Wideband microwave phase noise measurement based on photonic-assisted I/Q mixing and digital phase demodulation

A wideband microwave phase noise measurement system is proposed based on quadrature phase demodulation of the mixing components of a signal under test (SUT) and its delayed replica. The time delay is introduced by a low-loss optical fiber, which can be sufficiently large to achieve a high phase noise measurement sensitivity, and the quadrature phase demodulation is achieved by photonic-assisted in-phase and quadrate (I/Q) mixing together with digital signal processing. Thanks to the optoelectronic hybrid quadrature phase demodulation, the use of feedback loops, which are usually required in conventional photonic-delay-line-based phase noise measurement systems, is avoided, and the measurable frequency range is expanded. An experiment is implemented. Accurate phase noise measurement of SUTs in a frequency range of 5-35 GHz is demonstrated. With a 2-km single-mode fiber serving as the photonic delay line, the phase noise floor is as low as -131 dBc/Hz at the offset frequency of 10 kHz. The proposed scheme can be applied for evaluating the performance of microwave systems using low-phase-noise and wideband tunable microwave sources.