Yoshiaki Yamabayashi

OA&M framework for multiwavelength photonic transport networks

Photonic networks based on wavelength division multiplexing (WDM) and optical path technologies are expected to realize flexible, transparent, and cost-effective transport networks with a large transmission capacity. This paper explores the design framework of photonic transport networks taking into consideration the operation administration and maintenance (OA&M) functions required for the successful introduction of WDM systems based on the optical path concept. From the view point of network maintenance, clear distinction is made between the optical path layer and the optical section layer to facilitate accurate and smooth failure localization. The digital multiplexing span between physical multiplexing interfaces at the end-to-end digital nodes should have the same maintenance span as the corresponding optical path. We argue that cooperative maintenance by OA&M functions at both the digital and optical layers can be a practical way of network supervision. A supervisory (SV) signal transfer method and a configuration that is suitable for the terrestrial trunk network are also indicated. As an example, a practical SV system design methodology and an actual procedure developed for a single channel optical transmission system based on optical in-line amplifiers are introduced. Furthermore, application of the developed SV system and network restoration schemes is discussed for future WDM-based photonic networks. The OA&M aspects introduced will be valuable for creating future photonic network systems.

40-Gbit/s transmission systems

Summary form only given. The transmission capability of fiber-optic systems has reached the terabit/sec region. In order to realize such potential transmission performance using existing fiber cables, management of chromatic fiber dispersion is a significant issue. Research on high-speed TDM systems is focused on the zero dispersion wavelength region. On the other hand, WDM transmission technology requires some dispersion to reduce crosstalk due to four-wave mixing along the fiber. Recently, extremely wideband erbium-doped fiber amplifiers (EDFAs) were developed. Such a wideband optical amplifier enables simultaneous amplification of high-speed TDM and WDM signals. Future photonic networks have to optimize each transmission speed against intrinsic dispersion characteristics to fully utilize the bandwidth of currently existing fibers. It is natural that modulation scheme and dispersion equalization should be carefully considered. We describe simple and broadband optoelectronic technologies, which provide low-cost and upgradable transmitters and receivers. In order to realize a 40-Gbit/s system under these requirements, we propose several new technologies; automatic dispersion equalization technique, optical duobinary modulation scheme, which doubles the dispersion tolerance compared to conventional nonreturn to zero (NRZ) modulation, and several novel device technologies.

1-km transmission of 10 Gbit/s optical signal over legacy MMF using mode limiting transmission and incoherent light source

10 Gbit/s optical signals were transmitted through legacy multimode fibers (MMF) by using mode limiting and incoherent light sources. Stable transmission through a 1-km-long MMF was realized by inserting a singlemode fiber (SMF) at midpoint.

Hitless frame switching scheme for SDH networks

In current SDH transmission equipment, channel switching for channel cutoffs and hardware failures, etc., is automated. However, instantaneous signal loss can occur with such channel switching. Protecting a system from failures with a high reliability for network failures is an important task. In this paper, a new hitless frame-switching scheme that triggers switching by detecting bit errors for each frame is proposed. This scheme does not allow a loss of even one bit in downstream equipment even when a sudden failure occurs. In addition, it improves the error rate of the downstream equipment under normal operating conditions by switching to an error-free frame for each frame. It has been confirmed in a trial LSI with a path (virtual container-4: VC-4) as a frame that these capabilities are realized with precision.