Cladding Mode Suppressing Fiber for SFP Variable Optical Attenuator
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Solution Overview
Problem
Small Form Factor Pluggable (SFP) Variable Optical Attenuators (VOAs) suffer from higher Wavelength-Dependent Loss (WDL) and Polarization-Dependent Loss (PDL) due to modal interference between fundamental and cladding modes, which increases the complexity and cost of optical networks.
Innovation Solution
Incorporating a cladding mode suppressing double clad fiber for the output fiber in the SFP VOA, where the fiber has a core with a higher index of refraction than the inner cladding and the outer cladding with a higher index than the inner cladding, to minimize cladding mode propagation and interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a short double clad fiber is used in SFP VOA, then the device size is reduced and pluggability is improved, but WDL and PDL increase due to modal interference
Solution Approach 1:
The patent applies local quality by creating a refractive index profile where the inner cladding has a lower index than both the core and outer cladding. This localized modification of the refractive index in the inner cladding region creates a potential barrier that selectively suppresses cladding modes while preserving core mode propagation, thereby reducing modal interference and improving WDL and PDL performance in the compact SFP form factor
Solution Approach 2:
The patent employs composite material structure by implementing a double clad fiber with three distinct regions (core, inner cladding, outer cladding) having different refractive indices. This composite structure combines the benefits of mode confinement in the core with cladding mode suppression through the inner cladding barrier, enabling the short fiber length required for SFP form factor while maintaining reliable optical performance
2Loss of energy
If the output spot is misaligned relative to the output fiber core to achieve high attenuation, then attenuation level increases, but more light is launched into the fiber cladding causing modal interference
Solution Approach 1:
The patent converts the harmful effect of cladding mode launch into a beneficial suppression mechanism. By designing the inner cladding with a lower refractive index, the patent creates a potential barrier that causes cladding modes to be reflected back or dissipated, transforming what would normally be harmful modal interference into a controlled suppression mechanism that reduces WDL and PDL while maintaining high attenuation capability
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
This approach significantly reduces WDL and PDL degradation, achieving negligible loss within a short fiber length, as demonstrated by prototypes using double clad fibers, improving the performance of SFP VOAs compared to standard SMF28 fibers.
Implementation Method 1
the fiber has a core with a higher index of refraction than the inner cladding and the outer cladding with a higher index than the inner cladding
Data Source
AI summary
The invention relates to an electro-static variable optical attenuator suitable for use in a small form factor pluggable module. A short cladding suppressing fiber, such as a double clad optical fiber, dissipates attenuated light coupled to the cladding to reduce modal interference in the output light, while also reducing PDL and WDL introduced by the off set attenuation mechanism.