Measurement of pump induced refractive index change in erbium doped fibre amplifier

Abstract

What the authors believe to be the first spectral measurements of pump induced refractive index change in the erbium doped fibre amplifier (EDFA) are reported. The measurements were performed using a 980 nm pumped EDFA configured within a quadrature locked interferometer. A maximum pumped/unpumped change in refractive index of 5.5 × 10−2 per dB of absorption at 1.536 μm was measured. The spectral dependence of the refractive index associated with the 4I13/2–4I15/2 resonance transition was calculated by application of the Kramers–Kronig relations to the change in transmission data and was shown to be consistent with the experimentally measured data. The dispersion associated with the pumped index change was also calculated and systems implications are considered.