As the application areas of optical fibers continue to expand across various sectors of telecommunications, the fibers themselves have been continuously improved, acquiring new characteristics optimized for different applications.
Currently, several types of optical fibers are used, the characteristics of which are regulated by the ITU-T Recommendations issued by the Telecommunication Standardization Sector of the International Telecommunication Union.
| Class (Type) of Optical Fiber | ITU-T Recommendation |
| Multimode 50/125 μm with graded-index profile | G.651 |
| Standard single-mode | G.652 |
| Dispersion-shifted single-mode | G.653 |
| Cutoff wavelength shifted single-mode | G.654 |
| Non-zero dispersion-shifted single-mode | G.655 |
| Non-zero dispersion single-mode for broadband optical transmission | G.656 |
| Bend-insensitive single-mode with reduced bending losses at small radii | G.657 |
Each class (type) of optical fiber may include various subclasses (categories), in which fibers may differ in certain characteristics. The primary type of single-mode optical fiber used in FinMark cables complies with the ITU-T G.652.D recommendation. Among other features, this optical fiber has low attenuation in the hydroxyl peak region (1383 nm), allowing extensive use of CWDM technologies for data transmission.
Technical Characteristics of Standard Single-Mode Optical Fiber (SM) Compliant with ITU-T G.652.D Recommendation:
| Parameters | Values |
| Fiber Type | Single-mode |
| Attenuation Coefficient @ 1310 nm @ 1490 nm* @ 1550 nm @ 1625 nm* | ≤ 0.36 dB/km ≤ 0.26 dB/km* ≤ 0.22 dB/km ≤ 0.24 dB/km* |
| Attenuation Discontinuities | ≤ 0.05 dB |
| Cutoff Wavelength | ≤ 1260 nm |
| Zero Dispersion Wavelength | 1300 ~ 1324 nm |
| Zero Dispersion Slope | ≤ 0.092 ps/(nm²×km) |
| Chromatic Dispersion @ 1310 nm @ 1550 nm @ 1625 nm* | ≤ 3.5 ps/(nm×km) ≤ 18 ps/(nm×km) ≤ 22 ps/(nm×km)* |
| Polarization Mode Dispersion PMDQ (RMS) | ≤ 0.1 ps/km1/2 |
| Macrobending Losses 100 turns Ø 60 mm @ 1550 nm | ≤ 0.05 dB |
| Mode Field Diameter @ 1310 nm @ 1550 nm | 9.2 ± 0.4 μm 10.4 ± 0.5 μm |
| Core/Cladding Concentricity Error | ≤ 0.6 μm |
| Cladding Diameter | 125.0 ± 0.7 μm |
| Cladding Non-Circularity | ≤ 1.0% |
| Primary Coating Diameter | 245 ± 10 μm |
| Mechanical Strength | 0.69 GPa, 1% |
| Group Refractive Index @ 1310 nm @ 1550 nm | 1.4673 1.4682 |
* Note: At wavelengths of 1490 nm and 1625 nm, attenuation coefficient and chromatic dispersion are not standardized. The values provided are for informational purposes only.
For indoor and subscriber cables and cords installed in confined spaces, such as inside boxes, outlets, and patch panels, bend-insensitive single-mode fibers with reduced bending losses at radii of 15 mm and less may be used. These fibers comply with ITU-T G.657 recommendations. Currently, Class A and Class B fibers are used. Class A fibers are designed to be fully compatible with standard G.652 single-mode fibers. Class B fibers allow significantly smaller bending radii (R ≤ 10 mm), but their fusion splices with G.652 fibers are characterized by higher insertion losses.
Technical Characteristics of Bend-Insensitive Single-Mode Optical Fiber (BIF) Compliant with ITU-T G.657 Recommendation:
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