| Co-Investigator(Kenkyū-buntansha) |
TAKAHARA Junichi Osaka University, Graduate School of Engineering Science, Assistant Prof, 大学院・基礎工学研究科, 助手 (90273606)
MURATA Hiroshi Osaka University, Graduate School of Engineering Science, Assoc. Prof, 大学院・基礎工学研究科, 講師 (20239528)
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| Research Abstract |
The purpose of this study is to develop new kinds of electro-optical modulators together with domain inverted structure and wave-guide structure and to generate ultra-broad optical sideband and to find out new application of them. As results, we succeeded in materialization of the frequency comb generator which is very useful as light sources in the wavelength division multiplexing (WDM) system, of the frequency shifter, a single sideband (SSB) modulator and the compact integrated femtosecond optical pulse generators.
Adopting the waveguide structure makes it possible to decrease driving electric power drastically. The geometrical spatial modification of the domain-inverted structure makes multipath parallel operation of the modulator or various types of spatial light modulation possible.
First of all, the length and the width of the electrode and the optical waveguide were devised for the ultra-broad sideband generation, the frequency comb generator, and application to the light source
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in the WDM system, which require high modulation efficiency. As a result, efficient cw modulation and generation of broad cw optical sidebands became possible. The position shift of domain inverted area yields equivalently the phase shift of modulation rf signals, therefore, we can get sin and cos modulation by single rf signal. Using this effect, we constructed new kind of SSB modulator with simple wave-guide structure and succeeded in confirmation of its SSB operation.
The sidebands obtained by a usual phase modulation have Bessel function-like amplitude and lack in flatness. It is problem for frequency comb generator. We proposed the new spatial modulator, spatially separated sideband generator with flat distribution, which is constructed by adding the spatial deform to traveling phase grating produced by tilted periodic domain inverted structure. Moreover, we succeed in the composition of the ultra-broadband modulator by adopting the non-periodical domain inverted structure. The modulation bandwidth (-1 dB) of this device was estimated to be six times wider than that of the normal traveling-wave EO modulator. In addition, we integrated the phase modulator for the ultra-broad sideband generation and the group delay dispersion circuit on one LiTaO_3 tip. In preliminary experiment using this integrated device we succeeded in direct conversion from the continuous light-wave into the picosecond pulses. Less
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