Research Of Optical Centering Technology Based On Joint Transform Correlator

With the development of science and technology, optical lenses are widely used in the aerospace, national defense and military, industrial detection, semiconductor industry and other domains with increasing severe requirements of optical performance. It has bacame a key issue controlling the lens centering errors in the process of lens fabricating and assembly. Lens centering error is one of the main factors affecting the performance of the optical lens, and it cannot be ignored during the entire process of lens edging, gluing, testing and assembly, and optical system performance detection. Systems with extremely high performance requirements such as satellite photogrammetric calibration system and projection lithographic lens claim severely on assembly errors, and the centering error needs to be small enough. Conventional optical alignment methods cannot meet the requirements of such high-performance optical lens alignment any more, so in this paper we have designed a high-precision centering error control device aiming at assembling the large NA lithographic lens. The main contents are as follows:Firstly, comparing the domestic and foreign related equipment products and analyzing the centering error measurement instruments, several basic methods of measuring the lens centering error are summarized;Secondly, establish a mathematical model to calculate the centering error of lenses consisting of several surfaces, and analyze the impact of the cumulative centering error. By calculating the image position of the sphere centering and the lateral magnification of each surface, express the centering error of the under tested surface as the function of the centering error of other surfaces and the lateral magnification of every single surface. this model can effectively remove the impact of cumulative centering error of other surfaces during the detection;Thirdly, comparing kinds of methods detecting lens center error, we choose a reflective self-collimation way to detect the centering error. We have designed the measuring system and analyze the imaging quality of the system and the results show that the system can meet the requirements. And energy calculation and source selection have been done;Fourthly, a lens centering error measurement method based on optical joint transform correlator(JTC) is proposed, which is irrelevant with the specific forms of the reticle pattern plate. Through correlation operation between the target images and the reference image, sub-pixel detection of the image displacement measurement can be reached and by data fitting, high-precision measurement of centering error can be achieved. A two-phase encoded joint transform correlation algorithm is proposed based on the conventional JTC algorithm; the correlation output plane from the new algorithm retains only one cross-correlation peak which improves the measurement efficiency;Lastly, the main factors that influence the system precision in theory are analyzed, which mainly contains spindle error, magnification error, data processing error, the error of the optical system and the environment errors; Instrument repeatability evaluation experiment is carryed out and results show that the centering error measurement repeatability is ±0.7995 μm; In addition, we verify the effectiveness of the two-phase encoding based on the principle of centering Joint Transform Correlation technology by means of experiment, and compare the centering error control device we designed with the LAS(Laser Alignment and Assembly Station), and experimental results show that the use of the principle of joint transform correlator lens center deviation measurement is valid, the measurement error is less than LAS measurement error under the same conditions.