Taper Fiber High Refractive Index Core for NA Reduction
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Solution Overview
Problem
Conventional optical couplers face issues where the numerical aperture (NA) of light increases as it propagates through the taper fiber, leading to light leakage and potential burnout of the output optical fiber, especially when using optical fibers with smaller NA as output fibers.
Innovation Solution
Incorporating a high refractive index part within the taper fiber's core, where the end surfaces of input optical fibers overlap with the high refractive index part, to prevent the increase in NA and reduce light leakage by ensuring that at least a part of the exited light remains within the high refractive index part.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a taper fiber with a reduced diameter part is used to couple light from multiple input optical fibers, then the coupling efficiency is improved, but the numerical aperture (NA) of light increases during propagation, causing light leakage and potential burnout of the output optical fiber
Solution Approach 1:
The patent introduces a high refractive index part within the core of the taper fiber, creating a localized region with different optical properties. This high refractive index part is positioned to overlap with the end surfaces of input optical fibers, providing localized light confinement exactly where needed to prevent NA increase and light leakage, while maintaining the overall taper structure for efficient coupling.
Solution Approach 2:
The high refractive index part acts as an intermediary element between the input optical fibers and the tapering core. It mediates the light transition by providing a refractive index buffer that prevents abrupt changes in light propagation, thereby controlling the NA increase and preventing light leakage into the cladding.
2Quantity of substance
If the diameter of the entrance end surface of the taper fiber is increased to accommodate more input optical fibers, then the number of input fibers is increased, but the amount of reduced diameter per unit length increases, causing greater NA increase and light leakage
Solution Approach 1:
The high refractive index part is strategically positioned at the entrance end surface region of the taper fiber, creating a localized optical structure that addresses the light confinement problem at the critical interface where multiple input fibers connect. This localized modification allows the system to handle more input fibers without proportionally increasing light leakage.
3Device complexity
If a conventional optical coupler without a high refractive index part is used, then the device complexity is reduced, but the NA of light increases excessively, causing light leakage and burnout of the output optical fiber
Solution Approach 1:
The high refractive index part is nested within the core of the taper fiber, creating a concentric structure where the high refractive index region is contained within the lower refractive index core. This nested configuration provides the necessary light confinement function while maintaining a relatively simple overall device structure that integrates seamlessly with the existing taper fiber geometry.
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 configuration effectively reduces the NA of light exiting the taper fiber, minimizing light leakage and preventing burnout of the output optical fiber, even when using optical fibers with smaller NA as output fibers.
Implementation Method 1
the light, which has entered the taper fiber, increases in NA while propagating in the reduced diameter part due to reflection of the light at a boundary between a core and a cladding
Implementation Method 2
the taper fiber having a high refractive index part provided inside a core of the taper fiber, the high refractive index part having a refractive index greater than a refractive index ncore of the core
Data Source
AI summary
Provided is an optical coupler configured to cause an NA of light, which exits a taper fiber, to be smaller as compared with a conventional optical coupler. A taper fiber has a high refractive index part which is provided inside a core of the taper fiber and which has a refractive index smaller than a refractive index ncore of the core. An exit end surface of each GI fiber is bonded to an entrance end surface of the taper fiber so that at least a part of the exit end surface of the each GI fiber overlaps with a section of the high refractive index part. A relative refractive index difference of the taper fiber is smaller than 0.076%.