Research on Optical Modulators and Switches Based on Potential-Tailored Quantum Microstructures for the Advanced Optical Communication Infrastructure

1. 五步不对称耦合量子阱（FACQW）的提出与设计：提出并设计了一种基于势阱的量子阱结构。与传统的矩形量子阱（RQW）相比，该FACQW可以在远离吸收边缘的透明波长区域产生非常大的场致折射率变化DELTAn。以A1GaAs材料体系为例，计算结果表明，在距离吸收边缘40 nm的830 nm波长处，在10 kV/cm的电场作用下，An的值为0.002。超高速低电压光调制器的实现：作为FACQW的应用，制作了由20组FACQW组成的2 mm长光波导臂的行波型Mach-Zehnder干涉仪调制器。在850 nm波长处测得调制带宽为55 GHz，开关电压为3 V。据我们所知，这是第一个行波型多量子阱（MQW）波导调制器，并且上述调制带宽超过了半导体光调制器报道的最高值。FACQW的分析与改进：以上实验结果表明，FACQW中的DELTAn比RQW中的DELTAn大几倍，但比计算值小一个数量级左右。为了阐明其差异的原因，对层厚波动的影响进行了模拟分析。一些改进的FACQW结构也获得了更高的An或更好的deltan线性度。其他电位定制量子阱结构：提出并研究了两种新的电吸收调制器结构

1. Proposal and Design of the Five-Step Asymmetric Coupled Quantum Well (FACQW) :A potential-tailored quantum well structure named as above was proposed and designed. This FACQW, in contrast to the conventional rectangular quantum well (RQW), can produce very large field-induced refractive index change DELTAn in the transparency wavelength region far from the absorption edge. An example of calculated results for the A1GaAs material system is that An under applied field of 10 kV/cm is as large as 0.002 at 830 nm wavelength which is apart from the absorption edge by 40 nm.2. Implementation of Ultra-Fast and Low-Voltage Optical Modulator :As an application of the FACQW, a traveling-wave type Mach-Zehnder interferometer modulator with 2 mm-long arms of optical waveguide composed of 20 sets of the FACQW was fabricated. At 850 nm wavelength, the modulation bandwidth and the switching voltage were measured as 55 GHz and 3 V, respectively. To our knowledge, this is the first traveling-wave type multiple quantum well (MQW) waveguide modulator, and the above modulation bandwidth exceeds the highest value ever reported on semiconductor optical modulators.3. Analysis and Improvement of the FACQW :The above experimental result indicates that DELTAn in the FACQW is a few times as large as DELTAn in the RQW, but is smaller than the calculated value by about one order of magnitude. To clarify the reason for his discrepancy, some simulation analyses have been carried out concerning influences of the layer thickness fluctuation. Some modified structures of the FACQW have also been obtained with higher An or better linearity of DELTAn.4. Other Potential -Tailored Quantum Well Structures :Two new structures have been proposed and studied for electroabsorptive modulators for