On the Design of Video-Bandwidth Electric Field Sensing Systems Using Dielectric ${\rm LiNbO}_{3}$ Electro-Optic Sensors and Optical Delays as Signal Carriers

Abstract

As the measurement of wide-band (multimegahertz) electric fields is often of practical interest in industrial and commercial environments, in this paper, a methodology of design and implementation of a wide-band electric field sensing scheme, using optical delays as information carriers is described. The scheme is based on a lithium niobate (LiNbO 3 ) birefringent optical waveguide that performs simultaneously as an optical retarder and as a dielectric (electrode-less) sensor. In this scheme, the LiNbO 3 sensor introduces an optical delay and simultaneously senses an on-air electric field and imprints it around an optical delay. At the receiver, the sensed electric field is detected when the sensor and demodulator are optically matched, i.e., when both introduce identical optical delays. An important aspect, when sensing electric fields using LiNbO 3 dielectric sensors, is that the optically sensed field is weaker than the external field by a factor given by the ratio of the permittivity of the surrounding dielectric media over the LiNbO 3 permittivity (boundary condition for normal electric fields). When the surrounding media is air, the optically sensed electric field is 35 times weaker than the external field, as described in this paper. Another practical issue is that a birefringent optical waveguide is highly sensitive to optical polarization variations. Such a sensitivity implies that the output dc component of the received light changes with time (dc-drift). The dc-drift performance of the proposed electric field sensing scheme is measured and reported in this paper. The dc-drift can be minimized using polarization-insensitive LiNbO 3 unbalanced Mach-Zehnder interferometers.Index Terms-Lithium niobate LiNbO 3 , dielectric electro-optic sensors, wide-band electric field sensing, optical retarders.

Minimally invasive optical sensors for microwave-electric-field exposure measurements

“…The EO efficiency of CPI-based sensors is governed either by r 22 • n o 3 for Z-propagating guides 54 or by (r 33 • n e 3 to r 13 • n o 3 )/2 in the other cases, 74,75 where n o and n e are the extraordinary and ordinary refractive indices. However, r 13 and r 22 are more than three times lower than r 33 .…”

“…The two branches show a different EO sensitivity so that when the two signals recombine through another Y junction into the output waveguide, their phase difference is proportional to the external electric field. 69,[75][76][77] MZIs were the subject of intensive efforts in the 1980s and 1990s for E-field detection, as detailed in Ref. 27.…”

“…The differentiated EO sensitivity between the two arms is achieved either by reverse poling 78 or by antennas. 27,69,75,77,79,80 The phase bias φ o is set to π∕2 by a length difference of several micrometers between the two arms and can be corrected by applying force 81 or by laser writing 79,82 in case of fabrication imprecisions.…”

Electric field sensors based on optical retarders in lithium niobate (LiNbO3) integrated optics technology

“…A more detailed description of a complete sensing-detection scheme has been reported elsewhere [5]. The optical pathdifferences of the sensor and demodulator were measured in order to implement an electric filed sensingdetection process based on optical delays [6]. The measured autocorrelation of the cascaded sensor and demodulator is illustrated by Fig.…”