[GPON Technical Posts 17] Selection and Deployment of Optical Splitters

Hello, everyone!

In the previous section, we talked about ODN network planning. ODN node products are used to connect and protect optical cables. An optical splitter is a passive functional component that split an input optical channel into multiple output channels at an optical splitting point. 

The biggest difference between a PON network and a traditional optical network lies in the optical splitter which splits one channel of input optical signals into multiple channels of output optical signals and converts a traditional P2P optical transmission network into a P2MP PON tree.

An optical splitter is also called splitter or SPL. 

Optical splitters are classified into fused biconical taper (FBT) and planar lightwave circuit (PLC) types based on the production processes. 

A simple understanding of the FBT is that 2 optical fibers are fused at a high temperature to monitor the output of the split ratio in real time. After the split ratio reaches the requirement, the melt stretching ends. FBT splitters support optical signal splitting with equal or unequal ratios.

A PLC splitter is made by etching optical paths on a chip. It splits optical signals by means of physical optical path coupling. All PLC splitters provide equal-ratio splitting, which means that signals from 1 or 2 input channels are split and evenly distributed among multiple output channels. 

FBT splitters with a high split ratio can work only within the frequency bands of 1310±40 nm, 1490±10 nm, and 1550±40 nm. The insertion loss of other frequency bands is too high.

FBT splitters are easy to produce and therefore cheaper compared with PLC splitters. You can select FBT or PLC splitters by balancing the cost and performance. 

Among Huawei splitters, only those with a split ratio of 1:2 and 2:2 are FBT splitters. Splitters with other split ratios are all PLC splitters. 

Optical splitters are classified into the types shown in the following figure based on encapsulation modes:

Which encapsulation mode is applicable depends on where optical splitters are deployed. 

• Micro optical splitter without connector (SPL9102): Splitters of this type are generally installed in splicing trays. Both the input and output ends are spliced to transmit optical signals.

• Micro optical splitter with connector (SPL9105): Splitters of this type are generally installed in splicing trays or open splicing areas. The output end uses cable distribution to transmit optical signals. The input end uses splicing (the connector needs to be cut off) or cable distribution to transmit optical signals. 

• Modular optical splitter (SPL2803): Splitters are encapsulated into a module. You only need to connect the pigtails to an SPL2803 adapter as required. Modular optical splitters are mostly installed in SSCs and FATs. 

• Small case-shaped optical splitter with pigtail (SPL2605): Similar to modular optical splitters, splitters of this type also encapsulate multiple optical splitters. You only need to connect the pigtails to optical fibers in cable distribution mode. Splitters of this type are generally installed in FATs.

• 19-inch rack-mounted optical splitter: Optical splitters are encapsulated into a larger 19-inch standard module for easy installation in ODFs and FDTs.

The positions of optical splitting points directly affect the equipment cost and O&M cost of an entire ODN network.

Positions of Optical Splitters

Generally, optical splitters can be deployed in the positions listed in the following table. Note that the table lists possible positions for optical splitters, which does not mean that optical splitters can be deployed in these positions for one link at the same time.

At present, only 1-level (1 optical splitter per link) or 2-level (2 optical splitters per link) optical splitting are used. 3-level or further optical splitting is not used.

Differences Between 1-level and 2-level Optical Splitting

In 1-level optical splitting mode, the PON port usage is high, test and maintenance are simple, and optical power attenuation is low. 

In 2-level optical splitting mode, less optical cables are needed in the distribution section, and the network is more flexible compared with 1-level optical splitting. However, user management and line fault locating can be difficult, resulting in high maintenance costs in the future.

Application Scenario of 2-Level Optical Splitting

Now, do not hesitate to read through the post and give us your correct answers. If you have any difficulty understanding the content or want to learn more about the GPON technology, please leave a message and reply to the post. We are looking forward to your comments. 

Answers for the previous session:  

If the ODF and a fiber distribution terminal (FDT) are far away from each other, a splitting and splicing closure (SSC) is usually installed between the ODF and FDT to connect the ODF and FDT.

The section between the FDT and FAT is referred to as the distribution optical cable section. If the distance between the FDT and the FAT is large, an SSC is also installed for connection. 

Questions for this session:  

Please answer the advantages, disadvantages and application scenarios of the 2-level optical splitting.

Thank you for reading!

[GPON Technical Posts 16] Composition of a ODN Network   

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Mainstream OLT, MDU and ONT products that support GPON features include:

OLT: MA5800, EA5800, MA5680T, MA5600T

MDU: MA5633, MA5818, EA5821, MA5671

ONT: HG8240, HG8010H, HG8040, EG8080P, EG8040P