Optical Fiber Bridge for Low-Loss Splicing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional single mode fibers (CSMF) experience excessive connection loss when connected to semiconductor optical waveguides due to significant differences in mode field diameters, and existing methods using thermally expanded core (TEC) optical fibers do not sufficiently reduce this loss to 0.2 dB or less at fusion-splicing points.
Innovation Solution
An optical fiber design featuring a core doped with germanium as an updopant, an inner cladding doped with fluorine and germanium/phosphorus as updopants and downdopants, respectively, to achieve a refractive index increase rate within 0.25% to 0.5%, allowing the core to expand through thermal diffusion and reduce connection losses during fusion-splicing with CSMF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional single mode fiber (CSMF) is connected to a semiconductor optical waveguide, then the connection structure is simple, but the connection loss is excessively large due to mode field diameter mismatch
Solution Approach 1:
The patent introduces a bridge fiber as an intermediary component between the CSMF and semiconductor optical waveguide. This bridge fiber has a mode field diameter of approximately 4 μm, which serves as an intermediate value between the 10 μm CSMF and 1 μm waveguide, enabling gradual mode field transition and reducing connection loss at both interfaces
Solution Approach 2:
The connection path is segmented into three distinct sections: CSMF (10 μm mode field), bridge fiber (4 μm mode field), and semiconductor waveguide (1 μm mode field). This segmentation allows each interface to have optimized mode field matching, reducing overall connection loss compared to a direct connection
2Loss of energy
If the core of the optical fiber is expanded through thermal diffusion using conventional dopant concentrations, then the core expansion occurs, but the connection loss cannot be reduced sufficiently to 0.2 dB or less
Solution Approach 1:
The patent precisely controls the dopant concentration parameters in the bridge fiber core, specifically setting the germanium dioxide concentration to 2.0-4.0 wt% and fluorine concentration to 0.5-2.0 wt%. This parameter optimization enables the core to expand to the precise mode field diameter of 3.0-4.0 μm, achieving connection loss of 0.2 dB or less
Solution Approach 2:
The bridge fiber core uses a composite doping approach combining germanium dioxide (updopant) and fluorine (downdopant). This composite material strategy creates a refractive index distribution that facilitates controlled thermal diffusion and core expansion while maintaining the desired mode field characteristics
3Loss of energy
If the mode field diameter of the semiconductor optical waveguide is increased substantially to match the CSMF, then the connection loss is reduced, but a bridge fiber and additional fusion-splicing are required
Solution Approach 1:
Rather than expanding the waveguide mode field to match CSMF, the patent uses a bridge fiber with intermediate mode field diameter (4 μm) as a mediator. This allows the waveguide to maintain its original 1 μm mode field diameter while still achieving low connection loss through the gradual transition provided by the bridge fiber
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
The optical fiber design effectively reduces connection loss to 0.2 dB or less at fusion-splicing points, maintaining axial misalignment tolerance and achieving desired cutoff wavelengths and bending losses, while facilitating easier alignment with silicon waveguides.
Implementation Method 1
the core expands through thermal diffusion, because an updopant (i.e., additive for increasing a refractive index of quartz glass) added to form the core diffuses to surroundings of the core when being heated
Implementation Method 2
the core of the bridge fiber expands during fusion-splicing of the core to the CSMF or subsequent heating of the core
Data Source
AI summary
An optical fiber includes: a core that includes quartz glass doped with a core updopant; an inner cladding that includes quartz glass doped with a cladding updopant and a downdopant and that covers a circumferential surface of the core; and an outer cladding that includes quartz glass and that covers an outer circumferential surface of the inner cladding. A refractive index of the inner cladding is substantially equal to a refractive index of the outer cladding. The inner cladding contains the cladding updopant at a concentration such that a refractive index increase rate ascribed to the cladding updopant falls within a range of 0.25% to 0.5%.