Passive Optical Network Technology

The tremendous growth in IP traffic badly influenced the access network capacity. It’s believed that the copper-based access networks can’t provide either the minimum bandwidth or the required transmission distance for delivering services of voice, data, and video programs. Passive optical network (PON) is seemed as a promising and cost-effective way to solve this problem.

What’s PON?

PON is a telecommunication network that uses point-to-multipoint fiber to the end-points in which optical splitters are used to enable a single optical fiber to serve multiple end-points. It does not include any electrically powered switching equipment.

Three Devices in PON

There are three distinct devices in the network (as shown in the following picture): the OLT (optical line terminal), the ONUs (optical network units) or ONTs (optical network terminals) and the splitter. Each one has a necessary function in the passive optical network. PON always works under transmission between the OLT and the different ONT’s through optical splitters, which multiplex or demultiplex signals based on their origin and destination.


  • OLTs are located in provider’s central switching office. This equipment serves as the point of origination for FTTP (Fiber-to-the-Premises) transmissions coming into and out of the national provider’s network. An OLT, is where the PON cards reside.
  • ONU converts optical signals transmitted via fiber to electrical signals. These electrical signals are then sent to individual subscribers. ONUs are commonly used in fiber-to-the-home (FTTH) or fiber-to-the-curb (FTTC) applications. Using different wavelengths for each service makes it possible to transmit high-speed Internet and video services at the same time. Wavelength multiplexing is performed at the central office and a wavelength demultiplexing mechanism is provided at the customer’s house.
  • PON splitter is used to split the fiber optic light into several parts at a certain ratio. For example, a 1X2 50:50 fiber optic splitter will split a fiber optic light beam into two parts, each get 50 percent of the original beam.
Advantages of PON

There are many advantages given by the use of fiber and the passive elements that compose the network. The following will tell about the advantages of PON.

  • High bandwidth The bandwidth allowed by systems based on PON can reach the 10 Gbps rate down to the user. The need to increase the bandwidth and the speed is another justification for the use of PON.
  • Long distance A PON allows for longer distances between central offices and customer premises. While with the Digital Subscriber Line (DSL) the maximum distance between the central office and the customer is only 18000 feet (approximately 5.5 km), a PON local loop can operate at distances of over 20 km.
  • Low cost On one hand, the cost of passive elements is low. On the other hand, the installation of these PON elements is much more economic. And it avoids operation and maintenance costs, such as absence of falls or maintenance of the network feeds.

Of course PON has some disadvantages. Compared with an active optical network, it has less range. That means subscribers must be geographically closer to the central source of the data. PON also make it difficult to isolate a failure when they occur. However, these disadvantages can not avoid choosing PON as the best possible configuration. Because it saves the cost of deploying PON networks regarding other two configurations (point to point and active optical network). And the flexibility of the network allows the usage of a channel by a large number of users.

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Basic of PON

PON, namely, Passive Optical Network, is a telecommunications network that uses ponit-to-multipoint fiber to the premises in which unpowered optical splitters are used to enable a single optical fiber to serve multiple premises. It is an optical-fiber-based network architecture that can provide much higher bandwidth in the access network compared with traditional copper-based networks and is regarded as an ideal solution to last-mile bandwidth bottlenecks. Some of the most primary PON parts and their functions will be introduced in the rest of this article.

Passive optical network

PON consists of an Optical Line Termination (OLT) at the service provider’s Central Office (CO), a number of Optical Network Units (ONUs) and Optical Network Terminals (ONTs) near end users and Optical Distribution Network (ODN) within which optical fibers, fiber optic connectors, passive optical splitters, and auxiliary components collaborate with each other. The above picture shows passive optical network system applied in FTTH/FTTB/FTTC/FTTCab.

OLT is located at the CO. Its main function is to control the information float across the ODN, going both directions. OLT has two float directions: one is upstream getting an distributing different type of data and voice traffic from users, the other is downstream getting data, voice and video traffic from metro network or from a long-haul network and sending it to all ONT modules on the ODN.

Fiberstore EPON ONU with 1-PON Port and 8 10100M ports  Fiberstore OLT with 8-PON Ports

ONT and ONU are basically the same device. ONT is at the customer’s premises to use optical fiber for connecting to the PON on the one side, while interfacing with customers on the other side. ONU receives optical signal and converts it into an electrical signal. However, it is located outside the home, working in different temperature and weather conditions. Thus, ONU should resist water, winds and vandals. There should be an emergency battery backup in ONU in case that the power is off.

ODN containing optical fibers, fiber optic connectors, passive optical splitters, and auxiliary components, is an indispensable path for transmitting PON data and directly affects the performance, reliability, and scalability of a PON system.

Splitter Singlemode Dual Window 250µm Bare Fiber SplitterFiberstore ONT with 2 pots and wifi

The passive optical splitter or PON splitter in ODN is the main part of PON being passive. With a single PON splitter taking one input cable, 32 or 64 subscribers can be served at the same time. In PON the splitters can be arranged in star, ring or tree configurations to increase reliability. There are mainly two kinds of passive optical splitters: one is the traditional fused type splitter as known as FBT coupler or FBT WDM optical splitter, which features competitive price; the other is the PLC splitter based on the PLC (Planar Lightwave Circuit) technology, which has a compact size and suits for density applications.

Fiberstore PON Solution

The mentioned components are the basic parts of PON.  Fiberstore focusing on optical communication for more than 14 years in both technology and manufacturing, can offer perfect PON solution according to customers’ needs. All the mentioned components can be found in the online store of Fiberstore, including but not limited to: OLT, ONT, ONU, splitter, optical fiber and connectors.