Light measuring device capable of measuring optical power level easily with high accuracy

摘要

To measure the optical power level of light from an object to be measured, a bias section applies to a photo-detecting section such a reverse bias voltage as makes the current multiplication factor M almost zero to prevent the output current from flowing, and then applies such a reverse bias voltage as makes the M one or more to allow the output current to flow. A processing section determines an offset level from the output of a direct-current amplifying section during an offset data acquisition period that the M is almost zero. The time T0 from when the bias section applies to the photo-detecting section such a reverse bias voltage as makes the M one or more to when the reverse bias voltage is applied to make the M almost zero is determined to be a measurement state. The processing section measures the optical power with a clock faster than time T0. The processing section subtracts the offset level from the measured optical power level to compensate for the offset, thereby determining the correct optical power level of the measured object. This makes it possible to automatically perform offset compensation without shading light before measurement and realize highly accurate measurement.