Heterodyne self-mixing interferometry to large step height measurement based on a dual-wavelength single-longitudinal-mode optical fiber laser.

• The developed optical fiber laser can emit two single-mode wavelengths of laser. • The two wavelengths from the laser can be chosen according to requirement. • A dual-wavelength heterodyne self-mixing interferometry (HSMI) system is proposed. • Measurement range is large as a half synthetic wavelength of the two wavelengths. • Step height can be measured effectively by employing the HSMI system. An optical fiber laser that can emit two wavelengths of laser simultaneously and each wavelength is single-longitudinal-mode (SLM) has been developed, and its application to step height measurement by employing the two wavelengths heterodyne self-mixing interferometry (HSMI) has been demonstrated. The optical fiber laser includes two overlapped and independent ring resonant cavities, and each of which is a compound resonant cavity constructed with two sub-resonant cavities. The optical fiber laser will emit two wavelengths of laser with SLM simultaneously when it is pumped by a 980 nm LD. The light of the two wavelengths is projected onto the measured object after the two frequencies of the laser are shifted by acoustic-optical modulators (AOM). The light is reflected back by the measured object and each of the two wavelengths enters its corresponding resonant cavity again to combine with the photons in the cavity, and thus two HSMI signals of the two wavelengths are formed. By employing the HSMI signals of the two wavelengths, a step height has been measured experimentally. The maximum height that can be measured is as large as a half synthetic wavelength of the two wavelengths. During the experiments, a step height of 0.7 mm built with two gauge blocks has been measured. The standard deviation of 10 times repeating measurement results is 2.4 nm. [ABSTRACT FROM AUTHOR]