Novel method for measuring modulation depth and effective thickness of volume gratings

Based on the Kogelink's coupled wave theory and by measuring the relationship between the diffraction efficiency and Bragg angle deviation of volume grating, the refractive index modulation depth and effective thickness of the photorefractive volume grating can be calculated according to the 3 dB bandwidth, relative peak value of side lobe and its corresponding Bragg angle deviation in the relationship curve. The experimental results with LiNbO₃:Fe crystal are well in agreement with the theoretic analysis. The measurement accuracy is no worse than that of available methods based on digital holography and Mach-Zehnder interferometer. At the same time, the measurement process is much simpler.