Traditional ODN usually use balanced split ratio PLC splitter, the optical power of each output port is the average distribution ratio of that of input ports, commonly use 1xN and 2xN series. And the most widely used are mini module splitter, cassette splitter and modular splitter, the most widely used are 1×4, 1×8 and 1×16 splitlter
However, for balanced splitter, the more drop cable introduced, the higher the project cost. So in some specific scenarios (such as FTTR), unequal optical splitter begins to be gradually adopted in the ODN network.
What is unbalanced splitter?
The power of outputs of balanced splitter are all the same, that is the insertion loss of each output are the same. For example, the optical power of each output port of a 1:4 optical splitter is (approximately) 25% of the optical power of the input port.
Unequal ratio optical splitter is a fiber splitter with differnt optical power at output ports. Our company can provide 1×3 x1x5 1×6 1×9 1×12 unbalanced splitters.
The commonly used unequal ratio optical splitter in ODN is 1xN. There is 1 input port, 1 cascade port, and (N-1) output port. The commonly used model in projects are is 1×5 and 1×9. Take 1*2 splitter for example, the common optical ratio for 2 output ports are 10/90, 15/85, 20/80, 30/70, etc
At the beginning, the proportional splitter is usually cascaded with the lower output power of 1×2 optical splitters.
For example:
the 1*5 splitter is cascaded wiht a 1×4 splitter after the 15% output pigtail of 1×2 15%/85% splitter.
The 1×9 splitter is cascaded with a 1×8 splitter after the 30% output pigtail of 1×2 30%/70% splitter.
Among them, the direct output port of 1×2 unbalanced splitter is a cascade port, and the output port of equal ratio splitter is a service port.
Unbalanced splitter insertion loss
The insertion loss of the unbalanced splitter cascade port is relatively small, making it very suitable for cascading multiple splitters into a chain for ODN networking, as shown in Figure 5.
The maximum number of users that can be accessed by a single PON port during chain networking is proportional to the number of cascaded splitter. The number of splitters that can be cascaded in ODN links is mainly related to the insertion loss of the splitters.
| Split ratio | 1×2 split ratio | Port | Port insertion loss | Port insertion loss | Port insertion loss |
| Factory 1 | Factory 2 | Industry standards (not final) | |||
| 1×5 | 85% | Cascade port | 1.45 | 1.75 | 1.8 |
| 1×5 | 15% | Output port | 15.35 | 15.4 | 157 |
| 1×9 | 70% | Cascade port | 1.9 | 1.8 | 2.5 |
| 1×9 | 30% | Output port | 15.7 | 15.8 | 17 |
Link model of unbalanced splitter in ODN
The unbalances splitter ODN link mainly adopts single chain and double chain networking structures, and it is not suitable to use multi branch chain networking structures.
4.1 Single chain unbalanced splitter
When ODN adopts a single chain structure (see Figure 5), the transmission distance of PON is shown in Table 2. The calculation method of PON transmission distance can be found in the article “How to Calculate the Transmission Restricted Distance of XG-PON”. Due to the significant impact of the insertion loss of the cascaded ports of unbalanced splitters on link attenuation, this article combines the measured values of the insertion loss of corresponding products from some manufacturers, the insertion loss of the 1×9 splitter cascade port is 2.0dB, and the insertion loss of other ports is determined according to YD/T 2000.3 (to be released).
| Item | Unit | 1×5 | 1×9 |
| Maximum allowable channel insertion loss | dB | 29.0 | 29.0 |
| Cascaded insertion loss of optical splitters | dB | 1.8 | 2.0 |
| Optical splitter output insertion loss | dB | 15.7 | 17.0 |
| Other active connection losses (note) | dB | 1.5 | 1.5 |
| Line maintenance allowance | dB | 1.0 | 1.0 |
| Fiber optic fusion attenuation per km | Db/Km | 0.26 | 0.26 |
| Number of fiber distribution boxes | pc | 7 | 6 |
| Transmission limited distance | km | 6.9 | 5.8 |
| Maximum number of loading users | pc | 32 | 48 |
Note:Refers to the active connection loss at the ODF and fiber optic cable junction box.
From Table 2, it can be seen that when using the single chain network shown in Figure 5 for ODN, the total number of fiber distribution boxes on the chain should not exceed 6 pcs 1*9 splitter and 7 pcs 1×5 splitter.
4.2 Dual chain unblanced splitter
When the number of fiber distribution boxes in a “chain” is small, a PON port can also pass through 1×2 into a proportional splitter as shown in Figure 6.
When the ODN is the networking structure shown in Figure 6, the transmission distance of the PON and the maximum number of users that the PON port can access are shown in Table 3.
| Item | Unit | 1×5 | 1×5 | 1×9 | 1×9 |
| 1×2 balances splitter insertion loss | dB | 4.4 | 4.4 | 4.4 | 4.4 |
| Number of fiber distribution boxes in single chain | pc | 4 | 5 | 3 | 4 |
| Transmission limited distance | km | 10.8 | 3.8 | 11.9 | 4.2 |
| Maximum number of loading users | pc | 40 | 48 | 48 | 64 |
4.3 Multi branched chain unbalanced splitter
Although the unequal ODN link also supports four branch chains, as shown in Figure 7, this is not significantly different from the link model of unequal splitting and cannot fully leverage the advantages of unequal splitting.
When the ODN has 4 branch chains, the transmission distance and the maximum number of users that can be accessed by the PON port are shown in Table 4.
| Item | Unit | 1×5 | 1×5 | 1×9 |
| 1×4 balanced spliter insertion loss | dB | 8.0 | 8.0 | 8.0 |
| Number of fiber distribution boxes in single chain | pc | 2 | 3 | 2 |
| Transmission limited distance | km | 10.8 | 3.8 | 5.8 |
| Maximum number of loading users | pc | 48 | 64 | 64 |
Conclusion
Due to the fact that the transmission distance of PON in Tables 2 to 4 is calculated based on the worst-case values, when ODN is constructed according to the above link model, there is often an excess of 2.0dB to 4.0dB in ODN link attenuation. Therefore, the actual number of fiber splitters for each branch of ODN link is often one more than that in Figures 5 to 7.
Unbalanced splitter is suitable for chain based networking structures. Compared with balanced splitter, Unbalanced splitter has poor security and fewer users per PON port, making it more suitable for using GPON access in rural areas. Although unequal ratio splitting also supports multi chain and other flexible splitting methods, it will increase the difficulty of construction, maintenance, and management and is not recommended.
FAQ
Is 1:2 a PLC splitter or FTB coupler ?
If 1×2 is used to form an uneven splitter with other equal splitters, it is FBT coupler. But now there are unbalanced chips which replacing 1×2 coupler.
However, if there is no chip with a corresponding spectral ratio, it is necessary to use 1×2 fused splitter for docking.
Is 1×2 splitter Planar Waveguide Circuit splitter or fusion melt coupler ?
It can be made by PLC or fused. At the beginning, the fusion method was used because there were no chips, but with the deepening development of FTTR, uneven chips have been developed. However, not all unblanced splitter ratio can be made by PLC, if there is such ratio chip, can do by chip, if not, will use fusion technology too.
Which uneven splitters can be made with chips?
Yes, due to technological progress and increasing applications, some unbalanced splitter chips have been gradually developed without the need for fusion bonding. Below introduce some chips and the specification which we can offer for your reference.
| 1:3 Split Ratio | IL max (dB) Channel 1 | IL max (dB) Channel 2-3 | IL uni(dB) Channel 2-3 | PDL (dB) | Return Loss(dB) | Directivity(dB) |
| 80%：20% | 1.5 | 11.2 | 1.5 | 0.3 | 55 | 55 |
| 70%：30% | 1.9 | 9.3 | 1.5 | 0.3 | 55 | 55 |
| 60%：40% | 2.3 | 8 | 1.5 | 0.3 | 55 | 55 |
| 40%：60% | 4.3 | 6 | 1.5 | 0.3 | 55 | 55 |
| 1:5 Split Ratio | IL max (dB) Channel 1 | IL max (dB) Channel 2-3 | IL uni(dB) Channel 2-3 | PDL (dB) | Return Loss(dB) | Directivity(dB) |
| 85%:15% | 1.4 | 16.2 | 1.5 | 0.3 | 55 | 55 |
| 80%:20% | 1.5 | 14.8 | 1.5 | 0.3 | 55 | 55 |
| 70%:30% | 2.5 | 11.7 | 1.5 | 0.3 | 55 | 55 |
| 60%: 40% | 4.3 | 9.5 | 1.5 | 0.3 | 55 | 55 |
| 75%:25% | 1.6 | 14.5 | 0.6 | 0.2 | 55 | 55 |
| 67%:33% | 2.2 | 12.8 | 0.6 | 0.2 | 55 | 55 |
| 50%:50% | 3.6 | 10.2 | 0.6 | 0.2 | 55 | 55 |
| 95%:5% | 16 | 7.2 | 0.6 | 0.2 | 55 | 55 |
| 1:9 Split Ratio | IL max (dB) Channel 1 | IL max (dB) Channel 2-3 | IL uni(dB) Channel 2-3 | PDL (dB) | Return Loss(dB) | Directivity(dB) |
| 85%:15% | 1.3 | 20.7 | 1.5 | 0.3 | 55 | 55 |
| 80%:20% | 1.5 | 18.3 | 1.5 | 0.3 | 55 | 55 |
| 70%:30% | 1.9 | 16.2 | 1.5 | 0.3 | 55 | 55 |
| 60%: 40% | 2.4 | 14.8 | 1.5 | 0.3 | 55 | 55 |
Are uneven splitters made from chips more reliable than fused ones?
Yes, the fusion joint is easily subjected to external forces, which can increase the loss or cause fiber breakage due to bending. And the production process by fusion is more complex, the finished product contain two devices which may result in mess.
If use chips, the input and output spectral ratio is fixed and can be completed on a single device, fast and efficient, and is not easy to cause fiber breakage and disorder.
What are the commonly used fiber optic products?
We can put the splitter in the fiber optical termination box, optical distribution box, splice closure, cable cabinet, or fiber optic patch panels. Especially now hardened adapters is widely used outdoor application, we have a series of such box.
What is the difference between balanced and unbalanced cable splitters?
Balanced Splitters will have the same output power, while unblanced splitter have different output power. Those with odd numbers, in contrast, have less signal loss than others. If you are splitting a coaxial cable between one modem and several TVs, use unbalanced splitter.
What is a balanced splitter?
Balanced splitter is a device where the optical power of each output pigtails is the same, which is the average of the optical power of the input pigtails.
For example
- 1*2 splitter: input 100%, output each 50%
- 1*4 splitter: input 100%, output each 25%
- 1*8 splitter: input 100%, output each 12.5%
- 1*16 splitter: input 100%, output each 6.25%
- 1*32 splitter: input 100%, output each 3.125%
- 1*64 splitter: input 100%, output each1.5625%
- 1*128 splitter: input 100%, output each 0.78125%
Does balanced sound better than unbalanced?
One of the major differences between these cables is that balanced audio has less risk for unwanted noise, while unbalanced audio can pick up humming or buzzing sounds in certain environments. In general, balanced audio will give you a better, stronger audio signal without any extraneous noises.
How many types of splitters are there?
According to the production process, it can be divided into: cone melting type and planar waveguide type.
According to whether the optical power is evenly divided, there are two types: balanced splitter and unbalanced splitter.
According to packaging methods, it can be divided into: bare fiber splitter, steel tube splitter (mini module or blockless splitter ), ABS modular splitter, lgx module splitter or splitter cassette, splitter in rack mount patch panel, splitter in joint box, splitter distribution box, etc.
Is unbalanced splitter more expensive than balanced splitter?
Because the market usage of uneven splitters is not as large as that of even splitters, in terms of raw material costs, production efficiency, processing procedures, and labor, uneven splitters are relatively more expensive than even splitters. If applied widely in the future, the cost will definitely decrease accordingly.
