Generation of Ultrabroad Optical Sideband by Domain-Inversed Waveguide-Type Electro-Optic Modulators and Applications

本研究的目的是结合畴反转结构和波导结构开发新型电光调制器，产生超宽光边带，并探索其新的应用。结果，我们成功地实现了在波分复用（WDM）系统中作为光源的频率梳发生器、移频器、单边带（SSB）调制器和紧凑集成飞秒光脉冲发生器。采用波导结构使驱动功率大大降低成为可能。畴反转结构的几何空间修饰使得调制器的多径并行操作或各种类型的空间光调制成为可能。首先，对电极和光波导的长度和宽度进行了设计，以实现超宽带边带的产生、梳频发生器以及在WDM系统中对调制效率要求较高的光源中的应用。因此，有效的连续波调制和宽连续波光学边带的产生成为可能。畴反转区域的位置位移相当于调制射频信号的相移，因此，我们可以通过单个射频信号得到sin和cos调制。利用这一效应，我们构建了一种具有简单波导结构的新型SSB调制器，并成功地证实了其SSB工作。通过通常的相位调制得到的边带具有贝塞尔函数样的振幅和缺乏平坦度。这是频率梳状发生器存在的问题。本文提出了一种新的空间调制器——平面分布的空间分离边带发生器，该空间调制器是在倾斜周期域反转结构产生的行相光栅上加上空间变形而形成的。此外，我们还成功地采用非周期域反转结构组成了超宽带调制器。该器件的调制带宽（-1 dB）估计比普通行波EO调制器宽6倍。此外，我们还在一个LiTaO_3尖端集成了用于超宽带边带产生的相位调制器和群延迟色散电路。在初步实验中，我们成功地将连续光波直接转换为皮秒脉冲。少

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 … More 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