Passive Optical Network Splitters – What do they do?
Passive Optical Network (PON) splitters play an important role in Fibre to the Home (FTTH networks) by allowing a single PON network interface to be shared among many subscribers. There are two types of splitters available; either PLC Splitter (Planar Lightwave Circuit) or FBT Splitter (Fused Biconical).
PON splitters use a beam splitter to implement a point-to-multipoint framework. The benefit of a PON fiber optics network is to serve a lot of endpoints from one fibre optic cable.
Passive Optical Splitters make all of this possible.
PLC Splitters in each optical network are installed. They are then installed between the PON Optical Line Terminal (OLT) and the Optical Network Terminals (ONTs) that the OLT serves. Any Local Network using BPON, GPON, EPON, 10G EPON, and 10G GPON would all use these simple optical splitters. In place of an optical splitter, a WDM PON network will use an Arrayed Wave Guide (AWG).
A PON network may be designed with a single optical splitter, or it can have two or more splitters cascaded together. Each optical connection adds attenuation, a single splitter is superior to multiple cascaded splitters. When connecting two splitters together, one net additional coupling (and source of attenuation) is introduced.
The GPON network singular splitter image is shown below. The splitter can be used in the Central Office (CO) alongside the OLT, or in an Outside Plant (OSP) closer to the subscribers. For a Multiple Dwelling Unit (MDU) installation, a splitter can also be used in the basement.
Pros of Passive Optical Network Splitters:
– Splitters provide a cost-effective solution for both parties, as each customer doesn’t have to have their own fibre run to be linked to the hub as they can share one fibre between multiple users.
– Another pro is that Splitters contain no electronics and therefore use no power. They’re the network elements that put the passive in Passive Optical Networking (PON) and are available in a variety of split ratios, including a split configuration of 1:8, 1:16 and 1:32. In other words, for one single mode fiber link there can potentially be 8 subscribers.
-A PON network replaces copper cable with smaller and cost-effective single-mode fibre optic cable. POLAN (Passive Optical LAN) is a local area network (LAN) where PON is used.
Cons of Passive Optical Network Splitters:
– One of the biggest cons of a splitter is that it is very difficult to locate a problem when something goes wrong. It can be very time consuming and, therefore, expensive.
– Bad splices and fibre damage can cause lots of trouble. Finding and repairing there can prove to be difficult. To fix this problem, Fusion Splicing damaged fibre or bad splices is needed.
– Dust, Dirt or damaged Connectors: Dirty or damaged connectors can increase return loss (RL) and insertion loss (IL). Bit error rates (BER) could go up and loss of the signal often happens because of this. Cleaning the connector or replacing damaged connectors will fix this problem.
– Broken or Faulty Passive Optical Splitter: You could have a broken splitter doing nothing at all; Or you could have good and bad splits, causing some subscribers to have more loss but not others. Fixing or replacing the broken splitter will solve this issue.
– Cross Connections: Where connectors are put into the wrong port, Cross connections could happen. However, the place of this problem is not always easy to find. Finding the correct port and resuming service will solve this issue.
– Macro-bends: Finding a macro-bend requires the use of an OTDR. You will need to test the optical signals at 2 wavelengths on the optical fiber (1310 and 1550nm or 1625nm) to figure out where the bend is. Once the macro-bend has been located you gently move the fiber optic cables to remove the bend. This will resolve this issue.
The splitter in GPON Network
An interesting fact is that attenuation of light through an optical splitter is symmetrical. In other words, It’s the same in both directions. Whether a splitter is combining light in the upstream direction or dividing light in the direction of the downstream signal, it still introduces the same attenuation to an optical input signal (a little more than 3 dB for each 1:2 split)
In conclusion, the split ratio that will be required, not only for now but for future deployment as well is one of the cabling design concerns that will have to be made when using splitters.