Study On Mechanism Of Volume Holographic Wavelength Filtering Devices For Optical Communication

Volume holography is promising for devices such as dense wavelength division multiplexing (DWDM) 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. The analyses in most of the previous work were based on the well-known Kogelnik's coupled-wave theory. However, due to the one-dimensional (1-D) nature of this theory, it is best suitable for gratings in which the surface size is much larger than the grating thickness. Since most of the holographic devices are of finite size, two-dimensional (2-D) grating theory is more accurate than Kogelnik's coupled-wave theory in investigating the performances for these devices. In this paper, we research the basis theory of volume holographic gratings for wavelength filters, which is mainly 2-D coupled-wave theory. Diffraction properties, especially diffraction efficiency and Bragg selectivity are investigated. Design optimization of volume holographic gratings for wavelength filters is then given based on the 2-D coupled-wave theory. Firstly, the complete derivation of 2-D coupled wave equations is given for total overlap gratings in the Bragg regime. The analytical solution in closed mathematical form is also given. Mistakes that existed in a previously published similar work are rectified. General diffraction properties of total overlap gratings are researched based on the solution in this paper. In order to achieve the optimum insertion loss and channel spacing for 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...