recently successfully introduced into optics. Optical FMCW interference naturally generates a dynamic signal, both the
phase and frequency of which are relative to the optical path difference between the two interfering optical waves.
Hence, optical FMCW interference not only can measure the relative change of optical path difference (or other related
parameters) more accurately and easily, but also can measure the absolute value of optical path difference (or other
related parameters). The phase measurement gives a resolution thousands of times higher than the frequency
measurement. Particularly, since the signal of optical FMCW interference is a dynamic signal, to calibrate the fractional
phase, distinguish the phase-shift direction and count the number of full periods is quite easy. Therefore, compared with
traditional optical homodyne interference, optical FMCW interference can offer a higher accuracy and a longer
measurement range. During the last few years, some important achievements in both the theory and application of optical
FMCW interference have been made. Today, optical FMCW interference has become a well-defined new branch of
physical optics. The investigation of optical FMCW interference not only extends our knowledge about the nature of
light, but also offers a new advanced technology for optical metrology. Optical FMCW interference can be used to
upgrade some existing optical instruments and to create the new-conceptual optical instruments. In this paper, I attempt
to review the principle and applications of optical FMCW interference in metrology.