Vertical photonics: A new way to integrate photonic devices into optical fibers

Vertical photonics is the technique of direct integration of optical functional devices or their integration into optical fibers. In optical fiber systems, it is usually very difficult to match the modes of optical fibers to those of minute devices or to adjust their positions accurately. To solve such connection problems, the expanded core fibers are used, the aperture of the device is enlarged, and the optical path is shortened. In this paper, the concept of vertical photonics is discussed and the present status of the basic components (wavelength filters, polarizers, polarization splitters, etc.) and optical devices (isolators, optical switches, wavelength tunable filters, amplifiers, etc.) is reviewed.