Desensitization design of the off-axis three-mirror anastigmat freeform systems

Abstract

The off-axis three-mirror anastigmat (TMA) systems are widely used in optical telescopes because of the advantages of non-obscuration and large field of view (FOV). Combined with optical freeform surfaces, which have more optimization degrees of freedom (DOFs), hence with strong ability to correct aberrations, the off-axis TMA system can achieve higher optical performance. However, the off-axis TMA system has the shortcomings of high complexity of assembly and alignment, high error sensitivity, and high cost of manufacturing. Low error sensitivity optical systems, that is, the system has good robustness can resist the errors, reduce image quality degradation, and make the systems easy to achieve good imaging performance and reduce the cost of manufacturing simultaneously. Therefore, desensitization should be given sufficient attention in the design process of optical systems. In order to obtain an optical system with low error sensitivity and improve system achievability, we applied the low error sensitivity design method proposed by our team to desensitize off-axis TMA systems which use freeform surfaces. We compare these off-axis TMA systems with different freeform surface types and give the corresponding analysis, we obtained a freeform surface ranking that is conducive to reducing the error sensitivity in off-axis TMA systems. Using the desensitization design method proposed by our team, the error sensitivity of all the freeform off-axis TMA systems is reduced effectively.