CALCULATION OF THE TRANSVERSE ELECTRO-OPTICAL MODULATION CHARACTERISTICS OF LiNbO₃ CRYSTALS WITH THE ELECTRIC FIELD ALONG ITS OPTICAL AXIS

Starting from the refractive index ellipsoid equation and the electro-optic coefficient matrix of the LiNbO₃ crystal, the transverse electro-optic modulation characteristics of the LiNbO₃ crystal when an electric field is applied along the optical axis direction were calculated and analyzed. The results show that due to the presence of natural phase difference, the electro-optic modulation curve of the LiNbO₃ crystal does not necessarily pass through the coordinate origin. At the same time, the electro-optic modulation curve of the crystal is very sensitive to small deviations in the direction of light transmission within the plane determined by the y and z axes, leading to randomness in the demodulation signal waveform of the sine modulation signal at zero voltage in experiments, but this does not affect the measurement results of the half-wave voltage of the LiNbO₃ crystal. These results and conclusions can not only well answer the doubts students have in experiments but also serve as a good reference for experimental teachers and related experimental personnel.