Refractive index contrast

Refractive index contrast: In an optical fiber, a measure of the relative difference in refractive index of the core and cladding.

Note: Refractive index contrast, Δ, is given by Δ = (n ₁²- n ₂²)/(2n ₁²), where n ₁ is the maximum refractive index in the core and n ₂ is the refractive index of the homogeneous cladding.

Source: from Federal Standard 1037C and from MIL-STD-188