Reflection properties of guided wave in fiber taper for scanning near-field optical microscopy

The local mode-coupled model was used to analyze theoretically the light field property of fiber taper in scanning near-field optical optical microscopy. Differential equations of the forward and backward fundamental mode fields in fiber taper were given. The backward coupling coefficient of fundamental mode was obtained numerically, and it can reach about 1% at most. The reflection makes the fiber taper act as an output mirror of tapered fiber laser resonator. The parabolic taper has a lower reflected coupling coefficient than the truncated taper. The experimental results of the reflection wave from fiber probe were reported.