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Shigeki AISAWA Kazuhiro NOGUCHI Masafumi KOGA Takao MATSUMOTO Yoshihito AMEMIYA
A very-high-speed ten-neuron analog neural network LSI chip is fabricated for the first time using super self-aligned Si bipolar process technology. The LSI consists of ten neurons and 100 electrically modifiable synaptic weights. The neural network nonlinear mapping function to solve the four-bit parity problem is successfully demonstrated at 150 mega-patterns/sec. The operation speed of this neural network is, to the best of the authors, knowledge, the fastest yet reported.
Ken-ichi HAYASHI Shigeki AISAWA Yoshio IDA Kazuo ARAI
Spectral properties of an unlocked semiconductor laser under an external light injection are numerically analyzed and experimentally observed. It is found that the unlocked spectrum consists of a shifted carrier and a number of harmonics and that their distributions are varied by the detuning.
Yoshihisa SAKAI Shigeki AISAWA Ken-ichi HAYASHI Kazuo ARAI Yoshio IDA
The influence of 1/f noise in FM noise on the spectral linewidth of semiconductor lasers in a normal operation has been investigated. The linewidth calculated from the FM noise spectrum considering the 1/f noise agrees with that obtained from the delayed self-heterodyne method.
Masahiko JINNO Masaki FUKUI Tadashi SAKAMOTO Shigeki AISAWA Jun-ichi KANI Kimio OGUCHI
Dense WDM techniques that exploit the enormous bandwidth of dispersion-shifted fibers (DSFs) while avoiding the impairments due to nonlinear effects are described. First, the nature of four-wave mixing (FWM), the dominant impairment factor in WDM transmission systems, is investigated using DSF installed in the field and laboratory experiments. This provides useful information for the practical design of WDM networks based on DSF. Second, practical techniques to reduce FWM impairment, unequal channel allocation and off-lambda-zero channel allocation (equal channel allocation in the novel 1580 nm band) along with gain-shifted erbium-doped fiber amplifiers for the 1570 to 1600 nm band, is described. Comparisons between off-lambda-zero and unequal channel allocation are provided in terms of the maximum transmission distance for various numbers of channels. Two schemes to immunize WDM systems against group velocity dispersion, span-by-span dispersion compensation and optical duobinary format, are presented. The combination of unequal channel allocation with off-lambda-zero channel allocation as well as the combination of two bands: the conventional 1550 nm band and the novel 1580 nm band are proven to be very useful in expanding the usable bandwidth of DSFs.
Koichi IIYAMA Ken-ichi HAYASHI Yoshio IDA Shigeki AISAWA
The characteristic features of a mutual optical injection-locking system using semiconductor lasers are both analytically and experimentally examined. It is found that in the case of low injection level, locked frequency, locked powers and locking bandwidth of the system are suitably characterized in terms of both a figure of merit specifying unilaterality of optical injection and a modified round-trip phase angle of optical coupling circuit between lasers. The analysis is applicable not only to unilateral optical injection-locking system but also to mutual optical injection-locking system with an arbitrary inverse optical injection. The results of experiment using AlGaAs CSP lasers are found to be in good agreement with the analysis provided that the mutual injection levels are low.
Shigeki AISAWA Hiroshi MIYAO Noboru TAKACHIO Shigeru KUWANO
A simple method of compensating the DC drift of LiNbO3 Mach-Zehnder intensity modulators for very high speed optical transmission systems is proposed. This method adds low frequency perturbation to the modulator driving signal, and controls the bias voltage using the detected envelope of the modulator output signal. The control circuit is successfully demonstrated to work with less than a 0. 1-dB power penalty.