When optical signals are transmitted on an ODN link, some energy is converted into heat or absorbed and scattered by the transmission medium. As a result, signal strength decreases continuously. This phenomenon is called signal attenuation.
On an ODN, optical signal attenuation consists of 2 parts: attenuation generated by the optical cables and attenuation caused by connections (melt splicing, mechanical splicing, optical splitters, movable connectors, or quick connectors) along the optical path.
Let's look at the concept of optical cable attenuation which refers to the optical power loss caused by long-distance transmission along optical cables. The following table lists the attenuation of different wavelengths per kilometer for different types of optical fibers.
Now let's take a look at the connection loss (also referred to as insertion loss) which is the optical power loss caused by melt splicing, mechanical splicing, optical splitters, movable connectors, or quick connectors. The following table lists the insertion loss values of different components. Currently, there are 2 types of optical splitters: FBT and PLC splitters. FBT splitters are cheaper and easier to produce, and supports any split ratios, but have a large size and high insertion loss. PLC splitters are compact and have a small insertion loss, but are relatively expensive. Currently, most optical splitters are PLC splitters.
Now, let's talk about how to calculate the total link loss before construction.
Examine each component in the ODN network. The total loss of an ODN link consists of the following:
1) Optical splitter loss, usually the main loss of a system
2) Mechanical splicing and melt splicing loss
3) Connector and adapter (flange) loss
4) Optical fiber transmission loss
5) Line redundancy loss determined based on the length
For the integrated CATV service, the following factors also need to be considered:
6) WDM loss. The loss of each WDM coupler is usually about 0.7–1.0 dB.
7) If the 1550 nm wavelength is used for CATV transmission, the link power budget needs to be calculated separately. The attenuation of the 1550 nm wavelength is about 0.2 dB/km, and the minimum optical power of a CATV receiver is –8 dBm.
The total loss is the sum of the loss of various ODN components and transmission loss of optical fibers along an ODN link. For the loss of various components, see the following table.
0.35 x 4.5 + 0.1 x 6 + 0.3 x 6 + 0.5 x 1 + 20.5 x 1 + 1 = 25.98 dB
In this example, the calculated total loss is 25.98 dB, and the link attenuation meets the ITU G.984.2 class B+ standard. The calculation result indicates that the link design meets requirements, and further construction can be started.
Now, do not hesitate to read through the post and give us your correct answers. If you have any difficulty understanding the content or want to learn more about the GPON technology, please leave a message and reply to the post. We are looking forward to your comments.
Answers for the previous session:
In 2-level optical splitting mode, less optical cables are needed in the distribution section, and the network is more flexible compared with 1-level optical splitting. However, user management and line fault locating can be difficult, resulting in high maintenance costs in the future.
- For remote user convergence
- Capacity Expansion Requirements
- Multiple buildings with multiple floors for which one optical splitter with a large capacity is not applicable
- Improving bandwidt in the future
Questions for this session:
Which 2 parts do optical signal attenuation generally consist of?
Today is the 18th issue of the GPON technical posts, is also the last issue. Thank you for your attendance and persistence over the past month. Although the posting is over, knowledge is no end.
If you would like to know more about GPON, please give us feedback and hope to hear your suggestions about this event. Thanks again.
Mainstream OLT, MDU and ONT products that support GPON features include:
OLT: MA5800, EA5800, MA5680T, MA5600T
MDU: MA5633, MA5818, EA5821, MA5671
ONT: HG8240, HG8010H, HG8040, EG8080P, EG8040P
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