Research on the diffraction characteristics of reflecting volume Bragg gratings with different apodizing functions

Reflective Volume Bragg Grating (RBG) recorded in photo-thermo-refractive glass offers notable advantages, including high efficiency, narrow bandwidth, and multiplexing capabilities, making them ideal for applications in dense wavelength division multiplexing (DWDM) and demultiplexing. However, the side lobes caused by sudden changes in coupling strength at both ends of the grating always lead to interchannel interference, which evidently affects the effectiveness of multiplexing and demultiplexing. In this work, a theoretical model of the apodization for RBG, which based on Kogelnik's coupled wave theory and F-matrix theory. It is simulated and analyzed the effects of three apodization functions including cosine, gaussian, and hyperbolic secant functions is established. The simulation results indicate that the side lobes of the RBG with apodization is significantly reduced and the peak efficiency is determined by the total refractive index modulation. This work provides a theoretical design basis and parameters optimizing method for the development of apodized RBG.