Systems and methods for transmitting quantum and classical signals over an optical network are disclosed, wherein the quantum signal wavelength either falls within the classical signal wavelength band, or is very close to one of the classical signal wavelengths. The system includes a deep-notch optical filter with a blocking bandwidth that includes the quantum signal wavelength but not any of the classical signal wavelengths. The deep-notch optical filtering is applied to the classical signals prior to their being multiplexed with the quantum signals to prevent noise generated by the classical signals from adversely affecting transmission of quantum signals in the transmission optical fiber. Narrow-band filtering is also applied to the quantum signals prior to their detection in order to substantially exclude spurious non-quantum-signal wavelengths that arise from non-linear effects in the optical fiber. The present invention allows for the quantum and classical signals to have wavelengths within just a few nanometers of one another, which has benefits for both classical and quantum signal transmission on a common transmission optical fiber.