An optoelectronic oscillator (OEO) on the basis of two phase modulators is proposed. The incident continuous wave (CW) light is modulated firstly by a phase modulator (PM). The PM is driven by the electrical prescaled clock extracted from this improved OEO. The spectrum of the modulated CW light is then sliced by an optical band-pass filter (OBPF) on the blue side or red side to the original center wavelength. The generated 7.6 ps optical pulses are subsequently launched into a pulse compressor, which consists of a PM and a single-mode-fiber (SMF). Thereby, optical prescaled clock with a narrow width is then obtained. 25 GHz optical clock and electrical clock are experimentally extracted from 4×25 Gbit/s signal. The width of optical clock pulse is 3.1 ps, which corresponds to a duty cycle of 7.75%. The resulted timing-jitter (100 Hz to 10 MHz) is 135 fs. The carrier-to-noise ratio of electrical clock is 61.7 dB and its timing jitter (100 Hz to 10 MHz) is 118 fs.