Nobuhiko Kikuchi

Analysis of signal degree of polarization degradation used as control signal for optical polarization mode dispersion compensation

The basic property of degree of polarization (DOP) degradation of optical signal induced by polarization mode dispersion (PMD) in high-speed optical fiber transmission is investigated in detail. The DOP of the optical signal reflects the degree of waveform degradation caused by PMD, therefore, it is proposed to be used as the control signal judging the best compensation point for the optical adaptive PMD compensation techniques. However, the signal DOP is not only affected by PMD, but also by various factors, such as the modulation format, modulator chirp, fiber nonlinearity, amplified spontaneous emission (ASE), and so on. We use numerical simulations and experiments to explore the basic DOP property to detect PMD with these factors. We also show that using the signal DOP as control signal is especially useful for the optical duo-binary modulation because of its high sensitivity and wide PMD detection range.

Analytical evaluation technique of self-phase-modulation effect on the performance of cascaded optical amplifier systems

We propose an approximate analytical evaluation technique of self-phase-modulation (SPM) in cascaded optical amplifier systems. The effect of SPM on optical pulse distortion is represented by the increase in the /spl alpha/-parameter of the transmitter. The waveform distortion is approximated by assuming that the pulse is transmitted over a dispersive fiber without nonlinearity. This technique greatly reduces the calculation time, and is especially useful in designing cascaded amplifier systems, evaluating theoretical maximum transmission distance. >

Intersymbol Interference (ISI) Suppression Technique for Optical Binary and Multilevel Signal Generation

An intersymbol interference (ISI)-suppressed optical multilevel modulation technique that is applicable to a wide range of binary and multilevel signaling is proposed. It employs binary phase-shift keying modulations that are generated by Mach-Zehnder intensity modulators as basic building blocks, and complex multilevel modulations are synthesized using interferometric addition and tandem modulations. Its feasibility and ISI suppression effect are verified in various binary and multilevel signal synthesis schemes using numerical simulations. Furthermore, the generation of ISI-suppressed zero-chirp binary and quaternary amplitude-shift keying modulations is experimentally demonstrated. Finally, its applicability to complex optical multilevel signaling is shown in the generation of a 40-Gb/s 16-level amplitude- and phase-shift keying signal, which results in 3-dB sensitivity improvement compared with the one using a conventional four-level electrical driving signal.

Incoherent 32-Level Optical Multilevel Signaling Technologies

In order to explore the potential of optical multilevel signaling for high-speed optical fiber networks, an incoherent 50 Gbit/s 32-level optical multilevel signaling (combination of QASK and 8-DPSK) is demonstrated, for the first time. The application of an ISI-suppressed modulation technique, an orthogonally-coupled differential detection technique and the digital signal processing technique have also been proposed and verified to enhance the performance of multilevel signaling. A 100-km dispersion shifted fiber transmission has also been performed, and the degradation via optical fiber nonlinear effect, self-phase modulation (SPM), is observed. The receiver side simple digital cancellation technique of the SPM-induced phase shift is also proposed and experimentally demonstrated with more than 6.8 dB increase of fiber input power.

Highly Sensitive Optical Multilevel Transmission of Arbitrary Quadrature-Amplitude Modulation (QAM) Signals With Direct Detection

A proposal for the realization of highly sensitive optical direct-detection (incoherent) multilevel transmission with arbitrary signal constellation without optical chromatic dispersion (CD) compensation is reviewed in this paper. We introduce transmitter-side signal processing, ¿CD pre-equalization,¿ and ¿phase preintegration¿ techniques to realize direct-detection CD-compensation free transmission of arbitrary optical quadrature-amplitude modulation (QAM) signals. We also adopt receiver-side signal processing, ¿multi-symbol phase estimation (MSPE),¿ and ¿non-Euclidean metric-based symbol detection¿ to improve the optical SNR (OSNR) sensitivity. We have performed up to 160-km standard single-mode fiber transmission of a 40-Gbit/s 16QAM signal and achieved the OSNR sensitivities only 0.5-2.4 dB away from those of coherent detection.

4-level direct-detection polarization shift-keying (DD-PolSK) system with phase modulators

We propose and demonstrate a novel 4-level DD-PolSK system with LiNbO/sub 3/-based phase modulator and alternative allocation of constellations, which lead to a greatly simplified transceiver architecture. A 5 Gb/s (2.5 GS/s) testbed has been build to demonstrate the feasibility of the 4-PolSK transceiver.

Performance of chromatic dispersion monitoring using statistical moments of asynchronously sampled waveform histograms

The performance of the chromatic dispersion monitoring method using statistical moments of asynchronously sampled waveform histograms is investigated in detail. We show its robustness against signal-to-noise ratio degradation and its wide monitoring range using experiments and a newly developed numerical simulation method. We also show the effectiveness of radio frequency bandwidth reduction of the waveform monitor to widen its monitoring range, and also estimate its performance with duobinary and return-to-zero modulation formats.

Study on cross-phase modulation (XPM) effect on amplitude and differentially phase-modulated multilevel signals in DWDM transmission

The characteristic degradation mechanism of the cross-phase modulation (XPM) effect on multilevel amplitude and differentially phase-shift keying (APSK) signals in dense wavelength-division-multiplexing (DWDM) transmissions is analyzed and experimentally investigated, for the first time. Based on the results, we successfully demonstrate a 0.48-Tb/s (30-Gb/s/ch) 50-GHz-spaced 16-channel DWDM 160-km unrepeatered transmission of eight-level APSK signals suppressing the XPM-induced degradation.

A Novel Bias Control Technique for MZ Modulator with Monitoring Power of Backward Light for Advanced Modulation Formats

We propose a novel high-sensitive and cost-effective bias control scheme for MZ modulator with minimizing monitored power of backward-traveling light, and demonstrate its effectiveness with the experiments of 10-Gbit/s CSRZ and 43-Gbit/s RZ-DQPSK signals.

Experimental Demonstration of Incoherent Optical Multilevel Staggered-APSK (Amplitude- and Phase-Shift Keying) Signaling

Generation and incoherent detection of a 30-Gbit/s 8-level staggered APSK signal using two-state MLSE detection is successfully demonstrated with a 140-km fiber transmission. Its better constellation design results in 1.5-dB sensitivity improvement from 8-DPSK signaling.