Fiber bundle based probe with polarization for coherent anti-Stokes Raman scattering microendoscopy imaging

The ability to visualize cellular structures and tissue molecular signatures in a live body could revolutionize the practice of surgery. Specifically, such technology is promising for replacing tissue extraction biopsy and offering new strategies for a broad range of intraoperative or surgical applications, including early cancer detection, tumor margin identification, nerve damage avoidance, and surgical outcomes enhancement. Coherent anti-Stokes Raman scattering (CARS) microendoscopy offers a way to achieve this with label-free imaging capability and sub-cellular resolution. However, efficient collection of epi-CARS signals and reduction of nonlinear effects in fibers are two major challenges encountered in the development of fiber-based CARS microendoscopy. To circumvent this problem, we designed and developed a fiber bundle for a CARS microendoscopy prototype. The excitation lasers were delivered by a single multimode fiber at the center of the bundle while the epi-CARS signals were collected by multiple MMFs surrounding the central fiber. A polarization scheme was employed to suppress the four-wave mixing (FWM) effect in the excitation fiber. Our experimental results suggest that, with this fiber bundle and the polarization FWM-suppressing scheme, the signal-to-noise ratio of the CARS images was greatly enhanced through a combination of high collection efficiency of epi-CARS signals, isolation of excitation lasers, and suppression of FWM. Tissue imaging capability of the microendoscopy prototype was demonstrated by ex vivo imaging on mouse skin and lung tissues. This fiber bundle-based CARS microendoscopy prototype, with the polarization FWM-suppressing scheme, offers a promising platform for constructing efficient fiber-based CARS microendoscopes for label free intraoperative imaging applications.