Planar integrated plasmonic mid-IR spectrometer
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Planar integrated plasmonic mid-IR spectrometer Farnood K. Rezaie1, Chris J. Fredericksen2, Walter R. Buchwald3, 4, Justin W. Cleary5, Evan M. Smith1, Imen Rezadad1, Janardan Nath1, Pedro Figueiredo1, Monas Shahzad1, Javaneh Boroumand1, Mehmet Yesiltas1, Gautam Medhi1, Andrew Davis4 and Robert E. Peale1 1 Department of physics, University of Central Florida, FL 32816 2LRC Engineering, Inc., 9345 Chandon Dr., Orlando, FL 32825 3 Department of Physics and Engineering, University of Massachusetts, Boston, MA 02125 4 Solid State Scientific Corporation, 27-2 Wright Rd., Hollis, New Hampshire 03049 5 Sensors Directorate, AFRL, Wright Patterson AFB, Dayton, OH 45433 ABSTRACT A compact spectrometer-on-a-chip featuring a plasmonic molecular interaction region has been conceived, designed, modeled, and partially fabricated. The silicon-on-insulator (SOI) system is the chosen platform for the integration. The low loss of both silicon and SiO2 between 3 and 4 μm wavelengths enables silicon waveguides on SiO2 as the basis for molecular sensors at these wavelengths. Important characteristic molecular vibrations occur in this range, namely the bond stretching modes C-H (Alkynes), O-H (monomeric alcohols, phenols) and N-H (Amines), as well as CO double bonds, NH2, and CN. The device consists of a broad-band infrared LED, photonic waveguides, photon-to-plasmon transformers, a molecular interaction region, dispersive structures, and detectors. Photonic waveguide modes are adiabatically converted into SPPs on a neighboring metal surface by a tapered waveguide. The plasmonic interaction region enhances optical intensity, which allows a reduction of the overall device size without a reduction of the interaction length, in comparison to ordinary optical methods. After the SPPs propagate through the interaction region, they are converted back into photonic waveguide modes by a second taper. The dispersing region consists of a series of micro-ring resonators with photodetectors coupled to each resonator. Design parameters were optimized via electro-dynamic simulations. Fabrication was performed using a combination of photo- and electron-beam-lithography together with standard silicon processing techniques. INTRODUCTION Surface Plasmon Polaritons (SPP), inhomogeneous electromagnetic waves tightly confined to the surface of conductors, provide intense localized electromagnetic fields and a potential means information transport in nano-photonic applications. This work investigates the integration of plasmonic elements with silicon photonics to provide a chip scale chemical sensor and spectrometer compatible with CMOS fabrication technology [1]. Silicon on insulator (SOI) waveguides direct mid-IR light to an analyte interaction region, where surface plasmons are generated in metallic slot waveguides to pass through, and be selectively absorbed by, adsorbed chemical species. Efficiently reconverted back to photonic waveguide modes, the transmitted IR optical field is then spectrally analyzed by an array of ring-resonators and integrated detecto
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