A global stability analysis for symmetric self-electrooptic effectdevice systems using a potential function method

This paper proposes a novel analytical method for use in symmetric self-electrooptic effect device (S-SEED) systems, called the potential function method, based on a global stability analysis of differential equations for photocurrent in S-SEED circuits. The method provides intuitive views for analyzing the stability of the system, and is useful for tracking the temporal dynamics of S-SEED nonlinear electrical circuits. This paper also describes electro-absorption characteristics of SEED's, especially those based on Wannier Stark localization (WSL). In this type of SEED, the photocurrent versus reverse bias voltage characteristics has multiple peaks and multiple negative differential resistance regions, resulting from Stark ladder transitions due to thin barrier superlattices. Various types of stabilities, including the metastable state, as well as the temporal switching dynamics of WSL-S-SEEDs, can be explained clearly by using this potential function method     

Observing the Stimulated Raman Gain Spectra of Solutions Using an Infrared Pump Pulse with Narrow Linewidth and a Low-Noise CW Probe Laser

Stimulated Raman gain (SRG) spectroscopy using infrared pump pulses with narrow linewidth and a low-noise cw probe infrared laser was proposed. High-resolution Raman spectra of solutions were obtained. The SRG spectra of crystal GaP, benzene, and toluene were measured to confirm the spectral resolution and sensitivity over the terahertz (THz) region. We discuss the polarization dependence of the spectral measurement of carbon tetrachloride. Our system can detect organic molecules in aqueous solutions.     

Study on critical dimension of printable phase defects using an EUV microscope

We constructed an extreme ultraviolet microscopy (EUVM) system for actinic mask inspection that consists of Schwarzschild optics and an X-ray zooming tube. This system was used to inspect finished extreme ultraviolet lithography (EUVL) masks and Mo/Si glass substrates. A clear EUVM image of a 300-nm-wide pattern on a 6025 glass mask was obtained. The resolution was estimated to be 50 nm or less from this pattern. Programmed phase defects on the glass substrate were also used for inspection. The EUV microscope was able to resolve a programmed pit defect with a width of 40 nm and a depth of 10 nm and also one with a width of 70 nm and a depth of 2 nm. However, a 75-nm-wide 1.5-nm-deep pit defect was not resolved. Thus, in this study, one critical dimension of a pit defect was estimated to be a depth of 2 nm.     

Electrical properties of 1.5-nm SiON gate-dielectric using radical oxygen and radical nitrogen

We have developed a low-leakage and highly reliable 1.5-nm SiON gate-dielectric by using radical oxygen and nitrogen. In this development, we introduce a new method for determining an ultrathin SiON gate-dielectric thickness based on the threshold voltage dependence on the substrate bias in MOSFETs. It was found that oxidation using radical oxygen followed by nitridation using radical nitrogen provides the 1.5-nm (oxide equivalent thickness) SiON, in which leakage current is two orders of magnitude less than that of 1.5-nm SiO/sub 2/ without degrading device performance in NMOSFETs. The 1.5-nm (oxide equivalent thickness) SiON was also found to be ten times more reliable than 1.5-nm SiO/sub 2/.     

A mechanical sensorless control system for salient-pole brushlessDC motor with autocalibration of estimated position angles

In this paper, a mechanical sensorless control system is reported for salient-pole brushless DC motor drives. Here, two new methods are proposed for obtaining the position angle, the accuracy of which affects the operation of the switching devices of the inverter that drives the motor. First, the method for estimating the position angle is proposed. Secondly, the correcting method for reducing the errors involved in the estimation of position angle is given. The experimental results show that the estimated position angles are calibrated automatically, and then the proposed sensorless control system can control the speed and the position angles of the motor precisely     

Grain boundary atomic structures and light-element visualization in ceramics: combination of Cs-corrected scanning transmission electron microscopy and first-principles calculations

Grain boundaries and interfaces of crystals have peculiar electronic structures, caused by the disorder in periodicity, providing the functional properties, which cannot be observed in a perfect crystal. In the vicinity of the grain boundaries and interfaces, dopants or impurities are often segregated, and they play a crucial role in deciding the properties of a material. Spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM), allowing the formation of sub-angstrom-sized electron probes, can directly observe grain boundary-segregated dopants. On the other hand, ceramic materials are composed of light elements, and these light elements also play an important role in the properties of ceramic materials. Recently, annular bright-field (ABF)-STEM imaging has been proposed, which is now known to be a very powerful technique in producing images showing both light- and heavy-element columns simultaneously. In this review, the atomic structure determination of ceramic grain boundaries and direct observation of grain boundary-segregated dopants and light elements in ceramics were shown to combine with the theoretical calculations. Examples are demonstrated for well-defined grain boundaries in rare earth-doped Al(2)O(3) and ZnO ceramics, CeO(2) and SrTiO(3) grain boundary, lithium battery materials and metal hydride, which were characterized by Cs-corrected high-angle annular dark-field and ABF-STEM. It is concluded that the combination of STEM characterization and first-principles calculation is very useful in interpreting the structural information and in understanding the origin of the properties in various ceramics.     

Advanced quantum dot and photonic crystal technologies for integrated nanophotonic circuits

Two types of nanophotonic technologies—two-dimensional photonic crystal (2D PC) slab waveguides (WGs) and quantum dots (QDs)—were developed for key photonic device structures in the future. For an ultrafast digital photonic network, an ultrasmall and ultrafast symmetrical Mach–Zehnder (SMZ)-type all-optical switch (PC-SMZ) and an optical flip–flop device (PC-FF) have been developed. To realize these devices, one method is to develop a selective-area molecular beam epitaxial growth QD technique by employing a metal mask method. Another method is to establish a new design method, i.e., topology optimization of the 2DPC WG with a wide and flat bandwidth, high transmittance, and low reflectivity. We also fabricated an optical microcavity in a photonic crystal slab embedded with GaAs QDs by droplet epitaxy. The Purcell effect on the exciton emission of GaAs QDs was confirmed by microphotoluminescence and lifetime measurements.     

Transmission performance of chirp-controlled signal by usingsemiconductor optical amplifier

We examine the fiber transmission performance of the optical signal whose chirp is controlled by utilizing phase modulation in semiconductor optical amplifier (SOA) with both simulations and experiments. This chirp control technique converts a positive chirp created by electroabsorption (EA) modulator into negative chirp, which reduces the waveform degradation due to the chromatic dispersion in transmission over standard single-mode fiber (SMF). It also provides an optical gain that is sufficient to compensate the insertion loss of the EA modulator. We investigate how the chirp control is affected by the input power to the SOA and the carrier lifetime of the SOA. As the SOA input power increases, the negative chirp becomes large, while the waveform is largely distorted due to gain saturation. However, the waveform distortion at high SOA input powers can be shaped by using a frequency discriminator. The acceleration of the carrier lifetime also reduces the waveform distortion due to gain saturation. We demonstrate that the chirp control technique is effective even for a high bit rate optical signal up to 10 Gb/s, when the carrier lifetime is expedited by optical pumping