Nanometer-Scale Vibration Measurement Using an Optical Quadrature Interferometer Based on 3 × 3 Fiber-Optic Coupler

Abstract

We propose a nanometer-scale displacement or vibration measurement system, using an optical quadrature interferometer and the post-processing technique that extracts the parameters necessary for characterizing the interferometric system. Using a 3 × 3 fiber-optic coupler, the entire complex interference signal could be reconstructed with two interference signals measured at two return ports of the coupler. The intrinsic phase difference between the return ports was utilized to obtain the quadratic part of the interference signal, which allowed one to reconstruct the entire complex interference signal. However, the two measured signals were appreciably affected by the unequal detector gains and non-uniform intrinsic phases of the coupler. Fortunately, we could find that the Lissajous curve plotted by the two signals of the interferometric system would form an ellipse. Therefore, by fitting the measured Lissajous curve to an ellipse, we could extract the parameters characterizing the actual system, which allowed the nanometer-scale measurement. Experimental results showed that a 20 kHz sinusoidal vibration with an amplitude of 1.5 nm could be measured with a standard deviation of 0.4 nm.

Vital Signs Monitoring Based on Interferometric Fiber Optic Sensors

“…In the experiment, even if the optical path difference between the two arms is adjusted to π/2 in advance, the optical path difference between the two arms cannot be maintained at π/2 in the static state due to the slowly random phase drift noise and temperature changes. In order to solve this problem and make the FOS based on interferometer work stably, many demodulation schemes have been proposed [24][25][26][27][28][29][30][31][32][33][34]. However, there are some problems when demodulating vital signs signals based on optical fiber interferometers.…”

“…Kamenev et al used this scheme for the fiber optic MZI-based strainmeter [31], and D. Xu et al used the same scheme to measure the phase and frequency noise of the Michelson interferometer [32]. S. Park et al have achieved nanometer-scale displacement or vibration measurement using an interferometer based on a 3 × 3 fiber circulator [33,34]. The structure is shown in Figure 5.…”

“…Due to the high cost of the FBG sensors and the limited sensitivity of the intensity-based sensors, researchers chose the interferometric FOS for vital signs monitoring. Researchers have dedicated much time and effort to the design of sensor structures [12][13][14][15][16][17][18][19][20][21][22][23], demodulation methods [12,[24][25][26][27][28][29][30][31][32][33][34][35][36] and the application of vital signs monitoring [12][13][14]16,[18][19][20][21][22][23][35][36][37][38][39][40][41][42][43][44][45].…”

Towards non-contact photoacoustic imaging [review]

“…Therefore, the quadrature component of the signal measured at one particular return port can be calculated using the measured signal at any other return port of the same coupler [ 188 ]. Moreover, the long-term variation of intrinsic phase difference in a 3 × 3 fiber-optic coupler is rather stable; and in it has slight effect on the displacement measurement [ 189 ]. The proposed system eliminated the need for any feedback components.…”

“…PBS: polarized beamsplitter, QWP: quarter-waveplate, BC: beam combiner, PD: photodiode, GM: galvo-scanner mirrors, SMF: single mode fiber, OL: objective lens, L: lens. Reprinted with permission from [ 189 ]. …”