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Optical networks, such as wavelength-division multiplexing networks and elastic optical networks, require high reliability and efficient wavelength allocation. We propose a new physical topology optimization method that achieves both high reliability and efficient wavelength allocation. We compare the results of conventional algebraic connectivity optimization, which discusses physical topology optimization from the viewpoint of spectral graph theory, with those based on reliability optimization, which is important from the viewpoint of network operations. From the comparison analysis, it is shown that our proposed two-step degree bounded reliability-optimization model, which optimizes reliability with appropriate node degree constraints, leads to a physical topology that has high wavelength capacity without compromising reliability.

We demonstrate novel 100Gbit/s ODU4 path switching without bit disruption at relative delay difference up to 400 km experimentally. We confirmed ITU-T standard-compliant jitter characteristic and applicability for core and metro network by evaluating accommodation rate in European network.

Compensating for intercarrier nonlinear distortion allows launching higher power into the transmission fiber and it leads to an increase in the transmission distance. Numerical calculations show that the launch power is increased by 10 dB and the maximum transmission distance is more than tripled, when the optical repeater spacing of 80 km, dispersion-shifted fiber, and signal format of 10 Gb/s nonreturn-to-zero are assumed. It is experimentally demonstrated that waveform distortion due to the four-wave mixing (FWM) among different carriers in wavelength-division multiplexing (WDM) becomes deterministic by phase-locking optical carriers and that FWM distortion can be compensated at 5 Gb/s with three-channel condition by employing DSP at the transmitter or receiver.

We propose a novel optical orthogonal frequency-division multiplexing (OFDM) transmission, where the frequency spacing of subchannels is less than the symbol rate. We show experimentally that the novel OFDM transmission achieves an optical SNR (OSNR) sensitivity level and dispersion tolerance roughly equivalent to those of the conventional OFDM. We also show the influence of chromatic dispersion from the transmission channel on the OFDM signal. The chromatic dispersion causes a desynchronization of the symbol timing between subchannels and breaks the frequency orthogonality in OFDM. We confirm experimentally that it is possible to mitigate the signal degradation due to the chromatic dispersion by optimizing the symbol timing and orthogonally polarizing the subchannels to the neighboring subchannels.

A scheme that compensates the waveform distortion induced by nonlinear interchannel crosstalk such as four-wave mixing (FWM) and cross-phase modulation as well as self-phase modulation in phase-locked wavelength-division-multiplexing transmission systems is proposed. Reduction of FWM-induced waveform distortion by controlling the phase relationship between neighbouring channels and its cancellation by precompensation is successfully demonstrated

We propose a scalable and effective wavelength defragmentation algorithm that considers multiple fibers per link. The number of fibers is reduced by more than 14% in multi-ring-like networks based on numerical evaluation.

We present simultaneous measurement of femtosecond time-resolved nonlinear phase and amplitude changes around the excitonic resonance of the AlGaAs∕GaAs quantum well using polarization-division Sagnac interferometer. The nonlinear complex refractive index of the semiconductor material for all-optical devices is successfully determined from directly measured nonlinear phase and amplitude changes.

We propose a novel evaluation of optical path accommodation efficiency, and use it to quantify the effectiveness of the Least Fragmentation (LF) algorithm with reference to the optimal solution obtained by Integer Linear Programming (ILP). The evaluations show that the efficiency of the LF algorithm is close to the limit of path accommodation. Specifically, we indicate an advantage relative to the most path-provisioning order that LF algorithm achieves the high performance path-provisioning compared with the other algorithms.

We propose a novel OFDM scheme with the subchannel frequency spacing at 80% of the symbol rate. Experiment results show that the scheme achieves OSNR-sensitivity and dispersion-tolerance levels equal to those of the conventional OFDM.

We propose and demonstrate a bit-rate-flexible all-optical OFDM transceiver. Signals were successfully generated at 107, 42.8, 32.1, and 10.7Gbit/s and received through the transceiver. The 107-Gbit/s signal was successfully transmitted over 40-km-SMF without dispersion compensation.

We present the first experimental demonstration of a multi-granularity optical-cross-connect node toward 100-Tbit/s scalability. We successfully show 10.24-Tbit/s throughput with completely error-free operation and an 80-Gbit/s (2 × 40-Gbit/s) optical-virtual-concatenation function between different routes.

This paper shows electronic pre-compensation of nonlinear inter-channel crosstalk induced by four-wave mixing in 3-channel carrier phase-locked WDM. Experimental results show that carrier phase locking and electric pre-distortion successfully suppress the waveform distortion.

This paper proposes 100-Gbit/s optical-OFDM transmission using the ODB format. An OFDM signal generated using a simple multi-carrier generator and multi-carrier modulator is successfully transmitted over a 20-km SMF and 100-km DSF without dispersion compensation.

This paper introduces a technique that compensates for nonlinear inter-channel crosstalk in wavelength division multiplexing (WDM) transmission. Electronic pre- and post-compensation of four-wave mixing are experimentally shown in carrier phase-locked WDM.

The concept of nonlinear inter-channel crosstalk compensation in phase-locked WDM transmission systems is proposed. Cancellation of FWM-induced waveform distortion by pre-compensation and its reduction by proper setting of the phase relationship between neighbouring channels are successfully demonstrated.

A novel interferometer, a Sagnac interferometer (SI), is presented for the measurement of the difference phase and amplitude spectra induced by photoexcitation with a femtosecond time resolution. The SI has a remarkable advantage of high stability owing to the common-path configuration. In order to separate the phase and amplitude changes, the optical path difference is scanned between the probe and reference pulses making the best use of polarization. This improved polarization-division Sagnac interferometer (PSI) provides a nearly sinusoidal fringe. To demonstrate PSI we examined the nonlinear phase and amplitude changes in CS 2 and a GaAs/AlGaAs quantum well (QW) structure. The sepctral feature of the nonlinear dispersion relation in QW can be explained by the blue-shift of the excitonic resonance. The time dependence of these changes is observed to be determined by the exciton lifetime. These experimental results are consistently explained from neutralization of the built-in potential inside the QW sample.

The increase in WDM transmission distance at zero-dispersion wavelength made possible by pre-compensation to offset nonlinear interchannel crosstalk is studied. A simulation shows that pre-compensation allows higher fibre launched power and increases the transmission distance by 3.3 times for a 50 GHz-spaced 8-channel WDM system. Pre-compensation is shown to be limited by the undeterministic nonlinear distortion induced by the accumulated amplifier spontaneous emission noise from repeater amplifiers. Also, optical power tolerance of the pre-distorted waveform generated at the transmitter is studied.