Site: ATR Optical and Radio Communications
(see address above in P. Hager site report)
Date Visited: October 27, 1992
Report Author: V. Chan
Dr. Yoji Furuhama
Dr. Masayuki Fujise
Dr. Eiichi Ogawa
Mr. Toshihide Watanabe
Dr. Yoh'ichi Tohkura
Mr. Shigeki Sagayama
Mr. Fumio Kishino
For ATR's general background see the ATR site report by P. Hager (panel visit October 21, 1992). Figure ATR.1 contained in this report gives an outline of the organization of ATR, as well as funding level and employee make-up. It is a young laboratory (opened only in 1986) devoted to futuristic exploratory research. As such, the projects seen had longer time horizons than most R&D laboratories of other Japanese companies.
Figure ATR.1. Outline of ATR
See also P. Hager's site report.
ATR believes optical ISLs will play a very important role as one of the main infrastructure elements in future activities in space. There are two main foci for optical ISL efforts at ATR: optical modulation technology and precise beam control technology.
Optical Modulation. There are two types of systems under investigation, direct detection and coherent systems. For intensity modulated direct detection systems, a 100 mW 360 Mbits/sec transceiver was developed for GEO-GEO links. There are ongoing efforts to use a travelling wave semiconductor amplifier to increase output power. In a separate development, a 60 mW 2.5 Gbits/sec one-sixteenth-wave quality transceiver was developed for LEO-LEO communications. The limited power level of the transmitter makes it appropriate only for short links unless an amplifier is also used. From the pictures shown, the design seems to be at the breadboard level. For coherent systems, polarization modulation is being explored to mitigate the effect of phase noise on communication performance. (This is a variation of a scheme originated by Tamura of MIT.) A fiber-base receiver has been designed using a waveguide array sensor for beam tracking. A Nd:YAG laser is used as the transmitter laser and a conventional lithium niobate modulator is used for phase modulation.
Precise Beam Control Technologies. System studies are being conducted on spatial tracking designs for ISL with special attention to stable/unstable conditions for operation of a tracking system. A free-space simulator for laser transmission is operational. (For further details see the ATR site report by P. Hager.
Research on semiconductor materials includes growth and characterization of GaAs (111) A surfaces that have attractive features for device applications. For example, a Si dopant atom can act as either donor or acceptor on GaAs (111) A surfaces. This feature is thought to be able to yield useful device fabrication technologies that can allow complex device structures to be well fabricated in a simple way. Work is ongoing on super-lattice structures, quantum-well structures and delta-doped structures.
The thrust of device research is not primarily determined by system requirements. Rather, new device function and structures based on the above-mentioned material and structure research are being explored. For example, a light-emitting diode has been fabricated using only Si dopant atoms on GaAs (111) A surfaces. One of the goals of this work is ultimately to develop surface emitting lasers for possible applications in optical signal processing and opto-electronic integration and as high power arrays. Other devices that have been developed are Self-Electro-Optic-Effect Devices (SEED) that use the Wannier-Stark localization effect, and lateral tunnel transistors.
The objective of this research activity is to investigate the applicability of optical chaos in devices through computer simulations of and experiments on pre-chaos oscillation modes and chaotic-mode-hopping for memory and search functions in a ring-type optical storage device such as a fiber ring. A practical design for the generation and storage of optical pulse sequences in an electro-optic fiber ring has been built. "Write" and "erase" functions have been achieved. The experimental set-up seemed to indicate repeatable and stable operations, albeit over a short encounter.
To support simple and economical micro-cell technology for mobile communications, fiber RF links are used to conduct signals to and from micro-cell and base stations. The concept does not require invention of technology but rather centers on the economical packaging of optical and RF technologies in a small rugged package. Similar work was seen elsewhere, at NEC for example.
A high resolution fault locator has been developed using an optical step frequency radar technique. Resolving power on the order of microns was achieved by scanning the laser source over the wavelength range of 1.5 to 1.6 microns. Use of a Hopfield-type neural network is being explored to increase the resolution. It has been demonstrated that such a fault locator can detect the faults in an integrated optics device such as an optical guide. It has even been possible to make a non-destructive measurement of the cross-section of an optical fiber.
This laboratory is possibly the most avant garde seen at ATR. A video conferencing set-up was demonstrated where eye movement of a conferee's eye can be tracked by electronic means and remote cameras can be slewed to create stereoscopic effects. In an audio laboratory, an elaborate mechanical set-up is built to simulate the acoustics of a broad range of ambiance conditions to create different "presence." It is the Japanese laboratory seen closest in capability to the Media Laboratory of MIT.
This is an interesting system research area where spoken language translation is being explored. A system was demonstrated that translates Japanese to English and vice versa with a limited vocabulary.
ATR is a unique organization in Japan. Most of the research laboratories visited in Japan are very practical and "relevant," with excellent records of bringing research to the market place very quickly. ATR does relevant work, but has a longer time horizon. The organization is willing to invest in speculative research such as optical chaos. It seems to encourage creativity more than other Japanese laboratories. It can do so by virtue of a long term commitment to research by Japanese government and industry, and thus can also attract participation by foreign researchers. The research results of ATR may not be measurable in the short term; it is likely that the major benefits will only be identifiable years later when visiting scientists and engineers from participating Japanese companies return to their former companies with their creativity quotient increased.