What is ODN?
ODN is an optical distribution network. It is an optical transmission physical channel between OLT and ONU.
The main function is to complete the two-way transmission of optical signals. It usually consists of fiber optic cables, optical connectors, optical splitters, and supporting equipment for installing and connecting these devices.
The most important component is the optical splitter. Optical distribution network (ODN) mainly has two kinds of light splitting methods: primary splitting and secondary splitting, or centralized splitting and cascaded splitting.
The structure of the primary splitting is OLT – Splitter – ONU, and the optical splitters from the OLT to the ONU are all parallel. When using the primary splitting, the optical splitter is generally set at the intersection of the cabling.
The structure of the secondary splitting is OLT – splitter 1 – splitter 2 – ONU. The optical splitter from OLT to ONU is cascaded. When using a two-stage splitter, the first stage splitter is generally set at the optical intersection of cabling, and the second stage splitter is generally set at the fiber distribution box (FDB).
There are only one optical splitter in the primary splitting. Therefore, a splitter with large number of splitting ratio is a good choice, such as 1:32 or 1:64. On the contrary, the secondary splitting often use 1:8 or 1:16 in the first stage splitter, and 1:4 or 1:8 in the second stage fiber distribution box.
Generally, the first-level optical splitting solution is used in crowded city centers or urban areas to reduce costs and make it easier to maintain optical fiber distributed network (ODN) nodes. On the other hand, the secondary splitting solution is used in roadside or rural places to cover a wide range of ODN nodes, saving resources and saving money.
Optical splitter is a core passive component in FTTH System. It is also known as optical beam splitter, is an integrated waveguide optical power distribution device. An optical splitter can divide optical signal input into two or more outputs, and the optical input is evenly distributed on all output ports.
How it works
When a single-mode optical fiber transmits optical signals, the energy of light is not completely concentrated in the core, and a small amount is transmitted through the cladding close to the core. That is, if the cores of two optical fibers are close enough, the mode field of light transmitted in one optical fiber can enter another optical fiber. And the optical signal is redistributed between the two optical fibers.
For example, an optical splitter with a splitting ratio of 1:4 can divide an optical signal into four parts, and then transmit it in four different channels. At present, the general splitting ratio of optical splitter is 1: n or 2: n, such as 1:4, 1:8, 1:16, 1:32, 2:16 and 2:32.