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Large-core Fibers

Author: the photonics expert Dr. Rüdiger Paschotta (RP)

Acronym: LCF

Definition: optical fibers with relatively large fiber core

Category: article belongs to category fiber optics and waveguides fiber optics and waveguides

DOI: 10.61835/vma Cite the article: BibTex plain text HTML Link to this page LinkedIn

A large-core fiber is an optical fiber having a fiber core which is relatively large. It can be a multimode fiber or a single-mode fiber.

Large-core Multimode Fibers

Large-core multimode fibers have a core diameter which is well above the typically used 50 μm or 62.5 μm of telecom fibers – for example, 100 μm or even 400 μm. The core is often not much smaller than the fiber cladding (see Figure 1). The cladding diameter may substantially go beyond the usual 125 μm to realize even larger cores. The number of guided fiber modes is then usually very high.

Frequently, such fibers have a pure silica fiber core (rather than e.g. a germanosilicate core) and a fiber cladding with somewhat reduced refractive index, e.g. achieved with fluorine doping. For realizing a high numerical aperture, however, one may still use fibers with germanosilicate core.

Typical applications of large-core multimode fibers are the passive transport of light e.g. in the context of illumination, laser material processing or optical pumping of solid-state lasers.

Large-core Single-mode Fibers

If a large-core fiber is a single-mode fiber, it also has a large effective mode area. Here, the term large mode area fiber is more common and more appropriate, since the large mode area is a particularly important property: it results in reduced nonlinear effects combined with a high beam quality.

standard and large mode area fiber — Figure 2: Comparison of bare (uncoated) fibers with a standard core size (e.g. 8 μm diameter) and a large core (50 μm diameter).

More to Learn

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Suppliers

The RP Photonics Buyer's Guide contains 14 suppliers for large-core fibers. Among them:

NKT Photonics

Our Large Mode Area photonic crystal fibers are designed for diffraction-limited high-power delivery. The large mode area prevents nonlinear effects and material damage. With standard fibers, you trade large mode areas for single-mode operation. With our large mode area fibers, you get single-mode operation in a wide range of wavelengths. Also available in a polarization-maintaining version.

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