The Basic Principle And Experimental Study Of Hybrid Interferometer

The laser self-mixing interference technology is a rising sensing technology, which has the features of simple, compact, self-aligning and independent of optical coherent lengths compared to other laser interference. This technology has been applied to a great deal of aspects such as vibration measurement, displacement measurements and so on.The basic principle of the self-mixing interference and F-P interference effect have been demonstrated using the theory of standing wave and multi-beam interference. And the theory model have been established. The optical output power and frequency have been deduced as well. Moreover,the behavior of different conditions have been analyzed and simulated.In order to reduce the measurement error, the idea of hybrid interferometer used for measurement is presented, which uses a laser self-mixing interference pattern to achieve sub-micron level real-time displacement measurement, and FP interference pattern combined with the strength method, tracking slight vibration signal and achieving nanoscale real-time displacement measurement. The optical path of the hybrid interferometer is designed and some preliminary inquiry experiments are conducted.Based on the first order harmonic-based cavity-length locking technology, a novel kind of micro-displacement sensor, which combines F-P interferometer and intensity demodulation method, has been developed. The initial length of the F-P cavity has been actively scanned and dynamically locked. And then the change of the F-P cavity length induced by the motion of the target is coded on the variation of the optical output power of the cavity. As a consequence, a fast and direct micro-displacement sensing scheme through the intensity demodulation is available.The theoretical model of the displacement sensor and the technical scheme for actively locking the initial length of the FP cavity through the first order harmonic have been demonstrated in detail, respectively. Micro-displacement experiments provided by a commercial high-precision PZT with different vibrating parameters have been performed, and the experimental results agree well with the motion of the PZT within peak-to-peak amplitude of λ/4and frequency is no more than400Hz. The frequency error is less than0.5Hz, and the total measurement accuracy is1nm.