Expanding bandwidth horizons

Data flows endlessly through networks, powering everything from daily social interactions to scientific research. As demand for faster, more efficient connectivity soars, the need for advancements in optical communication has become undeniable. To keep pace, experts in the field are exploring new ways to stretch the capacity of existing fibre networks, especially in expanding into new regions of the optical spectrum. Here, Andrzej Wojnar Solutions Architect and Michał Owca, product manager at telecommunications network specialist Salumanus, explores expansions into the L-band and combined S+C+L-band spectrums.

We generate around 330 exabytes daily, a figure that dwarfs previous years and is propelled by digital transformation, AI, smart devices and e-commerce. According to Omdia, telecom operators face a 20 to 30 per cent annual growth in traffic, with ISPs seeing an even more dramatic rise of 50 to 100 per cent. Yet, as this growth surges, the pressure on our current optical networks intensifies.

The quest for more capacity

Currently, optical fibre communication primarily relies on a few spectral bands: the O-band for shorter-range, single or multichannel transmissions, and the C-band for dense wavelength division multiplexing (DWDM). Limited portions of the S and L-bands are also used for specific applications, but the majority of global network capacity flows through the C-band.

This reliance on the C-band is due to its low attenuation,  easy to compensate chromatic dispersion and mature technology. Semiconductor lasers and relatively affordable erbium-doped fibre amplifiers (EDFAs) that operate in this band make it an efficient, reliable choice for high-capacity data transmission.

While investing in new fibre cables or multi-core fibre for Spatial Division Multiplexing (SDM) could increase capacity, such investments are prohibitively costly. Instead, telecom companies are investigating ways to maximise existing fibre through expanded spectral bands.

The L-band is emerging as an immediate candidate for this purpose. With nearly identical properties to the C-band—attenuation, dispersion, and amplification possibilities—the L-band offers an almost seamless extension that can double transmission capacity with only a modest increase in total cost of ownership (TCO).

Amplifying connectivity with new bands

However, L-band integration is not straightforward. The C and L bands require separate amplifiers currently that split and recombine after amplification. Although Raman amplifiers could theoretically provide a broader amplification range, they demand high costs and complex implementation. Future advancements are exploring rare-earth doping with elements like thulium, bismuth, ytterbium or praseodymium to extend amplifier ranges, marking an exciting new area of research for multiband transmission.

Nevertheless, transmission performance is not solely reliant on fibre. Optical modules, particularly coherent modules designed for DWDM systems, also play a significant role in sustaining high-bandwidth applications. Coherent technology in pluggable modules rely on ultra-compact, high-speed digital signal processors (DSPs).

The next DSPs will utilise 3 nm lithography to minimize power consumption. Such advancements are essential as data rates approach and exceed 800G, necessitating breakthroughs in efficient modulation methods.

While production-ready 800G modules for C and L bands are expected soon, the industry roadmap extends to 1.6T and eventually 3.2T modules, allowing for even higher data rates. In recent lab tests, researchers achieved record-breaking data rates of 400 Tbps over a single pair of fibres using multiple bands. Such advancements showcase the vast potential of multiband transmission and signal a promising future for optical networks as they climb toward higher peaks in data capacity.

Salumanus is addressing the pressing need for expanded optical bandwidth by developing advanced solutions that bridge the gap between current C-band-focused networks and future-ready multiband systems. Our work includes high-performance amplifiers and transponders capable of supporting both C- and L-band transmissions, as well as pioneering work on multi-wavelength amplifiers that enable seamless transmission across multiple spectral bands.

The surge in global data demand is reshaping the landscape of optical communication. By exploring new bands and developing cutting-edge technology, the industry is paving the way for unprecedented growth in network capacity. The journey to harness the full potential of the optical spectrum is underway, and with ongoing innovation, the limits of data transmission will continue to expand—transforming our world in ways we have yet to imagine.

To find out more about the coherent optical solutions offered by Salumanus, contact us.