Signal processing device and transmission device

A transmission device comprising:

• a light receiving circuit that, among optical signals of a plurality of channels included in wavelength division multiplexed optical signal, receives the optical signal of a predetermined channel in a receiving bandwidth wider than a frequency interval of optical signals of the plurality of channels, and outputs electric field signals that indicate electric field components of the optical signal of the predetermined channel;
• a power measurement circuit that measures power of the optical signal of the predetermined channel;
• a first conversion circuit that converts the electric field signals from time domain signals into frequency domain signals;
• a filter circuit that passes the electric field signals converted into the frequency domain signals with a passband narrower than the receiving bandwidth;
• a second conversion circuit that converts the electric field signals passed by the filter circuit, from the frequency domain signals into the time domain signals;
• an amplitude measurement circuit that measures first amplitudes of the electric field signals input to the filter circuit from the first conversion circuit and second amplitudes of the electric field signals input to the second conversion circuit from the filter circuit, individually;
• and
• a notification circuit that notifies the power measurement circuit of the first amplitudes and the second amplitudes, wherein
• the power measurement circuit corrects a measurement error of the power of the optical signal of the predetermined channel, based on a ratio of the first amplitudes and the second amplitudes.