Controlled by an electric field, the interaction of two coupled TE-modes at the dynamic grating in a planar waveguide with a thin layer of nematic liquid crystal has been studied theoretically. The dynamic grating is induced by an external electric field due to the periodicity of the anchoring energy of nematic with waveguide surface. Metal and dielectric waveguides have been studied. The transmission of TE-modes and its reflection from the periodic structure of the nematic layer have been investigated. The intensity of a signal- mode at the output of the waveguide has been calculated. The dependence of intensity on the anchoring energy amplitude and modulation period, dimensions of the nematic layer and an external electric field has been analyzed. It was shown that the frequency interval of a TE-mode reflection expands with increasing of the electric field. The primary maximum of the reflected mode intensity, as function of the nematic layer length, increases monotonously with growing s number of anchoring energy periods placed on the layer length. The primary peak reaches the largest value of 1 for s approximate to 10 divided by 100 (metal waveguide) and for s approximate to 1000 (dielectric waveguide). The same dependence for the signal-mode, which propagates through the NLC layer, has nonmonotonous form and a complete energy exchange is reached only for certain values of s and the length of the nematic layer.