Takeshi Kawai

Bio: Takeshi Kawai is an academic researcher from Harvard University. The author has contributed to research in topics: Optical amplifier & Optical switch. The author has an hindex of 7, co-authored 22 publications receiving 144 citations.

Experimental demonstration of multi-degree colorless, directionless, contentionless ROADM for 127-Gbit/s PDM-QPSK transmission system

Abstract: We experimentally demonstrate the feasibility of a multi-degree colorless, directionless, and contentionless (C/D/C-less) ROADM node composed of high port count wavelength-selective switches and transponder aggregators using silica-based planar lightwave circuit technology. The experimental results show that the introduction of a C/D/C-less function to a multi-degree ROADM node induces no significant penalty in a 127-Gbit/s PDM-QPSK signal transmission.

Demonstration of translucent elastic optical network based on virtualized elastic regenerator

Abstract: We propose a translucent elastic optical network based on a virtualized elastic regenerator. Using a real-time 128-Gb/s spectrum-selective subchannel regenerator, we verify the concept through mixed-rate superchannel regeneration and frequency-slot merger with spectrum conversion.

Optimized multi-layer optical network using in-service ODU / wavelength path re-grooming

Abstract: We propose a multi-layer network with in-service traffic re-grooming. The combination of colorless multi-degree ROADM and ODU cross-connect with ODU reallocation functionality can offer significant cost reduction with no impact of re-grooming on services.

Fibre management technique for optical device integration on circuit board with hundreds of optical connections

Abstract: The authors present a technique for fibre management on a circuit board, which utilises newly-developed, flexible optical fibre circuits and multifibre physical contact connectors. The technique achieves compact fibre wiring and easy fibre connection for hundreds of fibres on a circuit board. The authors have fabricated a compact 8/spl times/16 delivery and coupling switch board using the technique.

Experimental demonstration of arrayed optical amplifiers with a shared pump laser for realizing colorless, directionless, contentionless ROADM.

Abstract: We propose arrayed optical amplifiers that share a single pump laser with the aim of realizing full-add/drop colorless, directionless, contentionless ROADM nodes and demonstrate its feasibility in experiments. The experimental results show that the fabricated arrayed optical amplifiers can be made to correspond properly to wavelength path reconfigurations by adjusting a splitting ratio of the variable splitter between the pump laser and eight EDFAs, and cause no significant penalty for 128-Gbit/s PDM-QPSK signal transmission.

Routing and spectrum assignment algorithm maximizes spectrum utilization in optical networks

Abstract: This paper proposes a routing and spectrum assignment algorithm for elastic optical networks. The algorithm achieves high utilization of spectrum resources by considering the consecutiveness of common available spectrum slots among relevant fibers.

BER Degradation Detection and Failure Identification in Elastic Optical Networks

Abstract: Optical connections support virtual links in MPLS-over-optical multilayer networks and therefore, errors in the optical layer impact on the quality of the services deployed on such networks. Monitoring the performance of the physical layer allows verifying the proper operation of optical connections, as well as detecting bit error rate (BER) degradations and anticipating connection disruption. In addition, failure identification facilitates localizing the cause of the failure by providing a short list of potential failed elements and enables self-decision making to keep committed service level. In this paper, we analyze several failure causes affecting the quality of optical connections and propose two different algorithms: one focused on detecting significant BER changes in optical connections, named as BANDO, and the other focused on identifying the most probable failure pattern, named as LUCIDA. BANDO runs inside the network nodes to accelerate degradation detection and sends a notification to the LUCIDA algorithm running on the centralized controller. Experimental measures were carried out on two different setups to obtain values for BER and received power and used to generate synthetic data used in subsequent simulations. Results show significant improvement anticipating maximum BER violation with small failure identification errors.

New devices enabling software-defined optical networks

Abstract: Next-generation ROADM networks are incorporating an extensive range of new features and capabilities including colorless, directionless, and contentionless multiplexing and demultiplexing, flexible spectrum channel definition, and higher-order modulation formats. To efficiently support these new features, both new ROADM node architectures along with complementary optical components and technologies are being synergistically designed. In this article, we describe these new architectures, components, and technologies, and how they work together to support these features in a compact and costefficient manner.

Architecture of a Single-Chip 50 Gb/s DP-QPSK/BPSK Transceiver With Electronic Dispersion Compensation for Coherent Optical Channels

Abstract: The architecture of a single-chip dual-polarization QPSK/BPSK 50 Gigabits per second (Gb/s) DSP-based transceiver for coherent optical communications is presented. The receiver compensates the chromatic dispersion (CD) of more than 3,500 km of standard single-mode fiber using a frequency-domain equalizer. A time-domain four-dimensional MIMO transversal equalizer compensates up to 200 ps of differential group delay (DGD) and 8000 ps 2 of second-order polarization-mode dispersion (SOPMD). Other key DSP functions of the receiver include carrier and timing recovery, automatic gain control, channel diagnostics, etc. A novel low-latency parallel-processing carrier recovery implementation which is robust in the presence of laser phase noise and frequency jitter is proposed. The chip integrates the transmitter, receiver, framer and host interface functions and features a 4-channel 25 Gs/s 6-bit ADC with a figure of merit (FOM) of 0.4 pJ/conversion. Each ADC channel is based on an 8-way interleaved flash architecture. The DSP uses a 16-way parallel processing architecture. Extensive measurement results are presented which confirm the design targets. Measured optical signal-to-noise ratio (OSNR) penalty when compensating 200 ps DGD and 8000 ps 2 is 0.1 dB, while OSNR penalty when compensating 55 ns/nm CD (corresponding to 3,500 km of standard single-mode fiber) is 0.5 dB.

$N \times N$ Cyclic-Frequency Router With Improved Performance Based on Arrayed-Waveguide Grating

Abstract: We have developed an NxN cyclic-frequency router with improved performance by employing two types of modified configuration; a uniform-loss and cyclic-frequency (ULCF) arrayed-waveguide grating (AWG) and an interconnected multiple AWG. We have demonstrated a compact 50-GHz-spacing 64x64 ULCF-AWG router with low and uniform insertion losses of 5.4-6.8 dB and frequency deviations from the grid of less than plusmn8 GHz. We have also demonstrated a 100-GHz-spacing 8x8 interconnected multiple-AWG router with a practical configuration, very low and uniform insertion losses of 2.3-3.4 dB, and frequency deviations from the grid of less than plusmn6 GHz. We discuss the suitable or realizable scale N of the two types of routers by comparison with a conventional AWG router in terms of optical and dimensional performance and productivity.