and protects the upper portion of the fiber 110 from damage from boe vapors as the etching process proceeds the initial outside cladding surface shown as dashed lines 103 decreases to the size shown by reference numeral 111 concomitantly the interface between the etching solution 109 and material 108 which forms a meniscus designated generally as 106 moves toward the center of the fiber to the position depicted by the line designated 107 the initial surface of the distal end of the fiber 110 is depicted as a dotted line 127 simultaneous with the etching of the cladding 102 as described above the core 101 which etches at a slower rate than the etching rate of the cladding 102 becomes a tapered core tip as shown by reference numeral 104 which protrudes from the etched end of the fiber 110 designated by reference numeral 128 the etching process is allowed to proceed so as to produce the form shown in fig2 where the cladding is etched to a taper designated by reference numeral 213 which meets the tapered surface of the tapered core tip 104 this requires a particular height 105 determined empirically as described below the initial interface 106 between the enchant 109 and the covering material 108 changes as described earlier and eventually disengages from the fiber 110 forming a flat surface designated by reference numeral 207 at this point the fiber 110 may be removed from the etching area and cleaned if necessary for use as an nsom probe tip the etched region of fiber 110 may be coated with a material for increasing the portion of a wave propagating within the core 101 as compared to the portion of the wave traveling outside the core 101 as an example the tapered core tip.