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Start event or non reflection event Reflection event
E
End event
The events on trace are all the points that the value of power loss fluctuates abnormally. It usually
contains various types of connection and bending, crack, broken and etc. The event points marked on
trace with special marks are the abnormal points in a fiber that cause the excursion of a normal trace.
The events can be divided into “Reflection-event” and “Non-reflection-event”.
Start event
The Start-Event on a OTDR trace is the initial point. Under the default setup, Start-Event is
located on the first event(usually it is an connection between the OTDR launching port and the
connector of a fiber) of a fiber. It is a Reflection-event.
End event
The End-Event on a OTDR trace is the end point of a fiber. Under the default setup, End-Event is
located on the last event(usually it is an end face or a broken down point of a fiber). Usually, it is a
Reflection-event.
Reflection event
The phenomenon on a trace that some power of the optical pulse is reflected called a reflection
event. Reflection-event is displayed as a peak signal on a trace.
Non reflection event
The phenomenon on a trace that there exists some abnormal loss in a optical line, but no
reflection occurred is called a Non-reflection-event. It is displayed as a drop with no peak on a trace.
Event detection
OTDR launches a bunch of optical pulse into a under-test fiber, receives the returned optical
signal and starts calculating the distance from a event. The more the distance from the event is, the
longer the returning time is cost. According to the receiving time,distance can be calculated. By
detecting the trace generated by the returned optical signal, the attributes of the fiber itself, the
connector of the fiber, adaptor in the fiber and splicing point in the fiber can be confirmed.
4.1.2 OTDR measurement content
The total length and total loss of optical fiber
The distance between any two points on the optical fiber curve
Test and display the loss and distance between any two points on the curve(dB) and fiber
attenuation constant(dB/km）
Test and display the connection loss of the connection point on the curve and the attenuation
loss of the fusion point (dB)
Test reflection loss value
Automatic search function of connection point
4.1.3 OTDR curve analysis
OTDR is a fully automatic analysis process for curves, which is located as follows:
The reflection events generated by connector and mechanical joints;
Non reflection event (usually fusion joint);
Optical fiber end: through scanning the first loss event greater than the end threshold, OTDR
detects it as the end of optical fiber;
Event list: event type, loss, reflection and distance are calculated and listed.