Photonic-assisted microwave spectrum sensing based on optical carrier-suppressed single-sideband modulation and coherent detection

A photonic-based approach for microwave spectrum sensing is proposed based on optical carrier-suppressed single-sideband (CS-SSB) modulation and coherent detection. Two dual-parallel Mach-Zehnder modulators (DP-MZMs) function as two CS-SSB modulators. A local oscillator (LO) signal with its frequency swept at a fixed step of Δf is applied to one DP-MZM, while the microwave signal to be detected is applied to the other DP-MZM. The two CS-SSB modulated optical signals from the two DP-MZMs are sent to a coherent receiver, which consists of a 90° optical hybrid and two balanced photodetectors. The two outputs of the coherent receiver are combined by a 90° electrical hybrid and filtered by an electrical low-pass filter with a bandwidth of Δf. Different frequency components in the unknown microwave signal are all frequency downconverted to within Δf and the signals in different frequency bands appear in different time periods, which can be used for spectrum sensing by sampling and processing the IF signal. In addition, due to the balanced detection, the direct current components are suppressed, and the frequency-swept LO signal only detects the microwave signal on its left or right side, avoiding the interference from the image frequency. To verify the proposed technique, spectrum sensing in a frequency range from 1 to 20 GHz is demonstrated by simulation.