Fluorine has become an important dopant in MCVD method

which is used to make a variety of single-mode optical fibers with inner cladding refractive index depression. Experiment shows that the refractive index depression due to the dopping of CCl

2

F

2

is proportional to the flow of CCL

3

F

2

. The deposition efficiency of SiO

2

is corresponding to the optical flow of CCl

2

F

2

. When excessive flow of CCl

2

F

2

is used

the formation of SiF

4

will decrease the deposition efficiency of SiO

2

.Therefore

suitable flow of CCl

2

F

2

will assit to increase the deposition rate and velocity of single-mode preforms and bring down the cost of the optical fibers.