Hello, everyone!
Today, I want to continue to explain a new topic – ODN engineering and maintenance. Now, I will continue to explain ODN engineering.
During propagation through the optical fiber, the optical power decreases. This is a normal process. How much attenuation the optical signal will depend on the type of optical fiber, the wavelength of light and the length of the optical fiber. Of course, here we are talking about a situation without events on the route. In the following table, we can see typical expected attenuation values.
In the following table, we can see typically acceptable attenuations for different events and optical splitters. Events can be reflective or non-reflective. Reflective events include: connector pairs, mechanical splices, and non-reflective events include: fusion splices and macro bands.
Typical optical splitters used in PON systems are: 1:2, 1:4, 1:8, 1:16, 1:32 and 1:64. There is also a universal formula for the calculation of attennuation for all optical splitters, which is:
as(dB) = 10*log(1/N), N = 2, 4, 8, 16, 32 and 64.
Knowing all this information, we can calculate the total attenuation of the optical link in the PON system using the following form:
Au= α * L + ass* Ns+ acs* Nc + as+ am,
α - attenuation coefficient of optical fiber (about 0.35 dB/km for 1310 nm and 0.2 dB/km for 1550 nm or 1490 nm),
L - length of optical fiber,
ass - average attenuation of fusion splice (about 0.1 dB/km),
Ns - total number of fusion splices on the optical trace,
acs - average attenuation of connector pair (about 0.5 dB/km),
Nc - total number of connector pairs on the optical trace,
as - all attenuation of optical splitters in this trace, and
am - margine of the optical trace (1 dB for 0 - 5 dB, 2 dB for 5 - 10 km, 3 dB for distance bigger than 10 km).
Calculations are made during the design, and after the implementation, it is checked whether the derived state and the project agree. If the PON system also has CATV, then WDM should also be considered, whose attenuation is usually about 0.7 to 1 dB.
In addition to attenuation, another important thing is reflection or ORL (Optical Return Loss). Reflection occurs at discontinuities. It is measured by OTDR, it is a pity because it can degrade the parameters of the link - to lead to the appearance of noise and a decrease in the S/N ratio. CATV service is particularly sensitive, which is why PON systems with CATV use connectors with APC, which have an ORL > 55 dB, otherwise, the minimum acceptable ORL is 35 dB.
This is the end of this article. I will continue to explain this topic in the next article >> ODN Engineering and Maintenance (25).
Thank you!
Reference:
HCIA-Access, ver. 2.5, Huawei Access Certification Training
