Measurement of low frequency electric field using Ti:LiNbO3 optical modulator

The use of an asymmetric MachZehnder interferometric amplitude modulator to measure a relatively low frequency electric field strength is described. The sensitivity of an electric field sensor using a Ti:LiNbO3 optical modulator is strongly affected by the shape of a electrode (probe antenna). To measure the low frequency electric field, a probe antenna of wide effective area is more useful than the usual dipole antenna. As proof of this, the optical modulator was fabricated with a plate-type probe antenna and the usefulness of this antenna tested for measuring low frequency electric field strength. Measurements were performed in the range 0.1 V/cm to 60 V/cm at 60 Hz through 100 kHz. Using a probe antenna of 10 mm × 10 mm, the output voltage of 10−2 mV was measured with respect to the electric field strength of 0.1 V/cm at 60 Hz. By increasing the effective area of the probe antenna, better sensitivity was obtained over the measured range.