Beyond 200 Gb/s/λ PAM4 Optical Transmission in the O, S, C and L Bands Over 6.1 km NANF

We experimentally demonstrate an ultra-wideband and high-speed optical transmission system based on intensity modulation and direct detection (IM/DD) with Nyquist 4-ary pulse amplitude modulation (PAM4), enabled by a 6.1 km span of hollow-core nested antiresonant nodeless fiber (NANF). This NANF exhibits significantly lower attenuation compared to previously reported ultra-wideband variants. To mitigate the impairments of high-baud rate signal induced by the accumulated chromatic distortion, a Tomlinson-Harashima precoding (THP) in conjunction of linear FFE scheme is applied. Experimental results show the successful transmission of PAM4 signal exceeding 200 Gb/s per wavelength across four major optical communication bands—the O, S, C and L bands for the first time. This achievement marks a critical advancement toward high-capacity IM/DD optical interconnects using hollow-core fiber technologies.