Hollow-core optical fiber and coreless optical fiber

Hollow-core optical fibers guide light through an air-filled core for ultra-low latency and nonlinearity, while coreless optical fibers lack a defined core, allowing light to spread freely with minimal guidance.

Hollow-Core Optical Fibers (HCFs)

Structure and Light Guidance: HCFs have an air-filled central core surrounded by a microstructured cladding, often using photonic bandgap or anti-resonant designs to confine light within the hollow region . This design allows light to propagate at nearly the speed of light in vacuum (~3×10^8 m/s), reducing latency by 30–50% compared to conventional solid-core fibers . Advantages:

• Low latency and high-speed data transmission .
• Ultra-low nonlinearity, minimizing Kerr, Brillouin, and Raman scattering .
• High power handling due to reduced interaction with glass .
• Wide low-loss spectrum, potentially spanning visible to 2100 nm .
• Temperature insensitivity and high damage threshold, suitable for high-power delivery and precise sensing . Applications: HCFs are promising for high-speed telecommunications, high-frequency trading, high-power laser delivery, interferometry, and sensing . Current challenges include low insertion loss, mode coupling, and integration with standard fibers .

Coreless Optical Fibers

Structure and Light Guidance: Coreless fibers consist of a uniform glass rod without a distinct core-cladding interface. Light is not tightly confined and spreads across the fiber cross-section, guided primarily by total internal reflection at the fiber boundary or by weak refractive index contrast. Advantages:

• Simple fabrication due to the absence of a core-cladding structure.
• Low modal dispersion for short-distance beam delivery.
• High damage threshold for high-power laser applications, as energy is distributed over a larger area. Applications: Coreless fibers are often used in beam delivery, fiber couplers, and mode-field expanders, where precise confinement is less critical, and high-power handling or uniform illumination is desired.

Key Differences

Summary: Hollow-core fibers excel in low-latency, high-power, and low-nonlinearity applications, making them suitable for next-generation optical networks and precision sensing. Coreless fibers, while simpler, are ideal for beam shaping and high-power delivery where tight confinement is unnecessary. Both fiber types offer unique advantages over conventional solid-core fibers, depending on the application requirements .