I. Overview

In recent years, with the continuous growth of data traffic, the data transmission and bandwidth pressure of traditional bearer networks have continued to increase, and the transmission rate of the backbone network will continue to be upgraded from 100G to 200G/400G and other higher rates. In the next two years, the super-100G network will account for more than 60% of the overall market share, and 400G+ will become the mainstream application of the super-100G network. Experts from China Mobile Research Institute said that from the perspective of the backbone network, single-wave 400G is about to open and enter a long-term cycle. Therefore, deploying fiber optic cable products supporting 200G and 400G systems in advance is the basis for building a high-speed information network. However, the G.652 fiber used in the existing network can no longer meet the ultra-high speed, ultra-large capacity, and ultra-long-distance transmission needs of future optical transmission networks.

As a low-loss and large-effective-area optical fiber, G.654.E can meet the needs of ultra-high-speed and ultra-long-distance transmission, and has stood on the stage of history.

two. Introduction to G.654E Fiber

1. What is G.654 fiber

  The G.654 series is a fiber optic standard primarily established for long distance transmissions such as undersea transmission systems. The official name of G.654 fiber is "Cut-off Shifted Fiber (CSF)", which is suitable for the C~L band (1530~1625nm) which minimizes the transmission attenuation loss.

According to the classification of the International Telecommunication Union ITU-T, the G.654 series of optical fibers can be divided into five sub-categories: A, B, C, D and E. Among them, G.654.C and G.654.D are characterized by ultra-low loss, expanded mode field diameter (MFD), and reduced nonlinear effects, resulting in greatly improved transmission performance (improved optical signal-to-noise ratio). In addition to submarine optical cables, the data transmission speed of terrestrial transmission systems is also becoming faster and larger, and the transmission capacity is also increasing, which also requires optical fibers to have low loss and low nonlinearity. As a result, a subcategory (G.654.E) was established for the first time in 2016 as a dedicated classification within the G.654 family for terrestrial transmission systems.

2.G.654.E fiber characteristics

The effective area of the new G.654.E fiber is increased by 62.5%, the fiber loss is reduced by 10%, and the transmission performance is improved. It has excellent performance in carrying over 100G, which is conducive to all-optical networking. Therefore, the G.654.E fiber with both low nonlinear effect (large effective area) and low attenuation coefficient is the preferred fiber for 200G, 400G and future Tbit/s ultra-high-speed transmission technologies.

(1) The material of the optical fiber

Standard fibers use GeO2 (silicon dioxide) to increase the refractive index in the core, and silica glass is used for the cladding. However, G.654 is the structure of pure silica core silica fiber: the core is made of pure silica glass, and the refractive index is lowered by adding elements such as F (fluorine) to the silica glass of the cladding. Since the core is made of pure silica glass, low transmission loss can be achieved and it is also best suited for long distance transmission.

(2) Low nonlinear effects

Improving network transmission performance is a systematic project. For example, 400G long-distance transmission faces key challenges such as the Shannon limit, high baud rate devices (high speed, high performance), and ultra-wide spectrum resource technology (C+L). The means to solve the Shannon limit problem is to improve the optical signal-to-noise ratio. G.654E fiber increases the mode field diameter of the fiber and supports higher incident power; the larger the mode field diameter of the fiber, the smaller the energy density through the fiber cross section, thereby improving the nonlinear effect of the fiber and improving the optical fiber communication system signal-to-noise ratio. Compared with G.652.D on the same cable, G.654E has an improved OSNR margin (1.82dB-2.78dB) for the same rate system, and about 1dB increase in fiber input power.

(3) The cost of the relay station can be controlled

Compared with G.652 fiber, G.654.E fiber has obvious advantages in distance without electric relay, which can extend the transmission distance without electric relay, which can reach more than 900km, reducing the number of relay station settings.

(4) Comparison of key indicators between G.652.D and G.654.E

three. Commercial Engineering of G.654.E Optical Cable

For a long time, the three major domestic operators have been actively promoting the testing and commercial use of G.654.E optical fibers. The most active one is China Unicom, which has been working with the industry to apply and promote G.654.E optical fibers. From 2015 to 2017, China Unicom carried out pilot projects on the eastern trunk network and the western trunk network respectively. Among them, the eastern pilot network selected Jinan-Qingdao, Shandong, which has a large bandwidth demand and is most likely to deploy 400G technology first. The length of the optical cable is about 430km. The transmission performance of the 400G system was tested and verified on the live network while the effects of manual and airflow method on the performance of large effective area optical fibers were laid out. The western test network selected the Hami-Balikun section of Xinjiang, which has a complex working environment and passes through the Gobi Desert, Tianshan Mountains and grasslands. The length of the optical cable is about 150km. performance.

China Telecom is also actively exploring and taking the lead in the industry to introduce G.654E ultra-low loss and large effective area new optical fibers. From 2019 to 2021, China Telecom carried out the Shanghai-Jinhua-Heyuan-Guangzhou G.654.E optical fiber and cable trial commercial project, all G.654.E deployment, the actual line is up to 2000km, the attenuation is ≤0.174dB/km, and the effective area is 130μm2 . And based on the optical cable, a single-wavelength 400Gb/s DWDM system ultra-long-distance transmission network test was carried out. Compared with the traditional G.652D fiber core environment, the application of G.654E optical cable can increase the OSNR of the system by 3.5dB, which can extend the transmission distance without electrical relays, reduce the number of electrical relays, and save energy and reduce consumption. It will provide strong support for the development and evolution of single-wave 1T and higher rate transmission systems in the future.

As early as 2016, China Mobile also launched a large effective area ultra-low loss optical fiber trial commercialization on the Beijing-Jinan-Nanjing line. The optical cable adopts the mixed fiber co-cable structure of G.654E+G.652D.

Due to the high input power, high transmission capacity and low transmission loss of G, 654.E optical fiber, it will be widely used in the line transmission of large data centers such as the State Grid and major operators in the future.

State Grid

China Mobile

China Unicom

China Telecom

In November 2021, China Telecom decided to focus on deploying G.654.E fiber optic cables in the four-circle six-axis area. The four-circle refers to the four economic circles of the Yangtze River Delta, Beijing-Tianjin-Hebei, Chengdu-Chongqing, Guangdong, Hong Kong and Macao. The six-axis is arbitrary. The backbone of the two economic circles.

Four. Test Criteria and Challenges

1. China Telecom Group on G.654.E ultra-low loss optical fiber centralized acquisition test items and test technical indicators

It can be seen from China Telecom Group's acceptance and maintenance requirements for G.654E optical cables:

In terms of the transmission performance of the optical cable, the loss test of 1625nm is added. The attenuation coefficient of 1625: the maximum attenuation coefficient does not exceed 0.20dB/km; the test requirements for polarization mode dispersion (PMD) and chromatic dispersion (CD) are still retained. 1550mm polarization mode dispersion coefficient maximum single disk: < 0.125p/m (single disk value), 1550 dispersion coefficient: 17~23ps/(nm·km).

Requirements for welding: Average value of joint loss: the average value should not be greater than 0.03dB, and the maximum value of joint loss: the maximum value should not be greater than 0.05dB.

2.G.654.E Trunk Optical Cable Project Acceptance and Maintenance Challenges

five. Limp's test solution

1. Sumitomo TYPE-82C+ proprietary G.654E fusion mode, facing the fusion problem of G.654.E

Sumitomo Electric's high-precision core-aligned fiber fusion splicer TYPE-82C+ is equipped with a number of special fusion splicing conditions suitable for G.654.E fibers.

(1) Nano welding technology: Through the use of exclusive artificial intelligence technology, the welding accuracy and welding efficiency are greatly improved. This technology can be used in harsh environments and does not require the skill level of the operator. Even in the case of off-axis, skew, etc., it can automatically make small adjustments to the discharge intensity and drive motor to give full play to the best performance.

(2) Welding time: SM FAST mode: 5 seconds; AUTO mode: 7 seconds.

(3) Automatically identify different types of optical fibers, and perform ultra-low loss fusion splicing.

(4) Double heating furnace, greatly improving the welding efficiency

(5) With G.654E special fusion splicing mode: using fiber core alignment technology, the estimated loss accuracy is high

(6) Automatic identification of G.654 and G.652 fiber cores: Through automatic fiber identification technology, even different types of fibers can accurately identify the fiber type, set the best suitable conditions, and can also achieve low-loss fusion splicing.

(7) Low splicing loss: It meets the acceptance standard of G.654E by Telecom Group, see the following table for details.

2.EXFO FTBx-750C OTDR, for 1625nm optical cable loss test

EXFO OTDR has a high market share in the industry and is mainly used in: trunk optical cable construction acceptance, maintenance and repair, optical cable factory production/factory inspection and third-party testing, etc.

The FTBx-750C combines high dynamic range and high resolution for very precise fiber/optic cable testing.

In terms of G.654E testing experience:

(1) Participate in the acceptance of China Telecom Group Shanghai Jinhua Heyuan Guangzhou trunk line optical cable line project;

(2) Participate in the G.654E optical cable factory inspection of YOFC, Fiberhome and Hengtong;

(3) Large-scale use in various production stations of optical cable factories such as YOFC, Fiberhome, Hengtong, Zhongtian and Futong.

Features:

(1) Display: 8 inches     

(2) Wavelength: 1310±20nm, 1550±20nm, 1625±10nm

(3) Dynamic range (pulse width 20us, SNR=1) 46dB

(4) Event dead zone: ≤ 0.5m

(5) Linearity: ±0.03dB/dB               

Long-distance testing is a test for the linearity of OTDR. EXFO's excellent linearity makes the repeatability of field test data very stable

The OTDR linearity is not good, the long-distance end curve is upturned and the average loss of the optical cable is small

3. EXFO FTB-5500B/5800, for PMD/CD testing

EXFO Dispersion Analyzers meet a variety of chromatic dispersion and polarization mode dispersion testing requirements, from validating fiber legacy capacity to upgrading networks to specified speeds. Designed for ultra-long-distance, high-speed transmission applications, it provides a guarantee of test speed, accuracy and performance.

(1) FTB-5500B Polarization Mode Dispersion (PMD) Analysis Module

The FTB-5500B PMD analyzer module is a PMD analyzer that complies with the latest FOTP-124A test standard and is based on extended interferometry. It can be used for the measurement of PMD of optical amplification lines or ordinary lines. It is the first instrument in the industry that can pass through EDFA for PMD test based on interferometry. The measurement is more accurate due to the removal of the effect of the autocorrelation peaks in the interference pattern on the PMD. This method is not only suitable for ordinary optical cable and device testing, but also for aerial optical cables and other tests with large environmental changes. It is also the first PMD analyzer in the industry that can measure PMD as low as zero. main feature:

● 4.5 seconds test within full PMD test range

● Without the influence of autocorrelation peak, the test accuracy is higher

● The detection method can be traced back to NIST (National Institute of Standards and Technology)

● Ideal for overhead fiber optic cables

● Patented technology for system-level testing through EDFA

● Accuracy for 100 Gbit/s

● Complies with the latest measurement standard FOTP-124-A, based on extended interferometry.

(2) FTB-5800 Chromatic Dispersion (CD) Analysis Module

FTB-5800 is a dispersion analyzer based on the principle of phase shift method for dispersion measurement. The test method conforms to the FOTP-169 standard. This method is a reference measurement method for dispersion and is suitable for dispersion analysis of all types of optical fibers. Using EXFO's patented technology, dispersion measurement can be performed without the need for communication between the receiving end and the transmitting end. In the link, it can be tested by unidirectional devices such as EDFA and isolators. main feature:

● 0.1nm actual dispersion test step size: 950 sampling points

● High accuracy based on phase shift method: it is possible to evaluate whether the dispersion compensation slope is suitable

● Precise testing of hybrid fibers

● Residual dispersion test capability, can penetrate EDFA

Seven. Summary

G.654.E optical fiber can significantly increase the transmission distance of high-speed systems such as 400G WDM without electrical relays. It is the construction of ultra-high-speed, ultra-long-distance, and large-capacity backbone optical networks. One of the main options for new fiber builds.

Linpu Instruments has 30 years of industry heritage in the field of optical fiber/optical cable testing, serving to provide a package of testing solutions for applications such as R&D, production, inspection, engineering acceptance, maintenance and repair of light rods/optical fibers/cables.

We are committed to providing excellent on-site test solutions for the welding, engineering acceptance and routine maintenance of G.654E construction.