Optical module, transmission device, and operating point control method

A transmission device that transmits an optical signal, the transmission device comprising:

• an optical device that outputs the optical signal with an optical output characteristic corresponding to a control voltage;
• a voltage controller that applies the control voltage on which a dither signal having a known frequency is superimposed to the optical device;
• a monitor unit that monitors the optical signal output from the optical device, and outputs a monitor signal corresponding to the optical signal output;
• a multiplier that multiplies the monitor signal by a reference signal having a frequency corresponding to the dither signal;
• a filter unit that extracts a direct-current component included in a multiplication result of the multiplier;
• and
• a controller that causes the voltage controller to change the control voltage in accordance with the direct-current component extracted with the filter unit, wherein
• the controller changes the frequency of the dither signal or the reference signal such that the frequency of the reference signal is twice as large as the frequency of the dither signal, when the direct-current component extracted with the filter unit satisfies a predetermined condition.

An operating point control method for an optical device that outputs an optical signal with an optical output characteristic corresponding to a control voltage, the method comprising:

• applying the control voltage on which a dither signal having a known frequency is superimposed to the optical device;
• monitoring the optical signal output from the optical device, and acquiring a monitor signal corresponding to the optical signal output;
• multiplying the monitor signal by a reference signal having a frequency corresponding to the dither signal;
• extracting a direct-current component included in a multiplication result;
• changing the control voltage in accordance with the direct-current component;
• and
• changing the frequency of the dither signal or the reference signal such that the frequency of the reference signal is twice as large as the frequency of the dither signal, when the direct-current component satisfies a predetermined condition.