Page 39 - Analysis Report of Global Market in the Submarine Cable Field (2017)

Where, E is the young’s modulus of the silica glass, r is the surface energy Fig.2 Tensile strength test of SeaCom ®
of the silica glass, a is the bond length of the Si-O chemical bond, and the
Sf is the cross-sectional area of the silica fiber. It can be calculated that
the theoretical fracture strength of the conventional 125μm fiber is about
15.6GPa. But in the process of preform manufacturing and melt drawing
of glass will inevitably produce defects or cracks because of stress and
impurity, and micro cracks will continue to growth. The fiber will break
when the crack expands to a certain extent as shown in figure 1.
Fig.1 Crack growth in optical fiber

Fig.3 Tensile strength test result before and after aging
According to the Griffith theory, the actual fracture strength of silica fiber is
deduced:
(2)

Where, L is the depth of micro crack, unit m. When the micro crack
depth is 0.1nm, the fracture strength of the optical fibers is only 7.5kg,
much lower than the theoretical strength, so the formation and growth
of micro cracks is the important factor which leads to the fracture and
the fatigue life decrease of optical fiber.

In the high temperature graphite furnace, the temperature of the fiber
is changed from the high temperature to the low temperature, the
chemical reaction is easy to occur in the region of 2200℃, and the silicon
monoxide vapor is produced:
(3)
When the fiber is in the region of 1400～-1600～, the silicon monoxide Subsequently, the Nd fatigue strength of the fiber was measured and
vapor will continue to react with carbon: calculated of the SeaCom® optical fiber, including initial, gel aged
(4) and damp-heat aged fiber, as shown in figure 4. All test results are
The silicon carbide solid particles produced in the reaction can be easily higher than 25, which indicate that the improvement of the silica glass
embedded into the silica glass that has not been transformed into solid and the coating material can improve the fatigue life. This makes it
state. possible to improve the reliability and safety of submarine optical cable,
which is of great significance to the important and expensive Marine
Therefore, the project has optimized the structure and temperature Communication.
field distribution of the drawing furnace in order to improve the tensile Fig.4 Nd test result before and after aging
strength and proof pass rate. In addition, the project also improved
the purification of the gas raw material, the pre release of the internal
stress of the preform, the concentration ratio of mixed acid, the acid
pickling time and the component of the resin coating material. It is
worth mentioning that the preform pickling time should be properly
controlled, mild corrosion will not be able to effectively remove
pollutants of the preform surface, in contrast, the severe corrosion will
leads to micro cracks on the surface of the perform.
High strength marine optical fiber were successfully prepared using
the above techniques and registered as the trademark "SeaCom®".The
tensile strength of the SeaCom® marine fiber is shown in figure 2. The
sample is taken as an example, the fracture force is 73.79N, and the
stress is 6012.788MPa. In the case of good fiber strength, stretch without
skidding, the tensile curve is close to a straight line.

The optical fiber gel aging (gel soaking, 85℃, 30d) and damp-heat
aging (85℃, 85% RH, 30d) test were also carried out. A large number of 2.2Large Reel Length Technology
tensile strength tests and analyses are performed on the initial fiber and After the improvement of the optical fiber strength, it can effectively
the aged fiber, as shown in figure 3. The results show a good distribution reduce the fiber breakage rate under the high tension proof, reduce
of tensile strength of initial, gel aged and damp-heat aged fiber. The the fiber splice point, thus greatly reduce the unreliable factors in the
median strength is more than 6.0GPa, and the Weibull slope is more than long distance communication. Therefore, it is necessary to enlarge the
130 with the cumulative probability 15%-85%. traditional 25km and 50km reel length for high strength optical fiber.
In the design of the optical fiber reel capacity, the optical fiber can be
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