Research On Computer-Generated Hologram Aspheric Surface Detection Method Based On Efficient Encoding

With the development of optical technology,the application of aspheric surface and freeform surface in modern optical systems is becoming more and more frequent,and the requirements for surface shape accuracy are getting higher and higher.ComputerGenerated Hologram is one of the high-precision detection methods of aspheric surface shape,and most of its existing encoding methods are linear encoding,which has the disadvantages of low encoding efficiency,large amount of encoded data,and large processing files.In order to solve the above problems,this thesis studies an encoding method that describes the engraved stripes in segments using arcs as primitives,aiming to improve the encoding efficiency of Computer-Generated Hologram and reduce the amount of encoded data.The main research in this thesis are as follows:Firstly,the optical path structure parameters of the aspheric surface detected by CGH are determined,and the compensated phase distribution of CGH is solved by ray tracing method.Then the projection distortion,the separation of interference diffraction levels and the minimum fringe spacing of the system are analyzed,which lays the foundation for subsequent encoding calculations.Secondly,this thesis studies an efficient encoding method for CGH,which divides the encoding process into two steps:binary encoding and curve description,and uses arcs as the basis to describe the stripes in segments.The binary encoding obtains the phase contour dividing line,and the Newtonian iterative method is used to discretize the stripe dividing line.The curve description combines the dichotomy and the minimum root mean square criterion of residual error,takes the encoding error as the feedback condition,and uses the circular arc to encode the stripe discrete points,so as to achieve the purpose of compressing the amount of encoded data.Then,according to the proposed encoding method,the CGH for an off-axis aspheric surface is encoding calculation,and the encoding DXF file is generated according to the arc parameters of the engraved stripe.Moreover,various error sources in the design,encoding and production process of CGH are analyzed and calculated in detail,which proves the feasibility of the encoding method in this thesis.Under the premise that the encoding accuracy is better than λ/1000,the operation time is only 3 hours,the encoding file is only 39M,and the etching time is only 40 minutes,which proves that this method can greatly improve the encoding efficiency while ensuring the encoding accuracy.Finally,in order to verify the correctness of the encoding method,the aberration-free point method and Computer-Generated Hologram method are respectively used to detect the surface shape of the off-axis aspheric surface,and the detection results of the two methods are compared.The experimental results show that the RMS difference of the detection results is only 0.004λ,and the distribution of surface shape error is similar.Subtracting the detection results of the two methods point-to-point,the residual PV of the two methods is close to 1/30λ,indicating that the encoding method can perform highprecision surface shape detection while ensuring high encoding efficiency.