Fiber Optical Coupler NA Reduction via Cladding Taper
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Solution Overview
Problem
Conventional tapered-fiber-bundle (TFB) optical couplers increase the numerical aperture (NA) of light at the output face, leading to more divergent light rays and less efficient coupling into other devices, which is undesirable for applications like optical amplifiers and high-power applications such as cutting and welding.
Innovation Solution
A fiber optical coupler design with a first and second axial section, where the cladding thickness is reduced in the second section to decrease the numerical aperture increase, achieved by either using thinner fibers or chemically removing cladding material, and optionally encasing the fibers in a low-index overclad tube to maintain light confinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the fibers are tapered from a larger diameter at the input interface to a smaller diameter at the output port, then the light is confined to a smaller cross-sectional area, but the numerical aperture (NA) of the light increases
Solution Approach 1:
The patent applies local quality by reducing the cladding thickness specifically in the second (tapered) section of the fiber bundle, while maintaining the original cladding thickness in the first section. This localized modification allows the tapered section to have different optical properties (lower NA increase) compared to the input section, resolving the contradiction between confining light to a smaller area and maintaining low NA.
Solution Approach 2:
The patent changes the physical parameter of cladding thickness in the tapered section to alter the optical characteristics. By reducing the cladding thickness parameter, the patent modifies the refractive index profile and waveguide properties, which directly affects how NA changes during tapering, thereby reducing the NA increase while maintaining area confinement.
2Quantity of substance
If the numerical aperture (NA) of light at the output port is increased, then more light can be coupled into the fiber bundle, but light rays diverge more and coupling into other devices becomes less efficient
Solution Approach 1:
The patent creates a local quality difference between the input section (first section) and the tapered section (second section) by having different cladding thicknesses. This allows the input section to maintain high NA for efficient light coupling into the bundle, while the tapered section has reduced cladding thickness to minimize NA increase, thereby preserving coupling efficiency to downstream devices.
Solution Approach 2:
The patent segments the fiber bundle into two distinct sections with different cladding characteristics: a first section with original cladding thickness optimized for input coupling, and a second tapered section with reduced cladding thickness optimized for maintaining low NA. This segmentation allows each section to optimize for its specific function, resolving the contradiction between input coupling and output efficiency.
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 design reduces the increase in numerical aperture at the output port, enhancing light confinement and brightness, allowing for more efficient coupling and improved performance compared to prior art TFB couplers.
Implementation Method 1
light is confined to a smaller cross-sectional area and will remain confined in the separate fibers only as long as the NA of the propagating light does not exceed that of the fiber waveguide
Implementation Method 2
optionally encasing the fibers in a low-index overclad tube to maintain light confinement
Data Source
AI summary
A fiber optical coupler comprises a bundle of optical fibers configured to couple light from a multiplicity of input light sources to an output port, each of the fibers comprising a multimode fiber having a core region and a cladding region surrounding the core region. The bundle has first and second axial sections arranged in tandem and adiabatically coupled to one another via a transition zone that includes an optical interface. Within the first section, the ratio of the cross-sectional core area of each of at least some of the fibers to the total cross-sectional area of each of those fibers is given by R1, and within the second section, the ratio of the cross-sectional core area of each of at least some of the fibers to the total cross-sectional area of each of those fibers is given by R2>R1, where R2 is substantially constant along the axial length of the second section. In one embodiment, the second section is tapered from a larger diameter at the optical interface to a smaller diameter at the output port. Methods of making such optical couplers are also described.