To increase measurement level sensitivity by cutting the high frequency noise
To detect only the light that the LS emitted, effective for free space measurement. In free space measurement, the detector can also receive ambient light, e.g. sunlight and ceiling light. If the LS emits chopped light, then the OPM measures only the chopped signal at the same frequency
To remove power measurement error due to the drift of the electrical amplifier's offset, effective for long term measurement. Since the amplifier's offset is temperature dependent, AC detection (CHOP mode) is ideal for long term measurement
In field testing, chopped light is commonly used for fiber identification