Active Fibers

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

Definition: optical fibers containing laser-active dopants in the fiber core

Categories: article belongs to category fiber optics and waveguides fiber optics and waveguides, article belongs to category laser devices and laser physics laser devices and laser physics

Opposite term: passive fibers

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

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📦 For purchasing, use the RP Photonics Buyer's Guide for rare-earth-doped fibers. It provides an expert-curated supplier directory, buyer-focused technical background information, and structured selection criteria to support professional procurement decisions.

What are Active Fibers?

Active fibers are optical fibers which have one or more laser-active dopants in the fiber core. In most cases, they are rare-earth-doped fibers, with dopants like ytterbium, erbium or thulium. Due to those dopants, they can be used as laser gain media, also for realizing fiber amplifiers. Only quite rarely, active fibers are made with transition metal ions.

Active fibers are generally made from some glass, in most cases from fused silica (→ silica fibers). However, there are also active single-crystal fibers.

Case Studies

Erbium-doped Fiber Amplifier for a Long-wavelength Signal

Amplified spontaneous emission (ASE) turns out to be a limiting factor, requiring a dual-stage amplifier design.

Case Studies

Erbium-doped Fiber Amplifier for Multiple Signals

We optimize an amplifier for equal output powers of signals spanning a substantial wavelength range. There is a trade-off between power efficiency and noise performance.

Besides the ability to amplify light (usually with high gain efficiency and often with a high power conversion efficiency and high beam quality of the output), active fibers usually exhibit higher propagation losses, which, however, are normally of little relevance, since one generally requires only a relatively short fiber. In most cases, they are single-mode or few-mode fibers, and sometimes large mode area fibers or polarization-maintaining fibers.

For more details, see the article on rare-earth-doped laser gain media, which also describes special variants such as double-clad fibers and triple-clad fibers.

Laser amplification is not the only possible physical mechanism to obtain gain in a fiber: stimulated Raman scattering (SRS) and the Kerr nonlinearity of the fiber can also be exploited for that purpose. In such cases, one may consider a fiber as active in the sense that it can amplify light.

Frequently Asked Questions

This FAQ section was generated with AI based on the article content and has been reviewed by the article’s author (RP).

What is an active fiber?

An active fiber is an optical fiber where the core is doped with laser-active ions, usually rare-earth elements such as ytterbium, erbium, or thulium. This doping allows the fiber to act as a laser gain medium in lasers and amplifiers.

What materials are active fibers made from?

Active fibers are typically made from fused silica glass, with the core containing a laser-active dopant, which is usually a rare-earth element. Less commonly, active fibers can be made from other glasses or from single-crystal materials, or can be doped with transition metal ions.

Suppliers

Sponsored content: The RP Photonics Buyer's Guide contains 21 suppliers for rare-earth-doped fibers. Among them:

⚙ hardware

rare-earth-doped fibers from NKT Photonics

Our ytterbium and thulium double clad fibers offer the largest single-mode cores in the world. They enable amplification to unprecedented power levels while keeping mode quality and stability. If you are building picosecond or femtosecond ultrafast fiber lasers, our Yb-doped aeroGAIN gain modules may be just what you are looking for.

⚙ hardware

rare-earth-doped fibers from Le Verre Fluore

Thanks to their high rare-earth solubility (up to 100,000 ppm) and low phonon energy, LVF fluoride fibers offer dozens of active transitions, enabling a broad range of applications from visible to the mid-infrared. LVF offers the largest range of rare-earth doped fibers in the world.

LVF active fibers are available as rare-earth-doped single-mode fibers and rare-earth-doped double cladding fibers.

Fibercore, supplier of rare-earth-doped fibers

⚙ hardware

Fibercore's portfolio of erbium-doped fiber, PM erbium fiber, dual-clad erbium/ytterbium-doped fiber, triple-clad doped fiber and other doped fibers offers ideal suitability for high-power erbium-doped fiber amplifiers (EDFAs) and fiber lasers.

Exail, supplier of rare-earth-doped fibers

⚙ hardware

Exail (formerly iXblue) offers a wide range of specialty optical fibers for lasers and amplifiers. We master erbium, erbium/ytterbium, ytterbium, thulium, holmium, thulium/holmium, neodymium, dysprosium, and phosphorous gain media. PM version are available, and Large Mode Area (LMA) or Very Large Mode Area (VLMA) versions as well. Depending of the requirement, single clad fibers are available for core pumping, double clad fibers for clad pumping. Triple clad and all glass structures are also available.

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