How new optical splitters can significantly reduce ODN expansion costs?

In the above article “How the new optical splitter doubles the access capability of the Combo port”, the current resource usage of the Combo port and the principle of the capacity-doubling optical splitter (hereinafter referred to as: new optical splitter) are introduced. The following section will introduce the use method and effect of the new optical splitter.

How to use new optical splitter

The new optical splitter can be used for both secondary splitting and primary splitting. When a new optical splitter is used for secondary optical splitting, taking an ordinary 1×4 splitter as an example, you only need to replace the original optical splitter in the fiber splitter box with a 4+4 optical splitter, plug the GPON user’s pigtail in the original splitter port into the GPON output port of the new optical splitter, and plug the XG-PON user’s pigtail into the XG-PON output port of the new optical splitter, as shown in Figure 1. After capacity expansion, the new optical splitter still has 4 free ports to accommodate users.

When the new optical splitter is used for first-level splitting, taking the ordinary 1×64 splitter as an example, you only need to replace the 1×64 splitter with a 64+64 type splitter. Although the average number of installed users of the Combo port in the first-level splitting scenario is nearly twice that of the second-level splitting scenario, the bandwidth utilization is still very low. After replacing with a new optical splitter, the bandwidth utilization threshold (usually 70%) can generally still be met within a few years.

When ODN adopts two-level splitting, the new optical splitter can also be installed in the distribution cabinet. In this case, the fiber distribution box needs to install two ordinary optical splitters of the same model. From the distribution cabinet to the fiber distribution box, 2 core fibers are required, as shown in Figure 2. This solution can be used in metropolitan area networks with a large number of optical cable cores (3 cores and above) configured from the distribution cabinet to the fiber distribution box section.

Cost analysis per port

Due to the addition of a mux&demux inside the new optical splitter, the unit price of the new optical splitter is several times higher than that of an ordinary splitter of the same capacity. For example, the unit price of a 1×16 splitter is only about 46 RMB, while the unit price of an 8+8 capacity doubling splitter is as high as 290 RMB.

However, after using the new optical splitter, the number of users with fiber access at the Combo port and the combining side can be doubled, thereby saving investment in Combo ports and fiber optic cables. Calculated based on the cost per port when the new optical splitter is installed in the fiber optic cable distribution box under secondary splitting, compared with conventional expansion splitters, the cost per port of using the new optical splitter in urban areas is only about 1/3 of the original plan, and in suburban and general rural areas is only about 1/5 of the original plan. The cost comparison of the two options in urban areas, suburbs and general rural areas is shown in Table 1.

In remote rural areas, because the number of users connected to the combo port is fewer and the length of the fiber on the combining side is longer, the cost per port of using new optical splitters in remote rural areas is relatively lower, even less than 1/10 of the original solution. The cost comparison of the two options in remote rural areas is shown in Table 2.

Using the same method, the per-port cost of a new optical splitter when installed at a wiring optical intersection under secondary splitting and first-level splitting can be estimated. Table 3 shows the cost comparison of each port of the two solutions in different scenarios.

Construction timeliness analysis

When fixed broadband port expansion adopts the conventional method, resource survey and verification of uplink resources are required before expansion. If the first-level splitter port is not sufficient, a new first-level splitter and related first- and second-level link cables are required, synchronization requires the entry of resources. In this scenario, no matter how large the expansion scale is, the minimum expansion time is 6 days. It usually takes 7 to 15 days to expand the capacity of an ODN with a distribution cross cabinet.

When using a new optical splitter to expand capacity, no resource survey is required, and the original resource information can be adjusted quickly to be activated. The activation time can be completed within 1 day at the fastest. Expanding a cross cabinet generally only takes 1 to 2 days, which can meet the timeliness requirements of the broadband market.

Insertion loss test of new optical splitter

Since the downlink of the Combo optical module includes two wavelengths, 1490nm and 1577nm, when using an ordinary power meter to test the downlink optical power of the PON in the ODN link, the test result is the sum of the optical power of the two wavelengths, which is about 3.0dB higher than the optical power of a single wavelength.

This issue has also been analyzed in the article “How to Calculate the Transmission Limited Distance of XG-PON”. When the ODN link uses an ordinary splitter, the splitter output port has two downlink wavelengths. However, after replacing the ordinary splitter with a new optical splitter, the splitter output port only has one downlink wavelength. Therefore, after replacing the optical splitter, use an ordinary power meter to test the insertion loss of the new optical splitter. The insertion loss will be 3.0dB greater than the normal value. Therefore, when the insertion loss of a new optical splitter is tested using an ordinary optical power meter, there will be an error of about 3.0dB. It is recommended to use the received optical power of the onu in the network management for testing. Compared with ordinary splitters, the insertion loss of splitters with doubled capacity is only about 0.5dB higher. For example, the insertion loss of an 8+8 optical splitter is only about 0.5dB higher than that of an ordinary 1×8 optical splitter.

Conclusion

In recent years, operators’ fixed Gigabit services have made great progress, but the number of users connected to each PON port and the bandwidth utilization of the Combo port are still very low. The new optical splitter doubles the number of users by separating the GPON and XG-PON channels in the ODN at the user end. Compared with traditional splitters, although the unit price of new optical splitters is higher, the cost per port is lower. It has significant cost advantages in urban, suburban and rural areas; no new optical cable lines are required, and capacity expansion is more convenient. In addition, the insertion loss of the new optical splitter is only slightly higher than that of traditional splitters, which will not affect network performance and is very suitable for users to expand the capacity of existing Combo ports.

Relatively speaking, in urban areas, ODNs that use first-level splitting have a high average number of Combo port users, and the investment saved by using new optical splitters for capacity expansion is limited. Therefore, it is not recommended to use new optical splitters for capacity expansion. For ODNs that use two-level optical splitting, especially the current combo port with a total splitting ratio of 1:32, the investment saved by using new optical splitters for capacity expansion is very considerable, and the application of new optical splitters should be actively promoted.