Yi-Ting Wu

Effect of Wood’s anomalies on the profile of extraordinary transmission spectra through metal periodic arrays of rectangular subwavelength holes with different aspect ratio

The extraordinary transmission through silver film perforated with rectangular hole array with different aspect ratio was investigated. It was found that when the aspect ratio exceeded 7, the propagating surface plasmon polaritons (SPPs) transformed to localized resonance mode. The role of the Woods anomaly on the shape of the transmission spectrum is investigated. By designing the rectangular hole arrays in a rectangular lattice, the Woods anomaly can be shifted far apart from the transmission peak, the real localized resonance peak wavelength was identified and fitted well with the theoretical calculation using a simplified transmission-line model.

Localized surface plasmon polaritons in Ag∕SiO2∕Ag plasmonic thermal emitter

The reflection dispersion relation and emission spectra of Ag∕SiO2∕Ag trilayer plasmonic thermal emitters with different lattice constant and Ag line width were investigated. The top Ag film is perforated with parallel line-shape hole array. The induced Ag∕SiO2 surface plasmons at both top and bottom Ag∕SiO2 interface are found coupled together. The coupling effect results in the localized surface plasmon polaritons confined at the top Ag∕SiO2 interface which exhibit the Fabry–Perot resonance. The thermal emission peak position coincides with the reflection minimum in the dispersion relation and shifts to long wavelength as the Ag line width increases, which proves that the emission is due to the excitation of localized surface plasmon polaritons. Moreover, the emitted light is polarized perpendicular to the parallel metal lines.

Coupling of surface plasmons between two silver films in a Ag/SiO2/Ag plasmonic thermal emitter with grating structure

The reflection and emission spectra of Ag/SiO2/Ag trilayer plasmonic thermal emitters with different SiO2 thicknesses are investigated. The top Ag film is perforated with periodic slits. It is found that the coupling of surface plasmons at the top and bottom Ag/SiO2 interface results in the redshift in thermal emission peaks. In this Ag/SiO2/Ag plasmonic thermal emitter, the electromagnetic field exhibits either Fabry–Perot resonance or propagating surface plasmons depending on the thickness of SiO2 layer. By varying the thickness of SiO2 layer, transition from localized to grating-coupled propagating surface plasmon modes is observed.

Wavelength selective plasmonic thermal emitter by polarization utilizing Fabry-Pérot type resonances

The experimental results of dispersion relations and thermal emittance spectra of a metal/insulator/metal (MIM) structure with rectangle metallic patch arrays as top layer are demonstrated. The structure exhibits wide-angle, multipeak and polarized emission characteristics caused by Fabry-Perot type resonances of surface plasmons. Emission modes in x- and y-polarization are totally distinct, and their position depends on the width and length of the rectangular metallic patch. Therefore the designing of mode positions has two degrees of freedom and could be applied to wavelength selective light sources.

Narrow Bandwidth Midinfrared Waveguide Thermal Emitters

This work describes innovative waveguide thermal emitters with top metal perforated with subwavelength holes arranged in a short period to eliminate Bragg scattered waveguide modes (WMs) and surface plasmon polariton (SPP) modes. A metal-dielectric-metal parallel-plate waveguide with top metal perforated with subwavelength holes arranged in a short period exhibits high output intensities and emission peaks (WMs) with a narrow bandwidth in the midinfrared region under heat treatment. The redundant SPP modes and Bragg scattered WMs are filtered automatically by shifting them to the short wavelength due to a short period where blackbody radiations are too weak to appear.

Narrow bandwidth and highly polarized ratio infrared thermal emitter

Polarized infrared thermal emitters consisting of a waveguide thermal emitter combined with silver grating structure were studied. For a device containing a perforated silver film under the grating, polarized infrared light was emitted only when the wavelength satisfied the standing wave condition, therefore the broad bandwidth SiO2 phonon vibration modes were suppressed in the thermal radiation spectrum. The polarized ratio with different grating thickness was investigated and the highly polarized ratio up to 0.875 was achieved. This study demonstrated that the integrated structure can be used as a narrow bandwidth and highly polarized ratio infrared light source.

Surface plasmon on aluminum concentric rings arranged in a long-range periodic structure

The enhanced optical transmission through the annular aluminum metal with different number of concentric rings arranged in a long-range periodic structure on the silicon substrate is investigated. The measured transmission spectra demonstrate that the surface plasmon modes depend sensitively on the structural parameters of the metallic rings. The degenerate (1,0), (1,1), and (2,1) Al∕Si surface plasmon modes are determined by the long periodicity of the structure. The localized modes in cavities with different length can be observed in this structure as well. These phenomena suggest that both surface plasmons and localized cavity modes are excited within super unit cell.

Characteristics of a waveguide mode in a trilayer Ag/SiO 2 /Au plasmonic thermal emitter

A suitably designed trilayer Ag/SiO(2)/Au thermal emitter can be used as the narrow bandwidth infrared light source. The thermal radiation generated in the SiO(2) layer resonates between the two metal films and results in not only the Ag/SiO(2) surface plasmon polaritons but also the waveguide mode (WM) in the Ag/SiO(2)/Au structure owing to the thick SiO(2) layer. This study investigated the influence of dielectric thickness on energy dispersion relations and derived the theoretical dispersion relation, which fit well with experimental results. This WM light source can be applied in the area of gas sensing and probing the response of the animal cells and plants to infrared radiation.

Localized surface plasmons in Al∕Si structure and Ag∕SiO2∕Ag emitter with different concentric metal rings

This paper reports the optical properties of Al∕Si structure and trilayer Ag∕SiO2∕Ag plasmonic thermal emitter with different concentric metal rings on top metal film. It is found that when the metal width is smaller than 40% of the period (=gap+metal width), the (1,0) Al∕Si surface plasmon leads to a maximum in the transmission spectra; otherwise, the opposite is observed. The dispersion relations and emission spectra of the plasmonic thermal emitters were investigated. The emission peaks are independent of the gap width and redshift as annular metal width increases. This phenomenon suggests the excitation of Fabry-Perot type resonance within cavity of Ag∕SiO2∕Ag structure. No (1,0) Ag∕SiO2 surface plasmon was observed.

Polarization rotation of shape resonance in Archimedean spiral slots

The experimental results of linear polarized light transmitting through an array of Archimedean spiral slots perforated on a thin metal film in the far-infrared region are demonstrated. The wavelength selective transmission spectra are examined, and the polarization selective shape resonance will lead to the polarization rotation. The sign of rotation not only depend on the handedness of the spiral but also related to specific initial polarization position. This phenomenon is different from the conventional optical activity in three-dimensional chiral molecules but rather similar to the polarization selective features in rectangular or elliptical slots.