Nondestructive analysis of the transverse structure of novel optical fibers by third-harmonic-generation microscopy

We demonstrate the suitability of the third-harmonic-generation technique as a new nonlinear microprobe for nondestructive determination of the index profile of optical fibers. Photonic bandgap (Bragg-type) and air-silica microstructure (ASM) fibers were tested. The complete spatial characteristics, such as hole diameter and spacing into ASM fibers or sandwiched layer thickness into Bragg fibers, were demonstrated to be attainable anywhere along a bare fiber.