Abstract: The present invention is to provide an optical receiver by which the avalanche photodiode (APD) can be protected from the self-breakdown when the signal light with excess power enters therein. The APD is biased by the DC/DC converter via the control circuit including a resistor and a variable current source connected in series to the resistor and in parallel to the APD. The resistor drops the bias voltage to the APD by the current provided from the variable current source. The controller adjusts the amount of the current flowing in the variable current source not to exceed the absolute maximum current for the APD. Accordingly, the multiplication factor of the APD is appropriately adjusted.

Abstract: The present invention is to provide an optical transmitter that includes an EA-modulator and has a function to monitor the optical output power from the EA-modulator with a simplified and small-sized circuit. The transmitter provides a semiconductor optical device integrating a laser diode with the EA-modulator, a driver, and a termination resistor. One terminal of the resistor is connected to the anode of the EA-modulator, while, the other terminal of the resistor is grounded in the AC mode. The driver is coupled in the AC mode with the terminal of the resistor and the anode of the EA-modulator via a capacitor to provide a modulation signal to the modulator. The EA-modulator is reversely biased through the resistor.

Abstract: The present light-receiving circuit provides a function capable of adjusting the temperature dependence and the output of the bias supply circuit independently. The light-receiving circuit includes a bias supply circuit, a voltage divider and a temperature compensation circuit that adjusts a division ratio of the voltage divider so as to depend linearly on the temperature. The temperature compensation circuit has a differential amplifier operating in the inverting mode, and a temperature-sensing resistor that connects the inverting input to the output of the differential amplifier. Since the temperature-sensing resistor has a linear dependence on the temperature and is connected as a feedback resistor, the output of the differential amplifier also depend linearly on the temperature.

Abstract: The present invention is to provide an optical receiver by which the avalanche photodiode (APD) can be protected from the self-breakdown when the signal light with excess power enters therein. The APD is biased by the DC/DC converter via the control circuit including a resistor and a variable current source connected in series to the resistor and in parallel to the APD. The resistor drops the bias voltage to the APD by the current provided from the variable current source. The controller adjusts the amount of the current flowing in the variable current source not to exceed the absolute maximum current for the APD. Accordingly, the multiplication factor of the APD is appropriately adjusted.