Hello, everyone!
In this theme, I will shortly explain the OTDR instrument and OTDR trace analysis. Let`s get started.
OTDR is a very important and useful instrument. However, we need to have proper documentation and know how to handle this instrument. Many technicians do not know how to use OTDR correctly. Therefore, all the information that can be obtained with this instrument is given here.
First, let me repeat the basic things about this instrument.
The OTDR(Optical Time Domain Reflection Meter) is an instrument that works like a radar. It has a transmitter and a receiver and based on backscattered light, OTDR can measure.
Figure 1. Portable OTDR
This instrument allows measurement at one end. But to get reliable information requires measurement at both ends. With this instrument, we can get the following parameters: length of optical fiber, total attenuation of optical fiber, attenuation and reflections at characteristic points (events), place of cable/fiber break or end of cable/fiber, etc.
The use of reference cables is mandatory for measurement. For multimode systems, the length of the reference cable should be about 100 m. For single-mode systems, the length of the reference cable should be about 1km. The reference cable is used to skip the “dead zone” and measure the hole optical trace including the connectors on both ends. In order to measure the connectors on both sides of the route, 2 reference cables are required (launch cable at the measuring point and receive cable on the far end).
If the fibers are connected by a fusion splice, measurement with an OTDR instrument is required. During the splicing process, the splicer displays the estimated value of splice attenuation, but this is not reliable. OTDR measurement is required.
Figure 2. OTDR trace
Basic measurement procedure:
Clean the optical connectors before measuring.
Use reference cables at both ends of the optical trace to be measured.
Pay attention to the type of optical connectors (do not connect e.g. SC/APC and SC/PC)
Use the appropriate wavelengths, the wavelengths used or to be used by the system,
If we need to test fibers, which are not known to have traffic, before measuring with OTDR, check the optical power with an OPM. There are also OTDR instruments that can measure live fiber,
Set the following OTDR parameters: fiber type and application (SM or MM), pulse width, range, averaging, and IOR (Index Of Refraction).
I will continue on the next article >> OTDR trace analysis (2)
Thank you!
