Synthetic Aperture Passive Millimeter Wave Imaging Based Electro-optic Modulation

Synthetic aperture passive millimeter wave imaging, which is one of the hot research topics in millimeter wave detecting domain, has been applied in military and civilian fields widely. With the development of optical fiber technology and applied optics, the up-conversion scheme based on electro-optic modulation has attracted more and more interests gradually. In up-conversion scheme, millimeter-wave signal received by the antenna array that is arranged in order to achieve the best imaging and optimal spatial frequency coverage is converted to the optical frequency by electro-optic modulator. Then the single-sideband modulation signal carried the information of the millimeter wave is achieved by filtering, and the image is realized at the end of the fiber array using the optical signal processing techniques.In this thesis, electro-optic modulation, aperture synthesis and optical signal processing are integrated in passive millimeter wave imaging system. Theoretical studies on passive millimeter wave imaging based on electro-optic modulation are firstly introduced, including the amplitude and phase information after up-conversion, the post-processing of the signals with complex correlation operation and inverse Fourier transformation to achieve real-time imaging in the optical domain, et al. Mathematical modeling and simulation analysis are then carried on. The simulation results demonstrated the viability of synthetic aperture passive millimeter wave imaging.The aperture array distribution affects the coverage of the spatial frequency and sampling of the visibility function of the view’s field, which is closely related with the image quality. The optimization criteria, the objective function and optimization algorithm of array optimization and the comparison between Simulated Annealing and Genetic Algorithm are introduced, based on which,8～16antenna array arranged in a circumferential array is optimized with real-coded genetic algorithm. Compared with the coverage of the spatial frequency, this optimization scheme has better spatial frequency coverage and has almost no redundant spatial frequency.A method based on Stimulated Brillouin Scattering (SBS) in optical fiber is proposed for the signal processing in synthetic aperture passive millimeter wave imaging system. In this scheme, the single-sideband suppressed-carrier modulation of the millimeter wave signal is achieved by using SBS. Therefore, it not only realizes electro-optic modulation of the millimeter wave but also realizes optical filtering and amplification. The principle for this scheme is theoretically discussed. And experimental setup is constructed and the experimental results demonstrated the viability of such scheme. Compared with the traditional scheme, this method is simple and can be applied in the low power millimeter wave imaging system.