A detection system including a receiver, a transmitter, and a processor for stealthy target detection or optical communications is described. Optical communications may be spread spectrum encoded communications over a bright background communication channel. The transmitter includes a quantum frequency entanglement source for outputting a signal beam and an idler beam, and transmission optics for directing the signal beam towards a remote surface. Photons in the idler beam are quantum-mechanically entangled in frequency with photons the signal beam. The transmitter includes a first spectrometer for measuring a frequency band associated with photons in the idler beam. The receiver includes a second spectrometer for identifying the frequency band associated with the photons in the received return beam. The system includes a processor configured to process the output of the spectrometers to determine the presence of a target in a target region or a message encoded in the received return beam.