Ultrahigh Sensitivity Optical Carrier-Based Microwave Interferometry Based on Phase Superposition

Optical carrier-based microwave interferometry (OCMI), which integrates the strengths of both the optical and microwave domains, has garnered significant interest and has been extensively applied in numerous fields for sensing physical, chemical, and other quantities. In this article, a phase superposition method is proposed to achieve ultrahigh sensitivity sensing for OCMI-based sensors. The proposed method does not focus on a particular frequency, but directly and simply superimposes the phases gained at all frequencies. The theory and formula derivation are described in detail and numerical simulations are performed to verify the feasibility. The simulation results reveal that the amplification of sensitivity is much greater than that of random phase noise. In addition, the proposed method is further demonstrated by temperature measurements. The results exhibit an excellent linear relationship between the superimposed phase and the applied temperature. Meanwhile, it reveals that the sensitivity can be significantly improved by increasing the number of scanning microwave frequencies or by making the interferometer farther inside the sensing fiber while keeping other conditions constant. Besides, the varying spatial and measurement resolution of OCMI-based sensors will not affect the sensitivity. Compared with the phase shift amplification technique that can realize a notable enhancement in sensitivity, the proposed phase superposition method can further improve the sensitivity by several orders of magnitude on this basis. The application of the proposed phase superposition method contributes to the sensing of tiny physical, chemical, and biological quantities in real industrial processes.