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    Untwisting the beginning of helical core fibers (HCFs) significantly improves light coupling efficiency and controls higher-order mode excitation. This method enhances HCF performance for various applications.

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    Area of Science:

    • Optical Fiber Technology
    • Photonics and Waveguide Devices

    Background:

    • Helical core fibers (HCFs) exhibit low coupling efficiency and unwanted higher-order mode excitation due to core tilt.
    • These issues limit the practical application of HCFs in optical systems.

    Purpose of the Study:

    • To propose and experimentally validate a method for enhancing coupling efficiency into HCFs.
    • To demonstrate control over higher-order mode excitation in HCFs.
    • To investigate the impact of fiber untwisting on coupling performance.

    Main Methods:

    • Untwisting the initial section of HCFs using a hydrogen flame.
    • Experimental characterization of coupling efficiency between standard single-mode fiber (SMF-28) and HCF.
    • Numerical and analytical modeling of coupling efficiency as a function of untwisted section pitch.

    Main Results:

    • The untwisting method successfully increases coupling efficiency to levels comparable to straight fibers.
    • The technique allows for control over higher-order mode excitation.
    • Studies reveal the relationship between pitch distance in the untwisted section and coupling efficiency.

    Conclusions:

    • Untwisting the beginning of HCFs is an effective technique to overcome coupling limitations.
    • This method is applicable to both splicing and free-space launching configurations.
    • The approach offers a practical solution for improving HCF performance in optical systems.