Design and analysis of polarization detection system for rail defects based on Q-type aspherical surface

Railroad track defects can lead to track breakage, train slowdown and other negative impacts, so in the "14th Five-Year Plan" under the railroad track defect detection is particularly important. In this study, we designed a polarization detection optical imaging system based on Q-Type aspherical surface through Zemax software: a CMOS image sensor of 8.45mm*7.07mm with an object-square telecentric lens and a focal length of 50mm is used. Optical parameters such as cutoff frequency were calculated to evaluate the difficulty of systematic aberration correction. Plated metal wire grids on the CCD to safeguard image quality. The Q-Type aspherical surface is introduced to optimize the higher order aberration. The experimental results show that the MTF plot, field curvature distortion plot, dot column plot, energy bracketing plot, relative illumination plot, and wavefront plot are good for evaluating the image quality of the system at a working distance of 70mm ± 2mm. Under this evaluation, the image quality results are excellent. It can perform well under ambient temperatures of 20-70°C, overcoming the influence of strong reflected light on the railroad track surface with higher clarity. Additionally, it can complete defect detection stably in colleges and universities.