High-accuracy absolute distance measurement using frequency comb referenced multiwavelength source

Abstract

We propose a new approach to multiple-wavelength interferometry, targeted to high bandwidth absolute distance measurement, with nanometer accuracy over long distances. Two cw lasers are stabilized over a wide range of frequency intervals defined by an optical frequency comb, thus offering an unprecedented large choice of synthetic wavelengths. By applying a superheterodyne detection technique, we demonstrated experimentally an accuracy of 8 nm over 800 mm for target velocities up to 50 mm/s.

Two-mode interference measurement for nanometer accuracy absolute ranging

“…In the electronic measurement of long distances, multiwavelength interferometry has been able to provide both long synthetic wavelength and sub-micron accuracy [1]. Using multiple 40 GHz phase modulations of a CW laser, MSTAR [2] has reached nm-scale accuracy.…”

Long distance measurement with femtosecond pulses using a dispersive interferometer

“…5(b) and Fig. 5(d) are functions of the frequency, the distance of 2 mm is always shown at the frequency 3.674×10 14 Hz, as labelled with the dot in both curves. This fact implies that, for deriving the distance information, it is not necessary to know the entire distance curve in Fig.…”

“…5(d) are approximately linear. This is mainly due to the fact that for a small frequency range around 3.674×10 14 Hz the refractive index of air is approximately a linear function of frequency.…”

“…Some schemes are either based on correlation measurement [6][7][8][9] or dispersive interferometry [10][11][12]. Other schemes exploit two combs [13], use the comb as a reference for multi-wavelength interferometry [14] or frequency sweeping interferometry [15].…”

Theoretical Considerations on Combined Optical Distance Measurements Using a Femtosecond Pulse Laser

“…To avoid the ambiguity problem in displacement interferometry, various research including synthetic wavelength interferometry [1], a frequency modulated continuous wave method [2], multiple wavelength interferometry [3], and frequency sweeping interferometry [4] have been applied to extend the unambiguity range. Recently, the application of a femtosecond pulse laser for distance metrology not only offers further improvements but also makes it possible to measure absolute distances precisely from industrial applications to space programs [5][6][7][8][9][10][11].…”