Multimode Optical Fiber Attenuator Design
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Solution Overview
Problem
Current optical attenuators in optical networks face challenges with improved attenuation properties and low bend losses, particularly in multimode optical fibers used for monitoring and adjusting optical signal power levels.
Innovation Solution
The development of a multimode optical fiber with a core portion having a graded relative refractive index profile and specific dopant concentrations, surrounded by a cladding portion with a low-index trench, to achieve enhanced attenuation and reduced bend losses across wavelengths from 800 nm to 1350 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional optical fibers are used in optical attenuators, then the device structure is simple, but the attenuation properties are insufficient and bend losses are high
Solution Approach 1:
The patent applies local quality by implementing a graded relative refractive index profile in the core portion where the refractive index varies locally from the centerline to the radius. This local variation in optical properties enables enhanced attenuation characteristics without requiring complex external structures, resolving the contradiction between improved attenuation properties and device complexity.
Solution Approach 2:
The patent changes physical parameters by specifying a graded relative refractive index profile with α value between 1 and 3, and by controlling dopant concentrations (up-dopant with graded concentration, attenuation dopant with constant or graded concentration). These parameter changes enable the fiber to achieve ≥0.5 dB/m attenuation while maintaining structural integrity and managing complexity.
2Reliability
If optical fiber has high attenuation (≥0.5 dB/m), then signal power control is improved, but bend losses increase
Solution Approach 1:
The patent implements local quality through a graded relative refractive index profile in the core portion, where the refractive index varies locally to confine optical modes more effectively. This local variation reduces mode coupling at bends, enabling the fiber to achieve ≥0.5 dB/m attenuation while minimizing bend-induced energy losses.
Solution Approach 2:
The patent uses composite material structures by combining multiple dopants (up-dopant with graded concentration, attenuation dopant with constant or graded concentration) within the core portion, and optionally a low-index trench layer. This composite doping strategy enables simultaneous achievement of high attenuation and low bend losses by balancing mode confinement and attenuation characteristics.
3Use of energy by moving object
If numerical aperture is increased (NA ≥ 0.15) for better signal collection, then light coupling efficiency improves, but attenuation control becomes more difficult
Solution Approach 1:
The patent applies parameter changes by precisely controlling the numerical aperture within the range 0.15 ≤ NA ≤ 0.25 through adjustment of the graded relative refractive index profile (α value between 1 and 3) and dopant concentrations. This parameter optimization enables sufficient light coupling efficiency while maintaining precise attenuation control through the structured refractive index variation.
Solution Approach 2:
The patent implements local quality through the graded refractive index profile that varies locally from the core center to the radius. This local variation allows the fiber to achieve adequate numerical aperture for light coupling while the gradual index transition provides precise control over attenuation characteristics, resolving the contradiction between coupling efficiency and attenuation control precision.
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 provides increased attenuation and improved bend performance, ensuring balanced optical signal output and reduced signal distortion, thereby enhancing the performance of optical attenuators in network nodes.
Implementation Method 1
a graded relative refractive index profile having a maximum relative refractive index ΔCmax and an α value greater than or equal to 1 and less than or equal to 3
Implementation Method 2
an attenuation dopant with a constant concentration from the centerline CL of the core portion to the radius rC of the core portion... an attenuation of the optical fiber for at least one wavelength between 800 nm and 1000 nm is greater than or equal to 0.5 dB/m
Data Source
AI summary
According to embodiments, an optical fiber may include a core portion comprising a radius rC, a centerline CL, a numerical aperture NA greater than or equal to 0.15 and less than or equal to 0.25, a graded relative refractive index profile having a maximum relative refractive index ΔCmax and an α value greater than or equal to 1 and less than or equal to 3. The core portion may include an up-dopant with a graded concentration from the radius rC to the centerline CL and an attenuation dopant with a constant concentration from the centerline CL of the core portion to the radius rC of the core portion. The optical fiber is multi-moded for wavelengths of light within a range from 800 nm to 1350 nm and an attenuation of the optical fiber wavelengths between 800 nm and 1000 nm is greater than or equal to 0.5 dB/m.