In the embodiments of the present disclosure, a transmit apparatus generates a to-be-processed optical signal and a quantum optical signal, where the to-be-processed optical signal includes at least a classical optical signal; and the transmit apparatus couples the to-be-processed optical signal and the quantum optical signal, to obtain a coupled optical signal, and sends the coupled optical signal. Because a wavelength of the classical optical signal is in an L band and/or a C band and a wavelength of the quantum optical signal is in an S band, a wavelength in the band of the classical optical signal is greater than a wavelength in the band of the quantum optical signal.