Dummy light signal generation apparatus and method, and reconfigurable optical add/drop multiplexer

A dummy light signal generation apparatus, comprising:

• a light source module configured to generate a first wavelength signal and a second wavelength signal, wherein the first wavelength signal has N first channels, the second wavelength signal has M second channels, and N and M each are an integer greater than 0;
• a polarization beam combiner configured to polarize and combine the first wavelength signal and the second wavelength signal to output a dummy light signal, wherein the dummy light signal has N+M channels, and the N+M channels comprise the N first channels and the M second channels, among the N+M channels of the dummy light signal, a polarization state of a wavelength signal on any first channel is orthogonal to a polarization state of a wavelength signal on any second channel, a service light signal fills each channel of a first subset of the N+M channels, and the dummy light signal is used to fill each channel in a second subset of the N+M channels that lacks the service light signal;
• and
• a wavelength selective switch configured to receive both the dummy light signal and the service light signal.