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Two-dimensional (2-D) metal nanodot arrays (NDAs) have been attracting significant attention for use in biological and chemical sensing applications. The unique optical properties of the metal NDAs originate from their localized surface plasmon resonance (LSPR). Nanofabrication methods that use nanoporous alumina masks (NAMs) have been widely used to produce metal NDAs. We report a fabrication technique for a 2-D Ag NDA and its utilization as a platform for LSPR-based sensing applications. A well-ordered Ag NDA of ∼70-nm diameter, arranged in a periodic pattern of 105 nm, was fabricated on an indium tin oxide (ITO) glass substrate using an NAM as an evaporation mask. The LSPR of the Ag NDA on the ITO glass was investigated using ultraviolet–visible spectroscopy. The LSPR wavelength shifts caused by the variations in the quantity of methylene blue adsorbed on the Ag NDA were examined. The results of this study suggest that the Ag NDA prepared using NAM can be used as a chemical sensor platform.

We have proposed a novel biosensor scheme based on a dual photonic crystal microcavity with a stadium-shaped ring resonator (PCM-SSRR) and characterized the resonance conditions for the first time. The Q of the dual PCM-SSRR was significantly enhanced when a single PCM or a dual PCM was in the same resonance condition with the SSRR. We demonstrated a mutual interference between the dual PCM. In this study, the Q of the dual PCM-SSRR was increased three times over that of the directional coupler structure used with the single PCM. Assuming a detectable spectral resolution of 10 pm, a refractive index resolution of 3.03×10-5 can be achieved on the dual PCM-SSRR.

We propose a novel optical decoder for a fiber-optic code-division multiple-access communication system. In particular, we discuss a means of reducing the effective multiple-access interference signal by inserting an optical hard limiter (optical thyristor). The optical decoder employs an AND gate logic element (AGLE) composed of a 1×M splitter, optical delay lines, an M×1 combiner, and the optical hard limiter. It is found that the AGLE suppresses the interference signal, so that the autocorrelation sidelobe and the cross-correlation peaks can be fully eliminated for any two users.

InGaAs/InP multiple quantum well (MQW) PnpN depleted op- tical thyristors (DOTs) operating at 1.55 mm are proposed and fabricated. To analyze their switching characteristics, we simulate nonlinear s-shape current-voltage curves using the finite difference method (FDM) associ- ated with the current-oriented method. Using the FDM, we calculate the effects of such parameters as doping concentration and the thicknesses of the outer and inner layers of the thyristor to determine an optimized structure in the view of fast and low-power-consuming operation. With these results, we fabricate waveguide- and vertical-type InGaAs/InP MQW PnpN DOTs. The waveguide-type DOT shows sufficient nonlinear s-shape I-V characteristics with a switching voltage of 4.03 V and a holding voltage of 1.77 V, and spontaneous emission along the wave- guide. The current-voltage characteristics of the vertical-type DOT are shown very well under 150 mW of input power, while the s-shape disap- pears at 200 mW. © 2003 Society of Photo-Optical Instrumentation Engineers.

We investigate the effects of high input power on the performance of optical bistable symmetric self-electro-optic effect devices (SSEEDs) using extremely shallow quantum wells (ESQWs). In this study we consider four ESQW SEEDs: antireflection (AR)-coated ESQW S-SEEDs (E-SEEDs), back-to-back AR-coated ESQW S-SEEDs (BBESEEDs), asymmetric Fabry-Pe´ rot (AFP)-ESQW S-SEEDs (AE-SEEDs), and back-to-back AFP-ESQW S-SEEDs (BBAE-SEEDs). As the input power increases, device performances such as on/off contrast ratio and on/off reflectivity difference are seriously degraded due to the ohmic heating and exciton saturation. But switching speed of the device increases up to a certain value and then begins to decrease. With reasonable optimization of the input power, we simulate and analyze the system bit rate of a cascading optical interconnection system using the various ESQW S-SEEDs changing the number of quantum wells for the external bias of 0 V and 25 V. The BBE-SEED with 48 quantum wells shows the maximum bit rate of 100 Mbytes/s at 0-V bias, while the E-SEED with 60 QWs shows the maximum bit rate of 109 Mbytes/s at 25-V bias. In AFP cavity structures, the AE-SEED with 18 QWs and the BBAE-SEED with 28 QWs show maximum bit rate of 311 and 156 Mbytes/s, respectively, at 0-V bias.

We propose and analyze novel fully depleted optical thyris- tors (DOTs) using multiple quantum wells (MQWs) and quarter- wavelength reflector stacks (QWRSs). MQWs are employed to enhance the absorption, while a QWRS is employed as a bottom mirror to en- hance the emission efficiency as well as the optical sensitivity. In order to analyze the switching characteristics, we simulate S-shaped nonlinear current-voltage curves using a coupled junction model associated with the current-oriented method. Furthermore, emission characteristics are obtained by using the scattering-matrix method and the van Roosbroeck-Shockley relation. According to our analysis, the novel DOTs significantly improve the switching and light emission characteris- tics. Compared to a conventional DOT, the optical switching energy and the bit rate of the novel DOT using both MQWs and a QWRS are im- proved by a factor of 0.45 and 1.61, respectively, for a cascading opera- tion. We also analyze the performances of free-space optical intercon- nects using the novel DOTs. © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)01703-1)