Parametric study of depressed inner cladding single-mode fibers

A parametric study on the depressed inner cladding (DIC) single-mode fibers shows the influence of the inner-cladding diameter on the effective cutoff wavelengths of the first two modes, determining a practical transmission window. The set of curves that is obtained can be considered universal, at least for a value of the inner-cladding/core index differences ratio close to 0.5. The behavior of the effective cutoff wavelengths is explained by studying the effective index of the modes and the fundamental mode diameter, this explanation being confirmed by a bending and microbending sensitivity test. It appears that DIC fibers optimized for long-range transmission should have an inner cladding to core diameter ratio greater than 3 and a relative depth of the inner cladding smaller than 0.5.