An all-fibre and integrated optics electric field sensing scheme using matched optical delays and coherence modulation of light

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Sensing electric fields occupying large bandwidths are interesting in practical applications related to natural phenomena and also in man-made hard electromagnetic industrial environments. In this work, an electric field sensor scheme, using coherence modulation of light, in an all-fibre configuration is described. The scheme uses lithium niobate (LiNbO3), integrated optics sensors. In a coherence modulation scheme, the LiNbO3 sensor detects the electric field and imprints it around an optical delay. The optical delay, acting as an information carrier, is transmitted through an optical fibre channel. At the receiver, light is demodulated by using a two-wave interferometer, introducing a second optical delay which is matched to the sensor's one. The demodulator can be implemented using either a second LiNbO3 crystal or an all-fibre optical retarder. Both alternatives are studied in this paper. The optical demodulator measures the optical autocorrelation around the optical delay and the electric field is recovered as a linear variation of the received optical power. Matching of the sensor and demodulator allows direct detection of the electric field, giving an unequal feature of an all-fibre scheme. The bandwidth of the sensing scheme is between 0 and 20 kHz.