Although it appears that enough researches have been made as regards the estimation of the optical feedback factor C of a self-mixing interferometer, no method of the C estimation can ensure its reliability if the operation of the self-mixing displacement sensor covers the strong feedback regime with fringe loss due to large displacement of a target.
That is the main reason why the precision of the sensor degenerates for measurement of large displacement.
Kim Chol Hyon, a researcher at the Faculty of Physical Engineering, has proposed a novel C estimation method called region tracking for C value, which is indispensable for measurement of long-range displacement, and demonstrated its fidelity experimentally.
He classified the fringe loss which arises in moderate and strong feedback regimes into an individual fringe loss and a collective fringe loss. Then, he clarified that the individual fringe loss is induced due to the hysteresis of the self-mixing effect and the collective fringe loss due to the minimum line width mode competition principle.
The displacement reconstruction based on the proposed region tracking method ensures better precision than a half wavelength, depending on the method of displacement retrieval. The approach presented will make a great contribution to further improvement of the accuracy of the self-mixing displacement sensor for large displacement.
For more information about this, please refer to his paper “Improvement of precision of self-mixing displacement sensor based on region tracking for large displacement” published in “Optics Communications” (SCI).
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