Dynamic focus control in high-speed optical coherence tomography based on a microelectromechanical mirror

In high-resolution optical coherence tomography (OCT), a high numerical aperture sample lens is required to achieve high lateral resolution. This situation leads to a limited depth of focus, which can yield sub-optimal lateral resolution outside the focal zone for deep-imaging OCT systems. To maintain high transverse resolution over the entire depth scan, we designed a high-speed dynamic focus control system based on a microelectromechanical mirror. The silicon nitride deformable mirror shifted the focus of the sample beam of the OCT interferometer in synchrony with the coherence-gate scan in the reference arm. As a result, the coherence gate remained at the beam focus during the whole imaging process. The prototype focus control setup was integrated into a high-speed (8 kHz depth scan frequency) OCT system. Improvement to the image quality was demonstrated with a standard resolution target. (C) 2004 Published by Elsevier B.V.