POF Measurement: Cutback Method
The cutback method is a destructive method of measuring attenuation of long run lengths of optical fiber. It typically takes the following form:
- Set up a transmitter and receiver on both ends of the fiber optic cable to be tested, with a known transmitter power, P0.
- Measure the power received, P1 (Part 1 in diagram).
- Cut the fiber, leaving 1 to 2 meters at the transmitter end, and repeat test, measuring the power received, P2 (Part 2 in diagram).
- Use the following equation to calculate attenuation of the cable under test, in dB/km. L1 and L2 are the original and cut lengths of the fiber in meters, respectively.
By cutting fiber on the receiver end, variables introduced by variations in signal launch conditions are mitigated. Note that power must be in linear units (watts), instead of dBm for this formula.
POF Data Book, Tokyo, Japan: MRC Techno Research Inc, 1993, pp.37