G652D-Low Water Peak Optical Fiber Characteristics and Applications

Low water peak fiber,  as known in the fiber optic industry in general, which is the ITU-T G652D compliant optical fiber in the series of ITU-T G.652 recommendations has many different brands introduced by different optical fiber manufacturers. Each one of the claims with sufficient reasons why their version is superior to others!

Some of the known brand names are Zero Water Peak (ZWP) fiber, Allwave(R) and Low water peak fiber – all pointing to the same optical fiber mentioned in the ITU-T G.652 recommendations, Table D.

Putting in a layman’s language, low water peak fibers are different from ITU-T G.652B fibers in two aspects. The first and foremost difference is that ITU-T g.652D fibers can utilize the water peak region for transmission. For a conventional optical fiber complying G.652B recommendations, it is not possible to utilize the spectrum ranging from 1360nm to 1480nm. The attenuation or loss is quite high in this region compared to the 1310nm and 1550nm spectral regions.

The water peak in a G.652B fiber occurs at 1383+/- 3 nm typically. Some manufacturers roughly specify it as 1383nm. The G.652B fibers drawn from the preforms made by using MCVD process shows comparatively higher attenuation at water peak region. VAD (Vapor Axial Deposition) preform manufacturing process to a great extent eliminates the presence of hydroxyl ions, which contributes towards lower attenuation values in the water peak region. On a higher side, these low attenuation values come near to less than 0.5dB/km, typically falling below 0.32dB/km. It is known that for MCVD process, the attenuation at 1383 nm region may go higher than 1dB/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 chamber in order to fill the voids in the glass material with Deuterium atoms. This prevents the penetration and occupation of hydroxyl ions to the glass structure when the optical fibers come in contact with a hydrogen generating environment such as water or other cable compounds.

The application of G.652D fiber is mainly in long-haul terrestrial, backbone, Metro-core and Access (from the central office to the splitter point). In reality, almost all requirements of G.652B category fibers have been replaced by G.652D fibers.

Leading optical fiber and component supplier OFS has Zero water peak fiber. There is an interesting, but silent technical debate between ‘Zero version’ versus the Low Version’. Another leading fiber supplier, Draka think that zero is not necessary for the fiber optic industry.

The second difference is in the Polarization Mode Dispersion (PMD) coefficient. ITU-T requirement for PMD coefficient for a G.652B fiber is less than or equal to 0.5 ps/sqrt.km. For a G.652D fiber, the values of PMD shall be less than or equal to 0.2ps/sqrt.km. Thus G.652D fibers can be used for high-speed transmissions such as 40Gbps or higher. With a reduced PMD, fiber can accommodate more signals over long distances. This makes the G.652D suitable for long-haul, metro-core, backbone and access telecommunication networks.

For a G.652D fiber, other transmission parameters such as Chromatic Dispersion (CD) at 1550nm, 1285nm~1340nm, Zero dispersion Wavelength, Cut-off Wavelength etc., are almost the same to that of a G.652B fiber.

Geometrical parameters of G.652D fibers offered by leading optical fiber manufacturers have improved in their performance compared to their own G.652B fibers. One reason could be their focus on improving the process for G.652D fibers as they know that G.65B fibers will soon be replaced by G.652D. Many of them are able to offer superior characteristics for parameters such as Cladding Non-Circularity and Core Concentricity Error both of which have an influence on the splice loss.

G.652D fibers claim a major share in the optical fiber market. The demand will keep on increasing in the coming years as many economies are now opening up for the fiber optic backbone infrastructure development. The price of G.652D fiber is almost near to the price of G.652B fiber. The market price for G.652D fiber falls in the range of US$ 9.0 to 11.0 depending on the region and fiber manufacturer.

Author: Kaniya

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