Using a Circulator to Make Insertion Loss Measurements in Transmission with the Optical Backscatter Reflectometer
Short Summary
For situations in which the Device Under Test (DUT) exhibits a total IL that exceeds the IL dynamic range of the OBR, it is commonly still possible to measure the accumulated IL by using a circulator.
Abstract
If the accumulated loss along the test fiber path causes the fiber Rayleigh scatter level to drop below the noise floor, accurate IL measurements can no longer be made. Thus, the difference in reflection amplitude between the Rayleigh scatter level at the instrument front panel to noise floor limits the dynamic range for these IL measurements. For the OBR 4600 using SMF-28 fiber, the single pass IL dynamic range is specified to be at least 18 dB, or 9 dB for a double-pass loss. For situations in which the Device Under Test (DUT) exhibits a total IL that exceeds the IL dynamic range of the OBR, it is commonly still possible to measure the accumulated IL by using a circulator. The circulator is used to route light which transmits through the DUT back to the OBR, so that the OBR can measure the transmission amplitude. If this result is compared to the transmission amplitude for the circulator alone, the total IL for the device can easily be computed, with a dynamic range in excess of 60 dB.
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