ABSTRACT
Photonic integrated circuits may be implemented in a variety of material systems. ™e high-speed optical modulator is a primary component, thus the material must have suitable electro-optical properties, limiting the practical choice to III-V semiconductors, ferroelectric ceramics (e.g., lithium niobate) or electro-optic polymers. Historically, gallium arsenide (GaAs) was the material of choice for mmwave devices owing to high electron mobility and the availability of low-loss semiinsulating substrate. Foundry processes developed originally for the fabrication of GaAs monolithic microwave integrated circuits are ideally suited for extension into the optical domain and it is no accident that most of the early development of GaAs optical modulators was undertaken by institutions with established monolithic microwave integrated circuits expertise.
