Shanghai Opto-mechanical Institute applies time-domain speckle technology to large-scale optical component measurement

[ Instrument Network Instrument Development ] Zhou Changhe Research Group, Information Optics and Optoelectronic Technology Laboratory, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, recently combined binocular measurement and time domain speckle technology for 300mm caliber large-size lens blank measurement and successful reconstruction The three-dimensional shape of the surface of the lens blank. This method enables fast, low-cost measurements of large-size lenses, and the results are published on Optics Express 27, 1098 (2019).

Binocular 3D measurement system structure

Large-sized optical components, especially aspherical components, are widely used in large-scale laser devices, such as the "Shenguang" II integrated experimental laser device. Surface inspection is critical during the production of components. In the rough grinding stage of the lens blank, the main testing device is a coordinate measuring machine. The measurement accuracy of the coordinate measuring machine is very high, but the efficiency of this point-by-point measurement method is low, especially when measuring large-size (for example, meter-level) lens blanks, large-scale coordinate measuring machines are expensive and difficult to move, which is inconvenient. use.

The research group proposed to reconstruct the surface of the lens rough by the binocular optical three-dimensional measurement method. The binocular vision principle is similar to the three-dimensional perception of the human eye. Cameras placed at different angles at different angles can be used to simultaneously capture the surface image of the blank. After homologous point matching and parallax calculation, the surface of the blank can be reconstructed in three dimensions by triangulation. However, due to the strong scattering characteristics of the lens blank, the spatial optical domain-based structured optical coding method may exhibit decoding errors. The research team proposed time-domain coding using time-domain speckle technique. In the experiment, 20 band-pass random digital speckle images were sequentially projected. For each pixel, there is a 20-dimensional code. By comparing the Hamming distance between the left and right to-be-matched point code values, a pair of homologous points can be found in the direction of the polar line. Polarization techniques, on the other hand, are used to eliminate multiple reflection problems in lens blanks. In the end, the 3D point cloud data of the audience was successfully reconstructed in a short time.

Compared with the coordinate measuring machine, this method realizes the fast, full-field and low-cost three-dimensional measurement of the surface of the lens blank. It is a promising measurement method, especially for the measurement of the lens blank of the meter size. .

The research results were supported by the Key Science Research Project of the Frontier Science of the Chinese Academy of Sciences, the Professional Technical Service Platform Project of the Shanghai Science and Technology Commission, and the Shanghai Natural Science Foundation Project.

(Original title: Shanghai Opto-mechanical Institute applies time-domain speckle technology to large-scale optical components)