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The dynamics of AlGaAs laser diodes under analog intensity modulation are characterized and the associated intensity noise is evaluated. The study is based on numerical solution of the stochastic rate equations of semiconductor lasers. Based on the shape of the modulated laser signal, the modulation dynamics are classified into eight distinct types. Four types are characterized by continuous periodic signals, and three types have periodic pulsing signals. These signals happen to have period doubling or superposed by sub-peaks from the relaxation oscillations of the laser. The last type is chaos, in which the signal is irregular and non-uniform. The noise results show that the relative intensity noise is closest to the quantum level under weak modulation where the laser signal is sinusoidal. LF-RIN is pronounced when the laser emits irregular spike-like pulses under low-frequency strong modulation. The chaotic dynamics dominate the region of strong with modulation frequencies around the relaxation frequency of the laser.