Absolute distance measurement using sinusoidal phase modulating frequency sweeping interferometry with a reference interferometer

Abstract

Frequency sweeping interferometry with reference interferometer based on sinusoidal phase modulating technique is proposed in this paper for absolute distance measurement. With the frequency of the external cavity diode laser (ECDL) swept continuously in sinusoidal, a HeNe laser was employed to monitor the drifts of the target and the reference length, and influences caused by drifts during the measurement were compensated in real time. Sinusoidal phase modulation with non-overlapping frequencies were applied to the two laser lights individually by two electro-optic modulators (EOM), and the interference phases corresponding to the two laser lights were extracted simultaneously using the phase generated carrier (PGC) demodulation based on frequency-division multiplex technique. Performance of the phase detection method has been verified by nanometer displacement measurements. Experimental results show that the measurement uncertainty can be considerably reduced by compensating the influences of drifts and by applying linear regression to get the ratio of interference phase changes between the measurement interferometer and the reference interferometer. Comparison of the absolute distance measurement with an incremental interferometer yields a measurement uncertainty of 10−5, which is in good agreement with the estimation of the measurement uncertainty.

Absolute distance measurement using frequency sweeping interferometry with large swept range and target drift compensation

“…As shown in figure 1, the measurement system composed of four interferometers [28], including the MI and RI that take ECDL as the laser source, and the measurement monitoring interferometer (MMI) and reference monitoring interferometer (RMI) employing a frequency stabilized HeNe laser. The lights of ECDL and HeNe laser travel along the same optical path in the interferometers, and the interference fringes of MI and MMI are detected by PD M , and the ones of RI and RMI are detected by PD R .…”

“…In our previous work, linear regression was performed in every sweep process to mitigate the effects of random noise in determining the ratio k [28]. Alternatively, increasing the frequency sweeping range is another way to reduce the uncertainty of k, since larger frequency sweep range corresponds to smaller synthetic wavelength (λ S = c/∆ν), and the phase changes of MI and RI can be extracted more accurate under the same phase demodulation accuracy.…”

“…In our previous work, FSI with an RI had been studied and a frequency stabilized HeNe laser was used to compensate the OPD drifts. Limited by the tuning range of cavity length using piezo-electric transducer (PZT) in external cavity diode laser (ECDL), the frequency sweeping range was only ∼76 GHz, and a measurement uncertainty of 10 −5 was achieved at a distance less than 0.4 m [28].…”

“…In this paper, ADM using FSI with large swept range and target drift compensation is proposed to improve the accuracy and stability of ADM based on the work presented in [28]. An auxiliary laser with fixed frequency is used to monitor the target drifts of the MI and RI.…”

High synchronization absolute distance measurement using a heterodyne and superheterodyne combined interferometer

“…Major techniques that overcome these challenges include time of flight (TOF), frequency (wavelength)-sweeping interferometry (FSI), and multiple-wavelength interferometry (MWI). However, the TOF method is limited to time detection accuracy, which is limited to millimeter scale, and FSI is limited by the frequency modulation, which cannot meet the real-time measurement requirement [3] . MWI achieves high resolution and a wide range [4,5] .…”