Abstract
We report on a frequency-comb-referenced absolute interferometer which instantly measures long distance by integrating multi-wavelength interferometry with direct synthetic wavelength interferometry. The reported interferometer utilizes four different wavelengths, simultaneously calibrated to the frequency comb of a femtosecond laser, to implement subwavelength distance measurement, while direct synthetic wavelength interferometry is elaborately introduced by launching a fifth wavelength to extend a non-ambiguous range for meter-scale measurement. A linearity test performed comparatively with a He–Ne laser interferometer shows a residual error of less than 70.8 nm in peak-to-valley over a 3 m distance, and a 10 h distance comparison is demonstrated to gain fractional deviations of ~3 × 10−8 versus 3 m distance. Test results reveal that the presented absolute interferometer enables precise, stable, and long-term distance measurements and facilitates absolute positioning applications such as large-scale manufacturing and space missions.
Highlights
Rapid, precise, and long-range absolute distance measurement (ADM) by optical interferometry is of extraordinary importance for industrial applications, such as large-scale aircraft machining, ultra-precision semiconductor manufacturing, and sub-aperture stitching measurement [1,2].Traditional laser ranging for distance flatly uses a laser-pulse-based time-of-flight method to measure distance with sub-millimeter resolutions
We extended the measurable non-ambiguity range (NAR) to a meter level, which is highly emphasized in modern large-scale manufacturing, such as the fabrication of ultra-broad flat panel displays and solar cell devices
The candidate for m1 could be a series of arithmetic progression, and the common difference between the two adjacent candidates corresponds to the so-called NAR of multi-wavelength interferometry (MWI)
Summary
Traditional laser ranging for distance flatly uses a laser-pulse-based time-of-flight method to measure distance with sub-millimeter resolutions. This method is limited in virtue of its electronic resolution because this leads to a far less precise than optical interferometry [3]. Laser interferometers that are based on a homodyne or heterodyne principle adeptly measure displacement with sub-wavelength precision via phase-counting techniques. These interferometers are unable to achieve ADM independently because of a 2π phase-ambiguity in single-wavelength interferometers, which substantially restricts the scope of applications [4]. On the basis of frequency combs, a series of applicable methods, including synthetic wavelength interferometry (SWI) [10,11], dispersive interferometry [12,13], multi-wavelength interferometry (MWI) [14,15,16], frequency modulated continuous wave interferometry [17], time-of-flight
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