Bend Insensitive Single Mode Optical Fiber Trench Cladding
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Solution Overview
Problem
Conventional optical fibers face challenges in achieving high bending resistance and long service life, especially at small bend radii, due to limitations in macro-bending performance and compatibility with existing standards like G.657.B3, which requires a balance in mode field diameter, cut-off wavelength, and refractive index profiles.
Innovation Solution
A bend-insensitive single-mode optical fiber design with a core and trench cladding layer structure, optimized by adjusting the diameters and refractive index differences of the core, inner cladding, and trench cladding layers, along with fluorine and germanium doping, to enhance bending resistance and maintain effective mode field diameter, while reducing fabrication costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the mode field diameter is reduced to improve bending performance, then macro-bending loss decreases, but connection loss with conventional single-mode optical fiber increases and incident optical power is limited
Solution Approach 1:
The patent applies local quality by creating a trench cladding layer with specific refractive index characteristics localized at a particular radius from the core center. This localized structural modification allows the fiber to achieve superior bending performance in specific regions without compromising the overall mode field diameter, thereby maintaining compatibility with conventional single-mode fibers while improving macro-bending resistance.
2Reliability
If the cut-off wavelength is increased to improve bending performance, then macro-bending loss decreases, but the space for wavelength optimization is limited and full band transmission cannot be achieved
Solution Approach 1:
The patent employs parameter changes by modifying the refractive index profile through the introduction of a trench cladding layer with specific relative refractive index difference (Δ3 between -0.003 and -0.007). This parameter adjustment allows the cut-off wavelength to be controlled within the range of 1260-1350 nm, achieving both improved bending performance and full band transmission capability across C, L, and S bands.
3Reliability
If a trench cladding layer with larger diameter is used to improve bending resistance, then macro-bending performance improves, but the effective area and mode field diameter may be affected
Solution Approach 1:
The patent applies another dimension by positioning the trench cladding layer at a specific radial distance (10-15 μm from core center) rather than simply increasing the overall cladding diameter. This spatial arrangement in the radial dimension allows the trench to provide bending resistance through its refractive index contrast while maintaining the effective mode field area within the core and inner cladding region.
Data Source
AI summary
In one aspect of the invention, the bend insensitive single-mode optical fiber includes a core layer and cladding layers having an inner cladding layer, a trench cladding layer and an outer cladding layer sequentially formed surrounding the core layer from inside to outside. For the core layer, the diameter is 7-7.9 μm, and the relative refractive index difference Δ1 is between 4.6×10−3 and 6.5×10−3. For the inner cladding layer, the diameter is 16.5-20 μm, and a relative refractive index difference Δ2 is between −3×10−4 and 3×10−4. For the trench cladding layer, the diameter is 33-40 μm, and the relative refractive index difference Δ3 is between −2.9×10−3 and −7.3×10−3, changes in a gradient manner and increases gradually from outside to inside, where a relative refractive index difference Δ32 at an outermost interface is smaller than a relative refractive index difference Δ31 at an innermost interface.