Stray light analysis and suppression of rigid endoscope system

On the structure of optical system, the causes of stray light of a rigid endoscope and its suppression methods were explored to eliminate the stray light and to improve its imaging performance. Firstly, the stray light in the optical and mechanical system was simulated and analyzed by ray tracing in Lighttools. By analysis of the stray light path, it points out that the stray light of the optical system comes from the total reflection of a relay system and an objective system. Then, with the possible causes, the suppression methods for the stray light were proposed, including adjusting objective structure and controlling ray path. Finally, a rigid arthroscopy with a Field of View (FOV) of 70° and an outer diameter of 2.7 mm was designed to suppress the stray light. With proposed methods, the Modulation Transfer Function (MTF) reaches diffraction limit, the values of all fields are higher than 0.4 at 100 lp/mm, and the size of spot diagram is smaller than 4 μm. Besides the high-definition imaging, simulation demonstrates that the stray light has been moved out entirely in the optical system, and the system shows excellent imaging quality.