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- Title
- INTEGRATED INP PHOTONIC SWITCHES.
- Creator
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May-Arrioja, Daniel, LiKamWa, Patrick, University of Central Florida
- Abstract / Description
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Photonic switches are becoming key components in advanced optical networks because of the large variety of applications that they can perform. One of the key advantages of photonic switches is that they redirect or convert light without having to make any optical to electronic conversions and vice versa, thus allowing networking functions to be lowered into the optical layer. InP-based switches are particularly attractive because of their small size, low electrical power consumption, and...
Show morePhotonic switches are becoming key components in advanced optical networks because of the large variety of applications that they can perform. One of the key advantages of photonic switches is that they redirect or convert light without having to make any optical to electronic conversions and vice versa, thus allowing networking functions to be lowered into the optical layer. InP-based switches are particularly attractive because of their small size, low electrical power consumption, and compatibility with integration of laser sources, photo-detectors, and electronic components. In this dissertation the development of integrated InP photonic switches using an area-selective zinc diffusion process has been investigated. The zinc diffusion process is implemented using a semi-sealed open-tube diffusion technique. The process has proven to be highly controllable and reproducible by carefully monitoring of the diffusion parameters. Using this technique, isolated p-n junctions exhibiting good I-V characteristics and breakdown voltages greater than 10 V can be selectively defined across a semiconductor wafer. A series of Mach-Zehnder interferometric (MZI) switches/modulators have been designed and fabricated. Monolithic integration of 1x2 and 2x2 MZI switches has been demonstrated. The diffusion process circumvents the need for isolation trenches, and hence optical losses can be significantly reduced. An efficient optical beam steering device based on InGaAsP multiple quantum wells is also demonstrated. The degree of lateral current spreading is easily regulated by controlling the zinc depth, allowing optimization of the injected currents. Beam steering over a 21 microns lateral distance with electrical current values as low as 12.5 mA are demonstrated. Using this principle, a reconfigurable 1x3 switch has been implemented with crosstalk levels better than -17 dB over a 50 nm wavelength range. At these low electrical current levels, uncooled and d.c. bias operation is made feasible. The use of multimode interference (MMI) structures as active devices have also been investigated. These devices operate by selective refractive index perturbation on very specific areas within the MMI structure, and this is again realized using zinc diffusion. Several variants such as a compact MMI modulator that is as short as 350 µm, a robust 2x2 photonic switch and a tunable MMI coupler have been demonstrated.
Show less - Date Issued
- 2006
- Identifier
- CFE0001368, ucf:47007
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001368
- Title
- DESIGN AND FABRICATION OF SPACE VARIANT MICRO OPTICAL ELEMENTS.
- Creator
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Srinivasan, Pradeep, LiKamWa, Patrick, University of Central Florida
- Abstract / Description
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A wide range of applications currently utilize conventional optical elements to individually transform the phase, polarization, and spectral transmission/reflection of the incident radiation to realize the desired system level function. The material properties and the feasibility of fabrication primarily impact the device and system functionality that can be realized. With the advancement in micro/nano patterning, growth, deposition and etching technology, devices with novel and multiplexed...
Show moreA wide range of applications currently utilize conventional optical elements to individually transform the phase, polarization, and spectral transmission/reflection of the incident radiation to realize the desired system level function. The material properties and the feasibility of fabrication primarily impact the device and system functionality that can be realized. With the advancement in micro/nano patterning, growth, deposition and etching technology, devices with novel and multiplexed optical functionalities have become feasible. As a result, it has become possible to engineer the device response in the near and far field by controlling the phase, polarization or spectral response at the micro scale. One of the methods that have been explored to realize unique optical functionalities is by varying the structural properties of the device as a function of spatial location at the sub-micron scale across the device aperture. Spatially varying the structural parameters of these devices is analogous to local modifications of the material properties. In this dissertation, the optical response of interference transmission filters, guided mode resonance reflection filters, and diffraction gratings operated in Littrow condition with strategically introduced spatial variation have been investigated. Spatial variations in optical interference filters were used to demonstrate wavelength tunable spatial filters. The effect was realized by integrating diffractive and continuous phase functions on the defect layer of a one-dimensional photonic crystal structure. Guided mode resonance filters are free space optical filters that provide narrow spectral reflection by combining grating and waveguide dispersion effects. Frequency dependent spatial reflection profiles were achieved by spatially varying the grating fill fraction in designed contours. Diffraction gratings with space variant fill fractions operating in Littrow condition were used to provide graded feedback profiles to improve the beam quality and spatial brightness of broad area diode lasers. The fabrication of space variant structures is challenging and has been accomplished primarily by techniques such as ruling, electron beam writing or complex deposition methods. In order to vary the desired structural parameter in a designed manner, a novel technique for the fabrication of space variant structures using projection lithography with a fidelity that rivals any of the current technologies was also developed as a part of this work. The devices exhibit wavelength dependent beam shaping properties in addition to spatial and spectral filtering and have potential applications in advanced imaging systems, graded reflectivity laser mirrors, and engineered illumination. The design, modeling, microfabrication and experimental characterization of space variant micro optical elements with novel optical functionalities are presented.
Show less - Date Issued
- 2009
- Identifier
- CFE0002843, ucf:48066
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002843
- Title
- INTEGRATED OPTICAL SPR (SURFACE PLASMON RESONANCE) SENSOR BASED ON OPTOELECTRONIC PLATFORM.
- Creator
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Bang, Hyungseok, LiKamWa, Patrick, University of Central Florida
- Abstract / Description
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Current major demands in SPR sensor development are system miniaturization and throughput improvement. Structuring an array of integrated optical SPR sensor heads on a semiconductor based optoelectronic platform could be a promising solution for those issues, since integrated optical waveguides have highly miniaturized dimension and the optoelectronic platform enables on-chip optical-to-electrical signal conversion. Utilizing a semiconductor based platform to achieve optoelectronic...
Show moreCurrent major demands in SPR sensor development are system miniaturization and throughput improvement. Structuring an array of integrated optical SPR sensor heads on a semiconductor based optoelectronic platform could be a promising solution for those issues, since integrated optical waveguides have highly miniaturized dimension and the optoelectronic platform enables on-chip optical-to-electrical signal conversion. Utilizing a semiconductor based platform to achieve optoelectronic functionality poses requirements to the senor head; the sensor head needs to have reasonably small size while it should have reasonable sensitivity and fabrication tolerance. This research proposes a novel type of SPR sensor head and demonstrates a fabricated device with an array of integrated optical SPR sensor heads endowed with optoelectronic functionality. The novel integrated optical SPR sensor head relies on mode conversion efficiency for its operational principle. The beauty of this type of sensor head is it can produce clear contrast in SPR spectrum with a highly miniaturized and simple structure, in contrast to several-millimeter-scale conventional absorption type or interferometer type sensor heads. The integrated optical SPR sensor with optoelectronic functionality has been realized by structuring a dielectric waveguide based SPR sensor head on a photodetector-integrated semiconductor substrate. A large number of unit sensors have been fabricated on a substrate with a batch fabrication process, which promises a high throughput SPR sensor system or low-priced disposable sensors.
Show less - Date Issued
- 2008
- Identifier
- CFE0002312, ucf:47841
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002312
- Title
- Non-Hermitian Optics.
- Creator
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Ulhassan, Absar, Christodoulides, Demetrios, Khajavikhan, Mercedeh, Likamwa, Patrick, Kaup, David, University of Central Florida
- Abstract / Description
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From the viewpoint of quantum mechanics, a system must always be Hermitian since all its corresponding eigenvalues must be real. In contrast, the eigenvalues of open systems-unrestrained because of either decay or amplification-can be in general complex. Not so long ago, a certain class of non-Hermitian Hamiltonians was discovered that could have a completely real eigenvalue spectrum. This special class of Hamiltonians was found to respect the property of commutation with the parity-time (PT)...
Show moreFrom the viewpoint of quantum mechanics, a system must always be Hermitian since all its corresponding eigenvalues must be real. In contrast, the eigenvalues of open systems-unrestrained because of either decay or amplification-can be in general complex. Not so long ago, a certain class of non-Hermitian Hamiltonians was discovered that could have a completely real eigenvalue spectrum. This special class of Hamiltonians was found to respect the property of commutation with the parity-time (PT) operator. Translated into optics, this implies a balance between regions exhibiting gain and loss. Traditionally, loss has been perceived as a foe in optics and something that needs to be avoided at all costs. As we will show, when used in conjunction with gain, the presence of loss can lead to a host of counterintuitive outcomes in such non-Hermitian configurations that would have been otherwise unattainable in standard arrangements. We will study PT symmetric phase transitions in various optical settings that include semiconductor microrings and coupled fiber cavities, and show how they can allow mode-selectivity in lasers. One of the key outcomes of this effort was the realization of higher order degeneracies in a three-cavity laser configuration that can exhibit orders-of-magnitude larger sensitivity to external perturbations. We will also consider systems that display nonlinear effects such as gain saturation, thus allowing novel phase transitions. Some interesting properties associated with degeneracies in non-Hermitian settings will be investigated as well. Such degeneracies, called exceptional points (EPs), are much more drastic compared to standard degeneracies of eigenvalues because the corresponding eigenvectors also coalesce, which in turn reduces the dimensionality of the phase space. We will show that dynamic parameter contours enclosing or close to EPs can lead to a robust chiral mode conversion process (-) something that can be potentially used to realize omni-polarizing optical devices.
Show less - Date Issued
- 2018
- Identifier
- CFE0007259, ucf:52182
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007259
- Title
- Analysis and Design of Non-Hermitian Optical Systems.
- Creator
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Kazemi Jahromi, Ali, Abouraddy, Ayman, Christodoulides, Demetrios, Likamwa, Patrick, Chini, Michael, University of Central Florida
- Abstract / Description
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From a very general perspective, optical devices can be viewed as constructions based on the spatial engineering of the optical index of refraction. Sculpting the real part of the refractive index produces the wide variety of known passive optical devices, such as waveguides, resonators, gratings, among a plethora of other possibilities for managing the transport of light. Less attention has been directed to engineering the imaginary part of the refractive index (-) that is responsible for...
Show moreFrom a very general perspective, optical devices can be viewed as constructions based on the spatial engineering of the optical index of refraction. Sculpting the real part of the refractive index produces the wide variety of known passive optical devices, such as waveguides, resonators, gratings, among a plethora of other possibilities for managing the transport of light. Less attention has been directed to engineering the imaginary part of the refractive index (-) that is responsible for optical gain and absorption (-) in conjunction with the real part of the refractive index. Optical gain is the building block of amplifiers and lasers, while optical absorption is exploited in photovoltaic devices, photodetectors, and as dopants in lasing media. Recently, the field of non-Hermitian photonics has emerged in which the new opportunities afforded by the spatial engineering of the optical gain and loss in an optical device are being exploited. Indeed, the judicious design of such active devices can result in counterintuitive physical effects, new optical functionalities that enable unexpected applications, and enhanced performance of existing devices.In this work, we have theoretically and experimentally demonstrated four different non-Hermitian arrangements exhibiting novel non-trivial features. First, we show that the direction of energy flow can be controlled inside an active cavity by tuning the optical gain. Reversing the direction of the energy flow within the cavity (-) such that Poynting's vector points backwards towards the source (-) takes place when the cavity gain exceeds a certain threshold value, which we have named 'Poynting's threshold'. To realize this effect, we have employed a fiber-based arrangement that allows for unambiguous determining of the direction of the energy flow within the cavity. Second, we have studied the implication of Poynting's threshold with respect to spectral reflection from an active cavity. Surprisingly, the reflection at Poynting's threshold becomes spectrally flat and is guaranteed to attain unity reflectivity while maintaining non-zero transmission. In other words, at Poynting's threshold, the cavity becomes a 'transparent perfect mirror'. We have realized this effect in an on-chip active waveguide device and in an optical-fiber-based system. Third, we have examined a parity-time (PT) symmetric fiber-based cavity consisting of two coupled sub-cavities, one of which contains gain and the other loss. In contrast to all previous on-chip PT-symmetric micro-devices, the exotic features of such a system may be expected to vanish when the length of the cavity is extremely large (exceeding 1 km in our experiments) due to the strong fluctuations in the optical phase. Nevertheless, we have found that some of the central features of such a system survive; e.g., loss-induced enhancement of lasing power is still observable. Finally, we have demonstrated (-) for the first time (-) the interferometric perfect absorption of light in a weakly absorbing (erbium-doped) fiber system. Additionally, we verified that this coherent effect is the most efficient configuration with respect to utilizing the absorbing species in the medium.
Show less - Date Issued
- 2018
- Identifier
- CFE0007206, ucf:52271
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007206
- Title
- Liquid crystal phase modulation for beam steering and near-eye displays.
- Creator
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Lee, Yun Han, Wu, Shintson, Moharam, Jim, Likamwa, Patrick, Dong, Yajie, University of Central Florida
- Abstract / Description
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Liquid crystal spatial phase modulator plays an important role in laser beam steering, wave-front shaping and correction, optical communication, optical computation and holography. One fundamental limitation lays in the response time of liquid crystal reorientation. To achieve fast response time, polymer-network liquid crystals are therefore proposed. By incorporating polymer network in a liquid crystal host, the response time can be reduced by a factor of 100. However, the polymer network...
Show moreLiquid crystal spatial phase modulator plays an important role in laser beam steering, wave-front shaping and correction, optical communication, optical computation and holography. One fundamental limitation lays in the response time of liquid crystal reorientation. To achieve fast response time, polymer-network liquid crystals are therefore proposed. By incorporating polymer network in a liquid crystal host, the response time can be reduced by a factor of 100. However, the polymer network introduces hysteresis, light scattering, and high voltage. The motivation for a fast-response liquid crystal phase modulator will be discussed in the first chapter. In the second chapter, we introduce our discovery that by modifying the polymer network structure with C12A, the hysteresis from the network can be eliminated, while keeping response time at the same order. In the third chapter, we introduce a new route toward fast response time. Instead of randomly generated network, we propose to utilize two-photon-polymerization method to create well-defined polymer scaffold. By introducing polymer scaffold, we demonstrated a 7-fold faster response in comparison with traditional phase modulators, while hysteresis, scattering, and high driving voltage are all eliminated. In the fourth chapter, we introduce phase modulation based on Pancharatnam-Berry (PB) phase principle. In this type of phase modulation, the defect at 2? phase reset in conventional phase modulators can be avoided. Therefore, a higher optical quality can be achieved, making them suitable for display and imaging applications. We demonstrated a fast PB lens with response time less than 1 ms, and using which we realized the first PB lens-based additive light field display to generate true (monocular) 3D content with computationally rendered images. In chapter five, we demonstrate the resolution enhancement based on pixel-shifting of fast PB gratings. By synchronizing display content with shifting pixels, we demonstrated ~2x enhanced resolution and significantly reduced screen-door artifact.In chapter six, we report our discovery of reflective polarization volume gratings (PVGs) based on self-organized liquid crystal helix. We achieved a large deflection angle ((>)50(&)deg; in glass), high diffraction efficiency ((>)95%), and unique polarization selectivity (distinction ratio (>) 100:1). A system integrating PB optical elements is described in chapter seven.Finally, we will summarize our major accomplishments in chapter eight.
Show less - Date Issued
- 2018
- Identifier
- CFE0007760, ucf:52389
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007760
- Title
- Room Temperature Operation of Quantum Cascade Lasers Monolithically Integrated Onto a Lattice-Mismatched Substrate.
- Creator
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Go, Rowel, Lyakh, Arkadiy, Delfyett, Peter, Likamwa, Patrick, Wu, Shintson, University of Central Florida
- Abstract / Description
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The experimental results of a 40-stage indium phosphide (InP) based quantum cascade laser (QCL) grown on a lattice-mismatched gallium arsenide (GaAs) substrate with metamorphic buffer (M-buffer) will be discussed. The QCL's strain-balanced active region was composed of Al0.78In0.22As/In0.73Ga0.27As and an 8 (&)#181;m-thick all-InP waveguide. Since the M-buffer was insulating, the wafer was processed into ridge-waveguide chips with lateral current injection scheme. Laser chips with high...
Show moreThe experimental results of a 40-stage indium phosphide (InP) based quantum cascade laser (QCL) grown on a lattice-mismatched gallium arsenide (GaAs) substrate with metamorphic buffer (M-buffer) will be discussed. The QCL's strain-balanced active region was composed of Al0.78In0.22As/In0.73Ga0.27As and an 8 (&)#181;m-thick all-InP waveguide. Since the M-buffer was insulating, the wafer was processed into ridge-waveguide chips with lateral current injection scheme. Laser chips with high reflection (HR) coating delivered total peak power in excess of 200 mW at cryogenic temperature (78 K), and lasing was observed up to 230 K. Partial HR coating was then utilized on the front facet to extend lasing range up to 303 K. After 200 minutes of preliminary reliability testing at maximum power, no sign of performance degradation was observed. Initial results of InP-based QCL on germanium-coated silicon substrate with M-buffer will also be covered in this work.
Show less - Date Issued
- 2018
- Identifier
- CFE0007568, ucf:52564
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007568
- Title
- Injection-locked semiconductor lasers for realization of novel RF photonics components.
- Creator
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Hoghooghi, Nazanin, Delfyett, Peter, Likamwa, Patrick, Li, Guifang, Malocha, Donald, University of Central Florida
- Abstract / Description
-
This dissertation details the work has been done on a novel resonant cavity linear interferometric modulator and a direct phase detector with channel filtering capability using injection-locked semiconductor lasers for applications in RF photonics. First, examples of optical systems whose performance can be greatly enhanced by using a linear intensity modulator are presented and existing linearized modulator designs are reviewed. The novel linear interferometric optical intensity modulator...
Show moreThis dissertation details the work has been done on a novel resonant cavity linear interferometric modulator and a direct phase detector with channel filtering capability using injection-locked semiconductor lasers for applications in RF photonics. First, examples of optical systems whose performance can be greatly enhanced by using a linear intensity modulator are presented and existing linearized modulator designs are reviewed. The novel linear interferometric optical intensity modulator based on an injection-locked laser as an arcsine phase modulator is introduced and followed by numerical simulations of the phase and amplitude response of an injection-locked semiconductor laser. The numerical model is then extended to study the effects of the injection ratio, nonlinear cavity response, depth of phase and amplitude modulation on the spur-free dynamic range of a semiconductor resonant cavity linear modulator. Experimental results of the performance of the linear modulator implemented with a multi-mode Fabry-Perot semiconductor laser as the resonant cavity are shown and compared with the theoretical model. The modulator performance using a vertical cavity surface emitting laser as the resonant cavity is investigated as well. Very low V? in the order of 1 mV, multi-gigahertz bandwidth (-10 dB bandwidth of 5 GHz) and a spur-free dynamic range of 120 dB.Hz2/3 were measured directly after the modulator. The performance of the modulator in an analog link is experimentally investigated and the results show no degradation of the modulator linearity after a 1 km of SMF.The focus of the work then shifts to applications of an injection-locked semiconductor laser as a direct phase detector and channel filter. This phase detection technique does not require a local oscillator. Experimental results showing the detection and channel filtering capability of an injection-locked semiconductor diode laser in a three channel system are shown. The detected electrical signal has a signal-to-noise ratio better than 60 dB/Hz. In chapter 4, the phase noise added by an injection-locked vertical cavity surface emitting laser is studied using a self-heterodyne technique. The results show the dependency of the added phase noise on the injection ratio and detuning frequency. The final chapter outlines the future works on the linear interferometric intensity modulator including integration of the modulator on a semiconductor chip and the design of the modulator for input pulsed light.
Show less - Date Issued
- 2012
- Identifier
- CFE0004385, ucf:49368
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004385
- Title
- Computationally Efficient Digital Backward Propagation for Fiber Nonlinearity Compensation.
- Creator
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Zhu, Likai, Li, Guifang, Schulzgen, Axel, Likamwa, Patrick, Wei, Lei, University of Central Florida
- Abstract / Description
-
The next generation fiber transmission system is limited by fiber nonlinearity. A distributed nonlinearity compensation method, known as Digital Backward Propagation (DBP), is necessary for effective compensation of the joint effect of dispersion and nonlinearity. However, in order for DBP to be accurate, a large number of steps are usually required for long-haul transmission, resulting in a heavy computational load.In real time DBP implementation, the FIR filters can be used for dispersion...
Show moreThe next generation fiber transmission system is limited by fiber nonlinearity. A distributed nonlinearity compensation method, known as Digital Backward Propagation (DBP), is necessary for effective compensation of the joint effect of dispersion and nonlinearity. However, in order for DBP to be accurate, a large number of steps are usually required for long-haul transmission, resulting in a heavy computational load.In real time DBP implementation, the FIR filters can be used for dispersion compensation and account for most of the computation per step. A method of designing a complementary filter pair is proposed. The individual errors in the frequency response of the two filters in a complementary filter pair cancel each other. As a result, larger individual filter error can be tolerated and the required filter length is significantly reduced.Unequal step size can be used in DBP to minimize the number of steps. For unrepeatered transmission with distributed Raman amplification, the Raman gain as a function of the distance and the effective fiber length of each DBP step need to be calculated by solving the differential equations of Raman amplification. The split-step DBP is performed only for transmission where the signal power is high.In comparison with solving the nonlinear Schrodinger equation (NLSE) for the total field of the WDM signal, solving the coupled NLSE requires a smaller step number and a lower sampling rate. In addition, the phase-locking between the local oscillators is not necessary for solving the coupled NLSE. The XPM compensation of WDM long-haul transmission by solving the coupled NLSE is experimentally demonstrated.At the optimum power level of fiber transmission, the total nonlinear phase shift is on the order of 1 radian. Therefore, for transoceanic fiber transmission systems which consist of many ((>)100) amplified fiber spans, the nonlinear effects in each span are weak. As a result, the optical waveform evolution is dominated by the dispersion. Taking advantage of the periodic waveform evolution in periodically dispersion managed fiber link, the DBP of K fiber spans can be folded into one span with K times the nonlinearity. This method can be called (")distance-folded DBP("). Under the weakly nonlinear assumption, the optical waveform repeats at locations where accumulated dispersions are identical. Consequently, the nonlinear behavior of the optical signal also repeats at locations of identical accumulative dispersion. Hence for a fiber link with arbitrary dispersion map, the DBP steps can be folded according to the accumulated dispersion. Experimental results show considerable savings in computation using this (")dispersion-folded DBP(") method. Simulation results show that the dramatically reduced computational load makes the nonlinearity-compensated dispersion-managed fiber link a competitive candidate for the next-generation transmission systems.
Show less - Date Issued
- 2011
- Identifier
- CFE0004492, ucf:49272
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004492
- Title
- Infrared Tapered Slot Antennas Coupled to Tunnel Diodes.
- Creator
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Florence, Louis, Boreman, Glenn, Likamwa, Patrick, Schoenfeld, Winston, Lail, Brian, University of Central Florida
- Abstract / Description
-
Tapered slot antennas (TSAs) have seen considerable application in the millimeter-wave portion of the spectrum. Desirable characteristics of TSAs include symmetric E- and H-plane antenna patterns, and broad non-resonant bandwidths. We investigate extension of TSA operation toward higher frequencies in the thermal infrared (IR), using a metal-oxide-metal diode as the detector. Several different infrared TSA design forms are fabricated using electron-beam lithography and specially developed...
Show moreTapered slot antennas (TSAs) have seen considerable application in the millimeter-wave portion of the spectrum. Desirable characteristics of TSAs include symmetric E- and H-plane antenna patterns, and broad non-resonant bandwidths. We investigate extension of TSA operation toward higher frequencies in the thermal infrared (IR), using a metal-oxide-metal diode as the detector. Several different infrared TSA design forms are fabricated using electron-beam lithography and specially developed thin-film processes. The angular antenna patterns of TSA-coupled diodes are measured at 10.6 micrometer wavelength in both E- and H-planes, and are compared to results of finite-element electromagnetic modeling using Ansoft HFSS. Parameter studies are carried out, correlating the geometric and material properties of several TSA design forms to numerical-model results and to measurements. A significant increase in antenna gain is noted for a dielectric-overcoat design. The traveling-wave behavior of the IR TSA structure is investigated using scattering near-field microscopy. The measured near-field data is compared to HFSS results. Suggestions for future research are included.
Show less - Date Issued
- 2012
- Identifier
- CFE0004376, ucf:49395
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004376
- Title
- Non-Reciprocal Wave Transmission in Integrated Waveguide Array Isolators.
- Creator
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Ho, Yat, Likamwa, Patrick, Christodoulides, Demetrios, Vanstryland, Eric, Kaup, David, University of Central Florida
- Abstract / Description
-
Non-reciprocal wave transmission is a phenomenon witnessed in certain photonic devices when the wave propagation dynamics through the device along one direction differs greatly from the dynamics along the counter-propagating direction. Specifically, it refers to significant power transfer occurring in one direction, and greatly reduced power transfer in the opposite direction. The resulting effect is to isolate the directionality of wave propagation, allowing transmission to occur along one...
Show moreNon-reciprocal wave transmission is a phenomenon witnessed in certain photonic devices when the wave propagation dynamics through the device along one direction differs greatly from the dynamics along the counter-propagating direction. Specifically, it refers to significant power transfer occurring in one direction, and greatly reduced power transfer in the opposite direction. The resulting effect is to isolate the directionality of wave propagation, allowing transmission to occur along one direction only.Given the popularity of photonic integrated circuits (PIC), in which all the optical components are fabricated on the same chip so that the entire optical system can be made more compact, it is desirable to have an easily integrated optical isolator. Common free-space optical isolator designs, which rely on the Faraday effect, are limited by the availability of suitable magnetic materials. This research proposes a novel integrated optical isolator based on an array of closely spaced, identical waveguides. Because of the nonlinear optical properties of the material, this device exploits the differing behaviors of such an array when illuminated with either a high power or a low power beam to achieve non-reciprocal wave transmission in the forwards and backwards directions, respectively. The switching can be controlled electro-optically via an integrated gain section which provides optical amplification before the input to the array. The design, fabrication, characterization and testing of this optical isolator are covered in this dissertation. We study the switching dynamics of this device and present its optimum operating conditions. ?
Show less - Date Issued
- 2012
- Identifier
- CFE0004305, ucf:49495
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004305
- 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
- Enhancement of Bandwidth and Laser Deflection Angle of Acousto-optic Deflectors by Dynamic Two-dimensional Refractive Index Modulation.
- Creator
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Wang, Tiansi, Kar, Aravinda, Likamwa, Patrick, Moharam, Jim, Vaidyanathan, Raj, University of Central Florida
- Abstract / Description
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Acousto-Optic Deflectors (AODs) are inertialess optical solid state devices that have advantages over conventional mechanically controlled mirror-based deflectors in numerous scientific and industrial applications. These applications include fluorescence microscopy, sensing, variable-focus lens, photolithography and laser materials processing. AODs are currently operated with a single piezoelectric transducer that modulates the refractive index only in one direction. This operating principle...
Show moreAcousto-Optic Deflectors (AODs) are inertialess optical solid state devices that have advantages over conventional mechanically controlled mirror-based deflectors in numerous scientific and industrial applications. These applications include fluorescence microscopy, sensing, variable-focus lens, photolithography and laser materials processing. AODs are currently operated with a single piezoelectric transducer that modulates the refractive index only in one direction. This operating principle limits the performance of AODs to a narrow acoustic bandwidth of the transducer and a small angle of laser deflection governed by the Bragg diffraction. To overcome these two limitations, the operation of AODs with phased array ultrasonic transducers is analyzed in this study. Only the amplitude and frequency of the acoustic waves are modulated in conventional AODs. The phased array mechanism enables modulating the acoustic phase in addition to the amplitude and frequency modulations. The latter two phenomena affect the refractive index variation and its periodicity in the AOD medium, respectively, and the phase modulation produces tilted wavefronts due to diffraction and interference of the ultrasonic waves. Consequently, a tilted phase grating is formed inside the AOD device and the tilt angle automatically modifies the laser incident angle on the grating compared to the original angle of incidence on the AOD device. The acoustic frequency and amplitude are, therefore, modulated to achieve the Bragg diffraction under the new angle of incidence and maximize the diffraction efficiency, respectively. The phase grating can be tilted at any arbitrary angle by steering the ultrasonic beam in different directions. The beam steering can be achieved by operating the transducers with various time delays to generate ultrasonic waves of different phases. Due to the diffraction pattern of the ultrasonic intensity distribution, the refractive index varies both longitudinally and transversely to the beam steering direction, and two-dimensional refractive index modulation occurs when the transducers are very long in the third dimension. The acoustic waves affect the refractive index through the photoelastic effect by inducing mechanical strain waves in the AOD medium. The ultrasonic beam steering and the mechanical strain are determined using a modified Rayleigh-Sommerfeld diffraction integral. This integral represents the mechanical displacement vector field produced by ultrasonic waves in solid media. An analytic expression is obtained for the displacement field and the resulting strain distribution is calculated using this expression. Based on the strain and the photoelastic constants, the two-dimensional variation in the refractive index is determined for single-crystal paratellurite TeO2 which is an excellent AOD material. Conventional two-dimensional coupled mode theory of AOD, which is based on only one-dimensional refractive index modulation, is extended in this study to analyze the effect of two-dimensional index variation on the performance of AODs. The diffraction efficiency and the laser beam deflection angle are determined for both plane waves and Gaussian laser beams by obtaining analytic solutions for the coupled mode equations. The diffraction efficiency is found to be nearly unity over a broad range of the acoustic frequency, and the deflection angle can also be increased by steering the ultrasonic beam at large angles.
Show less - Date Issued
- 2017
- Identifier
- CFE0006672, ucf:51219
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006672
- Title
- Parity-time and supersymmetry in optics.
- Creator
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Miri, Mohammad, Christodoulides, Demetrios, Abouraddy, Ayman, Likamwa, Patrick, Choudhury, Sudipto, University of Central Florida
- Abstract / Description
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Symmetry plays a crucial role in exploring the laws of nature. By exploiting some of the underlying analogies between the mathematical formalism of quantum mechanics and that of electrodynamics, in this dissertation we show that optics can provide a fertile ground for studying, observing, and utilizing some of the peculiar symmetries that are currently out of reach in other areas of physics. In particular, in this work, we investigate two important classes of symmetries, parity-time symmetry ...
Show moreSymmetry plays a crucial role in exploring the laws of nature. By exploiting some of the underlying analogies between the mathematical formalism of quantum mechanics and that of electrodynamics, in this dissertation we show that optics can provide a fertile ground for studying, observing, and utilizing some of the peculiar symmetries that are currently out of reach in other areas of physics. In particular, in this work, we investigate two important classes of symmetries, parity-time symmetry (PT) and supersymmetry (SUSY), within the context of classical optics. The presence of PT symmetry can lead to entirely real spectra in non-Hermitian systems. In optics, PT-symmetric structures involving balanced regions of gain and loss exhibit intriguing properties which are otherwise unattainable in traditional Hermitian systems. We show that selective PT symmetry breaking offers a new method for achieving single mode operation in laser cavities. Other interesting phenomena also arise in connection with PT periodic structures. Along these lines, we introduce a new class of optical lattices, the so called mesh lattices. Such arrays provide an ideal platform for observing a range of PT-related phenomena. We show that defect sates and solitons exist in such periodic environments exhibiting unusual behavior. We also investigate the scattering properties of PT-symmetric particles and we show that such structures can deflect light in a controllable manner. In the second part of this dissertation, we introduce the concept of supersymmetric optics. In this regard, we show that any optical structure can be paired with a superpartner with similar guided wave and scattering properties. As a result, the guided mode spectra of these optical waveguide systems can be judiciously engineered so as to realize new families of mode filters and mode division multiplexers and demultiplexers. We also present the first experimental demonstration of light dynamics in SUSY ladders of photonic lattices. In addition a new type of transformation optics based on supersymmetry is also explored. Finally, using the SUSY formalism in non-Hermitian settings, we identify more general families of complex optical potentials with real spectra.
Show less - Date Issued
- 2014
- Identifier
- CFE0005844, ucf:50915
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005844
- Title
- Advanced liquid crystal displays with supreme image qualities.
- Creator
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Chen, Haiwei, Wu, Shintson, Moharam, Jim, Likamwa, Patrick, Dong, Yajie, University of Central Florida
- Abstract / Description
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Several metrics are commonly used to evaluate the performance of display devices. In this dissertation, we analyze three key parameters: fast response time, wide color gamut, and high contrast ratio, which affect the final perceived image quality. Firstly, we investigate how response time affects the motion blur, and then discover the 2-ms rule. With advanced low-viscosity materials, new operation modes, and backlight modulation technique, liquid crystal displays (LCDs) with an unnoticeable...
Show moreSeveral metrics are commonly used to evaluate the performance of display devices. In this dissertation, we analyze three key parameters: fast response time, wide color gamut, and high contrast ratio, which affect the final perceived image quality. Firstly, we investigate how response time affects the motion blur, and then discover the 2-ms rule. With advanced low-viscosity materials, new operation modes, and backlight modulation technique, liquid crystal displays (LCDs) with an unnoticeable image blur can be realized. Its performance is comparable to an impulse-type display, like cathode ray tube (CRT). Next, we propose two novel backlight configurations to improve an LCD's color gamut. One is to use a functional reflective polarizer (FRP), acting as a notch filter to block the unwanted light, and the other is to combine FRP with a patterned half-wave plate to suppress the crosstalk between blue and green/red lights. In experiment, we achieved 97.3% Rec. 2020 in CIE 1976 color space, which is approaching the color gamut of a laser projector. Finally, to enhance an LCD's contrast ratio, we proposed a novel device configuration by adding an in-cell polarizer between LC layer and color filter array. The CR for a vertically-aligned LCD is improved from 5000:1 to 20,000:1, and the CR for a fringe field switching LCD is improved from 2000:1 to over 3000:1. To further enlarge CR to fulfill the high dynamic range requirement, a dual-panel LCD system is proposed and the measured contrast ratio exceeds 1,000,000:1. Overall speaking, such an innovated LCD exhibits supreme image qualities with motion picture response time comparable to CRT, vivid color to laser projector, and contrast ratio to OLED. Along with other outstanding features, like high peak brightness, high resolution density, long lifetime, and low cost, LCD would continue to maintain its dominance in consumer electronics in the foreseeable future.
Show less - Date Issued
- 2017
- Identifier
- CFE0006864, ucf:51758
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006864
- Title
- Optical Parity Time Metasurface Structures.
- Creator
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El Halawany, Ahmed, Christodoulides, Demetrios, Rahman, Talat, Peale, Robert, Likamwa, Patrick, University of Central Florida
- Abstract / Description
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In the last few years, optics has witnessed the emergence of two fields namely metasurfaces and parity-time (PT) symmetry. Optical metasurfaces are engineered structures that provide unique responses to electromagnetic waves, absent in natural materials. Optical metasurfaces are known for their reduced dimensionality i.e. subwavelength and consequently lower losses are anticipated. The other paradigm is the PT symmetric materials, also known as photonic synthetic matter. PT symmetry has...
Show moreIn the last few years, optics has witnessed the emergence of two fields namely metasurfaces and parity-time (PT) symmetry. Optical metasurfaces are engineered structures that provide unique responses to electromagnetic waves, absent in natural materials. Optical metasurfaces are known for their reduced dimensionality i.e. subwavelength and consequently lower losses are anticipated. The other paradigm is the PT symmetric materials, also known as photonic synthetic matter. PT symmetry has emerged from quantum mechanics when a new class of non-Hermitian Hamiltonian quantum systems was highlighted to have real eigenvalues, hence eradicating Hermiticity of the Hamiltonian as an essential condition to the existence of real eigenvalues.The first half of the thesis is focused on the experimental and numerical realization of PT symmetric metasurfaces. A systematic methodology is developed to implement this class of metasurfaces in both one-dimensional and two-dimensional geometries. In two dimensional systems, PT symmetry can be established by employing either H-like diffractive elements or diatomic oblique Bravais lattices. It is shown that the passive PT symmetric metasurfaces can be utilized to appropriately engineer the resulting far-field characteristics. Such PT-symmetric structures are capable of eliminating diffraction orders in specific directions, while maintaining or even enhancing the remaining orders. Later, it is shown a first ever attempt of PT metasurface fabricated on a flexible polymer (polyimide) substrate. The studied PT metasurface exhibits the ability to direct light, i.e. Poynting vector in a desired direction. Herein, the light scattered from the fabricated device in the undesired direction is attenuated by at least an order of magnitude. The proposed PT symmetric metasurface is essentially diatomic Honeycomb Bravais lattice, where both the passive and lossy elements exist side by side on each site separated by 50 nm. The unidirectionality of the studied metasurface is not limited to a single wavelength, on the contrary, it is observed to be effective on the entire visible band (400 (-) 600 nm). The PT symmetric meatsurface is also fabricated on a high strength substrate; sapphire (Al2O3). An excellent agreement between the experimental and numerical (COMSOL) results is found for both substrates. Customized modifications to the current design can open avenues to study the unidirectionality of metasurfaces to different optical bands, for example IR.The second part of the thesis deals with the theoretical modeling of the dynamics of an electron that gets trapped by means of decoherence and quantum interference in the central quantum dot (QD) of a semiconductor nanoring (NR) made of five QDs, between 100 and 300 K. The electron's dynamics is described by a master equation with a Hamiltonian based on the tight-binding model, taking into account electron(-)LO phonon interaction. Based on this configuration, the probability to trap an electron with no decoherence is almost 27%. In contrast, the probability to trap an electron with decoherence is 70% at 100 K, 63% at 200 K and 58% at 300 K. Our model provides a novel method of trapping an electron at room temperature.This setup is then used to propose a theoretical model for an electrically driven single photon source operating at high temperatures. It is shown that the decoherence, which is usually the main obstacle for operating single photon sources at high temperatures, ensures an efficient operation of the presented electrically driven single photon source at high temperatures. The single-photon source is driven by a single electron source attached to a heterostructure semiconductor nanoring. The electron's dynamics in the nanoring and the subsequent recombination with the hole is described by the generalized master equation with a Hamiltonian based on tight-binding model, taking into account the electron-LO phonon interaction. As a result of decoherence, an almost 100% single photon emission with a strong antibunching behavior i.e. g(2)(0) (<)(<) 1 at high temperature up to 300 K is achieved.
Show less - Date Issued
- 2016
- Identifier
- CFE0006454, ucf:51421
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006454
- Title
- High dynamic range display systems.
- Creator
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Zhu, Ruidong, Wu, Shintson, Moharam, Jim, Likamwa, Patrick, Fang, Jiyu, University of Central Florida
- Abstract / Description
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High contrast ratio (CR) enables a display system to faithfully reproduce the real objects. However, achieving high contrast, especially high ambient contrast (ACR), is a challenging task. In this dissertation, two display systems with high CR are discussed: high ACR augmented reality (AR) display and high dynamic range (HDR) display. For an AR display, we improved its ACR by incorporating a tunable transmittance liquid crystal (LC) film. The film has high tunable transmittance range, fast...
Show moreHigh contrast ratio (CR) enables a display system to faithfully reproduce the real objects. However, achieving high contrast, especially high ambient contrast (ACR), is a challenging task. In this dissertation, two display systems with high CR are discussed: high ACR augmented reality (AR) display and high dynamic range (HDR) display. For an AR display, we improved its ACR by incorporating a tunable transmittance liquid crystal (LC) film. The film has high tunable transmittance range, fast response time, and is fail-safe. To reduce the weight and size of a display system, we proposed a functional reflective polarizer, which can also help people with color vision deficiency. As for the HDR display, we improved all three aspects of the hardware requirements: contrast ratio, color gamut and bit-depth. By stacking two liquid crystal display (LCD) panels together, we have achieved CR over one million to one, 14-bit depth with 5V operation voltage, and pixel-by-pixel local dimming. To widen color gamut, both photoluminescent and electroluminescent quantum dots (QDs) have been investigated. Our analysis shows that with QD approach, it is possible to achieve over 90% of the Rec. 2020 color gamut for a HDR display. Another goal of an HDR display is to achieve the 12-bit perceptual quantizer (PQ) curve covering from 0 to 10,000 nits. Our experimental results indicate that this is difficult with a single LCD panel because of the sluggish response time. To overcome this challenge, we proposed a method to drive the light emitting diode (LED) backlight and the LCD panel simultaneously. Besides relatively fast response time, this approach can also mitigate the imaging noise. Finally yet importantly, we improved the display pipeline by using a HDR gamut mapping approach to display HDR contents adaptively based on display specifications. A psychophysical experiment was conducted to determine the display requirements.
Show less - Date Issued
- 2017
- Identifier
- CFE0006930, ucf:51668
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006930
- Title
- Advanced Blue Phase Liquid Crystal Displays.
- Creator
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Xu, Daming, Wu, Shintson, Moharam, Jim, Likamwa, Patrick, Fang, Jiyu, University of Central Florida
- Abstract / Description
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Thin-film transistor (TFT) liquid crystal displays (LCDs) have become indispensable in our daily lives. Their widespread applications range from smartphones, laptops, TVs to navigational devices, data projectors and wearable displays. Over past decades, massive efforts have been invested in device development, material characterization and manufacturing technology. As a result, the performance of LCDs, such as viewing angle, contrast ratio, color gamut and resolution, have been improved...
Show moreThin-film transistor (TFT) liquid crystal displays (LCDs) have become indispensable in our daily lives. Their widespread applications range from smartphones, laptops, TVs to navigational devices, data projectors and wearable displays. Over past decades, massive efforts have been invested in device development, material characterization and manufacturing technology. As a result, the performance of LCDs, such as viewing angle, contrast ratio, color gamut and resolution, have been improved significantly. Nonetheless, there are still urgent needs for fast response time and low power consumption. Fast response time helps reduce motion image blurs and enable color sequential displays. The latter is particularly attractive since it eliminates spatial color filters, which in turn triples optical efficiency and resolution density. The power consumption can be reduced greatly by using color sequential displays, but liquid crystals with submillisecond response time are required to minimize color breakup. The state-of-the-art gray-to-gray response time of nematic LCDs is about 5ms, which is too slow to meet this requirement.With the urgent needs for submillisecond response time, polymer-stabilized blue phase liquid crystal is emerging as a strong candidate for achieving this goal. Compared to conventional nematic LCDs, blue phase LCDs exhibit several revolutionary features: submillisecond gray-to-gray response time, no need for alignment layer, optically isotropic voltage-off state, and large cell gap tolerance. However, some bottlenecks such as high operation voltage, low optical transmittance, noticeable hysteresis and slow TFT charging remain to be overcome before their widespread applications can be realized. This dissertation is dedicated to addressing these challenges from material development and device design viewpoints.First, we started to investigate the device physics of blue phase LCDs. We have built a numerical model based on the refraction effect for simulating the electro-optics of blue phase devices. The model well agrees with experimental data. Based on this model, we explored approaches from device and material viewpoints to achieve low operation voltage. On the device side, with protrusion and etched electrodes, we can reduce the operating voltage to below 10V and enhance the transmittance to over 80%. On the material side, high Kerr constant is indeed helpful for lowering the operation voltage, but we also need to pay attention to the individual ?n and ?? values of liquid crystal host according to the device structures employed. High-?? LC hosts help enhance Kerr constant, leading to a reduced operation voltage; but they may be subject to serious capacitance charging issues due to the huge dielectric anisotropy. Our model provides important guidelines for future device design and material development.To further enhance transmittance and reduce voltage, we have proposed a Z-shaped electrode structure. By optimizing the device structure, we have successfully reduced the operating voltage to ~8V and enhanced optical transmittance to (>) 95% based on a lower-?? LC host not subjecting to charging issues, showing comparable or even better performance than the mainstream LCDs. This is the first approach to achieve such a high transmittance in blue phase devices without using a directional backlight. By using zigzag structure, the color shift and gray inversion are in unnoticeable range.In addition, hysteresis affects the accuracy of grayscale control and should be suppressed. We have proposed a double exponential model to analyze the electric field effects of blue phase, and found that electrostriction effect is the root cause for hysteresis under strong electric field. To suppress the electrostriction effect in blue phase, a method to stabilize the blue phase lattice via linear photo-polymerization is demonstrated for the first time. By illuminating the mono-functional and the di-functional monomers with a linearly polarized UV beam, we can form anisotropic polymer networks, which in turn lead to anisotropic electrostrictions. In experiments, we found that when the polarization of UV light is perpendicular to the stripe electrodes, the electrostriction effect can be strongly suppressed. The resulting hysteresis is reduced from 6.95% to 0.36% and response time is improved by a factor of two. We foresee this approach will guide future manufacturing process.The approaches and studies presented in this dissertation are expected to advance the blue phase LCDs to a new level and accelerate their emergence as next-generation display technology. It is foreseeable that the widespread application of blue phase LCDs is around the corner.
Show less - Date Issued
- 2016
- Identifier
- CFE0006200, ucf:51101
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006200
- Title
- Atmospheric Pressure Chemical Vapor Deposition of Functional Oxide Materials for Crystalline Silicon Solar Cells.
- Creator
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Davis, Kristopher, Schoenfeld, Winston, Likamwa, Patrick, Moharam, Jim, Habermann, Dirk, University of Central Florida
- Abstract / Description
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Functional oxides are versatile materials that can simultaneously enable efficiency gains and cost reductions in crystalline silicon (c-Si) solar cells. In this work, the deposition of functional oxide materials using atmospheric pressure chemical vapor deposition (APCVD) and the integration of these materials into c-Si solar cells are explored. Specifically, thin oxide films and multi-layer film stacks are utilized for the following purposes: (1) to minimize front surface reflectance without...
Show moreFunctional oxides are versatile materials that can simultaneously enable efficiency gains and cost reductions in crystalline silicon (c-Si) solar cells. In this work, the deposition of functional oxide materials using atmospheric pressure chemical vapor deposition (APCVD) and the integration of these materials into c-Si solar cells are explored. Specifically, thin oxide films and multi-layer film stacks are utilized for the following purposes: (1) to minimize front surface reflectance without increasing parasitic absorption within the anti-reflection coating(s); (2) to maximize internal back reflectance of rear passivated cells, thereby increasing optical absorption of weakly absorbed long wavelength photons (? (>) 900 nm); (3) to minimize recombination losses by providing excellent surface passivation; and (4) to improve doping processes during cell manufacturing (e.g., emitter and surface field formation) by functioning as highly controllable dopant sources compatible with in-line diffusion processes. The oxide materials deposited by APCVD include amorphous and polycrystalline titanium oxide, aluminum oxide, boron-doped aluminum oxide, silicon oxide, phosphosilicate glass, and borosilicate glass. The microstructure, optical properties, and electronic properties of these films are characterized for different deposition conditions. Additionally, the impact of these materials on the performance of different types of c-Si solar cells is presented using both simulated and experimental current-voltage curves.
Show less - Date Issued
- 2015
- Identifier
- CFE0005599, ucf:50267
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005599
- Title
- Low Absorption Liquid Crystal Materials for Midwave Infrared.
- Creator
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Creekmore, Amy, Wu, Shintson, Moharam, Jim, Likamwa, Patrick, University of Central Florida
- Abstract / Description
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Liquid crystal is an amazing class of soft matters with applications spanning from visible, infrared, millimeter wave, to terahertz. In addition to direct-view displays and projection displays, liquid crystal is also widely used in adaptive optics, tunable-focus lens, and laser beam steering. Although the visible region has well developed materials and mixtures for the vast variety of applications, the midwave infrared (MWIR) region of the electromagnetic spectrum invites much development as...
Show moreLiquid crystal is an amazing class of soft matters with applications spanning from visible, infrared, millimeter wave, to terahertz. In addition to direct-view displays and projection displays, liquid crystal is also widely used in adaptive optics, tunable-focus lens, and laser beam steering. Although the visible region has well developed materials and mixtures for the vast variety of applications, the midwave infrared (MWIR) region of the electromagnetic spectrum invites much development as only a few materials have been developed with these applications in mind. Unlike visible region, the major challenge for mid-wave infrared liquid crystal is inherently large absorption loss. To reduce absorption, some molecular engineering approaches have been considered, such as deuteration, fluorination, and chlorination. The fluorine and chlorine not only act as the polar group to provide dipole moment but also helps shift some vibration absorption bands outside the MWIR window. Long phenyl ring compounds, fluorinated tolane materials, and chlorinated terphenyl mixtures are explored; as well as a look as the potential bromine might introduce for future development. In this thesis, we first review the current materials and their performance in the mid-wave infrared region, explain the need for higher performing liquid crystals, and then discuss the methodology of compound development and mixture formulation. Some new chlorinated liquid crystal compounds are synthesized, mixture formulated, and their properties evaluated. Finally, we will explain the future work which needs to be performed in this field.
Show less - Date Issued
- 2014
- Identifier
- CFE0005594, ucf:50243
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005594
