Bend-Resistant Multimode Fiber With Depressed-Index Cladding
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Solution Overview
Problem
Existing multimode optical fibers face challenges in achieving high bandwidth and low bend-induced attenuation, particularly in macrobending scenarios, which limits their performance in flexible and compact optical communication systems.
Innovation Solution
The development of bend-resistant multimode optical fibers with a graded-index core and a depressed-index annular cladding region, featuring a refractive index profile that includes a parabolic shape and a depressed-index annular portion with a refractive index delta less than -0.2% and a width of at least 2 microns, which reduces macrobend-induced attenuation and enhances bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional multimode optical fiber structure is used, then the fiber can transmit optical signals, but the bandwidth is limited and bend-induced attenuation is high
Solution Approach 1:
The patent applies local quality by creating a depressed-index annular cladding region with specific refractive index characteristics (delta less than -0.2%) positioned at a specific location (adjacent to or spaced from the core by less than 4 microns). This localized modification of the cladding region's refractive index properties enables the fiber to achieve both high bandwidth (overfilled bandwidth greater than 700 MHz-km) and low macrobend-induced attenuation simultaneously, resolving the technical contradiction between these two performance parameters.
2Reliability
If the core diameter is increased to improve bandwidth, then the numerical aperture increases, but the fiber becomes more sensitive to bend losses
Solution Approach 1:
The patent applies parameter changes by precisely controlling the refractive index delta of the depressed-index annular cladding region to be less than -0.2% and its width to be at least 2 microns. This specific parameter modification in the cladding region enables the fiber to maintain high overfilled bandwidth (greater than 700 MHz-km) while reducing bend sensitivity, allowing the core diameter to be optimized for bandwidth without excessive penalty in bend loss 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
These fibers exhibit overfilled bandwidths greater than 700 MHz-km at 850 nm with minimal bend loss, maintaining low attenuation even under tight mandrel wraps, and support high numerical apertures, enabling efficient data transmission across a wide wavelength range.
Implementation Method 1
a depressed-index annular cladding region which is depressed relative to another portion of the cladding... the depressed-index annular cladding region preferably has a refractive index delta less than about −0.1
Implementation Method 2
a graded-index core region having a core radius greater than 30 microns... the refractive index profile of the core has a parabolic or substantially parabolic shape
Data Source
AI summary
Bend resistant multimode optical fibers are disclosed herein. Multimode optical fibers disclosed herein comprise a core region having a radius greater than 30 microns and a cladding region surrounding and directly adjacent to the core region, the cladding region comprising a depressed-index annular portion comprising a depressed relative refractive index. The fiber has a total outer diameter of less than 120 microns, and exhibits an overfilled bandwidth at 850 nm greater than 500 MHz-km.