Low-Loss Reverse Tapering of Antiresonant Hollowcore Fibers with Submicron-Tailored Elliptical-Shaped Tubes

We demonstrate an efficient method for reversely tailoring the tubes of an antiresonant hollow-core fiber (AR-HCF). Furthermore, we have achieved and characterized the tapered AR-HCF with elliptical-shaped tubes, implemented by a traditional flame brushing technique. The measured results show that the extra loss as small as 0.1 dB in the passband and the out-of-band suppression of up to 28 dB in the lossband are realized. The ability to tailor the shape and thickness of tubes of AR-HCF in a submicron-scale using a traditional flame taper rig will benefit the fabrication of in-fiber HCF devices such as the low-loss HCF bandpass filter with high out-of-band suppression.