7 May 2012 Mach-Zehnder interferometer for movement monitoring
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Proceedings Volume 8370, Fiber Optic Sensors and Applications IX; 83700R (2012); doi: 10.1117/12.919349
Event: SPIE Defense, Security, and Sensing, 2012, Baltimore, Maryland, United States
Abstract
Fiber optical interferometers belong to highly sensitive equipments that are able to measure slight changes like distortion of shape, temperature and electric field variation and etc. Their great advantage is that they are insensitive on ageing component, from which they are composed of. It is in virtue of herewith, that there are evaluated no changes in optical signal intensity but number interference fringes. To monitor the movement of persons, eventually to analyze the changes in state of motion we developed method based on analysis the dynamic changes in interferometric pattern. We have used Mach- Zehnder interferometer with conventional SM fibers excited with the DFB laser at wavelength of 1550 nm. It was terminated with optical receiver containing InGaAs PIN photodiode. Its output was brought into measuring card module that performs on FFT of the received interferometer signal. The signal rises with the composition of two waves passing through single interferometer arm. The optical fiber SMF 28e in one arm is referential; the second one is positioned on measuring slab at dimensions of 1x2m. A movement of persons around the slab was monitored, signal processed with FFT and frequency spectra were evaluated. They rose owing to dynamic changes of interferometric pattern. The results reflect that the individual subjects passing through slab embody characteristic frequency spectra, which are individual for particular persons. The scope of measuring frequencies proceeded from zero to 10 kHz. It was also displayed in experiments that the experimental subjects, who walked around the slab and at the same time they have had changed their state of motion (knee joint fixation), embodied characteristic changes in their frequency spectra. At experiments the stability of interferometric patterns was evaluated as from time aspects, so from the view of repeated identical experiments. Two kinds of balls (tennis and ping-pong) were used to plot the repeatability measurements and the gained spectra at repeated drops of balls were compared. Those stroked upon the same place and from the same elevation and dispersion of the obtained frequency spectra was evaluated. These experiments were performed on the series of 20 repeated drops from highs of 0,5 and 1m. The evaluation of experiments displayed that the dispersion of measured values is lower than 4%. Frequency response has been verified with the loudspeaker connected to signal generator and amplifier. Various slabs have been measured and frequency ranges were compared for particular slab designs.
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Vladimir Vasinek, Jakub Cubik, Stanislav Kepak, Jan Doricak, Jan Latal, Petr Koudelka, "Mach-Zehnder interferometer for movement monitoring", Proc. SPIE 8370, Fiber Optic Sensors and Applications IX, 83700R (7 May 2012); doi: 10.1117/12.919349; https://doi.org/10.1117/12.919349
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KEYWORDS
Interferometers

Signal processing

Mach-Zehnder interferometers

Interferometry

Optical fibers

Fourier transforms

Motion analysis

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