Usage Scenarios Of ODN Unbalanced PLC Splitter

In the article “What Is Unbalanced Splitter And Application in ODN Networking?” (hereinafter referred to as “Unbalanced splitter”), it is introduced that due to the low insertion loss of the cascaded ports of unbalanced splitter, ODN links are suitable for chain type networking. This article continues to discuss the specific scenarios for which unbalanced splitter is applicable for, as well as the networking solutions for specific scenarios.

Adaptation Scenario Analysis

The traditional balanced splitter ODN link usually adopts a tree network structure for drop cable, each fiber distribution box like a “leaf” and generally allocated with 2 cores (one main and one backup), as shown in Figure 1. This structure can adapt to the access needs of various scenarios.

If ODN adopts unbalanced splitter, we can use a single core cable to cascade the fiber distribution box along the optical cable route to form a single chain structure, as shown in Figure 2. But when there are many branches and longer branch routes in the fiber optic cable, the single chain structure will double the link length due to the circuitous routing of the fiber optic link, thereby increasing the engineering cost and reducing the security of the link.

To reduce the routing detour, unbalanced splitting ODN can adopt dual chain and multi chain networks (refer to Figures 6 and 7 of the “Unbalanced splitter” article) 加上文章链接或者锚点？. The end of the fiber optic cable routing without branches adopts a single core fiber optic cable, while where with branches adopts a regular fiber optic cable, as shown in Figure 3. The double chain 1×2 or multi chain 1×4 optical splitters are centrally installed in the junction box / cabinet / fiber distribution box.

In the actual ODN drop cable network, the situation of cable routing branch is very complex. If build network as figure 3, the setting and connection of optical splitters will be more complex, which bring great challenges to engineering design, construction, and ODN maintenance. Therefore, when there is a large number of fiber optic cable routing branches, it is not suitable for ODN to use unequal optical splitting.

Unbalanced splitter is suitable for use in scenarios where optical cables are routed into chains. Because unbalanced splitting always use single core cable, and traditional equal ratio splitter distribution boxes are equipped with reserved fibers. Therefore, unbalanced splitter is particularly suitable for scenarios where the fiber optic box in the original line need to continues to extend towards the end, as shown in Figure 4.

Unequal splitter ODN networking Types

According to branch chains distribution and the quantity of fiber distribution boxes in each chain, the unbalanced splitting ODN should adopt dual chain or single chain networking.

When there are 4 to 6 pcs fiber distribution boxes on the optical cable chain, ODN should adopt single chain networking (the upper limit of the number of fiber distribution boxes on the chain is related to the optical power budget of PON, see the article “Unbalanced splitter” for details); When there are 2 or 3pcs fiber distribution boxes, the ODN should adopt dual chain networking.

Single chain unbalanced splitter

If there are short distance branch fiber optic cables in the route, the fiber distribution box (box ⑤ in Figure 5) in the branch cable can be connected in series into the chain.

If fiber distribution boxes exceeds 6pcs, the 4 to 6 fiber distribution boxes at the end should use unbalanced splitter, while the rest fiber distribution boxes use balanced splitter.

Double chain unbalanced splitter

When extending 2-3 fiber distribution boxes from the existing cable line to the end, as shown in Figure 4, we can set a 1×2 balanced splitter in the distribution cabinet to combines two branch chains under the same cabinet into one PON port, thus double chain network is built.

In dual chain structure, need only the two chains belongs to the same distribution cabinet, not request the two chains to be terminated in the same drop cable in the distribution cabinet.

In the fiber optic network structure shown in Figure 5, if the branch cable of the fiber optic distribution box ⑤ is long, it is not advisable to connect the distribution box ⑤ in series to the chain. Instead, the fiber optic distribution box ⑤ and box ④ can be formed into a separate branch chain, as shown in Figure 7.

The ODN in Figure 7 should consist of a double chain structure as shown in Figure 8. There are a 1×2 balanced splitter + a 1×9 unbalanced splitter installed inside the fiber distribution box ④.  In distribution box ⑤ install a 1×8 splitter.

Investment Comparison, balanced splitter vs unbalanced splitter

 If the scene shown in Figure 5 adopts proportional splitting, the fiber optic cable network structure is shown in Figure 9.      

According to Figures 5 and 9, we can count the differences in ODN investment under different optical splitting methods (referring to the cost level of a certain province in central China in 2023), As shown in Table 1, the lengths of each optical cable section in Figure 5 refer to Figure 9.

From Table 1, it can be seen that when utilizing the spare fibers of existing cables, the investment of using unbalanced splitter can be greatly reduced. The longer the length of the used cable, the more the investment is reduced. Due to the fact that the number of fibers used for unbalanced splitter is much lower than that for equal ratio splitter, even if the length of the constructed optical cables is the same, the ODN cost for unbalanced splitter is only about 89% of that for balanced splitter.

Characteristics of unbalanced splitter

Except the network and investment difference, there are other difference like below:

• Easy to manage. Due to the fact that each cascade of splitters generates approximately 2.0dB of insertion loss, the connection between the splitter box and the user in the ODN link can be seen from the receiving power of the user ONU.
•  In addition, the fiber cores of optical cables that end at the distribution cabinet with unbalanced splitter are often only 10% to 20% of that of balanced splitter, greatly reducing the difficulty of fiber management.

• Low safety. Due to its chain structure, any failure in the ODN link will have an impact on users below the point of failure.
• The construction difficulty is small. In the circuit, only single core optical cables are often involved, and the optical cables only need to be terminated at the fiber distribution box. There is even no optical cable joint in the circuit.
• Poor expansion capacity. Each fiber distribution box with balanced splittter usually reserves one core for expansion; However, the expansion capacity of unbalanced splitter is very limited, and only when there is a certain surplus in the optical power of the link, can replace 1×5 splittter with 1×9 splitter to expand the capacity.  
• Poor business integration ability. The balanced splitter ODN cable have a large number of fibers, it can integrate wireless forward transmission services, data dedicated lines, and other services, while unbalanced splitter ODN often use single core cable and can only access PON services.

Application suggestions for unbalanced splitter

In summary, unequal splitting is not suitable for scenarios that require access to various services such as wireless, data dedicated lines, home broadband, or scenarios with multiple fiber optic routing branches.

Unequal split ratio is suitable for scenarios where cable distribution with chain network, users’ services are accessed through PON, and the security requirements for accessing services are not high. It is particularly suitable for situations where the remaining fibers of existing fiber distribution boxes are extended towards the ends.

Currently, unbalanced splitter mainly use single core cable, which leads to low link security, difficulty in expanding capacity, and difficulty in adapting to local detours of optical fiber links (such as the access link of fiber distribution box ⑤ in Figure 5), duplex optical cables may be a better choice.         

FAQ:

What is an unbalanced splitter?

Unbalanced splitter is a optical passive device which split the input light power unevenly at outputs, like 1%:99%, 2%:98%,…10%:90%, 20%:80%, 30%:70%,40%:60% 50%:50%, 30%:70%. The evenly split ratio is 50%:50%. This is mainly the parameters of the 1×2 splitter.

Before the unbalanced splitter chip was developed, 1×3, 1×5 1×9 splitter are all made on the basis of 1×2 splitter.

Now the chip already fix the split ratio, so if you need unbalanced splitter 1×9 70/30,then everything is clear: input is 1 pigtail, output 9 pigtails– output 1  of input power, the rest 8 channels share the rest 30% power by 3.75% each.

What is a balanced splitter?

Balanced splitter is a optical passive device which split the input light power  evenly at outputs, and with balanced signal loss at the output too.

For example:

• 1×2 splitter outputs are: 50%:50%
• 1×4 splitter outputs are: 25%:25%:25%:25%
• 1×8 splitter outputs are: 12.5%:12.5%:12.5%:12.5%:12.5%:12.5%:12.5%:12.5%
• 1×16 splitter oputputs are:6.25%:6.25%:6.25%…
• 1×32 splitter oputputs are:3.125%:3.125%:3.125%…
• 1*64 splitter outputs are:1.5625%:1.5625%:1.5625%…
• 1×128 splitter outputs are:0.78125%:0.78125%:0.78125%…

Does balanced sound better than unbalanced?

No, can not say which is better, all should decide on the real situation.  

Please read above article carefully to find the answers.