Nancy Lahoud

Demonstration of integrated optics elements based on long-ranging surface plasmon polaritons

An experimental investigation of long-ranging surface plasmonpolariton waves guided along thin finite width Au structures embedded in a homogeneous background dielectric is reported. The operation of key passive integrated optics elements such as straight waveguides, s-bends, y-junctions and couplers is demonstrated at a free space optical wavelength of 1550 nm. The influence of some important design parameters on the performance of these elements is presented and discussed.

Characterization of long-range surface-plasmon-polariton waveguides

Measurements of the attenuation and excitation efficiency of the long-range surface-plasmon-polariton mode supported by waveguides comprised of one or many thin metal films of finite width embedded in dielectric were made in the near infrared (λ0=1550nm). Au films 31, 25, and 20 nm thick, and Ag films 20 nm thick were used to implement the structures. The lowest attenuations measured among the Au and Ag waveguides are 0.42 and 0.32dB∕mm, respectively, corresponding to propagation lengths of 10 340, and 13572μm, respectively. These propagation lengths are longer than those of the single-interface surface-plasmon polariton in the corresponding semi-infinite structures by factors of 93 and 138, respectively. These factors are the largest reported to date for long-range surface-plasmon-polariton waves. The largest excitation efficiency measured among the set of Au structures is 98%. Theoretical results were obtained for all of the structures characterized experimentally using an accurate electromagnetic-field...

Passive integrated optics elements based on long-range surface plasmon polaritons

Waveguides and passive integrated optics elements constructed from thin metal films of finite width embedded in a homogeneous background dielectric and propagating long-range surface plasmon polaritons (LRSPPs) have been characterized experimentally at free-space optical wavelengths near 1550 nm. Straight and curved waveguides, s-bends, four-port couplers, y-junctions, and Mach-Zehnder interferometers have been carefully characterized. Additionally, rigorous models based on modal decomposition have been proposed for all of these elements and validated via comparisons with the measurements. Excellent qualitative and quantitative agreement between theory and experiment is observed for all structures over all measurement wavelengths. It is hoped that this work will help further establish this new integrated optics technology, taking it beyond demonstrators.

Thermally Activated Variable Attenuation of Long-Range Surface Plasmon-Polariton Waves

A thermally activated variable attenuator for long-range (low-loss) surface plasmon-polariton (LRSPP) waves is discussed in this paper. The surface plasmon waveguide consists of a thin Au stripe on a thick layer of SiO2, which is covered by a thick layer of index-matched polymer. The structure is optically symmetric near room temperature, supporting an LRSPP. Increased attenuation of the mode occurs upon heating of the Au stripe via the passage of current therein. Heating substantially changes the refractive index of the polymer near the stripe, rendering the structure highly optically asymmetric and cutting off the mode. Thermal modeling results that link the injected current density to the refractive-index perturbation are presented and discussed. Experimental results validate the thermal modeling and demonstrate the operation of the device at a free-space optical wavelength near 1550 nm. The resistivity of the stripe is also measured as a function of the drive current, and the simultaneous use of the stripe as a thermal monitor is discussed and demonstrated

Demonstration of Bragg gratings based on long-ranging surface plasmon polariton waveguides.

An experimental investigation of long-ranging surface plasmon-polariton waves guided along Bragg gratings fabricated from a thin finite width Au film embedded in a homogeneous background dielectric is reported. The operation of four grating families is demonstrated near the free space optical wavelength of 1550 nm. The influence of the length of the grating and the depth of effective index modulation on the performance of these elements is presented and discussed.

Bragg gratings based on long-range surface plasmon-polariton waveguides: comparison of theory and experiment

Measured optical spectra are presented for a family of third-order uniform step-in-width Bragg gratings operating in the long-range surface plasmon-polariton mode supported by thin finite-width Au films in a homogeneous dielectric background. The spectra are compared quantitatively with theoretical predictions generated by a model proposed for the gratings. Physical measurements of critical features achieved on-wafer have been made and the results used in the theoretical model. The measured and modeled results are generally in good agreement. The largest reflectance measured among the set of gratings characterized is 47.4%, the bandwidths (full width at half maximum) measured range from 0.2 to 0.4 nm, and the measured Bragg wavelengths coincide to 1544.2 nm for all of the gratings.

Long-range surface plasmon-polariton waveguides and devices in lithium niobate

Long-range surface plasmon-polariton waveguides and devices based on a thin narrow Au stripe buried in z-cut LiNbO3 claddings and designed for operation at free-space optical wavelengths near 1550nm are described and discussed. Parallel or antiparallel crystal orientations for the claddings lead to phase modulation or intensity modulation via mode cutoff, respectively. Theoretical results are given for straight waveguides, curved waveguides, and Bragg gratings in symmetric claddings, and for straight waveguides in electro-optically induced asymmetric claddings. The main theoretical findings are that 1dB∕mm of attenuation (or less) is achievable using Au stripes of reasonable dimensions (0.5–1μm wide, 20–40nm thick), that low overlap losses (<1dB) to large and small modes are achievable for the same stripe thickness, that radii of curvature in the range of 10–30mm are required for stripes having a moderate (10−3) confinement, that first order gratings having a reflectance of 0.9 and a bandwidth of 0.75nm a...

Long-Range Surface Plasmons Along Membrane-Supported Metal Stripes

Long-range surface plasmon-polaritons propagating along a thin metal stripe on a supporting ultrathin freestanding dielectric membrane (the ldquo<i>membrane-supported metal stripe</i> rdquo) have been investigated in detail theoretically and experimentally. The materials considered for the structure are Au on a thin Cr or Ti adhesion layer as the stripe, Si₃N₄ or SiO₂ as the membrane, and vacuum (air) or H₂O as the background. Three operating wavelengths were considered: lambda₀ = 632.8, 1310, and 1550 nm. Theoretical results reveal that the long-range mode in this structure has a moderate mode power attenuation (MPA ~ &nbsp;2-12 dB/mm at lambda₀ = 1310 nm), good confinement [ <i>n</i>_eff - <i>n</i>₁&nbsp; ~ (1-3) &times;10^-3 ], a good <i>M</i>₂ figure of merit (10-25), and a reasonable range extension factor (<i>R</i>_<i>e</i>&nbsp; ~ &nbsp;3-25), when operated in vacuum or in H₂O and for reasonable dimensions. The adhesion layer was found to modestly impact the attenuation. Structures were fabricated as Au/Cr stripes (25 or 20 nm thick) on freestanding (20 or 30 nm thick) large-area Si₃N₄ membranes clamped around their perimeter, and propagation of the long-range mode was observed and characterized in air and in H₂O (and similar optical fluids). The measurements reported include an optical streak, mode outputs, output polarization, and MPA. Errors between measured and theoretical attenuations were below about 7% for all of the structures tested.

Wafer-bonded surface plasmon waveguides

Direct wafer bonding and thinning were explored as an approach for constructing long-range surface plasmon waveguides. The structures consist of a thin metal stripe deposited into a shallow trench etched into one of the claddings, to which another cladding of the same material is directly bonded. The approach was developed first using Pyrex wafers in order to assess feasibility and then using lithium niobate wafers. Optical and electro-optical measurements validate the approach.

Fabrication of surface plasmon waveguides and integrated components on ultrathin freestanding membranes

The fabrication and physical characterisation of waveguides and integrated components on freestanding membranes are described. The waveguides consist of a thin (20–25nm) narrow (∼5μm) Au∕Cr stripe, on an ultrathin (20–30nm) large-area (∼1mm2) freestanding Si3N4 membrane clamped around its perimeter to an underlying Si substrate. The integrated components are implemented with this waveguide and consist of Mach-Zehnder interferometers and couplers. The waveguide and components are dimensioned such that they propagate long-range surface plasmon-polariton waves in a vacuum (air) or H2O background. The fabrication process flow adopted and some specific process steps are described. Physical characterisation was conducted on structures having undergone intermediate process steps and on finished structures, and characterisation results are given and discussed. The structures were found to be robust enough for careful use, and to routinely sustain ∼3μN of point force without shattering.