Cross-Sectional Structure of Nested Antiresonant Nodeless Fiber for Single-Mode and Few-Mode Transmission

Nested Antiresonant Nodeless Fiber (NANF) is a promising candidate for next-generation optical communication systems due to its low-loss, low-latency and low-nonlinearity characteristics. This study focuses on the high degree of design flexibility inherent in NANF, demonstrating through numerical analysis that a single platform can be tailored for two distinct applications required in future networks: single-mode transmission and few-mode transmission for space-division multiplexing. Although low-loss HCFs are by nature multimode fibers, we show that the fiber's modal properties can be actively controlled by adjusting one of the key design parameters: the radius of the inner nested tubes (r2​). A design with a smaller radius (r2​=5.31 µm) achieves quasi-single-mode transmission by maintaining the fundamental mode loss below 1 dB/km while establishing a loss ratio greater than a factor of ten on a decibel scale relative to higher-order modes. Conversely, a design optimized with a larger radius (r2​=7.2 µm) demonstrates quasi-two-mode operation at a wavelength of 1.3 µm, where both the fundamental (0.22 dB/km) and the first higher-order (0.81 dB/km) modes propagate with low loss. These results reveal that NANF is an highly versatile optical fiber platform whose performance can be switched from single-mode to few-mode simply by adjusting one structural parameter. This capability indicates that NANF could play a crucial role in meeting the diverse requirements of future optical communication networks.