Browsing by Subject "Nonlinear optics"
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Item Design and Fabrication of Integrated Optical Waveguides and Sidewall Bragg Gratings(2014-11-20) Wang, XinIn this dissertation, a novel design platform with arsenic tri-sulfide (As2S3) on titanium-diffused lithium niobate substrate (Ti:LiNbO3) is introduced to provide physical foundation for integrated optical device applications. LiNbO3 possesses excellent birefringence, electro-optical and acousto-optical effects that enable its high efficiency in nonlinear parametric frequency conversions and flexible tuning capabilities. Secondly, high-quality, low-loss channel waveguide can be made by thin-film metal diffusion or proton exchange with high reproducibility. The mode area size of the channel waveguide is close to single-mode fiber, leading to negligible coupling loss. As2S3 has a large index that provides strong mode confinement and tight bending radii for high integration densities. Both materials exhibit broad transparency: 0.4-5.0 ?m for LiNbO3 and 0.63-11.0 ?m for As2S3, making it possible to extend their applications to mid-infrared (3-20 ?m) regime. On this design platform, a hybrid waveguide structure is optimized for efficient mid-infrared radiation at 4.0-4.9 ?m by phase-matched difference frequency generation (DFG). The hybrid waveguide is designed for single mode operation. A normalized power conversion efficiency of 20.52%W^-1cm^-2 is theoretically predicted on a 1 mm-long waveguide pumped at 50 mW, which is the highest efficiency record for LiNbO3. Using a tunable pump at 1.38-1.47 ?m or signal at 1.95-2.15 ?m, a tuning range at 4.0-4.9 ?m is achieved. Such hybrid optical waveguides are feasible for mid-infrared emission with mW powers and sub-nanometer linewidths. Besides, sidewall Bragg gratings in As2S3-Ti:LiNbO3 waveguides are fabricated by electron beam lithography and metal liftoff process. Spectrum measurements are in good agreement with numerical fittings. The measured rejection bandwidth is at 2.4-6.7 nm. Coupling coefficients ranging from 2.5 mm^-1 to 8.9 mm^-1 are obtained by altering the grating depth. A transmission peak with a 3-dB bandwidth of ~0.25 nm is observed on a 432 ?m -long phase-shifted grating. Such integrated sidewall gratings are useful for various optical devices including optical filters, switches, modulators, lasers, sensors, and wavelength division multiplexing (WDM). In addition, optical refractive index sensors are designed with phase-shifted sidewall gratings in slot waveguide based on silicon-on-insulator (SOI) platform. The designed optical sensors have a minimum detection limit on the order of 10-6, a linear response and a compact device dimension as small as 11.7 ?m offering the capabilities for optical sensor array deployment and lab-on-a-chip integration.Item Design, synthesis, and application of lithographic resists and nonlinear optical materials(2009-05) Long, Brian Keith; Willson, C. G. (C. Grant), 1939-Fluorinated norbornene monomers exhibit the requisite properties for inclusion in 157 nm photoresists, but traditional addition and radical polymerizations with these monomers have failed. Norbornanediols provide an alternate route to these materials via condensation polymerization, and methods have been developed for the efficient synthesis of the exo-2-syn-7- and endo-2-exo-3-dihydroxynorbornanes. Synthesis of the fluorinated analogues is complicated by steric and electronic effects; however, a high-yielding synthesis of endo-2-exo-3-dihydroxynorbornane bearing a 5-endo-[2,2-bis(trifluoromethyl)hydroxyethyl] substituent as well as its corresponding polymer are reported. As an alternative to 157 nm and other optical lithographies, Step and Flash Imprint Lithography, or S-FIL®, was introduced in 1999 by The University of Texas at Austin. It has proven to be a cost effective, high resolution alternative to traditional optical lithography. Often in the S-FIL process, residual resist may become imbedded within the template features resulting in device defects due to the imprint and repeat nature of S-FIL. The high silicon and cross-linking content of the resist formulations are extremely difficult, if not impossible to remove from quartz imprint mold without template degradation. Our approach to this problem was the synthesis of a family of thermally reversible, cross-linkable monomers that will facilitate resist removal while maintaining template integrity. Our monomers utilize classic Diels-Alder chemistry to provide thermal reversibility, while pendant acrylate functionalities facilitate cross-linking. Herein we report the synthesis of several Diels-Alder compounds, incorporate them into resist formulations, and test their efficacy for resist removal. In an effort to develop unique patternable materials, our laboratory is currently engaged in the design and development of photonic crystals comprised of organic elements with highly stable electro-optic activity. Fabrication of these devices requires polymers that can be patterned at high resolution, have large second order nonlinear optical (NLO) coefficients, and that are thermally stable after poling. Our route to these materials involves the synthesis of a prepolymer that can be spin coated, poled, and then fixed by a photochemical cross-linking reaction. We now describe an efficient synthetic route to a new class of biscross-linkable monomers and the characteristics of their corresponding nonlinear optical polymers.Item Development of femtosecond laser endoscopic microsurgery(2011-05) Hoy, Christopher Luk, 1982-; Ben-Yakar, Adela; Hall, Matthew J.; Ho, Paul S.; Sokolov, Konstantin V.; Tunnell, James W.Femtosecond laser microsurgery has emerged as a remarkable technique for precise ablation of biological systems with minimal damage to their surrounding tissues. The combination of this technique with nonlinear optical imaging provides a means of microscopic visualization to guide such surgery in situ. A clinical endoscope capable of image-guided femtosecond laser microsurgery will provide physicians a means for cellular-level microsurgery with the highest precision. This dissertation focuses the development of a miniaturized fiber-coupled probe for image-guided microsurgery, towards future realization as a clinical endoscope. The first part of the dissertation describes the development of an 18-mm diameter probe. This development includes delivery of femtosecond laser pulses with pulse energy in excess of 1 µJ through air-core photonic bandgap fiber, laser beam scanning by a microelectromechanical system scanning mirror, and development of a new image reconstruction methodology for extracting increased temporal information during Lissajous beam scanning. During testing, the 18-mm probe compares favorably with the state-of-the-art as a microscopic imaging tool and we present the first known demonstration of cellular femtosecond laser microsurgery through an optical fiber. The second part of the dissertation explores further refinement of the design into a streamlined package with 9.6 mm diameter and improved imaging resolution. Study of the optical performance through analytical and computer-aided optical design indicates that simple custom lenses can be designed that require only commercial-grade manufacturing tolerances while still producing a fully aberration-corrected microsurgical endoscope. With the 9.6-mm probe, we demonstrate nonlinear optical imaging, including tissue imaging of intrinsic signals from collagen, using average laser powers 2-3× lower than the current state-of-the-art. We also demonstrate the use of the 9.6-mm probe in conjunction with gold nanoparticles for enhanced imaging and microsurgery through plasmonics. Finally, in the third part of this dissertation, we detail bench-top development of a new clinical application for combined femtosecond laser microsurgery and nonlinear optical imaging: the treatment of scarred vocal folds. We show the utility of femtosecond laser microsurgery for creating sub-epithelial voids in vocal fold tissue that can be useful for enhancing localization of injectable biomaterial treatments. We demonstrate that a single compact fiber laser system can be utilized for both microsurgery and imaging. Furthermore, the proposed clinical technique is shown to be achievable with parameters (e.g., pulse energy, focused spot size) that were found to be attainable with fiber-coupled probes while still achieving ablation speeds practical for clinical use.Item Nonlinear and wavelength-tunable plasmonic metasurfaces and devices(2014-12) Lee, Jongwon; Belkin, Mikhail A.Wavelength-tunable optical response from solid-state optoelectronic devices is a desired feature for a variety of applications such as spectroscopy, laser emission tuning, and telecommunications. Nonlinear optical response, on the other hand, has an important role in modern photonic functionalities, including efficient frequency conversions, all-optical signal processing, and ultrafast switching. This study presents the development of optical devices with wavelength tunable or nonlinear optical functionality based on plasmonic effects. For the first part of this study, widely wavelength tunable optical bandpass filters based on the unique properties of long-range surface plasmon polaritons (LR SPP) are presented. Planar metal stripe waveguides surrounded by two different cladding layers that have dissimilar refractive index dispersions were used to develop a wide wavelength tuning. The concept was demonstrated using a set of index-matching fluids and over 200nm of wavelength tuning was achieved with only 0.004 of index variation. For practical application of the proposed concept, a thermo-optic polymer was used to develop a widely tunable thermo-optic bandpass filter and over 220 nm of wavelength tuning was achieved with only 8 ºC of temperature variation. Another novel approach to produce a widely wavelength tunable optical response for free-space optical applications involves integrating plasmonic metasurfaces with quantum-electronic engineered semiconductor layers for giant electro-optic effect, which is proposed and experimentally demonstrated in the second part of this study. Coupling of surface plasmon modes formed by plasmonic nanoresonators with Stark tunable intersubband transitions in multi-quantum well structures induced by applying bias voltages through the semiconductor layer was used to develop tunable spectral responses in the mid-infrared range. Experimentally, over 310 nm of spectral peak tuning around 7 μm of wavelength with 10 ns response time was achieved. As the final part of this study, highly nonlinear metasurfaces based on coupling of electromagnetically engineered plasmonic nanoresonators with quantum-engineered intersubband nonlinearities are proposed and experimentally demonstrated. In the proof-of-concept demonstration, an effective nonlinear susceptibility over 50 nm/V was measured and, after further optimization, over 480 nm/V was measured for second harmonic generation under normal incidence. The proposed concept shows that it is possible to engineer virtually any element of the nonlinear susceptibility tensor of the nonlinear metasurface.Item Nonlinear optical spectroscopy of silicon-boron and other silicon-adsorbate systems(2001-08) Lim, Daeyoung; Downer, Michael CoffinItem Resonant optical nonlinearities in cascade and coupled quantum well structures(2009-05-15) Xie, FengResonant or near resonant optical nonlinearities in semiconductor coupled quantum-well systems are discussed. Quantum engineered coupled or cascade quantumwell structures can provide giant nonlinear susceptibilities for various optical nonlinear processes. Nonlinearities integrated within quantum cascade lasers (QCL) showed great potential in various applications in the infrared range. Several schemes of nonlinearities are proposed and discussed in this work. Integrating difference frequency generation (DFG) with QCL can yield long wavelength radiation, such as terahertz light. The DFG process does not require population inversion at a transition associated with low photon energy; however, this requirement is necessary to lasers, such as QCL, and is hard to meet, because of the thermal backfilling and inefficient injection or pumping at room temperature. Therefore terahertz radiation due to DFG QCL for room temperature is proposed. On the other hand, the second harmonic generation can double laser frequency, and then push radiation frequency of AlInAs/GaInAs/InP based QCL to short wavelengths such as 3 ?m and shorter. Optical nonlinearities can extend working frequencies of light sources, and also can help to improve light detection. For example, a sum frequency generation can upconvert mid/far-IR signal into near-IR signal with strong near-IR pump light, namely high efficient near-IR photon detector could be employed to detect mid/far-IR light. A specific designed quantum well structure of this frequency up-conversion scheme is discussed. A scheme of monolithic in-plane integration of the optical nonlinearities with QCL is also proposed. In this scheme, an optical nonlinear section is made from the same quantum well structure of a QCL, and is under an independent applied bias. Due to the independence of the applied bias, the nonlinearities can be tuned flexibly. In particular, a widely tunable Raman laser based on this scheme could be achieved. A frequency up-conversion based on sum frequency generation process in coupled quantum-well structure is also proposed for mid-infrared detection. By converting mid-IR signal to near-IR, superior near-IR detector such as silicon avalanche photo diode (APD) can be employed. The scheme can provide lower noise equivalent power (NEP) or higher detectivity compared with regular semiconductor photo detectors. A scheme of lasing without inversion (LWI) based on QCL for THz radiation is proposed. A ladder type three-level system for LWI process is integrated into a boundto- continue high power QCL at 10 ?m. The proposed LWI generates THz signal at 69 ?m. An optical gain about 80 cm-1 is achieved, against a waveguide loss about 30 cm-1 in a semi insulator (SI) surface plasmon waveguide.Item The effect of nonlinearity in robotic vision systems(Texas Tech University, 2000-08) Chanda, RupenIn this thesis, an application of generic approach to nonlinear image processing is described which is implemented in real-life application. Consideration is given to the general geometrical resampling process in which output pixels are estimated by interpolation of input pixels. However, here the geometrical resampling process is not at regular time interval. This generic approach can be used to solve several kinds of nonlinear image restoration problems when the image is being grabbed by a line scan camera. With a little modification, this algorithm can be easily implemented in hardware, so that image can be corrected during the grabbing period.