Inner pressure control method in optical fiber preform fabrication by vapor-phase axial deposition

A method to control inner pressure variation in a vapor-phase axial-deposition (VAD) apparatus is developed. It uses a flame-detection technology to explain temperature fluctuations. Primary causes of the inner pressure fluctuations are analyzed, and suppression techniques are described. They include the adoption of a large buffer-tank and bias gas addition. An inner pressure-feedback control mechanism operates by adjusting the bias gas flow, keeping fluctuations of the inner pressure to less than half of that with no control.>