New high-performance optical modulators based on potential-tailored quantum wells

External optical modulators and switches with multiple quantum well (MQW) waveguide structures are becoming more and more important in various areas of optoelectronics, especially in optical communications. These devices usually employ quantum well structures with rectangular potential distribution. Device performance is governed by the quantum-confined Stark effect (QCSE) in the conventional rectangular quantum well (RQW). There exist certain limitations in the device performance or even device functionality in some cases. If we introduce more sophisticated potential-tailored QW structures with potential distribution different from the rectangular one, some of the limitations can be eliminated and devices with higher performance or novel functionality can be created. In this paper, the author presents two examples of the above-mentioned direction of the research we have been pursuing for some ten years. One is an optical modulator with very high polarization independence. The other is a traveling-wave type ultra-fast and low-voltage optical modulator.