Robert Charbonneau

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.

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.

Long-range surface plasmon-polariton mode cutoff and radiation in embedded strip waveguides

Using a fully vectorial formulation, the normal mode analysis method is used to model the radiative spreading of surface plasmon-polariton mode input into regions where the bound surface mode is cut off or radiative. The analysis was performed at λ0=1.55μm for embedded finite width strip metal waveguides, where the metal was Au and the surrounding dielectrics were SiO2 and LiNbO3. Mode cutoff is induced by an asymmetry between the index of refraction of the top clad and the bottom clad. Comparisons between predictions and experimental results show very good agreement. The analysis was performed for a range of waveguide dimensions, and results show that a change in insertion loss of better than 20dB is possible for an appropriate waveguide and dielectric asymmetry. Practical applications to make use of this cutoff effect are outlined.

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...

Infrared Performance of Symmetric Surface-Plasmon Waveguide Schottky Detectors in Si

The internal quantum efficiency, responsivity, and sensitivity of symmetric surface-plasmon waveguide Schottky detectors in silicon are investigated theoretically at room temperature at λ0 = 1310 and 1550 nm. The detectors consist of a thin metal stripe buried in Si, forming Schottky contacts along all metal/Si interfaces, with detection occurring via internal photoemission over the Schottky barriers. Several metals are considered for the stripe (Au, Ag, Al, Cu, CoSi2). The internal quantum efficiency is significantly enhanced for stripes that are thin compared to the hot carrier attenuation length. Responsivities of 0.1 to 0.21 A/W and receiver sensitivities of -24 and -18 dBm are predicted for 1.5 and 10 GHz electrical bandwidths (~2.5 Gbit/s and >; 10 Gbit/s), respectively. This predicted performance, at room temperature, is competitive with the best cryogenically cooled conventional Schottky detectors and is adequate for optical interconnect and power monitoring. The detectors are attractive for applications requiring broadband (electrical and optical) infrared detectors in Si.

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.

Long-range surface plasmon-polariton mode cutoff and radiation

The normal-mode-analysis method is used to model the radiative spreading of long-range surface plasmon polariton modes injected into regions where the bound surface mode is cutoff or radiative. Mode cutoff is induced by an asymmetry between the index of refraction of the top cladding layer and that of the bottom. The analysis was performed at lambda(0)=1.55 microm for infinite-width (slab) metal waveguides where the metal was Au and the bounding dielectrics were SiO(2). Results show that a change in insertion loss of > 20 dB is possible for an appropriate waveguide geometry and dielectric asymmetry.