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31.
Choi D Hiro-Oka H Furukawa H Yoshimura R Nakanishi M Shimizu K Ohbayashi K 《Optics letters》2008,33(12):1318-1320
We describe high-speed Fourier domain optical coherence tomography (OCT) using optical demultiplexers (ODs) for spectral dispersion. The OD enables separation of a narrow spectral band of 14 GHz (0.11 nm) from a broadband incident light at 256 different frequencies in 25.0 GHz intervals centered at 192.2 THz (1559.8 nm). OCT imaging of 60,000,000 axial scans per second was achieved through parallel signal acquisition using 256 balanced photoreceivers to simultaneously detect all the output signals from the ODs in a Fourier domain OCT system. OCT imaging at a 16 kHz frame rate, 1100 A-lines per frame, 3 mm depth range, and 23 microm resolution was demonstrated using a resonant scanner for lateral scanning. 相似文献
32.
Yong Lee Kazuhiko Hosomi Hiroyuki Uchiyama Toshio Katsuyama Shinya Kominami Tomoyoshi Mishima 《Optical Review》2003,10(1):38-42
An InGaAsP slab-type asymmetric-coupled-waveguide-based dispersion compensator with a mode selector has been designed and fabricated. The mode selector is necessary to select either a symmetric [with a positive group-velocity dispersion (GVD)] or antisymmetric (with a negative GVD) supermode. These supermodes exist simultaneously in the dispersion-compensation region of the device. Pulse-compression experiments were used to test the dispersion compensator, evaluating the function of the mode selector. A theoretical study of the experimental results shows that the mode selector obtains a very strong selectivity (nearly 100%) for the antisymmetric supermode. 相似文献
33.
Reliability of mean transit time obtained using perfusion-weighted MR imaging; comparison with positron emission tomography 总被引:2,自引:0,他引:2
Mihara F Kuwabara Y Tanaka A Yoshiura T Sasaki M Yoshida T Masuda K Matsushima T 《Magnetic resonance imaging》2003,21(1):33-39
The purpose of this project was to assess the reliability of the cerebral mean transit time (MTT) obtained using perfusion-weighted MR imaging by comparing it with the MTT obtained when performing positron emission tomography (PET). Ten patients with chronic occlusive cerebrovascular disease were investigated. They had either unilateral internal carotid artery occlusion or middle cerebral artery occlusion. The regions-of-interest were placed in non-infarcted areas within the territory of the middle cerebral artery on the affected side. Control regions-of-interest were placed in mirrored regions of the contralateral side. Linear regression analyses were performed using the parameters of the MTT obtained with perfusion-weighted MR imaging and the MTT, cerebral blood flow, vascular reactivity, and oxygen extraction fraction obtained with PET. The respective MTTs of the affected and non-affected sides obtained with perfusion-weighted MR imaging versus those with PET were 7.3 +/- 2.2 s and 6.0 +/- 1.2 s versus 8.2 +/- 3.0 s and 6.4 +/- 1.7 s. The MTT obtained using perfusion-weighted MR imaging and PET demonstrated statistically significant correlation (r = 0.87, p < 0.0001). The MTT obtained with perfusion-weighted MR imaging correlated statistically with cerebral blood flow (r = -0.74, p < 0.001), vascular reactivity (r = -0.73, p < 0.001) and oxygen extraction fraction (r = 0.61, p < 0.01). Similarly, the MTT obtained using PET statistically correlated with cerebral blood flow (r = -0.78, p < 0.0001), vascular reactivity (r = -0.51, p < 0.05) and oxygen extraction fraction (r = 0.68, p < 0.01). The reliability of the MTT obtained using perfusion-weighted MR imaging appears to be approximately equal to that obtained with positron emission tomography. 相似文献
34.
We successfully demonstrated low power penalty operation of a cross-phase modulated (XPM) wavelength converter using a semiconductor optical amplifier (SOA) power equalizer. We also clarified the SOA equalizing level for more adaptive wavelength conversion and achieved a power penalty of less than 1 dB over the wide input dynamic range of 15 dB. 相似文献
35.
Hideaki Furukawa Tsuyoshi Konishi Yoshinori Oshita Wanji Yu Kazuyoshi Itoh Yoshiki Ichioka 《光学学报》2003,23(Z1)
We demonstrate a suppression effect of a crosstalk among a target and similar header signals using the header recognition filter designed by a design technique of the multiple-object discriminant filter. 相似文献
36.
Butler J.M. Wharton C.B. Furukawa S. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1990,18(3):490-496
The operation of a backward wave oscillator (BWO) is shown to be critically dependent on the energy of the slow space-charge wave of the electron beam. Experimental work parameterizing the dependence of microwave frequency on effective beam energy, γbeam, reveals that through an understanding of electron-beam dynamics, a BWO could be systematically tuned through a desired frequency range while maintaining a high power of a few hundred megawatts and narrow frequency bandwidth, which was 400 MHz. Through variation of γbeam, 1.2 to 1.5 for the experiment, the lack of scaling of peak microwave power with the kinetic energy of the electron beam for γbeam >1.32 was observed. This effect was previously found in numerical simulation. In order to explain this effect, the relationship of the beam current to the space-charge-limiting current for increasing γbeam is examined. Dramatic evidence of pulse shortening, a phenomenon known to relativistic oscillators, was also seen 相似文献
37.
Inner shell ionization cross sections by low-energy positron impact have been measured. Development of an x-ray detector with thin Si(Li) crystals has enabled the first measurements of the absolute cross sections for the positron impacts in the energy range below 30 keV. Threshold behavior of the measured cross sections for the Cu K shell and Ag L shell are compared with the theoretical results of Gryzinski and Kowalski [Phys. Lett. A 183, 196 (1993)]] and Khare and Wadehra [Can. J. Phys. 74, 376 (1996)]]. Good agreement has been found for the Cu K shell, while the experimental values for the Ag L shell were found to be smaller than the corresponding theoretical results. 相似文献
38.
39.
A network for motion detection of an approaching object without influence of the moving background was proposed based on the
insect visual system. The two-dimensional array of the analog complementary metal oxide semiconductor (CMOS) circuits for
extracting the edge signals of the approaching object without outputting those of the moving background was inserted at the
first stage of the network. At the next stage, analog CMOS circuits for detection of approaching velocity and direction, which
accept the extracted edge signals, were inserted based on the locust vision system. A chip of the proposed network was fabricated
with the 1.2 mm CMOS process. It was clarified from the measured results and the simulation results with the simulation program
with integrated circuit emphasis (SPICE) that the two-dimensional circuits of the first stage can only generate the signals
of target edges. The measured results showed that the chip can detect the approaching velocity and direction of the target
in the image which contains the moving background. 相似文献
40.
Kazuhiko Hosomi Toshihiko Fukamachi Hiroji Yamada Toshio Katsuyama Yasuhiko Arakawa 《Photonics and Nanostructures》2006,4(1):30-34
We demonstrate optical properties of one-dimensional photonic crystals (PC), which are fabricated using high-aspect-ratio etching on a V-grooved silicon wafer. The measured transmission spectrum has an obvious band gap; the suppression is over 30 dB. The quite small insertion loss of 1.9 dB is achieved by induced coupled plasma (ICP) cryogenic etching and direct coupling to the optical fiber aligned in the V-groove. We also successfully observed peaks originating from a localized cavity mode. Such a microcavity enables control of the light, which qualifies photonic crystal as a fundamental structure of optical functional devices. These results lead to achievement of integrated Si-based photonic circuits. 相似文献