An intensity modulator is a key component in an optoelectronic oscillator (OEO). It is necessary to investigate the effects of some of the operating parameters of the modulator on OEO phase noise. Since the OEO optimized oscillation power is related to the nonlinear effect of the modulator, an extended analysis is made by considering both the saturation effects of the modulator and the radio frequency amplifier. Experimental results show that a 5-dB improvement of phase noise performance is achieved. In addition, a theoretical and experimental study on the DC bias-drifting problem of the modulator and its induced phase noise fluctuations is proposed. It is found that the saturated operation of the amplifier is helpful in reducing the fluctuation range. The presented results can be used to guide the design of high-quality OEOs.