Electric Field Sensing Scheme Based on Matched $ \hbox{LiNbO}_{3}$ Electro-Optic Retarders

In this paper, a wideband-electric-field-sensing scheme that uses optically matched integrated optics electrooptic devices and coherence modulation of light is described. In a coherence modulation scheme, the integrated optics sensor detects the electric field and imprints it around an optical delay. The optical delay is generated by a birefringent optical waveguide in a lithium niobate (LiNbO₃) integrated optics two-wave interferometer. The modulated optical delay, acting as an information carrier, is transmitted through an optical fiber channel. At the receiver, light is demodulated by a second integrated optics two-wave interferometer, which also introduces a second optical delay. The optical delays on the sensor and demodulator are matched at the same value. The integrated optics demodulator measures the autocorrelation of light around the optical delay value, and the imprinted electric field is recuperated as a linear variation of the received optical power. The matching of the sensor and demodulator allows a direct detection of the electric field, giving a unique feature to this fiber-integrated optics scheme. The experimental setup described here uses two pigtailed LiNbO₃ electrooptic crystals: one acting as the electric field sensor and the other acting as the optical demodulator. The wideband sensing range on the experimental setup corresponds to frequencies between 0 and 20 kHz.

I. Introduction

Measurement of high- and low-intensity electric fields, coming either from natural phenomena or from human activities, is an important subject because it impacts scientific, industrial, and commercial environments, among others. Static and dynamic electric fields are produced by different sources, including electric power equipment, power generation and distribution facilities, high-voltage transmission lines, telecommunication equipment, electromagnetic interferences, and human medical signals. More common electric field meters use conductive electrodes that are linked to the measuring electronics by cables, and very often, such arrangements distort the unknown field. Different techniques and apparatuses for the measurement of electric fields are reported in the technical literature, for instance, measurement of ac and dc electric fields in high-voltage transmission lines using fluorescent tubes and electromechanical field mills [1]–[4]. Human electroencephalograms are recorded by using sensitive electric field sensors in the form of probe electrode disks to characterize brain activity [5].