Site: KDD R&D Laboratories
2-1-5 Ohara Kamifukuoka
Saitama 356
Japan

Date Visited: October 29, 1992

Report Author: V. Chan

ATTENDEES

NASA/NSF:

V. Chan
R. DePaula

HOSTS:

Dr. Kazuo Sakai

Dr. Shigeyuki Akiba

Dr. Yuichi Matsushima

Dr. Masatoshi Suzuki

Mr. Shiro Ryu

Mr. Masayoshi Horita

BACKGROUND

See site report by B. Edelson on Oct. 23, 1992 visit to KDD R&D Labs.

RESEARCH AND DEVELOPMENT ACTIVITIES

See Edelson site report for overview. This visit (October 29), reported below, focused on fiber optics communications.

KDD R&D Labs has four main research objectives:

1. Digital transmission technology.
2. Networks, switching and software technology.
3. New services.
4. Basic technology.

The organization chart included in the Edelson site report, Figure KDD.1, presents the structure of KDD R&D Laboratories. The October 29 visit was hosted by the Opto-Electronics and Lightwave Communication Systems Groups. Research efforts at KDD R&D Labs in fiber communications focuses on long-haul, high bit-rate systems (of the order of 5 to 10 Gbits/sec). Both coherent and soliton systems are being pursued.

Coherent systems are being considered for long-haul transmission because the detection mechanism is more immune to spontaneous emission in optical amplifiers. Fiber dispersion is a major concern and IF equalization after optical detection at the receiver is the technique of choice to mitigate this effect. Spectral broadening due to the Kerr effect is also a concern. This effect limits unrepeatered transmission to a few thousand kilometers, depending on the bit rate. Experimental data has confirmed such degradation in long-haul ( > 5,000 km) systems.

Soliton systems are an alternative to coherent systems. A 5 Gbits/sec system using erbium-doped amplifiers has been demonstrated over a 3,000 km fiber optic path. This is typical of results published by AT&T, NTT and NEC.

Activities in the Opto-Electronics Group are categorized into optical semiconductor devices and fluoride-glass fibers. In the optical devices area there are five activities, three of which are detailed below:

1. A electro-absorption modulator using buried-heterostructure with Fe-doped InP was used to generate soliton streams at 15 Gbits/sec and 14 picosecond pulse width. This technique may be the answer to economical generation of high rate transform-limited pulses for soliton transmission over distances in excess of 10,000 km.
2. InGaAs/InGaP strained-layer quantum-well lasers are grown by gas-source MBE (molecular beam epitaxy) for high power applications, such as pumping er-doped fiber amplifiers.
3. Multiple-Section ( > 4 ) quarter-wave-shifted distributed-feedback lasers are designed and fabricated to achieve wavelength tuning over wide frequency ranges for FDM applications. A highly efficient and flat FM response was also demonstrated.
4. Research is ongoing on a semiconductor optical switch, and a short wavelength light source, at 0.4 to 0.5 microns, using a CdZnSe system grown by MOVPE.
5. Fluoride-glass fiber still seems to be an active area for research. Although no dramatic results are reported so far, research is being performed on the HF/Zr/Ba/La/Al/Na system. In parallel, fiber lasers are also being investigated.

SUMMARY

KDD R&D Labs is at the forefront of research in long-haul fiber optics communication systems. The techniques used are sophisticated and KDD is, and no doubt will be, a serious player in the long-haul market.