UNDERSTANDING FIBER SPECIFICATIONS

Optical fiber products are defined by many parameters that will vary for each application and for each potential system design within those applications.

If you are using Coractive optical fibers or looking at the solutions we offer, understanding standard fiber specification nomenclature is important to identify the right product for your application.

With this article, you will have a guide to better understand our standard fiber nomenclature when browsing our catalogue and will know what to expect as typical specs for different fiber types.

Standard Parameters of an Optical Fiber

The most basic parameters that define an optical fiber are its core and cladding diameters. They define the actual physical dimensions of the fiber, critical when filing them in cables or placing them in optical devices. In the telecommunications industry, optical fiber parameters are standardized to assure long-term reliability and enable integration in global networks. In more industrial applications, fiber dimensions can give a general idea of the expected application power handling, since more power requires a bigger fiber to reduce its heat density.

To give an idea of typical optical fiber dimensions, commonly used fibers in telecommunication systems have a core diameter of less than 10 microns and a cladding diameter of 125 microns, with the outer protective coating layer around 250 microns. For comparison, a single hair can be as large as 100 microns!

In the field of specialty optical fibers like the ones we manufacture at Coractive, two more parameters are essential to know to classify the different optical fiber types. First, the number of optical claddings can vary and will define if light can only be guided in the core or if the cladding layer also has guiding properties. Second, for fiber laser and amplifier applications, the fibers’ core will be doped with rare earth chemical compounds to give the fibers special absorption and emission spectra that can be harnessed to generate light amplification at different wavelengths. Fibers with this type of rare earth dopant are called “active fibers” or “gain fibers,” as opposed to “passive fibers” which refer to fibers with core material to provide guiding conditions.

Single Clad Fiber

Double Clad Fiber

The typical active fiber we offer at Coractive contains the following dopants:

Ytterbium: used to build fiber lasers and amplifiers in the 1 µm wavelength range. Typical applications require the use of double-clad fibers, where 915 nm or 976 nm multimode laser diodes are combined to pump the laser or amplifier by injecting into the cladding.
Erbium: used to build fiber lasers and amplifiers in the 1.5 µm wavelength range. Mostly used in single-clad fibres for core-pumped applications, pumped around 980 nm, 1450 nm or 1530 nm.
Erbium/Ytterbium: used to build fiber lasers and amplifiers also in the 1.5 µm wavelength range, but mostly used in double-clad fiber for clad-pumped applications, unlike Erbium-doped fibers. The absorption spectrum enables the laser or amplified light to be pumped with different sources, usually around 915 nm, 940 nm or 976 nm.

Additional Specifications Available on Some Products

Two fibers can seem similar but exhibit very different behaviours in a real-world application because of differences in underlying parameters that are not always explicit when looking at data sheets. Some examples of those parameters are:

Cladding shape: Round or octagonal. An octagonal shape is mainly used for active fiber to enhance pump absorption.

Core and cladding background losses: The composition of the glass, the dopants and their purity can influence unwanted levels of additional losses at specific wavelengths.
Dispersion: The light velocity in a fiber can vary as a function of the wavelength. While this phenomenon is useful in certain applications, it can be detrimental in others.
Full absorption/emission spectra: Absorption levels are generally specified at specific wavelengths, but the full spectrum of absorption and emission can have an impact on the behaviour of a laser or amplifier system.
MFD and cutoff wavelength: The propagating light fundamental mode can have a specific Mode Field Diameter for some fibers, and thus, can have a specific cutoff wavelength from which it behaves as a single-mode fiber.
Glass material chemistry: The composition of the glass matrix, the host material of the fiber and its different dopants, can have an impact on the fiber performance and on other optical properties like the absorption spectrum.

Coractive Product Code Options

A quick look at an optical fiber product code will give you some information on critical parameters. Coractive’s optical fiber product codes follow a simple nomenclature with standard and optional components, and follows the structure presented in the table below. In addition, we show the meaning of typical abbreviations that are used in the description of each part of the product code.

Green item = Always present

Grey = Optional additional specifications

For example, the product code DCF-EY-10/128H means a double-clad, Erbium/Ytterbium-doped active fiber with a core diameter of 10 µm and a cladding diameter of 128 µm, with a high absorption level.

A more precise fiber code would be DCF-YB-20/128P-08-FA-G2, meaning double-clad, Ytterbium-doped, 20 µm core diameter, 128 µm cladding diameter, with a pedestal feature and a core NA of 0.08, a flat absorption profile and in its 2nd generation.

Look at our portfolio of products on our website and see if you can read all our fiber nomenclature! Not sure about a specification or need more detailed information on a parameter? Don’t hesitate to contact us. Our experts will help you find the right fiber for your specific needs!

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