Optical-receiving apparatus and bias-voltage-control method used for the optical-receiving apparatus
According to an optical-receiving apparatus including an APD converting input light into an electric signal and a bias-voltage-control method used for the optical-receiving apparatus, a multiplication factor appropriate for the APD is predetermined and a multiplication factor used for the APD can be maintained at the level of the predetermined multiplication factor at all times according to a change in the ambient temperature of the APD so that the intensity of input light-transmitted to the APD can be monitored with accuracy. The optical-receiving apparatus further includes a bias circuit generating a bias voltage applied to the APD based on a control signal, a temperature-monitor circuit monitoring the ambient temperature, and an operating circuit that stores data on the predetermined multiplication factor and that controls the bias circuit so that the multiplication factor corresponding to the monitored temperature becomes the predetermined multiplication factor.
1. An optical-receiving apparatus comprising;
an avalanche photodiode converting input light to an electric signal;
a bias circuit generating a bias voltage applied to the avalanche photodiode based on a control signal;
a temperature monitor circuit monitoring an ambient temperature of the avalanche photodiode;
a current monitor circuit monitoring a current flowing through the avalanche photodiode;
an amplification circuit amplifying the current flowing through the avalanche photodiode at a predetermined magnification;
a selection circuit selectively transmitting a signal so that when a current value monitored by the current monitor circuit is larger than a predetermined value, the signal of the current value is transmitted, and when the current value is smaller than or equal to the predetermined value, the signal of a current value amplified by the amplification circuit is transmitted; and
an operating circuit generating an attenuated signal so that when the current value is smaller than or equal to the predetermined value the operation circuit attenuates the signal transmitted from the selection circuit at the predetermined magnification, and controlling the bias circuit so that a multiplication factor corresponding to the ambient temperature monitored by the temperature monitor circuit becomes equal to a predetermined multiplication factor.
2. The optical-receiving apparatus according to claim 1 ;
wherein the predetermined multiplication factor is a multiplication factor corresponding to the bias voltage at which a signal error of the input light is minimized.
3. The optical-receiving apparatus according to claim 2 ;
wherein the operating circuit includes a memory part storing each of:
data related to a temperature inclination of a breakdown voltage of the avalanche photodiode;
data on a standard temperature and the breakdown voltage of the avalanche photodiode, the break down voltage being obtained at the standard temperature;
data related to a constant based on a composition of the avalanche photodiode element; and
data related to the multiplication factor corresponding to the bias voltage obtained when the signal error is minimized.