ABSTRACT
The anchoring energy of liquid crystals was shown to be tunable by surface nanopatterning of periodic lines and spaces. Both the pitch and height were varied using hydrogen silsesquioxane negative tone electron beam resist, providing for flexibility in magnitude and spatial distribution of the anchoring energy. Using twisted nematic liquid crystal cells, it was shown that this energy is tunable over an order of magnitude. These results agree with a literature model which predicts the anchoring energy of sinusoidal grooves.
ABSTRACT
We have established a method to quantify and optimize the plasmonic behavior of aluminum thin films by coupling spectroscopic ellipsometry into surface plasmon polaritons using a liquid prism cell in a modified Otto configuration. This procedure was applied to Al thin films deposited by four different methods, as well as to single crystal Al substrates, to determine the broadband optical constants and calculate plasmonic figures of merit. The best performance was achieved with Al films that have been sputter-deposited at high temperatures of 350°C, followed by chemical mechanical polishing. This combination of temperature and post-processing produced aluminum films with both large grain size and low surface roughness. Comparing these figures of merit with literature values of gold, silver, and copper shows that at blue and ultraviolet wavelengths, optimized aluminum has the highest figure of merit of all materials studied. We further employ the Ashcroft and Sturm theory of optical conductivity to extract the electron scattering times for the Drude and effective interband transitions, interband transition energies, and the optical mass of electrons.
ABSTRACT
Actively tunable metal-insulator-metal waveguides that employ vanadium dioxide films as the active medium are analyzed numerically. Vanadium dioxide exhibits strong contrast between the optical properties of its insulating and metallic phases. In particular, the large optical absorption in the metallic phase makes it straightforward to implement broadband attenuation modulators and switches, but this strong loss can also complicate the design of other types of devices. We present a plasmonic waveguide that functions as an index modulator with Δn > 20% at λ0 = 1,550 nm (0.80 eV), by using a thin active layer to strike a balance between maximizing index contrast while mitigating attenuation. A second device is configured as a band-stop absorption modulator, taking advantage of symmetry to selectively suppress the TM1 and TM3 modes, with relatively minimal attenuation of the TM0 and TM2 modes.
ABSTRACT
We report a method for obtaining unity-order refractive index changes in the accumulation layer of a metal-oxide-semiconductor heterostructure with conducting oxide as the active material. Under applied field, carrier concentrations at the dielectric/conducting oxide interface increase from 1 x 10(21)/cm(3) to 2.8 x 10(22)/cm(3), resulting in a local refractive index change of 1.39 at 800 nm. When this structure is modeled as a plasmonic waveguide, the change corresponds to a modal index change of 0.08 for the plasmonic mode.
ABSTRACT
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(3)N(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 microm 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.
Subject(s)
Gold/chemistry , Light , Silicon Compounds/chemistry , Silver/chemistry , Color , Electromagnetic Phenomena , FiltrationABSTRACT
Hybrid Si/III-V, Fabry-Perot evanescent lasers are demonstrated, utilizing InGaAsP as the III-V gain material for the first time to our knowledge. The lasing threshold current of 300-mum-long devices was as low as 24 mA, with a maximal single facet output power of 4.2 mW at 15 degrees C. Longer devices achieved a maximal single facet output power as high as 12.7 mW, a single facet slope efficiency of 8.4%, and a lasing threshold current density of 1 kA/cm2. Continuous wave laser operation was obtained up to 45 degrees C. The threshold current density, output power, and efficiency obtained improve upon those of previously reported devices having a similar geometry. Facet images indicate that the output light is largely confined to the Si waveguide.
ABSTRACT
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.
