Block diagram of Optical Time-Domain Reflectometer (OTDR)
An optical time domain reflector is used in fiber optics to measure the time and intensity of light reflected on an optical fiber. It is used as a troubleshooting device to find faults, splices and bends in fiber optic cables with an eye toward identifying light loss. Light loss is important in fiber optic cables because it can interface with the transmission of data. An OTDR can detect such light loss and pinpoint trouble areas making repair easy. The more quickly trouble areas are identified and addressed the less fiber optic network will suffer from data transfer problems. An OTDR test can anywhere along the length of fiber from ten seconds to three minutes. It emits a high power pulse that hits the fiber and bounces back. What comes back is measured, factoring in time and distance and results in "trouble spots" which radiate and can be targeted for repair. Some OTDR systems are equipped with PC-linking capabilities that the data recorded during testing can be downloaded to a computer for analysis and storage.
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| Block Diagram Of OTDR |
The above figure is the block diagram. The main blocks of the reflectometer are the generator of the testing impulse and detection system of the backscattered light. The remaining blocks provide the suitable timing of signals and the interpretation of the measured data(display).
A light pulse is launched into the fiber in the forward direction from an injection laser using either a directional coupler or a beam splitter. Beam splitter or coupler makes possible to couple the optical power impulse into the tested fiber and simultaneously to deviate the backscattered power to the optical receiver. The backscattered light is detected using avalanche photodiode receiver. Output of photodiode receiver drivers an integrator. Integrator improves the received signal to noise ratio by giving an arithmetic receiver over a number of measurements taken at one point within the fiber. The signal from the integrator is fed through a log amplifier and average measurements for successive points within the fiber are plotted on as a chart recorder.
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