Electro-optic Sensors For High Power Microwave

High Power Microwave(HPM) has gained worldwide attention due to its application in both military affairs and industry. The need of military and scientific research brings HPM to higher frequency and higher power. To study HPM, the diagnose technology has been an important and effective way. Among all the techniques, electro-optic(EO) sensing has attracted much attention in virtue of a flat response over a much wider frequency bandwidth(~8 decades), a much higher spatial resolution, and much less interference of the field under detection as no metal is used. But most researchers had to use polarizer, Wollaston prism, half-wave plates or quarter-wave plates to realize E-field measurement based on the EO sensor, which needs complex modulation and can’t be movable. This paper will show an all fiber-coupled EO sensor system which will overcome these disadvantages mentioned. Besides, detailed theoretical and experimental study has been done based on the system. The main contents are as following:Firstly, we analyze the principle of EO sensing and how to choose the EO crystal available, different principles of measuring the E-field with different crystals is analyzed, too. In addition, five commonly used structures of EO probe are summarized. And different techniques of the microwave measurement in an antenna system, a coaxial waveguide and a rectangular waveguide are analyzed.Secondly, parameters such as the thickness of the crystal, the space between fiber and crystal and the incident angle of the laser are analyzed to get an optimized EO probe.Thirdly, an all fiber-coupled EO sensor system is built with the working wavelength of 1550 nm.Fourthly, a tapered coaxial waveguide is built as the under tested object, in which the maximal E-field reach 1MV/m or more.Fifthly, during experiment on coaxial waveguide or rectangular waveguide under 25MHz、680MHz、1.3GHz、9GHz, no obvious significant signal modulated by the microwave appears. The main reason is because the optical interference is too low while the noise is in a high degree.Sixthly, some parameters are redesigned after the experiment, but further research can’t be done as time is limited. Improvement can be made by increasing the thickness of the EO crystal, covering a coat beside the crystal and change the coupling mode of the crystal and fiber.