Research On White Light Phase-shifting Algorithm For White Light Profiler

As an important optical surface measurement method,white light scanning interferometry can be used to measure the surface height with a resolution of 0.1 nm,which has the advantages of fast measurement speed and non-contact detection.It is suitable for precision parts measurement such as precision parts of aero engine,optical components,optical fiber products,3C glass of liquid crystal displays,etc.In this paper,the white light scanning interferometry is firstly analyzed,and then by establishing a white light interferogram model under the influence of random noise,a white light interference signal processing algorithm is established by noise averaging technique.This method uses a pair of dynamic orthogonal bases to decompose the one-dimensional white light interference signal into the two-dimensional signal space.Through the averaging of random noise,the repeatability error of the measurement result is reduced.This algorithm has been applied and verified on the constructed white light profiler.The calibration experiment used SHS-1800 QC step standard from VLSI.The calibration result shows that the measurement repeatability error of the white light profiler is 0.93 nm and the relative error is 0.52%.Tests on the oil plug of transmission shaft in the turbofan engine,the protected aluminum mirror and the end face of the optical fiber also show that this algorithm has higher measurement accuracy and better performance in measurement repeatability.The main research results involved in this article include:1.A white light interferogram model under the influence of noise is established.The model divided the noise into two parts: systematic noise and random noise.The two parts of noise are taken into consideration in the model according to the performance of influence.2.A white light interference signal processing algorithm with higher accuracy and lower repeatability error is designed.This algorithm analyzes the white light interference signal model under the influence of noise,and uses a pair of unit orthogonal bases that dynamically change with the sampling ordinal number to decompose the one-dimensional white light interference signal into the two-dimensional signal space,and then the two-dimensional signal is demodulated to calculate the phase of wavefront.Finally,the height of the envelope obtained by Fourier transform was used to convert the wavefront phase information to the precise surface topography.3.A white light profiler is set up using the proposed algorithm.The equipment is compact in structure,easy to use,and has the advantages of low production cost,high measurement accuracy,and good repeatability.It is equipped with self-designed measurement software,which can meet the surface measurement needs of aero-engine precision parts,optical components,and MEMS(Micro-Electro-Mechanical System).