| 摘要 |
PROBLEM TO BE SOLVED: To compensate for the offset without shielding the light before measurement by subtracting the output level when a reverse bias voltage is applied to block the output power from the output level when a reverse bias voltage is applied such that the output current flows into the light receiving section. SOLUTION: A bias section 6 applies a bias voltage for bringing the amplification factor M≈0 to a light receiving section 5 in response to a control signal S3a indicative of an offset command from a processing section 9. Consequently, output current from the light receiving section 5 is blocked and an output, e.g. a dark current, is amplified through a DC amplifying section 7 and inputted, as an offset data at the time of measuring the optical power level, to the processing section 9 along with an offset voltage. On the other hand, the bias section 6 applies a bias voltage for bringing about such a state as the amplification factor M>=0 to the light receiving section 5 in response to a control signal S3b indicative of a measurement command. Offset is compensated by subtracting the offset data when the amplification factor M≈0 from the output level of the light receiving section 5 inputted to the processing section 9 through the DC amplifying section 7 and an A/D converter 8.
|
