Opto-Electronics Research Laboratories
1-1, Miyazaki 4-chome,
Kanagawa 216, Japan
Date Visited: October 26, 1992
Report Author: V. Chan
Dr. Kohroh Kobayashi
Dr. Katsumi Emura
Mr. Tatsuya Shiragaki
Mr. Naoki Shimosaka
Mr. Naoki Kitamura
Dr. Paul T. Muto
For more background information about NEC, see the site report by W. Brandon for the October 20, 1992 site visit.
The NEC Research and Development Group is responsible for creating computer and communications technologies and identifying those areas which have greatest potential for important technological breakthroughs. To accomplish this mission, the R&D Group conducts research in both technical and human behavioral fields. In l980 the NEC Kawasaki Central Research Laboratory was reorganized into the R&D Planning and Technical Service Division, the Basic Technology and Research Laboratory, the Opto-Electronics Research Laboratory and the Computer and Communications Systems Research Laboratory. The Kawasaki Central Research Laboratories act as the focal point for computer and communications technology by bringing together and integrating advanced technologies from different fields. The R&D Group currently employs l,665; the research budget represents 1% and developmental efforts 10% of annual sales. Seventy percent of the funding comes from headquarters and 30% comes from business groups.
Research here emphasizes high-bit-rate (1 to 100 Gbits/sec) and long-haul transmission. The current approach is to use cascaded fiber amplifiers to extend transmission range to well over 1000 Km (as much as 10,000 Km) without using electronic repeaters. Coherent FDM systems are used to increase capacity to as much as 100 Gbits/sec. Linear dispersion in fibers limits the transmission distance at high rates, and IF equalization is used.
Very long-haul (>10,000 km) systems are contemplated. The technologies are in an advanced state of development and, in some cases, in production. For example, a packaged 10 Gbits/sec optical receiver with Si bipolar ICs is well ahead of U.S. development. Receiver sensitivity within a few dBs of the quantum limit for detection of light was demonstrated at 10 Gbits/sec using an erbium-doped amplifier as a preamplifier.
There is considerable concern about non-linear fiber effects that degrade communication performance. Extensive simulations are being performed to quantify (in 2.5 Gbits/sec systems) effects such as the Kerr effect, and linear and higher order dispersion. It has been found that significant degradation can occur at between 5,000 and 10,000 km in 2.5 Gbits/sec systems. This was confirmed in a fiber-loop experiment simulating long distances. To compensate for dispersion and nonlinear effects, polarization shift-keying systems and prechirped waveform equalization are being investigated. All were found to be able to extend transmission range.
When the number of cells must increase in a mobile communication system to handle more traffic, cell cost is a major driver. Micro-base stations with simple RF transceivers and analog fiber links to central base stations are an attractive architecture. NEC has developed and packaged such a system, and it appears to have very desirable form factor and simplicity. The equipment is in an advanced state of development.
A WD/TD hybrid multiplexed network concept has been developed for broadcasting studio application. Approximately twenty wavelengths and a wavelength switching time of several microseconds are required. The principal wavelength selection mechanism is an acousto-optical filter of the same design as ones seen in the literature. The achieved crosstalk level of the filter is only 13.6 dB whereas 26 dB was predicted. The system is at the hardware system demonstration stage.
Research on optical switching focuses on polarization-independent titanium-diffused lithium niobate waveguide switches. The fabricated switches have good crosstalk isolation (greater than 20 dB).
NEC is a world leader in opto-electronics and fiber optic communication systems. The research performed at the Kawasaki Central Research Laboratory is of high quality and goal-oriented towards products including large systems. Corporate support for R&D has been very stable over the years and will definitely affect NEC's long-term future in very positive ways.