Copper doped KTN crystals with different doping concentrations were grown by the Czochralski method. The XRD patterns show that all of the crystals are in cubic phase at room temperature. The influences of the CuO doping concentrations on dielectric properties of the crystals were measured. Cu: KTN crystals exhibited color changes depending on the doping concentrations. It was found that the inhomogeneous composition property can be used to form gradient refractivity effect in the case of ion doping. The refractive index gradient reaches 33x10(-3)/mm for the grown Cu: KTNN crystals. Base on the interaction between the quadratic electro-optic effect and the gradient refractivity effect, the deflection and the intensity of a Cu: KTa0.62Nb0.38O3 sample were modulated in different orientations of the crystal. The deflection efficiency and the half-wave voltage of the modulation are 45 mrad/kV and 75 V, respectively.