Hollow core optical fiber enabled by epsilon-near-zero materials

In this study, we present a novel approach to guiding light within air core fibers by coating the zero-index materials (epsilon-near-zero (ENZ) materials) [16,17] in the inner cladding of hollow core fibers. At the design wavelength of 1550nm, the permittivity of indium tin oxide (ITO) ENZ material approaches zero, enabling the refractive index to dip below 1 in this vicinity. Consequently, total internal reflection can occur within the core of the fiber, facilitating sustained fundamental optical mode with markedly reduced losses compared to uncoated air core fibers. We observe a notable reduction in losses when the ENZ fiber is coupled to its core mode, achieving a maximum improvement of 34dB/cm over the uncoated fiber, particularly near the ENZ wavelength, with a full width at half maximum (FWHM) bandwidth of approximately 550 nm.