Design of ultra-low loss multi-nested hollow-core antiresonant fibers.

Benefiting from the increasing number of nested layers, the loss of hollow-core antiresonant fibers (HC-ARFs) has been rapidly decreasing. However, merely increasing the number of cladding unit layers (N) does not always reduce loss, even ignoring fabrication difficulties. Proper air layer thickness (h) is also critical. With a fixed core radius (R), increasing N often reduces the number of cladding units (M). This study systematically explores how N, h, and M affect confinement loss (CL) and bending loss (BL), leading to the design of ultra-low loss multi-nested HC-ARFs. The results indicate that the optimal h/R for the multilayer truncated nested antiresonant fiber with uniformly thick air layers and the multilayer nested antiresonant nodeless fiber with crescent-shaped air layers are 0.34-0.66 and 0.35-0.71, respectively. Under the structural configuration of M = 4 and N = 5, these designs achieve ultralow CL of 1.43 × 10-8 dB/m and 3.93 × 10-8 dB/m, respectively. These results offer key design principles for next-generation multi-nested HC-ARFs that combine ultralow loss with manufacturability, ideal for long-haul communications and high-power laser delivery.