Evanescent field imaging of an optical fiber Bragg grating

We have investigated the evanescent field associated with an optical fiber Bragg grating using the subwavelength imaging properties of scanning near-f ield optical microscopy. Imaging of either the field distribution within th e grating, or the periodic refractive index changes along the grating can b e performed by tuning the launched light on or off the grating resonance. T hese measurements reveal nonuniformity in the resonant standing-wave patter n that occur due to phase errors in the refractive index profile of the gra ting under study. (C) 1999 American Institute of Physics. [S0003-6951(99)03 752-3].