A system for measuring gains of a plurality of photo diodes includes a chamber adapted to host the plurality of photo diodes and a temperature control unit configured to control the temperature within the chamber to a predetermined temperature. A control unit selects at least one of the plurality of photo diodes. A hosting unit is configured to provide a bias voltage to the selected photo diode at the predetermined temperature. A light source transmits photo signals to the selected photo diode at the predetermined temperature. A measurement unit configured to measure current signals generated by the selected photo diode in response to the photo signals under the bias voltage at the predetermined temperature.