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Chen, LiHybrid Silicon and Lithium Niobate Integrated Photonics
Doctor of Philosophy, The Ohio State University, 2015, Electrical and Computer Engineering
A hybrid silicon and lithium noibate (LiNbO3) material system is developed to combine the high index contrast of silicon and the second order susceptibility of lithium niobate. Ion-sliced single crystalline LiNbO3 thin film is bonded to silicon-on-insulator (SOI) waveguides via Benzocyclobutene (BCB) as the top cladding. The LiNbO3 thin films are patterned to achieve desired size, shape and crystal orientations. Integrated electrodes are integrated to confine electric fields to the LiNbO3 thin film. Empowered by the linear electro-optic effect of LiNbO3, compact chip-scale hybrid Si/LiNbO3 integrated photonic devices are enabled on the SOI platform, including radio-frequency electric field sensors, tunable optical filters, high speed electro-optical modulators for optical interconnects, and high linearity modulators for analog optical links. Compact and metal-free electric field sensors based on indirect bonding of z-cut ion-sliced LiNbO3 thin film to silicon microrings are demonstrated. The demonstrated sensitivity to electric fields is 4.5 V m-1Hz-1/2 at 1.86 GHz. Tunable optical filters based on hybrid Si/LiNbO3 microring resonators with integrated electrodes are also demonstrated with a tunability of 12.5 pm/V, which is over an order of magnitude greater than electrode-free designs. By integrating metal thin film electrode and utilizing silicon as an optically transparent electrode, voltage induced electric fields in the LiNbO3 are enhanced. We also presented low power compensation of thermal drift of resonance wavelengths in hybrid Si/LiNbO3 ring resonators. A capacitive geometry and low thermal sensitivity result in the compensation of 17 oC of temperature variation using tuning powers at sub-nanowatt levels. The method establishes a route for stabilizing high quality factor resonators in chip-scale integrated photonics subject to temperature variations. Gigahertz speed hybrid Si/LiNbO3 electro-optical microring modulators are enabled by optimizing the RC time constant of the biasing electrodes. Fabricated devices exhibit a resonance tuning of 3.3 pm/V and a small-signal electrical-to-optical 3 dB bandwidth of 5 GHz. Digital modulation with an extinction ratio greater than 3 dB is demonstrated up to 9 Gb/s. High-speed and low tuning power chip-scale modulators that exploit the high-index contrast of silicon with the second order susceptibility of lithium niobate are envisioned. An alternative design with x-cut LiNbO3 thin films on silicon racetrack resoantors enables compact highly linear integrated optical modulator for high spectral free dynamic range (SFDR) analog optical links. The measured third order intermodulation distortion SFDR is 98.1 dB·Hz2/3 at 1 GHz and 87.6 dB·Hz2/3 at 10 GHz. The demonstrated SFDR is over an order of magnitude greater than silicon ring modulators based on the plasma dispersion effect, and is comparable to commercial LiNbO3 Mach-Zehnder interferometer modulators, but with a footprint three orders of magnitude smaller. The hybrid Si/LiNbO3 photonic platform is promising for applications in optical interconnections, microwave photonics, optical computing and sensing. More broadly, empowering silicon with second-order susceptibility opens a suite of nonlinear optic applications to the chip scale.

Committee:

Ronald Reano (Advisor); Joel Johnson (Committee Member); Fernando Teixeira (Committee Member); Gregory Lafyatis (Committee Member)

Subjects:

Electrical Engineering; Electromagnetics; Nanotechnology; Optics

Keywords:

silicon photonics; integrated optics devices; electro-optical devices; sensors; waveguides; resonators; optical modulators; optical interconnects; microwave photonics; hybrid photonics; integrated optics materials; lithium niobate; micro-fabrication;

Kota, AkashSpectral Analysis of Bragg and Non-Bragg Orders in Dynamic Holography Using Photorefractive Materials
Master of Science (M.S.), University of Dayton, 2016, Electrical Engineering
The photorefractive effect is a nonlinear optical effect that refers to change in refractive index of a material when it is illuminated by light. When illuminated by an interference pattern of coherent light source, this PR effect is responsible for two-beam coupling in PR materials, sometimes leading to energy exchange between the beams. PR materials can also be used as holographic storage media. In fact, dynamic real-time holographic interferometry can be implemented using photorefractive materials. To achieve this, two beams, one called the pump and one called the object beam, are introduced onto a photorefractive material to write the hologram of the object. During the hologram writing process, these beams can couple in intensity and/or phase which thereafter are responsible for self-diffraction of these beams, and can also give rise to Bragg and non-Bragg orders. The information from the Bragg and non-Bragg orders plays an important role in determining the 3D information of the object. In this thesis, an exact study is performed to examine the spatial evolution of Bragg and non-Bragg orders in photorefractive iron doped lithium niobate for different types of beam profiles such as Gaussian and flattops using an angular plane wave spectral decomposition technique. For Gaussian beam incidence, it has been found that higher or non-Bragg orders shows evidence of mode conversion of incident beam profiles. The numerical technique developed in this work should be useful in determining the phases of the Bragg and non-Bragg orders which have applications in dynamic phase-shifting digital holography and holographic interferometry.

Committee:

Partha Banerjee, Dr (Committee Chair); Monish Chatterjee, Dr (Committee Member); Joseph Haus, Dr (Committee Member)

Subjects:

Electrical Engineering; Optics

Keywords:

photorefractive materials; dynamic holography; Bragg and non Bragg orders; lithium niobate; angular spectrum; phase shifting digital holography

Krupa, Sean J.Nonlinear Optical Properties of Traditional and Novel Materials
Doctor of Philosophy (PhD), Ohio University, 2016, Physics and Astronomy (Arts and Sciences)
Nonlinear optical processes are an excellent candidate to provide the heralded, indistinguishable, or entangled photons necessary for development of quantum mechanics based technology which currently lack bright sources of these photons. In order to support these technologies, and others, two classes of materials: traditional and novel, were investigated via optical characterization methods with goal of gaining insight into which materials and experimental conditions yield the greatest nonlinear optical effects. Optical characterization of periodically poled lithium niobate (PPLN) helped support the development of a simple, efficient photon pair source that could be easily integrated into optical networks. Additionally, an in-situ measurement of the 2nd order nonlinear optical coefficient was developed to aid in the characterization of PPLN pair sources. Lastly, an undergraduate demonstration of quantum key distribution was constructed such that students could see the primary application for PPLN photon pair sources in an affordable, approachable demonstration. A class of novel optical materials known as 2D materials has been identified as potential replacements to the traditional nonlinear optical materials discussed in Part I. Through optical characterization of second harmonic generation (SHG) the ideal conditions for spontaneous parametric downconversion were established as well as signal thresholds for successful detection. Attempts to observe SPDC produces hints that weak generate SPDC may be present in WS2 samples however this is incredibly difficult to confirm. As growth techniques of 2D materials improve, a photonic device constructed from these materials may be possible, however it will need some mechanism e.g. stacking, a cavity, etc. to help enhance the SPDC signal.

Committee:

Eric Stinaff (Advisor); Alexander Govorov (Committee Member); Savas Kaya (Committee Member); Nancy Sandler (Committee Member)

Subjects:

Optics; Physics

Keywords:

Optics; Photonics; Lithium Niobate; 2D Materials; 2D Transition Metal Dichalcogenides; Quantum Key Distribution

Tuncay, OrbayWireless Strain Gauge System in a Multipath Environment
Master of Science, The Ohio State University, 2008, Electrical and Computer Engineering

A wireless strain sensing system utilizing passive, wireless, physically small and light weight sensors is desirable for measuring strain in harsh environments such as jet engine compressor and turbine blades. A cluttered and time varying environment results in high loss, blockage, multipath and modulation of the electromagnetic wave. Also, temperature changes affect the sensitivity of the strain measurement. Isolating the information signal from the reverberations in the environment requires time delays in the order of 100s of ns for jet engine environment. Therefore, a wireless strain gauge system that utilizes surface acoustic wave (SAW) strain sensors was studied and tested.

SAW strain sensors are designed to operate at 2.45GHz. Electron beam lithography is used to achieve minimum required feature size at this frequency. The fabrication process is outlined and scanning electron microscope images of some results are given.

A transceiver circuit is designed and constructed. The circuit is tested in free space, in the presence of signal blockage and a time varying channel. Measurements are shown to be in good agreement with predicted data. Sources of errors in the setup are identified to be leakage from transceiver circuit switches and bounce waveforms from the transceiver antenna.

A General Electric J85 jet engine compressor section is analyzed for signal propagation characteristics. Minimum frequency that can propagate through the compressor section is determined to be 5.2GHz. Measurements are done to show that circumferential polarization propagates stronger than radial inside the compressor section. An analytical approximation for the compressor section is generated by modeling compressor section blades as rectangular waveguides. Good agreement on cutoff frequency is achieved for circumferential polarization with the analytical predictions and measurement.

SAW temperature and strain sensors are measured in comparison to traditional gauges. This concept can be generalized to measuring many different physical quantities wirelessly without disturbing the operation of the equipment.

Committee:

Roberto Rojas-Teran (Advisor); Eric Walton K. (Committee Member); Jonathan Young D. (Committee Member)

Subjects:

Electrical Engineering; Engineering; Experiments

Keywords:

wireless strain sensor; surface acoustic wave (SAW); jet engine; multipath; RFID; strain gauge; wireless strain measurement; SAW fabrication; Lithium Niobate