Design and evaluation of an arbitration-free passive optical crossbar for on-chip interconnection networks

With recent advances in silicon nanophotonics, optical crossbars based on CMOS-compatible microring resonators have emerged as viable on-chip optical interconnection networks to deliver high-bandwidth communication at low power dissipation with a small footprint. This paper describes the design, fabrication and evaluation of an arbitration-free passive crossbar based on a microring resonator matrix that can be used to route wavelength division multiplexing (WDM) signals across the chip. The salient feature of the proposed design is the ability to support multicasting and many-to-one communication efficiently (without arbitration), which makes it suitable for implementing cache coherency protocols and on-chip interconnect in future many-core processors.     

Microcontact printing of self-assembled monolayers to pattern the light-emission of polymeric light-emitting diodes

By patterning a self-assembled monolayer (SAM) of thiolated molecules with opposing dipole moments on a gold anode of a polymer light-emitting diode (PLED), the charge injection and, therefore, the light-emission of the device can be controlled with a micrometer-scale resolution. Gold surfaces were modified with SAMs based on alkanethiols and perfluorinated alkanethiols, applied by microcontact printing, and their work functions have been measured. The molecules form a chemisorbed monolayer of only ∼1.5 nm on the gold surface, thereby locally changing the work function of the metal. Kelvin probe measurements show that the local work function can be tuned from 4.3 to 5.5 eV, which implies that this anode can be used as a hole blocking electrode or as a hole injecting electrode, respectively, in PLEDs based on poly(p-phenylene vinylene) (PPV) derivatives. By microcontact printing of SAMs with opposing dipole moments, the work function was locally modified and the charge injection in the PLED could be controlled down to the micrometer length scale. Consequently, the local light-emission exhibits a high contrast. Microcontact printing of SAMs is a simple and inexpensive method to pattern, with micrometer resolution, the light-emission for low-end applications like static displays. Both authors (J.J. Brondijk and X. Li) contributed equally.     

General analyses of infinite impulse microwave photonic filters with an intensity modulator in an opto–electronic feedback loop

Designs of coherence-free microwave photonic filters with infinite impulse response (IIR) are presented. They are based on an electrical–optical modulator or electrical-absorption modulator with an opto–electronic feedback loop. General theoretical analyses for those configurations are obtained. When an electrical–optical intensity modulator is used for the IIR filter, the stopband of the filter can be switched to passband and vice versa. Measured results match closely with the theoretical expressions and demonstrate more than 30 dB rejection ratio and high frequency selectivity.     

Nitric acid method for fabrication of gate oxides in TFT

We have developed low temperature formation methods of SiO₂ layers which are applicable to gate oxide layers in thin film transistors (TFT) by use of nitric acid (HNO₃). Thick (>10 nm) SiO₂ layers with good thickness uniformity (i.e., ±4%) can be formed on 32 cm × 40 cm substrates by the two-step nitric acid oxidation method in which initial and subsequent oxidation is performed using 40 and 68 wt% (azeotropic mixture) HNO₃ aqueous solutions, respectively. The nitric acid oxidation of polycrystalline Si (poly-Si) thin films greatly decreases the height of ridge structure present on the poly-Si surfaces. When poly-Si thin films on 32 cm × 40 cm glass substrates are oxidized at azeotropic point (i.e., 68 wt% HNO₃ aqueous solutions at 121 °C), ultrathin (i.e., 1.1 nm) SiO₂ layers with a good thickness uniformity (±0.05 nm) are formed on the poly-Si surfaces. When SiO₂/Si structure fabricated using plasma-enhanced chemical vapor deposition is immersed in 68 wt% HNO₃, oxide fixed charge density is greatly decreased, and interface states are eliminated. The fixed charge density is further decreased by heat treatments at 200 °C, and consequently, capacitance-voltage characteristics which are as good as those of thermal SiO₂/Si structure are achieved.     

Quantum Key Distribution System with Six Polarization States Encoded by Phase Modulation

An intrinsically stable quantum key distribution system （QKD） with six polarization states encoded by phase modulation is introduced. The encoder and decoder are in the same structures that consist of two polarizing Sagnac interferometers connected in tandem. The six polarization states are determined and distinguished by different sets of phase shifts induced by two respective electrically-driven integrated phase modulators. A mean visibility of interference fringes is kept stable at 97.58% for an hour＇s performance. Theoretical and experimental analyses show that the proposed QKD system features intrinsically stability immune from environment fluctuation.     

Theory of the photoacoustic effect of semiconductor quantum wells

We develop a theory of the photoacoustic effect of semiconductor quantum wells. Assuming a multilayer system of optically uniaxial media with dissipation we describe the generation of heat and the conduction of the heat through the system by a generalized transfer-matrix method. It is shown by applying this theory to a semiconductor quantum well that the photoacoustic signal is very sensitive on the quantum-size effect and the longitudinal and transverse relaxation times. Our theory predicts that photoacoustics should be a profitable method for the investigation of semiconductor micro- and nanostructures.     

Dielectric breakdown of rubber materials by femtosecond irradiation

We report the reversible micro-structuring of a synthetic rubber polymer (cis1,4-polybutadiene (PB)) by femtosecond laser illumination. Visco-elastic relaxation of the optically damaged region was observed. The recovery time, typically 10²–10⁴ ms, can be varied by changing the irradiation pulse energy. Multi-shot-induced damage recovers on the much longer scale of 10¹–10² s. It was found that the doping of PB by 4 wt. % of pentazadiene ([4-NO₂]–phenyl–N=N–N(C₃H₇)–N=N–phenyl–[4-NO₂]) reduces the threshold of light-induced photo-modification by 20%. This is explained by photo-induced (homolytic) cleavage of the pentazadiene bonds and formation of gaseous N₂, which facilitates material failure at the irradiated spot. The recovery of optical transmission can be applied to optical memory, optical and micro-mechanical applications. The underlying mechanism of the phenomenon is discussed in terms of anelastic α- and β-relaxation (polymer backbone and chains/coils relaxation, respectively). Received: 11 October 2001 / Accepted: 9 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +81-88/656-7598, E-mail: misawa@eco.tokushima-u.ac.jp     

Depth control of a silicon structure fabricated by 100q keV Ar ion beam lithography

Ion beam lithography of a silicon surface using an Ar ion beam with an ion energy in the order of hundreds of keV is demonstrated in this study. A specially designed ion irradiation facility was employed that enabled generation and irradiation with a highly accelerated and highly charged Ar ion beam. An ion-beam-induced amorphous layer on a silicon substrate can be selectively etched in hydrofluoric acid, whereas, a non-irradiated area is scarcely etched and, consequently, a concave structure can be fabricated on the irradiated area. To control the depth of the structure, parameters for dependence of the depth on ion irradiation were investigated. As a result, the depth of irradiated area can be controlled by the ion energy that is adjusted by the acceleration voltage and the ion charge. In addition, the etch resistance of the irradiated area increases with an increase in ion energy due to the crystalline layer formed on the surface. Simulation results reveal that the depth is strongly related to the defect distribution induced by ion irradiation. These results indicate the potential use of this method for novel three-dimensional lithography.     

Dispersion characteristics for low-frequency magnetoelectric coefficients in bulk ferrite-piezoelectric composites

Ferrite-piezoelectric composites are magnetoelectric (ME) due to the interaction between magnetic and electrical subsystems through mechanical forces. A theory for the low-frequency Maxwell-Wagner relaxation in ME coefficients is discussed for bulk composites of nickel or cobalt ferrite and lead zirconate titanate (PZT). ME coefficients versus frequency spectra show two types of relaxation, over 0.1-100 μHz and 1-1000 Hz. The relaxation frequencies and the magnitude of the ME coefficients are dependent on the electrical and composite parameters and volume fraction for the two phases. The ME coefficient α_E is in the range 10⁻¹-10⁴ mV/cm Oe, higher in cobalt ferrite-PZT than for nickel ferrite-PZT, and is strongly dependent on PZT volume fraction v. Estimates of α_E and relaxation frequencies versus v provided here are useful for engineering composites with maximum ME effects for specific frequency bands.     

Display method with compensation of the spatial frequency response of a liquid crystal spatial light modulator for holographic femtosecond laser processing

Liquid crystal spatial light modulators, which are widely used as display devices for computer-generated holograms, have modulation characteristics that depend on spatial frequency. We describe a method for displaying a computer-generated hologram on a liquid crystal spatial light modulator with compensation of its spatial frequency response. Using this method, we demonstrate a binary phase grating with smaller dependence on the spatial frequency. We also demonstrate application of the display method to holographic femtosecond laser processing.