Quadruply clad fiber

In telecommunication, a quadruply clad fiber is a single-mode optical fiber that has four claddings.

Note 1: Each cladding has a refractive index lower than that of the core. With respect to one another, their relative refractive indices are, in order of distance from the core, lowest, highest, lower, higher.

Note 2: A quadruply clad fiber has the advantage of very low macrobending losses. It also has two zero-dispersion points, and moderately low dispersion over a wider wavelength range than a singly clad fiber or a doubly clad fiber.

Source: from Federal Standard 1037C