Method of measuring absolute distance based on spectral interferometry using an electro-optic comb

Abstract

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.

Advances of Research on Dual-Frequency Solid-State Lasers for Synthetic-Wave Absolute-Distance Interferometry

“…The synthetic-wave absolute-distance interferometric measurement is a kind of high-accuracy no-guideway ranging technology based on the fraction-coincident method of the interference fringes, which provides an effective way to solve the technical problems of precision measurement and ultra-precision measurement of large-dimension workpieces. At present, the dual-frequency lasers [ 1 , 2 ] and optical-frequency combs [ 3 , 4 , 5 , 6 ] are normally used as the light sources for synthetic-wave absolute-distance interferometric systems, in which dual-frequency lasers have attracted great attention and strong research interests of scholars worldwide due to the advantages of simple structure and low cost. As the typical representatives of dual-frequency lasers, the Zeeman dual-frequency He-Ne laser at 632.8 nm [ 7 ], the two-longitudinal-mode He-Ne laser at 632.8 nm [ 8 ], and the birefringent dual-frequency He-Ne laser at 632.8 nm [ 9 ] have been successfully applied to the synthetic-wave absolute-distance interferometric system.…”