Non-Circular Optical Fiber Rectangular-to-Circular Mode Conversion
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Solution Overview
Problem
Current fiber optics systems face challenges in efficiently coupling light from diode arrays into high-power fiber lasers due to the asymmetric divergence and rectangular shape of diode bars, requiring complex beam shaping optics that can lead to loss of brightness.
Innovation Solution
The development of non-circular optical fibers that can capture and reshape optical radiation from diode arrays, allowing direct coupling without significant loss of brightness, using tapered fibers and photonic crystal lanterns to transform the beam from a rectangular to a circular cross-section, or vice versa, with minimal loss of intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If complex beam shaping optics are used to couple light from diode arrays into fiber lasers, then the light can be focused into the pump cladding, but brightness is lost due to asymmetric divergence and rectangular shape of diodes
Solution Approach 1:
The patent applies asymmetry by using a non-circular (rectangular) fiber core that matches the asymmetric rectangular emission pattern of the diode array. Instead of forcing the asymmetric diode output into a symmetric circular fiber, the invention accepts the asymmetric input shape and transforms it through mode mixing to achieve uniform intensity distribution in the circular pump cladding, thereby preserving brightness while enabling high power coupling.
2Ease of manufacture
If free space lenses and diffractive optic schemes are used to reshape diode light, then the light can be fitted into circular fiber cross-section, but the system becomes complex and expensive
Solution Approach 1:
The invention extracts the beam shaping function from the external free space optics and integrates it directly into the fiber structure itself. The rectangular fiber core acts as the beam shaping element, eliminating the need for separate free space lenses and diffractive optics. This integration simplifies the overall system while maintaining the ability to transform rectangular diode output into circular fiber output.
3Adaptability or versatility
If photonic crystal lanterns are used for mode conversion, then single mode inputs can be converted to multimode output, but this is not compatible with collecting light from highly asymmetric high-power diode bars
Solution Approach 1:
The patent inverts the conventional approach by using a large rectangular core that accepts the highly asymmetric diode input directly, then uses mode mixing in a tapered section to transform the modes. Instead of trying to force single-mode compatibility, the invention embraces the asymmetric high-power diode output and uses the rectangular fiber geometry to naturally accommodate and transform these modes into the desired circular symmetric output.
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
Enables efficient collection and delivery of optical radiation from diode arrays to fiber lasers, maintaining brightness by redistributing intensity in both spatial and angular domains, with the ability to adapt to various fiber cladding shapes, reducing the need for complex optics and preserving power.
Implementation Method 1
tapered fibers and photonic crystal lanterns to transform the beam from a rectangular to a circular cross-section, or vice versa, with minimal loss of intensity
Implementation Method 2
photonic crystal lanterns to transform the beam from a rectangular to a circular cross-section
Data Source
AI summary
A class of fibers is described that have a non-circular cross section on one or both ends that can by optimized to capture the optical radiation from a laser diode or diode array and deliver the light in the same or different shape on the opposite end of the fiber. A large multimode rectangular waveguide may be provided which can accept the radiation from a high-power diode bar and transform it into a circular cross section on the opposite end, while preserving brightness.