Observations of ultrafast nonlinear refraction in an InGaAsP optical amplifier

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Abstract
Spectral broadening due to self-phase modulation has been observed for ultrashort pulses propagating through an InGaAsP optical amplifier. This is not associated with gain saturation or absorption saturation, since it can be observed at the transparency current. At transparency, the broadening and structure of the spectra are symmetrical for pulses of approximately 27 ps duration, implying that the underlying nonlinearity has a relatively fast recovery time. The associated nonlinear index coefficient n2 is estimated to be approximately −2×10−11 cm2 W−1.