Single-core transmission using multimode fiber

Single-core multimode fiber can achieve extremely high data rates by combining multiple light modes with advanced optical components, enabling record-breaking transmission capacities.

Overview of Single-Core Multimode Fiber

A single-core multimode fiber (MMF) uses a single fiber core, typically 50 µm or 62.5 µm in diameter, to transmit multiple light modes simultaneously . Unlike single-mode fiber, which supports only one propagation path, multimode fiber allows multiple transverse modes to travel, which can lead to modal dispersion and limits the distance and bandwidth of traditional multimode links . Single-core MMF is distinct from multi-core fibers, which use multiple separate cores to increase capacity; here, all data is transmitted through a single physical core .

High-Capacity Transmission Achievements

Recent research has demonstrated that single-core multimode fibers can support extremely high data rates, surpassing previous multimode records. A team led by NICT, Nokia Bell Labs, and Prysmian Group achieved over 1 petabit per second in a single-core multimode fiber, which is 2.5 times higher than previous multimode fiber records . This was accomplished by guiding 15 fiber modes over a standard 0.125 mm cladding diameter fiber and using wideband optical transmission over more than 80 nm, covering a distance of 23 km . This demonstrates that single-core MMF can be optimized for high-density, large-capacity transmission using standard fiber manufacturing techniques.

Enabling Technologies

High-speed single-core multimode transmission relies on advanced optical components:

• Mode multiplexers: Combine multiple spatial modes efficiently into the fiber core.
• VCSELs (Vertical-Cavity Surface-Emitting Lasers): Multi-aperture VCSEL arrays with narrow emission spectra and high modulation bandwidths can launch light into specific modes, reducing modal dispersion and increasing effective modal bandwidth (EMB), .
• Digital signal processing (DSP): Compensates for modal dispersion and intermodal interference, which become more significant as the number of modes increases .

Advantages and Applications

• High spatial-signal density: Single-core MMF can carry multiple modes, increasing data throughput without requiring multiple physical cores .
• Ease of manufacturing: Compared to multi-core fibers, single-core MMF is simpler to produce and compatible with existing multimode fiber infrastructure .
• Short- to medium-range high-capacity links: Ideal for data centers and metropolitan networks where distances are typically tens of meters to a few kilometers .

Challenges

• Modal dispersion: Multiple modes traveling at different speeds can cause pulse broadening, limiting distance and bandwidth if not properly managed .
• Complex DSP requirements: High-capacity single-core MMF systems require sophisticated signal processing to separate and recover data from multiple modes .
• Component precision: VCSELs and mode launchers must be carefully designed to control mode excitation and minimize crosstalk .

Summary

Single-core multimode fiber combines the large core of multimode fiber with advanced optical and signal processing techniques to achieve extremely high data rates. Recent experiments have shown that over 1 petabit per second is possible, making single-core MMF a promising solution for high-capacity, short- to medium-range optical networks. The combination of mode multiplexing, multi-aperture VCSELs, and DSP enables efficient utilization of multiple modes while mitigating modal dispersion, opening new possibilities for data center and metropolitan network applications .