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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 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)
In order to mitigate the signal spectrum narrowing caused by optical filtering at nodes, an adequate guard band is needed between optical channels, which degrades the frequency utilization of optical fibers. In this study, we propose a grouped routing based network architecture that minimizes spectrum narrowing while greatly improving spectral efficiency.(More)
This article presents the development of a timberjack-like pruning robot. The climbing principal is an imitation of the climbing approach of timberjacks in Japan. The robot’s main features include having its center of mass outside the tree, and an innovative climbing strategy fusing straight and spiral climbs. This novel design brings both lightweight and(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)
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)
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)
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)
A new optical cross-connect (OXC) configuration that yields hitless port-count expansion to meet traffic growth at minimum cost is presented. We introduce a control algorithm that uses a simple criterion for scaling up OXC port count. The scheme exploits the difference between node degree and fiber degree. Numerical experiments verify that our node(More)