Optical Fiber Preform Thermal Stress Reduction
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Solution Overview
Problem
Existing methods for producing optical fiber preforms are prone to cracking at the tapered portions due to density issues and thermal stress during thermal treatment, which current countermeasures fail to adequately address.
Innovation Solution
A production method involving forming a porous preform by depositing silica particles around a core rod, followed by a thermal treatment process where the end portions are heated before the center, using a multi-stage-heating or stroke-type vitrification furnace to control temperature differences and reduce stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermal shrink is increased at the tapered portion to increase silica particle density, then cracking is restrained, but core decentralization occurs
Solution Approach 1:
The thermal treatment process is segmented into multiple stages with different temperature profiles for different portions of the preform. The tapered portions receive different thermal treatment compared to the central parallel portion, allowing density improvement at tapered portions without affecting core positioning in the central region.
Solution Approach 2:
Different thermal treatment conditions are applied to different locations of the preform. The tapered portions undergo thermal shrink treatment to increase density and prevent cracking, while the central portion maintains conditions that preserve core positioning accuracy.
2Stability of the object's composition
If thermal treatment is applied to vitrify the porous preform, then the preform structure is stabilized, but thermal stress causes cracking at tapered portions
Solution Approach 1:
The preform undergoes preliminary thermal treatment stages before final vitrification. Initial thermal treatment at controlled temperatures prepares the preform structure and reduces thermal stress accumulation, preventing cracking during subsequent high-temperature vitrification.
Solution Approach 2:
The thermal treatment process uses periodic heating cycles with multiple stages. Temperature is increased in steps with holding periods, allowing stress relaxation at each stage and preventing thermal shock that would cause cracking.
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 method significantly reduces the occurrence of cracking in the optical fiber preform, achieving a cracking rate of less than 0.1% by controlling temperature gradients and stress release during thermal processing.
Implementation Method 1
forming a porous preform by depositing silica particles at an outer periphery of a core rod
Implementation Method 2
vitrifying the porous preform by conducting thermal treatment steps
Implementation Method 3
the porous preform is heated so that internal temperatures at two end portions in a longitudinal direction of the porous preform increase before an internal temperature of a center portion in the longitudinal direction increases
Data Source
AI summary
A production method of an optical fiber preform includes: forming a porous preform by depositing silica particles at an outer periphery of a core rod; and vitrifying the porous preform by conducting thermal treatment steps. At a first thermal treatment step that is an initial thermal treatment step of the thermal treatment steps, the porous preform is heated so that internal temperatures at two end portions in a longitudinal direction of the porous preform increase before an internal temperature of a center portion in the longitudinal direction increases.