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

Abstract

The aim of this paper is to describe the use of Lithium Niobate (LiNbO3) electrooptic retarders as electric field sensors. There are two types of optical retarders that can be implemented on LiNbO3 crystals: birefringent optical waveguides (BOW) and asymmetric Mach-Zehnder interferometers(AMZI). These devices can be used for configuring electric field sensing schemes, taking advantage of their potential of generating practical optical delays. An optical delay becomes practical when its equivalent optical path-difference is longer than the coherence-length of the optical source and ranges between some hundreds of micrometers and some millimeters. This goal can be achieved when using incoherent optical sources as light emitting diodes (LEDs) or super-luminiscent diodes(SLDs) whose coherence-length is around 100 micrometers. In an optical retarder-based electric field sensing scheme, an optical delay can be modulated by the sensed electric field and transmitted to an optical receiver. The demodulation of the optical delay is achieved when a second optical delay is introduced on the received light. The detection of the sensed electric field is ensured only when the sensing and demodulating delays are optically matched. The technique of modulating and demodulating optical delays for the transmission of information signal is more generally known as coherence modulation. The operating principle of the modulation-demodulation of optical delays as well as the use of BOW and AMZI as optical retarders and their use for configuring electric field sensing schemes are describe in this paper.

References