Optical Module Fiber Feedthrough Compression Seal
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Solution Overview
Problem
Conventional optical fiber feedthrough designs face challenges with high costs and potential damage to fibers due to the use of metal or glass solders for hermetic sealing, which introduce stress and weaken the optical fibers.
Innovation Solution
The use of a ceramic ferrule with a closely matched inner diameter to the optical fiber, sealed with a low-viscosity epoxy adhesive and glass solder, eliminating the need for high-temperature solder processes and reducing stress on the fibers, while a metal housing with a higher coefficient of thermal expansion provides a compression seal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal or glass solder is used to fill the gap between optical fiber and metal tube for hermetic sealing, then hermetic sealing is achieved, but the high compression force can cause damage or breakage in the optical fibers
Solution Approach 1:
The patent changes the material parameters by replacing metal/glass solder with epoxy adhesive, which has different mechanical properties (lower compression force, higher flexibility). This parameter change allows the seal to maintain hermeticity while reducing stress on the optical fiber, preventing fiber damage.
Solution Approach 2:
The patent uses a composite sealing structure consisting of multiple materials: the metal tube provides structural support, the epoxy adhesive provides hermetic sealing with low stress, and the glass sleeve provides additional protection. This composite approach combines the advantages of each material to achieve both hermetic sealing and fiber protection.
2Reliability
If high-temperature solder process is used to create hermetic seal, then hermetic sealing is achieved, but the process may weaken the optical fiber and add stress upon cooling
Solution Approach 1:
The patent changes the temperature parameter by replacing high-temperature soldering (typically >400°C) with low-temperature epoxy curing (typically 50-150°C). This temperature reduction prevents thermal damage to the optical fiber and eliminates thermal stress during the sealing process.
Solution Approach 2:
The patent replaces expensive, complex high-temperature soldering processes with a simpler, lower-cost epoxy bonding process. The epoxy provides sufficient hermetic sealing without requiring the expensive equipment and precise control needed for high-temperature soldering.
3Ease of manufacture
If metal tube with large inner diameter is used, then manufacturing is easier, but gap filling with solder is required to create hermetic seal
Solution Approach 1:
The patent extracts the gap-filling function from the sealing process by using a glass sleeve that fits tightly around the optical fiber. This eliminates the need to fill the gap between the fiber and metal tube with solder, simplifying the sealing structure while maintaining hermeticity.
Solution Approach 2:
The patent introduces a glass sleeve as an intermediary component between the optical fiber and metal tube. This sleeve acts as a mediator that provides both mechanical support and hermetic sealing, eliminating the need for complex solder filling operations.
4Reliability
If optical fiber is metalized to enable soldering, then hermetic sealing is achieved, but cost increases and fiber strength may be reduced
Solution Approach 1:
The patent extracts the metalization step from the manufacturing process by using epoxy adhesive that can bond directly to the optical fiber coating without requiring metallic deposition. This eliminates the costly and time-consuming metalization process while maintaining sealing effectiveness.
Solution Approach 2:
The patent replaces the mechanical/thermal bonding mechanism of soldering with a chemical bonding mechanism using epoxy adhesive. This substitution allows direct bonding to the fiber coating without metalization, reducing cost and complexity.
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 reduces the risk of fiber damage, lowers production costs, and maintains a hermetic seal with improved optical-electrical performance by minimizing residual stress and using more affordable materials.
Implementation Method 1
a glass solder filling a gap between the ferrule and the section of the housing and being under compression by the section of the housing due to a difference in the first and second CTEs forming a hermetic seal
Implementation Method 2
an adhesive hermetically sealing the optical fiber in the longitudinally extending passage
Data Source
AI summary
A molded ceramic or glass ferrule has at least one longitudinal passage, which enables an optical fiber feed through, sealed into a metal housing with glass solder. The metal material in the housing has a slightly higher coefficient of thermal expansion (CTE) than the ferrule material and the sealing glass so that hermetic seal is maintained by a compression stress applied to the ferrule and sealing glass by the housing at operating conditions. When the housing has to be fabricated from a low CTE material, e.g. metal or ceramic, a metal sleeve and stress relief bracket is used to apply the compression stress.