Modelling and experimental linearisation of electric field sensing using electrode‐less LiNbO ₃ interferometers and incoherent light

Abstract

Electrode-less integrated optics lithium niobate (LiNbO 3) asymmetric Mach-Zehnder interferometers (AMZIs) can be used as electric field (e-field) sensors. Electrode-less sensors are attractive for practical use as such devices do not perturb the sensed variable. A critical issue when using electrode-less sensors is to ensure a linear sensing process. This requires the electro-optic transfer function (EOTF) to be adjusted at its quadrature point. For this purpose, an electrode-less sensor can be optically biased. However, an accurate optical bias is strongly limited by the fabrication tolerances of the AMZIs. Hence a linear sensing-detection process is not actually ensured. To explore a linear e-field sensing-detection process, a simple linearising scheme is proposed in this Letter. The scheme is configured by cascading two optically matched AMZIs. The first AMZI is an electrode-less sensor; the second one, which is provided of electrodes performs simultaneously as an optical demodulator and an EOTF tuner. The EOTF of the demodulating AMZI can be tuned to its quadrature point by a DC voltage on its associated electrodes. The sensingdetection scheme is modelled and experimentally tested when illuminated either by coherent and incoherent light. The sensed e-field is linearly recuperated only when incoherent light is used.