Compact dark-field confocal microscopy based on an annular beam with orbital angular momentum.

This study proposes a dark-field confocal microscopy (DFCM) based on fiber-mode excitation-assisted orbital angular momentum annular beam generation with a two-mode fiber to avoid diffraction distortion. The application of optical fibers compresses the DFCM volume, providing new ideas for system miniaturization. System adjustment difficulty is reduced and feasibility is verified by imaging 2D and 3D samples. High imaging contrast is achieved by fully blocking the reflected light and annular illumination with a steady central dark-spot within a propagation distance of 3 m. The application of our scheme can be further extended to detect subsurface defects in optical components and high-contrast biological imaging.