We experimentally demonstrated graphene plasmon resonant absorption in mid-IR by utilizing an
array of graphene nanoribbon resonators on SiO2 substrate. By tuning resonator width we probed
the graphene plasmons with λp ≤ λ0/100 and plasmon resonances as high as 0.240 eV (2100 cm-1) for 40 nm wide nanoresonators. Resonant absorption spectra revealed plasmon dispersion as well
as plasmon damping due to the interaction of graphene plasmons with the surface polar phonons in
SiO2 substrate and intrinsic graphene optical phonons. Graphene nanoribbons with varying
widths enabled us to identify the damping mechanisms of graphene plasmons and much reduced
damping was observed when the plasmon resonance frequencies were close to the substrate polar
phonon frequencies. Then, by direct ebeam exposure of graphene nanoresonators, we effectively
changed the carrier density and caused red-shift of the plasmon spectra. This work will provide
insight into light-sensitive, frequency-tunable photodetectors based on graphene’s plasmonic
excitations.
In this invited paper, we review some of our latest works on plasmonic antennas and their interactions with photonic
angular momentum. As receiving antennas, both theoretical and experimental results reveal that spiral plasmonic
antenna responds differently to photons with left-hand circular polarization and right-hand circular polarization. This
spin degeneracy removal finds many potential applications including extremely small circular polarization analyzer for
polarimetric imaging, parallel near field probes for optical imaging and sensing, nano-lithography and high density heat assisted magnetic recording. On the transmitter side, through coupling quantum dot nano-emitters to spiral plasmonic antenna, nano-scale spin photon sources with high directivity and circular polarization extinction ratio is demonstrated. Numerical modeling and experimental evidences also indicate that the emitted photons can be imprinted with the photonic spin angular momentum and orbital angular momentum information simultaneously via the interactions between photonic angular momentum and plasmonic antennas. These findings not only are useful for the fundamental understanding of the interaction between plasmonic antennas and photonic angular momentum but also illustrate the versatility of plasmonic antennas as building blocks for practical spin optics and quantum optics devices and systems.
Optical phased arrays are promising candidates for both RF signal processing and optical beam forming and steering.
These platforms not only enable accurate electrically controlled beam steering at high frequencies but also have the
potential to significantly improve the performance of future free-space optical communications systems. In this work we
exploit recent advancements in both nano-scale hybrid silicon-slot waveguides and electro-optic (EO) polymers to
demonstrate an integrated optical phased-array antenna. Specifically, we create a hybrid integrated "photonic circuit"
that connects an array of optical phase modulators, fed by a common optical signal and a 1x4 splitter, to a compact
optical waveguide diffraction array for optical beam steering applications. The fundamental characteristics of the
resulting integrated optical beam former, including the optical insertion loss, driving voltage, and phase control from the
waveguide aperture are summarized in this letter.
Silicon slot waveguide based Mach Zender interferometric modulators were built with electro-optic (EO) polymers in the slot as the modulated media. In order to enhance the macroscopic electro-optic effect in the polymers the molecules that provide the large polarizability need to be aligned prior to operation to match the direction of the applied modulating field. This aligning process, also called as poling process, is difficult in the slot waveguide modulators due to the unique structure and small dimensionality of the slots in the waveguides. While hybrid silicon-EO polymer modulators have been demonstrated with ultra low drive voltage, the polymer EO activity was low compared to thin film performances. We compared alternatives to enhance the poling field over the electro optic polymer and concluded that the well known surface states in silicon affect the conductivity of silicon significantly when thin silicon is used as poling electrode. A solution to this negative effect was attempted by passivating the surface with a 5 nm thin TiO2 conforming atomic layer deposition over the silicon prior to spin casting and poling the EO polymers. We achieved a factor of 2 enhancement in the polymer's electro optic activity after poling as a result and achieved a low 0.52 V*cm voltage length product in the MZ modulator we built with this technique.
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