The development of integrated optical circuits has made use of three different material groups: glass, electro-optic crystals, such as LiNbO3, and semiconductors. The prominent properties of each material group are well known. Glass and LiNbO3 waveguides are cheap, easy to fabricate and have lower insertion loss than semiconductors. Moreover, LiNbO3 has high electro-optic coefficients allowing control of the phase, polarization and amplitude of the guided light. Semiconductors offer band-gap engineering and carrier doped layers allowing the fabrication of waveguides, detectors, sources and high-speed electronics.
A. Yi-Yan, A. Yi-Yan,
"Integrated Optical Devices With Grafted III-V Semiconductor Layers", Proc. SPIE 1177, Integrated Optics and Optoelectronics, (5 January 1990); doi: 10.1117/12.963353; https://doi.org/10.1117/12.963353