Polarization-Maintaining Optical Coupler Design for Low-Loss Signal Feed-Through
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical couplers for fiber lasers are sensitive to vibration and thermal effects, require painstaking alignment, and often induce unacceptable losses or are incompatible with polarization-maintaining fibers, limiting their efficiency and beam quality.
Innovation Solution
A polarization-maintaining optical coupler design featuring a tube with a wide end and a narrow end, where a polarization-maintaining feed-through optical fiber with reduced diameter is fused within the tube, minimizing birefringence-inducing elements' extension to the outer surface, allowing for low-loss signal feed-through and minimal polarization degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If all-fiber pump couplers are used, then coupling efficiency is improved, but they induce unacceptable losses to pump light and/or fed-through signal
Solution Approach 1:
The optical coupler is divided into distinct functional sections: a first section for pump light coupling and a second section for signal feed-through. This segmentation allows each section to be optimized independently, with the first section designed for efficient pump coupling and the second section designed for low-loss signal transmission, thereby resolving the contradiction between coupling efficiency and optical loss.
Solution Approach 2:
Different regions of the optical coupler are given different structural properties. The first section has a configuration optimized for pump light coupling (with specific core/cladding diameter ratios), while the second section has a configuration optimized for signal feed-through (with different diameter ratios). This local differentiation allows each region to perform its function with minimal loss, addressing both the coupling efficiency and optical loss requirements.
2Adaptability or versatility
If existing coupler designs are used, then coupling function is achieved, but they are incompatible with polarization-maintaining fibers
Solution Approach 1:
The optical coupler employs asymmetric structural design with different core-to-cladding diameter ratios in different sections, and the birefringence-inducing elements are positioned asymmetrically within the fiber structure. This asymmetric configuration is specifically designed to maintain polarization characteristics while achieving efficient coupling, making the device compatible with polarization-maintaining fibers and improving both adaptability and reliability.
3Ease of operation
If free-space optics are used for pump coupler, then alignment flexibility is improved, but sensitivity to vibration and thermal effects increases
Solution Approach 1:
The pump coupling function and signal feed-through function are merged into a single integrated all-fiber optical coupler structure. This integration eliminates the need for free-space optical components and complex alignment mechanisms, thereby maintaining alignment flexibility while dramatically reducing sensitivity to vibration and thermal effects through the inherent stability of fiber-optic connections.
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 provides a low-loss, high-efficiency coupling of optical radiation with minimal degradation of beam quality and polarization, addressing the limitations of prior art by reducing birefringence and optimizing the coupler's design for stability and performance.
Implementation Method 1
at least the narrow end of the tube being fused around a first length of the polarization-maintaining feed-through optical fiber
Implementation Method 2
one or more birefringence-inducing elements disposed in the cladding
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The present invention relates generally to optical waveguides for the transmission of electromagnetic energy. The present invention relates more particularly to optical couplers for coupling optical fibers, and methods for making them. One aspect of the present invention is an optical coupler for use with a polarization-maintaining input optical fiber and a polarization-maintaining output optical fiber. The coupler includes: a tube having a wide end, a narrow end having an end face, and a taper therebetween; a polarization-maintaining feed-through optical fiber having a first end having an end face and a second end, the polarization- maintaining feed-through optical fiber being disposed within the tube from the wide end to the narrow end, at least the narrow end of the tube being fused around a first length of the polarization-maintaining feed-through optical fiber including the first end of the polarization-maintaining feed-through optical fiber to form a coupler end face comprising the end face of the tube and the end face of the first end of the polarization-maintaining feed-through optical fiber. In one aspect of the invention, the polarization-maintaining feed-through optical fiber has an outer diameter no greater than about 200 µm in the region in which the tube is fused around it. In another aspect of the invention, the polarization-maintaining feed-through optical fiber has an outer diameter at the coupler end face no greater than about 75% of the diameter of the polarization-maintaining input optical fiber.