Optical bias angle control method for electric field sensor using Mach-Zehnder interferometer

An electric field sensor using a Mach-Zehnder interferometer can be made co mpact, used for wide-band applications, and does not disturb the surroundin g electromagnetic field. Because of these merits, its application to EMC me asurement is promising. However, because it is not clear how to adjust the operating point (optical bias angle) of the optical modulator used for the electric field sensor, its dynamic range is limited. This paper proposes a method to adjust the operating point by applying force to a point on the op tical crystal substrate used for the optical modulator. First, the relation ship between the applied force and optical bias angle is theoretically anal yzed, taking into account the change in waveguide length and change in the refractive index when load is applied. Then, it is shown that the change in the waveguide length is more dominating than the change in the refractive index. An electric field sensor was actually fabricated to show that the op tical bias angle can be adjusted as theoretically predicted and that its te mperature dependence is comparable to that of a conventional electric field sensor. (C) 2000 Scripta Technica.