Browsing by Subject "Lithium niobate"
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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 Integration of Arsenic Trisulfide and Titanium Diffused Lithium Niobate Waveguides(2011-08-08) Solmaz, Mehmet E.A chalcogenide glass (arsenic-trisulfide, As2S3) optical waveguide is vertically integrated onto titanium-diffused lithium-niobate (Ti:LiNbO3) waveguides to add optical feedback paths and to create more compact optical circuits. Lithium-niobate waveguides are commonly used as building blocks for phase and amplitude modulators in high speed fiber communication networks due to its high electrooptic coefficient and low mode coupling loss to single-mode optical fibers. Although it can easily be modulated using an RF signal to create optical modulators, it lacks the intrinsic trait to create optical feedback loops due to its low core-to-cladding index contrast. Ring resonators are main building blocks of many chip-scale optical filters that require these feedback loops and are already demonstrated with other material systems. We have, for the first time, incorporated As2S3 as a guiding material on Ti:LiNbO3 and fabricated s-bends and ring resonators. We have examined As2S3-on-Ti:LiNbO3 waveguides at simulation, microfabrication, and optical characterization levels.Item Investigation of a Polarization Controller in Titanium Diffused Lithium Niobate Waveguide near 1530 nm Wavelength(2013-12-10) Sung, Won JuOptical polarization control in Ti diffused channel waveguides onto LiNbO_(3) substrates have been investigated near 1530 nm wavelength regime by utilizing electro-optic effects of the substrate material. A device configuration composed of two polarization converters with a phase shifter centered between them and all integrated on a single optical channel waveguide was used. The polarization converters provided a means to control the polarization, and the phase shifter offered a tool to maintain the required phase condition between them. Single mode channel waveguides were fabricated by diffusing 7?m-wide Ti stripes into the LiNbO_(3) substrate. The polarization converters and phase shifter were formed by patterning aluminum surface electrodes on top of a SiO_(2) buffer layer. The polarization converters were produced in an interdigitated electrode form with a spatial period of 21 ?m, over 10.5 mm coupling length. The phase shifter was implemented in the form of a 6,000 ?m long electrode with 17 ?m gap. The characteristics of each electro-optic element in the integrated configuration were individually evaluated first, and then the behavior of the overall device as a polarization controller was investigated. Polarization conversion efficiency of 99.5% between TE and TM orthogonal modes was realized for the converters, and ?-radian phase shift between orthogonal modes was achieved with 40 V on the phase shifter. Using an optical vector analyzer (OVA) for characterizing the output, transformation of orthogonal or arbitrary incident polarization to either TE or TM polarization at the output was successfully realized. Suppression for the unwanted polarization at the output of approximately -40 dB near 1529.4 nm wavelength was obtained with voltages on both converters for TE?TM transformation, as well as 45o and 56^(o) incident polarization. For the incident orthogonal polarization case the transformation was realized without a voltage on the phase shifter supporting the implemented design parameters, and transformation of the obtained output back to its incident polarization through an induced ?-radian retardation was confirmed by applying 40 V on the phase shifter.