Absolute positioning by multi-wavelength interferometry referenced to the frequency comb of a femtosecond laser

Abstract

A multi-wavelength interferometer utilizing the frequency comb of a femtosecond laser as the wavelength ruler is tested for its capability of ultra-precision positioning for machine axis control. The interferometer uses four different wavelengths phase-locked to the frequency comb and then determines the absolute position through a multi-channel scheme of detecting interference phases in parallel so as to enable fast, precise and stable measurements continuously over a few meters of axis-travel. Test results show that the proposed interferometer proves itself as a potential candidate of absolute-type position transducer needed for next-generation ultra-precision machine axis control, demonstrating linear errors of less than 61.9 nm in peak-to-valley over a 1-meter travel with an update rate of 100 Hz when compared to an incremental-type He-Ne laser interferometer.

Distance Measurements Using Mode-Locked Lasers: A Review

“…As a result, conventional schemes of multi-wavelength interferometers were not capable of achieving absolute distance measurements over several meters without losing the superb sub-wavelength measurement resolution of laser-based phase-measuring interferometers. Figure 3 shows the basic concept of multi-wavelength interferometry implemented by generating four wavelengths with reference to the frequency comb of a modelocked laser [49,50]. Each wavelength k i (i = 1,2,3,4) is phase-locked individually to its pre-assigned modes of the frequency comb, so the target distance L is given in terms of k i as L i = (k i /2n i )/(m i ?…”

“…In recent years, in order to meet evergrowing industrial demands on the measurement precision and functionality, quit a few attempts have been made worldwide. Examples include synthetic wavelength interferometry [43][44][45], multi-wavelength interferometry [46][47][48][49][50], spectrally resolved interferometry [51][52][53][54], timeof-flight measurement [55][56][57][58][59] and dual-comb interferometry [60][61][62][63][64].…”

Comb-referenced laser distance interferometer for industrial nanotechnology

“…In addition, the comb can be used for simultaneous generation of multiple arbitrary wavelengths; by phase-locking tunable laser diodes individually to selected optical modes within the comb11 or by filtering out several optical modes separately with power amplification by injection-locking12. This approach of comb-referenced wavelength generation offers excellent frequency stability and uncertainty, allowing for implementation of advanced techniques such as absolute distance measurement by multi-wavelength interferometry131415161718 and real-time compensation of the refractive index of air by two-colour interferometry1920.…”

“…In fact, during the past decade, many attempts have been made to use the comb as the light source for long-distance measurements with various progressive principles; inter-mode synthetic wavelength interferometry212223, many-wavelength dispersive interferometry24252627, multi-wavelength interferometry131415161718, dual-comb frequency-down-conversion interferometry28293031, and optical cross-correlation time-of-flight measurement323334. These newly proposed methods proved effective in extending the non-ambiguity distance range by taking advantage of the comb’s unique spectral or temporal characteristics.…”

“…In fact, the interferometer system was previously proposed in ref. 18 by the authors together with primary measurement results. In this study, with further experimental data obtained via more elaborate environment control, comprehensive analysis is made to validate the proposed interferometer system as a practical means of realizing the definition of the meter with an utmost level of uncertainty and stability.…”