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.