FDTD analysis of a near-field optical fiber probe with a double tapered structure

Using the finite-difference time-domain method, we evaluated the performance of apertured near-field fiber probes with a double-tapered structure, which have exhibited, in recent experiments, a much higher collection efficiency of localized light in comparison with single-tapered probes. We clarified that this high collection efficiency could be attributed to the shortening of the cutoff region, and the efficient coupling to the guiding mode of the optical fiber. By reproducing the experimental results in terms of the spatial resolution and the collection efficiency as a function of the aperture diameter, our calculation was confirmed to be valid and useful for the design of probes in a variety of applications.