K. Oguchi

A 1580-nm band WDM transmission technology employing optical duobinary coding

This paper reports 1580-nm band wavelength division multiplexed (WDM) transmission employing optical duobinary coding over dispersion-shifted fibers. By using the 1580 nm band, the generation of four-wave mixing (FWM) over dispersion-shifted fibers (DSFs) can he suppressed. Optical duobinary coding is dispersion-tolerant because of its narrow bandwidth, and enables the use of the conventional binary intensity modulated direct detection (IM-DD) receiver. First, comparisons are made for WDM transmission performance in the 1580-nm band between conventional binary nonreturn-to-zero (NRZ) coding with and without postdispersion compensation, and optical duobinary coding by computer simulation is described. From the numerical simulations, it is found that the optical duobinary coding has superior transmission performance to the conventional binary coding without any dispersion compensation, and that the difference in the transmission performance between two coding methods is very small even if postdispersion compensation at the optical receiver is applied to the NRZ coding method. Second, transmission performance between the conventional binary NRZ and the optical duobinary signals without any dispersion compensation is compared with the straight-line experiment over 500-km dispersion-shifted fiber. The experimental results reveal that the transmission distance with optical duobinary coding is doubled in comparison with that of the conventional binary NRZ signals. Finally, 16-channel, 10-Gb/s optical duobinary WDM signals in the 1580-nm band are successfully transmitted over 640 km (80 km/spl times/8) of DSF without any dispersion compensation or management.

Bidirectional transmission to suppress interwavelength-band nonlinear interactions in ultrawide-band WDM transmission systems

Interwavelength-band nonlinear interactions are investigated as possible causes of performance degradation in ultrawide band wavelength-division-multiplexed transmission. These interactions can severely limit the performance of transmission over dispersion-shifted fibers (DSFs) and nonzero DSFs. Bidirectional transmission is found to be effective in suppressing interwavelength-band nonlinear interactions.

1580-nm band, equally spaced 8 x 10 Gb/s WDM channel transmission over 360 km (3 x 120 km) of dispersion-shifted fiber avoiding FWM impairment

Optically repeated wavelength-division multiplexed (WDM) transmission over dispersion-shifted fibers (DSFs) in the novel 1580-nm wavelength band is reported. WDM systems operating on DSFs are severely impaired by nonlinear crosstalk caused by four-wave mixing (FWM). We avoid this impairment by using novel 1580-nm band instead of the conventional 1550-nm band. Newly developed erbium-doped fiber amplifiers (EDFAs) for 1570-1600-nm wavelength band (gain-shifted EDFAs) are used as pre- and post amplifiers as well as in-line amplifiers. We demonstrate, for the first time, that long in-line amplifier span (120 km, span loss /spl sim/30 dB), high-bit rate (10 Gb/s), optically repeated WDM transmission over a 360 km (3/spl times/120 km) DSF is possible by using 1580-nm band channels without FWM impairment.

Interwavelength-band nonlinear interactions and their suppression in multiwavelength-band WDM transmission systems

We describe the effects of interwavelength-band nonlinear interactions, such as nondegenerate four-wave mixing, stimulated Raman scattering, and cross-phase modulation in multiwavelength-band WDM transmission systems. Through both numerical analysis and transmission experiments, these interactions are shown to cause serious degradation, especially when the walk-off between the utilized wavelength bands is small. Focusing on suppressing both these interwavelength-band nonlinear interactions and traditional intrawavelength-band nonlinear interactions, we present the guidelines for designing ultra wide-band WDM transmission systems over various types of fibers. The guidelines include band-by band bidirectional transmission, which offers large walk-off and minimizes the degradation caused by interwavelength-band nonlinear interactions. Finally, several dual-wavelength-band transmissions over dispersion-shifted fibers and standard single-mode fibers are demonstrated according to the guidelines.

PLC-based optical add/drop switch with automatic level control

A novel switch configuration for an optical add/drop multiplexer is proposed. By utilizing a certain Mach-Zehnder interferometer both as a component of a double-gate switch and as a level equalizer, we reduced the number of Mach-Zehnder interferometers from five in a conventional switch configuration to three. The add/drop switch simultaneously provides high-isolation switching and polarization-independent automatic level control. The use of planar lightwave circuit (PLC) technology enables this switch to be fabricated with three thermooptic switches (TOSWs) and a monitor tap. High isolation of more than 44 dB and automatic level control accuracy of better than 0.3 dB are achieved. Bit error rate (BER) measurements confirmed switchs usability in the optical add/drop multiplexer.

All-PLC-based optical ADM with high isolation and polarization-independent level equalizer

A novel add/drop switch configuration with only three thermo-optic switches is designed to realize all-PLC-based optical ADM together with a pair of arrayed waveguide gratings. Penalty-free operation with high isolation and polarization-independent level equalization is confirmed by bit error rate measurement.

Ultra-wide band WDM networks and supporting technologies

Wavelength division multiplexing (WDM) offers higher capacity and more flexibility to optical networks, and is being actively researched and developed throughout the world. The fully wavelength furnished optical network (FWFON) which uses ultra-wide bandwidth and wavelength-based network functions will offer channel capacity enhancement, node processing improvement, and flexible service provisioning, in addition to other new functions based on wavelength. This paper first clarifies network evolution through the utilization of wavelength to realize several network functions together with the implication of technology enhancement; and key issues are summarized.

Recirculating loop experiment for 1580-nm-band large-scale WDM network using dispersion-shifted fiber

Feasibility of a 1580-mm-band large-scale wavelength-division multiplexing (WDM) network employing add-drop. Multiplexers (ADMs) is shown from the results of a recirculating loop experiment. The limitation due to four-wave mixing (FWM) are avoided by shifting the signal wavelength band from the conventional 1550-1580-nm band, which enables us to construct a 1200-km large-scale network with the large-node spacing of 120 km over dispersion-shifted fiber.

Management of optical networks

Network management is a major key issue for the optical transport networks. This paper describes objectives and basic model of the network management. Then, generic requirements and implementation of the management signals that are being discussed in ITU-T are also described.

Future fully wavelength-furnished optical network and supporting technologies

This paper describes the evolution of future network which uses multi-wavelength as several network functions together with implication of technology enhancement, key issues to increase the number of wavelengths, and new 1580 nm band technology to extend transmission bandwidth.