Double-clad fiber coupler for low-loss endoscopy imaging
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Solution Overview
Problem
Double-clad fiber couplers in medical imaging techniques, such as endoscopy and confocal endomicroscopy, face challenges with light coupling and speckle noise, leading to significant signal loss and vulnerability to mechanical misalignment.
Innovation Solution
A double-clad fiber coupler composed of two fused and tapered double-clad fibers, allowing light to propagate with minimal loss in the single-mode core and enabling efficient collection of backreflected light through both the core and inner cladding, with a tapered section that optimizes signal transmission and reduces speckle contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a free space beam splitter setup is used to couple light in and out of a double-clad fiber, then light coupling can be achieved, but signal loss increases (greater than 6 dB loss of the weak SM signal and greater than 3 dB loss in the MM signal) and the system becomes vulnerable to misalignment due to mechanical motions
Solution Approach 1:
The patent merges the beam splitter functionality directly into the fiber structure by fusing two double-clad fibers together and applying a tapered section. This integration eliminates the free space beam splitter setup, removing the interfaces that cause misalignment vulnerability and reducing signal loss through direct fiber-to-fiber coupling.
Solution Approach 2:
The tapered section acts as an intermediary region between the two fused double-clad fibers, enabling mode field matching and efficient light coupling. The taper gradually transforms the mode fields, serving as a mediator that facilitates low-loss coupling between the core and inner cladding modes without requiring external beam splitters.
2Measurement precision
If a double-clad fiber is used to reduce speckle contrast and improve signal collection, then imaging quality improves, but coupling remains an issue due to the complexity of separating and combining SM and MM signals
Solution Approach 1:
The patent segments the light propagation paths by utilizing the distinct core and inner cladding regions of the double-clad fiber. The tapered section creates separate coupling channels: one for the fundamental core mode and another for the inner cladding modes. This segmentation allows independent control and optimization of single-mode and multi-mode signal coupling without complex external optics.
Solution Approach 2:
The fused and tapered double-clad fiber structure serves multiple functions simultaneously: it acts as both a coupler and a mode separator/combiner. The same tapered region that enables low-loss coupling also naturally separates the SM and MM signals by their different mode field distributions, eliminating the need for separate coupling and separation components.
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 solution achieves high transmission efficiency (>90%) and reduces speckle contrast, enhancing imaging quality by allowing 3D reconstructions and stereoscopic vision, while being robust against misalignments and improving signal collection over traditional free space beam splitter setups.
Implementation Method 1
the first core and the second core remain separate and the first inner cladding and the second inner cladding are coupled to form a fused inner cladding
Implementation Method 2
the fused region comprising a first diameter transition section, a constant diameter section, and a second diameter transition section, the first diameter transition section corresponding to a down-taper of the fused region and the second diameter transition section corresponding to an up-taper of the fused region
Data Source
AI summary
There is described a double-clad fiber coupler (DCFC) composed of two double-clad fibers that have been fused together and tapered. The DCFC allows the propagation of light in the fundamental mode in its single-mode core with very little loss. Back reflected light may be collected two ways: by the core of the double-clad fiber and by the inner cladding of the double-clad fiber.