Active Metal-Insulator-Metal Plasmonic Devices

As the field of photonics constantly strives for ever smaller devices, the diffraction limit of light emerges as a fundamental limitation in this pursuit. A growing number of applications for optical "systems on a chip" have inspired new ways of circumventing this issue. One such solution to this problem is active plasmonics. Active plasmonics is an emerging field that enables light compression into nano-structures based on plasmon resonances at a metal-dielectric interface and active modulation of these plasmons with an applied external field. One area of active plasmonics has focused on replacing the dielectric layer in these waveguides with an electro-optic material and designing the resulting structures in such a way that the transmitted light can be modulated. These structures can be utilized to design a wide range of devices including optical logic gates, modulators, and filters. This thesis focuses on replacing the dielectric layer within a metal-insulator-metal plasmonic waveguide with a range of electrically active materials. By applying an electric field between the metal layers, we take advantage of the electro-optic effect in lithium niobate, and modulating the carrier density distribution across the structure in n-type silicon and indium tin oxide. The first part of this thesis looks at fabricating metal-insulator-metal waveguides with ion-implantation induced layer transferred lithium niobate. The process is analyzed from a thermodynamic standpoint and the ion-implantation conditions required for layer transfer are determined. The possible failure mechanisms that can occur during this process are analyzed from a thin-film mechanics standpoint, and a metal-bonding method to improve successful layer transfer is proposed and analyzed. Finally, these devices are shown to naturally filter white light into individual colors based on the interference of the different optical modes within the dielectric layer. Full-field electromagnetic simulations show that these devices can preferentially couple to any of the primary colors and can tune the output color of the device with an applied field. The second part of this thesis looks at fabricating metal-insulator-metal waveguides with n-type silicon and indium tin oxide. With the silicon device, by tuning the thicknesses of the layers used in a metal-oxide semiconductor geometry, the device we call the "plasMOStor" can support plasmonic modes as well as exactly one photonic mode. With an applied field, this photonic mode is pushed into cutoff and modulation depths of 11.2 dB are achieved. With the indium tin oxide device, the doping density within the material is changed and as a result, the plasma frequency is shifted into the near-infrared and visible wavelengths. Using spectroscopic ellipsometry, the structure is characterized with and without an applied electric field, and measurements show that when an accumulation layer is formed within the structure, the index of refraction within that layer is significantly changed and as a result, will change the optical modes supported in such a structure.</p

Single crystalline BaTiO_3 thin films synthesized using ion implantation induced layer transfer

Layer transfer of BaTiO3 thin films onto silicon-based substrates has been investigated. Hydrogen and helium ions were co-implanted to facilitate ion-implantation-induced layer transfer of films from BaTiO3 single crystals. From thermodynamic equilibrium calculations, we suggest that the dominant species during cavity nucleation and growth are H2, H+, H2O, Ba2+ and Ba–OH, and that the addition of hydrogen to the Ba–Ti–O system can effectively suppress volatile oxide formation during layer transfer and subsequent annealing. After ion implantation, BaTiO3 layers contain microstructural defects and hydrogen precipitates in the lattice, but after layer transfer, the single crystal is found to be stoichiometric. Using direct wafer bonding and layer splitting, single crystal BaTiO3 thin films were transferred onto amorphous Si3N4 and Pt substrates. Micro-Raman spectroscopy indicated that the density of defects generated by ion implantation in BaTiO3 can be significantly reduced during post-transfer annealing, returning the transferred layer to its single crystal state. Characterization using piezoresponse force microscopy shows that the layer transferred thin films are ferroelectric, with domain structures and piezoresponse characteristics similar to that of bulk crystals

A Survey of Selected Middle School Programs in Washington, Oregon, and California

It was the purpose of this study (1) to determine if the reasons for implementing middle schools have been justified by practice; (2) to determine the major problems principals have encountered with the middle school; and (3) to provide recommendations for school districts considering the adoption of a middle school program

PlasMOStor: A metal-oxide-Si field effect plasmonic modulator

Realization of chip-based all-optical and optoelectronic computational networks will require ultracompact Si-compatible modulators, ideally comprising dimensions, materials, and functionality similar to electronic complementary metal−oxide−semiconductor (CMOS) components. Here we demonstrate such a modulator, based on field-effect modulation of plasmon waveguide modes in a MOS geometry. Near-infrared transmission between an optical source and drain is controlled by a gate voltage that drives the MOS into accumulation. Using the gate oxide as an optical channel, electro-optic modulation is achieved in device volumes of half of a cubic wavelength with femtojoule switching energies and the potential for gigahertz modulation frequencies

Origin of undesirable cracks during layer transfer

We investigate the origin of undesirable transverse cracks often observed in thin films obtained by the layer transfer technique. During this process, two crystals bonded to each other containing a weak plan produced by ion implantation are heated to let a thin layer of one of the material on the other. The level of stress imposed on the film during the heating phase due to the mismatch of thermal expansion coefficients of the substrate and the film is shown to be the relevant parameter of the problem. In particular, it is shown that if the film is submitted to a tensile stress, the microcracks produced by ion implantation are not stable and deviate from their straight trajectory making the layer transfer process impossible. However, if the compressive stress exceeds a threshold value, after layer transfer, the film can buckle and delaminate, leading to transverse cracks induced by bending. As a result, we show that the imposed stress \sigma_m - or equivalently the heating temperature - must be within the range -\sigma_c < \sigma_m < 0 to produce an intact thin film where \sigma_c depends on the interfacial fracture energy and the size of defects at the interface between film and substrate.Comment: 26 page

Active plasmonic devices and optical metamaterials

We studied active near-infrared metamaterials based on phase transition of vanadium oxide thin films, asymmetrically coupled split-ring resonators for narrowing resonance line-widths , field effect modulation of plasmon propagation and 3D single layer, plasmonic negative-index metamaterials

Advanced silicon processing for active planar photonic devices

Using high quality, anisotropically etched Si waveguides bonded to InGaAsP, the authors demonstrate a hybrid laser, whose optical profile overlaps both Si and III-V regions. Continuous wave laser operation was obtained up to 45 °C, with single facet power as high as 12.7 mW at 15 °C. Planar Si optical resonators with Q = 4.8 × 10^6 are also demonstrated. By using a SF_6/C_(4)F_8 reactive ion etch, followed by H_(2)SO_4/HF surface treatment and oxygen plasma oxide, the optical losses due to the waveguide and the bonding interface are minimized. Changes of optical confinement in the silicon are observed due to waveguide width variation

Hybrid Electrically Pumped Evanescent Si/InGaAsP Lasers

Hybrid Si/InGaAsP Fabry-Perot evanescent lasers are fabricated via wafer bonding. Compared with previous similar devices, the current threshold density, turn-on voltage, output power and slope efficiency are all improved. Images show modal confinement to Silicon

Tunable color filters based on metal-insulator-metal resonators

We report a method for filtering white light into individual colors using metal−insulator−metal resonators. The resonators are designed to support photonic modes at visible frequencies, and dispersion relations are developed for realistic experimental configurations. Experimental results indicate that passive Ag/Si_3N_4/Au resonators exhibit color filtering across the entire visible spectrum. Full field electromagnetic simulations were performed on active resonators for which the resonator length was varied from 1−3 μm and the output slit depth was systematically varied throughout the thickness of the dielectric layer. These resonators are shown to filter colors based on interference between the optical modes within the dielectric layer. By careful design of the output coupling, the resonator can selectively couple to intensity maxima of different photonic modes and, as a result, preferentially select any of the primary colors. We also illustrate how refractive index modulation in metal−insulator−metal resonators can yield actively tunable color filters. Simulations using lithium niobate as the dielectric layer and the top and bottom Ag layers as electrodes, indicate that the output color can be tuned over the visible spectrum with an applied field