Site: Fujitsu Laboratories, Ltd.
10-1, Morinosato - Wakamiya
Atsugi 243-01, Japan

Date Visited: December 16, 1994

Report Author: P. Shumate

ATTENDEES

JTEC:

L. Coldren
G. Day
M. DeHaemer
P. Shumate
L. Warren

HOSTS:

Dr. Hajime Imai
Deputy Gen. Mgr., Fujitsu Laboratories, Ltd. (Atsugi)
S. Yamakoshi
Manager, Optical Semiconductor Devices Laboratory
Haruhisa Soda
Senior Researcher, Optical Semiconductor Devices Lab
Toshiyuki Tanahashi
Senior Researcher, Optical Semiconductor Devices Lab

BACKGROUND

Fujitsu Laboratories provides R&D support to its parent company, Fujitsu Ltd., a major supplier of telecommunications and computing equipment, with 164,000 employees, 1994 revenues of $30.5 billion, and 1994 R&D expenditures of $3.2 billion. Fujitsu's corporate goal is to become the leading information technology company, supplying products for computing (PCs to supercomputers), communications (including switching), multimedia, software, and services. It is a leader in broadband ISDN, with Gbit/s transmission products, ATM switches, and fiber subscriber-loop equipment. Fujitsu Laboratories carries out R&D in these areas, including development of new materials and devices to support related new products.

Fujitsu Laboratories was created in 1962 by merging R&D sections that were previously managed by separate technical divisions, and it became a wholly owned subsidiary of Fujitsu, Ltd. in 1968. The staff numbers approximately 1,650 people who are trained predominantly in electronics and physics (48% and 19%, respectively) and have master's and bachelor's degrees (52% and 29%, respectively). The capitalization is approximately $50 million. Fujitsu currently has five functional laboratories at four locations, according to R&D focus:

Kawasaki

Multimedia Systems Laboratories (24% of staff)

Akashi

Personal Systems Laboratories (16% of staff)

Numazu

Institute for Social Information Science (4% of staff)

Atsugi

Electronic Systems Laboratories (9% of staff)

Electron Devices and Materials Laboratories (30% of staff)

DISCUSSION

Multimedia Labs

As described to the JTEC panel, the Multimedia Labs has a systems division looking at, for example, computer networking and natural-language processing; a technology division developing broadband-ISDN systems, high-speed (e.g., 10 Gbit/s and optical FDM) transmission systems, wireless communication systems, and neurocomputers; and a devices division for LSI and packaging as related to multimedia interfaces.

Personal Systems Labs

The Personal Systems Labs has two divisions: a systems division that works on distributed systems (including information networking, information retrieval, and security), personal computing (including multimedia workstations and memobooks, and speech recognition and synthesis), and human-computer interfaces (including artificial reality). A devices division concentrates on magneto-optic storage, multimedia I/O devices (including pen-input panels and field-emission flat-panel displays), advanced electronics packaging for portable equipment, and medical equipment (including ultrasonic imaging and digital radiography).

Institute for Social Information Science

The Institute for Social Information Science, established in 1972, investigates themes that are consistent with the needs and requirements of the new information society. It is organized into five research groups with work spanning machine learning; mechanisms for simulating human thought, senses, and motion; basic mathematics and computing; information-processing capabilities of biological systems, including biomolecular and DNA sequences; and expert systems and interfaces for information processing.

PRESENTATIONS

H. Soda presented his work on MQW (multi-quantum-well) local-loop lasers and MQW DFB (distributed feedback) lasers with integrated modulators. The local-loop lasers incorporate a spot-sized transformer to expand the mode-field diameter and thereby desensitize coupling to single-mode fiber. This facilitates the design (fewer precision parts) and production (less-critical alignments) of low-cost packages for loop applications. The unpumped MQW and SCH (separate confinement heterostructure) transformer region is thinned down by about 5 times from the active-region heights, expanding the laser mode-field diameter from its normal 1 microns diameter to about 3.5 microns. At 50% coupling efficiency, 1 dB additional loss corresponds to +/-2 microns of fiber transverse motion rather than the usual +/-0.7 microns. The output beam shape is almost circular.

The MQW DFB laser with modulator is intended for 1.55 microns, 10 Gbit/s upgrades in 1.3 microns transmission systems that use previously installed conventional single-mode fiber. Chirp from a directly modulated laser at 1.55 microns, where fiber dispersion is approximately 17 ps/nm/km, would induce severe penalties and reduce span lengths, negating the advantage of lower attenuation at 1.55 microns. Solutions are to combine a narrow-linewidth laser with an external modulator (plus isolator to prevent reflections from reentering the DFB), or integrate the modulator with the laser. Fujitsu uses a strained-layer MQW-active-region DFB laser (10 mA room-temperature threshold) followed by a short isolation (unpumped) region and an integrated MQW absorption modulator having a 3 dB bandwidth of 12 GHz. This combination introduces only a 3 dB loss relative to 8 dB expected using an external modulator. The company has performed 50 km and 70 km transmission experiments at 10 mW and 10 Gbit/s, and found negligible dispersion penalties. At higher power levels (narrower linewidths), distances up to 120 km are expected.

Soda presented work on the high-efficiency, low-astigmatism visible lasers for optical storage. The s (self-aligned stepped substrate) structure is a simple means for obtaining real-refractive-index (RRI) guiding rather than gain guiding. The s structure results in one-step MOVPE growth, high yield, and low threshold and astigmatism. (The JTEC team saw the far-field pattern later in a lab tour, and it appeared almost perfectly circular, although Fujitsu specifies a 11 x 17 degree far-field.) The astigmatism is nearly independent of power level. Accelerated aging tests at 50 deg. C and 60 deg. C, and 35 mW output power, show no significant changes in threshold after 2 kh and 1.4 kh, respectively.

Following these presentations, the panel visited several laboratories and heard other presentations by researchers on optical transmission devices.

SUMMARY

Fujitsu Laboratories, Ltd., is a world-class R&D facility, organized along strategic thrusts for future products and for efficient technology transfer. (See next site report on Fujitsu Quantum Devices, Ltd.) The quality of the research, as judged by progress in materials and devices as well as publications, is very high. The Atsugi Lab offers excellent materials-growth, fabrication, and characterization facilities. Furthermore, its geographic location offers an attractive, campus-like environment.


Published: February 1996; WTEC Hyper-Librarian