Ultra-Short broadband dual-hollow-core fiber coupler in E + S + C + L + U band

• A novel ultra-short broadband coupler based on a polymer dual-hollow-core anti-resonant fiber operating in E+S+C+L+U band is proposed. • By introducing a pair of elliptical tubes between two cores to form an air gap channel and two elliptical-like cores, the decoupling phenomenon can be efficiently suppressed and the coupling length of the fiber can be reduced, which is beneficial to develop an ultra-short broadband fiber coupler. • A 5.03-mm-long DHC-ARF can be used to construct an ultra-short 3 dB coupler with a wide bandwidth of 370 nm covering over the wavelength range from 1.305 μm to 1.675 μm, in which coupling ratio is stabilized at 50±2%, coupling ratio difference changes within ±0.82%. We propose a novel ultra-short broadband coupler based on a polymer dual-hollow-core anti-resonant fiber (DHC-ARF) operating in E + S + C + L + U band. By introducing a pair of elliptical tubes between two cores to form an air gap channel and two elliptical-like cores, the decoupling phenomenon can be efficiently suppressed and the coupling length of the fiber can be reduced, which is beneficial to develop an ultra-short broadband fiber coupler. Besides, wavelength and polarization dependence of the DHC-ARF-based coupler can be effectively suppressed through adjusting the air gap region between two cores and the core shape of the fiber. Simulation shows that a 5.03-mm-long DHC-ARF can be used to construct an ultra-short 3 dB coupler with a wide bandwidth of 370 nm covering over the wavelength range from 1.305 μm to 1.675 μm, in which the coupling ratio is stabilized at 50 ± 2 %, the coupling ratio difference changes within ± 0.82 %, and the total loss of the coupler is 0.025 ± 0.013 dB. This DHC-ARF-based coupler is made of the polymer, thus it can be fabricated by high-resolution 3D printing, which is easier to manufacture in comparison to a silica-host DHC-ARF based coupler. The proposed ultra-short broadband polymer coupler is very promising in the application of next-generation high speed and large-capacity hollow-core fiber communication systems.