Improvement of frequency characteristics of electric field sensor using Mach-Zehnder interferometer

With the progress in electronic equipment, evaluation of the electromagneti c compatibility (EMC) of the equipment has become an important issue. To ev aluate the EMC it is necessary to accurately understand the electromagnetic field surrounding the equipment. Therefore, various sensors for measuring the electric field have been developed. Among them, since the electric fiel d sensor using a Mach-Zehnder interferometer features wide bandwidth, high sensitivity, and high resolution, its application in EMC measurement is exp ected. However, its sensitivity changes at a frequency higher than a few me gahertz due to unknown reasons and this makes the intensity measurement of the electric field much more difficult. In this paper, the sensitivity vari ation is considered to be caused by the resonance due to the piezoelectric effect of the optical crystal substrate used to form the optical modulator. By comparing the measured and theoretical resonance frequencies it is foun d that the sensitivity variation is due to the resonance in the width direc tion of the substrate. Based on this result, a method is proposed to suppre ss the resonance by varying the width of the substrate along the propagatin g direction. Finally, the improvement of the frequency response is demonstr ated by using an optical interferometer with a variable width crystal subst rate as the electric field sensor: (C) 2000 Scripta Technica.