We demonstrate an ultra-compact on-chip spectrometer for near-infrared (NIR) spectroscopy based on narrow-band band-pass filter array. Each individual filter consists of a plasmonic metallic grating with subwavelength period and extremely narrow slits on a quartz substrate, with a polymer cover layer as the waveguide layer. A narrow-band guided-mode resonance (GMR) associated with a surface-plasmon resonance (SPR) gives rise to the narrow-band transmission spectrum. Full width at half maximum (FWHM) of fabricated filter’s spectrum is measured to be from 7 to 13 nm, and the operation bandwidth of the entire filter array covers wavelength range over 270 nm from 1510 to 1780 nm. We measure the NIR absorbance spectrum of xylene using our filter array device to demonstrate its application as a spectrometer.
Nanoantenna is used for coupling free space radiation to subwavelength plasmonic waveguide. We provide a theoretical design of ultra-compact dipole nanoantennas --- Yagi-Uda antenna with a reflector in telecom range and experimentally demonstrate efficient optical coupling between lensed fiber and plasmonic slot waveguide by utilizing our designed nanoantenna. We also prove that the couple-in efficiency of 8% from the lensed fiber does not equal to the couple-out efficiency of 50% from the plasmonic slot waveguide using the same nanoantenna design, which is different than many published and experimental results. We also study the relationship between couple in efficiency and the incident light spot size, which is experimentally characterized.
We present theoretical design and experimental demonstration of electro-optic modulation in metallic slits infiltrated by polymer. Dynamic control over surface plasmon plaritons(SPPs) was achieved by modulating the refractive index of the polymer layer adjacent to the metal surface with interdigitated configuration. Intensity modulation of the Fano resonance of the sub-wavelength plasmonic structure was observed and expected to achieve high-speed operation.
Diatoms are single-celled algaes that make photonic-crystal-like silica shells or frustules with hierarchical micro- and
nano-scale features consisting of two-dimensional periodic pores. In this paper, we present an innovative label-free
optical sensor based on a biological-plasmonic hybrid nanostructure by self-assembling silver (Ag) nanoparticles into
diatom frustules. The photonic-crystal-like diatom frustules provide a spatially confined electric field with enhanced
intensity that can form hybrid photonic-plasmonic modes through the optical coupling with Ag nanoparticles. The
experimental results demonstrate 4-6x and 9-12x improvement of sensitivities to detect the Raman dye for resonance
and nonresonance SERS sensing, respectively.
We present a surface-normal plasmonic modulator structure for three-dimensional (3-D) optical interconnects using subwavelength metallic photonic crystals. Optical transmission of the metallic slab was controlled by modulating the plasmonic bandgap of the metallic photonic crystal slab with a moderate index perturbation induced by thermo-optic effects. Our experimental results show that more than 60% modulation depth is achieved with only an index modulation of 0.0043.
We design and fabricate metallic photonic crystals that are integrated with highly-efficient third-order nonlinear polymers. Compared with nanoparticle-doped composite materials, metallic photonic crystals are favorable due to the presence of Bragg-grating-modulated surface plasmon polaritons (SPPs) with strong light localization in large spatial volumes to uniformly enhance the harmonic signals. We experimentally observed extraordinary emission of THG signals from the surface-plasmon-enhanced organic thin film using telecommunication wavelength pulsed laser. This hybrid organic-plasmonic nanostructure opens a new avenue to develop innovative nonlinear optical devices.
Diatoms are a group of single-celled photosynthetic algae that make skeletal shells of hydrated amorphous silica, called
frustules, which possess hierarchical nanoscale photonic crystal features made by a bottom-up approach at ambient
temperature and pressure. In this paper, we theoretically investigate electric field enhancements of plasmonic
nanoparticles coated on the surface of diatom skeletal shells. Surface-Enhanced Raman Scattering substrates are
prepared by evaporating 10 nm thick silver film and self-assembling silver nanoparticles on diatom surfaces, which show
significantly better SERS signals than silver nanoparticles on flat glass substrates.