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Fiber fabrication

Fiber fabrication. Double crucible method:. The molten core glass is placed in the inner crucible. The molten cladding glass is placed in the outer crucible. The two glasses come together at the base of the outer crucible and a fibre is drawn.

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Fiber fabrication

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  1. Fiber fabrication

  2. Double crucible method: • The molten core glass is placed in the inner crucible. • The molten cladding glass is placed in the outer crucible. • The two glasses come together at the base of the outer crucible and a fibre is drawn. • Long fibres can be produced (providing you don't let the content of the crucibles run dry!). • Step-index fibres and graded-index fibres can be drawn with this method.

  3. Rod-in-Tube method: • A rod of core glass is placed inside a tube of cladding glass. The end of this assembly is heated; both glass are softened and a fibre is drawn. • Rod and tube are usually 1 m long. The core rod has typically a 30 mm diameter. The core glass and the cladding glass must have similar softening temperatures. • However, one must be very careful not to introduce impurities between the core and the cladding.

  4. Modified Chemical Vapour Deposition: • Chemicals are mixed in vapour phase and react inside a glass tube rotating on a lathe. Fine particles of solid germano or phosphoro silicate glass deposit on the inside of the tube. • A travelling burner moving along the tube stimulates a chemical reaction and also fuses the particles into glass on the inner wall of the tube. • Outer cladding layers are deposited first, then core layers further in. • Next the tube is heated to 2000 C and collapses into a “preform” • The preform is then put into a furnace and is drawn into fibre.

  5. Modified Chemical Vapour Deposition:

  6. Plasma activated chemical vapor deposition • Similar to MCVD process in that deposition occurs within a silica tube. • However, a nonisothermal microwave plasma operating at low pressure initiates the chemical reaction. • With the silica tube held at temperatures in the range of 1000 - 1200C to reduce mechanical stresses in the growing glass films, a moving microwave resonator operating at 2.45GHz generates a plasma inside the tube to activate the chemical reaction. • This process deposits clear glass material directly on the tube wall, no soot formation. • No sintering required. • Once the deposition results in the desired glass thickness, the tube is collapsed into a preform just as in the MCVD case.

  7. The deposition is slow, but very precise. A modified method with particularly high precision is plasma impulse chemical vapor deposition (PICVD), where short microwave pulses is used.

  8. PCVD SiCl4+GeCl4+C2F6+O2 Furnace Resonator Plasma Magnetron Silica Tube Pumping system There is also plasma-enhanced chemical vapor deposition (PECVD), operating at atmospheric pressure with fairly high deposition rate.

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