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We demonstrate unrepeated 200-km transmission of 40-Gbit/s 16-QAM signals using a digital coherent receiver, where the decision-directed carrier-phase estimation is employed. The phase fluctuation is effectively eliminated in the 16-QAM system with such a phase-estimation method, when the linewidth of semiconductor lasers for the transmitter and the local(More)
We propose a novel configuration of the finite-impulse-response (FIR) filter adapted by the phase-dependent decision-directed least-mean-square (DD-LMS) algorithm in digital coherent optical receivers. Since fast carrier-phase fluctuations are removed from the error signal which updates tap coefficients of the FIR filter, we can achieve stable adaptation of(More)
A novel resilient optical routing network architecture that adopts finely granular protection and finely granular add/drop is presented. The routing scheme defines optical pipes such that multiple optical paths can be carried by each pipe and can be dropped or added at any node on the route of a pipe. The routing scheme also makes it possible to enhance(More)
We propose a novel and unified algorithm that estimates linear impairments in optical transmission systems from tap coefficients of an adaptive finite-impulse response (FIR) filter in a coherent optical receiver. Measurable impairments include chromatic dispersion (CD), differential group delay (DGD) between two principal states of polarization,(More)
The wide deployment of ROADM based photonic networks, particularly in metro areas, compels an increase in the number of WSSs traversed by the average optical path. The impairment caused by optical filtering of WSSs, called spectrum narrowing effect, can be a serious problem in transparent optical networks. To resolve this impairment and to enable higher(More)
We propose a highly scalable and compact optical-node architecture that combines the subsystemmodular optical cross-connect (OXC) and transponderbank add/drop, where multiple M × M wavelength-selective switches are effectively introduced. Numerical experiments verify that the proposed architecture offers large-scale nodes with substantially relaxed hardware(More)
Hierarchical optical networks will be a viable solution in creating large-scale networks of the future. The networks control optical network resources in granularity of both wavelength and waveband that consists of a fixed number of wavelengths; thereby, they can reduce signalling processing load and efficiently create virtual private networks. Meanwhile,(More)
We propose a cost-effective and scalable OXC/ROADM that consists of a subsystem-modular express switch part and a transponder-bank-based add/drop part. The effectiveness of the proposed architecture is verified via a hardware scale evaluation, network performance simulations, and transmission experiments. The architecture enables large throughput and offers(More)
In this paper, we propose a machine-learning-based novel dynamic performance control method for routers that supports several performance levels. The method utilizes support vector machine (SVM) to determine performance level change points. We utilize a traffic normalization technique with a corresponding performance threshold that allows us to apply the(More)
To offset the impairment caused by imperfect optical filtering at ROADMs/OXCs, guard bands must be inserted between optical channels. The resulting degradation in frequency utilization detracts from the benefit of next-generation elastic optical path networks. To overcome this problem and achieve an ICT infrastructure with the required level of resiliency,(More)