A new system based on optical external modulator frequency multiplication is proposed to generate W-band linear frequency modulated (LFM) signals for high-resolution ranging. The LFM signals from the arbitrary waveform generator (AWG) are modulated to the sideband of the optical carrier through the optical modulator. The photoelectric conversion is completed in the photodetector (PD) to generate quadruple frequency W-band LFM signals, whose center frequency and bandwidth are four times the original LFM signal. This broadband LFM signal is emitted to free space for target detection. For distance measurements, the two targets are separated by 50 cm, and the measured value is 48.8 cm with an error of 1.2 cm. The distance between the two objects is set to 40 cm to demonstrate the reliability of the experiment. The measured value is 38.9 cm, and the error is 1.1 cm. The system overcomes the “electronic bottleneck” that is difficult to directly generate high-frequency signals in the electrical domain and achieves high-resolution ranging via photonics-aided generation of the broadband LFM signal. Thus, the proposed method provides a solution for future ultrahigh-resolution LFM continuous-wave radar systems.