Connecting Hollow-Core and Standard Single-Mode Fibers With Perfect Mode-Field Size Adaptation

We propose an approach to interconnect a hollow-core fiber (HCF) of arbitrary core size with standard single-mode fiber with perfect mode-field size adaptation and experimentally achieve for the first time insertion loss agreeing with that predicted by simulations. We demonstrate this using three low-loss HCFs, including 1st window nested antiresonant nodeless fiber (NANF), 2nd window NANF and the state-of-the-art double NANF (DNANF). The connection with a minimum achieved insertion loss of 0.079 dB was permanently secured via gluing and did not degrade during 4 weeks of continuous measurement. To the best of our knowledge, this is the lowest reported value and is comparable to or lower than the connection between dissimilar single-mode fibers (e.g., standard single-mode fiber and dispersion-compensating fiber). We also show that such connection leads to excellent suppression of higher-order modes coupling, of importance to all applications sensitive to multi-path interference. Importantly, obtaining agreement between simulations and experiments validates for the first time the accuracy of the simulations and opens the door to further optimization via simulations with the ability to subsequently achieve the same result experimentally.