On the basis of the Kogelnik’s coupled-wave theory
the diffraction efficiency equation of transmitting Volume Body Grating(VBG) is derived.The dependence of the angle and wavelength selectivity of the VBG on the refractive index modulation and crystal thickness are analyzed by numerical simulation.The results indicate that when the incident light satisfies the Bragg condition
the refractive efficiency of a 2-mm-thick VBG with a 250×10-6 refractive index modulation is 100%
while when the incident light deviates the Bragg condition for a very small quantity
the VBG diffraction efficiency drops rapidly and when the deviation quantity surpasses a certain scope