How OTDR calculate the optical length?

How OTDR calculate the optical length? : Perhaps this is a very important question because we all know that OTDR is the only device that shows optical length, but how OTDR calculates optical length, we rarely consider this matter. As we know OTDR is know as (Optical Time Domain Reflectometer) which is used for the testing of fibers and optical networks. The main purpose of to use the OTDR is to detect the optical length, measure and locate the events at any location in the fiber link.

OTDR detection and measurement is performed by transmitting and analyzing pulsed laser light traveling through optical fiber. The measurement is called unidirectional because light is inserted at the extremities of a fiber optic cable link. System of OTDR to reflect the information received from the resulting light signature or to be scattered back to the original point, the OTDR acts as an optical radar system, providing the user with detailed location information and residuals, connections, faults and other points of interest. Provides information about attributes. 

OTDR Calculate Optical length

To know how OTDR calculates optical length, first of all we have to understand the block diagram of OTDR properly. Light energy injected by OTDR into the fiber through a laser diode and pulse generator. In the measuring process of OTDR the returning light energy is separated from the injected signal using a coupler and fed to the photodiode. The optical signal is converted into an electrical value, which is amplified, sampled and then displayed on the screen.

A pulse generator controls a laser diode that sends powerful light pulses across the fiber. These pulses may have a width Sequence of 2 ns up to 20 ms and repetition of a few kHz. Pulse duration (pulse width) can be selected by the operator for different measuring positions.

The repetition rate of pulses is limited the rate at which the pulse return completes is preceded by another pulse Launched. Light goes into coupler / splitter and fiber under test. OTDR device measures the time difference between the outgoing and incoming pulse and the incoming backscatter pulses hence the term "time domain".

The power level of the backscatter signal and the reflected signal are sampled. For a long time. Each measured sample is called an "acquisition point" and Points can be plotted on an amplitude scale, relative to which Launch pulse time.

It currently converts domain information depending on the user entered the index of refraction of the fiber in the distance. The index of refraction entered by the user is inversely proportional to the velocity Of diffusion of light into fibers. OTDR uses this data to convert Distance on OTDR display and time to divide this value by two Round trip (or two way) into account. If the user enters the refractive index  false, the resulting in the distance displayed by the OTDR Can happen by error. In this way OTDR calculates optical length.

In OTDR also uses photo diode which is especially used to measure very low level backscatter light at 0.0001% is sent by the laser diode. The controller unit of OTDR is called the brain of the OTDR device. It takes all acquisitions the numeral, which performs the average, plots them as logs. time and work, the OTDR then displays the resulting trace on the screen.

You can also READ :  How to understand the OTDR trace?

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