Design optimization of volume holographic gratings for wavelength filters

Abstract

Volume holography is promising for devices such as wavelength filters. However, in previously reported work with these holographic devices the diffraction efficiency and wavelength selectivity were not so satisfactory, which affected the insertion loss and channel spacing of the device respectively. In order to investigate the performances for most of the volume holographic devices which are of finite size and with 90 degree geometry, two-dimensional (2-D) coupled-wave theory is more accurate than that based on the well-known Kogelnik’s coupled-wave theory. In this paper a close-form analytical solution to 2-D coupled wave theory for 2-D restricted gratings is presented firstly. Then in order to achieve the optimum insertion loss and channel spacing for dense wavelength division multiplexing (DWDM) filters, diffraction properties, especially effects of the grating strength and grating size ratio on the peak diffraction efficiency and wavelength selectivity are researched based on the 2-D coupled-wave theory and its solution. The results show that this solution is capable of design optimization of volume holographic gratings for various devices, including wavelength filters. And the design optimization is given in order to gain the optimum peak diffraction efficiency and wavelength selectivity. Finally, some experimental results showing the angular selectivity for different grating size ratio are given, which agree well with the 2-D coupled-wave theory.