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Used for new ultra-low attenuation large effective area single-mode fiber of the next-generation terrestrial transmission network
publish:R & D Center Zhangdate:2016-07-29

The terrestrial network in China is mainly subject to the ordinary G.652.D optical fiber currently, while most of the optical cable laid in 1990s and have reached 20 --25 years’ service life, therefore, the backbone network should be upgraded gradually in the next few years. Therefore, how to choose the right optical fiber for the long-distance  terrestrialoptical cable is a key problem urgent to be solved for the network operators and optical communication companies. In order to obtain the best system performance, if we can  combine the ultra-low attenuation and large effective area characteristics into an optical fiber, such optical fiber will be the best optical fiber in the next-generation communication optical fiber.

1. G.654.E Recommended indicators

The following table shows the currently discussed G.654.E optical fiber indicators and YOFC ultra-low loss large effective area optical fiber datasheet.  the ultra-low attenuation large effective area optical fiber (FarBand ® Ultra) of YOFC Company can meet and even be better than the most existing stringent G.654.E standard recommendation proposals.

Parameter name

G.654.E discussion paper

YOFC

Scope of product manual

Proposal 1

Recommendation 2

E1

E2

Optical parameters

 

*Mode field diameter @ 1550nm (um)

Nominal

11.5-13.0

11.0-12.0

12.0-13.0

11.4-12.2 Typical: 11.8

Deviations

±0.7

±0.7

±0.7

 

Effective area typical value @ 1550nm (um2)

\

\

\

110

*Optical cable cut-off wavelength (nm)

≤1510

≤1530

≤1530

≤1530

Typical value 1440nm

*Attenuation coefficient @ 1550nm (dB / km)

≤0.20

≤0.20-0.25

≤0.174 (Typical 0.160)

*Macro-bending (R30mm × 100 turns)

1550nm (dB)

TBD

TBD

TBD

≤0.1

1625nm (dB)

≤0.2

≤0.5

≤0.5

≤0.2

*Dispersion coefficient @ 1550nm (ps / nm / km)

≤22

≤22

≤22

≤22

 dispersion slop @ 1550nm (ps / nm2 / km)

≤0.070

≤0.070

≤0.070

≤0.070

PMD (ps/km1/2)

≤0.2

≤0.2

≤0.2

≤0.2

Geometric Parameter

 

 

 

 

Cladding outer diameter (um)

125±1

125±1

125±1

125±1

Core cladding concentricity (um)

≤0.8

≤0.8

≤0.8

≤0.8

Cladding circularity (%)

≤1.0

≤1.0

≤1.0

≤1.0

*Still under discussion, ITU-T Q5 group has no specific recommendations.

2. Design and manufacturing of optical fiber

 

Schematic diagram for optical fiber refractive index profile structure

Compared YOFC the ultra-low loss large effective area optical fiber with the traditional fluorine-doped external cladding structure ULL fiber, YOFC adopts pure silicon dioxide  (SiO2) as the optical fiber cladding, due to the reduction in the use amount of fluorine-doped materials, in terms of material preparation cost, preparation technology difficulty, environmental protection and other points of view, our ultra-low attenuation large effective area optical fiber products are more competitive in the cost.

3. Optical fiber and optical cable performance

3.1 Optical fiber attenuation

In terms of theory and practical points of view, the lower attenuation can reduce the number of repeaters and reduce the maintenance costs of long-haul communication network; therefore the continuous reduction in the optical fiber attenuation coefficient is the long-term goal of optical fiber research and development. For optical fiber R & D and manufacturing enterprises, if we can carry out the qualitative and quantitative analysis on various parts composed by the attenuation in theory, it can effectively help us find the best way to reduce attenuation and guide our work direction in the practical work.

The following table shows the specific comparison value for each loss contribution factors of the ultra-low loss and large effective area optical fiber and the standard G.652.D optical fiber at 1550nm.Currently, YOFC Company is reaching and developing the second-generation ultra-low attenuation optical fiber technology and a key breakthrough has been made, it is expected that the second-generation ultra-low attenuation large effective area optical fiber product will be released in early 2016, its effective area will be greater and the typical attenuation value will also be lower.

Standard G.652.D and ultra-low attenuation optical fiber attenuation spectral decomposition

 

Standard G.652.D

Ultra-low loss & Large Aeff. fiber

Rayleigh scattering contribution

0.162 dB/km

0.136 dB/km

Infrared absorption contribution

0.014 dB/km

0.014 dB/km

Others

0.016 dB/km

0.012 dB/km

Total attenuation

0.192 dB/km

0.162 dB/km

3.2 Fusion performance

Select ultra-low loss large effective area optical fiber as the next-generation long-distance communication optical fiber, and the optical fiber fusion performance is a critical parameter. G654 optical fiber fusion can be divided into two areas: The first is the self-fusion loss of G654 optical fiber; The second is the loss when it is mutually fused with G.652.D optical fiber network extensively used in the current network.

There are many factors affecting the fusion loss, but the mode field diameter mismatch is the most critical factor. As shown in the figure below, the typical fusion loss value of the ultra-low loss large effective area optical fiber with an effective area of 110μm2 and the standard G652 optical fiber is significantly lower than the typical fusion loss value of the large effective area optical fiber with an effective area of 130μm2 and standard G652 optical fiber. It is generally believed that the splicing loss of the optical fiber must be less than or equal to 0.08dB, while when the optical fiber with an effective area of 130μm2 is spliced  with standard G652, the splicing loss will be significantly greater than 0.08dB. It is the main reason for us to select 110μm2 as the optimal effective area of the next-generation communication optical fiber

 

 Comparison of the fusion performances when standard G652 optical fibers are fused with the optical fibers of different effective areas (110μm2 and 130μm2)

It should be noted that there are two kinds of fusing situations required for the optical fiber in the current network deployment: The first is the fusion between the optical cables, this part is mainly the mutual fusion between the optical fibers of the same kind, the larger mode field diameter mismatch situation may not be occurred; The second is the connection between the optical cable and a variety of active and passive equipment, in this case, we can avoid mode field diameter mismatch by the way of changing the equipment jumper to G654 optical fiber jumper, there are very fewer fusing connectors of all G654 optical fibers and G652 optical fibers in the actual deployment, which will not affect the overall link loss.

 

Comparison of self-fusion losses between G652 and G654 optical fibers: G652 typical value: 0.035dB, G654 typical value: 0.15dB

As shown in the above figure, we have tested and compared the self-splicing loss of the ultra-low loss large effective area optical fiber with an effective area of 110μm2 and the self-splicing loss of the standard G.652.D optical fiber. Compared with the traditional G652 single-mode fiber, because the large effective area can relatively reduce the impact of the mode field diameter mismatch, the self-splicing loss of ultra-low loss optical fiber with an effective area of 110μm2 is lower than the standard G.652.D optical fiber, and the typical value is about 0.015dB. Considering that most of splicings in the long-distance communication network is the self-splicing of the optical fibers of the same kind fibers, therefore, the use of the ultra-low loss large effective area optical fiber as the next-generation communication optical fiber can significantly reduce the link loss increase arising from the fusion loss.

3.3 Macro-bending loss

Another factor affecting the use of large effective area optical fiber on land is that the terrestrial cable installation and application environment are more complex than the submarine cable, it often needs to go through some of the corners or needs to leave enough cable or fiber lenth in the junction box, therefore, we must ensure that the terrestial optical fiber has better macro-bending resistance performance than the submarine optical fiber.

The main factor affecting the macro-bending is the profile design of the optical fiber. The depressed  trench structure is the main design scheme used for bend-insensitive G.657 optical fiber, while in our ultra-low loss large effective area optical fiber design, we use a similar structure, which can optimize the volume of the depressed trench to a reasonable value in order to obtain a better bending resistance performance. As shown in the following figure, compared with the standard G.652.D single-mode fiber, our ultra-low loss large effective area optical fiber has more excellent anti-bending performance, it can fully meet and be better the standard G.657.A1, thereby meeting various harsh and complex environment requirements in the actual deployment of the terrestrial cable application.

 

Comparison of macro-bending loss

3.4 Micro-bending loss

 

Comparison of micro-bending losses between the ultra-low loss large effective area optical fiber and the standard G652 optical fiber

The most worried thing for the use of the large effective area optical fiber on land is the micro-bending performance. Micro-bending is an important factor affecting the cabling design and cabling process, better micro-bending performance can reduce the difficulties in the cabling design and cabling process and improve the performance stability of the optical cable under different application conditions, especially in extreme environments. But the current mainstream methods for increasing the effective area of the optical fiber is to increase the fiber core layer diameter or reduce the fiber core layer relative refractive index, both designs will have a negative effect on the micro-bending of the optical fiber. For the ultra-low loss large effective area optical fiber in YOFC Company, we have effectively reduced the micro-bending loss of the ultra-low loss large effective area optical fiber by using the specially optimized and designed depressed trench structure design and combining with the special optical fiber coating process. The above figure shows the comparison of the micro-bending performances between our ultra-low loss optical fiber with an effective area of 110μm2 and the standard G.652.D single-mode fiber, it can be seen that our optical fiber has excellent micro-bending performance and its typical micro-bending loss is less than 0.5dB / km in the whole wavelength range.

3.5  Optical cable TCT performance

As discussed above, since the application environment of the terrestrial optical cable is more complex and harsh than the environment of the submarine optical cable, the terrestrials  optical cable needs to keep the link loss stability even under the more fierce temperature change conditions. To further validate the performance of our optical fiber after cabling, we have performed the relevant cabling experiments. In the summary of the relevant standards, the optical fiber temperature cycle test is commonly used to detect the changes in loss with temperature. In the experiment, we placed 12-core ultra-low loss large effective area (110μm2) optical fiber in an optical cable pipe of a GYTA for TCT experiment; the following figure shows the schematic diagram for our optical cable structure.

The figure below is the schematic diagram for optical cable structure

We can see from the following figure, when the temperature changes in the range of -40 degrees Celsius to +70 degrees Celsius, the loss changes of our ultra-low loss large effective area (110μm2) optical cable will be less than 0.01dB / km and far superior to 0.05dB / km specified by the IEC and ITU-T standards.

 

Changes in the optical fiber loss with temperature: 12 colors represent the loss changes of 12-core optical fiber

3.6 Loss changes during the cabling

The following figure shows the loss changes for YOFC ultra-low loss large effective area optical fiber optic in each procedure of cabling, the color histogram in different colors but in the same group represents the loss changes of one optical fiber in different technology processes of cabling. The blue strip in the left-most in each group is the original loss of the optical fiber, while the orange strip in the right most is the loss of the optical fiber after laying-up;12 groups indicate 12 different optical fibers in one tube. From the experiment, we can see that, as our optical fiber has excellent macro-bending and micro-bending performance, the loss of the optical fiber at 1550nm after  cabling will be at same level or lower than the original loss of the optical fiber before cabling. Therefore, the ultra  low loss and large effective area of YOFC increase the flexibility of the cable design, which does not require other special process to control during the laying up process, and reduce the time and costs for cabling.

 

Loss changes of  of 12-core optical fiber in same sleeve along with the laying up process

The ultra low loss and large effective area of YOFC  optical fiber has super low loss coefficient, larger effective area, excellent macro-bending and micro-bending performance as well as excellent adaptability of laying up, and is compatible to the existing G652 optical fiber, which is the best choice of the next generation 400G and super 400G terrestrial communication system.

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