Coherence-Based 3-D and Spectral Imaging and Laser-Scanning Microscopy

The basics of three-dimensional (3-D) and spectral imaging techniques that are based on the detection of coherence functions and other related techniques are reviewed. The principle of the 3-D source retrieval is based on understanding the propagation law of optical random field through the free space. The 3-D and spectral information are retrieved from the cross-spectral density function of optical random field or numerical calculation of the inverse propagation of the cross-spectral density. We will first introduce the coherence-based spectral tomography techniques with low-coherence light sources. These techniques limit their scheme of coherence detection only along the optical axis and some of them achieve simultaneously the high resolution and high speed of detection taking advantage of an imaging lens. We then provided explanations of the principle of 3-D source retrieval that is based on the propagation law of optical random field through the free space along with the introduction of the numerical holography and computed tomography techniques. We will lastly show 3-D spectral imaging schemes with the concurrent laser-scanning cross-sectioning techniques: one is the confocal laser scanning microscopy and the other is the two-photon laser-scanning fluorescence microscopy.     

Development of quasi-end-fired waveguide plastic dye laser

A quasi-end-fire (QEF) pumping scheme was proposed and studied as a novel laser-pumping-scheme for a laser-dye-doped plastic waveguide laser with distributed feedback. This pumping scheme resembled longitudinal pumping, but also has the advantage of controllable absorption length of the injected pump beam. A first demonstration of the QEF was performed and the pumping beam controlling was also investigated.     

Uncertainty evaluation of an in vivo near-field exposure setup for testing biological effects of cellular phones

In designing an in vivo near-field exposure setup for testing biological effects of cellular phones, one generally uses a small still animal because a plastic holder is used to restrain it. One also takes no account of the exposure box with radio wave absorbers as well as the plastic holder. In this paper, for the in vivo exposure setup developed in the National Institute of Information and Communications Technology (NICT), which was used for testing the promoting effect of 1.439- and 1.95-GHz digital cellular phones on rat brain carcinogenesis, we investigated the effects of the above-mentioned factors on the dosimetry design using the finite-difference time-domain (FDTD) method in conjunction with an anatomical rat model. As a result, we found that the specific absorption rate (SAR) averaged in the brain was 18% higher at maximum than the previously designed level due to the existence of the exposure box and the plastic holder and that the variation due to the rotation of the rat's head inside the plastic holder was within 10%. The backward movement of the rat along the plastic holder was more serious, which yielded a decrease of nearly 20% for the average SAR in the brain.     

UV pre-ionized wide-aperture XeCl laser using magnetic pulsecompression

To provide a spatially homogeneous and sufficiently high-voltage discharge, the laser described here used LC inversion and two-stage magnetic pulse compression in the excitation circuit and used UV radiation for pre-ionization. It also employed one commercial thyratron as a high-voltage switch. Evaluation of the dynamic magnetic characteristics of four magnetic materials in a magnetic pulse compression circuit showed that the Fe-based nanocrystalline soft magnetic alloy was the best core material for a compact switch with low core loss. At a 10 Hz repetition rate the maximum output energy obtained in a 80×60 nm discharge cross section and in 70 ns pulses (FWHM) was 6.2 J     

Low-power 1:16 DEMUX and one-chip CDR with 1:4 DEMUX using InP-InGaAs heterojunction bipolar transistors

Using InP-InGaAs heterojunction bipolar transistor (HBT) technology, we have successfully designed and fabricated a low-power 1:16 demultiplexer (DEMUX) integrated circuit (IC) and one-chip clock and data recovery (CDR) with a 1:4 DEMUX IC for 10-Gb/s optical communications systems. The InP-InGaAs HBTs were fabricated by a nonself-aligned process for high uniformity of device characteristics and producibility. The 1:16 DEMUX IC and the one-chip CDR with the 1:4 DEMUX IC consist of approximately 1200 and 460 transistors, respectively. We have confirmed error-free operation at 10 Gb/s for all data outputs of both ICs. The 1:16 DEMUX IC and the one-chip CDR with the 1:4 DEMUX IC consume only 1 W and 950 mW, respectively. These results demonstrate the feasibility of InP-InGaAs HBTs for low power high-integration optical communication ICs.     

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.     

Organic field-effect transistors based on J-aggregate thin films of a bisazomethine dye

We report on the fabrication and the characterization of p-type organic field-effect transistors based on vapor-deposited J-aggregate bisazomethine dye thin films. The absorption spectra of this non-ionic organic semiconductor in the solid state show a strong influence of the film thickness on the J-aggregate formation. However, the electrical characteristics of the devices demonstrate that the hole transport properties do not vary significantly in films thicker than 100 nm. This is due to the fact that the J-aggregates are formed in this material at the surface of the crystalline grains and do not influence the semiconductor/gate dielectric interface and the charge transport properties of the devices. Hole field-effect mobilities as high as 2.4 × 10^?4 cm² V^?1 s^?1 were obtained and could be slightly improved by a solvent vapor treatment due to changes in the film crystallinity. Overall, this study demonstrates that J-aggregate bisazomethine dye thin films are good candidates for the realization of organic electronic devices.     

Improved Sellmeier Equations and Phase-Matching Characteristics in Deep-Ultraviolet Region of ${hbox {KBe}}_{2}{hbox {BO}}_{3}{hbox {F}}_{2}$ Crystal

A 3.0-mm-thick KBe ₂BO₃F₂ (KBBF) crystal has been successfully grown and used to fabricate a right angle prism. Its refractive indices were accurately measured with a prism technique at seven wavelengths from 0.4047 to 0.6562 mum . Its phase-matching characteristics in deep-ultraviolet (UV) region were investigated. Using the measured indices and phase-matching angles from deep-UV to near infrared, improved Sellmeier equations for KBBF have been derived.     

A Reliable All-2D Materials Artificial Synapse for High Energy-Efficient Neuromorphic Computing

High-performance artificial synaptic devices are indispensable for developing neuromorphic computing systems with high energy efficiency. However, the reliability and variability issues of existing devices such as nonlinear and asymmetric weight update are the major hurdles in their practical applications for energy-efficient neuromorphic computing. Here, a two-terminal floating-gate memory (2TFGM) based artificial synapse built from all-2D van der Waals materials is reported. The 2TFGM synaptic device exhibits excellent linear and symmetric weight update characteristics with high reliability and tunability. In particular, the high linearity and symmetric synaptic weight realized by simple programming with identical pulses can eliminate the additional latency and power consumption caused by the peripheral circuit design and achieve an ultralow energy consumption for the synapses in the neural network implementation. A large number of states up to ≈3000, high switching speed of 40 ns and low energy consumption of 18 fJ for a single pulse have been demonstrated experimentally. A high classification accuracy up to 97.7% (close to the software baseline of 98%) has been achieved in the Modified National Institute of Standards and Technology (MNIST) simulations based on the experimental data. These results demonstrate the potential of all-2D 2TFGM for high-speed and low-power neuromorphic computing.     

Ocular Effects of Exposure to 40, 75, and 95 GHz Millimeter Waves

The objective of this study was to develop a model of ocular damage induced by 40, 75, and 95 GHz continuous millimeter waves (MMW), thereby allowing assessment of the clinical course of ocular damage resulting from exposure to thermal damage-inducing MMW. This study also examined the dependence of ocular damage on incident power density. Pigmented rabbit eyes were exposed to 40, 75, and 95 GHz MMW from a spot-focus-type lens antenna. Slight ocular damage was observed 10 min after MMW exposure, including reduced cornea thickness and reduced transparency. Diffuse fluorescein staining around the pupillary area indicated corneal epithelial injury. Slit-lamp examination 1 day after MMW exposure revealed a round area of opacity, accompanied by fluorescence staining, in the central pupillary zone. Corneal edema, indicative of corneal stromal damage, peaked 1 day after MMW exposure, with thickness gradually subsiding to normal. Three days after exposure, ocular conditions had almost normalized, though corneal thickness was slightly greater than that before exposure. The 50% probability of ocular damage (DD₅₀) was in the order 40?>?95?≈?75 GHz at the same incident power densities.