Optical Fiber with Depressed Index Cladding for Low Microbending Losses
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Solution Overview
Problem
Existing optical fibers face challenges in achieving both low bend loss and low cable cutoff wavelength simultaneously, particularly in applications with tight bend radii and high power systems, where non-linear optical effects and attenuation degrade signal transmission.
Innovation Solution
The development of optical fibers with a central core region, inner cladding region, and outer cladding region, where the relative refractive indices are specifically configured to achieve a large mode field diameter and low microbending losses, using a refractive index profile that includes a depressed index cladding region and coatings with varying moduli to minimize mechanical disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the effective area is increased to reduce non-linear optical effects, then signal degradation from non-linear effects is reduced, but macrobending and microbending losses increase
Solution Approach 1:
The patent applies local quality by creating distinct regions with different refractive indices within the fiber structure. The core has a higher refractive index than the cladding, and the depressed index cladding region has a lower refractive index than the inner cladding region. This localized variation in optical properties allows the fiber to maintain a large mode field diameter while confining the optical mode effectively, thereby reducing both non-linear effects and bending losses simultaneously.
Solution Approach 2:
The patent employs composite material structure by combining multiple cladding regions with different refractive index characteristics. The inner cladding region, depressed index cladding region, and outer cladding region form a composite structure that works together to achieve the desired optical performance. This composite approach allows optimization of both mode field diameter and bending loss characteristics.
2Object-affected harmful factors
If the mode field diameter is increased to reduce non-linear optical effects, then signal transmission quality improves, but microbending-induced losses increase
Solution Approach 1:
The patent applies parameter changes by carefully controlling the refractive index values and their distributions across different fiber regions. The depressed index cladding region has a refractive index that is specifically lowered compared to the inner cladding region, creating a refractive index difference that enhances mode confinement. This parameter optimization allows the fiber to achieve both large mode field diameter and low microbending losses.
Solution Approach 2:
The depressed index cladding region acts as an intermediary between the inner cladding region and the outer cladding region. This intermediate layer with its lower refractive index helps to smoothly transition the optical mode while providing additional confinement, thereby reducing microbending losses even when the mode field diameter is large.
3Loss of energy
If the refractive index difference between cladding regions is increased to reduce microbending losses, then bending loss performance improves, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies segmentation by dividing the cladding region into multiple sub-regions (inner cladding, depressed index cladding, and outer cladding) with progressively different refractive indices. This segmentation allows each region to be optimized independently for its specific function while maintaining overall manufacturability. The stepwise refractive index profile is easier to manufacture than continuous gradients while achieving the desired performance.
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 fibers exhibit reduced microbend-induced attenuation, maintaining a large mode field diameter while achieving low bend losses, thus enhancing signal transmission over long distances and in systems with large spacing between regenerators.
Implementation Method 1
a cladding region comprising an inner cladding region having an outer radius r2 and relative refractive index Δ2 and an outer cladding region having relative refractive index Δ4, where Δ1 > Δ4 > Δ2
Data Source
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AI summary
Optical fibers having a mode field diameter at 1310 nm of at least 8.8 µm, wire mesh covered drum microbending losses at 1550 nm less than 0.03 dB/km, and a 2 m cutoff wavelength less than 1320 nm. The fibers may include a central core region, an inner cladding region, an outer cladding region, a primary coating with an in situ modulus less than 0.20 MPa and glass transition temperature less than -35 ℃, and a secondary coating with an in situ modulus greater than 1500 MPa. The fibers may further include a depressed index cladding region. The relative refractive index of the central core region may be greater than the relative refractive index of the outer cladding region may be greater than the relative refractive index of the inner cladding region. The fibers may be produced at draw speeds of 30 m/s or greater.