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- Title
- DECOHERENCE IN QUANTUM DOT CHARGE QUBITS: THE ROLE OFELECTROMAGNETIC FLUCTUATIONS.
- Creator
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McCracken, James, Mucciolo, Eduardo, University of Central Florida
- Abstract / Description
-
Lateral semiconductor quantum dot structures have been proposed as an effective quantum bit (qubit) for quantum computation. A single excess electron with the freedom to move between two capacitively coupled quantum dots creates a `pseudo'-spin system with the same qubit behavior as the more natural two level system of a single electron spin. The excess electron in the double dot system is restricted to one of the two dots, thereby creating two separate and distinct states (usually referred...
Show moreLateral semiconductor quantum dot structures have been proposed as an effective quantum bit (qubit) for quantum computation. A single excess electron with the freedom to move between two capacitively coupled quantum dots creates a `pseudo'-spin system with the same qubit behavior as the more natural two level system of a single electron spin. The excess electron in the double dot system is restricted to one of the two dots, thereby creating two separate and distinct states (usually referred to as |L> and |R>). The benefit of these charge qubits lie in the relative ease with which they can be manipulated and created. Experiments have been performed in this area and have shown controllable coherent oscillations and thus efficient single-qubit operations. However, the decoherence rates observed in the experiments is still quite high, making double dot charge qubits not very appealing for large-scale implementations. The following work describes the effect of the electromagnetic (EM) environment of the double quantum dot system on the decoherence of the charge state. Sources of decoherence in similar systems have been extensively investigated before and this paper follows a close theoretical framework to previous work done in the area. The effect of the EM environment can been seen in the calculations discussed below, although it is clear that the decoherence seen in experiments cannot be fully explained by the voltage fluctuations as they are investigated here. The limitations of the calculations are discussed and improvements are suggested.
Show less - Date Issued
- 2006
- Identifier
- CFE0001167, ucf:46850
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001167
- Title
- High Efficiency and Wide Color Gamut Liquid Crystal Displays.
- Creator
-
Luo, Zhenyue, Wu, Shintson, Kik, Pieter, Schoenfeld, Winston, Fang, Jiyu, University of Central Florida
- Abstract / Description
-
Liquid crystal display (LCD) has become ubiquitous and indispensable in our daily life. Recently, it faces strong competition from organic light emitting diode (OLED). In order to maintain a strong leader position, LCD camp has an urgent need to enrich the color performance and reduce the power consumption. This dissertation focuses on solving these two emerging and important challenges. In the first part of the dissertation we investigate the quantum dot (QD) technology to improve the both...
Show moreLiquid crystal display (LCD) has become ubiquitous and indispensable in our daily life. Recently, it faces strong competition from organic light emitting diode (OLED). In order to maintain a strong leader position, LCD camp has an urgent need to enrich the color performance and reduce the power consumption. This dissertation focuses on solving these two emerging and important challenges. In the first part of the dissertation we investigate the quantum dot (QD) technology to improve the both the color gamut and the light efficiency of LCD. QD emits saturated color and grants LCD the capability to reproduce color vivid images. Moreover, the QD emission spectrum can be custom designed to match to transmission band of color filters. To fully take advantage of QD's unique features, we propose a systematic modelling of the LCD backlight and optimize the QD spectrum to simultaneously maximize the color gamut and light efficiency. Moreover, QD enhanced LCD demonstrates several advantages: excellent ambient contrast, negligible color shift and controllable white point. Besides three primary LCD, We also present a spatiotemporal four-primary QD enhanced LCD. The LCD's color is generated partially from time domain and partially from spatial domain. As a result, this LCD mode offers 1.5(&)#215; increment in spatial resolution, 2(&)#215; brightness enhancement, slightly larger color gamut and mitigated LC response requirement (~4ms). It can be employed in the commercial TV to meet the challenging Energy star 6 regulation. Besides conventional LCD, we also extend the QD applications to liquid displays and smart lighting devices. The second part of this dissertation focuses on improving the LCD light efficiency. Conventional LCD system has fairly low light efficiency (4%~7%) since polarizers and color filters absorb 50% and 67% of the incoming light respectively. We propose two approaches to reduce the light loss within polarizers and color filters. The first method is a polarization preserving backlight system. It can be combined with linearly polarized light source to boost the LCD efficiency. Moreover, this polarization preserving backlight offers high polarization efficiency (~77.8%), 2.4(&)#215; on-axis luminance enhancement, and no need for extra optics films. The second approach is a LCD backlight system with simultaneous color/polarization recycling. We design a novel polarizing color filter with high transmittance ((>)90%), low absorption loss (~3.3%), high extinction ratio ((>)10,000:1) and large angular tolerance (up to (&)#177;50?). This polarizing color filter can be used in LCD system to introduce the color/polarization recycling and accordingly boost LCD efficiency by ~3 times. These two approaches open new gateway for ultra-low power LCDs. In the final session of this dissertation, we demonstrate a low power and color vivid reflective liquid crystal on silicon (LCOS) display with low viscosity liquid crystal mixture. Compared with commercial LC material, the new LC mixture offers ~4X faster response at 20oC and ~8X faster response at ?20oC. This fast response LC material enables the field-sequential-color (FSC) driving for power saving. It also leads to several attractive advantages: sub-millisecond response time at room temperature, vivid color even at ?20oC, high brightness, excellent ambient contrast ratio, and suppressed color breakup. With this material improvement, LCOS display can be promising for the emerging wearable display market.
Show less - Date Issued
- 2015
- Identifier
- CFE0006225, ucf:51078
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006225
- Title
- TUNNELING CONDUCTANCE CHARACTERIZATION OF A QUANTUM DOT IN THE FRACTIONAL QUANTUM HALL REGIME.
- Creator
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Willard, Douglas, Johnson, Michael, University of Central Florida
- Abstract / Description
-
This work represents a first-principles calculation of the electron tunneling current into quantum dots in the fractional quantum Hall effect regime. The system under consideration consists of an idealized Scanning Tunneling Microscope (STM) tip and a quantum dot with disk geometry and interacting electrons in a transverse magnetic field. Within the context of this model the tunneling current between the STM tip and the dot is examined for spin-polarized electrons at and around a filling...
Show moreThis work represents a first-principles calculation of the electron tunneling current into quantum dots in the fractional quantum Hall effect regime. The system under consideration consists of an idealized Scanning Tunneling Microscope (STM) tip and a quantum dot with disk geometry and interacting electrons in a transverse magnetic field. Within the context of this model the tunneling current between the STM tip and the dot is examined for spin-polarized electrons at and around a filling factor of 1/3. The current expression is based on a second-quantized Hamiltonian in which electrons in the dot are interacting, confined, and restricted to the lowest Landau level, necessary to capture the physics of the fractional quantum Hall effect. The Hamiltonian includes simple approximations for the STM tip and the tip-dot tunneling. An exact analytic expression for the first-order tunneling current is derived using a Green's function approach. To calculate the tunneling current numerically the infinite Hilbert space of the dot is truncated to have a finite dimension within the lowest Landau level. This simplification is appropriate for a low temperature system in the fractional quantum Hall regime because of the finite size of the quantum dot and the large energy gap between Landau levels. The tunneling current is then solved in two steps. First, many-electron energy eigenstates are calculated from the truncated Hamiltonian by numerical diagonalization. This is carried out for varying numbers of electrons N. The energy eigenstates form a set of complete basis states of the system and are used in the expression for the tunneling current. In the second step, the chemical potential in the dot is chosen to select a desired number of electrons and the tunneling current evaluated. We have carried out this program for filling factors near 1/3 while modulating the system parameters of interest to determine functional dependencies.
Show less - Date Issued
- 2011
- Identifier
- CFE0003990, ucf:48677
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003990
- Title
- Coated Quantum Dots: Engineering of Surface Chemistry for Biomedical and Agricultural Applications.
- Creator
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Maxwell, Tyler, Santra, Swadeshmukul, Gesquiere, Andre, Harper, James, Zou, Shengli, Leon, Lorraine, University of Central Florida
- Abstract / Description
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Quantum dots (QDs) are crystalline nanoparticles made from semiconductor material with sizes ranging from 1 to 10 nm in diameter. QDs are attractive fluorophores for bioimaging and sensing due to their size-dependent optical properties, broad absorption bands, high extinction coefficients and superior photostability. The combination of imaging and drug delivery in a single particle can provide valuable information and improve the efficacy of existing treatments. This dissertation highlights...
Show moreQuantum dots (QDs) are crystalline nanoparticles made from semiconductor material with sizes ranging from 1 to 10 nm in diameter. QDs are attractive fluorophores for bioimaging and sensing due to their size-dependent optical properties, broad absorption bands, high extinction coefficients and superior photostability. The combination of imaging and drug delivery in a single particle can provide valuable information and improve the efficacy of existing treatments. This dissertation highlights the use of QDs for biomedical and agricultural applications. Chapter 1 of this dissertation presents a background of QDs and outlines the synthesis methods of producing and functionalizing QDs. A discussion of the advantages and limitations of each method for producing water-soluble QDs and the rationale for the proposed research is also presented. Chapter 2 describes an activatable QD design for tracking of drug delivery for cancer treatment. QDs synthesized by microemulsion (ME) were cross-linked in a one-step procedure. Enhanced binding affinity of the probe to cell lines overexpressing folate receptors was shown through fluorescence microscopy. However, this system is not practical for the large-scale synthesis due to its complexity and can not be translated for clinical development. Chapter 3 presents a sol-gel synthesis method for producing water-soluble QDs utilizing the thiol-based small molecule capping agent as the stabilizer as an alternative to ME technique. This method was designed to be a simple (one-step), cost-effective, and scalable for making both manganese doped CdS and ZnS QDs. QDs were synthesized through sol-gel method with a library of organic thiol coatings and characterized by size, surface charge, stability, and optical properties. These particles were compared to QDs produced from ME synthesis and were found to have similar properties. Chapter 4 reports the sol-gel QDs as slow-release antibiotic delivery system for application as agricultural bactericide. Utilizing electrostatic interactions, the QDs were shown to be capable of improving the leaf adhesion and slowing the rate of release of streptomycin. Chapter 5 presents a summary of the major findings of this research and discusses the future research directions.
Show less - Date Issued
- 2019
- Identifier
- CFE0007681, ucf:52476
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007681
- Title
- QUANTUM DOT BASED MODE-LOCKED SEMICONDUCTOR LASERS AND APPLICATIONS.
- Creator
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Kim, Jimyung, Delfyett, Peter, University of Central Florida
- Abstract / Description
-
In this dissertation, self-assembled InAs/InGaAs quantum dot Fabry-Pérot lasers and mode-locked lasers are investigated. The mode-locked lasers investigated include monolithic and curved two-section devices, and colliding pulse mode-locked diode lasers. Ridge waveguide semiconductor lasers have been designed and fabricated by wet etching processes. Electroluminescence of the quantum dot...
Show moreIn this dissertation, self-assembled InAs/InGaAs quantum dot Fabry-Pérot lasers and mode-locked lasers are investigated. The mode-locked lasers investigated include monolithic and curved two-section devices, and colliding pulse mode-locked diode lasers. Ridge waveguide semiconductor lasers have been designed and fabricated by wet etching processes. Electroluminescence of the quantum dot lasers is studied. Cavity length dependent lasing via ground state and/or excited state transitions is observed from quantum dot lasers and the optical gain from both transitions is measured. Stable optical pulse trains via ground and excited state transitions are generated using a grating coupled external cavity with a curved two-section device. Large differences in the applied reverse bias voltage on the saturable absorber are observed for stable mode-locking from the excited and ground state mode-locking regimes. The optical pulses from quantum dot mode-locked lasers are investigated in terms of chirp sign and linear chirp magnitude. Upchirped pulses with large linear chirp magnitude are observed from both ground and excited states. Externally compressed pulse widths from the ground and excited states are 1.2 ps and 970 fs, respectively. Ground state optical pulses from monolithic mode-locked lasers e.g., two-section devices and colliding pulse mode-locked lasers, are also studied. Transformed limited optical pulses (~4.5 ps) are generated from a colliding pulse mode-locked semiconductor laser. The above threshold linewidth enhancement factor of quantum dot Fabry-Pérot lasers is measured using the continuous wave injection locking method. A strong spectral dependence of the linewidth enhancement factor is observed around the gain peak. The measured linewidth enhancement factor is highest at the gain peak, but becomes lower 10 nm away from the gain peak. The lowest linewidth enhancement factor is observed on the anti-Stokes side. The spectral dependence of the pulse duration from quantum dot based mode-locked lasers is also observed. Shorter pulses and reduced linear chirp are observed on the anti-Stokes side and externally compressed 660 fs pulses are achieved in this spectral regime. A novel clock recovery technique using passively mode-locked quantum dot lasers is investigated. The clock signal (~4 GHz) is recovered by injecting an interband optical pulse train to the saturable absorber section. The excited state clock signal is recovered through the ground state transition and vice-versa. Asymmetry in the locking bandwidth is observed. The measured locking bandwidth is 10 times wider when the excited state clock signal is recovered from the ground state injection, as compared to recovering a ground state clock signal from excited state injection.
Show less - Date Issued
- 2010
- Identifier
- CFE0003295, ucf:48493
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003295
- Title
- Spin Pumping in Lateral Double Quantum Dot Systems.
- Creator
-
Pelton, Sabine, Mucciolo, Eduardo, Ishigami, Marsahir, Leuenberger, Michael, University of Central Florida
- Abstract / Description
-
Electron transport in single lateral quantum dot (QD) and parallel lateral doublequantum dot (DQD) systems is modeled using semiclassical rate equations. The Zeemaneffect, in conjunction with resonant tunneling, is used to select the spin of electronsinvolved in transport. We show adiabatic spin pumping by periodic variation of thesystems' confining parameters, namely the quantum point contacts (QPCs) dictating theboundaries of the dots, and the gate voltage applied to each dot. The...
Show moreElectron transport in single lateral quantum dot (QD) and parallel lateral doublequantum dot (DQD) systems is modeled using semiclassical rate equations. The Zeemaneffect, in conjunction with resonant tunneling, is used to select the spin of electronsinvolved in transport. We show adiabatic spin pumping by periodic variation of thesystems' confining parameters, namely the quantum point contacts (QPCs) dictating theboundaries of the dots, and the gate voltage applied to each dot. The limitations ofadiabatic spin pumping are subsequently examined by counting the average spin pumpedper cycle when frequency and interdot capacitance are adjusted.
Show less - Date Issued
- 2012
- Identifier
- CFE0004334, ucf:49435
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004334
- Title
- MODELING AND DESIGN OF A PHOTONIC CRYSTAL CHIP HOSTING A QUANTUM NETWORK MADE OF SINGLE SPINS IN QUANTUM DOTS THAT INTERACT VIA SINGLE PHOTONS.
- Creator
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Seigneur, Hubert, Schoenfeld, Winston, University of Central Florida
- Abstract / Description
-
In this dissertation, the prospect of a quantum technology based on a photonic crystal chip hosting a quantum network made of quantum dot spins interacting via single photons is investigated. The mathematical procedure to deal with the Liouville-Von Neumann equation, which describes the time-evolution of the density matrix, was derived for an arbitrary system, giving general equations. Using this theoretical groundwork, a numerical model was then developed to study the spatiotemporal dynamics...
Show moreIn this dissertation, the prospect of a quantum technology based on a photonic crystal chip hosting a quantum network made of quantum dot spins interacting via single photons is investigated. The mathematical procedure to deal with the Liouville-Von Neumann equation, which describes the time-evolution of the density matrix, was derived for an arbitrary system, giving general equations. Using this theoretical groundwork, a numerical model was then developed to study the spatiotemporal dynamics of entanglement between various qubits produced in a controlled way over the entire quantum network. As a result, an efficient quantum interface was engineered allowing for storage qubits and traveling qubits to exchange information coherently while demonstrating little error and loss in the process; such interface is indispensable for the realization of a functional quantum network. Furthermore, a carefully orchestrated dynamic control over the propagation of the flying qubit showed high-efficiency capability for on-chip single-photon transfer. Using the optimized dispersion properties obtained quantum mechanically as design parameters, a possible physical structure for the photonic crystal chip was constructed using the Plane Wave Expansion and Finite-Difference Time-Domain numerical techniques, exhibiting almost identical transfer efficiencies in terms of normalized energy densities of the classical electromagnetic field. These promising results bring us one step closer to the physical realization of an integrated quantum technology combining both semiconductor quantum dots and sub-wavelength photonic structures.
Show less - Date Issued
- 2010
- Identifier
- CFE0003433, ucf:48391
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003433
- Title
- ELECTRO-OPTICAL AND ALL-OPTICAL SWITCHING IN MULTIMODE INTERFERENCE WAVEGUIDES INCORPORATING SEMICONDUCTOR NANOSTRUCTURES.
- Creator
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Bickel, Nathan, LiKamWa, Patrick, University of Central Florida
- Abstract / Description
-
The application of epitaxially grown, III-V semiconductor-based nanostructures to the development of electro-optical and all-optical switches is investigated through the fabrication and testing of integrated photonic devices designed using multimode interference (MMI) waveguides. The properties and limitations of the materials are explored with respect to the operation of those devices through electrical carrier injection and optical pumping. MMI waveguide geometry was employed as it offered...
Show moreThe application of epitaxially grown, III-V semiconductor-based nanostructures to the development of electro-optical and all-optical switches is investigated through the fabrication and testing of integrated photonic devices designed using multimode interference (MMI) waveguides. The properties and limitations of the materials are explored with respect to the operation of those devices through electrical carrier injection and optical pumping. MMI waveguide geometry was employed as it offered advantages such as a very compact device footprint, low polarization sensitivity, large bandwidth and relaxed fabrication tolerances when compared with conventional single-mode waveguide formats. The first portion of this dissertation focuses on the characterization of the materials and material processing techniques for the monolithic integration of In0.15Ga0.85As/GaAs self-assembled quantum dots (SAQD) and InGaAsP/InGaAsP multiple quantum wells (MQW). Supplemental methods for post-growth bandgap tuning and waveguide formation were developed, including a plasma treatment process which is demonstrated to reliably inhibit thermally induced interdiffusion of Ga and In atoms in In0.15Ga0.85As/GaAs quantum dots. The process is comparable to the existing approach of capping the SAQD wafer with TiO2, while being simpler to implement along-side companion techniques such as impurity free vacancy disordering. Study of plasma-surface interactions in both wafer structures suggests that the effect may be dependent on the composition of the contact layer. The second portion of this work deals with the design, fabrication, and the testing of MMI switches which are used to investigate the limits of electrical current control when employing SAQD as the active core material. A variable power splitter based on a 3-dB MMI coupler is used to analyze the effects of sub-microsecond electrical current pulses in relation to carrier and thermal nonlinearities. Electrical current controlled switching of the variable power splitter and a tunable 2 x 2 MMI coupler is also demonstrated. The third part of this dissertation explores the response of In0.15Ga0.85As/GaAs SAQD waveguide structures to photogenerated carriers. Also presented is a simple, but effective, design modification to the 2 x 2 MMI cross-coupler switch that allows control over the carrier distribution within the MMI waveguide. This technique is combined with selective-area bandgap tuning to demonstrate a compact, working, all-optical MMI based switch.
Show less - Date Issued
- 2010
- Identifier
- CFE0003220, ucf:48568
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003220
- Title
- ULTRASHORT, HIGH POWER, AND ULTRALOW NOISE MODE-LOCKED OPTICAL PULSE GENERATION USING QUANTUM-DOT SEMICONDUCTOR LASERS.
- Creator
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Choi, Myoung-Taek, Delfyett, Peter, University of Central Florida
- Abstract / Description
-
This dissertation explores various aspects and potential of optical pulse generation based on active, passive, and hybrid mode-locked quantum dot semiconductor lasers with target applications such as optical interconnect and high speed signal processing. Design guidelines are developed for the single mode operation with suppressed reflection from waveguide discontinuities. The device fabrication procedure is explained, followed by characteristics of FP laser, SOA, and monolithic two-section...
Show moreThis dissertation explores various aspects and potential of optical pulse generation based on active, passive, and hybrid mode-locked quantum dot semiconductor lasers with target applications such as optical interconnect and high speed signal processing. Design guidelines are developed for the single mode operation with suppressed reflection from waveguide discontinuities. The device fabrication procedure is explained, followed by characteristics of FP laser, SOA, and monolithic two-section devices. Short pulse generation from an external cavity mode-locked QD two-section diode laser is studied. High quality, sub-picosecond (960 fs), high peak power (1.2 W) pulse trains are obtained. The sign and magnitude of pulse chirp were measured for the first time. The role of the self-phase modulation and the linewidth enhancement factor in QD mode-locked lasers is addressed. The noise performance of two-section mode-locked lasers and a SOA-based ring laser was investigated. Significant reduction of the timing jitter under hybrid mode-locked operation was achieved owing to more than one order of magnitude reduction of the linewidth in QD gain media. Ultralow phase noise performance (integrated timing jitter of a few fs at a 10 GHz repetition rate) was demonstrated from an actively mode-locked unidirectional ring laser. These results show that quantum dot mode-locked lasers are strong competitors to conventional semiconductor lasers in noise performance. Finally we demonstrated an opto-electronic oscillator (OEO) and coupled opto-electronic oscillators (COEO) which have the potential for both high purity microwave and low noise optical pulse generation. The phase noise of the COEO is measured by the photonic delay line frequency discriminator method. Based on this study we discuss the prospects of the COEO as a low noise optical pulse source.
Show less - Date Issued
- 2006
- Identifier
- CFE0001410, ucf:47068
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001410
- Title
- CONTROLLED ASSEMBLY AND ELECTRONIC TRANSPORT STUDIES OF SOLUTION PROCESSED CARBON NANOTUBE DEVICES.
- Creator
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Stokes, Paul, Khondaker, Saiful I., University of Central Florida
- Abstract / Description
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Developing techniques for the parallel fabrication of Complementary Metal Oxide Semiconductor (CMOS) compatible single walled carbon nanotube (SWNT) electronic devices is of great importance for nanoelectronic applications. In this thesis, solution processed SWNTs in combination with AC dielectrophoresis (DEP) were utilized to fabricate CMOS compatible SWNT field effect transistors (FETs) and single electron transistors (SETs) with high yield and their detailed electronic transport properties...
Show moreDeveloping techniques for the parallel fabrication of Complementary Metal Oxide Semiconductor (CMOS) compatible single walled carbon nanotube (SWNT) electronic devices is of great importance for nanoelectronic applications. In this thesis, solution processed SWNTs in combination with AC dielectrophoresis (DEP) were utilized to fabricate CMOS compatible SWNT field effect transistors (FETs) and single electron transistors (SETs) with high yield and their detailed electronic transport properties were studied. Solution processing of SWNTs is attractive not only for the high throughput and parallel manufacturing of SWNT devices but also due to the ease of processing at room temperature, and compatibility with various substrates. However, it is generally believed that solution processing introduces defects and can degrade electronic transport properties. The results presented in this dissertation show that devices assembled from stable solutions of SWNT can give rise to high quality FET devices at room temperature and relatively clean SET behavior at low temperature. This is a strong indication that there are no or few intrinsic defects in the SWNTs. The dissertation will also discuss the controlled fabrication of size tunable SWNT SET devices using a novel mechanical template approach which offers a route towards the parallel fabrication of room temperature SET devices. The approach is based on the formation of two tunnel barriers created in a SWNT a distance L apart by bending the SWNT at the edge of a local Al/Al2O3 bottom gate. The local gate tunes individual electrons one by one in the device and defines the size of the quantum dot though its width. By tuning both the back gate and local gate, it is possible to tune the transparency of tunnel barriers and the size of the quantum dot further. Detailed transport spectroscopy of these devices will be presented.
Show less - Date Issued
- 2010
- Identifier
- CFE0003061, ucf:48310
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003061
- Title
- NEW LASER TECHNOLOGIES: ANALYSIS OF QUANTUM DOT ANDLITHOGRAPHIC LASER DIODES.
- Creator
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Demir, Abdullah, Deppe, Dennis, University of Central Florida
- Abstract / Description
-
The first part of this dissertation presents a comprehensive study of quantum dot (QD) lasers threshold characteristics. The threshold temperature dependence of a QD laser diode is studied in different limits of p-doping, hole level spacing and inhomogeneous broadening. Theoretical analysis shows that the threshold current of a QD laser in the limit of uniform QDs is not temperature independent and actually more temperature sensitive than the quantum well laser. The results also explain the...
Show moreThe first part of this dissertation presents a comprehensive study of quantum dot (QD) lasers threshold characteristics. The threshold temperature dependence of a QD laser diode is studied in different limits of p-doping, hole level spacing and inhomogeneous broadening. Theoretical analysis shows that the threshold current of a QD laser in the limit of uniform QDs is not temperature independent and actually more temperature sensitive than the quantum well laser. The results also explain the experimental trends of negative characteristic temperature observed in QD lasers and clarify how the carrier distribution mechanisms inside and among the QDs affect the threshold temperature dependence of a QD laser diode. The second part is on the experimental demonstration of lithographic lasers. Today's vertical-cavity surface-emitting lasers (VCSELs) based on oxide-aperture suffer from serious problems such as heat dissipation, internal strain, reliability, uniformity and size scaling. The lithographic laser provides solutions to all these problems. The transverse mode and cavity are defined using only lithography and epitaxial crystal growth providing simultaneous mode- and current-confinement. Eliminating the oxide aperture is shown to reduce the thermal resistance of the device and leading to increased power density in smaller lasers. When it is combined with better mode matching to gain for smaller devices, high output power density of 58 kW/cm2 is possible for a 3 micron VCSEL with threshold current of 260 microamperes. These VCSELs also have grating-free single-mode single-polarization emission. The demonstration of lithographic laser diodes with good scaling properties is therefore an important step toward producing ultra-small size laser diodes with high output power density, high speed, high manufacturability and high reliability. Lithographic VCSELs ability to control size lithographically in a strain-free, high efficiency device is a major milestone in VCSEL technology.
Show less - Date Issued
- 2010
- Identifier
- CFE0003304, ucf:48494
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003304
- Title
- Semiconductor Laser Based on Thermoelectrophotonics.
- Creator
-
Liu, Xiaohang, Deppe, Dennis, Vanstryland, Eric, Dogariu, Aristide, Bass, Michael, University of Central Florida
- Abstract / Description
-
This dissertation presents to our knowledge the first demonstration of a quantum well (QW) laser monolithically integrated with internal optical pump based on a light emitting diode (LED). The LED with high efficiency is operated in a thermoelectrophotonic (TEP) regime for which it can absorb both its own emitted light and heat. The LED optical pump can reduce internal optical loss in the QW laser, and enables monolithically integrated TEP heat pumps to the semiconductor laser. The design,...
Show moreThis dissertation presents to our knowledge the first demonstration of a quantum well (QW) laser monolithically integrated with internal optical pump based on a light emitting diode (LED). The LED with high efficiency is operated in a thermoelectrophotonic (TEP) regime for which it can absorb both its own emitted light and heat. The LED optical pump can reduce internal optical loss in the QW laser, and enables monolithically integrated TEP heat pumps to the semiconductor laser. The design, growth and fabrication processes of the laser chip are discussed, and its experimental data is presented. In order to further increase the TEP laser efficiency the development of QDs as the active region for TEP edge emitting laser (EEL) is studied. The usage of QD as TEP laser's active region is significant in terms of its low threshold current density, low internal optical loss and high reliability, which are mainly due to low transparency in QD laser. The crystal growth of self-organized QDs in molecular beam epitaxial (MBE) system and characterization of QDs are mentioned. The design, growth, processing and fabrication of a QD laser structure are detailed. The characteristics of laser devices with different cavity length are reported. QD active regions with different amount of material are grown to improve the active region performance. Theoretical calculations based on material parameters and semiconductor physics indicate that with proper design, the combination of high efficiency LED in TEP regime with a QD laser can result in the integrated laser chip power conversion efficiency exceeding unity.
Show less - Date Issued
- 2014
- Identifier
- CFE0005369, ucf:50477
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005369
- Title
- COMPUTATIONAL STUDY OF THE NEAR FIELD SPONTANEOUS CREATION OF PHOTONIC STATES COUPLED TO FEW LEVEL SYSTEMS.
- Creator
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Tafur, Sergio, Leuenberger, Michael, University of Central Florida
- Abstract / Description
-
Models of the spontaneous emission and absorption of photons coupled to the electronic states of quantum dots, molecules, N-V (single nitrogen vacancy) centers in diamond, that can be modeled as artificial few level atoms, are important to the development of quantum computers and quantum networks. A quantum source modeled after an effective few level system is strongly dependent on the type and coupling strength the allowed transitions. These selection rules are subject to the Wigner-Eckert...
Show moreModels of the spontaneous emission and absorption of photons coupled to the electronic states of quantum dots, molecules, N-V (single nitrogen vacancy) centers in diamond, that can be modeled as artificial few level atoms, are important to the development of quantum computers and quantum networks. A quantum source modeled after an effective few level system is strongly dependent on the type and coupling strength the allowed transitions. These selection rules are subject to the Wigner-Eckert theorem which specifies the possible transitions during the spontaneous creation of a photonic state and its subsequent emission. The model presented in this dissertation describes the spatio-temporal evolution of photonic states by means of a Dirac-like equation for the photonic wave function within the region of interaction of a quantum source. As part of this aim, we describe the possibility to shift from traditional electrodynamics and quantum electrodynamics, in terms of electric and magnetic fields, to one in terms of a photonic wave function and its operators. The mapping between these will also be presented herein. It is further shown that the results of this model can be experimentally verified. The suggested method of verification relies on the direct comparison of the calculated density matrix or Wigner function, associated with the quantum state of a photon, to ones that are experimentally reconstructed through optical homodyne tomography techniques. In this non-perturbative model we describe the spontaneous creation of photonic state in a non-Markovian limit which does not implement the Weisskopf-Wigner approximation. We further show that this limit is important for the description of how a single photonic mode is created from the possibly infinite set of photonic frequencies $\nu_k$ that can be excited in a dielectric-cavity from the vacuum state. We use discretized central-difference approximations to the space and time partial derivatives, similar to finite-difference time domain models, to compute these results. The results presented herein show that near field effects need considered when describing adjacent quantum sources that are separated by distances that are small with respect to the wavelength of their spontaneously created photonic states. Additionally, within the future scope of this model,we seek results in the Purcell and Rabi regimes to describe enhanced spontaneous emission events from these few-level systems, as embedded in dielectric cavities. A final goal of this dissertation is to create novel computational and theoretical models that describe single and multiple photon states via single photon creation and annihilation operators.
Show less - Date Issued
- 2011
- Identifier
- CFE0003881, ucf:48739
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003881
- Title
- EXPERIMENTAL AND THEORETICAL STUDY OF THE OPTICAL PROPERTIES OF SEMICONDUCTOR QUANTUM DOTS.
- Creator
-
Nootz, Gero, Cuenya , Beatriz, University of Central Florida
- Abstract / Description
-
The aim of this dissertation is to gain a better understanding of the unique electronic structure of lead salt quantum dots (QDs) and its influences on the nonlinear optical (NLO) properties as well as the time dynamics of the photogenerated charge carriers. A variety of optical techniques such as Z-scan, two-photon excited fluorescence and time-resolved pump probe spectroscopy are used to measure these properties. The one-photon as well as the degenerate and nondegenerate two-photon...
Show moreThe aim of this dissertation is to gain a better understanding of the unique electronic structure of lead salt quantum dots (QDs) and its influences on the nonlinear optical (NLO) properties as well as the time dynamics of the photogenerated charge carriers. A variety of optical techniques such as Z-scan, two-photon excited fluorescence and time-resolved pump probe spectroscopy are used to measure these properties. The one-photon as well as the degenerate and nondegenerate two-photon absorption (2PA) spectra are measured and the electronic wave functions from a four-band envelope function formalism are used to model the results. We observe local maxima in the 2PA spectra for QD samples of many different sizes at energies where only 1PA is predicted by the model. This is similar to the previously measured transitions in the 1PA spectra which are not predicted by the model but accrue at the energies of the two-photon allowed transitions. Most importantly we observe 2PA peaks for all samples at the energy of the first one-photon allowed transition. This result can only be understood in terms of symmetry breaking and therefore is strong evidence that other transitions, not predicted by the model if the selection rules are left intact, also have the origin in the lifted spatial symmetry of the wave functions. On the other hand, the uniquely symmetric eigenenergies of these quantum-confined energy states in the conduction and valance bands explain the observed trend toward larger two-photon cross-sections as the quantum confinement is increased in smaller QDs. Moreover, this unique feature is shown to reduce the possible relaxation channels for photoexcited carriers, which is confirmed experimentally by the reduced carrier relaxation rate as compared to CdSe QDs which lack this symmetry. Carrier multiplication (CM), a process in which several electrons are excited by the absorption of a single photon is studied in PbS QDs. We show that for PbS QDs with radius smaller than 2.5 nm the parameters of CM get very close to the theoretical optimum. Next-generation solar cells operating under these ideal conditions could potentially have conversion efficiency of up to 42%. This compares favorably to the 30% efficiency limit of a single junction silicon solar cell.
Show less - Date Issued
- 2010
- Identifier
- CFE0003396, ucf:48413
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003396
- Title
- WAVELENGTH-DIVISION-MULTIPLEXED TRANSMISSION USING SEMICONDUCTOR OPTICAL AMPLIFIERS AND ELECTRONIC IMPAIRMENT COMPENSATION.
- Creator
-
LI, XIAOXU, Li, Guifang, University of Central Florida
- Abstract / Description
-
Over the last decade, rapid growth of broadband services necessitated research aimed at increasing transmission capacity in fiber-optic communication systems. Wavelength division multiplexing (WDM) technology has been widely used in fiber-optic systems to fully utilize fiber transmission bandwidth. Among optical amplifiers for WDM transmission, semiconductor optical amplifier (SOA) is a promising candidate, thanks to its broad bandwidth, compact size, and low cost. In transmission systems...
Show moreOver the last decade, rapid growth of broadband services necessitated research aimed at increasing transmission capacity in fiber-optic communication systems. Wavelength division multiplexing (WDM) technology has been widely used in fiber-optic systems to fully utilize fiber transmission bandwidth. Among optical amplifiers for WDM transmission, semiconductor optical amplifier (SOA) is a promising candidate, thanks to its broad bandwidth, compact size, and low cost. In transmission systems using SOAs, due to their large noise figures, high signal launching powers are required to ensure reasonable optical signal-to-noise ratio of the received signals. Hence the SOAs are operated in the saturation region and the signals will suffer from SOA impairments including self-gain modulation, self-phase modulation, and inter channel crosstalk effects such as cross-gain modulation, cross-phase modulation, and four-wave mixing in WDM. One possibility to circumvent these nonlinear impairments is to use constant-intensity modulation format in the 1310 nm window where dispersion is also negligible. In this dissertation, differential phase-shift keying (DPSK) WDM transmission in the 1310 nm window using SOAs was first considered to increase the capacity of existing telecommunication network. A WDM transmission of 4 × 10 Gbit/s DPSK signals over 540 km standard single mode fiber (SSMF) using cascaded SOAs was demonstrated in a recirculating loop. In order to increase the transmission reach of such WDM systems, those SOA impairments must be compensated. To do so, an accurate model for quantum-dot (QD) SOA must be established. In this dissertation, the QD-SOA was modeled with the assumption of overall charge neutrality. Static gain was calculated. Optical modulation response and nonlinear phase noise were studied semi-analytically based on small-signal analysis. The quantitative studies show that an ultrafast gain recovery time of ~0.1 ps can be achieved when QD-SOAs are under high current injection, which leads to high saturation output power. However more nonlinear phase noise is induced when the QD-SOAs are used in the transmission systems operating at 10 Gbit/s or 40 Gbit/s. Electronic post-compensation for SOA impairments using coherent detection and digital signal processing (DSP) was investigated next in this dissertation. An on-off keying transmission over 100 km SSMF using three SOAs at 1.3 um were demonstrated experimentally with direct detection and SOA impairment compensation. The data pattern effect of the signal was compensated effectively. Both optimum launching power and Q-factor were improved by 8 dB. For advanced modulation formats involving phase modulation or in transmission windows with large dispersion, coherent detection must be used and fiber impairments in WDM systems need to be compensated as well. The proposed fiber impairment compensation is based on digital backward propagation. The corresponding DSP implementation was described and the required calculations as well as system latency were derived. Finally joint SOA and fiber impairment compensations were experimentally demonstrated for an amplitude-phase-shift keying transmission.
Show less - Date Issued
- 2009
- Identifier
- CFE0002932, ucf:47960
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002932
- Title
- LONG CAVITY QUANTUM DOT LASER DIODE AND MONOLITHIC PASSIVELY MODE-LOCKED OPERATION.
- Creator
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Shavitranuruk, K, Deppe, Dennis, University of Central Florida
- Abstract / Description
-
Advantage of the single QD active layer is its potential for very low threshold current density, which in turn can produce low internal optical loss. The low threshold current density and low internal loss thus enable a significant increase in laser diode cavity length. Because of the importance of the threshold current density in heatsinking, future technology of broad-area monolithic laser diodes can be implemented. The dissertation describes the development and the unique characteristics...
Show moreAdvantage of the single QD active layer is its potential for very low threshold current density, which in turn can produce low internal optical loss. The low threshold current density and low internal loss thus enable a significant increase in laser diode cavity length. Because of the importance of the threshold current density in heatsinking, future technology of broad-area monolithic laser diodes can be implemented. The dissertation describes the development and the unique characteristics of single QD active layer laser with long cavity. The data are presented on single layer QD laser diodes that reach threshold current densities values of 11.7 A/cm2 in a p-up mounted 2 cm long cavity and as low as 10 A/cm2, with CW output power of 2 W in a p-down mounted 1.6 cm long cavity. The 8.8 A/cm2 in a p-down mounted 2 cm long cavity is reported. To our knowledge the value 8.8 A/cm2 is the lowest threshold current density ever reported for a room temperature laser diode. These single layer QD laser diodes reach an internal loss of ~0.25 cm-1, which is also the lowest ever reported for a room temperature laser diode. These unique characteristics of single layer QD and laser diode size are potentially promising for the monolithic mode-locked laser because of relatively high peak power with a low repetition rate that is on the order of a few GHz, which can be the novel device for external clocking in the optical interconnect applications. In this dissertation, the stable optical pulse train in a 40 µm wide stripe with a repetition rate of 3.75 GHz with 1.1 cm cavity length through the passive mode-locked onto the monolithic two-section device fabricated from this single layer QD laser is observed.
Show less - Date Issued
- 2010
- Identifier
- CFE0003145, ucf:48646
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003145
- Title
- On-Chip Optical Stabilization of High-Speed Mode-locked Quantum Dot Lasers for Next Generation Optical Networks.
- Creator
-
Ardey, Abhijeet, Delfyett, Peter, Chow, Lee, Peale, Robert, Likamwa, Patrick, University of Central Florida
- Abstract / Description
-
Monolithic passively mode-locked colliding pulse semiconductor lasers generating pico- to sub-picosecond terahertz optical pulse trains are promising sources for future applications in ultra-high speed data transmission systems and optical measurements. However, in the absence of external synchronization, these passively mode-locked lasers suffer from large amplitude and timing jitter instabilities resulting in broad comb linewidths, which precludes many applications in the field of coherent...
Show moreMonolithic passively mode-locked colliding pulse semiconductor lasers generating pico- to sub-picosecond terahertz optical pulse trains are promising sources for future applications in ultra-high speed data transmission systems and optical measurements. However, in the absence of external synchronization, these passively mode-locked lasers suffer from large amplitude and timing jitter instabilities resulting in broad comb linewidths, which precludes many applications in the field of coherent communications and signal processing where a much narrower frequency line set is needed. In this dissertation, a novel quantum dot based coupled cavity laser is presented, where for the first time, four-wave mixing (FWM) in the monolithically integrated saturable absorber is used to injection lock a monolithic colliding pulse mode-locked (CPM) laser with a mode-locked high-Q ring laser. Starting with a passively mode-locked master ring laser, a stable 30 GHz optical pulse train is generated with more than 10 dB reduction in the RF noise level at 20 MHz offset and close to 3-times reduction in the average optical linewidth of the injection locked CPM slave laser. The FWM process is subsequently verified experimentally and conclusively shown to be the primary mechanism responsible for the observed injection locking. Other linear scattering effects are found to be negligible, as predicted in the orthogonal waveguide configuration. The novel injection locking technique is further exploited by employing optical hybrid mode-locking and increasing the Q of the master ring cavity, to realize an improved stabilization architecture. Dramatic reduction is shown with more than 14-times reduction in the photodetected beat linewidth and almost 5-times reduction in the optical linewidth of the injection locked slave laser with generation of close to transform limited pulses at ~ 30 GHz. These results demonstrate the effectiveness of the novel injection locking technique for an all-on-chip stability transfer and provides a new way of stabilizing monolithic optical pulse sources for applications in future high speed optical networks.
Show less - Date Issued
- 2014
- Identifier
- CFE0005299, ucf:50518
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005299
- Title
- Fluorescence Lifetime Imaging and Spectroscopy Aided Tracking of ZnO and CdS:Mn/ZnS/ N-acetyl cysteine (NAC) Quantum Dots in Citrus Plants.
- Creator
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Washington, Torus, Gesquiere, Andre, Rajaraman, Swaminathan, Zhai, Lei, University of Central Florida
- Abstract / Description
-
In this thesis, we present an efficacious way of tracking nanoparticle movement in plant tissue through the use of fluorescence lifetime imaging (FLIM) and spectroscopy as well as a review of nanoparticle uptake in plants and the proposed mechanisms governing them. Given the increasing number of nanomaterials in agriculture and society as a whole, proper imaging tools and proactive measures must be taken to track nanoparticle movement in plant tissues and create infrastructure and products to...
Show moreIn this thesis, we present an efficacious way of tracking nanoparticle movement in plant tissue through the use of fluorescence lifetime imaging (FLIM) and spectroscopy as well as a review of nanoparticle uptake in plants and the proposed mechanisms governing them. Given the increasing number of nanomaterials in agriculture and society as a whole, proper imaging tools and proactive measures must be taken to track nanoparticle movement in plant tissues and create infrastructure and products to keep things sustainable and safe. Herein we report a ZnO comparable nanoparticle(-) a CdS:Mn/ZnS/ N-acetyl cysteine (NAC) quantum dot(-) which boasts longer lifetimes and suitable fluorescent properties above ZnO to properly delineate from plant tissue fluorescence of chlorophyll and cinnamic acids. In addition to FLIM mapping, quantum dot localization in plant vascular tissue was clearly seen and confirmed via characteristic emission spectra and time correlated single photon counting decay curves (TCSPC). Most quantum dots were seen to reside in the xylem. Plant age and structure was seen to affect uptake. QD size likely restricted extensive translocation. Inhibitive effects of QDs were likely water and mechanical stress. We surmise that travel of the cadmium quantum dots up the leaf and branch plant tissues is likely most governed by diffusion as the quantum dots bound to the cell structures create a diffusion gradient which aids travel up the leaf.
Show less - Date Issued
- 2017
- Identifier
- CFE0006820, ucf:51772
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006820
- Title
- Photoactivatable Organic and Inorganic Nanoparticles in Cancer Therapeutics and Biosensing.
- Creator
-
Mathew, Mona, Gesquiere, Andre, Hickman, James, Ye, Jingdong, Campiglia, Andres, Schoenfeld, Winston, University of Central Florida
- Abstract / Description
-
In photodynamic therapy a photosensitizer drug is administered and is irradiated with light. Upon absorption of light the photosensitizer goes into its triplet state and transfers energy or an electron to oxygen to form reactive oxygen species (ROS). These ROS react with biomolecules in cells leading to cell damage and cell death. PDT has interested many researchers because of its non-invasiveness as compared to surgery, it leaves little to no scars, it is time and cost effective, it has...
Show moreIn photodynamic therapy a photosensitizer drug is administered and is irradiated with light. Upon absorption of light the photosensitizer goes into its triplet state and transfers energy or an electron to oxygen to form reactive oxygen species (ROS). These ROS react with biomolecules in cells leading to cell damage and cell death. PDT has interested many researchers because of its non-invasiveness as compared to surgery, it leaves little to no scars, it is time and cost effective, it has potential for targeted treatment, and can be repeated as needed. Different photosensitizers such as porphyrines, chlorophylls, and dyes have been used in PDT to treat various cancers, skin diseases, aging and sun-damaged skin. These second generation sensitizers have yielded reduced skin sensitivity and improved extinction coefficients (up to ~ 105 L mol-1 cm-1). While PDT based on small molecule photosensitizers has shown great promise, several problems remain unsolved. The main issues with current sensitizers are (i) hydrophobicity leading to aggregation in aqueous media resulting in reduced efficacy and potential toxicity, (ii) dark toxicity of photosensitizers, (iii) non-selectivity towards malignant tissue resulting in prolonged cutaneous photosensitivity and damage to healthy tissue, (iv) limited light absorption efficiency, and (v) a lack of understanding of where the photosensitizer ends up in the tissue. In this dissertation research program, these issues were addressed by the development of conducting polymer nanoparticles as a next generation of photosensitizers. This choice was motivated by the fact that conducting polymers have large extinction coefficients ((>) 107 L mol-1 cm-1), are able to undergo intersystem crossing to the triplet state, and have triplet energies that are close to that of oxygen. It was therefore hypothesized that such polymers could be effective at generating ROS due to the large excitation rate that can be generated. Conducting polymer nanoparticles (CPNPs) composed of the conducting polymer poly[2-methoxy-5-(2-ethylhexyl-oxy)-p-phenylenevinylene] (MEH-PPV) were fabricated and studied in-vitro for their potential in PDT application. Although not fully selective, the nanoparticles exhibited a strong bias to the cancer cells. The formation of ROS was proven in-vitro by staining of the cells with CellROX Green Reagent, after which PDT results were quantified by MTT assays. Cell mortality was observed to scale with nanoparticle dosage and light dosage. Based on these promising results the MEH-PPV nanoparticles were developed further to allow for surface functionalization, with the aim of targeting these NPs to cancer cell lines. For this work targeting of cancers that overexpress folate receptors (FR) were considered. The functionalized nanoparticles (FNPs) were studied in OVCAR3 (ovarian cancer cell line) as FR+, MIA PaCa2 (pancreatic cell line) as FR-, and A549 (lung cancer cell line) having marginal FR expression. Complete selectivity of the FNPs towards the FR+ cell line was found. Quantification of PDT results by MTS assays and flow cytometry show that PDT treatment was fully selective to the FR+ cell line (OVCAR3). No cell mortality was observed for the other cell lines studied here within experimental error. Finally, the issue of confirming and quantifying small molecule drug delivery to diseased tissue was tackled by developing quantum dot (Qdot) biosensors with the aim of achieving fluorescence reporting of intracellular small molecule/drug delivery. For fluorescence reporting prior expertise in control of the fluorescence state of Qdots was employed, where redox active ligands can place the Qdot in a quenched OFF state. Ligand attachment was accomplished by disulfide linker chemistry. This chemistry is reversible in the presence of sulfur reducing biomolecules, resulting in Qdots in a brightly fluorescent ON state. Glutathione (GSH) is such a biomolecule that is present in the intracellular environment. Experimental in-vitro data shows that this design was successfully implemented.
Show less - Date Issued
- 2014
- Identifier
- CFE0005839, ucf:50923
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005839
