (saturable absorber and all-optical modulator) and investigating light scattering from nanoparticles for underwater navigation and energy sector application. Saturable absorbers and all-optical modulators are essential to generate ultrashort high-power laser pulses and high-speed communications. Graphene-based devices are broadband, ultrafast, and compatible with different substrates and fibers. Nevertheless, the required fluence to saturate or modulate the optical signal with graphene is still high to realize low-threshold, compact broadband devices, which are essential for many applications. This dissertation emphasizes that the strong light-matter interaction in graphene-plasmonic hybrid metasurface greatly enhances monolayer graphene’s saturable absorption and optical signal modulation effect while maintaining graphene’s ultrafast carrier dynamics. Furthermore, based on this concept, simulation models and experimental demonstrations are presented in this dissertation to demonstrate both subwavelength (~λ/5 in near-infrared and ~λ/10 in mid-infrared) thick graphene-based saturable absorber (with record-low saturation fluence (~0.1μJ/cm2), and ultrashort recovery time (~60fs) at near-infrared wavelengths) and all-optical modulators ( with 40% reflection modulation at 6.5μm with ~55μJ/cm2 pump fluence and ultrafast relaxation time of ~1ps at 1.56μm with less than 8μJ/cm2 pump fluence).
Underwater navigation is essential for various underwater vehicles. However, there is no reliable method for underwater navigation. This dissertation presents a numerical simulation model and algorithm for navigation based on underwater polarization mapping data. With the methods developed, for clear water in the swimming pool, it is possible to achieve a sun position error of 0.35˚ azimuth and 0.03˚ zenith angle, and the corresponding location prediction error is ~23Km. For turbid lake water, a location determination error of ~100Km is achieved. Furthermore, maintenance of heliostat mirrors and receiver tubes is essential for properly operating concentrated solar power (CSP) plants. This dissertation demonstrates a fast and field deployable inspection method to measure the heliostat mirror soiling levels and receiver tube defect detection based on polarization images. Under sunny and clear sky conditions, accurate reflection efficiency (error ~1%) measurement for mirrors with different soiling levels is achieved, and detection of receiver tube defects is demonstrated.
ContributorsRafique, Md Zubair Ebne (Author) / Yao, Yu (Thesis advisor) / Palais, Joseph (Committee member) / Zhang, Yong-Hang (Committee member) / Sukharev, Maxim (Committee member) / Arizona State University (Publisher)
Created2022
Description
This dissertation consists of four parts: design of antenna in lossy media, analysisof wire antennas using electric field integral equation (EFIE) and wavelets, modeling and measurement of grounded waveguide coplanar waveguide (GCPW) for automotive radar, and E-Band 3-D printed antenna and measurement using VNA. In the first part, the antenna is modeled and simulated in lossy media. First, the vector wave functions is solved in the fundamental mode. Next the energy flow velocity is plotted to show near-field energy distribution for both TM and TE in air and seawater environment. Finally the power relation in seawater is derived to calculate the source dipole moment and required power.
In the second part, the current distribution on the antenna is derived by solving EFIE with moment of methods (MoM). Both triangle and Coifman wavelet (Coiflet) are used as basis and weight functions. Then Input impedance of the antenna is computed and results are compared with traditional sinusoid current distribution assumption. Finally the input impedance of designed antenna is computed and matching network is designed and show resonant at designed frequency.
In the third part, GCPW is modeled and measured in E-band. Laboratory measurements are conducted in 75 to 84 GHz. The original system is embedded with error boxes due to misalignment and needed to be de-embedded. Then the measurement data is processed and the results is compared with raw data.
In the fourth part, the horn antennas and slotted waveguide array antenna (SWA) are designed for automotive radar in 75GHz to 78GHz. The horn antennas are fabricated using 3D printing of ABS material, and electro-plating with copper. The analytic solution and HFSS simulation show good agreement with measurement.
ContributorsZhou, Sai (Author) / Pan, George (Thesis advisor) / Aberle, James (Committee member) / Palais, Joseph (Committee member) / Allee, David (Committee member) / Arizona State University (Publisher)
Created2021
Description
Antenna arrays are widely used in wireless communication, radar, remote sensing, and other fields. Compared to traditional linear antenna arrays, novel nonlinear antenna arrays have fascinating advantages in terms of structural simplicity, lower cost, wider bandwidth, faster scanning speed, and lower side-lobe levels. This dissertation explores a novel design of a phased array antenna with an augmented scanning range, aiming to establish a clear connection between mathematical principles and practical circuitry. To achieve this goal, the Van der Pol (VDP) model is applied to a single-transistor oscillator to obtain the isolated limit cycle. The coupled oscillators are then integrated into a 1 times 7 coupled phased array, using the Keysight PathWave Advanced Design System (ADS) for tuning and optimization. The VDP model is used for analytic study of bifurcation, quasi-sinusoidal oscillation, quasi-periodic chaos, and oscillator death, while ADS schematics guide engineering implementation and physical fabrication. The coupled oscillators drive cavity-backed antennas, forming a one-dimensional scanning antenna array of 1 times 7. The approaches for increasing the scanning range performance are discussed.
ContributorsZhang, Kaiyue (Author) / Pan, George (Thesis advisor) / Yu, Hongbin (Committee member) / Aberle, James (Committee member) / Palais, Joseph (Committee member) / Arizona State University (Publisher)
Created2023