Specialty Optical Fibers Handbook

of X (X < 5), the GeO

2

-doped core etches at faster rate compared to fluorine-

doped silica cladding and pure silica cladding. As the concentration of HF in the

mixture decreases (X > 5), GeO

2

-doped core etches at a slower rate. The

fluorine-doped silica region etched at a faster rate than GeO

2

-doped core and

pure silica cladding and the rate is independent of the proportion of the con-

stituents of the etchant. The relatively different etch rates enable a selective etch

to the cladding and core according to the needs.

16.4.3 Standard Etching (Etch to Reach

Evanescent Field)

Because the etching rate is strongly dependent on the etching conditions,

accurate ...