Conservation of AM index of a rf subcarrier in IM–DD optical link

This paper presents experimental observations on amplitude modulation (AM) index conservation of an amplitude modulated (AM) rf subcarrier which produces direct intensity modulation (IM) of a laser diode (LD) lasing at 1557.1 nm and subsequently detected in a InGaAs photodiode (PD). The AM index of the input subcarrier is identical with that of the detected subcarrier at the output of the photodiode. This confirms the linearity of the direct modulation process as well as the linearity of the responsivity curve of the photodiode.