Optical design of a line-focused forward-viewing scanner for optical coherence tomography

Abstract

We report an optical design of a line-focused forward-viewing optical coherence tomography (OCT) scanner for high-speed endoscopic imaging. To avoid a complex lens system, an off-axis cylindrical mirror is used for focusing the line illumination onto the sample surface. Because of its insensitivity to the broadband spectrum, the mirror-focused scanner improves the image quality compared to a lens-focused scanner. In this work, a feasibility study is carried out on the use of a reflective-optics-focused line scanner in OCT imaging, instead of the traditional refractive optics scanner. The Strehl ratio, chromatic focal shift, and field analysis were carried out for a plano-convex cylindrical lens, an achromatic cylindrical lens, and a cylindrical-mirror-focused scanner. ZEMAX optical modeling analysis showed that mirror-focused scanning provides better Strehl ratio in comparison to plano-convex cylindrical-lens-focused scanning, and that the Strehl ratio is comparable to achromatic cylindrical-lens-focused scanning. However, field analysis on the edges of the scanning elements within the scan range shows that mirror-focused scanning is more robust when compared to a cylindrical achromatic lens. Overall, a mirror-focused scanner shows better performance compared to lenses.