We propose a plasmonic surface that produces an electrically controlled reflectance as a high-speed intensity modulator. The device is conceived as a metal-oxide-semiconductor capacitor on silicon with its metal structured as a thin patch bearing a contiguous nanoscale grating. The metal structure serves multiple functions as a driving electrode and as a grating coupler for perpendicularly incident p-polarized light to surface plasmons supported by the patch. Modulation is produced by charging and discharging the capacitor and exploiting the carrier refraction effect in silicon along with the high sensitivity of strongly confined surface plasmons to index perturbations. The area of the modulator is set by the area of the incident beam, leading to a very compact device for a strongly focused beam (∼2.5 μm in diameter). Theoretically, the modulator can operate over a broad electrical bandwidth (tens of gigahertz) with a modulation depth of 3 to 6%, a loss of 3 to 4 dB, and an optical bandwidth of about 50 nm. About 1000 modulators can be integrated over a 50 mm(2) area producing an aggregate electro-optic modulation rate in excess of 1 Tb/s. We demonstrate experimentally modulators operating at telecommunications wavelengths, fabricated as nanostructured Au/HfO2/p-Si capacitors. The modulators break conceptually from waveguide-based devices and belong to the same class of devices as surface photodetectors and vertical cavity surface-emitting lasers.
Long range surface plasmon-polariton waveguides and devices suitable for biosensing were fabricated and characterized physically and optically. The structures consist of thin (∼35 nm) patterned Au stripes embedded in thick Cytop claddings (∼8 μm each). Portions of Au stripes were exposed by patterning and etching though the top Cytop cladding using an O2 plasma etch. The etched Cytop cavities act as microfluidic channels to contain and direct the sensing fluid. Intermediate process steps were verified through physical characterization as were fully fabricated structures. Optical testing was performed on Cytop-embedded structures and on channel-filled (with sensing fluid) structures. The structures were excited through end-fire coupling to optical fibers.
We propose and demonstrate
a thin Au stripe on a truncated 1D dielectric
photonic crystal covered with Cytop as a waveguide for Bloch long-range
surface plasmon polaritons. High-quality mode outputs were observed
and a mode power attenuation of 12–17 dB/mm measured at λ0 = 1310 nm for propagation in the plane of the truncated photonic
crystal and within its stopband. The truncated 1D photonic crystal
advantageously enables the use of a large range of materials for the
substrate, breaking free from the constraint of material symmetry
to support long-range plasmons. An input grating coupler implemented
as a periodic array of nanoscale Au ridges on a Au stripe was used
to excite the mode via perpendicularly incident p-polarized light. The output was provided by adding a second grating
coupler near the end of a waveguide to diffract light upward or by
polishing the output facet and allowing the mode to radiate into a
free-space beam. Advantageously, grating coupling eliminates the need
for high-quality end facets, and optical alignment is simplified.
Given its practicality, the structure proposed is of strong interest
for biosensing.
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