The Effect of Au/Ag Bimetallic Thin-Films on Surface Plasmon Resonance Properties Comparing with Those of Au and Ag Single Thin-Films.

The surface plasmon resonance (SPR) properties of Au/Ag bimetallic thin-film nanostructures were investigated to improve the chemical stability and the figure of merit (FOM) in the SPR sensors. The SPR characteristics such as resonance angle, extinction ratio, and full width half maximum (FWHM) were calculated by the simulation of the finite-difference time-domain method and were measured using the laser with a 632.8 nm wavelength in the Kretschmann-Raether configuration. The measured resonance angle, extinction ratio, FWHM of Au(20 nm)/Ag(20 nm) thin-film nanostructure were found to be 44°, 0.8, and 1.4°, respectively. The FOM values were determined to be 56.9 for Au/Ag bimetallic thin-film, 47.9 for Au(50 nm) single thin-film, and 89.1 for Ag(50 nm) single thin-film. Also the sensitivity values were about 53.5, 57.0, and 57.8°/RIU for Au(50 nm), Ag(50 nm), and Au(20 nm)/Ag(20 nm) thin-film nanostructures in the SPR sensors, respectively. The SPR properties of Au/Ag bimetallic thin-film nanostructures were compared with those of the Au and Ag single thin-film nanostructures.

Optical Characteristics of Double Layered Plasmonic Structure Using Nanopatterning Process.

A double layered plasmonic device based on transferring technique with polystyrene nano-beads is analyzed and demonstrated to increase the sensing characteristics of plasmonic sensor system. The double layered plasmonic devices are calculated using the three-dimensional finite-difference time-domain method for the width and thickness of the nano-hole structures. The double layered plasmonic devices with different diameters of the Au nano-hole are fabricated by transferring method with commercially available chloromethyl latex with a diameter of 0.42 µm. The optimum sensing characteristic of the proposed plasmonic device is obtained with the film and the hole thickness of 15 and 15 nm in the 246 nm wide nano-hole size. The best sensitivity of the proposed plasmonic sensor is 67.7 degree/RIU when the sensitivity of the conventional plasmonic sensor is 42.2 degree/RIU.

Short-wavelength infrared photodetector on Si employing strain-induced growth of very tall InAs nanowire arrays.

One-dimensional crystal growth enables the epitaxial integration of III-V compound semiconductors onto a silicon (Si) substrate despite significant lattice mismatch. Here, we report a short-wavelength infrared (SWIR, 1.4-3 µm) photodetector that employs InAs nanowires (NWs) grown on Si. The wafer-scale epitaxial InAs NWs form on the Si substrate without a metal catalyst or pattern assistance; thus, the growth is free of metal-atom-induced contaminations, and is also cost-effective. InAs NW arrays with an average height of 50 µm provide excellent anti-reflective and light trapping properties over a wide wavelength range. The photodetector exhibits a peak detectivity of 1.9 × 10(8) cm · Hz(1/2)/W for the SWIR band at 77 K and operates at temperatures as high as 220 K. The SWIR photodetector on the Si platform demonstrated in this study is promising for future low-cost optical sensors and Si photonics.

Compact polarizing beam splitter based on a metal-insulator-metal inserted into multimode interference coupler.

We propose and analyze a compact polarizing beam splitter (PBS) based on a metal-insulator-metal (MIM) structure inserted into a multimode interference coupler (MMI). Owing to the MIM structure, the TE polarized state is reflected by the cut-off condition while the TM polarized state is transmitted by the surface plasmon polariton, and the two polarized states can thus be separated. In this paper, the dependence of the reflected TE and transmitted TM field intensities on the MIM length and the gap thickness has been studied systematically. The proposed PBS structure, with a total size of 4 × 0.7 × 44 µm(3) is designed with MIM length, gap thickness, and metal thickness of 0.6 µm, 0.5 µm, and 0.05 µm, respectively. In the designed PBS, the transmittance for the TM polarized light, reflectance for the TE polarized light, extinction ratio, and insertion losses of the TE and TM modes are obtained using a 3D finite-difference time-domain method to be 0.9, 0.88, 12.55 dB, and 1.1 dB and 0.9 dB, respectively. The designed PBS has a much shorter length, 44 µm, compared to previous PBS devices.

Design of ultra-sensitive biosensor applying surface plasmon resonance to a triangular resonator.

We propose an ultra-sensitive integrated photonic sensor structure using an InP-based triangular resonator, in which a surface plasmon resonance (SPR) gold film is applied on a total internal reflection mirror. We have analyzed and optimized the triangular resonator sensor structure with an extremely small SPR mirror sensing area of 3.3 × 0.35 µm2. Due to the large phase shift in the SPR mirror, a significantly enhanced sensitivity of 930 nm/RIU (refractive index unit) and the maximum peak shift of half free spectral range have been obtained at the SPR angle of 24.125° with Au thickness of 33.4 nm for the change of the refractive index Δn = 1x10(-3). This value is larger than the previous largest value in micro resonator-type biosensors. Moreover, the proposed triangular resonator sensor can be easily made in a micro structure with optical source integration.

The characterization of GH shifts of surface plasmon resonance in a waveguide using the FDTD method.

We have explicated the Goos-Hänchen (GH) shift in a mum-order Kretchmann-Raether configuration embedded in an optical waveguide structure by using the finite-difference time-domain method. For optical waveguide-type surface plasmon resonance (SPR) devices, the precise derivation of the GH shift has become critical. Artmann's equation, which is accurate enough for bulk optics, is difficult to apply to waveguide-type SPR devices. This is because Artmann's equation, based on the differentiation of the phase shift, is inaccurate at the critical and resonance angles where drastic phase changes occur. In this study, we accurately identified both the positive and the negative GH shifts around the incidence angle of resonance. In a waveguide-type Kretchmann-Raether configuration with an Au thin film of 50 nm, positive and negative lateral shifts of -0.75 and + 1.0 microm are obtained on the SPR with the incident angles of 44.4 degrees and 47.5 degrees, respectively, at a wavelength of 632.8 nm.

Extremely small multimode-interference coupled triangular resonator with sharp angle of incidence.

Novel triangular ring resonators combining extremely small multimode-interference (MMI) coupler, low loss total internal reflection (TIR) mirrors, and semiconductor optical amplifiers are reported for the first time. The MMI length of 90 microm is among the shortest reported. The incidence angle of the TIR mirror inside the resonator is 22 degrees. A free-spectral range of approximately 2 nm is observed near 1550 nm along with an on-off ratio of 17 dB. The triangular resonators with a sharp angle are very attractive components due to their promise of compact size and high levels of integration. Therefore, large numbers of resonators can be integrated on a chip to increase functionality in future optical wavelength division multiplexing system.

Optical AND/OR gates based on monolithically integrated vertical cavity laser with depleted optical thyristor structure.

Latching optical switches and optical logic gates with AND and OR functionality are demonstrated for the first time by the monolithic integration of a vertical cavity lasers with depleted optical thyristor structure. The thyristors have a low threshold current of 0.65 mA and a high on/off contrast ratio of more than 50 dB. By simply changing a reference switching voltage, this single device operates as two logic functions, optical logic AND and OR. The thyristor laser fabricated by using the oxidation process and has achieved high optical output power efficiency and a high sensitivity to the optical input light.