In theory, no more than 80% of the light diffracted by a circular aperture can be directly coupled into one mode of an ordinary optical fiber. To improve coupling efficiency, and illustrate an inverse method for designing optical fibers with a desired mode shape, we have made an optical fiber that guides an approximate Airy pattern as one of its modes. The fiber’s attenuation was 11.0 dB/km at a 1550 nm wavelength, the match between the fiber’s mode and the ideal infinite Airy pattern was 93.7%, and the far field resembled a top-hat beam. The guidance mechanism has strong similarities to photonic bandgap guidance.
Gris-Sánchez, I., Van Ras, D., & Birks, T. A. (2016). The airy fiber: an optical fiber that guides light diffracted by a circular aperture. Optica, 3(3), 270-276. https://doi.org/10.1364/OPTICA.3.000270