Where, D is the distance of electrode, n_e is the refractive index of LiNbO_3 crystal, r_33is the electrooptics coefficient, L is the length of modulate waveguides, is the superpose coefficient of the light field and eiectric field, ...is the wavelength.the parameters of Y waveguide half-wave voltage is reiated to temperature,which is caused by its own material and inevitable,thereby it affecting the modulation of Y waveguide.Differentiating formula on temperature