133-Tbps 1040-km (13$ imes$80 km) Lumped-Amplified Transmission Over 22 THz in S-to-U-Band Using Hybrid Multiband Repeater with PPLN-Based Optical Parametric Amplifiers and EDFAs

We demonstrated 22.05-THz four-band long-haul transmission with a S-to-U-band lumped repeater consisting of PPLN-based optical parametric amplifiers and EDFAs over an 80-km-span SMF link. The achieved net bitrate was 133.06 Tbps at 1040 km with the 25.5-dBm fibre launch power designed by accounting for ISRS.

💡 Research Summary

This paper presents a groundbreaking demonstration of long-haul optical fiber transmission achieving a net data rate of 133.06 Tbps over 1040 km (13 spans of 80 km each) using an unprecedented signal bandwidth of 22.05 THz across four optical bands: S, C, L, and U. The key innovation enabling this record capacity is a novel hybrid lumped repeater architecture that seamlessly integrates conventional Erbium-Doped Fiber Amplifiers (EDFAs) with Periodically Poled Lithium Niobate (PPLN)-based Optical Parametric Amplifiers (OPAs).

The central challenge addressed is the amplification of signals outside the conventional C and L bands, where EDFAs are inefficient. The solution employs PPLN-OPAs for their unique wavelength conversion capability. In the U-band path, an L-band signal is converted to the U-band via an OPA before transmission over the fiber span, then reconverted back to the L-band by a second OPA for amplification using standard L-band EDFAs. A more complex scheme is used for the wider S-band, employing multiple OPAs for the conversion from C/L-band to S-band and a single OPA with positive conversion efficiency for the collective reconversion back to C/L-band after transmission, minimizing OSNR penalty.

A critical aspect of the system design is the sophisticated management of Inter-Channel Stimulated Raman Scattering (ISRS), a nonlinear effect that becomes significant over such a wide bandwidth. Instead of treating ISRS purely as an impairment, the team used a closed-form Gaussian Noise model accounting for ISRS to optimally design the launch power and spectral tilt for each band. This resulted in a high launch power of 23.0 dBm for the loss-prone S-band and lower powers for other bands, with a total launch power of 25.5 dBm. This design intentionally uses ISRS to transfer energy from shorter to longer wavelengths, effectively creating a “Raman tilt” that helps equalize performance across the ultra-wide spectrum.

The experiment utilized 144-Gbaud probabilistically shaped QAM signals (PCS-64QAM for C/L/U, PCS-16QAM for S-band) and offline digital signal processing. The result is a uniform, high-performance transmission across all 147 channels, proving the viability of extending terrestrial optical networks far beyond the C+L bands. This work demonstrates that by complementing the ubiquitous EDFA infrastructure with compact, nonlinear PPLN-OPA modules for selective band conversion, future systems can achieve massive capacity upgrades without requiring a complete overhaul of amplification technology or the widespread deployment of distributed Raman amplification.