Liquid lens-based endoscopic OCT probe with adjustable focus for 3D imaging in cross-sectionally irregular lumens

For imaging and inspecting lumens in industrial components, endoscopic optical coherence tomography (OCT), with its high resolution and compact probe, is a promising method. The majority of OCT probes possess a fixed depth of field (DOF) and suffer from missing point clouds when measuring cross-sectionally irregular lumens, limiting their application scenarios. To address this problem, we developed an endoscopic OCT probe that incorporates dual electrically tunable liquid lenses for dynamic focal length adjustment, making the system adaptable for imaging irregularly shaped lumens. Furthermore, an automated focus tracking method was developed to adjust (1) the focal position of the probe, thereby ensuring continuous alignment with target surfaces, and (2) the optical path length of the reference arm to sustain optimal interference conditions, guided by feedback derived from the depth information of interference signals. Experimental results demonstrated that the probe with adjustable focus achieved a lateral resolution of better than 20 <i>μ</i>m within a DOF range of 10-40 mm. Tests on diverse cross-sectionally irregular lumens confirmed the effectiveness of the proposed method.