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Title: Thin-film Lithium Niobate Photonics for Electro-optics, Nonlinear Optics, and Quantum Optics on Silicon.
Creator: Rao, Ashutosh, Fathpour, Sasan, Delfyett, Peter, Li, Guifang, Thomas, Jayan, University of Central Florida
Abstract / Description: Ion-sliced thin-film lithium niobate (LN) compact waveguide technology has facilitated the resurgence of integrated photonics based on lithium niobate. These thin-film LN waveguides offer over an order of magnitude improvement in optical confinement, and about two orders of magnitude reduction in waveguide bending radius, compared to conventional LN waveguides. Harnessing the improved confinement, a variety of miniaturized and efficient photonic devices are demonstrated in this work. First,...
Show moreIon-sliced thin-film lithium niobate (LN) compact waveguide technology has facilitated the resurgence of integrated photonics based on lithium niobate. These thin-film LN waveguides offer over an order of magnitude improvement in optical confinement, and about two orders of magnitude reduction in waveguide bending radius, compared to conventional LN waveguides. Harnessing the improved confinement, a variety of miniaturized and efficient photonic devices are demonstrated in this work. First, two types of compact electrooptic modulators are presented (-) microring modulators, and Mach-Zehnder modulators. Next, two distinct approaches to nonlinear optical frequency converters are implemented (-) periodically poled lithium niobate, and mode shape modulation (grating assisted quasi-phase matching). Following this, stochastic variations are added to the mode shape modulation approach to demonstrate random quasi-phase matching. Afterward, broadband photon-pair generation is demonstrated in the miniaturized periodically poled lithium niobate, and spectral correlations of the biphoton spectrum are reported. Finally, extensions of the aforementioned results suitable for future work are discussed.
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Date Issued: 2018
Identifier: CFE0007085, ucf:52013
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007085

Title: Broadband Mid-infrared Frequency Combs Generated via Frequency Division.
Creator: Ru, Qitian, Vodopyanov, Konstantin, Fathpour, Sasan, Wu, Shintson, Peale, Robert, University of Central Florida
Abstract / Description: Frequency combs have revolutionized metrology and demonstrated numerous applications in science and technology. Combs operating in the mid-infrared region could be beneficial for molecular spectroscopy for several reasons. First, numerous molecules have their spectroscopic signatures in this region. Furthermore, the atmospheric window (3-5(&)#181;m and 8-14(&)#181;m) is located here. Additionally, a mid-infrared frequency comb could be employed as a diagnostic tool for the many components of...
Show moreFrequency combs have revolutionized metrology and demonstrated numerous applications in science and technology. Combs operating in the mid-infrared region could be beneficial for molecular spectroscopy for several reasons. First, numerous molecules have their spectroscopic signatures in this region. Furthermore, the atmospheric window (3-5(&)#181;m and 8-14(&)#181;m) is located here. Additionally, a mid-infrared frequency comb could be employed as a diagnostic tool for the many components of human breath, as well as for detection of harmful gases and contaminants in the atmosphere. In this thesis, I used synchronously pumped subharmonic optical parametric oscillators (OPOs) operating at degeneracy to produce ultra-broadband outputs near half of the pump laser frequency. One attractive property of the subharmonic OPOs is that the signal/idler waves of the OPO are frequency- and phase-locked to the pump frequency comb. We explored three new nonlinear materials in the subharmonic OPO and demonstrated a broadband spectrum for mid-infrared frequency comb generation. (1) Orientation-patterned (OP) gallium arsenide (GaAs) was selected as the first material because it has high nonlinearity. We found that the OP-GaAs based OPO yielded an approximately two-octave wide spectrum (2.8(-)11(&)#181;m). (2) Gallium phosphide (GaP) has near zero group velocity dispersion (GVD) at 4.7 (&)#181;m and a large bandgap. The OP-GaP OPO yielded a spectrum of more than two octaves (3(-)12.5(&)#181;m). Also, because of the large bandgap, GaP is suitable for telecom 1.56-(&)#181;m pumping, having the advantage of much smaller GVD than in periodically-poled-lithium-niobite (PPLN). The telecom laser (1.56(&)#181;m) pumped OP-GaP OPO was demonstrated with more than one octave wide spectrum. (3) Finally, we explored the phenomenon of random phase matching in the zinc selenide (ZnSe) polycrystalline material. The first random phase matched OPO was demonstrated with more than one octave spectrum (3.1(-) 9(&)#181;m), which is also the first OPO based on ZnSe.
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Date Issued: 2019
Identifier: CFE0007718, ucf:52430
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007718

Title: Mode-locked Laser Based on Large Core Yb3+-Doped Fiber.
Creator: Jia, Fei, Amezcua Correa, Rodrigo, Schulzgen, Axel, Fathpour, Sasan, University of Central Florida
Abstract / Description: The thesis reviews principle of laser cavity and gives a general introduction to mode-locked laser (MLL). By using Yb3+-doped fiber as gain medium, passive MLL cavity is developed in experiment, aiming to obtain femtosecond pulses with high pump power from 25W to 35W. The gain medium fiber with 65(&)#181;m core diameter is cleaved with one flat end and another angled. Pump laser with 976nm wavelength is coupled into Yb3+-doped fiber to excite signal from 1020nm to 1040nm in the core. 9W is...
Show moreThe thesis reviews principle of laser cavity and gives a general introduction to mode-locked laser (MLL). By using Yb3+-doped fiber as gain medium, passive MLL cavity is developed in experiment, aiming to obtain femtosecond pulses with high pump power from 25W to 35W. The gain medium fiber with 65(&)#181;m core diameter is cleaved with one flat end and another angled. Pump laser with 976nm wavelength is coupled into Yb3+-doped fiber to excite signal from 1020nm to 1040nm in the core. 9W is threshold for laser setup. After locking all modes, picosecond pulses are output from laser cavity and coupled into dispersion delay fiber. By compressing pulse width, pulses are in soliton mode and then femtosecond laser pulses are obtained pulses are obtained. To measure ultrafast pulse width effectively, an auto-correlator based on Mach(-)Zehnder interferometer is developed. In the receiver terminal, a photodiode with range 320 nm to 1000 nm is used to detect signal and two photon absorption (TPA) method is applied.
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Date Issued: 2018
Identifier: CFE0007199, ucf:52249
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007199

Title: Third-order optical nonlinearities for integrated microwave photonics applications.
Creator: Malinowski, Marcin, Fathpour, Sasan, Delfyett, Peter, Christodoulides, Demetrios, Lyakh, Arkadiy, University of Central Florida
Abstract / Description: The field of integrated photonics aims at compressing large and environmentally-sensitive opticalsystems to micron-sized circuits that can be mass-produced through existing semiconductor fabri-cation facilities. The integration of optical components on single chips is pivotal to the realizationof miniature systems with high degree of complexity. Such novel photonic chips find abundant ap-plications in optical communication, spectroscopy and signal processing. This work concentrateson...
Show moreThe field of integrated photonics aims at compressing large and environmentally-sensitive opticalsystems to micron-sized circuits that can be mass-produced through existing semiconductor fabri-cation facilities. The integration of optical components on single chips is pivotal to the realizationof miniature systems with high degree of complexity. Such novel photonic chips find abundant ap-plications in optical communication, spectroscopy and signal processing. This work concentrateson harnessing nonlinear phenomena to this avail.The first part of this dissertation discusses, both from component and system level, the developmentof a frequency comb source with a semiconductor mode-locked laser at its heart. New nonlinear de-vices for supercontinuum and second-harmonic generations are developed and their performance isassessed inside the system. Theoretical analysis of a hybrid approach with synchronously-pumpedKerr cavity is also provided. The second part of the dissertation investigates stimulated Brillouinscattering (SBS) in integrated photonics. A fully-tensorial open-source numerical tool is developedto study SBS in optical waveguides composed of crystalline materials, particularly silicon. SBS isdemonstrated in an all-silicon optical platform.
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Date Issued: 2019
Identifier: CFE0007674, ucf:52497
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007674

Title: Broadband Coherent Perfect Absorption in One-Dimensional Optical Systems.
Creator: Villinger, Massimo Maximilian, Abouraddy, Ayman, Dogariu, Aristide, Fathpour, Sasan, University of Central Florida
Abstract / Description: Absorption plays a critical role in a variety of optical applications (-) sometimes it is desirable to minimize it as in optical fibers and waveguides, or to enhance it as in solar cells and photodetectors. We describe here a new optical scheme that controllably produces high optical absorption over a broad wavelength range (hundreds of nm) in systems that have low intrinsic absorption over the same range. This effect, 'coherent perfect absorption' or CPA, arises from a subtle interplay...
Show moreAbsorption plays a critical role in a variety of optical applications (-) sometimes it is desirable to minimize it as in optical fibers and waveguides, or to enhance it as in solar cells and photodetectors. We describe here a new optical scheme that controllably produces high optical absorption over a broad wavelength range (hundreds of nm) in systems that have low intrinsic absorption over the same range. This effect, 'coherent perfect absorption' or CPA, arises from a subtle interplay between interference and absorption of two beams incident on a weakly absorbing medium. In the first part of this study, we present an analytical model that captures the relevant physics of CPA in one-dimensional photonic structures. This model elucidates an absorption-mediated interference effect that underlies CPA (-) an effect that is normally forbidden in Hermitian systems, but is allowed when conservation of energy is violated due to the inclusion of loss. As a concrete example, we consider a Fabry-P(&)#233;rot resonator containing a lossy dielectric and confirm this model through a computational study of a 1-micron-thick silicon layer in a cavity formed of dispersive mirrors with aperiodic multilayer design. We confirm that one may achieve 100% absorption in this thin silicon layer (whose intrinsic absorption is only ~ 3%) in the near-infrared. We then design two device models using few-micron-thick aperiodic planar dielectric mirrors and demonstrate (computationally, as well as experimentally) spectrally flat, coherently enhanced absorption at the theoretical limit in a 2-micron-thick film of polycrystalline silicon embedded in symmetric and asymmetric cavities. This coherent effect is observed over an octave-spanning wavelength range of ~800 (-) 1600 nm utilizing incoherent light in the near-infrared, exploiting mirrors that have wavelength-dependent reflectivity devised to counterbalance the decline in silicon's intrinsic absorption at long wavelengths. We anticipate that the design principles established here may be extended to other materials, broader spectral ranges, and large surface areas. Finally, we study the effect of the angle of incidence on CPA in planar structures. The results of this study point to a path for realizing CPA in such systems continuously over large bandwidths.
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Date Issued: 2015
Identifier: CFE0006059, ucf:50985
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006059

Title: Frequency Selective Detection of Infrared Radiation in Uncooled Optical Nano-Antenna Array.
Creator: Modak, Sushrut, Chanda, Debashis, Schoenfeld, Winston, Fathpour, Sasan, University of Central Florida
Abstract / Description: Mid-infrared (mid-IR) detection and imaging over atmospheric transparent 3-5 ?m and 8-12 ?m bands are increasingly becoming important for various space, defense and civilian applications. Various kinds of microbolometers offer uncooled detection of IR radiation. However, broadband absorption of microbolometers makes them less sensitive to spectrally resolved detection of infrared radiation and the fabrication is also very tedious involving multiple complex lithography steps. In this study, we...
Show moreMid-infrared (mid-IR) detection and imaging over atmospheric transparent 3-5 ?m and 8-12 ?m bands are increasingly becoming important for various space, defense and civilian applications. Various kinds of microbolometers offer uncooled detection of IR radiation. However, broadband absorption of microbolometers makes them less sensitive to spectrally resolved detection of infrared radiation and the fabrication is also very tedious involving multiple complex lithography steps. In this study, we designed an optical nano-antenna array based detector with narrow frequency band of operation. The structure consists of a two-element antenna array comprised of a perforated metallic hole array coupled with an underneath disk array which trap incident radiation as dipole currents. The energy is dissipated as electron plasma loss on the hole-disk system inducing close to ~100% absorption of the incident radiation. This near perfect absorption originates from simultaneous zero crossing of real component of permittivity and permeability due to the geometrical arrangement of the two antenna elements which nullifies overall charge and current distributions, prohibiting existence of any propagating electromagnetic modes at resonance. Moreover, the continuous perforated film allows probing of the induced (")micro-current(") plasma loss on each nano hole-disk pair via a weak bias current. Such optical antenna design enables flexible scaling of detector response over the entire mid-infrared regime by change in the antenna dimensions. Furthermore, the development of simple nanoimprint lithography based large area optical antenna array fabrication technique facilitates formation of low cost frequency selective infrared detectors.
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Date Issued: 2014
Identifier: CFE0005845, ucf:50932
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005845

Title: Intrinsic Modulation Response Modeling and Analysis for Lithographic Vertical-Cavity Surface-Emitting Lasers.
Creator: Li, Mingxin, Deppe, Dennis, Fathpour, Sasan, Wu, Shintson, Malocha, Donald, University of Central Florida
Abstract / Description: Vertical-cavity surface-emitting lasers (VCSELs) have been greatly improved and successfully commercialized over the past few decades owing to their ability to provide both mode and current confinement that enables low energy consumption, high efficiency and high modulation speed. However, further improvement of oxide VCSELs is limited by the nature of the oxide aperture because of self-heating, internal strain and difficulties in precise size control. In this dissertation, VCSELs using...
Show moreVertical-cavity surface-emitting lasers (VCSELs) have been greatly improved and successfully commercialized over the past few decades owing to their ability to provide both mode and current confinement that enables low energy consumption, high efficiency and high modulation speed. However, further improvement of oxide VCSELs is limited by the nature of the oxide aperture because of self-heating, internal strain and difficulties in precise size control. In this dissertation, VCSELs using lithographic approach are demonstrated to overcome the limitations of oxide VCSELs, in which an intra-cavity phase shifting mesa is applied to define the device size and provide optical mode and electrical current confinement instead of an oxide aperture. A newly developed model of intrinsic modulation response is proposed and analyzed to focus on the thermal limit of the modulation speed of VCSELs. The results show that both the temperature dependent differential gain and stimulated emission rate impact laser speed and the stimulated emission rate dominates the speed limit. Thermal limits of modulation response are compared for oxide and lithographic VCSELs for various sizes. The results predict that the intrinsic modulation response can be significantly increased by using lithographic VCSELs due to low thermal resistance and reduced mode volume while maintaining high efficiency. The intrinsic bandwidth could exceed 100 GHz for a 2-?m-diameter lithographic VCSEL. Combined with low electrical parasitics, it is expected to produce over 100 Gb/s data rate from a single directly modulated laser. VCSELs designed for high speed are discussed and their characteristics are demonstrated.
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Date Issued: 2016
Identifier: CFE0006346, ucf:51556
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006346

Title: Electrical Parasitic Bandwidth Limitations of Oxide-Free Lithographic Vertical-Cavity Surface-Emitting Lasers.
Creator: Yang, Xu, Deppe, Dennis, Fathpour, Sasan, Wu, Shintson, Gong, Xun, University of Central Florida
Abstract / Description: Nowadays, Vertical-Cavity Surface-Emitting Lasers (VCSELs) are the most popular optical sources in short-reach data communications. In the commercial oxide VCSEL technology, an oxide aperture is created inside resonant cavity in realizing good mode and current confinement, however, high electrical resistance comes along with forming the oxide aperture and the electrical parasitic bandwidth becomes the main limitation in modulation speed. In this report, electrical bandwidths of oxide-free...
Show moreNowadays, Vertical-Cavity Surface-Emitting Lasers (VCSELs) are the most popular optical sources in short-reach data communications. In the commercial oxide VCSEL technology, an oxide aperture is created inside resonant cavity in realizing good mode and current confinement, however, high electrical resistance comes along with forming the oxide aperture and the electrical parasitic bandwidth becomes the main limitation in modulation speed. In this report, electrical bandwidths of oxide-free lithographic VCSELs have been studied along with their general lasing properties. Due to the new ways of fabricating the aperture, record low resistances have been achieved in oxide-free lithographic VCSELs with various sizes, while high slope efficiencies and high output powers have been maintained. High speed simulation has been performed showing the very low differential resistances will benefit much to the electrical parasitic bandwidths, and are expected to produce higher modulation speed. A bottom emitting structure has been proposed and analyzed, showing reduction in both mirror resistance and capacitance will further improve the modulation speed. The total 3-dB modulation bandwidth is expected to be 50-80 GHz, much higher than the bandwidth reached in existing oxide VCSELs. Lithographic VCSELs also show superior lasing characteristics, including record low thermal resistance and record high output power. The maximum power exceeds 19 mW in a 6 (&)#181;m device and over 50 % power conversion efficiency has been achieved. A maximum single mode operation power of 5 mW has been observed from a 1 (&)#181;m diameter VCSEL. High temperature stress testing has been performed showing lithographic VCSELs can operate more reliably than oxide VCSELs under extreme operating conditions. Lithographic VCSEL with low electrical resistance, single-mode operation, high efficiency, and high power will be a strong candidate as the optical source in high speed data communications, as well as other applications such as high power VCSEL arrays and optical sensing.
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Date Issued: 2016
Identifier: CFE0006425, ucf:51491
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006425

Title: Hybrid Integrated Photonic Platforms and Devices.
Creator: Chiles, Jeffrey, Fathpour, Sasan, Vodopyanov, Konstantin, Khajavikhan, Mercedeh, Chanda, Debashis, University of Central Florida
Abstract / Description: Integrated photonics has the potential to revolutionize optical systems by achieving drastic reductions in their size, weight and power. Remote spectroscopy, free-space communications and high-speed telecommunications are critical applications that would benefit directly from these advancements. However, many such applications require extremely wide spectral bandwidths, leading to significant challenges in their integration. The choice of integrated platform influences the optical...
Show moreIntegrated photonics has the potential to revolutionize optical systems by achieving drastic reductions in their size, weight and power. Remote spectroscopy, free-space communications and high-speed telecommunications are critical applications that would benefit directly from these advancements. However, many such applications require extremely wide spectral bandwidths, leading to significant challenges in their integration. The choice of integrated platform influences the optical transparency and functionality which can be ultimately achieved. In this work, several new platforms and technologies have been developed to meet these needs. First, the silicon-on-lithium-niobate (SiLN) platform is discussed, on which the first compact, integrated electro-optic modulator in the mid-infrared has been demonstrated. Next, results are shown in the development of the all-silicon-optical-platform (ASOP), an ultra-stable suspended membrane approach which offers broad optical transparency from 1.2 to 8.5 um and enables efficient nonlinear frequency conversion in the mid-IR. This fabrication approach is then taken further with (")anchored-membrane waveguides,(") (T-Guides) enabling single-mode and single-polarization waveguiding over a span exceeding 1.27 octaves. Afterward, a new photonic technology enabling integrated polarization beam-splitters and polarizers over unprecedented bandwidths is introduced, called topographically anisotropic photonics (TAP). Next, results on high-performance microphotonic chalcogenide glass waveguides are presented. Finally, several integrated photonics concepts suitable for further work will be discussed, such as augmentations to T-Guides and a novel technique for quasi-phase-matching.
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Date Issued: 2016
Identifier: CFE0006447, ucf:51408
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006447

Title: Picosecond Yb-Doped Fiber Amplifier.
Creator: Zhu, Weibin, Amezcua Correa, Rodrigo, Schulzgen, Axel, Fathpour, Sasan, University of Central Florida
Abstract / Description: Due to its versatility, rare earth doped fiber amplifier (RDFA) has attracted a lot of researchers worldwide in recent years. Depends on different kinds of rare earth ion, RDFA can be categorized into neodymium doped fiber amplifier (NDFA), erbium doped fiber amplifier (EDFA), thulium doped fiber amplifier (TDFA), and so forth. Among many kinds of RDFA, the ytterbium doped fiber amplifier (YDFA) has received even more interest, especially in high power application, mainly because of its broad...
Show moreDue to its versatility, rare earth doped fiber amplifier (RDFA) has attracted a lot of researchers worldwide in recent years. Depends on different kinds of rare earth ion, RDFA can be categorized into neodymium doped fiber amplifier (NDFA), erbium doped fiber amplifier (EDFA), thulium doped fiber amplifier (TDFA), and so forth. Among many kinds of RDFA, the ytterbium doped fiber amplifier (YDFA) has received even more interest, especially in high power application, mainly because of its broad gain bandwidth and high conversion efficiency which are due to its relatively simple electronic structure.The purpose of this research is to study the YDFA by developing a model and building a YDFA setup in free space configuration. The active fiber used in the setup is a few modes, polarization-maintaining double-cladding ytterbium-doped large mode area (LMA) fiber and the length is 1m. The pump used is a tunable 975nm laser diode and a 1064nm laser diode was used as the seed which has 630 ps pulse duration time and 9.59 kHz repetition rate. This setup produces 2.514W average power, corresponding to a pulse peak power of 423kW, with 15W absorbed pump power. The spectrum of the output power has also been investigated.
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Date Issued: 2017
Identifier: CFE0006678, ucf:51214
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006678

Title: Nonlinear integrated photonics on silicon and gallium arsenide substrates.
Creator: Ma, Jichi, Fathpour, Sasan, Hagan, David, Li, Guifang, Peale, Robert, University of Central Florida
Abstract / Description: Silicon photonics is nowadays a mature technology and is on the verge of becoming a blossoming industry. Silicon photonics has also been pursued as a platform for integrated nonlinear optics based on Raman and Kerr effects. In recent years, more futuristic directions have been pursued by various groups. For instance, the realm of silicon photonics has been expanded beyond the well-established near-infrared wavelengths and into the mid-infrared (3 (-) 5 (&)#181;m). In this wavelength range,...
Show moreSilicon photonics is nowadays a mature technology and is on the verge of becoming a blossoming industry. Silicon photonics has also been pursued as a platform for integrated nonlinear optics based on Raman and Kerr effects. In recent years, more futuristic directions have been pursued by various groups. For instance, the realm of silicon photonics has been expanded beyond the well-established near-infrared wavelengths and into the mid-infrared (3 (-) 5 (&)#181;m). In this wavelength range, the omnipresent hurdle of nonlinear silicon photonics in the telecommunication band, i.e., nonlinear losses due to two-photon absorption, is inherently nonexistent. With the lack of efficient light-emission capability and second-order optical nonlinearity in silicon, heterogeneous integration with other material systems has been another direction pursued. Finally, several approaches have been proposed and demonstrated to address the energy efficiency of silicon photonic devices in the near-infrared wavelength range. In this dissertation, theoretical and experimental works are conducted to extend applications of integrated photonics into mid-infrared wavelengths based on silicon, demonstrate heterogeneous integration of tantalum pentoxide and lithium niobate photonics on silicon substrates, and study two-photon photovoltaic effect in gallium arsenide and plasmonic-enhanced structures.Specifically, performance and noise properties of nonlinear silicon photonic devices, such as Raman lasers and optical parametric amplifiers, based on novel and reliable waveguide technologies are studied. Both near-infrared and mid-infrared nonlinear silicon devices have been studied for comparison. Novel tantalum-pentoxide- and lithium-niobate-on-silicon platforms are developed for compact microring resonators and Mach-Zehnder modulators. Third- and second-harmonic generations are theoretical studied based on these two platforms, respectively. Also, the two-photon photovoltaic effect is studied in gallium arsenide waveguides for the first time. The effect, which was first demonstrated in silicon, is the nonlinear equivalent of the photovoltaic effect of solar cells and offers a viable solution for achieving energy-efficient photonic devices. The measured power efficiency achieved in gallium arsenide is higher than that in silicon and even higher efficiency is theoretically predicted with optimized designs. Finally, plasmonic-enhanced photovoltaic power converters, based on the two-photon photovoltaic effect in silicon using subwavelength apertures in metallic films, are proposed and theoretically studied.
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Date Issued: 2014
Identifier: CFE0005373, ucf:50441
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005373

Title: Self-heating control of edge emitting and vertical cavity surface emitting lasers.
Creator: Zhang, Yu, Deppe, Dennis, Fathpour, Sasan, Likamwa, Patrick, Wu, Thomas, University of Central Florida
Abstract / Description: Self-heating leads to temperature rise of laser diode and limits the output power, efficiency and modulation bandwidth due to increased loss and decreased differential gain. The main heat sources in laser diode during continuous wave operation are Joule heating and free carrier absorption loss. To control device self-heating, the epi structure needs to be designed with low electrical resistance and low absorption loss, while the heat flux must spread out of the device efficiently. This...
Show moreSelf-heating leads to temperature rise of laser diode and limits the output power, efficiency and modulation bandwidth due to increased loss and decreased differential gain. The main heat sources in laser diode during continuous wave operation are Joule heating and free carrier absorption loss. To control device self-heating, the epi structure needs to be designed with low electrical resistance and low absorption loss, while the heat flux must spread out of the device efficiently. This dissertation presents the control of self-heating of both edge emitting laser diodes and vertical cavity surface emitting lasers (VCSELs). For the 980nm high power edge emitting laser, asymmetric waveguide is used for low free carrier absorption loss. The waveguide and cladding materials are optimized for high injection efficiency. BeO heatsink is applied to spread the heat efficiently. Injection efficiency of 71% and internal loss of 0.3 cm-1 have been achieved. A total output power of 9.3 W is measured from 0.5cm long device at 14.5A injection current. To further reduce the internal loss, the development of 980nm quantum dot active region is studied. Threshold current density as low as 59A/cm2 is reached. For the VCSELs, oxide-free structure is used to solve the self-heating problem of oxide VCSELs. Removing the oxide layer and using AlAs in the DBRs leads to record low thermal resistance. Optimization of the DBRs leads to low resistance and low free carrier absorption. Power conversion efficiency higher than 50% is achieved. To further reduce device voltage and heat generation, the development of intracavity contacts devices is introduced.
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Date Issued: 2014
Identifier: CFE0005749, ucf:50076
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005749

Title: Fabrication of Metallic Antenna Arrays using Nanoimprint Lithography.
Creator: Lin, Yu-wei, Kik, Pieter, Schoenfeld, Winston, Fathpour, Sasan, University of Central Florida
Abstract / Description: This Thesis describes the development of a cost-effective process for patterning nanoscale metal antenna arrays. Soft ultraviolet (UV) Nanoimprint Lithography (NIL) into bilayer resist was chosen since it enables repeatable large-scale replication of nanoscale patterns with good lift-off properties using a simple low-cost process. Nanofabrication often involves the use of Electron Beam Lithography (EBL) which enables the definition of nanoscale patterns on small sample regions, typically (
Show moreThis Thesis describes the development of a cost-effective process for patterning nanoscale metal antenna arrays. Soft ultraviolet (UV) Nanoimprint Lithography (NIL) into bilayer resist was chosen since it enables repeatable large-scale replication of nanoscale patterns with good lift-off properties using a simple low-cost process. Nanofabrication often involves the use of Electron Beam Lithography (EBL) which enables the definition of nanoscale patterns on small sample regions, typically (<) 1 mm2. However its sequential nature makes the large scale production of nanostructured substrates using EBL cost-prohibitive. NIL is a pattern replication method that can reproduce nanoscale patterns in a parallel fashion, allowing the low-cost and rapid production of a large number of nano-patterned samples based on a single nanostructured master mold.Standard NIL replicates patterns by pressing a nanostructured hard mold into a soft resist layer on a substrate resulting in exposed substrate regions, followed by an optional Reactive Ion Etching (RIE) step and the subsequent deposition of e.g. metal onto the exposed substrate area. However, non-vertical sidewalls of the features in the resist layer resulting from an imperfect hard mold, from reflow of the resist layer, or from isotropic etching in the RIE step may cause imperfect lift-off. To overcome this problem, a bilayer resist method can be used. Using stacked resist layers with different etch rates, undercut structures can be obtained after the RIE step, allowing for easy lift-off even when using a mold with non-vertical sidewalls. Experiments were carried out using a nanostructured negative SiO2 master mold. Various material combinations and processing methods were explored. The negative master mold was transferred to a positive soft mold, leaving the original master mold unaltered. The soft mold consisted of a 5 ?m thick top Poly(methyl methacrylate) (PMMA), or Polyvinyl alcohol (PVA) layer, a 1.5 mm thick Polydimethylsiloxane (PDMS) buffer layer, and a glass supporting substrate. The soft mold was pressed into a bilayer of 300 nm PMMA and 350 nm of silicon based UV-curable resist that was spin-coated onto a glass slide, and cured using UV radiation. The imprinted patterns were etched using RIE, exposing the substrate, followed by metal deposition and lift-off. The experiments show that the use of soft molds enables successful pattern transfer even in the presence of small dust particles between the mold and the resist layer. Feature sizes down to 280 nm were replicated successfully.
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Date Issued: 2013
Identifier: CFE0005026, ucf:49990
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005026

Title: Lithographic Vertical-Cavity Surface-Emitting Lasers.
Creator: Zhao, Guowei, Deppe, Dennis, Likamwa, Patrick, Fathpour, Sasan, Sundaram, Kalpathy, University of Central Florida
Abstract / Description: Remarkable improvements in vertical-cavity surface-emitting lasers (VCSELs) have been made by the introduction of mode- and current-confining oxide optical aperture now used commercially. However, the oxide aperture blocks heat flow inside the device, causing a larger thermal resistance, and the internal strain caused by the oxide can degrade device reliability, also the diffusion process used for the oxide formation can limit device uniformity and scalability.Oxide-free lithographic VCSELs...
Show moreRemarkable improvements in vertical-cavity surface-emitting lasers (VCSELs) have been made by the introduction of mode- and current-confining oxide optical aperture now used commercially. However, the oxide aperture blocks heat flow inside the device, causing a larger thermal resistance, and the internal strain caused by the oxide can degrade device reliability, also the diffusion process used for the oxide formation can limit device uniformity and scalability.Oxide-free lithographic VCSELs are introduced to overcome these device limitations, with both the mode and current confined within the lithographically defined intracavity mesa, scaling and mass production of small size device could be possible. The 3 ?m diameter lithographic VCSEL shows a threshold current of 260 ?A, differential quantum efficiency of 60% and maximum output power density of 65 kW/cm2, and shows single-mode single-polarization operation with side-mode-suppression-ratio over 25 dB at output power up to 1 mW. The device also shows reliable operation during 1000 hours stress test with high injection current density of 142 kA/cm2. The lithographic VCSELs have much lower thermal resistance than oxide-confined VCSELs due to elimination of the oxide aperture. The improved thermal property allows the device to have wide operating temperature range of up to 190 (&)deg;C heat sink temperature, high output power density especially in small device, high rollover current density and high rollover cavity temperature. Research is still underway to reduce the operating voltage of lithographic VCSELs for high wall plug efficiency, and the voltage of 6 (&)#181;m device at injection current density of 10 kA/cm2 is reduces to 1.83 V with optimized mesa and DBR mirror structure. The lithographic VCSELS are promising to become the next generation VCSEL technology.
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Date Issued: 2012
Identifier: CFE0004634, ucf:49912
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004634

Title: True linearized intensity modulation for photonic analog to digital conversion using an injection-locked mode-locked laser.
Creator: Sarailou, Edris, Delfyett, Peter, Likamwa, Patrick, Fathpour, Sasan, Malocha, Donald, University of Central Florida
Abstract / Description: A true linearized interferometric intensity modulator for pulsed light has been proposed and experimentally presented in this thesis. This has been achieved by introducing a mode-locked laser into one of the arms of a Mach-Zehnder interferometer and injection-locking it to the input light (which is pulsed and periodic). By modulating the injection-locked laser, and combining its output light with the light from the other arm of interferometer in quadrature, one can achieve true linearized...
Show moreA true linearized interferometric intensity modulator for pulsed light has been proposed and experimentally presented in this thesis. This has been achieved by introducing a mode-locked laser into one of the arms of a Mach-Zehnder interferometer and injection-locking it to the input light (which is pulsed and periodic). By modulating the injection-locked laser, and combining its output light with the light from the other arm of interferometer in quadrature, one can achieve true linearized intensity modulator. This linearity comes from the arcsine phase response of the injection-locked mode-locked laser (as suggested by steady-state solution of Adler's equation) when it is being modulated. Mode-locked lasers are fabricated using a novel AlGaInAs-InP material system. By using the BCB for planarization and minimizing the metal pad size and directly modulating the laser, we have achieved very effective fundamental hybrid mode-locking at the repetition rate of ~ 23 GHz. This laser also provided the short pulses of 860 fs and 280 fs timing jitter integrated from 1 Hz- 100 MHz.The linearized intensity modulator has been built by using two identical two-section mode-locked lasers with the same length, one as the slave laser in one of the arms of the Mach-Zehnder interferometer injection-locked to the other one as the master which is the input light to the modulator. A low V? of 8.5 mV is achieved from this modulator. Also the current of the gain section or the voltage of the saturable absorber section of the slave laser has been used to apply the modulation signal. A spur free dynamic range of 70 dB.Hz2/3 is achieved when modulating the modulator through the saturable absorber. Modulating the saturable absorber provides a reduced third-order intermodulation tone with respect to modulating the gain. This is simply because of the unwanted amplitude modulation created when modulating the gain section current.Finally an improved design is proposed and demonstrated to improve the modulator performance. This is achieved by introducing a third section to the laser. Using the impurity free vacancy disordering technique the photoluminescence peak of this section is blue-shifted selectively and therefore there would not be any absorption in that passive section. By applying the modulation signal to this passive section rather than applying it to the gain section or saturable absorber section, the amplitude and phase modulation could be decoupled. The experimental results have presented here and an almost six-fold reduction in V? and 5 dB improvement in spur free dynamic range have been achieved. The proposed and demonstrated configuration as an analog optical link has the potential to increase the performance and resolution of photonic analog-to-digital converters.
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Date Issued: 2015
Identifier: CFE0005707, ucf:50118
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005707

Title: MONOLITHICALLY INTEGRATED WAVELENGTH TUNABLE LASER DIODE FOR INTEGRATED OPTIC SURFACE PLASMON RESONANCE SENSING.
Creator: Tabbakh, Thamer, Likamwa, Patrick, Batarseh, Issa, Fathpour, Sasan, Mikhael, Wasfy, Khajavikhan, Mercedeh, University of Central Florida
Abstract / Description: In this work, we demonstrate an InGaAsP multiple quantum well tunable laser diode that amalgamates two gain sections with different bandgap energies. This is achieved using selective area intermixing of the multiple quantum wells, and impurity-free vacancy induced disordering. When different current combination is injected into each section, that leads to a laser wavelength peak whose position depends on the relative magnitudes of the two injected currents. The laser wavelength can be fine...
Show moreIn this work, we demonstrate an InGaAsP multiple quantum well tunable laser diode that amalgamates two gain sections with different bandgap energies. This is achieved using selective area intermixing of the multiple quantum wells, and impurity-free vacancy induced disordering. When different current combination is injected into each section, that leads to a laser wavelength peak whose position depends on the relative magnitudes of the two injected currents. The laser wavelength can be fine-tuned from 1538 nm to 1578 nm with relatively constant output power. The free spectral range FSR of the tunable laser found to be 0.25 nm. This tunable laser was launched into an optical surface plasmon resonance sensor head to provide an input light source for the SPR sensor.Using the tunable laser diode, we have demonstrated an optical surface plasmon resonance sensor head that is based on an inverted rib dielectric waveguide, in which the resonance wavelength of the surface plasmon excited at the gold metal-dielectric interface depends on the refractive index of the liquid in contact with it. The inverted-rib waveguide of the SPR sensor head is made of a layer of SU-8 polymer with a refractive index of 1.568. While the lower cladding layer consists of silicon oxynitride (SiOxNy) with a refractive index of 1.526. The top surface is coated with 20 nm of chromium followed by a 50 nm thick layer of gold or with 4 nm of titanium followed by a 25 nm thick layer of gold. The SPR sensor head was designed, to allow monitoring of analyte media with a refractive index, ranging from 1.43 to the 1.52. Using a set of reference liquids representing the analyte medium, the sensitivity of the SPR sensor was measured using the fabricated tunable laser, an optical spectrum analyzer, and a photodiode. It was found that with various calibrated sample liquids in contact with the gold metal, a sharp resonance dip in the transmission spectrum occurred, and its position shifted to a shorter wavelength when the refractive index of the sample liquids was increased. The average sensitivity of the SPR sensor devices was determined to be S = 334 nm/RIU.
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Date Issued: 2018
Identifier: CFE0007769, ucf:52390
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007769

Title: Hybrid integration of second- and third-order highly nonlinear waveguides on silicon substrates.
Creator: Camacho Gonzalez, Guillermo Fernando, Fathpour, Sasan, Likamwa, Patrick, Amezcua Correa, Rodrigo, Peale, Robert, University of Central Florida
Abstract / Description: In order to extend the capabilities and applications of silicon photonics, other materials and compatible technologies have been developed and integrated on silicon substrates. A particular class of integrable materials are those with high second- and third-order nonlinear optical properties. This work presents contributions made to nonlinear integrated photonics on silicon substrates, including chalcogenide waveguides for over an octave supercontinuum generation, and rib-loaded thin-film...
Show moreIn order to extend the capabilities and applications of silicon photonics, other materials and compatible technologies have been developed and integrated on silicon substrates. A particular class of integrable materials are those with high second- and third-order nonlinear optical properties. This work presents contributions made to nonlinear integrated photonics on silicon substrates, including chalcogenide waveguides for over an octave supercontinuum generation, and rib-loaded thin-film lithium niobate waveguides for highly efficient second-harmonic generation. Through the pursuit of hybrid integration of the two types of waveguides for applications such as on-chip self-referenced optical frequency combs, we have experimentally demonstrated fabrication integrability of chalcogenide and thin-film lithium niobate waveguides in a single chip and a pathway for both second- and third-order nonlinearities occurring therein. Accordingly, design specifications for an efficient nonlinear integrated waveguide are reported, showing over an octave supercontinuum generation and frequency selectivity for second-harmonic generation, enabling potentials of on-chip interferometry techniques for carrier-envelope offset detection, and hence stabilized optical combs.
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Date Issued: 2019
Identifier: CFE0007607, ucf:52560
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007607

Title: The Consequences of a Reduced Superlattice Thickness on Quantum Cascade LASER Performance.
Creator: Figueiredo, Pedro, Lyakh, Arkadiy, Peale, Robert, Klemm, Richard, Fathpour, Sasan, University of Central Florida
Abstract / Description: Coherent infrared radiation sources are essential for the operability of a wide range of scientific, industrial, military and commercial systems. The importance of the mid-infrared spectral region cannot be understated. Numerous molecules have some vibrational band in this range, allowing for identification of species by means of absorption, emission or some other form of spectroscopy. As such, spectroscopy alone has numerous applications ranging from industrial process control to disease...
Show moreCoherent infrared radiation sources are essential for the operability of a wide range of scientific, industrial, military and commercial systems. The importance of the mid-infrared spectral region cannot be understated. Numerous molecules have some vibrational band in this range, allowing for identification of species by means of absorption, emission or some other form of spectroscopy. As such, spectroscopy alone has numerous applications ranging from industrial process control to disease diagnosis utilizing breath analysis. However, despite the discovery of the LASER in the 60s, to this day the amount of coherent sources in this range is limited. It is for this reason that the quantum cascade laser has gained such momentum over the past 23 years.Quantum Cascade LASERS (QCL) are semiconductor LASERS which are based on the principle of bandgap engineering. This incredible technique is a testament to the technological maturity of the semiconductor industry. It has been demonstrated that by having precise control of individual material composition (band gap control), thicknesses on the order of monolayers, and doping levels for each individual layer in a superlattice, we have unprecedented flexibility in designing a LASER or detector in the infrared. And although the technology has matured since it's discovery, there still remain fundamental limitations on device performance. In particular, active region overheating limits QCL performance in a high duty cycle mode of operation.In this dissertation, along with general discussion on the background of the QCL, we propose a solution of where by limiting the growth of the superlattice to a fraction of typical devices, we allow for reduction of the average superlattice temperature under full operational conditions. The consequences of this reduction are explored in theory, experiment and system level applications.
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Date Issued: 2017
Identifier: CFE0006592, ucf:51273
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006592

Title: Ultrafast Laser Material Processing For Photonic Applications.
Creator: Ramme, Mark, Richardson, Martin, Fathpour, Sasan, Sundaram, Kalpathy, Kar, Aravinda, University of Central Florida
Abstract / Description: Femtosecond Laser Direct Writing (FLDW) is a viable technique for producing photonic devices in bulk materials. This novel manufacturing technique is versatile due to its full 3D fabrication capability. Typically, the only requirement for this process is that the base material must be transparent to the laser wavelength. The modification process itself is based on non-linear energy absorption of laser light within the focal volume of the incident beam.This thesis addresses the feasibility of...
Show moreFemtosecond Laser Direct Writing (FLDW) is a viable technique for producing photonic devices in bulk materials. This novel manufacturing technique is versatile due to its full 3D fabrication capability. Typically, the only requirement for this process is that the base material must be transparent to the laser wavelength. The modification process itself is based on non-linear energy absorption of laser light within the focal volume of the incident beam.This thesis addresses the feasibility of this technique for introducing photonic structures into novel dielectric materials. Additionally, this work provides a deeper understanding of the light-matter interaction mechanism occurring at high pulse repetition rates. A novel structure on the sample surface in the form of nano-fibers was observed when the bulk material was irradiated with high repetition rate pulse trains.To utilize the advantages of the FLDW technique even further, a transfer of the technology from dielectric to semiconductor materials is investigated. However, this demands detailed insight of the absorption and modification processes themselves. Experiments and the results suggested that non-linear absorption, specifically avalanche ionization, is the limiting factor inhibiting the application of FLDW to bulk semiconductors with today's laser sources.
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Date Issued: 2013
Identifier: CFE0004914, ucf:49626
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004914

Title: Silicon photonic devices for optical delay lines and mid infrared applications.
Creator: Khan, Saeed, Fathpour, Sasan, Likamwa, Patrick, Gong, Xun, Delfyett, Peter, Schoenfeld, Winston, University of Central Florida
Abstract / Description: Silicon photonics has been a rapidly growing subfield of integrated optics and optoelectronic in the last decade and is currently considered a mature technology. The main thrust behind the growth is its compatibility with the mature and low-cost microelectronic integrated circuits fabrication process. In recent years, several active and passive photonic devices and circuits have been demonstrated on silicon. Optical delay lines are among important silicon photonic devices, which are essential...
Show moreSilicon photonics has been a rapidly growing subfield of integrated optics and optoelectronic in the last decade and is currently considered a mature technology. The main thrust behind the growth is its compatibility with the mature and low-cost microelectronic integrated circuits fabrication process. In recent years, several active and passive photonic devices and circuits have been demonstrated on silicon. Optical delay lines are among important silicon photonic devices, which are essential for a variety of photonic system applications including optical beam-forming for controlling phased-array antennas, optical communication and networking systems and optical coherence tomography. In this thesis, several types of delay lines based on apodized grating waveguides are proposed and demonstrated. Simulation and experimental results suggest that these novel devices can provide high optical delay and tunability at very high bit rate. While most of silicon photonics research has focused in the near-infrared wavelengths, extending the operating wavelength range of the technology into in the 3(-)5 (&)#181;m, or the mid-wave infrared regime, is a more recent field of research. A key challenge has been that the standard silicon-on-insulator waveguides are not suitable for the mid-infrared, since the material loss of the buried oxide layer becomes substantially high. Here, the silicon-on-sapphire waveguide technology, which can extend silicon's operating wavelength range up to 4.4 (&)#181;m, is investigated. Furthermore, silicon-on-nitride waveguides, boasting a wide transparent range of 1.2(-)6.7 ?m, are demonstrated and characterized for the first time at both mid-infrared (3.39 ?m) and near-infrared (1.55 ?m) wavelengths.
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Date Issued: 2013
Identifier: CFE0005014, ucf:49996
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005014

Integrated photonics (3)	+ -
VCSEL (3)	+ -
integrated photonics (3)	+ -
nonlinear optics (3)	+ -
Mid-infrared (2)	+ -

silicon photonics (2)	+ -
Acoustic Optic Modulator (1)	+ -
Active Region Temperature (1)	+ -
Auto-correlator (1)	+ -
Bolometers (1)	+ -
Broadband spectrum (1)	+ -
CPA (1)	+ -
Coherent Perfect Absorption (1)	+ -
Fabry-Pérot resonator (1)	+ -
Frequency combs (1)	+ -
Grating waveguides (1)	+ -
IR (1)	+ -
Infrared (1)	+ -
Infrared Detectors (1)	+ -
LASER (1)	+ -
Linear modulators (1)	+ -
Luminescent Solar Concentration (1)	+ -
MQW (1)	+ -
Mode-locked Laser (1)	+ -
NIR (1)	+ -
Nano-antenna array (1)	+ -
Nanoimprint (1)	+ -
Optical parameric osicllators (1)	+ -
Photo-Voltaics (1)	+ -
Plasmonics (1)	+ -

Fathpour, Sasan (22)	+ -
University of Central Florida (22)	+ -
Likamwa, Patrick (6)	+ -
Delfyett, Peter (4)	+ -
Deppe, Dennis (4)	+ -

Peale, Robert (4)	+ -
Amezcua Correa, Rodrigo (3)	+ -
Gong, Xun (3)	+ -
Malocha, Donald (3)	+ -
Schoenfeld, Winston (3)	+ -
Sundaram, Kalpathy (3)	+ -
Wu, Shintson (3)	+ -
Abouraddy, Ayman (2)	+ -
Chanda, Debashis (2)	+ -
Khajavikhan, Mercedeh (2)	+ -
Li, Guifang (2)	+ -
Lyakh, Arkadiy (2)	+ -
Schulzgen, Axel (2)	+ -
Vodopyanov, Konstantin (2)	+ -
Banaei, Seyed Esmaeil (1)	+ -
Batarseh, Issa (1)	+ -
Camacho Gonzalez, Guillermo Fernando (1)	+ -
Chiles, Jeffrey (1)	+ -
Christodoulides, Demetrios (1)	+ -
Dogariu, Aristide (1)	+ -
Figueiredo, Pedro (1)	+ -
Hagan, David (1)	+ -
Jha, Sumit (1)	+ -
Jia, Fei (1)	+ -
Kar, Aravinda (1)	+ -

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