December 12, 2016

In-Depth Understanding of Fiber Optic Splitter

Fiber optic splitter plays an important role in passive optical network (PON), where a point-to-multipoint architecture is implemented without any electrically power switching equipment involved. It is used to enable a single optical fiber to serve multiple end-points, like customers, without having to provision individual fibers between the hub and customer, which greatly reduces time and capital cost. In this post, we will introduce fiber optic splitter from three aspect which can make you have a deep understanding of it.

Fiber Optic Splitter Types: PLC VS. FBT

Generally, based on different working principles, fiber optic splitter can be divided into FBT splitter and PLC splitter.

FBT Splitter: Based on traditional technology, FBT (fused biconical taper) splitter contains two fibers which are placed closely together, typically twisted around each other and fused together by applying heat while the assembly is being elongated and tapered. It is made out of materials that are easily available, such as steel, fiber, hot dorm. All of these materials are low-price, making the device itself inexpensive. With its low cost and easy installation, FBT splitters are widely adopted in passive networks, especially for instances where the split configuration is smaller (like 1×2, 1×4, 2×2, etc.). The following image shows a 2×2 FBT splitter.

2×2 FBT splitter

PLC Splitter: PLC (planar lightwave circuit) splitter is the recent addition in fiber optic technology to exhibit uniform signal splitting among the most advanced optical networks. PLC splitter is a fully passive optical branching device that is based on planar light wave circuit technology and precision aligning process, which can evenly split or distribute a single optical signal/input into many outputs with high accuracy and minimal loss in an efficient manner. PLC splitter is a high-quality device, which offers a better solution for larger applications. Here is a picture of 1×64 PLC splitter.

1×64 PLC splitter.

Splitting Ratios: 1×N VS. 2×N

There are a number of splitting ratios available for splitter deployment, but the most common splitters deployed in a PON system is a uniform power splitter with a 1×N or 2×N splitting ratio, where the letter “N” means the number of output ports. The 1×N splitters are usually deployed in networks with a star configuration, while 2×N splitters are more suitable in networks with a ring configuration as shown below to provide physical network redundancy. The optical input power is distributed uniformly across all output ports. Although non-uniform power distribution is also available for fiber optic splitters, such splitters are usually custom-made and command a premium. Besides, based on different data transmission distances, there are also some suggestions for splitting ratios selection. If your distance between OLT (optical line terminal) and ONU (optical network unit) is long, like 20 km, you can use splitting ratio 1:32 to receive qualified fiber optic signals, and when the distance between OLT and ONU is short, like 5 km, you can consider about 1:64 splitting ratio.

star configuration vs. ring configuration

Splitting Levels: Cascaded Splitting VS. Centralized Splitting

Depending on the customer distribution, there are two common deployment strategies of Fiber optic splitter—cascaded splitting and centralized splitting.

Cascaded Splitting: In most cases, a cascaded splitter approach as shown below has no splitters in the central office. The OLT port is connected/spliced directly to an outside plant fiber. A first level of splitting (1:4 or 1:8) is installed in a closure, not far from the central office. A second level of splitters (1:16 or 1:8) resides in terminal boxes, very close to the customer premises (each splitter covering 8 to 16 homes). The inputs of these splitters are the fibers coming from the outputs of the first level splitters described above.

cascaded splitting

Centralized Splitting: A centralized splitter approach generally uses a combined splitting ratio of 1:64 (with a 1:2 splitter in the central office, and a 1:32 in an outside plant enclosure such as cabinet). These single-stage splitters can be placed at several locations in the network or housed at a central location. The 1:64 splitter could even be placed within the central office to provide a point-to-multipoint (P2P) outside plant network that still shares bandwidth across multiple customers as shown below, for instance a group of subscribers a short distance from the central office. But most often, the splitters are placed in the outside plant to reduce the amount of overall fiber required.

centralized splitting

Summary

Most FTTH applications are favored PON network, which offers many favorable advantages. Fiber optic splitter, as an indispensable component in PON networks, are gained much attention. We have mentioned three aspects of fiber optic splitters, including common types, common splitting ratios, and common splitting levels, which can help you choose the suitable splitters for your project.

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