Design of an ultra-wideband low-loss miniaturized 3 dB coupler

A novel ultra-wideband low-loss miniaturized 3 dB coupler based on a polymer dual-hollow-core anti-resonant fiber (DHC-ARF) is proposed. The wavelength dependence can be effectively reduced by adopting two identical elliptical cores in the DHC-ARF and the polarization dependence can be greatly weakened by introducing two small nested tubes into two cladding tubes at both sides of the air-gap channel between two cores. The 3 dB coupler can be constructed by a 4.92 mm long DHC-ARF with an extremely low loss of 0.005 dB. An ultra-wide bandwidth as high as 391 nm covering the wavelength range from 1325 nm to 1716 nm can be attained, in which the coupling ratio is stable within 50 ± 2% and the coupling ratio difference is maintained within ±1.77%. The 3 dB coupler based on the DHC-ARF exhibits high performance of an ultra-wide bandwidth, low loss, and miniaturization; thus, it has tremendous application potential in hollow-core fiber application systems.