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Author

Hiroki Kishikawa

Other affiliations: Harvard University
Bio: Hiroki Kishikawa is an academic researcher from University of Tokushima. The author has contributed to research in topics: Phase-shift keying & Modulation. The author has an hindex of 9, co-authored 112 publications receiving 348 citations. Previous affiliations of Hiroki Kishikawa include Harvard University.


Papers
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Journal ArticleDOI
TL;DR: Bidirectional transmission over 450 km of newly-developed dual-ring structured 12-core fiber with large effective area and low crosstalk is demonstrated, and 409-Tb/s capacities are achieved for both directions.
Abstract: We demonstrate bidirectional transmission over 450 km of newly-developed dual-ring structured 12-core fiber with large effective area and low crosstalk. Inter-core crosstalk is suppressed by employing propagation-direction interleaving, and 409-Tb/s capacities are achieved for both directions.

97 citations

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a novel method of wavelength preserved conversion for polarization division multiplexed QPSK signal with arbitrary polarization rotation angle to the x-axis on the xy polarization plane which is orthogonal to the propagation axis.
Abstract: Flexible conversion between multi-level modulation formats is one of the key processing functions to realize adaptive modulation techniques for flexible networking aimed at high spectral efficiency in optical fiber transmission. The authors have proposed an all-optical format conversion systems from binary phase-shift keying (BPSK) to quadrature PSK (QPSK) and its reverse conversion from QPSK to BPSK. The latter had an advantage of wavelength-shift-free conversion from an incident QPSK to simultaneous two BPSK outputs without loss of the transmitting data. However, it was limited only for a single polarization signal. In this paper, we propose a novel method of wavelength preserved conversion for polarization division multiplexed QPSK signal with arbitrary polarization rotation angle to the x-axis on the x-y polarization plane which is orthogonal to the propagation axis. The method is based on the orthogonal dual-pump four-wave-mixing (FWM) in the highly nonlinear fiber with a nonlinear optical loop mirror configuration, which has advantages that it separately outputs the original signal and the phase conjugate signal and has independent FWM efficiency of the signal polarization angle. We show the system performances such as bit-error-rate and optical signal-to-noise ratio penalty evaluated by numerical simulations.

24 citations

Journal ArticleDOI
TL;DR: This paper proposes an all-optical modulation format conversion system between on-off keying, quadrature phase-shiftkeying, and 8-ary quadratures amplitude modulation using optical nonlinear effects in semiconductor optical amplifier and optical threshold device and evaluates the conversion performances by numerical simulation.
Abstract: Modulation format conversion is useful when the signal is transmitted through networks employing different modulation formats. It is also expected to increase the spectral efficiency and reduce power consumption in network nodes by applying all-optical signal processing to the modulation format conversion. In this paper, we propose an all-optical modulation format conversion system between on - off keying, quadrature phase-shift keying, and 8-ary quadrature amplitude modulation using optical nonlinear effects in semiconductor optical amplifier and optical threshold device. We also evaluate the conversion performances of the system by numerical simulation in terms of optical signal-to-noise ratio, optical signal power, and accumulated chromatic dispersion.

21 citations

Journal ArticleDOI
TL;DR: An all-optical switch consisting of two-stage Mach-Zehnder interferometers, whose arms contain graphene saturable absorption films, which is theoretically analyzed and numerically simulated by the finite-difference beam propagation method (FD-BPM).
Abstract: At routing nodes in future photonic networks, pico-second switching will be a key function. We propose an all-optical switch consisting of two-stage Mach-Zehnder interferometers, whose arms contain graphene saturable absorption films. Optical amplitudes along the interferometers are controlled to perform switching between two output ports instead of phase control used in conventional switches. Since only absorption is used for realizing complete switching, insertion loss of 10.2 dB is accompanied in switching. Picosecond response can be expected because of the fast response of saturable absorption of graphene. The switching characteristics are theoretically analyzed and numerically simulated by the finite-difference beam propagation method (FD-BPM).

17 citations

Journal ArticleDOI
TL;DR: AnOptical neural-network circuit to recognize BPSK labels for photonic label routing is proposed, whose neuron consists of optical amplitude amplifiers and phase shifters as weighting connections, a combiner and a nonlinear threshold device for an activation function.
Abstract: Optical neural-network circuit to recognize BPSK labels for photonic label routing is proposed, whose neuron consists of optical amplitude amplifiers and phase shifters as weighting connections, a combiner and a nonlinear threshold device for an activation function. The parameters of these weighting connections are learned with back-propagation of teacher signals. The performance of the neural network circuits as recognition of two to four bit BPSK labels is clarified by computer simulation. For routing application, classification of routing labels into several groups corresponding to the output ports of the router is also discussed and is successfully simulated.

16 citations


Cited by
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Journal ArticleDOI
TL;DR: In the past several years, two-dimensional black phosphorus (BP) has captured the research community's interest because of its unique electronic, photonic, and mechanical properties.
Abstract: In the past several years, two-dimensional black phosphorus (BP) has captured the research community's interest because of its unique electronic, photonic, and mechanical properties. Remarkable efforts have been made regarding the synthesis, fundamental understanding, and applications of BP in the fields of nanoelectronics, nanophotonics, and optoelectronics. In this review, we summarize the recent developments in the study of BP, which covers the state-of-the-art synthesis methods for preparing single-layer or few-layer BP, the recent advances in characterizing its electronic, optical and mechanical properties, and the reported functional devices utilizing such properties. Finally we discuss the existing challenges in developing BP-based nanoelectronics and optoelectronics, and describe the prospects for future BP-related research.

274 citations

Journal ArticleDOI
TL;DR: This paper discusses crosstalk estimation in multicore fibers (MCFs) using coupled-mode theory and coupled-power theory, and the combination of MCF and few-mode fiber (FMF), which is FM-MCF, is a very promising approach to realize space multiplicity over 50.
Abstract: Multicore fibers (MCFs) are expected as a good candidate for overcoming the capacity limit of a current optical communication system. This paper describes the recent progress on the MCFs for space-division multiplexing to be utilized in future large capacity long-distance transmission systems. Tradeoff issue between low crosstalk and high core density in MCFs is presented and prospect of large-space multiplicity of MCFs is discussed.

273 citations

Journal ArticleDOI
TL;DR: Results show that SDM fibers achieve a 1185-fold (18-fold) spectral-spatial efficiency increase compared with the 276-SMF bundle (single-core fiber) currently installed on the ground.
Abstract: Single-mode fiber's physical capacity boundaries will soon be reached; hence, alternative solutions are much needed to overcome the multiplying and remarkably large bandwidth requests. Space division multiplexing (SDM) using multicore fibers (MCFs), multielement fibers, multimode fibers, and their combination; few-mode MCFs; or fibers based on orbital angular momentum are considered to be the propitious stepping-stones to overcome the capacity crunch of conventional single-core fibers. We critically review research progress on SDM fibers and network components, and we introduce two figures of merit aiming for quantitative evaluation of technologies such as amplifiers, fan-in/fan-out multiplexers, transmitters, switches, and SDM nodes. Results show that SDM fibers achieve a 1185-fold (18-fold) spectral–spatial efficiency increase compared with the 276-SMF bundle (single-core fiber) currently installed on the ground. In addition, an analysis of crosstalk in MCFs shows how SDM concepts can be further exploited to fit in various optical networks such as core, metro, and especially future intra-data center optical interconnects. Finally, research challenges and future directions are discussed.

272 citations

09 May 2007

178 citations