Due to the central wavelength drift of the laser，it is difficult to produce observable beat signal in the experiment.

Inspired by the transformation between electric domain and optical domain in microwave photonic technology，an

optical beat frequency method based on microwave frequency difference conversion is proposed. By means of intensity

modulation and phase modulation，two microwave signals with small frequency difference are modulated to the

same optical carrier. Two stable optical signals with minimum frequency difference are obtained by combining with

optical filter. Optical beat is realized by using photoelectric detector. Visual low-frequency beat signal is obtained

by the simulation and experiment. This method provides an experimental scheme for college physics and optical experiments

combined with the cutting-edge of science. It can expand the teaching content and depth，and can also

help to cultivate students’scientific literacy.