Hollow-Core Fiber: A Revolutionary Solution for Data Center Optical Interconnects

Introduction

With the rapid development of cloud computing, artificial intelligence, and 5G technology, global data traffic is growing at approximately 30% annually. Traditional solid-core fibers are increasingly facing bandwidth bottlenecks and power consumption challenges in intra-data center interconnects. Hollow-core fiber (HCF), as a disruptive optical transmission medium, is bringing revolutionary changes to data center optical interconnections with its unique optical properties. This article provides an in-depth exploration of the technical principles of hollow-core fibers and their multidimensional application scenarios in data centers.

I. Technical Analysis of Hollow-Core Fibers

1 Basic Structure and Working Principle

Hollow-core fibers employ special microstructural designs with an air channel at the center surrounded by periodically arranged air holes or reflective layers. Their operation primarily relies on two mechanisms:

• Photonic Bandgap Effect: Forms a photonic bandgap through periodic structures to confine light within the air core for transmission
• Anti-Resonant Reflecting: Utilizes the anti-resonant effect of thin-wall structures to achieve optical waveguiding

Compared to traditional step-index fibers, hollow-core fibers exhibit the following characteristics:

2 Technical Advantages

The core value of hollow-core fibers for data centers is reflected in:

1. Ultra-Low Latency: Light travels 47% faster in air than in glass, significantly reducing network latency
2. Ultra-High Bandwidth: Supports dense wavelength division multiplexing (DWDM) with >100 wavelength channels
3. Extremely Low Nonlinearity: Nonlinear effects reduced by 4-5 orders of magnitude, improving signal fidelity
4. Reduced Power Consumption: Transmission loss as low as 0.28 dB/km (1550nm), minimizing relay requirements
5. EMI Immunity: Completely unaffected by electromagnetic pulses (EMP)

II. Typical Data Center Application Scenarios

1 High-Speed Inter-Rack Interconnects

In Leaf-Spine network architectures, hollow-core fibers optimize connections at different levels:

• Leaf Switch Interconnects: Replaces traditional DAC cables, achieving <100ns inter-rack latency
• Spine Switch Backbone: Single fiber supports >10Tbps aggregate bandwidth
• Optical Module Innovation: Enables CPO (Co-Packaged Optics) architecture with silicon photonics

Performance Comparison:

• Transmission distance: Up to 2km (no repeaters needed)
• Power budget: 40% lower power consumption than multimode solutions
• Density advantage: Outer diameter reducible to 125μm, improving cable management efficiency

2 Memory Pooling Optical Interconnects

Enables in disaggregated architectures:

• CXL over Fiber: Supports memory access latency <200ns
• Photonics Memory Bus: Replaces DDR physical layer, 10x bandwidth density improvement
• Heterogeneous Computing Interconnect: Sub-microsecond synchronization between GPU/FPGA clusters

3 Optical Computing Interconnect Networks

Provides ideal interconnects for emerging photonic computing:

• Optical Neural Networks: Supports parallel transmission of pulsed optical signals
• Coherent Optical Interconnects: Maintains quantum state over long-distance transmission
• Wavelength-Routed Computing: Enables on-chip integration of wavelength selective switches (WSS)

III. Key Technical Challenges and Solutions

1 Connector Technology

Challenges:

• Micron-level alignment precision requirements
• End-face reflection control

Innovative Solutions:

• Self-aligned lens coupling technology
• 3D-printed collimators
• Anti-reflection microstructured end-faces

2 System Integration

Breakthrough Directions:

• Heterogeneous integration of silicon photonics chips with HCF
• Fan-in/fan-out devices for multi-core HCF
• MEMS-based dynamic coupling systems

Conclusion

Hollow-core fiber technology is breaking through the dual limitations of “power wall” and “bandwidth wall” in data centers. As manufacturing processes mature and costs decline, the technology is expected to gradually proliferate from hyperscale data centers within the next 3-5 years. This innovation will not only reshape internal data center network architectures but also provide critical infrastructure for cutting-edge directions like memory-compute integration and photonic computing.