G.652D Low Water Peak Optical Fiber Characteristics and Applications

Low water peak fiber as called generally by the fiber optic industry, the ITU-T G.652D compliant optical fiber in the series of ITU-T G.652 recommendations has many different brands introduced by different optical fiber manufacturers. Each of them claims with sufficient reasons why their version is superior to others!

Putting in a layman’s language, Low water peak fibers are different from ITU-T G.652B fibers in two respects. The first and foremost difference is in the use of water peak region for transmission in ITU-T G.652D fibers. For a conventional fiber complying with G.652B recommendations, it is not possible to transmit the 1360nm to 148nm region of the light spectrum as the attenuation is quite high compared to the attenuation at 1310nm or 1550nm.

The water peak in a G.652B fiber occurs at 1383 +/- 3nm nominally. Some manufacturers roughly specify it as 1383nm. G.652B fibers, drawn from the preforms made by using the MCVD process show comparatively high attenuation at the water peak region. VAD process or Vapor axial deposition preform manufacturing method to a great extent eliminates the presence of hydroxyl ions and hence the attenuation of optical fibers made out of preforms manufactured by VAD is low. Usually, this low value of attenuation comes near to 0.5dB/km. For the MCVD process, the attenuation at the water peak region is higher than 1dB/km and many times near to 2dB/km.

So, attenuation at the water peak region has reduced to less than or equal to the attenuation at 1310nm for an ITU-T G.652D compliant optical fiber. This is the first difference from G.652B fiber. Since the attenuation is low at the 1383nm region, the whole spectrum ranging from 1310nm to 1625nm can be used for transmission if a G.652D fiber is used in a telecommunication network. This opens up a huge window for transmission.

G.652D fibers are treated in a deuterium environment in order to fill all the voids in the glass material with the Deuterium atoms so that in the future also, there is no provision or space available for the hydroxyl ions to sit inside glass after getting in contact with the hydrogen generating environment like water or other cable components.

The application of G.652D fiber is mainly in long haul terrestrial application, Backbone, metro access, and now recently from the Central office to the splitter point. Virtually the positions of G.652B fibers were almost replaced by the G.652D fibers. OFS says they have Zero water peak fiber. There is an interesting technical debate between the Zero water peak fiber and the Low water peak fiber. Draka finds it an investment waste to invent a zero water peak fiber when the fiber optic industry and the ITU do not specifically require such a fiber.

The second difference between the G.652B fiber and G.652D fiber is in the Polarization mode dispersion coefficient. ITU-T requirement for PMD on a G.652B fiber is less than or equal to 0.5ps/sqrt.km. For G.652D fibers the value of PMD as per ITU-T recommendation is less than or equal to 0.2ps/sqrt.km. Thus G.652D fibers can be used for high speed transmission like 40Gbps and more. With the small PMD value, more signals can be transmitted over G.652D fiber for long distances. This makes it suitable for long haul terrestrial applications, Metro access, and backbone services.

Other transmission parameters like Chromatic dispersion at 1550nm, 1285nm-1340nm range, Zero dispersion wavelength, Cut-off wavelength, etc are almost the same as the conventional G.652B fibers.

Geometrical parameters of G.652D fibers of many of the manufacturers have improved performance than G.652B fibers. They offer superior characteristics for Cladding non-circularity, Core concentricity error, etc which have an influence on the splicing too.

G.652D fibers have a major share in the optical fiber market. G.652D fiber dominates the fiber optic market. The demand will still be going on in the coming years as many economies are now opening up for fiber optic backbone infrastructure development. The price of G.652D fiber is almost near to the price of a G.652B fiber. The price of G.652D fiber is in the range of US$ 9.0 to 11 depending on the region and the manufacturer (edited in 2020: The fiber price has come down to the range of US$4.0/km)

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