Light from the system light source, in the coupler is divided into two beams of the same frequency, the initial phase difference is constant parallel light, respectively, into the reference arm of the structure of the Michaelson interferometer and the sample arm, which the reference arm of the light by the reference mirror reflection and return to the subsequent optical path, the sample arm of the light to go through the sample layer of the scattering and reflection of the role of the light back to the optical path. If the optical range difference between the two returning beams is kept within a coherence length, interference can occur in the coupler. For time-domain OCT, the interference signals of different optical ranges can be obtained by moving the reference arm or changing the delay, while for frequency-domain OCT, single-point full-depth information can be obtained from a single scan by calculating the interference term through a fast Fourier transform.