Development of Linear Astigmatism Free Confocal Off-axis Reflective Collimator for Automatic Alignment Device for Aviation

Our linear astigmatism-free confocal off-axis collimator comprises two off-axis mirrors and one flat mirror with an aperture size of 73 mm and a focal length of 1200 mm. The off-axis mirrors, along with all other opto-mechanical parts, will be fabricated from the same material, such as aluminum alloy 6061-T6. This concept inherently creates an athermalized structure, meaning the entire system expands or contracts by the same amount as the thermal coefficient of expansion, ensuring that the image remains consistently in focus. We approached this collimator’s design as if it were an astronomical telescope, reversing the optical path directions, and conducted tolerance analysis using Optic Studio (ZEMAX) to define the opto-mechanical design requirements. The collimator’s target or telescope imaging sensor size is 4 × 4 mm, with a required imaging resolution of 13.7 cycles/mm at a wavelength of 750 nm. To achieve this, we divided the full field (4 × 4 mm) into 3 × 3 subfields, ensuring that the average Modulation Transfer Function (MTF) value exceeds 10%. We performed Monte-Carlo Simulations 5000 times to determine tolerance ranges with a 90% confidence level. Furthermore, we conducted stray light analysis for our off-axis collimator design. In comparison to typical on-axis Cassegrain designs, where baffles block some parts of the target rays and reduce intensity, our designed confocal off-axis collimator accommodates baffles without obstructing any light from the target.