Experimental data for waveguide-coupled surface-plasmon-polariton (SPP) cones generated from dielectric waveguides is presented. The results demonstrate a simpler route to collect plasmon waveguide resonance (i.e., PWR) data. In the reverse-Kretschmann configuration (illumination from the sample side) and Kretschmann configuration (illumination from the prism side), all the waveguide modes are excited simultaneously with p-or s-polarized incident light, which permits rapid acquisition of PWR data without the need to scan the incident angle or wavelength, in the former configuration. The concentric SPP cone properties depend on the thickness and index of refraction of the waveguide. The angular intensity pattern of the cone is well-matched to simulation results in the reverse-Kretschmann configuration, and is found to be dependent on the polarization of the incident light and the polarization of the waveguide mode. In the Kretschmann geometry, all waveguide-coupled SPP cones are measured at incident angles that produce attenuated light reflectivity. In addition, the enhanced electric field produced under total internal reflection allows high signal-to-noise ratio multimodal spectroscopies (e.g., Raman scattering, luminescence) to measure the chemical content of the waveguide film, which traditionally is not measured with PWR. AbstractExperimental data for waveguide-coupled surface-plasmon-polariton (SPP) cones generated from dielectric waveguides is presented. The results demonstrate a simpler route to collect plasmon waveguide resonance (i.e., PWR) data. In the reverse-Kretschmann configuration (illumination from the sample side) and Kretschmann configuration (illumination from the prism side), all the waveguide modes are excited simultaneously with p-or s-polarized incident light, which permits rapid acquisition of PWR data without the need to scan the incident angle or wavelength. The concentric SPP cone properties depend on the thickness and index of refraction of the waveguide. The angular intensity pattern of the cone is well-matched to simulation results in the reverse-Kretschmann configuration, and is found to be dependent on the polarization of the incident light and the polarization of the waveguide mode. In the Kretschmann geometry, all waveguide-coupled SPP cones are measured at incident angles that produce attenuated light reflectivity. In addition, the enhanced electric field produced under total internal reflection allows high signal-to-noise ratio multimodal spectroscopies (e.g., Raman scattering, luminescence) to measure the chemical content of the waveguide film, which traditionally is not measured with PWR.

We extend the patterning capability of laser interference lithography (LIL) to fabricate complex two-dimensional quasicrystal lattices, superlattices, and Moiré lattices. Traditional interference lithography is typically used to create single-pitch linear gratings or simple square or hexagonal patterns. In this work, we demonstrate how using multiple exposures at various defined orientations and with different interference pitch values results in a cumulative surface pattern that encompasses a diverse group of complex lattice structures. We demonstrate the fabrication of quasicrystal lattices of symmetry order ranging from 2-fold to 22-fold by repeated exposure of a one-dimensional interference pattern over multiple fixed sample rotation angles. More complex superlattice structures are prepared by overlapping two-dimensional lattices at controlled offset angles. Overlapping interference patterns with different pitch values and at different offsets are used to create various sophisticated incommensurate Moiré lattices. The increasing complexity of these surfaces is determined using a numerical algorithm to predict their structure. The structure and optical diffraction of these lattices were measured and compared to model results. This work extends the capabilities of LIL to provide access to a wide variety of complex nanostructures with tunable periodicity and controllable symmetry. We anticipate that these structures will prove useful in the fabrication of surfaces and devices based upon periodic two-dimensional nanostructures, including photonic bandgap materials with tunable band gaps, as platforms for plasmonic devices with complex engineered structures, as novel diffractive optical elements, and as templates for controlling the self-assembly and crystallization of colloidal crystals.

This paper reports a tunable photonic device that incorporates a thin layer of phase-change material, Ge 2 Sb 2 Te 5 (GST), in a photonic crystal (PC) structure. The PC structure is based on a one-dimensional grating waveguide with a metal cladding. The metal-cladded PC structure supports a guided-mode resonance (GMR) that selectively absorbs light at a particular wavelength. Inserting the GST material into the gating waveguide makes it possible to control the GMR mode. Here, the GST-PC device was numerically designed and optimized to obtain significant tuning of the GMR mode around 1550 nm. The tuning phenomena were experimentally demonstrated by the heat-induced phase change between crystalline and amorphous phases of the GST thin film. A spectral shift of the resonant wavelength from 1440 to 1610 nm was achieved via the crystallization process. The phase tuning of GST exhibits good repeatability as demonstrated by switching between amorphous and crystalline phases of GST for multiple cycles. The GST-PC device represents a new approach for tuning optical resonances with potential applications including but not limited to integrated photonic circuits, optical communications, and high-performance optical filters.

We report a method for controlling the lattice geometry of monodisperse colloidal crystals formed by confined convective self-assembly on a substrate patterned with a chirped surface relief grating. Chirped gratings were fabricated using laser interference lithography and a curved mirror reflector to create photoresist patterns with pitch values ranging from ∼500 to >10 000 nm spread over a planar surface. These surface nanostructures are shown to guide the formation of various lattice geometries not normally found via colloidal assembly on planar surfaces. It is shown that when the pitch of the grating is much larger than the diameter of the colloidal particles, the grating trenches serve as compartments for deposition and the particles form close-packed, linear chains. Various ordered structures are observed as the dimensions of the grating pitch decrease and approach the diameter of the particles. The grating nanostructures guide the formation of various lattice geometries due to specific particle-surface and particle-particle interactions. Observed crystal lattices include square, hexagonal, and rhombic structures. The formation of these structures is explained in terms of the geometrical constraints imposed by the surface pattern and the particle diameter. These crystal lattices can be translated into large area samples when using corresponding single-pitch grating substrates. The initial monolayer lattice can also serve as a template for the growth of unique, bilayer structures that include rectangular lattices, chains of particle pairs or triplets, and graphitelike structured lattices. In addition, when coated with a thin silver layer, these various lattice configurations are shown to produce optical reflection features that are precisely controlled by the underlying structure as it varies from widely spaced particle chains to close-packed lattice geometries.

We demonstrate how distinct surface plasmon resonance modes on opposite sides of a metal-coated grating can be coupled across the metal film. This coupling occurs by matching the resonance conditions on each side of the grating by tuning the refractive index directly adjacent to the metal film. In the first example, we deposited a high refractive index layer of tin oxide on top of the grating to red-shift the front side surface plasmon until it coupled with the backside surface plasmon across a semitransparent ∼45 nm thin silver grating. By shifting the resonance condition of the nearby surface plasmon, this high refractive index coating creates an effective matching of wave vectors across the metal film, allowing them to couple and enhance the optical response. A massive increase in the magnitude of enhanced transmission is observed, increasing from a 6-fold transmission enhancement through a bare silver grating to a near 100-fold enhancement after deposition of a tin oxide layer of appropriate thickness (∼310 nm). This optical transmission enhancement is then probed through computational modeling and by experiments with liquids of various refractive index values. The matched system shows an increased amplitude sensitivity with respect to refractive index changes and a waveguide like behavior within the tin oxide film. As an alternative configuration, we also demonstrate coupling the front and back-side plasmon modes by using a lower refractive index substrate in order to blue-shift the back-side surface plasmon. Coupling between the two plasmon modes is then demonstrated by introducing aqueous solutions of various refractive index values. Under the proper conditions, this matched system also shows a substantial enhancement in transmission. This technique of wave vector matching provides a route to substantially increasing the plasmon enhanced optical transmission through metal gratings, which has potential application in improved plasmonic sensing, spectroscopy, and plasmon-based optical devices.