Specialty Optical Fibers Handbook

the core center is 10 mm. Wet etch removes the cladding silica and fluorine-

doped silica isotropically. By fine control of the etching process, the tail of the

evanescent wave can be accessed from the direction of the fiber flat. By modify-

ing the cladding material close to the core–cladding interface, the waveguide

characteristics will be changed and consequently the propagation characteristics

and that of the guiding light will be also changed.

Besides the wet-etching fiber method, there are several other techniques to

access the evanescent wave in D-shape fibers, which include: tapering the fiber in

heat [40], heating the fiber to defuse the dopants in the core (e.g., germanium)

into cladding [42], etching to reduce the whole cladding diameter ...