Subwavelength imaging of an etched fiber with an intracore Bragg grating by apertured photon scanning tunneling microscope

Abstract

Apertured photon scanning tunneling microscopy (APSTM) was used to image the internal structure of an etched optical fiber with an intracore Bragg grating. Direct evidence of the subwavelength periodic variation of the index of refraction along the fiber is obtained by probing evanescent field intensity modulated by the etched fiber grating structure. The images we observed suggests local non-uniformity in the grating structure. Local anomalies appear in the values of the grating spacing. The modulation of the evanescent field intensity originates from variations in the index of refraction as well as from surface structure induced by etching of the fiber.