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How to design your FTTH network? and calculate the splitting level and ratio  


In Passive Optical Network (PON), optical splitters play an important role in Fiber to the Home (FTTH) networks by allowing a single PON interface to be shared among many subscribers. Optical Splitters are installed in each optical network between the PON Optical Line Terminal (OLT) and the Optical Network Terminals (ONTs) that the OLT serves. During the deployment of fiber to the home passive optical network, usually, we will face some physical access network design problems. This article may help you solve FTTH splitting level and ratio design problems.

Choose Optical Splitter: PLC Splitter or FBT Splitter?

Before we start to discuss the splitting level and ration design, it’s necessary to choose the right optical splitter type for your FTTH network. There are two types of optical splitters in our current FTTH application—PLC splitter and FBT splitter. Here we have a comparison between these two splitter types:

Parameters PLC Splitter FBT Splitter
Wavelength Range 1260-1650 nm Single/dual/triple window
Splitting Ratio Equal division Equal or non-equal division
Dimensions Small Large size for multi-channel
Wavelength Sensitivity Low High
Cost Low splitting channel, high price Price is lower for small channel spliter

As we can see in the table above, with the rapid growth of FTTH worldwide, the requirement for larger split configurations (1×32, 1×64, etc) in these networks has also grown in order to serve mass subscribers, since PLC splitters offer very accurate and even splits with minimal loss in an efficient package, they are offer a better solution for today’s FTTH applications than FBT splitters.

FTTH Network Splitting Level Design

The PON is the optical fiber infrastructure of an FTTH network. The first crucial architectural decision for the PON network is that of optical splitter placement. The PON splitting may be achieved by centralized splitting (one-level) or by cascaded splittings (two-level or more). A centralized approach typically uses a 1×32 splitter located in a fiber distribution hub (FDH). The splitter is directly connected via a single fiber to a OLT in the central office. On the other side of the optical splitter, 32 fibers are routed to 32 customers’ homes, where it is connected to an ONT. Thus, the PON network connects one OLT port to 32 ONTs.

A cascaded approach may use a 1×4 splitter residing in an outside plant enclosure. This is directly connected to an OLT port in the central office. Each of the four fibers leaving this lever 1 splitter is routed to an access terminal that houses a 1×8 level 2 splitter. In this scenario, there would be a also total of 32 fibers (4×8) reaching 32 homes. It is possible to have more than two splitting levels in a cascaded system, and the overall split ratio may vary (1×16 = 4×4, 1×32 = 4×8, 1×64 = 4x4x4).

A centralized architecture typically offers greater flexibility, lower operational costs and easier access for technicians. A cascaded approach may yield a faster return-on-investment with lower first-in and fiber costs. Usually, the centralized splitting solution is used in crowded city center or town areas, in order to reduce cost and easy to maintain the optical distributed network (ODN) nodes. In the other hand, two-level and multi-level cascaded splitting solution is used in curb or village places, to cover widely ODN nodes, conserve resources and save the money.

FTTH Network Splitting Ratio Design

The most common optical splitters deployed in a PON system is a uniform power splitter with a 1:N or 2:N splitting ratio (N=2~64), where N is the number of output ports. The optical input power is distributed uniformly across all output ports. Different ratio splitters may perform differently in your network. Then, how to design your splitting ratio? According to the passage mentioned above, if you choose the centralized splitting solution, you may need to use 1×32 or 1×64 splitter. However, if you choose the cascaded splitting solution, 1×4 and 1×8 splitter may be used more often. Besides, based on our EPON/GPON project experience, when the splitting ratio is 1:32, your current network can receive qualified fiber optic signal in 20 km. If your distance between OLT and ONU is small, like in 5 km, you can also consider about 1:64.


When to design your FTTH network splitting level, in fact, centralized splitting and cascaded splitting both has its advantages and disadvantages. We had to weight these factors and select an appropriate splitting level for our network. As for splitting ratio design, to ensure a reliable signal transmission, the longer the transmission distance, the lower splitting ratio should be used. 

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