Research On New Optical High Precision Measurement Based On Orbital Angular Momentum

In recent years,with the increasing demand for high-precision measurement in the fields of industry and medicine,laser measurement has become a hot research topic as one of the means of high-precision measurement.Laser measurement has the advantages of high accuracy,fast measurement speed and non-contact property.In general,current laser measurement technology is being researched in the direction of higher precision,faster speed and how to mitigate the impact of external environment.However,most of the lasers used in these measurements are ordinary beams.Research in this paper innovatively proposes a new method to use optical vortices(OV)with orbital angular momentum(OAM)for optical measurement.First of all,the current research status and the application of OAM and laser measurement are introduced.The problems existing in the current laser measurement are also analyzed,which leads to the research topic of this paper: a new optical high-precision measurement based on OAM.Secondly,vortex beams with OAM are studied.The OAM of a single photon is derived by means of quantum operators.Then,the characteristics of three common types of vortex beams,such as Laguerre-Gaussian(LG)beam,Bessel-Gaussian(BG)beam and array vortex beam are studied.Then,the spiral phase plate(SPP)method,the computer-generated holograms(CGH)method and the spatial light modulator(SLM)method are introduced,which are common methods for preparing vortex beams.The research has successfully prepared vortex beams with different modes by using the reflective liquid crystal SLM in the laboratory.Also,the interference characteristics between vortex beams are studied,which lays a theoretical foundation for the subsequent laser measurement based on OAM.Thirdly,this paper proposes a laser interferometry method to measure velocity of object based on OAM.Theoretical analysis shows that there is a simple formula relationship between the moving velocity of object and the angular velocity of the interference field.Correctness of the theory is then verified by simulation.Since the external atmospheric environment is an important factor affecting the results of laser measurements,this paper then simulates the phase screen of atmospheric turbulence.The results show that atmospheric turbulence changes the shape of the interference pattern,so the velocity cannot be measured by the angular velocity of the interference pattern.Therefore,Fourier transform is proposed to solve this problem by analyzing the normalized map of light intensity spectrum distribution.Finally,based on the theory above,this paper proposes a method to measure weak displacement based on OAM.The displacement of an object in the conventional laser interferometry method is obtained by counting the number of movements of the interference fringes,and the number of the fringes has the limitation that the value is not an integer and the fractional value is difficult to calculate.It has been found that the displacement of object in the method proposed in this paper can be obtained by calculating the rotation angle of the interference pattern.Requirements that the new displacement measurement method is superior to the traditional method in terms of measurement accuracy is get according toanalysis.Then research uses centroid algorithm and scale-invariant feature transform(SIFT)algorithm to calculate the rotation angle of the interference pattern and the effects of the two algorithms have been compared.Simulation results show that the accuracy of the new measurement method is higher than traditional method and SIFT has superiority over centroid algorithm in the measurement precision of image rotation angle.At the end of the paper,the future research work is prospected.