Optical fibers

Presented to:

Engr. Abdul Waheed Khawaja

Presented by:

Muhammad Faisal Bashir

Melting Methods

Vapor-phase Deposition Methods

Outside Vapor-phase oxidation methodVapor axial deposition methodModified chemical vapor deposition methodPlasma-activated chemical vapor deposition method

Fiber fabrication methods

In this diagram we see how preform is made.A seed rod is slowly rotated and pulled upwards.As the seed rod is pulled, two burners deposit fine glass soot.The lower burner deposits core glass material.Above is burner depositing the cladding glass material.Rate at which seed rod is pulled is determined by servomechanism.

Lower burner : O2 + H2 + metal halide vapors (e.g. SiCl4, GeCl4 etc.)

Upper burner: O2 + H2 + metal halide vapors (e.g. SiCl4, BBr3 etc.)

Preform temperature ~ 1100o C degree

Any water vapor in the preform is removed through the following reaction: SOCl2 + H2O S O2 + 2HCl

Materials & Temperature

The porous preform is then heated to about 1500o C in a carbon furnace where it is sintered into a transparent solid glass rod.

• A central axis of the first torch is inclined w.r.t. vertical axis at an acute angle.

• A flame is thrown to the end of the soot preform to grow the core downwardly from the end of the soot preform.

• The torch provides a glass raw material such as SiCl4 and GeCl4 and fuel material in which hydrogen and oxygen are mixed.

• The soot is generated by the hydrolysis of the raw material in the thrown flame. Reactions:SiCl4 + 2H2O SiO2 + 4HClGeCl4 + 2H2O GeO2 + 4HCl

• The second torch is upwardly separated from the first torch. • The second torch’s central axis is inclined w.r.t. verticalaxis at an acute angle. • The second torch grows the clad on the circumferentialface of the core. • The second torch provides a glass raw material such as SiCl4 and GeCl4 and fuel material in which hydrogenand oxygen are mixed. • The soot is generated by the hydrolysis of the glass rawmaterial in the thrown flame.• For illustrative purposes only, GeO2 or P2O5 increases a refractive index and F or B2O3 reduces the refractiveindex.

• A good control over the index profile may be achieved with germania-doped cores.

• Graded-index fiber with an attenuation level less than 0.5 dB/km at 1.3 micrometer has been produced by this method.

• Optical characteristics of an optical fiber acquired from the soot preform and the surface temperature of a portion in which soot deposition is performed.

Important points:

Drawing

• After the fiber is pulled from the preform, a protective coating is applied very quickly after the formation of the hair-thin fiber (Figure).

• The coating is necessary to provide mechanical protection and prevent the ingress of water into any fiber surface cracks. The coating typically is made up of two parts, a soft inner coating and a harder outer coating.

• The overall thickness of the coating varies between 62.5 and 187.5 µm, depending on fiber applications.

United States Patent Application Publication (publication no. US 2007/0151298 A1)

Fiber Optics and Optoelectronics by R.P. Khare (OUP)

References