High-attenuation fiber with cladding mode suppression for all-fiber optical attenuator

摘要

Disclosed is an optical device which combines a controlled level of attenuation, a high degree of wavelength insensitivity and a substantial decrease in modal interference problems. The optical device has a core having a core diameter and a core refractive index; an inner cladding having an inner cladding outer diameter less than ten times the core diameter and a refractive index less that the core refractive index; and an outer cladding having a refractive index higher that the inner cladding refractive index. At least one part of the core, the inner cladding or the outer cladding is doped with at least one absorbing element. Preferably, the core is doped with cobalt in an appropriate concentration, providing the same degree of attenuation at 1310 nm and 1550 nm, while also considerably reducing modal interference. The optical device can be used as an attenuator between a transmission fiber and a detection fiber or can be used to couple a transmission fiber directly to a detector.