Semiconductor FACQW (Five-Layer Asymmetric Coupled Quantum Well) EOM

In optoelectronic devices based on their phase modulation, a large electric field–induced change in refractive index with a small absorption loss is required. So far, a large linear electro-optic effect (Pockels effect) in ferroelectric materials such as lithium niobate, bulk semiconductors, and nonlinear optical polymers, and the carrier plasma effect in silicon are mainly used for high-speed Mach–Zehnder modulators (MZM) and other photonic devices. The electro-optic effect in III–V semiconductor multiple quantum wells is also a promising candidate for a large electric field–induced index change because the change in index caused by the quantum-confined Stark effect (QCSE) can be utilized in addition to the Pockels effect. In this chapter, a five-layer asymmetric coupled quantum well (FACQW) for large electric field–induced index change as so-called a potential-tailored quantum well is discussed, and their applications to photonic devices, such as an MZM, microring resonator (MRR)-based devices, and antenna-integrated modulators for radio-over-fiber systems, are presented. The FACQW is expected to exhibit a giant electric field–induced index change in the transparent wavelength region, which is over one order of magnitude larger than that of a conventional rectangular quantum well.