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A measurement system using a pulsed RF signal is presented for extraction of nonlinear parameters of a large-signal model (LSM) of a dispersive avalanche photodiode. Nonlinear model of the avalanche photodiode was considered as two-port network and vector reflection measurement was carried out using a microwave transition analyzer in pulsed RF mode in conjunction with synchronized pulsed optical stimulus on the photodiode. Square-wave optical stimulus of 5-μs width (full width at half maximum) and 5-kHz pulse-repetition frequency (quasi-dc) were synchronized with the pulsed RF excitation using a synchronization circuit. High-frequency dispersion effects were taken into consideration for deriving the current through the photodiode and the theoretical background was given for the derivation of optical and bias-dependent parameters. Nonlinear parameters of LSM of the avalanche photodiode were extracted from the small-signal vector reflection measurement at different bias points and optical conditions. Thermal impedance of the device limits the continuous-wave measurement up to 0.1 mW of optical power, whereas when using the current method, it was possible to characterize the device up to 1.3 mW of peak optical power.