Ewa Lisicka-Skrzek

Fabrication of surface plasmon waveguides and devices in Cytop with integrated microfluidic channels

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.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.

Mach-Zehnder refractometric sensor using long-range surface plasmon waveguides

We demonstrate refractometric sensing using long-range surface plasmons on a compact integrated Mach-Zehnder interferometer (MZI) formed from thin Au stripes in Cytop with an etched microfluidic channel defining the sensing arm. The transfer characteristics of MZIs were obtained by sequentially injecting solutions of increasing refractive index in the sensing arm. A detection limit of 9 × 10−7 RIU was achieved at λ0 = 1310 nm, limited by unbalanced losses in the sensing and reference arms. A model is proposed for the MZIs, taking into account all loss mechanisms, and may be applied to MZI sensors in other technologies.

Plasmonic Nanostructured Metal–Oxide–Semiconductor Reflection Modulators

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.

Broadside excitation of surface plasmon waveguides on Cytop

Long-range surface plasmon waveguides consisting of a Au stripe on Cytop, covered with an index-matched aqueous solution, are described and characterized. The waveguides are tested using a broadside coupling technique, whereby tapered single-mode fibers are positioned in direct contact with the stripe such that the slow mode of the fiber couples through partial modal overlap to the long-range surface plasmon. Attenuation measurements obtained at λ0=1310 nm agree well with theory, thus validating the waveguide fabrication and experimental techniques. The waveguides are useful for (bio)chemical sensing and the broadside coupling technique is useful for on-wafer optical probing.

Long-range plasmon-polariton wave propagation in thin metal films of finite width excited using an end-fire technique

ZnSe/GaAs/GaAs heterostructures grown by Molecular Beam Epitaxy have been studied by Photoreflectance. From Franz-Keldysh oscillations we found the electric fields at ZnSe. It was observed that the electric field value decreases with the temperature. The calculated values (<58 kV/cm) are in agreement with the typical values in semiconductors and are higher than those at the interfacial GaAs. The electric field strength is conelated with the presence of superficial states due to defects such as dislocations.

Multichannel Transmission Through a Gold Strip Plasmonic Waveguide Embedded in Cytop

In this paper, we experimentally characterize a low-loss polymer-based plasmonic waveguide and present its system-level performance for transmitting multiple on-off keying modulated channels (4 × 49 Gb/s). The same waveguide also exhibits the capability of transmitting multiple differential phase shift keying modulated channels (4 × 10 Gb/s). Signal transmission has been verified through bit-error-rate measurements. The plasmonic waveguide consists of a 3.6-mm-long, 5-μm-wide, and 35-nm-thick gold strip embedded in Cytop polymer and exhibits a total optical insertion loss of approximately 13 dB at a free-space optical wavelength of 1.55 μm.

Fabrication of a plasmonic modulator incorporating an overlaid grating coupler

The fabrication of a novel plasmonic reflection modulator is presented and described. The modulator includes plasmon excitation using a diffraction grating coupler and is based on a metal-insulator-semiconductor structure on silicon. Fabrication includes a thin thermal oxide, a plasmonic metal surface defined by optical lithography, a metal grating coupler defined by overlaid e-beam lithography, a passivation layer with metalized vias, and electrical contacts. Physical characterization of intermediate structures is provided along with modulation measurements at λ0 ∼ 1550 nm which verify the concept.

Surface plasmon waveguide devices with Tg-bonded Cytop claddings

Surface plasmon waveguide devices were fabricated in symmetric Cytop claddings by bonding the claddings with Au waveguides and microfluidic channels at the interface. Au features were patterned and deposited on the bottom wafer and microfluidic channels were patterned and etched into the top wafer. Aligned wafer bonding and annealing were performed at temperatures slightly above the glass transition temperature (Tg) of Cytop. The bond strength is high, allowing dicing, ultrasonic cleaning, and polishing of facets. The bond is also of good hermiticity as assessed by fluid injection, and of reasonable optical quality as verified by measurements of long-range surface plasmon propagation at λ = 1310 and 1550 nm.

Sensing of bacteria immobilised under static conditions using long-range surface plasmon waveguides in Cytop

Waveguides consisting of Au embedded in Cytop with micro-fluidic channels etched into the cladding are used for sensing via the propagation of long-range surface plasmons. Initially, a range of water/glycerol solutions with varying refractive indices were sequentially injected in a waveguide section in order to assess its bulk sensitivity and to find a solution supporting a strong high quality mode. Au waveguide surfaces were then functionalized with antibodies against Gram negative bacteria (Anti-Gneg) by first forming a self-assembled monolayer (SAM) of 16-mercaptohexadecanoic acid (16-MHA) and subsequent conjugation with antibodies through carbodiimide chemistry. E.Coli XL-1 Blue was used as an analyte in static incubations. Wavelength sweeps of 16-MHA covered waveguides were compared against waveguides covered with E-coli. The results indicate that very few bacteria cells are required to obtain a measurable change in output signal.

Measurement of long-range surface plasmon-polariton devices in Cytop

Long-range surface plasmon-polariton (LRSPP) waveguide structures fabricated of gold stripes (5 μm wide and 35 nm thick) embedded in CYTOP were characterized. TM polarized 1310 nm light emerging from a polarisationmaintaining optical fibre was injected into the structures via butt-coupling and the output light was measured so that the loss could be calculated. Cutback measurements were carried out on straight waveguides so as to determine their attenuation as well as the butt-coupling loss per facet. Various other passive elements were also characterized. The results were compared with theoretical expectations and errors are surmised to be caused by fabrication imperfections. Thermo-optic modulation measurements were also carried out on straight waveguides. These elements are of interest for biosensors, where propagation through an aqueous solution (having an index of refraction very close to that of Cytop) is necessary.