For GPON networking, such as using MA5800 and EG8145V5 to provide customers with high-quality networks in the 5G frequency band, we need to plan the distance and connection factors between OLT and ONT during layout.
During the transmission of optical signals on ODN links, part of the energy will be converted into heat energy or absorbed and scattered by the transmission medium, causing the signal strength to continuously weaken. This phenomenon is called signal attenuation.
In ODN networks, optical signal attenuation generally consists of two parts. One is the attenuation caused by the optical cable itself, and the other is caused by the connections in the optical path (fusion splicing, cold splicing, optical splitters, movable connectors, and fast connectors), etc. attenuation.
Let’s first look at the concept of optical cable attenuation. Attenuation is the reduction in optical power caused by distance loss during long-distance transmission of optical cables. The following table shows the attenuation values per kilometer of different wavelengths in different types of optical cables.
| Name | Type | Loss(db) |
| Optical Fiber(G.652D) | 1310nm/1 km | ≤0.35 |
| 1550nm/1 km | ≤0.21 | |
| 1490nm/1 km | ≤0.23 |
Let’s take a look at insertion loss, which is the optical loss caused by the use of welding, cold splicing, optical splitters, movable connectors, quick connectors and other devices. The following table shows the insertion loss values of different devices. It should be noted that there are currently two main types of optical splitters: FBT and PLC. FBT is a tapered optical splitter, which is characterized by relatively simple production, low cost, and can produce any number of splitting ratios, but it is large in size and has high insertion loss. PLC is a planar optical waveguide splitter, which is characterized by small size and low insertion loss, but it is relatively expensive. At present, most optical splitters use PLC technology.
| Name | Type | Average loss(dB) |
| Junction | Quick connector | ≤0.5 |
| Cold connection | ≤0.2 | |
| Welding | ≤0.1 | |
| Active connection | ≤0.3 | |
| Optical splitter | 1:64 | ≤20.5 |
| 1:32 | ≤17 | |
| 1:16 | ≤13.8 | |
| 1:8 | ≤10.6 | |
| 1:4 | ≤7.5 | |
| 1:2 | ≤3.8 |
Next, let’s take a look at how to calculate the total loss of the link before construction.
According to the planned ODN network, check each element of the ODN network. The total ODN link loss includes the following aspects:
1) Splitter loss, usually the main loss of the system
2) Welding and cold splicing losses
3) Loss of connectors and adapters (flanges)
4) Fiber transmission loss
5) Line redundancy loss, select redundancy based on line distance
| Distance (km) | Redundancy (dB) |
| ≤5 | 1 |
| 5~10 | 2 |
| ≤10 | 3 |
For integrated CATV services, additional considerations need to be made:
6) WDM loss, the loss of each WDM coupler is usually about 0.7 to 1.0 dB.
7) When the 1550nm wavelength is used for CATV transmission, the link power budget needs to be calculated separately. The attenuation of 1550 nm is about 0.2 dB/km, and the minimum optical power of the CATV receiver is -8 dBm.
The total loss is the sum of the transmission losses of various ODN devices in the optical link and the optical cable itself.
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