A nonlinear optical microscope based on double-clad photonic crystal fibers

Nonlinear optical microscopy by using nonlinear optical effects such as two-photon absorption and second harmonic generation (SHG) exhibits advantages of intrinsic sectioning ability, direct imaging of highly polarisable structures, and deep optical penetration. To achieve a compact and miniature microscope, flexible fiber-optic components such as optical fibers and optical fiber couplers are usually integrated into the imaging system to replace complicated bulk optics. More recently, the emergency of photonic crystal fibers (PCF) has been a renaissance of fundamental research and development on optical fibers. Several attractive properties of double-clad PCF, including a large mode area in the core for single-mode delivery and high N.A. in the inner cladding for signal collection, may add a new dimension in the conventional fiber-optic nonlinear microscopy.