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We experimentally demonstrate a method for absolute distance measurement using a triple-comb-based multi-heterodyne interferometer which has the capacity to simultaneously balance the non-ambiguous range, resolution, update rate, and cost. Three flat-top electro-optic combs generated via cascaded intensity and phase modulators are adopted to form a measurement scheme including rough and fine measurements, and the unknown distance is determined by detecting the phase changes of the consecutive synthetic wavelengths. Experimental results demonstrate an agreement within 750 nm over 80 m distance at an update rate of 167 μs.

To explore a new generation of ranging method suitable for industrial applications, in this paper, a spectral interferometry ranging method based on electro-optic (EO) comb is proposed. The mathematical model of EO comb and the principle of spectral expansion are analyzed in detail. Besides, the factors affecting the non-ambiguous range and resolution of the spectral interferometry method are also discussed. According to the theoretical analysis, the resolution of spectral interference ranging is mainly affected by the spectrum width of the optical frequency comb, and the non-ambiguous range is affected by the resolution of the optical spectrum analyzer (equal to the highest sampling rate of the optical spectrum analyzer). In the experiment, triple cascaded EO phase modulator is used to modulate a single frequency laser to generate more than 40 high-power sidebands. Then, the laser spectrum output from the EO modulator is expanded by single mode fiber and high nonlinearity fiber. Owing to the use of erbium doped fiber amplifier between the dispersion compensation fiber (single mode fiber) and the highly nonlinearity fiber, the polarization disturbance does not affect the spectrum width of the optical frequency comb significantly. However, the width of spectrum will be still affected by the phases of light, and the phases of light can be adjusted by the phase shifters in the front of the electro-optic modulators. Finally, the EO comb with a repetition frequency of 10 GHz and spectrum width of 30 nm is obtained. The EO comb can be used as the source of spectral interferometry scheme. Since the repetition frequency of the EO comb is high enough, which can meet the distortion-free sampling of optical spectrum analyzer. Hence, there is no “dead zone” in the measurement range. Besides, the equal frequency interval resampling algorithm and quadratic equation fitting algorithm are used in the data processing. Through the use of these algorithms, we can eliminate the measurement errors caused by non-equal frequency interval sampling of the optical spectrum analyzer and improve the ranging accuracy. The experimental results show that within the range of 1 m, the absolute ranging accuracy of 15 μm can be achieved at arbitrary position.

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Method to accurately measure both refractive index and the thickness of glass is investigated. The method combines equal inclination interference with dispersive interferometry. The interference signal, which is detected by the spectrometer, contains different frequencies and can be demodulated with high accuracy. The experiments indicate that the standard deviation of the thickness is better than the 35 nm, while the standard deviation of the measured refractive indices is below 5.76 × 10 −6. Furthermore, absolute angles, between 0 • and 51 • , can be measured with a repeatability within 5 .