Optical Fiber LP11 Attenuation Loop Design
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Solution Overview
Problem
Existing optical fibers with small loop diameters attenuate the fundamental mode (LP01) and decrease mechanical reliability, while there is a need to propagate electromagnetic radiation in only the fundamental mode (LP01) while suppressing higher order modes to prevent dispersion and signal degradation.
Innovation Solution
An optical fiber design featuring a positive index core region with specific dimensions and refractive index characteristics, a depressed index cladding region, and a first outer cladding region with a no-slope portion, which attenuates the first higher order mode (LP11) to a much greater degree than the fundamental mode (LP01) when looped, thereby enhancing mechanical reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the optical fiber is looped with small loop diameter to control bend radius and improve alignment, then coupling efficiency is improved, but the fundamental mode (LP01) is attenuated and mechanical reliability decreases
Solution Approach 1:
The patent applies local quality by creating a depressed index cladding region with specific refractive index characteristics (Δ3 from -0.45% to -0.30%) that is localized to a specific radial range (r2 < r < r3). This localized structural modification enables the fiber to tolerate small loop bends without excessive attenuation while maintaining differential mode attenuation properties. The depressed index region acts as a buffer that protects the fundamental mode from bend-induced losses.
Solution Approach 2:
The patent utilizes parameter changes by carefully controlling the refractive index profile parameters including the depressed index cladding region parameters (Δ3, r2, r3) and core region parameters (Δ1max, r1, α). By optimizing these parameters, the fiber achieves differential mode attenuation where LP11 is suppressed more than LP01 during looping, allowing small loop diameters to be used without excessive LP01 loss.
2Ease of operation
If the optical fiber is looped to control alignment, then coupling efficiency is improved, but higher order modes (LP11) are not sufficiently suppressed causing dispersion and signal degradation
Solution Approach 1:
The depressed index cladding region creates a localized refractive index modification that differentially affects mode propagation. The specific radial positioning and index depression level create conditions where LP11 modes experience higher attenuation than LP01 modes during looping, effectively suppressing higher order modes while preserving the fundamental mode for signal transmission.
Solution Approach 2:
The patent achieves differential mode attenuation by optimizing specific parameters of the refractive index profile. The depressed index cladding region parameters (Δ3 from -0.45% to -0.30%, outer radius r3 from 14 μm to 28 μm) and core parameters work together to create a mode-selective attenuation effect that suppresses LP11 while maintaining LP01 during looped configurations.
3Ease of operation
If conventional optical fiber structure is used with small loop diameter, then alignment is improved, but fundamental mode (LP01) attenuation increases
Solution Approach 1:
The depressed index cladding region provides localized refractive index modification that protects the fundamental mode from bend-induced attenuation. This localized structural feature allows the fiber to maintain low LP01 attenuation even when looped with small diameters for alignment control purposes.
Solution Approach 2:
The patent reduces LP01 attenuation in looped configurations by optimizing the refractive index profile parameters. The depressed index cladding region (Δ3 from -0.45% to -0.30%, outer radius r3 from 14 μm to 28 μm) and core region parameters create a profile that is resilient to bend losses, enabling small loop diameters to be used without excessive fundamental mode attenuation.
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 effectively suppresses the higher order mode (LP11) while maintaining low attenuation of the fundamental mode (LP01), even when looped, thus improving mechanical reliability and signal quality.
Implementation Method 1
an optical fiber includes: (1) a positive index core region... (2) a depressed index cladding region surrounding the core region... (3) a first outer cladding region
Data Source
AI summary
An optical fiber including: (1) a first outer cladding region including a no-slope portion establishing a 0% baseline (Δ0); (2) a core region surrounded by the first outer cladding region, the core region including (i) an outer radius (r1) from 4.0 μm to 6.5 μm and (ii) a maximum relative refractive index (Δ1max) from 0.3% to 0.6%, the core region exhibiting an α value of 5 or greater; and (3) a depressed index cladding region surrounding the core region and surrounded by the first outer cladding region, the depressed index cladding region including (i) an outer radius (r3) from 14 μm to 28 μm, (ii) a relative refractive index (Δ3) from −0.45% to −0.30%, and (iii) a trench volume (VT) from 65%-μm2 to 140%-μm2. The optical fiber exhibits lower LP01 bending loss than LP11 bending loss at operating wavelengths in the O- and C-bands.