An approximate analytic method is presented that permits the calculation of all the output waves, both backward and forward traveling, for slanted, transmission-type volume gratings replayed at the Bragg angle and perfectly index matched to their surroundings. The predictions of the resulting analytic expressions are compared with numerical results produced by using the rigorous coupled-wave method and found to be accurate over a large range of parameters to the first order of the permittivity variation of the volume grating, all second order terms being assumed negligible.
