Optical Fiber Preform Manufacturing via Dual-Stage Alkali Metal Salt Drying
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Solution Overview
Problem
Conventional optical fiber preform manufacturing methods face difficulties in doping multiple alkali metal elements within the intended concentration range, leading to insufficient reduction of Rayleigh scattering loss and high OH loss in the optical fiber, particularly with a peak absorption loss exceeding 2 dB/km at a wavelength of 1.38 µm.
Innovation Solution
The method involves a multi-step process including first and second drying steps for alkali metal salt raw materials, followed by thermal diffusion within a silica-based glass pipe, where the materials are heated to generate vapor and undergo oxidation, allowing for the precise diffusion of multiple alkali metal elements, and subsequent core rod fabrication and cladding addition to reduce losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional diffusion method is used to dope alkali metal elements, then the viscosity of core portion can be lowered, but it is difficult to dope each alkali metal element within intended concentration range and OH loss increases
Solution Approach 1:
The drying process is divided into two distinct stages: first drying at temperature ≤ lowest melting point of all alkali metal salts, then second drying at temperature ≥ highest melting point but with controlled vapor pressure ≤ 266.645 Pa. This segmentation allows selective evaporation and diffusion of different alkali metal elements based on their melting points and vapor pressures, enabling precise concentration control while preventing OH group formation.
Solution Approach 2:
The invention changes the temperature and vapor pressure parameters during the drying process to achieve different diffusion rates for different alkali metal elements. By controlling the second drying temperature to be at or above the highest melting point but maintaining vapor pressure at or below 266.645 Pa, the process optimizes the diffusion of multiple alkali metals simultaneously, achieving intended concentration ranges while minimizing OH loss.
2Loss of energy
If two or more kinds of alkali metal elements are doped to reduce Rayleigh scattering loss, then transmission loss can be reduced, but it becomes difficult to control the concentration of each element within intended range
Solution Approach 1:
The drying process is divided into two distinct stages: first drying at temperature ≤ lowest melting point of all alkali metal salts, then second drying at temperature ≥ highest melting point but with controlled vapor pressure ≤ 266.645 Pa. This segmentation allows selective evaporation and diffusion of different alkali metal elements based on their melting points and vapor pressures, enabling precise concentration control while preventing OH group formation.
Solution Approach 2:
The invention changes the temperature and vapor pressure parameters during the drying process to achieve different diffusion rates for different alkali metal elements. By controlling the second drying temperature to be at or above the highest melting point but maintaining vapor pressure at or below 266.645 Pa, the process optimizes the diffusion of multiple alkali metals simultaneously, achieving intended concentration ranges while minimizing OH loss.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the manufacturing of optical fibers with reduced Rayleigh scattering and OH losses, achieving a transmission loss increase of 1.0 dB/km or less due to OH group absorption at 1.38 µm, thereby improving the optical fiber's performance.
Implementation Method 1
the two or more kinds of alkali metal salt raw materials are simultaneously heated to generate vapor of the two or more kinds of alkali metal salt raw materials
Implementation Method 2
vapor and a carrier gas generated from one end side of the glass pipe are supplied to the inside of the glass pipe so as to cause an oxidation reaction of two or more kinds of alkali metal elements contained in the vapor
Implementation Method 3
a thermal diffusion step... a step of thermally diffusing two or more kinds of alkali metal element oxides on an inner surface of a silica-based glass pipe
Data Source
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AI summary
The present embodiment relates to an optical fiber preform manufacturing method in which two or more kinds of alkali metal elements are diffused and doped to an inner surface of a glass pipe. The manufacturing method includes: a first drying step performed at a temperature equal to or lower than a lowest temperature among melting point temperatures of the alkali metal salt raw materials; and a second drying step performed at a temperature which is equal to or higher than a highest temperature among the melting point temperatures of the alkali metal salt raw materials and at which vapor pressures of the alkali metal salt raw materials are 2 mmHg or lower.