會田田人
非線形ダイナミックスを利用した新機能素子の研究
Abstract:Theoretical and experimental studies on nonlinear delayed feedback (DF) systems
such as nonlinear optical cavities have shown the existence of a large variety of
multistable bifurcated oscillation modes leading to chaos. Ikeda et al. clarified
the hierarchical tree structure of the bifurcation of the oscillation modes excited
in a nonlinear optical ring cavity and suggested the applicability of the multistable
modes for data storage.
Following up this suggestion, Davis et.al. theoretically proposed that selective
excitation of the multistable modes, useful for optical signal generation and memory,
is possible by two complementary methods. The one is seeded bifurcation (SB)
switch and the other chaotic search/switch (CS). The SB switch is a direct,
deterministic selection of a mode by injecting a seed signal. The CS is an approach
to selection of mode using chaotic mode transitions, which is complementary to
the SB switch and results in stochastic selection of a mode which satisfies a given
constraint. These proposals have for the first time given the concrete images for
making use of chaos and physical experiments for the proposals have been expected
to test the feasibility.
This report mainly summarizes the experimental works done by T. Aida and P.
Davis from 1988 to 1993 in ATR to test the feasibility of the functions proposed. The
success of the experiments is owing mainly to the good performance of the electrooptical
hybrid DF system, which has much larger delays, and thus more modes, and
better controllability of system parameters than previous systems.
In Chapter II, we first describe the design of the DF system for the experiments,
in particular the reason why we employed the combination of infrared (1.3 μm) optical
communication components and waveguide modulator, and discuss the typical
stability of the bifurcated higher-harmonic oscillations of a non-ideal DF system with large delay. We then describe the experiments of SB switch, in which the feasibility
of memory function using multistable nonlinear oscillation modes is confirmed.
In Chapter III, we propose a new configuration of an optical loop memory using
multistable nonlinear oscillation modes, and demonstrates the basic functions
for memory, 'write' and 'erase', using optical pulse sequences in an electro-optical
nonlinear ring resonator.
In Chapter IV, we demonstrates the CS experiments, in which the effectiveness
of making use of chaotic mode transitions for searching and switching among a large
number of multistable modes is confirmed. The coding of multistable and chaotic
oscillation modes and the quantitative characterization of chaotic mode transitions
are also described, related to the CS experiments.
In Chapter V, we describe a digital electronic system, designed for a real-time
simulator for systematic study of dynamics of nonlinear DF systems, and to test the
applicability of such a digital electronic system itself as a signal generator.