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166 results on '"Kasahara R"'

40. Optical phase‐sensitive amplification of higher‐order QAM signal with single Mach–Zehnder amplitude modulator.

Author

Shimizu, S., Kobayashi, T., Kazama, T., Umeki, T., Enbutsu, K., Kasahara, R., and Miyamoto, Y.

Abstract

An optical phase‐sensitive amplifier (PSA) has the potential of low‐noise optical amplification. A frequency non‐degenerate PSA (ND‐PSA) can amplify arbitrary modulation formats including higher‐order QAM. The ND‐PSA requires a co‐propagating phase conjugated light (idler light) that has been conventionally created with an optical phase conjugator at the transmitter side. We propose a transmitter configuration using simultaneous signal generation of both a signal and its idler by double‐sideband modulation for transmission systems with ND‐PSAs. The proposed scheme provides a simple configuration with a single Mach–Zehnder amplitude modulator without optically creating the idler light. We performed experiments using 16QAM, 32QAM, and probabilistically shaped 256QAM signals. As a result, a phase‐sensitive amplification with each modulation format was successfully demonstrated using the proposed transmitter configuration. [ABSTRACT FROM AUTHOR]

Published
2021
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44. Tuning technique to optimize input power of a cross-phase modulation wavelength converter.

Author

Sato, R., Ito, T., Magari, K., Endo, J., Ogawa, I., Inoue, Y., Kasahara, R., Tohmori, Y., Suzuki, Y., and Tohno, S.

Abstract

This paper proposes a tuning technique to optimize the input power of a cross-phase modulation wavelength converter (XPM-WC). The focus is on an output signal whose wavelength is the same as the input signal. The optimum input power can be easily set by keeping the output signal (not converted signal) power constant. Input continuous-wave (CW) power should be increased or decreased with increasing or decreasing input signal power so that the output signal power stays fixed at the optimum level. Observing the eye pattern of the converted signal is unnecessary. Wavelength conversion from a fixed optical channel to a random one (30 channels with 100-GHz spacing) is successfully demonstrated by using this technique. A low-power penalty (<1dB) and a low-power fluctuation (<1dB) were confirmed in all optical channels. An XPM-WC unit containing a variable CW light source and its level controller were fabricated and simultaneous and automatic operation was confirmed. [ABSTRACT FROM PUBLISHER]

Published
2004
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48. Spectral intensities and phase distributions of supercontinuum pulses generated in low-dispersion fibers

Author

Sone, H., Yoshitomi, D., Zhou, X., Kikuchi, K., Kasahara, R., Abrishamian, F., Nakamura, S., Harada, Y., and Torizuka, K.

Abstract

It was reported recently that optical pulses propagating through a tapered fiber (TF) immersed in heavy water (D2O) or photonic crystal fiber (PCF) of special design yield a broad and flat supercontinuum (SC) spectrum because the fiber dispersion characteristics are of low dispersion: around 1000 nm. This work was undertaken to investigate spectral intensities and phase distributions of SC pulses generated in low-dispersion fibers. Results show that PCF with group velocity dispersion (GVD) distributions having an extremum value of zero dispersion can be used at short fiber length for applications where the phase distribution is a concern.

Published
2011
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50. Fretting Fatigue Behaviour of Alloy Steel in the Very High Cycle Region

Author

Shimamura Yoshinobu, Kasahara Reo, Ishii Hitoshi, Tohgo Keiichiro, Fujii Tomoyuki, Yagasaki Toru, and Sumida Soichiro

Subjects
Engineering (General). Civil engineering (General), TA1-2040
Abstract

It is well known that fretting fatigue strength is much lower than the fatigue strength of smooth specimens and the fatigue limit disappears. Many studies on fretting fatigue have been reported but most of the studies have not cover fatigue properties in the very high cycle regime more than 107 cycles. In this study, an accelerated fretting fatigue testing method was developed by using an ultrasonic torsional fatigue testing machine with a clamping fretting pad. Fretting fatigue tests of CrMo steel were conducted by using the developed method. Test results showed that fretting fatigue failure occurs in the very high cycle region.

Published
2019
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