The High Precision Vibration Measurement Algorithm For Self-mixing Interference With Weak Light Feedback

The measurement technology based on optical feedback self-mixing interference has the advantages of simple structure,easy alignment of the optical path,high precision and fast speed.It can use non-contact measurement to measure the speed,vibration,displacement and topography of the object.Among them,the measurement of vibration and micro displacement of the object plays an indispensable role in the fields of biotechnology,power machinery,construction,transportation and so on.The optical feedback self-mixing interferometry to vibration and micro displacement measurement can not only achieve high precision measurement of the nanometer scale,but also can solve the problem which can not be implemented contact measurement in complex environments.It has a wide range of application prospect and has gradually became a hot topic of domestic and abroad.The paper proposes the idea of "soft and hard separation and module integration",and the design of the optical feedback self-mixing interference vibration displacement measurement system has been redesigned to improve the traditional measurement system period and solve the difficulty of upgrading and single function deficiency.This paper presents a method of ‘direction estimation' for vibration displacement of objects under weak light feedback.Under the condition of weak optical feedback,the tilt degree of the optical feedback self-mixing interference fringe is not obvious,which makes the vibration direction of the object difficult to distinguish.For this reason,the concept of "extreme slope ratio" is proposed to quantify the degree of inclination of stripes,and the direction of vibration displacement is judged according to the quantization value of the degree of stripes,and the accuracy of judgment is improved.It analyzed the weak optical feedback level of ‘three mirror cavity' model method of equation,and also put forward a kind of high precision,large range and easy to realize the vibration displacement measurement ‘equiphase intercept method'.The algorithm uses the time domain processing,carries on the equal initial phase sampling to the model equation,and the control accuracy is controlled by controlling the sampling quantity to achieve the controllability of the measurement accuracy.The method overcomes the shortcomings of the traditional method that the precision and the range can not be taken into account,and realizes the organic unification of high precision in the range from the wavelength limit to the case of nano-level.This paper introduces the concept of the direction function and the judgment vector to avoid the non-linearized data processing and simplifies the algorithm.The algorithm is relatively simple.The use of Matlab software process to achieve "direction judgment" algorithm and the "phase truncation method" for the simulation,and the waveforms are compared and analyzed by 18 kinds of waveforms.The results show that the range of the algorithm is not limited by the wavelength,and the maximum measurement error can be controlled within 4nm,which verifies the correctness and feasibility of the algorithm.