Maximizing modulation contrast of KTN electro-optic modulator

•A novel scheme to maximize the modulation contrast based on the transmittance derivative function model is proposed.•The proposed scheme can solve the optimization deviation of the optimization modulation contrast method based on 50% transmittance point for KTN electro-optic modulator.•By using the optimal modulation point selected by the proposed method in this paper, the maximum modulation contrast can reach 0.106 and 0.05 at 1 kHz and 500 kHz, which is 3.5 times and 2 times of the traditional method based on 50% light transmittance.