Fig. 1. AR-HCF structure and ARROW theoretical model. (a) AR-HCF structure; (b) ARROW theoretical model

Fig. 2. Schematic of the fabrication of NANF by stack-and-draw technique

Fig. 3. Effect of the diameter difference between the external and internal tubes on the attenuation performance in NANF^[21]

Fig. 4. Variation trend of micro-bending loss of AR-HCF with wavelength^［19］

Fig. 5. Material loss suppression factor in NANF^[19]

Fig. 6. Evolution of AR-HCF structure and loss reduction process. (a) Hypocycloid Kagome AR-HCF^[24]; (b) negative curvature AR-HCF with nodes^[26]; (c)‒(e) nodeless single-ring AR-HCF^[27-29]; (f) conjoined-tube AR-HCF^[30]; (g) 6-NANF^[31]; (h) 5-NANF^[33]; (i)‒(j) 5-DNANF^{[35, 37]}; (k) 4T-DNANF^[38]; (l) 4-DNANF^[39]

Fig. 7. Comparison of attenuation spectra between AR-HCF and standard single-mode fiber^[37]

Fig. 8. Simulated and measured chromatic dispersion values of standard single-mode fiber and NANF^[40]

Fig. 9. Backscattering coefficients of air and glass surface in NANF obtained by theoretical calculation under atmospheric pressure^[43]. (a) Backscattering coefficient as a function of wavelength when core diameter equals 36 μm; (b) backscattering coefficient as a function of core diameter at the wavelength of 1550 nm

Fig. 10. 4T-DNANF structures and performances^[38]. (a) Fiber structures; (b) fiber attenuation coefficient, high-order mode suppression ratio, and fiber structure parameters

Fig. 11. Comparison of transmission latency in standard single-mode fiber, NZ-DSF, and NANF^[40]

Fig. 12. Plug-and-play connector for AR-HCF^[47]

Fig. 13. Side-view image of AR-HCF under misalignment and alignment conditions^[50]

Fig. 14. Schematic diagram of the principle of AR-HCF and single-mode fiber adapter based on the optical fiber connector method. (a) Illustration of the physical picture and test results of the large-effective area optical fiber connector scheme^[55]; (b) illustration of the physical picture and test results of the multi-direction casing scheme^[56]

Fig. 15. Schematic diagram of the principle of glued fiber array assembling method^[57]. (a) Illustration of the single-mode fiber spliced with GRIN fiber; (b) illustration of assembling a AR-HCF into an optical fiber array and aligning its end face with that of the array; (c) schematic of the mode field propagation at the GRIN-AR-HCF interface

Fig. 16. Schematic diagram of the fusion splicing method principle based on GRIN and angle-cleaved fiber^[53]

Fig. 17. Erbium doped fiber amplifier-assisted OTDR scheme and result^[63]. (a) Experimental setup; (b) OTDR traces for a fiber consisting of 509 m single-mode fiber and 885 m NANF measured using FOTR-203 without and with the pulse amplification unit

Fig. 18. Integrated single-wave 800 Gbit/s widened C+L-band real time transmission and sensing system based on AR-HCF^[65]. Transmitter (a) and receiver (c) of widened C+L-band wavelength division multiplexing transmission system; (b) 100 km AR-HCF link; (d) FDM-OTDR system; (e) signal parameters of wavelength division multiplexing and FDM-OTDR

Fig. 19. Ultra-long-haul loop transmission system based on 11.5 km AR-HCF^[70]. (a) Experimental setup; (b) distribution diagram of transmission distance for each channel

Fig. 20. S+C+L-band coherent optical transmission system^[71]. (a) Experimental setup; (b) throughput of each channel after fiber transmission

Fig. 21. Transmission system setup and results based on 2 km NANF and single-mode fiber^[76]. (a) Experimental setup; (b) NGMI results; (c) transmission spectrum results

Fig. 22. Setup and results of single-wave 400 Gbit/s and 800 Gbit/s loop transmission system based on AR-HCF^[79]. (a) Experimental setup; (b) relationship between test channel frequency and transmission distance

Fig. 23. Real-time co-frequency co-time full duplex transmission system^[80]. (a) Experimental setup; measured pre-forward error correction bit error rates (b) and OSNR penalties (c) of all 7 channels for both bidirectional and unidirectional transmission