Wavelength-modulated standing-wave interferometry for small out-of-plane displacement measurement

Development of a Compound Speckle Interferometer for Precision Three-Degree-of-Freedom Displacement Measurement

“…According to the system specifications of the instruments used in the experiments, if one only considers the minimum interference signal which can be measured and analyzed using the signal analysis module in our system, the minimum phase variation which can be demodulated by our test equipment (National Instruments, PCI-6133, 14-Bit) and software lock-in program is approximately 0.022°, thus the “theoretical resolution” can then be calculated as approximately 0.111 nm accordingly, which would be the minimum displacement without considering the effects of disturbance. As such, it is necessary to determine the actual resolution of a measurement technique either by the minimum discernible displacement [ 6 , 11 , 12 , 13 ] or the discernible noise level that can be achieved or observed [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. However, as indicated in the studies of Williamson et al [ 14 ], Fleming et al [ 15 ] and Lu et al [ 16 ], if the measurement noise roughly corresponds to the Gaussian distribution, the resolution can be quantified by the standard deviation (σ) or root-mean-square (RMS) values of the noise level.…”

“…Since the proposed method is developed for displacement measurement and system calibration, several state-of-art methods of displacement measurement or system calibration are listed in Table 3 for comparison. As can be seen from the table, the method proposed by Lee et al [ 12 ] is capable of measuring 1-DOF displacement with the resolution and repeatability of 2 nm and 2 nm, respectively. The measurement system is compact consisting of only a few optical components and one photodetector.…”