Ultra Wideband and Ultrahigh Speed Optical Modulation Devices with Five-Layer Asymmetric Coupled Quantum Wells

本课题旨在研究和开发利用核心层五层不对称耦合量子阱（FACQW）巨电折变效应的宽带超高速光调制器/开关。FACQW可以在远离吸收边缘的透明波长区域产生巨大的电折射率变化Δn。我们得到的结果如下：1。GaAs/AlGaAs FACQW及其在光学调制器件中的应用(1)facqw中巨大电折射率变化的观察我们利用分子束外延（MBE）技术制作了FACQW相位调制器，并首次成功观察到理论上预期的巨大ER折射率变化。从理论和实验两方面研究了FACQW的偏振依赖性。(2) FACQW Mach-Zehnder调制器的制作与表征我们设计并制作了一个核心层含有多个FACQW的Mach-Zehnder调制器。成功地降低了调制器的驱动电压。1.55微米InGaAs/InAlAs FACQW及其在光学调制器件中的应用(1)InGaAs/InAlAs FACQW中ER效应的理论分析利用k-p摄动理论对InGaAs/InAlAs FACQW的效应进行了理论研究。因此，我们发现了一种可以产生巨大ER效应的新结构GaAs/AlGaAs FACQW。(2) MBE法制备FACQW及其表征利用MBE法制备InGaAs/InAlAs FACQW，并对其晶体结构和光学性质进行了表征。光电流测量结果显示了与计算吸收光谱相似的趋势。(3) FACQW Mach-Zehnder调制器的制造和表征我们开发了一种具有多模干涉（MMI）的紧凑型Mach-Zehnder调制器的制造技术。采用湿蚀刻技术成功制备了MMI器件。

The aim of this research project was to study and develop wideband and ultrahigh speed optical modulators/switches with the giant electrorefractive (ER) effect of the five-layer asymmetric coupled quantum well (FACQW) in the core layer. The FACQW can produce giant electrorefractive index change Δn in the transparency wavelength region far from the absorption edge. We obtained the results as follows :1.GaAs/AlGaAs FACQW and its application to optical modulation devices(1)Observation of giant electrorefractive index change in the FACQWWe fabricated an FACQW phase modulator using molecular beam epitaxy (MBE), and for the first time, giant ER index change was successfully observed, as theoretically expected. Polarization dependence of the FACQW was also investigated theoretically and experimentally.(2)Fabrication and characterization of FACQW Mach-Zehnder modulatorWe designed and fabricated a Mach-Zehnder modulator with multiple FACQW in its core layer. The driving voltage of the modulator was successfully reduced.2.InGaAs/InAlAs FACQW for 1.55 micron and its application to optical modulation devices(1)Theoretical analyses of ER effect in InGaAs/InAlAs FACQWER effect of InGaAs/InAlAs FACQW was theoretically studied using k-p perturbation theory. As a result, we found a new structure that can produce giant ER effect as GaAs/AlGaAs FACQW.(2)Fabrication of FACQW using MBE and its characterizationWe grew InGaAs/InAlAs FACQWs using MBE, and characterized their crystal structures and optical properties. Results of photocurrent measurements showed the tendency similar to the calculated absorption spectra.(3)Fabrication and characterization of FACQW Mach-Zehnder modulatorWe developed fabrication techniques for a compact Mach-Zehnder modulator with multi-mode interferers (MMI). MMI devices were successfully fabricated using wet-etching technique.