Microwave Signal Detection Based on the Nonpolarimetric Frequency Down-Conversion Technique

We report a method for electro-optic (EO) microwave detection based on a nonpolarimetric frequency down-conversion technique. The detection principle is based on the coherent detection of the modulation sideband generated based on the interaction between the optical frequency comb and the microwave signal in the EO crystal. We theoretically analyzed the frequency characteristics of this technique. The theoretical calculation showed that the negative interference of the beat signals between the comb component and the modulation sidebands generated from the higher order comb components decreases the EO detection sensitivity, suggesting that the steeper roll-off characteristics of the optical bandpass filter will increase the sensitivity at the lower frequency side. We further demonstrate that the calculated frequency characteristic agrees well with the experimental measurements from 1 MHz to 10 GHz. Finally, we demonstrate the electric field visualization between the signal line and ground plane of the microstrip line. The proposed method is applicable to antenna measurements and measurements for electromagnetic compatibility.